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Granier, Cyril, Chris R. Abbiss, Anaël Aubry, Yvon Vauchez, Sylvain Dorel, Christophe Hausswirth, and Yann Le Meur. "Power Output and Pacing During International Cross-Country Mountain Bike Cycling." International Journal of Sports Physiology and Performance 13, no. 9 (October 1, 2018): 1243–49. http://dx.doi.org/10.1123/ijspp.2017-0516.
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Purpose: To characterize the physiological profiles of elite cross-country mountain-bike (XCO-MTB) cyclists and to examine their pacing and power-output (PO) distribution during international races. Methods: Over 2 competitive seasons, 8 male XCO-MTB cyclists (VO2max 79.9 [5.2] mL·min−1·kg−1, maximal aerobic power [MAP] 411 [18] W and 6.3 [0.4] W·kg−1) regularly undertook incremental tests to assess their PO and heart rate (HR) at first and second ventilatory thresholds (VT1 and VT2) and at VO2max. During the same period, their PO, HR, speed, and cadence were recorded over 13 international races (total of 30 recorded files). Results: Mean PO, speed, cadence, and HR during the races were 283 (22) W (4.31 [0.32] W·kg−1, 68% [5%] MAP), 19.7 (2.1) km·h−1, 68 (8) rpm, and 172 (11) beats·min−1 (91% [2%] HRmax), respectively. The average times spent below 10% of MAP, between 10% of MAP and VT1, between VT1 and VT2, between VT2 and MAP, and above MAP were 25% (5%), 21% (4%), 13% (3%), 16% (3%), and 26% (5%), respectively. Both speed and PO decreased from the start loop to lap 1 before stabilizing until the end of the race.Conclusions: Elite off-road cyclists demonstrated typical values of world-class endurance cyclists with an excellent power-to-mass ratio. This study demonstrated that XCO-MTB races are performed at higher intensities than reported in previous research and are characterized by a fast start followed by an even pace.
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Aedo Muñoz, Esteban, Alberto Rötger Guarda, Ignacio Ria Gamboa, Natalia Rodríguez Zárate, Cristian Rojas Reyes, Nelson Aedo Muñoz, Diego Valenzuela Pérez, et al. "Variaciones cinemáticas de ascenso en los ciclistas de montaña (Kinematic variations of uphill in mountain bikers)." Retos, no. 40 (November 8, 2020): 257–63. http://dx.doi.org/10.47197/retos.v1i40.81430.
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El propósito de este estudio fue determinar los indicadores cinemáticos relevantes entre categorías Elite y Sub-23 de ciclistas de cross country mountain bike (MTB) en la técnica de ascenso. La muestra fue compuesta por ciclistas Sub-23 (n=5; 18.8±0.5 años) y Elite (n=7; 24.2±2.0 años), todos los participante varones, diestros y ciclistas federados de competiciones de cross country MTB. Los datos fueron registrados desde el plano sagital al ascender por un terreno con una pendiente de 9.5±0.5% con la técnica de videofotogrametría. Los indicadores que presentaron diferencias entre categorías fueron: velocidad angular ciclo pedaleo izquierdo (p=0.04; g=-1.22), tiempo ciclo pedaleo izquierdo (p=0.02; g=1.44), velocidad angular ciclo pedaleo izquierdo de la fase preparatoria (p=0.03; g=-1.37), mientras que para la velocidad articular; velocidad de la cadera izquierda en fase de envión (p=0.029; g=-1.38), velocidad del tobillo izquierdo (p=0.005; g=-1.94) y tobillo derecho (p=0.002; g=-2.17) en fase de recuperación.
Abstract. The purpose of this study was to determine the relevant kinematic indicators between Elite and Under-23 categories of cross country mountain bike (MTB) cyclists in the climbing technique. The sample was made up of Under-23 (n=5; 18.8±0.5 years) and Elite (n=7; 24.2±2.0 years) cyclists, all male and right-handed, federated participants of cross-country MTB competitions. The data were recorded from the sagittal plane to the ascending one through a terrain with a slope of 9.5±0.5% with videophotogrammetry. The indicators that showed differences between categories were: left pedaling cycle angular velocity (p=0.04; g=-1.22), left pedaling cycle time (p=0.02; g=1.44), left pedaling cycle angular velocity of the preparatory phase (p=0.03; g=-1.37), while for joint speed; speed of the left hip in clean and jerk phase (p=0.029; g =-1.38), speed of the left ankle (p=0.005; g=-1.94) and right ankle (p=0.002; g=-2.17) in recovery phase.
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Che Ibrahim, Nur Syuhada, Syamsul Herman Mohammad Afandi, and Zaiton Samdin. "Factors Affecting the Demand for Mountain Biking at Putrajaya Challenge Park, Putrajaya." Journal of Business and Social Review in Emerging Economies 5, no. 1 (June 30, 2019): 149–54. http://dx.doi.org/10.26710/jbsee.v5i1.616.
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The popularity of Mountain Biking (MTB) in Malaysia is increasing.This adds to the demand for more cycling sites and special events for MTB. In line the growing demand, the Malaysian government encourages participation in active sports and recreation as a healthy lifestyle. One of the approaches is through the establishment of the Putrajaya Challenge Park (PCP). This study is conducted at PCP, one of a well-known MTB site in Malaysia. It has a network of treks where these treks are rated with different difficulty level for cyclists to choose from according to their abilityandpreferences. MTB is known to be associated with risks and high technical skills, hence it is great interest to understand the factors affecting demand in such sport. Therefore, the purpose of this study is to determine the factors affecting the demand in MTB participation at PCP. Data was collected using a structured questionnaire and obtained a total of 302 usable questionnaires. A multiple linear regression analysis is employed and it is found that three factors were significant at 95% confidence level; total travel cost, years of participation and cost of equipment upgrades. The finding from the study is to supply PCP management with the information for future adventurous recreational events in PCP or in other similar establishments. This research also identifies some key findings and makes some recommendations for future research and management.
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Rose, SC, HA Chipps, and EM Peters. "Fluid use in mountain bikers - self-reported practices." South African Journal of Sports Medicine 19, no. 2 (June 15, 2007): 52. http://dx.doi.org/10.17159/2078-516x/2007/v19i2a266.
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Background and objectives. Little is known of the fluid replacement habits of participants in mountain bike (MTB) endurance events. This survey set out to determine the current perceptions and practices of this group of endurance athletes. Method. Four hundred and twelve participants in the 3- day 2006 Sani2C (MTB) race completed questionnaires that elicited information regarding their regular fluid intake practices during competitive MTB endurance events. This included their general approach to fluid replacement, their fluid intake practices (type, amount and frequency), urine output and hydration status. Results. While 70% (N = 290) reported that they based their fluid intake practices on personal past experiences, less than half the group (N = 177, 43%) were aware of official sport-specific guidelines. Although 86% (N = 354) reported making use of commercially available sport-specific drinks, consumption of water alone was reported by 34% of respondents (N = 140). The majority (N = 225, 55%) of the mountain bikers reported drinking every 16 - 30 minutes during an endurance ride, while 35% (N = 144) reported drinking every 0 - 15 minutes. Fifty-three per cent (N = 182) of the male respondents and 45% (N = 23) of female respondents reported a routine intake of ≥ 750 ml per hour during endurance rides. This included 2 women who reported regular intakes of between 1 500 and 2 000 ml/hr. Only 7 (2%) reported receiving medical care for dehydration following their participation in previous MTB rides. Conclusions. This survey indicates that although more than half of the mountain bikers did not acknowledge specific awareness of the official fluid replacement guidelines, over 80% reported drinking regularly during a race, and 52% (N = 212) reported a usual intake of ≥ 750 ml/hr during endurance races. Until scientific studies have carefully examined the hydration status and fluid replacement needs of mountain bikers, MTB cyclists are cautioned against the practice of over-hydrating. South African Journal of Sports Medicine Vol. 19 (2) 2007: pp. 52-58
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Prudnikova, M. "Assessment of the level of functional state and the course of a specific biological cycle of cyclists and wrestlers 15-16 years." Єдиноборства, no. 3(21) (June 1, 2021): 33–43. http://dx.doi.org/10.15391/ed.2021-3.04.
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Purpose: to determine the functioning of the cardiovascular and reproductive system of cyclists and wrestlers 15-16 years under the influence of specific physical activity. Material and methods. 14 athletes took part in the research, 7 of them were freestyle wrestling (3 – I category, 4 – candidates for master of sports) and 7 – Mountain Bike (MTO) races (4 – I category, 3 – candidates for master of sports). Research methods: theoretical analysis and generalization of scientific and methodological literature, pedagogical and biomedical research methods, methods of mathematical statistics. Results: the analysis of educational programs (freestyle wrestling, cycling-MTV) of the age group of 15-16 years showed that in these kinds of sports a different mode of educational and training work during the annual cycle. So, for freestyle wrestling athletes in the age group 15-16 years old, special physical training is planned for 100 hours, psychological training for 20 hours, competitive training for 42 hours, for 70 hours – rehabilitation means for 6 hours – medical control, while female cyclists – MTB is 12 hours more than general physical training, 144 hours more – technical and tactical. After the training year, the analysis of the trainers' plans showed that in freestyle wrestling, the percentage of general physical training has changed and amounted to 16 %, special physical – 24 %, technical and tactical – 33 %, psychological – 4 %, while in cycling general physical training – 19 %, special physical – 25 %, technical and tactical – 34 %, psychological – 6 %. Special and technical-tactical work by 1 % and psychological work by 2 % more were performed by cyclists relative to wrestlers. Comparison of the indicators of the cardiovascular system of female athletes showed a statistical difference in systolic blood pressure (t=3,60; t=8,92; p<0,001), in diastolic blood pressure (t=3,56; t=6,00, p<0,001), in the aerobic metabolic capacity (t=5,08; t=7,07; p<0,001), in the anaerobic metabolic capacity (t=12,20; t=8,14; p<0,001). According to a survey of female athletes, it was determined that in September 2019, 33 % of athletes 15-16 years old had irregular menstruation and 67% – regular, in December 2019 4 3% – irregular and 57 % – regular, in May 2020 50% – irregular and 50 % – regular, in September 2020 57 % – irregular and 43 % – regular menstruation. Conclusions. The analysis of curricula for the chosen sport and training plans of coaches by types of training showed that the specificity of the training process is the specificity of the discipline in which relatively independent types are clearly visible, and the distribution of training and competitive physical loads is interconnected with the stage of training. Comparison of the indicators of the cardiovascular system of female athletes 15-16 years old showed that higher performance in cyclists as a result of training (physiologically athletic heart. At the same time, among wrestlers it was recognized as more optimal indicators of the heart muscle for further improvement of sportsmanship. The negative dynamics of the ovarian cycle at the age of 15-16 years was determined, which amounted to 21 % of irregular menstruation. Keywords: freestyle wrestling, cycling-MTB, specific biological cycle, cardiovascular system.
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Frank, Laura Lewis, Janine T. Baer, Charles P. Lambert, and Mark L. Anderson. "The Effects of a Pre-exercise Feeding with or Without Fungal Carbohydrases (Carbogen™) on Blood Parameters and Exercise Performance in Elite Cyclists: A Preliminary Study." International Journal of Sport Nutrition and Exercise Metabolism 12, no. 3 (September 2002): 310–17. http://dx.doi.org/10.1123/ijsnem.12.3.310.
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The effect of fungal carbohydrases (Carbogen™ [C]) consumed with a meal replacement bar (MBR) on glucose metabolism and exercise performance was determined in 5 male competitive cyclists. After a 12-hour fast, subjects performed two 60-min cycling bouts at 80% V̇O2max followed by a time-to-exhaustion (TE) ride at 100% V̇O2max. One hour prior to each cycling bout, subjects ingested a MRB + 160-mg C or 160-mg CaCO3 placebo (PL) in a double-blind, counterbalanced fashion. Blood was drawn for determination of glucose, insulin, and lactate at: fasting, 1 hour post-feeding, minutes 30 and 60 of exercise, and after TE. Two-way ANOVA revealed a significant (p < .05) treatment and time effect for glucose, with C being higher than PL. Interaction effects were ob-· served for insulin and lactate. An increase in TE (min) at 100% V̇O2max was observed in the C versus PL trial (6.3 ± 3.4 vs. 4.4 ± 2.9, p < .001). A MRB+C may benefit cyclists due to increased BG and improved exercise performance.
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Resnitzky, D., M. Gossen, H. Bujard, and S. I. Reed. "Acceleration of the G1/S phase transition by expression of cyclins D1 and E with an inducible system." Molecular and Cellular Biology 14, no. 3 (March 1994): 1669–79. http://dx.doi.org/10.1128/mcb.14.3.1669.
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Conditional overexpression of human cyclins B1, D1, and E was accomplished by using a synthetic cDNA expression system based on the Escherichia coli tetracycline repressor. After induction of these cyclins in asynchronous Rat-1 fibroblasts, a decrease in the length of the G1 interval was observed for cyclins D1 and E, consistent with an acceleration of the G1/S phase transition. We observed, in addition, a compensatory lengthening of S phase and G2 so that the mean cell cycle length in populations constitutively expressing these cyclins was unchanged relative to those of their uninduced counterparts. We found that expression of cyclin B1 had no effect on cell cycle dynamics, despite elevated levels of cyclin B-associated histone H1 kinase activity. Induction of cyclins D1 and E also accelerated entry into S phase for synchronized cultures emerging from quiescence. However, whereas cyclin E exerted a greater effect than cyclin D1 in asynchronous cycling cells, cyclin D1 conferred a greater effect upon stimulation from quiescence, suggesting a specific role for cyclin D1 in the G0-to-G1 transition. Overexpression of cyclins did not prevent cells from entering into quiescence upon serum starvation, although a slight delay in attainment of quiescence was observed for cells expressing either cyclin D1 or cyclin E. These results suggest that cyclins D1 and E are rate-limiting activators of the G1-to-S phase transition and that cyclin D1 might play a specialized role in facilitating emergence from quiescence.
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Inoue, Kazushi, and Charles J. Sherr. "Gene Expression and Cell Cycle Arrest Mediated by Transcription Factor DMP1 Is Antagonized by D-Type Cyclins through a Cyclin-Dependent-Kinase-Independent Mechanism." Molecular and Cellular Biology 18, no. 3 (March 1, 1998): 1590–600. http://dx.doi.org/10.1128/mcb.18.3.1590.
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ABSTRACT A novel 761-amino-acid transcription factor, DMP1, contains a central DNA binding domain that includes three imperfect myb repeats flanked by acidic transactivating domains at the amino and carboxyl termini. D-type cyclins associate with a region of the DMP1 DNA binding domain immediately adjacent to the myb repeats to form heteromeric complexes which detectably interact neither with cyclin-dependent kinase 4 (CDK4) nor with DNA. The segment of D-type cyclins required for its interaction with DMP1 falls outside the “cyclin box,” which contains the residues predicted to contact CDK4. Hence, D-type cyclin point mutants that do not interact with CDK4 can still bind to DMP1. Enforced coexpression of either of three D-type cyclins (D1, D2, or D3) with DMP1 in mammalian cells canceled its ability to activate gene expression. This property was not shared by cyclins A, B, C, or H; did not depend upon CDK4 or CDK2 coexpression; was not subverted by a mutation in cyclin D1 that prevents its interaction with CDK4; and was unaffected by inhibitors of CDK4 catalytic activity. Introduction of DMP1 into mouse NIH 3T3 fibroblasts inhibited entry into S phase. Cell cycle arrest depended upon the ability of DMP1 to bind to DNA and to transactivate gene expression and was specifically antagonized by coexpression of D-type cyclins, including a D1 point mutant that does not bind to CDK4. Taken together, these findings suggest that DMP1 induces genes that inhibit S phase entry and that D-type cyclins can override DMP1-mediated growth arrest in a CDK-independent manner.
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Resnitzky, D., and S. I. Reed. "Different roles for cyclins D1 and E in regulation of the G1-to-S transition." Molecular and Cellular Biology 15, no. 7 (July 1995): 3463–69. http://dx.doi.org/10.1128/mcb.15.7.3463.
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Ectopic expression of cyclins D1 and E was previously shown to accelerate the G1/S-phase transition, indicating that both classes of G1 cyclin control an event(s) that is rate limiting for entry into S phase. In order to determine whether cyclins D1 and E control the same or two different rate-limiting events, we have created cell lines that express both cyclins in an inducible manner. We show here that ectopic expression of both cyclins E and D1 in the same cell has an additive effect on shortening of the G1 interval relative to expression of any single cyclin. In order to further explore the molecular basis for G1 cyclin action, we used cell lines capable of expressing cyclin D1, E, or both prematurely and measured the effect of cyclin expression in early G1 on phosphorylation of the retinoblastoma susceptibility gene product (pRb). We show here that while premature expression of either cyclin alone advances the G1/S-phase transition to the same extent, premature expression of cyclin D1 leads to immediate appearance of hyperphosphorylated pRb, while premature expression of cyclin E does not. Ectopic expression of both cyclins E and D1 in the same cell has an additive effect on shortening of the G1 interval, while the effect on pRb phosphorylation is similar to the effect of cyclin D1 alone. These results suggest that cyclins E and D1 control two different events, both rate limiting for the G1/S-phase transition, and that pRb phosphorylation might be the rate-limiting event controlled by cyclin D1.
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Resnitzky, D., M. Gossen, H. Bujard, and S. I. Reed. "Acceleration of the G1/S phase transition by expression of cyclins D1 and E with an inducible system." Molecular and Cellular Biology 14, no. 3 (March 1994): 1669–79. http://dx.doi.org/10.1128/mcb.14.3.1669-1679.1994.
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Conditional overexpression of human cyclins B1, D1, and E was accomplished by using a synthetic cDNA expression system based on the Escherichia coli tetracycline repressor. After induction of these cyclins in asynchronous Rat-1 fibroblasts, a decrease in the length of the G1 interval was observed for cyclins D1 and E, consistent with an acceleration of the G1/S phase transition. We observed, in addition, a compensatory lengthening of S phase and G2 so that the mean cell cycle length in populations constitutively expressing these cyclins was unchanged relative to those of their uninduced counterparts. We found that expression of cyclin B1 had no effect on cell cycle dynamics, despite elevated levels of cyclin B-associated histone H1 kinase activity. Induction of cyclins D1 and E also accelerated entry into S phase for synchronized cultures emerging from quiescence. However, whereas cyclin E exerted a greater effect than cyclin D1 in asynchronous cycling cells, cyclin D1 conferred a greater effect upon stimulation from quiescence, suggesting a specific role for cyclin D1 in the G0-to-G1 transition. Overexpression of cyclins did not prevent cells from entering into quiescence upon serum starvation, although a slight delay in attainment of quiescence was observed for cells expressing either cyclin D1 or cyclin E. These results suggest that cyclins D1 and E are rate-limiting activators of the G1-to-S phase transition and that cyclin D1 might play a specialized role in facilitating emergence from quiescence.
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Carthon, Bradley C., Carola A. Neumann, Manjusri Das, Basil Pawlyk, Tiansen Li, Yan Geng, and Piotr Sicinski. "Genetic Replacement of Cyclin D1 Function in Mouse Development by Cyclin D2." Molecular and Cellular Biology 25, no. 3 (February 1, 2005): 1081–88. http://dx.doi.org/10.1128/mcb.25.3.1081-1088.2005.
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ABSTRACT D cyclins (D1, D2, and D3) are components of the core cell cycle machinery in mammalian cells. It is unclear whether each of the D cyclins performs unique, tissue-specific functions or the three proteins have virtually identical functions and differ mainly in their pattern of expression. We previously generated mice lacking cyclin D1, and we observed that these animals displayed hypoplastic retinas and underdeveloped mammary glands and a presented developmental neurological abnormality. We now asked whether the specific requirement for cyclin D1 in these tissues reflected a unique pattern of D cyclin expression or the presence of specialized functions for cyclin D1 in cyclin D1-dependent compartments. We generated a knock-in strain of mice expressing cyclin D2 in place of D1. Cyclin D2 was able to drive nearly normal development of retinas and mammary glands, and it partially replaced cyclin D1's function in neurological development. We conclude that the differences between these two D cyclins lie mostly in the tissue-specific pattern of their expression. However, we propose that subtle differences between the two D cyclins do exist and they may allow D cyclins to function in a highly optimized fashion. We reason that the acquisition of multiple D cyclins may allow mammalian cells to drive optimal proliferation of a diverse array of cell types.
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Measday, V., L. Moore, R. Retnakaran, J. Lee, M. Donoviel, A. M. Neiman, and B. Andrews. "A family of cyclin-like proteins that interact with the Pho85 cyclin-dependent kinase." Molecular and Cellular Biology 17, no. 3 (March 1997): 1212–23. http://dx.doi.org/10.1128/mcb.17.3.1212.
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In budding yeast, entry into the mitotic cell cycle, or Start, requires the Cdc28 cyclin-dependent kinase (Cdk) and one of its three associated G1 cyclins, Cln1, Cln2, or Cln3. In addition, two other G1 cyclins, Pcl1 and Pcl2, associate with a second Cdk, Pho85, to contribute to Start. Although Pho85 is not essential for viability, Pcl1,2-Pho85 kinase complexes become essential for Start in the absence of Cln1,2-Cdc28 kinases. In addition, Pho85 interacts with a third cyclin, Pho80, to regulate acid phosphatase gene expression. Other cellular roles for Pho85 cyclin-Cdk complexes are suggested by the multiple phenotypes associated with deletion of PHO85, in addition to Start defects and deregulated acid phosphatase gene expression. Strains with pho80, pcl1, and pcl2 deletions show only a subset of the pho85 mutant phenotypes, suggesting the existence of additional Pho85 cyclins (Pcls). We used two-hybrid screening and database searching to identify seven additional cyclin-related genes that may interact with Pho85. We found that all of the new genes encode proteins that interacted with Pho85 in an affinity chromatography assay. One of these genes, CLG1, was previously suggested to encode a cyclin, based on the protein's sequence homology to Pcl1 and Pcl2. We have named the other genes PCL5, PCL6, PCL7, PCL8, PCL9, and PCL10. On the basis of sequence similarities, the PCLs can be divided into two subfamilies: the Pcl1,2-like subfamily and the Pho80-like subfamily. We found that deletion of members of the Pcl1,2 class of genes resulted in pronounced morphological abnormalities. In addition, we found that expression of one member of the Pcl1,2 subfamily, PCL9, is cell cycle regulated and is decreased in cells arrested in G1 by pheromone treatment. Our studies suggest that Pho85 associates with multiple cyclins and that subsets of cyclins may direct Pho85 to perform distinct roles in cell growth and division.
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Yeong, Foong May, Hong Hwa Lim, Ya Wang, and Uttam Surana. "Early Expressed Clb Proteins Allow Accumulation of Mitotic Cyclin by Inactivating Proteolytic Machinery during S Phase." Molecular and Cellular Biology 21, no. 15 (August 1, 2001): 5071–81. http://dx.doi.org/10.1128/mcb.21.15.5071-5081.2001.
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ABSTRACT Periodic accumulation and destruction of mitotic cyclins are important for the initiation and termination of M phase. It is known that both APCCdc20 and APCHct1 collaborate to destroy mitotic cyclins during M phase. Here we show that this relationship between anaphase-promoting complex (APC) and Clb proteins is reversed in S phase such that the early Clb kinases (Clb3, Clb4, and Clb5 kinases) inactivate APCHct1 to allow Clb2 accumulation. This alternating antagonism between APC and Clb proteins during S and M phases constitutes an oscillatory system that generates undulations in the levels of mitotic cyclins.
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Gómez Lahoz, Enrique, Nanette J. Liegeois, Pumin Zhang, Jeffrey A. Engelman, James Horner, Adam Silverman, Ronald Burde, et al. "Cyclin D- and E-Dependent Kinases and the p57KIP2 Inhibitor: Cooperative Interactions In Vivo." Molecular and Cellular Biology 19, no. 1 (January 1, 1999): 353–63. http://dx.doi.org/10.1128/mcb.19.1.353.
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ABSTRACT This study examines in vivo the role and functional interrelationships of components regulating exit from the G1 resting phase into the DNA synthetic (S) phase of the cell cycle. Our approach made use of several key experimental attributes of the developing mouse lens, namely its strong dependence on pRb in maintenance of the postmitotic state, the down-regulation of cyclins D and E and up-regulation of the p57 KIP2 inhibitor in the postmitotic lens fiber cell compartment, and the ability to target transgene expression to this compartment. These attributes provide an ideal in vivo context in which to examine the consequences of forced cyclin expression and/or of loss of p57 KIP2 inhibitor function in a cellular compartment that permits an accurate quantitation of cellular proliferation and apoptosis rates in situ. Here, we demonstrate that, despite substantial overlap in cyclin transgene expression levels, D-type and E cyclins exhibited clear functional differences in promoting entry into S phase. In general, forced expression of the D-type cyclins was more efficient than cyclin E in driving lens fiber cells into S phase. In the case of cyclins D1 and D2, ectopic proliferation required their enhanced nuclear localization through CDK4 coexpression. High nuclear levels of cyclin E and CDK2, while not sufficient to promote efficient exit from G1, did act synergistically with ectopic cyclin D/CDK4. The functional differences between D-type and E cyclins was most evident in the p57 KIP2 -deficient lens wherein cyclin D overexpression induced a rate of proliferation equivalent to that of the pRb null lens, while overexpression of cyclin E did not increase the rate of proliferation over that induced by the loss of p57 KIP2 function. These in vivo analyses provide strong biological support for the prevailing view that the antecedent actions of cyclin D/CDK4 act cooperatively with cyclin E/CDK2 and antagonistically with p57 KIP2 to regulate the G1/S transition in a cell type highly dependent upon pRb.
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Laman, Heike, Dawn Coverley, Torsten Krude, Ronald Laskey, and Nic Jones. "Viral Cyclin–Cyclin-Dependent Kinase 6 Complexes Initiate Nuclear DNA Replication." Molecular and Cellular Biology 21, no. 2 (January 15, 2001): 624–35. http://dx.doi.org/10.1128/mcb.21.2.624-635.2001.
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ABSTRACT The cyclins encoded by Kaposi sarcoma-associated herpesvirus and herpesvirus saimiri are homologs of human D-type cyclins. However, when complexed to cdk6, they have several activities that distinguish them from D-type cyclin-cdk6 complexes, including resistance to cyclin-dependent kinase inhibitors and an enhanced substrate range. We find that viral cyclins interact with and phosphorylate proteins involved in replication initiation. Using mammalian in vitro replication systems, we show that viral cyclin-cdk6 complexes can directly trigger the initiation of DNA synthesis in isolated late-G1-phase nuclei. Viral cyclin-cdk6 complexes share this capacity with cyclin A-cdk2, demonstrating that in addition to functioning as G1-phase cyclin-cdk complexes, they function as S-phase cyclin-cdk complexes.
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Diep, Bao Tri, Hiep Le Dai, Duy Quoc Bui, Quoc Khai Tran, Minh Huy Huynh, and Quoc Hung Nguyen. "Designing, Manufacturing and Testing the Cycling Training System Featuring Magnetorheological Brake." Applied Mechanics and Materials 889 (March 2019): 346–54. http://dx.doi.org/10.4028/www.scientific.net/amm.889.346.
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In this study, a dual-disc magneto-rheological brake (MRB) with two coils placed on each side housing is proposed for a cycling training system. The cycling training system is integrated a positioning system to simulate the cycling process in different slope ranging from 0 to 150. By adjusting position of the bicycle, braking torque of the brake, a cyclist can experience different riding condition such as riding on flat road or steep road with the slope up to 15o.
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Hautbergue, Guillaume, and Valérie Goguel. "The Yeast C-Type Cyclin Ctk2p Is Phosphorylated and Rapidly Degraded by the Ubiquitin-Proteasome Pathway." Molecular and Cellular Biology 19, no. 4 (April 1, 1999): 2527–34. http://dx.doi.org/10.1128/mcb.19.4.2527.
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ABSTRACT The yeast CTDK-I complex has been implicated in phosphorylation of the carboxy-terminal domain of the RNA polymerase II and in transcription control. It is composed of three polypeptides: Ctk1p and Ctk2p, a cyclin-dependent kinase and a C-type cyclin subunit, respectively; and Ctk3p, a third subunit of unknown function. Cyclins are regulatory proteins whose expression is tightly controlled at the protein level. In this study, we examined the regulation of Ctk2p expression in vivo. Surprisingly, unlike what has been described for cell cycle cyclins, steady-state levels of Ctk2p are composed of two relatively abundant forms, one of them phosphorylated. We show that this phosphorylated form is extremely unstable (half-life, 5 min) and that rapid proteolysis of Ctk2p exhibits growth-related regulation. Furthermore, our data establish that similar to the case for other naturally short-lived proteins, Ctk2p degradation is mediated by the ubiquitin-proteasome pathway. This is the first demonstration that a C-type cyclin is phosphorylated and targeted to the proteasome. Strikingly, neither phosphorylation nor destruction of Ctk2p requires its associated kinase Ctk1p, a feature fundamentally different from that which has been observed for cell cycle cyclins.
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Izumi, T., and J. L. Maller. "Phosphorylation of Xenopus cyclins B1 and B2 is not required for cell cycle transitions." Molecular and Cellular Biology 11, no. 8 (August 1991): 3860–67. http://dx.doi.org/10.1128/mcb.11.8.3860.
Full textAbstract:
The cdc2 kinase and B-type cyclins are known to be components of maturation- or M-phase-promoting factor (MPF). Phosphorylation of cyclin B has been reported previously and may regulate entry into and exit from mitosis and meiosis. To investigate the role of cyclin B phosphorylation, we replaced putative cdc2 kinase phosphorylation sites in Xenopus cyclins B1 and B2 by using oligonucleotide site-directed mutagenesis. We found that Ser-90 of cyclin B2 and Ser-94 or Ser-96 of cyclin B1 are the main phosphorylation sites both in functional Xenopus egg extracts and after phosphorylation with purified MPF in vitro. Microtubule-associated protein (MAP) kinase from Xenopus eggs phosphorylated cyclin B1 significantly at Ser-94 or Ser-96, whereas it was largely inactive against cyclin B2. The substitutions that ablated phosphorylation at these sites, however, resulted in no functional differences between mutant and wild-type cyclin, as judged by the kinetics of M-phase degradation, induction of mitosis in egg extracts, or induction of oocyte maturation. These results indicate that the phosphorylation of Xenopus B-type cyclins by cdc2 kinase or MAP kinase is not required for the hallmark functions of cyclin.
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Jung, J. U., M. Stäger, and R. C. Desrosiers. "Virus-encoded cyclin." Molecular and Cellular Biology 14, no. 11 (November 1994): 7235–44. http://dx.doi.org/10.1128/mcb.14.11.7235.
Full textAbstract:
Herpesvirus saimiri contains an open reading frame called eclf2 with homology to the cellular type D cyclins. We now show that the eclf2 gene product is a novel virus-encoded cyclin (v-cyclin). The protein encoded by the v-cyclin gene of this oncogenic herpesvirus was found to have an apparent molecular size of 29 kDa in transformed cells. v-Cyclin protein was found to be associated with cdk6, a cellular cyclin-dependent kinase known to interact with cellular type D cyclins. cdk6/v-cyclin complexes strongly phosphorylated Rb fusion protein and histone H1 as substrates in vitro. Mutational analyses showed that highly conserved amino acids in the cyclin box of v-cyclin were important for association with cdk6 and for activation of cdk6 kinase activity. Thus, v-cyclin resembles cellular type D cyclins in primary sequence, in its association with cdk6, by its ability to activate protein kinase activity, and by the presence of functional cyclin box sequences. v-Cyclin exhibited a selective preference for association with cdk6 over other cyclin-dependent kinases and a high level of kinase activation. The properties of v-cyclin suggest a likely role in oncogenic transformation by this T-lymphotropic herpesvirus.
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Medina, Catalina, Martin Romero-Martinez, Sergio Bautista-Arredondo, Simón Barquera, and Ian Janssen. "Move on Bikes Program: A Community-Based Physical Activity Strategy in Mexico City." International Journal of Environmental Research and Public Health 16, no. 10 (May 14, 2019): 1685. http://dx.doi.org/10.3390/ijerph16101685.
Full textAbstract:
Open streets programs are free and multisectoral programs in which streets are temporally closed allowing access to walkers, runners, rollerbladers, and cyclists. The Move on Bikes program (by its name in Spanish Muévete en Bici) (MEB) consists of 55 km of interconnected streets in middle-high income areas of Mexico City. There is scarce evidence on the evaluation of this program in Mexico. The purposes of this study were to estimate the participation, physical activity levels among the MEB participants, and the association of the frequency of participation with sociodemographic, physical, and program characteristics. Methods: From October 2017 to July 2018, six hundred seventy-nine MEB participants were surveyed using a questionnaire that contains sociodemographic, physical, and program characteristics. A wide-angle video camera was used to estimate the average speed of each activity per event per participant. Based on the information collected by the program authorities and survey interviews, we estimated the number of participants per event. Results: On a typical MEB program day, 21,812 people participated. MEB program users accumulated an average of 221 min of moderate-to-vigorous physical activity (MVPA) per typical Sunday and 88.4% accumulated at least 150 min of MVPA. In total, 29.6% of users attended the program every Sunday. Those who were more likely to attend the program frequently included: men, those aged 41 to 64 years old, users classified as very and sufficiently active, those that used active transportation to travel to the program, and participants that came alone. Conclusions: This study provides evidence that the MEB program adds an extra 71 min/week of MVPA to more than 20,000 users.
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Xiong, W., R. Pestell, and M. R. Rosner. "Role of cyclins in neuronal differentiation of immortalized hippocampal cells." Molecular and Cellular Biology 17, no. 11 (November 1997): 6585–97. http://dx.doi.org/10.1128/mcb.17.11.6585.
Full textAbstract:
The proto-oncogene cyclin D1 and the neuron-specific cyclins p35 and p39 are expressed during brain maturation. To investigate the role of these cyclins in neuronal differentiation, we used a conditionally immortalized rat hippocampal cell line, H19-7, that expresses cyclin-dependent kinases 4 and 5 (cdk4 and -5). Cyclin D1, which activates cdk4 and binds but does not activate cdk5, was increased upon differentiation of the H19-7 cells. However, microinjection of either sense or antisense cyclin D1 cDNA or anti-cyclin D1 antibodies had no effect on morphological differentiation of the cells. On the other hand, neurite outgrowth was stimulated by expression of p35 or p39, both of which activate cdk5. A dominant-negative mutant of cdk5 blocked both p35- and p39-induced neurite extension as well as basic fibroblast growth factor (bFGF)-induced neuronal differentiation. However, of these cyclins, only antisense p39 prevented bFGF-induced neurite outgrowth. These studies indicate that cyclin D1 is neither necessary nor sufficient for morphological differentiation, that p35 is sufficient but not required, and that p39 is both necessary and sufficient for neurite outgrowth in the hippocampal cells. Taken together, these results represent the first demonstration of a specific role for p39 in neuronal differentiation, implicate the cyclin-activated kinase cdk5 in this process, and indicate that p39 is able to mediate neurite outgrowth in the presence or absence of cyclin D1.
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Kato, J. Y., M. Matsuoka, D. K. Strom, and C. J. Sherr. "Regulation of cyclin D-dependent kinase 4 (cdk4) by cdk4-activating kinase." Molecular and Cellular Biology 14, no. 4 (April 1994): 2713–21. http://dx.doi.org/10.1128/mcb.14.4.2713.
Full textAbstract:
The accumulation of assembled holoenzymes composed of regulatory D-type cyclins and their catalytic partner, cyclin-dependent kinase 4 (cdk4), is rate limiting for progression through the G1 phase of the cell cycle in mammalian fibroblasts. Both the synthesis and assembly of D-type cyclins and cdk4 depend upon serum stimulation, but even when both subunits are ectopically overproduced, they do not assemble into complexes in serum-deprived cells. When coexpressed from baculoviral vectors in intact Sf9 insect cells, cdk4 assembles with D-type cyclins to form active protein kinases. In contrast, recombinant D-type cyclin and cdk4 subunits produced in insect cells or in bacteria do not assemble as efficiently into functional holoenzymes when combined in vitro but can be activated in the presence of lysates obtained from proliferating mammalian cells. Assembly of cyclin D-cdk4 complexes in coinfected Sf9 cells facilitates phosphorylation of cdk4 on threonine 172 by a cdk-activating kinase (CAK). Assembly can proceed in the absence of this modification, but cdk4 mutants which cannot be phosphorylated by CAK remain catalytically inactive. Therefore, formation of the cyclin D-cdk4 complex and phosphorylation of the bound catalytic subunit are independently regulated, and in addition to the requirement for CAK activity, serum stimulation is required to promote assembly of the complexes in mammalian cells.
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Hirai, H., M. F. Roussel, J. Y. Kato, R. A. Ashmun, and C. J. Sherr. "Novel INK4 proteins, p19 and p18, are specific inhibitors of the cyclin D-dependent kinases CDK4 and CDK6." Molecular and Cellular Biology 15, no. 5 (May 1995): 2672–81. http://dx.doi.org/10.1128/mcb.15.5.2672.
Full textAbstract:
Cyclin D-dependent kinases act as mitogen-responsive, rate-limiting controllers of G1 phase progression in mammalian cells. Two novel members of the mouse INK4 gene family, p19 and p18, that specifically inhibit the kinase activities of CDK4 and CDK6, but do not affect those of cyclin E-CDK2, cyclin A-CDK2, or cyclin B-CDC2, were isolated. Like the previously described human INK4 polypeptides, p16INK4a/MTS1 and p15INK4b/MTS2, mouse p19 and p18 are primarily composed of tandemly repeated ankyrin motifs, each ca. 32 amino acids in length, p19 and p18 bind directly to CDK4 and CDK6, whether untethered or in complexes with D cyclins, and can inhibit the activity of cyclin D-bound cyclin-dependent kinases (CDKs). Although neither protein interacts with D cyclins or displaces them from preassembled cyclin D-CDK complexes in vitro, both form complexes with CDKs at the expense of cyclins in vivo, suggesting that they may also interfere with cyclin-CDK assembly. In proliferating macrophages, p19 mRNA and protein are periodically expressed with a nadir in G1 phase and maximal synthesis during S phase, consistent with the possibility that INK4 proteins limit the activities of CDKs once cells exit G1 phase. However, introduction of a vector encoding p19 into mouse NIH 3T3 cells leads to constitutive p19 synthesis, inhibits cyclin D1-CDK4 activity in vivo, and induces G1 phase arrest.
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Müller-Tidow, Carsten, Ping Ji, Sven Diederichs, Jenny Potratz, Nicole Bäumer, Gabriele Köhler, Thomas Cauvet, et al. "The Cyclin A1-CDK2 Complex Regulates DNA Double-Strand Break Repair." Molecular and Cellular Biology 24, no. 20 (October 15, 2004): 8917–28. http://dx.doi.org/10.1128/mcb.24.20.8917-8928.2004.
Full textAbstract:
ABSTRACT Vertebrates express two A-type cyclins; both associate with and activate the CDK2 protein kinase. Cyclin A1 is required in the male germ line, but its molecular functions are incompletely understood. We observed specific induction of cyclin A1 expression and promoter activity after UV and γ-irradiation which was mediated by p53. cyclin A1 −/− cells showed increased radiosensitivity. To unravel a potential role of cyclin A1 in DNA repair, we performed a yeast triple hybrid screen and identified the Ku70 DNA repair protein as a binding partner and substrate of the cyclin A1-CDK2 complex. DNA double-strand break (DSB) repair was deficient in cyclin A1 −/− cells. Further experiments indicated that A-type cyclins activate DNA DSB repair by mechanisms that depend on CDK2 activity and Ku proteins. Both cyclin A1 and cyclin A2 enhanced DSB repair by homologous recombination, but only cyclin A1 significantly activated nonhomologous end joining. DNA DSB repair was specific for A-type cyclins because cyclin E was ineffective. These findings establish a novel function for cyclin A1 and CDK2 in DNA DSB repair following radiation damage.
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Chow, K. N., P. Starostik, and D. C. Dean. "The Rb family contains a conserved cyclin-dependent-kinase-regulated transcriptional repressor motif." Molecular and Cellular Biology 16, no. 12 (December 1996): 7173–81. http://dx.doi.org/10.1128/mcb.16.12.7173.
Full textAbstract:
Progression through the cell cycle is dependent on the sequential expression of cyclins, which combine with cyclin-dependent kinases (cdks) to form active kinases. The transition from G1 to S phase is dependent on D cyclins in complex with cdk4 or cdk6 and cyclin E complexed with cdk2. One target of G1 cyclins is the retinoblastoma susceptibility protein (Rb). Rb is a transcriptional repressor that is selectively targeted to genes through interaction with the E2F family of cell cycle transcription factors. Rb is a member of a family of proteins that include p107 and p130. The three proteins share a region known as the pocket that is important for binding E2F and is also the binding site for oncoproteins from DNA tumor viruses that inactivate Rb. We have found that two conserved domains within the Rb pocket (A and B) interact to form a transcriptional repressor motif (K. N. B. Chow and D. C. Dean, Mol. Cell. Biol. 16:4862-4868, 1996). Here we demonstrate that p107 also has an A-B repressor motif, and using domain swapping and coimmunoprecipitation assays, we compare A and B from Rb and p107. Finally and most importantly, we demonstrate that the A-B interaction which forms the repressor motif is blocked by G1 cdk phosphorylation, thereby blocking repressor activity. This A-B repressor motif is then the first example of a cdk-regulated transcriptional repressor.
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Basco, R. D., M. D. Segal, and S. I. Reed. "Negative regulation of G1 and G2 by S-phase cyclins of Saccharomyces cerevisiae." Molecular and Cellular Biology 15, no. 9 (September 1995): 5030–42. http://dx.doi.org/10.1128/mcb.15.9.5030.
Full textAbstract:
Cell cycle progression in the budding yeast Saccharomyces cerevisiae is controlled by the Cdc28 protein kinase, which is sequentially activated by different sets of cyclins. Previous genetic analysis has revealed that two B-type cyclins, Clb5 and Clb6, have a positive role in DNA replication. In the present study, we show, in addition, that these cyclins negatively regulate G1- and G2-specific functions. The consequences of this negative regulation were most apparent in clb6 mutants, which had a shorter pre-Start G1 phase as well as a shorter G2 phase than congenic wild-type cells. As a consequence, clb6 mutants grew and proliferated more rapidly than wild-type cells. It was more difficult to assess the role of Clb5 in G1 and G2 by genetic analysis because of the extreme prolongation of S phase in clb5 mutants. Nevertheless, both Clb5 and Clb6 were shown to be responsible for down-regulation of the protein kinase activities associated with Cln2, a G1 cyclin, and Clb2, a mitotic cyclin, in vivo. These observations are consistent with the observed cell cycle phase accelerations associated with the clb6 mutant and are suggestive of similar functions for Clb5. Genetic evidence suggested that the inhibition of mitotic cyclin-dependent kinase activities was dependent on and possibly mediated through the CDC6 gene product. Thus, Clb5 and Clb6 may stabilize S phase by promoting DNA replication while inhibiting other cell cycle activities.
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Lundberg, Ante S., and Robert A. Weinberg. "Functional Inactivation of the Retinoblastoma Protein Requires Sequential Modification by at Least Two Distinct Cyclin-cdk Complexes." Molecular and Cellular Biology 18, no. 2 (February 1, 1998): 753–61. http://dx.doi.org/10.1128/mcb.18.2.753.
Full textAbstract:
ABSTRACT The retinoblastoma protein (pRb) acts to constrain the G1-S transition in mammalian cells. Phosphorylation of pRb in G1 inactivates its growth-inhibitory function, allowing for cell cycle progression. Although several cyclins and associated cyclin-dependent kinases (cdks) have been implicated in pRb phosphorylation, the precise mechanism by which pRb is phosphorylated in vivo remains unclear. By inhibiting selectively either cdk4/6 or cdk2, we show that endogenous D-type cyclins, acting with cdk4/6, are able to phosphorylate pRb only partially, a process that is likely to be completed by cyclin E-cdk2 complexes. Furthermore, cyclin E-cdk2 is unable to phosphorylate pRb in the absence of prior phosphorylation by cyclin D-cdk4/6 complexes. Complete phosphorylation of pRb, inactivation of E2F binding, and activation of E2F transcription occur only after sequential action of at least two distinct G1cyclin kinase complexes.
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Meyerson, M., and E. Harlow. "Identification of G1 kinase activity for cdk6, a novel cyclin D partner." Molecular and Cellular Biology 14, no. 3 (March 1994): 2077–86. http://dx.doi.org/10.1128/mcb.14.3.2077.
Full textAbstract:
A family of vertebrate cdc2-related kinases has been identified, and these kinases are candidates for roles in cell cycle regulation. Here, we show that the human PLSTIRE gene product is a novel cyclin-dependent kinase, cdk6. The cdk6 kinase is associated with cyclins D1, D2, and D3 in lysates of human cells and is activated by coexpression with D-type cyclins in Sf9 insect cells. Furthermore, we demonstrate that endogenous cdk6 from human cell extracts is an active kinase which can phosphorylate pRB, the product of the retinoblastoma tumor suppressor gene. The activation of cdk6 kinase occurs during mid-G1 in phytohemagglutinin-stimulated T cells, well prior to the activation of cdk2 kinase. This timing suggests that cdk6, and by analogy its homolog cdk4, links growth factor stimulation with the onset of cell cycle progression.
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Jeoung, Doo-Il, L. J. W. M. Oehlen, and Frederick R. Cross. "Cln3-Associated Kinase Activity inSaccharomyces cerevisiae Is Regulated by the Mating Factor Pathway." Molecular and Cellular Biology 18, no. 1 (January 1, 1998): 433–41. http://dx.doi.org/10.1128/mcb.18.1.433.
Full textAbstract:
ABSTRACT The Saccharomyces cerevisiae cell cycle is arrested in G1 phase by the mating factor pathway. Genetic evidence has suggested that the G1 cyclins Cln1, Cln2, and Cln3 are targets of this pathway whose inhibition results in G1 arrest. Inhibition of Cln1- and Cln2-associated kinase activity by the mating factor pathway acting through Far1 has been described. Here we report that Cln3-associated kinase activity is inhibited by mating factor treatment, with dose response and timing consistent with involvement in cell cycle arrest. No regulation of Cln3-associated kinase was observed in a fus3 kss1 strain deficient in mating factor pathway mitogen-activated protein (MAP) kinases. Inhibition occurs mainly at the level of specific activity of Cln3-Cdc28 complexes. Inhibition of the C-terminally truncated Cln3-1-associated kinase is not observed; such truncations were previously identified genetically as causing resistance to mating factor-induced cell cycle arrest. Regulation of Cln3-associated kinase specific activity by mating factor treatment requires Far1. Overexpression of Far1 restores inhibition of C-terminally truncated Cln3-1-associated kinase activity. G2/M-arrested cells are unable to regulate Cln3-associated kinase, possibly because of cell cycle regulation of Far1 abundance. Inhibition of Cln3-associated kinase activity by the mating factor pathway may allow this pathway to block the earliest step in normal cell cycle initiation, since Cln3 functions as the most upstream G1-acting cyclin, activating transcription of the G1 cyclins CLN1 and CLN2 as well as of the S-phase cyclins CLB5 and CLB6.
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Bond, Gareth L., Carol Prives, and James L. Manley. "Poly(A) Polymerase Phosphorylation Is Dependent on Novel Interactions with Cyclins." Molecular and Cellular Biology 20, no. 14 (July 15, 2000): 5310–20. http://dx.doi.org/10.1128/mcb.20.14.5310-5320.2000.
Full textAbstract:
ABSTRACT We have previously shown that poly(A) polymerase (PAP) is negatively regulated by cyclin B-cdc2 kinase hyperphosphorylation in the M phase of the cell cycle. Here we show that cyclin B1binds PAP directly, and we demonstrate further that this interaction is mediated by a stretch of amino acids in PAP with homology to the cyclin recognition motif (CRM), a sequence previously shown in several cell cycle regulators to target specifically G1-phase-type cyclins. We find that PAP interacts with not only G1- but also G2-type cyclins via the CRM and is a substrate for phosphorylation by both types of cyclin-cdk pairs. PAP's CRM shows novel, concentration-dependent effects when introduced as an 8-mer peptide into binding and kinase assays. While higher concentrations of PAP's CRM block PAP-cyclin binding and phosphorylation, lower concentrations induce dramatic stimulation of both activities. Our data not only support the notion that PAP is directly regulated by cyclin-dependent kinases throughout the cell cycle but also introduce a novel type of CRM that functionally interacts with both G1- and G2-type cyclins in an unexpected way.
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Kushner, Jake A., Maria A. Ciemerych, Ewa Sicinska, Lynn M. Wartschow, Monica Teta, Simon Y. Long, Piotr Sicinski, and Morris F. White. "Cyclins D2 and D1 Are Essential for Postnatal Pancreatic β-Cell Growth." Molecular and Cellular Biology 25, no. 9 (May 1, 2005): 3752–62. http://dx.doi.org/10.1128/mcb.25.9.3752-3762.2005.
Full textAbstract:
ABSTRACT Regulation of adult β-cell mass in pancreatic islets is essential to preserve sufficient insulin secretion in order to appropriately regulate glucose homeostasis. In many tissues mitogens influence development by stimulating D-type cyclins (D1, D2, or D3) and activating cyclin-dependent kinases (CDK4 or CDK6), which results in progression through the G1 phase of the cell cycle. Here we show that cyclins D2 and D1 are essential for normal postnatal islet growth. In adult murine islets basal cyclin D2 mRNA expression was easily detected, while cyclin D1 was expressed at lower levels and cyclin D3 was nearly undetectable. Prenatal islet development occurred normally in cyclin D2 − / − or cyclin D1 +/ − D2 − / − mice. However, β-cell proliferation, adult mass, and glucose tolerance were decreased in adult cyclin D2 − / − mice, causing glucose intolerance that progressed to diabetes by 12 months of age. Although cyclin D1 +/ − mice never developed diabetes, life-threatening diabetes developed in 3-month-old cyclin D1 − /+ D2 − / − mice as β-cell mass decreased after birth. Thus, cyclins D2 and D1 were essential for β-cell expansion in adult mice. Strategies to tightly regulate D-type cyclin activity in β cells could prevent or cure diabetes.
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Jung, J. U., M. Stäger, and R. C. Desrosiers. "Virus-encoded cyclin." Molecular and Cellular Biology 14, no. 11 (November 1994): 7235–44. http://dx.doi.org/10.1128/mcb.14.11.7235-7244.1994.
Full textAbstract:
Herpesvirus saimiri contains an open reading frame called eclf2 with homology to the cellular type D cyclins. We now show that the eclf2 gene product is a novel virus-encoded cyclin (v-cyclin). The protein encoded by the v-cyclin gene of this oncogenic herpesvirus was found to have an apparent molecular size of 29 kDa in transformed cells. v-Cyclin protein was found to be associated with cdk6, a cellular cyclin-dependent kinase known to interact with cellular type D cyclins. cdk6/v-cyclin complexes strongly phosphorylated Rb fusion protein and histone H1 as substrates in vitro. Mutational analyses showed that highly conserved amino acids in the cyclin box of v-cyclin were important for association with cdk6 and for activation of cdk6 kinase activity. Thus, v-cyclin resembles cellular type D cyclins in primary sequence, in its association with cdk6, by its ability to activate protein kinase activity, and by the presence of functional cyclin box sequences. v-Cyclin exhibited a selective preference for association with cdk6 over other cyclin-dependent kinases and a high level of kinase activation. The properties of v-cyclin suggest a likely role in oncogenic transformation by this T-lymphotropic herpesvirus.
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Izumi, T., and J. L. Maller. "Phosphorylation of Xenopus cyclins B1 and B2 is not required for cell cycle transitions." Molecular and Cellular Biology 11, no. 8 (August 1991): 3860–67. http://dx.doi.org/10.1128/mcb.11.8.3860-3867.1991.
Full textAbstract:
The cdc2 kinase and B-type cyclins are known to be components of maturation- or M-phase-promoting factor (MPF). Phosphorylation of cyclin B has been reported previously and may regulate entry into and exit from mitosis and meiosis. To investigate the role of cyclin B phosphorylation, we replaced putative cdc2 kinase phosphorylation sites in Xenopus cyclins B1 and B2 by using oligonucleotide site-directed mutagenesis. We found that Ser-90 of cyclin B2 and Ser-94 or Ser-96 of cyclin B1 are the main phosphorylation sites both in functional Xenopus egg extracts and after phosphorylation with purified MPF in vitro. Microtubule-associated protein (MAP) kinase from Xenopus eggs phosphorylated cyclin B1 significantly at Ser-94 or Ser-96, whereas it was largely inactive against cyclin B2. The substitutions that ablated phosphorylation at these sites, however, resulted in no functional differences between mutant and wild-type cyclin, as judged by the kinetics of M-phase degradation, induction of mitosis in egg extracts, or induction of oocyte maturation. These results indicate that the phosphorylation of Xenopus B-type cyclins by cdc2 kinase or MAP kinase is not required for the hallmark functions of cyclin.
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Musgrove, E. A., J. A. Hamilton, C. S. Lee, K. J. Sweeney, C. K. Watts, and R. L. Sutherland. "Growth factor, steroid, and steroid antagonist regulation of cyclin gene expression associated with changes in T-47D human breast cancer cell cycle progression." Molecular and Cellular Biology 13, no. 6 (June 1993): 3577–87. http://dx.doi.org/10.1128/mcb.13.6.3577.
Full textAbstract:
Cyclins and proto-oncogenes including c-myc have been implicated in eukaryotic cell cycle control. The role of cyclins in steroidal regulation of cell proliferation is unknown, but a role for c-myc has been suggested. This study investigated the relationship between regulation of T-47D breast cancer cell cycle progression, particularly by steroids and their antagonists, and changes in the levels of expression of these genes. Sequential induction of cyclins D1 (early G1 phase), D3, E, A (late G1-early S phase), and B1 (G2 phase) was observed following insulin stimulation of cell cycle progression in serum-free medium. Transient acceleration of G1-phase cells by progestin was also accompanied by rapid induction of cyclin D1, apparent within 2 h. This early induction of cyclin D1 and the ability of delayed administration of antiprogestin to antagonize progestin-induced increases in both cyclin D1 mRNA and the proportion of cells in S phase support a central role for cyclin D1 in mediating the mitogenic response in T-47D cells. Compatible with this hypothesis, antiestrogen treatment reduced the expression of cyclin D1 approximately 8 h before changes in cell cycle phase distribution accompanying growth inhibition. In the absence of progestin, antiprogestin treatment inhibited T-47D cell cycle progression but in contrast did not decrease cyclin D1 expression. Thus, changes in cyclin D1 gene expression are often, but not invariably, associated with changes in the rate of T-47D breast cancer cell cycle progression. However, both antiestrogen and antiprogestin depleted c-myc mRNA by > 80% within 2 h. These data suggest the involvement of both cyclin D1 and c-myc in the steroidal control of breast cancer cell cycle progression.
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Lukas, J., J. Bartkova, M. Rohde, M. Strauss, and J. Bartek. "Cyclin D1 is dispensable for G1 control in retinoblastoma gene-deficient cells independently of cdk4 activity." Molecular and Cellular Biology 15, no. 5 (May 1995): 2600–2611. http://dx.doi.org/10.1128/mcb.15.5.2600.
Full textAbstract:
To elucidate the regulator-versus-target relationship in the cyclin D1/cdk4/retinoblastoma protein (pRB) pathway, we examined fibroblasts from RB-1 gene-deficient and RB-1 wild-type littermate mouse embryos (ME) and in human tumor cell lines that differed in the status of the RB-1 gene. The RB+/+ and RB-/- ME fibroblasts expressed similar protein levels of D-type cyclins, cdk4, and cdk6, showed analogous spectra and abundance of cellular proteins complexed with cdk4 and/or cyclins D1 and D2, and exhibited comparable associated kinase activities. Of the two human cell lines established from the same sarcoma biopsy, the RB-positive SKUT1B cells contained cdk4 that was mainly associated with D-type cyclins, contrary to a predominant cdk4-p16INK4 complex in the RB-deficient SKUT1A cells. Antibody-mediated neutralization of cyclin D1 arrested the RB-positive ME and SKUT1B cells in G1, whereas this cyclin appeared dispensable in the RB-deficient ME and SKUT1A cells. Lack of requirement for cyclin D1 therefore correlated with absence of functional pRB, regardless of whether active cyclin D1/cdk4 holoenzyme was present in the cells under study. Consistent with a potential role of cyclin D/cdk4 in phosphorylation of pRB, monoclonal anti-cyclin D1 antibodies supporting the associated kinase activity failed to significantly affect proliferation of RB-positive cells, whereas the antibody DCS-6, unable to coprecipitate cdk4, efficiently inhibited G1 progression and prevented pRB phosphorylation in vivo. These data provide evidence for an upstream control function of cyclin D1/cdk4, and a downstream role for pRB, in the order of events regulating transition through late G1 phase of the mammalian cell division cycle.
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Schmidt, Marc, Sylvia Fernandez de Mattos, Armando van der Horst, Rob Klompmaker, Geert J. P. L. Kops, Eric W. F. Lam, Boudewijn M. T. Burgering, and René H. Medema. "Cell Cycle Inhibition by FoxO Forkhead Transcription Factors Involves Downregulation of Cyclin D." Molecular and Cellular Biology 22, no. 22 (November 15, 2002): 7842–52. http://dx.doi.org/10.1128/mcb.22.22.7842-7852.2002.
Full textAbstract:
ABSTRACT The FoxO forkhead transcription factors FoxO4 (AFX), FoxO3a (FKHR.L1), and FoxO1a (FKHR) represent important physiological targets of phosphatidylinositol-3 kinase (PI3K)/protein kinase B (PKB) signaling. Overexpression or conditional activation of FoxO factors is able to antagonize many responses to constitutive PI3K/PKB activation including its effect on cellular proliferation. It was previously shown that the FoxO-induced cell cycle arrest is partially mediated by enhanced transcription and protein expression of the cyclin-dependent kinase inhibitor p27kip1 (R. H. Medema, G. J. Kops, J. L. Bos, and B. M. Burgering, Nature 404:782-787, 2000). Here we have identified a p27kip1-independent mechanism that plays an important role in the antiproliferative effect of FoxO factors. Forced expression or conditional activation of FoxO factors leads to reduced protein expression of the D-type cyclins D1 and D2 and is associated with an impaired capacity of CDK4 to phosphorylate and inactivate the S-phase repressor pRb. Downregulation of D-type cyclins involves a transcriptional repression mechanism and does not require p27kip1 function. Ectopic expression of cyclin D1 can partially overcome FoxO factor-induced cell cycle arrest, demonstrating that downregulation of D-type cyclins represents a physiologically relevant mechanism of FoxO-induced cell cycle inhibition.
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Jänicke, R. U., X. Y. Lin, F. H. Lee, and A. G. Porter. "Cyclin D3 sensitizes tumor cells to tumor necrosis factor-induced, c-Myc-dependent apoptosis." Molecular and Cellular Biology 16, no. 10 (October 1996): 5245–53. http://dx.doi.org/10.1128/mcb.16.10.5245.
Full textAbstract:
c-Myc is an important mediator of apoptosis in cytokine- or serum-deprived cells and sensitizes various cell types to tumor necrosis factor alpha (TNF) cytotoxicity. However, downstream mediators of c-Myc-dependent apoptosis are largely unknown. In this study, we investigated whether one or more cyclins which, like c-Myc, are important regulators of the cell cycle are involved in TNF-induced apoptosis downstream of c-Myc. Cyclin D3 and c-Myc levels in HeLa and fibrosarcoma cells correlated with sensitivity of these cells to TNF-induced apoptosis, as both proteins were highly expressed in TNF-sensitive HeLa D98 cells and HT-1080 fibrosarcoma cells but not in their TNF-resistant counterparts, HeLa H21 and SS-HT-1080 cells, respectively. All other cyclins tested were equally expressed in all tumor cell lines. Reduction in the expression of c-Myc by dexamethasone or inhibition of the transcriptional activity of c-Myc by introduction of a dominant negative form of c-Myc into TNF-sensitive HeLa D98 cells strongly suppressed the expression of cyclin D3 (but none of the other cyclins) and rendered the cells resistant to TNF-induced apoptosis. Conversely, introduction of the c-myc gene into TNF-resistant, c-Myc- and cyclin D3-deficient HeLa H21 cells resulted in enhanced cyclin D3 expression and TNF killing. When cyclin D3 expression in HeLa cells was altered by sense or antisense cyclin D3 cDNA, there was a concomitant alteration in their susceptibility to TNF-induced apoptosis without any change in c-Myc levels. Overall, our results show that cyclin D3 sensitizes tumor cells to TNF-induced apoptosis and indicate that the expression of c-Myc and expression of cyclin D3 in HeLa and in HT-1080 fibrosarcoma cells are closely linked.
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Levine, K., K. Huang, and F. R. Cross. "Saccharomyces cerevisiae G1 cyclins differ in their intrinsic functional specificities." Molecular and Cellular Biology 16, no. 12 (December 1996): 6794–803. http://dx.doi.org/10.1128/mcb.16.12.6794.
Full textAbstract:
The three budding yeast CLN genes appear to be functionally redundant for cell cycle Start: any single CLN gene is sufficient to promote Start, while the cln1 cln2 cln3 triple mutant is Start defective and inviable. Both quantitative and apparently qualitative differences between CLN genes have been reported, but available data do not in general allow distinction between qualitative functional differences as opposed to simply quantitative differences in expression or function. To determine if there are intrinsic qualitative differences between Cln proteins, we compared CLN2, CLN3, and crippled (but still partially active) CLN2 genes in a range of assays that differentiate genetically between CLN2 and CLN3. The results suggest that different potencies of Cln2, Cln3, and Cln2 mutants in functional assays cannot be accounted for by a simple quantitative model for their action, since Cln3 is at least as active as Cln2 and much more active than the Cln2 mutants in driving Swi4/Swi6 cell cycle box (SCB)-regulated transcription and cell cycle initiation in cln1 cln2 cln3 bck2 strains, but Cln3 has little or no activity in other assays in which Cln2 and the Cln2 mutants function. Differences in Cln protein abundance are unlikely to account for these results. Cln3-associated kinase is therefore likely to have an intrinsic in vivo substrate specificity distinct from that of Cln2-associated kinase, despite their functional redundancy. Consistent with the idea that Cln3 may be the primary transcriptional activator of CLN1, CLN2, and other genes, the activation of CLN2 transcription was found to be sensitive to the gene dosage of CLN3 but not to the gene dosage of CLN2.
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Parry, David, Daniel Mahony, Ken Wills, and Emma Lees. "Cyclin D-CDK Subunit Arrangement Is Dependent on the Availability of Competing INK4 and p21 Class Inhibitors." Molecular and Cellular Biology 19, no. 3 (March 1, 1999): 1775–83. http://dx.doi.org/10.1128/mcb.19.3.1775.
Full textAbstract:
ABSTRACT The D-type cyclins and their major kinase partners CDK4 and CDK6 regulate G0-G1-S progression by contributing to the phosphorylation and inactivation of the retinoblastoma gene product, pRB. Assembly of active cyclin D-CDK complexes in response to mitogenic signals is negatively regulated by INK4 family members. Here we show that although all four INK4 proteins associate with CDK4 and CDK6 in vitro, only p16INK4a can form stable, binary complexes with both CDK4 and CDK6 in proliferating cells. The other INK4 family members form stable complexes with CDK6 but associate only transiently with CDK4. Conversely, CDK4 stably associates with both p21CIP1 and p27KIP1 in cyclin-containing complexes, suggesting that CDK4 is in equilibrium between INK4 and p21CIP1- or p27KIP1-bound states. In agreement with this hypothesis, overexpression of p21CIP1 in 293 cells, where CDK4 is bound to p16INK4a, stimulates the formation of ternary cyclin D-CDK4-p21CIP1 complexes. These data suggest that members of the p21 family of proteins promote the association of D-type cyclins with CDKs by counteracting the effects of INK4 molecules.
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Slingerland, J. M., L. Hengst, C. H. Pan, D. Alexander, M. R. Stampfer, and S. I. Reed. "A novel inhibitor of cyclin-Cdk activity detected in transforming growth factor beta-arrested epithelial cells." Molecular and Cellular Biology 14, no. 6 (June 1994): 3683–94. http://dx.doi.org/10.1128/mcb.14.6.3683.
Full textAbstract:
Transforming growth factor beta (TGF-beta) is a potent inhibitor of epithelial cell growth. Cyclins E and A in association with Cdk2 have been shown to play a role in the G1-to-S phase transition in mammalian cells. We have studied the effects of TGF-beta-mediated growth arrest on G1/S cyclins E and A. Inhibition of cyclin A-associated kinase by TGF-beta is primarily due to a decrease in cyclin A mRNA and protein. By contrast, while TGF-beta inhibits accumulation of cyclin E mRNA, the reduction in cyclin E protein is minimal. Instead, we find that the activation of cyclin E-associated kinase that normally accompanies the G1-to-S phase transition is inhibited. A novel inhibitor of cyclin-Cdk complexes was detected in TGF-beta-treated cell lysates. Inhibition is mediated by a heat-stable protein that targets both Cdk2 and Cdc2 kinases. In G0-arrested cells, a similar inhibitor of Cdk2 kinase was detected. These data suggest the existence of an inhibitor of cyclin-dependent kinases induced under different conditions to mediate antiproliferative responses.
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Bagui, Tapan K., Subhra Mohapatra, Eric Haura, and W. J. Pledger. "p27Kip1 and p21Cip1 Are Not Required for the Formation of Active D Cyclin-cdk4 Complexes." Molecular and Cellular Biology 23, no. 20 (October 15, 2003): 7285–90. http://dx.doi.org/10.1128/mcb.23.20.7285-7290.2003.
Full textAbstract:
ABSTRACT Our studies address questions pertaining to the regulation of D cyclin-cdk4 activity, and the following results were obtained. Conditions that increased the abundance of the D cyclins also increased the abundance of enzymatically active D cyclin-cdk4 complexes in mouse embryo fibroblasts (MEFs) lacking both p27Kip1 and p21Cip1 (p27/p21−/−). Such conditions included ectopic expression of cyclin D1 and inhibition of D cyclin degradation by the proteasome inhibitor MG132. However, as determined by treatment of wild-type MEFs with MG132, maximal accumulation of D cyclin-cdk4 complexes required p27Kip1 and p21Cip1 and coincided with the formation of inactive D cyclin-cdk4-p27Kip1 or -p21Cip1 complexes. p27Kip1 or p21Cip1 also increased the abundance of D cyclin-cdk4 complexes and reduced amounts of cdk4 activity when ectopically expressed in p27/p21−/− MEFs. Lastly, increases in the stability of the D cyclins accounted for their greater abundance in wild-type MEFs than in p27/p21−/− MEFs. We conclude that (i) D cyclin-cdk4 complexes are formed and become active in the absence of p27Kip1 and p21Cip1 and (ii) p27Kip1 and p21Cip1 maximize the accumulation but inhibit the activity of D cyclin-cdk4 complexes. We suggest that D cyclin-cdk4 complexes are more stable when bound to p27Kip1 or p21Cip1 and that formation of ternary complexes also stabilizes the D cyclins.
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Kato, J. Y., M. Matsuoka, D. K. Strom, and C. J. Sherr. "Regulation of cyclin D-dependent kinase 4 (cdk4) by cdk4-activating kinase." Molecular and Cellular Biology 14, no. 4 (April 1994): 2713–21. http://dx.doi.org/10.1128/mcb.14.4.2713-2721.1994.
Full textAbstract:
The accumulation of assembled holoenzymes composed of regulatory D-type cyclins and their catalytic partner, cyclin-dependent kinase 4 (cdk4), is rate limiting for progression through the G1 phase of the cell cycle in mammalian fibroblasts. Both the synthesis and assembly of D-type cyclins and cdk4 depend upon serum stimulation, but even when both subunits are ectopically overproduced, they do not assemble into complexes in serum-deprived cells. When coexpressed from baculoviral vectors in intact Sf9 insect cells, cdk4 assembles with D-type cyclins to form active protein kinases. In contrast, recombinant D-type cyclin and cdk4 subunits produced in insect cells or in bacteria do not assemble as efficiently into functional holoenzymes when combined in vitro but can be activated in the presence of lysates obtained from proliferating mammalian cells. Assembly of cyclin D-cdk4 complexes in coinfected Sf9 cells facilitates phosphorylation of cdk4 on threonine 172 by a cdk-activating kinase (CAK). Assembly can proceed in the absence of this modification, but cdk4 mutants which cannot be phosphorylated by CAK remain catalytically inactive. Therefore, formation of the cyclin D-cdk4 complex and phosphorylation of the bound catalytic subunit are independently regulated, and in addition to the requirement for CAK activity, serum stimulation is required to promote assembly of the complexes in mammalian cells.
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Stack, J. H., and J. W. Newport. "Developmentally regulated activation of apoptosis early in Xenopus gastrulation results in cyclin A degradation during interphase of the cell cycle." Development 124, no. 16 (August 15, 1997): 3185–95. http://dx.doi.org/10.1242/dev.124.16.3185.
Full textAbstract:
Previous work identified a developmental timer that controls the stability of cyclin A protein in interphase-arrested Xenopus embryos. It was shown that cyclins A1 and A2 abruptly become unstable in hydroxyurea-treated embryos at the time that untreated embryos are beginning gastrulation (early gastrulation transition; EGT). We have demonstrated here that cyclins A1 and A2 are degraded at the equivalent of the EGT by the ICE-like caspases that are responsible for programmed cell death or apoptosis. Analysis of embryos treated with hydroxyurea or cycloheximide showed widespread cellular apoptosis coincident with cyclin A cleavage. Our data further indicate that the apoptotic pathway is present in Xenopus embryos prior to the EGT; however, it is maintained in an inactive state in early cleaving embryos by maternally encoded inhibitors. Characterization of the timing of the activation of apoptosis implicates the initiation of zygotic transcription at the mid-blastula transition (MBT) in the suppression of apoptosis in normal embryos. The decreased biosynthetic capacity of embryos treated with hydroxyurea or cycloheximide most likely interferes with the ability to maintain sufficient levels of apoptotic inhibitors and results in widespread apoptosis. Our results suggest a scenario whereby the apoptotic pathway is suppressed in the early cleaving embryo by maternally contributed inhibitors. Degradation at the EGT of maternal RNAs encoding these inhibitors is compensated for by new zygotic transcription beginning at the MBT. This indicates that the interval between the MBT and the EGT represents a critical developmental period during which the regulation of embryonic cellular processes is transferred from maternal to zygotic control.
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Philpott, A., and S. H. Friend. "E2F and its developmental regulation in Xenopus laevis." Molecular and Cellular Biology 14, no. 7 (July 1994): 5000–5009. http://dx.doi.org/10.1128/mcb.14.7.5000.
Full textAbstract:
The transcription factor E2F has been implicated in cell cycle control by virtue of its association with cyclins, cyclin-dependent kinases, and pRb-related tumor suppressor gene products. Eggs and embryos from the frog Xenopus laevis have been used to investigate the characteristics of E2F-like molecules in the Xenopus cell cycle and throughout early development. We find multiple E2F species in Xenopus eggs, at least one of which is modified by phosphorylation. The vast majority of E2F remains in the free form throughout the very early embryonic cell cycle, and it also remains predominantly free until some time after the mid-blastula transition, the onset of zygotic transcription. At this time, E2F complexes significantly to pRb but not to cdk2, although cdk2 binding is found in tissue culture cells from a very advanced stage in embryogenesis. This suggests that the complexing of E2F to cyclins, cyclin-dependent kinases, and tumor suppressor gene products may be controlled separately in early Xenopus development. Thus, the association of E2F with other molecules may not result solely from processes affecting cell cycle progression but may also reflect developmental and differentiation cues.
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Audic, Yann, Christina Anderson, Robert Bhatty, and Rebecca S. Hartley. "Zygotic Regulation of Maternal Cyclin A1 and B2 mRNAs." Molecular and Cellular Biology 21, no. 5 (March 1, 2001): 1662–71. http://dx.doi.org/10.1128/mcb.21.5.1662-1671.2001.
Full textAbstract:
ABSTRACT At the midblastula transition, the Xenopus laevis embryonic cell cycle is remodeled from rapid alternations between S and M phases to become the complex adult cell cycle. Cell cycle remodeling occurs after zygotic transcription initiates and is accompanied by terminal downregulation of maternal cyclins A1 and B2. We report here that the disappearance of both cyclin A1 and B2 proteins is preceded by the rapid deadenylation of their mRNAs. A specific mechanism triggers this deadenylation. This mechanism depends upon discrete regions of the 3′ untranslated regions and requires zygotic transcription. Together, these results strongly suggest that zygote-dependent deadenylation of cyclin A1 and cyclin B2 mRNAs is responsible for the downregulation of these proteins. These studies also raise the possibility that zygotic control of maternal cyclins plays a role in establishing the adult cell cycle.
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Meyerson, M., and E. Harlow. "Identification of G1 kinase activity for cdk6, a novel cyclin D partner." Molecular and Cellular Biology 14, no. 3 (March 1994): 2077–86. http://dx.doi.org/10.1128/mcb.14.3.2077-2086.1994.
Full textAbstract:
A family of vertebrate cdc2-related kinases has been identified, and these kinases are candidates for roles in cell cycle regulation. Here, we show that the human PLSTIRE gene product is a novel cyclin-dependent kinase, cdk6. The cdk6 kinase is associated with cyclins D1, D2, and D3 in lysates of human cells and is activated by coexpression with D-type cyclins in Sf9 insect cells. Furthermore, we demonstrate that endogenous cdk6 from human cell extracts is an active kinase which can phosphorylate pRB, the product of the retinoblastoma tumor suppressor gene. The activation of cdk6 kinase occurs during mid-G1 in phytohemagglutinin-stimulated T cells, well prior to the activation of cdk2 kinase. This timing suggests that cdk6, and by analogy its homolog cdk4, links growth factor stimulation with the onset of cell cycle progression.
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Bremner, R., B. L. Cohen, M. Sopta, P. A. Hamel, C. J. Ingles, B. L. Gallie, and R. A. Phillips. "Direct transcriptional repression by pRB and its reversal by specific cyclins." Molecular and Cellular Biology 15, no. 6 (June 1995): 3256–65. http://dx.doi.org/10.1128/mcb.15.6.3256.
Full textAbstract:
It was recently shown that the E2F-pRB complex is a negative transcriptional regulator. However, it was not determined whether the whole complex or pRB alone is required for repression. Here we show that pRB and the related protein p107 are capable of direct transcriptional repression independent of E2F. When fused to the DNA binding domain of GAL4, pRB or p107 represses transcription of promoters with GAL4 binding sites. Thus, E2F acts as a tether for pRB or p107 but is not actively involved in repression of other enhancers. This function of pRB maps to the pocket and is abrogated by mutation of this domain. This result suggests an intriguing model in which the pocket has a dual function, first to bind E2F and second to repress transcription directly, possibly through interaction with other proteins. We also show that direct transcriptional repression by pRB is regulated by phosphorylation. Mutations which render pRB constitutively hypophosphorylated potentiate repression, while phosphorylation induced by cyclin A or E reduces repression ninefold.
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Clotet, Josep, Eloi Garí, Martí Aldea, and Joaquín Ariño. "The Yeast Ser/Thr Phosphatases Sit4 and Ppz1 Play Opposite Roles in Regulation of the Cell Cycle." Molecular and Cellular Biology 19, no. 3 (March 1, 1999): 2408–15. http://dx.doi.org/10.1128/mcb.19.3.2408.
Full textAbstract:
ABSTRACT Yeast cells overexpressing the Ser/Thr protein phosphatase Ppz1 display a slow-growth phenotype. These cells recover slowly from α-factor or nutrient depletion-induced G1 arrest, showing a considerable delay in bud emergence as well as in the expression of the G1 cyclins Cln2 and Clb5. Therefore, an excess of the Ppz1 phosphatase interferes with the normal transition from G1 to S phase. The growth defect is rescued by overexpression of the HAL3/SIS2 gene, encoding a negative regulator of Ppz1. High-copy-number expression of HAL3/SIS2has been reported to improve cell growth and to increase expression of G1 cyclins in sit4 phosphatase mutants. We show here that the described effects of HAL3/SIS2 onsit4 mutants are fully mediated by the Ppz1 phosphatase. The growth defect caused by overexpression ofPPZ1 is intensified in strains with low G1cyclin levels (such as bck2Δ or cln3Δ mutants), whereas mutation of PPZ1 rescues the synthetic lethal phenotype of sit4 cln3 mutants. These results reveal a role for Ppz1 as a regulatory component of the yeast cell cycle, reinforce the notion that Hal3/Sis2 serves as a negative modulator of the biological functions of Ppz1, and indicate that the Sit4 and Ppz1 Ser/Thr phosphatases play opposite roles in control of the G1/S transition.
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Mondesert, O., C. H. McGowan, and P. Russell. "Cig2, a B-type cyclin, promotes the onset of S in Schizosaccharomyces pombe." Molecular and Cellular Biology 16, no. 4 (April 1996): 1527–33. http://dx.doi.org/10.1128/mcb.16.4.1527.
Full textAbstract:
Cdc2, a catalytic subunit of cyclin-dependent kinases, is required for both the G1-to-S and G2-to-M transitions in the fission yeast Schizosaccharomyces pombe. Cdc13, a B-type cyclin, is required for the M-phase induction function of Cd2. Two additional B-type cyclins, Cig1 and Cig2, have been identified in S. pombe, but none of the B-type cyclins are individually required for the onset of S. We report that Cdc13 is important for DNA replication in a strain lacking Cig2. Unlike deltacdc13 cells, double-mutant deltacdc13 deltacig2 cells are defective in undergoing multiple rounds of DNA replication. The conclusion that Cig2 promotes S is further supported by the finding that Cig2 protein and Cig2-associated kinase activity appear soon after the completion of M and peak during S, as well as the observation that S is delayed in deltacig2 cells as they recover from a G1 arrest induced by nitrogen starvation. These studies indicate that Cig2 is the primary S-phase-promoting cyclin in S. pombe but that Cdc13 can effectively substitute for Cig2 in deltacig2 cells. These observations also suggest that the gradual increase in the activity of Cdc2-Cdc13 kinase can be sufficient for the correct temporal ordering of S and M phases in deltacig2 cells.
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Musgrove, E. A., J. A. Hamilton, C. S. Lee, K. J. Sweeney, C. K. Watts, and R. L. Sutherland. "Growth factor, steroid, and steroid antagonist regulation of cyclin gene expression associated with changes in T-47D human breast cancer cell cycle progression." Molecular and Cellular Biology 13, no. 6 (June 1993): 3577–87. http://dx.doi.org/10.1128/mcb.13.6.3577-3587.1993.
Full textAbstract:
Cyclins and proto-oncogenes including c-myc have been implicated in eukaryotic cell cycle control. The role of cyclins in steroidal regulation of cell proliferation is unknown, but a role for c-myc has been suggested. This study investigated the relationship between regulation of T-47D breast cancer cell cycle progression, particularly by steroids and their antagonists, and changes in the levels of expression of these genes. Sequential induction of cyclins D1 (early G1 phase), D3, E, A (late G1-early S phase), and B1 (G2 phase) was observed following insulin stimulation of cell cycle progression in serum-free medium. Transient acceleration of G1-phase cells by progestin was also accompanied by rapid induction of cyclin D1, apparent within 2 h. This early induction of cyclin D1 and the ability of delayed administration of antiprogestin to antagonize progestin-induced increases in both cyclin D1 mRNA and the proportion of cells in S phase support a central role for cyclin D1 in mediating the mitogenic response in T-47D cells. Compatible with this hypothesis, antiestrogen treatment reduced the expression of cyclin D1 approximately 8 h before changes in cell cycle phase distribution accompanying growth inhibition. In the absence of progestin, antiprogestin treatment inhibited T-47D cell cycle progression but in contrast did not decrease cyclin D1 expression. Thus, changes in cyclin D1 gene expression are often, but not invariably, associated with changes in the rate of T-47D breast cancer cell cycle progression. However, both antiestrogen and antiprogestin depleted c-myc mRNA by > 80% within 2 h. These data suggest the involvement of both cyclin D1 and c-myc in the steroidal control of breast cancer cell cycle progression.