Artículos de revistas: "BHLH-PAS proteins"

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Bersten, David C., Adrienne E. Sullivan, Daniel J. Peet y Murray L. Whitelaw. "bHLH–PAS proteins in cancer". Nature Reviews Cancer 13, n.º 12 (22 de noviembre de 2013): 827–41. http://dx.doi.org/10.1038/nrc3621.

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Kolonko, Marta y Beata Greb-Markiewicz. "bHLH–PAS Proteins: Their Structure and Intrinsic Disorder". International Journal of Molecular Sciences 20, n.º 15 (26 de julio de 2019): 3653. http://dx.doi.org/10.3390/ijms20153653.

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The basic helix–loop–helix/Per-ARNT-SIM (bHLH–PAS) proteins are a class of transcriptional regulators, commonly occurring in living organisms and highly conserved among vertebrates and invertebrates. These proteins exhibit a relatively well-conserved domain structure: the bHLH domain located at the N-terminus, followed by PAS-A and PAS-B domains. In contrast, their C-terminal fragments present significant variability in their primary structure and are unique for individual proteins. C-termini were shown to be responsible for the specific modulation of protein action. In this review, we present the current state of knowledge, based on NMR and X-ray analysis, concerning the structural properties of bHLH–PAS proteins. It is worth noting that all determined structures comprise only selected domains (bHLH and/or PAS). At the same time, substantial parts of proteins, comprising their long C-termini, have not been structurally characterized to date. Interestingly, these regions appear to be intrinsically disordered (IDRs) and are still a challenge to research. We aim to emphasize the significance of IDRs for the flexibility and function of bHLH–PAS proteins. Finally, we propose modern NMR methods for the structural characterization of the IDRs of bHLH–PAS proteins.

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Crews, Stephen T. y Chen-Ming Fan. "Remembrance of things PAS: regulation of development by bHLH–PAS proteins". Current Opinion in Genetics & Development 9, n.º 5 (octubre de 1999): 580–87. http://dx.doi.org/10.1016/s0959-437x(99)00003-9.

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Reisz-Porszasz, S., M. R. Probst, B. N. Fukunaga y O. Hankinson. "Identification of functional domains of the aryl hydrocarbon receptor nuclear translocator protein (ARNT)". Molecular and Cellular Biology 14, n.º 9 (septiembre de 1994): 6075–86. http://dx.doi.org/10.1128/mcb.14.9.6075-6086.1994.

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The activated aryl hydrocarbon receptor (AHR) and the AHR nuclear translocator (ARNT) bind DNA as a heterodimer. Both proteins represent a novel class of basic helix-loop-helix (bHLH)-containing transcription factors in that (i) activation of AHR requires the binding of ligand (e.g., 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD]), (ii) the xenobiotic responsive element (XRE) recognized by the AHR/ARNT heterodimer differs from the recognition sequence for nearly all other bHLH proteins, and (iii) both proteins contain a PAS homology region, which in the Drosophila PER and SIM proteins functions as a dimerization domain. A cDNA for mouse ARNT has been cloned, and potential functional domains of ARNT were investigated by deletion analysis. A mutant lacking all regions of ARNT other than the bHLH and PAS regions is unimpaired in TCDD-dependent dimerization and subsequent XRE binding and only modestly reduced in ability to complement an ARNT-deficient mutant cell line, c4, in vivo. Both the first and second alpha helices of the bHLH region are required for dimerization. The basic region is required for XRE binding but not for dimerization. Deletion of either the A or B segments of the PAS region slightly affects TCDD-induced heterodimerization, while deletion of the complete PAS region severely affects (but does not eliminate) dimerization. Thus, ARNT possesses multiple domains required for maximal heterodimerization. Mutants deleted for PAS A, PAS B, and the complete PAS region all retain some degree of XRE binding, yet none can rescue the c4 mutant. Therefore, both the PAS A and PAS B segments, besides contributing to dimerization, apparently fulfill additional, unknown functions required for biological activity of ARNT.

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Reisz-Porszasz, S., M. R. Probst, B. N. Fukunaga y O. Hankinson. "Identification of functional domains of the aryl hydrocarbon receptor nuclear translocator protein (ARNT)." Molecular and Cellular Biology 14, n.º 9 (septiembre de 1994): 6075–86. http://dx.doi.org/10.1128/mcb.14.9.6075.

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The activated aryl hydrocarbon receptor (AHR) and the AHR nuclear translocator (ARNT) bind DNA as a heterodimer. Both proteins represent a novel class of basic helix-loop-helix (bHLH)-containing transcription factors in that (i) activation of AHR requires the binding of ligand (e.g., 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD]), (ii) the xenobiotic responsive element (XRE) recognized by the AHR/ARNT heterodimer differs from the recognition sequence for nearly all other bHLH proteins, and (iii) both proteins contain a PAS homology region, which in the Drosophila PER and SIM proteins functions as a dimerization domain. A cDNA for mouse ARNT has been cloned, and potential functional domains of ARNT were investigated by deletion analysis. A mutant lacking all regions of ARNT other than the bHLH and PAS regions is unimpaired in TCDD-dependent dimerization and subsequent XRE binding and only modestly reduced in ability to complement an ARNT-deficient mutant cell line, c4, in vivo. Both the first and second alpha helices of the bHLH region are required for dimerization. The basic region is required for XRE binding but not for dimerization. Deletion of either the A or B segments of the PAS region slightly affects TCDD-induced heterodimerization, while deletion of the complete PAS region severely affects (but does not eliminate) dimerization. Thus, ARNT possesses multiple domains required for maximal heterodimerization. Mutants deleted for PAS A, PAS B, and the complete PAS region all retain some degree of XRE binding, yet none can rescue the c4 mutant. Therefore, both the PAS A and PAS B segments, besides contributing to dimerization, apparently fulfill additional, unknown functions required for biological activity of ARNT.

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6

Greb-Markiewicz, Beata y Marta Kolonko. "Subcellular Localization Signals of bHLH-PAS Proteins: Their Significance, Current State of Knowledge and Future Perspectives". International Journal of Molecular Sciences 20, n.º 19 (24 de septiembre de 2019): 4746. http://dx.doi.org/10.3390/ijms20194746.

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The bHLH-PAS (basic helix-loop-helix/ Period-ARNT-Single minded) proteins are a family of transcriptional regulators commonly occurring in living organisms. bHLH-PAS members act as intracellular and extracellular “signals” sensors, initiating response to endo- and exogenous signals, including toxins, redox potential, and light. The activity of these proteins as transcription factors depends on nucleocytoplasmic shuttling: the signal received in the cytoplasm has to be transduced, via translocation, to the nucleus. It leads to the activation of transcription of particular genes and determines the cell response to different stimuli. In this review, we aim to present the current state of knowledge concerning signals that affect shuttling of bHLH-PAS transcription factors. We summarize experimentally verified and published nuclear localization signals/nuclear export signals (NLSs/NESs) in the context of performed in silico predictions. We have used most of the available NLS/NES predictors. Importantly, all our results confirm the existence of a complex system responsible for protein localization regulation that involves many localization signals, which activity has to be precisely controlled. We conclude that the current stage of knowledge in this area is still not complete and for most of bHLH-PAS proteins an experimental verification of the activity of further NLS/NES is needed.

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Gilles-Gonzalez, Marie-Alda y Gonzalo Gonzalez. "Signal transduction by heme-containing PAS-domain proteins". Journal of Applied Physiology 96, n.º 2 (febrero de 2004): 774–83. http://dx.doi.org/10.1152/japplphysiol.00941.2003.

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The most common physiological strategy for detecting the gases oxygen, carbon monoxide, and nitric oxide is signal transduction by heme-based sensors, a broad class of modular proteins in which a heme-binding domain governs the activity of a neighboring transmitter domain. Different structures are possible for the heme-binding domains in these sensors, but, so far, the Per-ARNT-Sim motif, or PAS domain, is the one most commonly encountered. Heme-binding PAS (heme-PAS) domains can accomplish ligand-dependent switching of a variety of partner domains, including histidine kinase, phosphodiesterase, and basic helix-loop-helix (bHLH) DNA-binding modules. Proteins with heme-PAS domains occur in all kingdoms of life and are quite diverse in their physiological roles. Examples include the neuronal bHLH-PAS carbon monoxide sensor NPAS2 that is implicated in the mammalian circadian clock, the acetobacterial oxygen sensor AxPDEA1 that directs cellulose production, and the rhizobial oxygen sensor FixL, which governs nitrogen fixation. What factors determine the range of detection of these sensors? How do they transduce their signal? This review examines the recent advances in answering these questions.

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8

Kolonko-Adamska, Marta, Vladimir N. Uversky y Beata Greb-Markiewicz. "The Participation of the Intrinsically Disordered Regions of the bHLH-PAS Transcription Factors in Disease Development". International Journal of Molecular Sciences 22, n.º 6 (11 de marzo de 2021): 2868. http://dx.doi.org/10.3390/ijms22062868.

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The basic helix–loop–helix/Per-ARNT-SIM (bHLH-PAS) proteins are a family of transcription factors regulating expression of a wide range of genes involved in different functions, ranging from differentiation and development control by oxygen and toxins sensing to circadian clock setting. In addition to the well-preserved DNA-binding bHLH and PAS domains, bHLH-PAS proteins contain long intrinsically disordered C-terminal regions, responsible for regulation of their activity. Our aim was to analyze the potential connection between disordered regions of the bHLH-PAS transcription factors, post-transcriptional modifications and liquid-liquid phase separation, in the context of disease-associated missense mutations. Highly flexible disordered regions, enriched in short motives which are more ordered, are responsible for a wide spectrum of interactions with transcriptional co-regulators. Based on our in silico analysis and taking into account the fact that the functions of transcription factors can be modulated by posttranslational modifications and spontaneous phase separation, we assume that the locations of missense mutations inducing disease states are clearly related to sequences directly undergoing these processes or to sequences responsible for their regulation.

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9

Zelzer, E., P. Wappner y B. Z. Shilo. "The PAS domain confers target gene specificity of Drosophila bHLH/PAS proteins". Genes & Development 11, n.º 16 (15 de agosto de 1997): 2079–89. http://dx.doi.org/10.1101/gad.11.16.2079.

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10

Aitola, Marjo H. y Markku T. Pelto-Huikko. "Expression of Arnt and Arnt2 mRNA in Developing Murine Tissues". Journal of Histochemistry & Cytochemistry 51, n.º 1 (enero de 2003): 41–54. http://dx.doi.org/10.1177/002215540305100106.

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The basic helix-loop-helix (bHLH-PAS) proteins aryl hydrocarbon receptor nuclear translocator (Arnt) and Arnt2 are transcriptional regulators that function as dimerizing partners for several bHLH-PAS proteins and also some nonrelated partners. They are involved in various biological functions, including regulation of developmental genes. In earlier studies, the developmental expression of Arnt was reported to be almost ubiquitous, whereas Arnt2 expression has been shown to be more limited, comprising neuronal tissues as the main site of expression. Here we provide a detailed description of the expression of Arnt and Arnt2 mRNA in mouse tissues during embryonic and early postnatal development. Arnt and also Arnt2 transcripts, in contrast to earlier reports, are shown to be expressed more widely during development yet show a temporally and spatially specific pattern.

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11

LI, YUMIN, YUCAI WEI, JIWU GUO, YUSHENG CHENG y WENTING HE. "Interactional role of microRNAs and bHLH-PAS proteins in cancer (Review)". International Journal of Oncology 47, n.º 1 (15 de mayo de 2015): 25–34. http://dx.doi.org/10.3892/ijo.2015.3007.

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12

Antonsson, C., M. L. Whitelaw, J. McGuire, J. A. Gustafsson y L. Poellinger. "Distinct roles of the molecular chaperone hsp90 in modulating dioxin receptor function via the basic helix-loop-helix and PAS domains." Molecular and Cellular Biology 15, n.º 2 (febrero de 1995): 756–65. http://dx.doi.org/10.1128/mcb.15.2.756.

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The intracellular dioxin receptor mediates signal transduction by dioxin and functions as a ligand-activated transcription factor. It contains a basic helix-loop-helix (bHLH) motif contiguous with a Per-Arnt-Sim (PAS) homology region. In extracts from nonstimulated cells the receptor is recovered in an inducible cytoplasmic form associated with the 90-kDa heat shock protein (hsp90), a molecular chaperone. We have reconstituted ligand-dependent activation of the receptor to a DNA-binding form by using the dioxin receptor and its bHLH-PAS partner factor Arnt expressed by in vitro translation in reticulocyte lysate. Deletion of the PAS domain of the receptor resulted in constitutive dimerization with Arnt. In contrast, this receptor mutant showed low levels of xenobiotic response element-binding activity, indicating that the PAS domain may be important for DNA-binding affinity and/or specificity of the receptor. It was not possible to reconstitute dioxin receptor function with proteins expressed in wheat germ lysate. In line with these observations, reticulocyte lysate but not wheat germ lysate promoted the association of de novo synthesized dioxin receptor with hsp90. At least two distinct domains of the receptor mediated interaction with hsp90: the ligand-binding domain located within the PAS region and, surprisingly, the bHLH domain. Whereas ligand-binding activity correlated with association with hsp90, bHLH-hsp90 interaction appeared to be important for DNA-binding activity but not for dimerization of the receptor. Several distinct roles for hsp90 in modulating dioxin receptor function are therefore likely: correct folding of the ligand-binding domain, interference with Arnt heterodimerization, and folding of a DNA-binding conformation of the bHLH domain. Thus, the dioxin receptor system provides a complex and interesting model of the regulation of transcription factors by hsp90.

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Michael, Alicia K., Jennifer L. Fribourgh, Yogarany Chelliah, Colby R. Sandate, Greg L. Hura, Dina Schneidman-Duhovny, Sarvind M. Tripathi, Joseph S. Takahashi y Carrie L. Partch. "Formation of a repressive complex in the mammalian circadian clock is mediated by the secondary pocket of CRY1". Proceedings of the National Academy of Sciences 114, n.º 7 (31 de enero de 2017): 1560–65. http://dx.doi.org/10.1073/pnas.1615310114.

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The basic helix–loop–helix PAS domain (bHLH-PAS) transcription factor CLOCK:BMAL1 (brain and muscle Arnt-like protein 1) sits at the core of the mammalian circadian transcription/translation feedback loop. Precise control of CLOCK:BMAL1 activity by coactivators and repressors establishes the ∼24-h periodicity of gene expression. Formation of a repressive complex, defined by the core clock proteins cryptochrome 1 (CRY1):CLOCK:BMAL1, plays an important role controlling the switch from repression to activation each day. Here we show that CRY1 binds directly to the PAS domain core of CLOCK:BMAL1, driven primarily by interaction with the CLOCK PAS-B domain. Integrative modeling and solution X-ray scattering studies unambiguously position a key loop of the CLOCK PAS-B domain in the secondary pocket of CRY1, analogous to the antenna chromophore-binding pocket of photolyase. CRY1 docks onto the transcription factor alongside the PAS domains, extending above the DNA-binding bHLH domain. Single point mutations at the interface on either CRY1 or CLOCK disrupt formation of the ternary complex, highlighting the importance of this interface for direct regulation of CLOCK:BMAL1 activity by CRY1.

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Li, M., E. A. Mead y J. Zhu. "Heterodimer of two bHLH-PAS proteins mediates juvenile hormone-induced gene expression". Proceedings of the National Academy of Sciences 108, n.º 2 (27 de diciembre de 2010): 638–43. http://dx.doi.org/10.1073/pnas.1013914108.

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15

Crews, S. T. "Control of cell lineage-specific development and transcription by bHLH-PAS proteins". Genes & Development 12, n.º 5 (1 de marzo de 1998): 607–20. http://dx.doi.org/10.1101/gad.12.5.607.

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16

Godlewski, Jakub, Shaoli Wang y Thomas G. Wilson. "Interaction of bHLH-PAS proteins involved in juvenile hormone reception in Drosophila". Biochemical and Biophysical Research Communications 342, n.º 4 (abril de 2006): 1305–11. http://dx.doi.org/10.1016/j.bbrc.2006.02.097.

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17

Choi, Yoon-Jeong, Eun-Jeong Kwon, Joung-Sun Park, Ho-Sung Kang, Young-Shin Kim y Mi-Ae Yoo. "Transcriptional regulation of the Drosophila caudal homeobox gene by bHLH–PAS proteins". Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression 1769, n.º 1 (enero de 2007): 41–48. http://dx.doi.org/10.1016/j.bbaexp.2006.11.008.

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18

Jiang, Lan y Stephen T. Crews. "The Drosophila dysfusion Basic Helix-Loop-Helix (bHLH)-PAS Gene Controls Tracheal Fusion and Levels of the Trachealess bHLH-PAS Protein". Molecular and Cellular Biology 23, n.º 16 (15 de agosto de 2003): 5625–37. http://dx.doi.org/10.1128/mcb.23.16.5625-5637.2003.

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ABSTRACT The development of the mature insect trachea requires a complex series of cellular events, including tracheal cell specification, cell migration, tubule branching, and tubule fusion. Here we describe the identification of the Drosophila melanogaster dysfusion gene, which encodes a novel basic helix-loop-helix (bHLH)-PAS protein conserved between Caenorhabditis elegans, insects, and humans, and controls tracheal fusion events. The Dysfusion protein functions as a heterodimer with the Tango bHLH-PAS protein in vivo to form a putative DNA-binding complex. The dysfusion gene is expressed in a variety of embryonic cell types, including tracheal-fusion, leading-edge, foregut atrium cells, nervous system, hindgut, and anal pad cells. RNAi experiments indicate that dysfusion is required for dorsal branch, lateral trunk, and ganglionic branch fusion but not for fusion of the dorsal trunk. The escargot gene, which is also expressed in fusion cells and is required for tracheal fusion, precedes dysfusion expression. Analysis of escargot mutants indicates a complex pattern of dysfusion regulation, such that dysfusion expression is dependent on escargot in the dorsal and ganglionic branches but not the dorsal trunk. Early in tracheal development, the Trachealess bHLH-PAS protein is present at uniformly high levels in all tracheal cells, but since the levels of Dysfusion rise in wild-type fusion cells, the levels of Trachealess in fusion cells decline. The downregulation of Trachealess is dependent on dysfusion function. These results suggest the possibility that competitive interactions between basic helix-loop-helix-PAS proteins (Dysfusion, Trachealess, and possibly Similar) may be important for the proper development of the trachea.

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Romero, Nuria M., Maximiliano Irisarri, Peggy Roth, Ana Cauerhff, Christos Samakovlis y Pablo Wappner. "Regulation of the Drosophila Hypoxia-Inducible Factor α Sima by CRM1-Dependent Nuclear Export". Molecular and Cellular Biology 28, n.º 10 (10 de marzo de 2008): 3410–23. http://dx.doi.org/10.1128/mcb.01027-07.

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ABSTRACT Hypoxia-inducible factor α (HIF-α) proteins are regulated by oxygen levels through several different mechanisms that include protein stability, transcriptional coactivator recruitment, and subcellular localization. It was previously reported that these transcription factors are mainly nuclear in hypoxia and cytoplasmic in normoxia, but so far the molecular basis of this regulation is unclear. We show here that the Drosophila melanogaster HIF-α protein Sima shuttles continuously between the nucleus and the cytoplasm. We identified the relevant nuclear localization signal and two functional nuclear export signals (NESs). These NESs are in the Sima basic helix-loop-helix (bHLH) domain and promote CRM1-dependent nuclear export. Site-directed mutagenesis of either NES provoked Sima nuclear retention and increased transcriptional activity, suggesting that nuclear export contributes to Sima regulation. The identified NESs are conserved and probably functional in the bHLH domains of several bHLH-PAS proteins. We propose that rapid nuclear export of Sima regulates the duration of cellular responses to hypoxia.

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Epstein, D. J., L. Martinu, J. L. Michaud, K. M. Losos, C. Fan y A. L. Joyner. "Members of the bHLH-PAS family regulate Shh transcription in forebrain regions of the mouse CNS". Development 127, n.º 21 (1 de noviembre de 2000): 4701–9. http://dx.doi.org/10.1242/dev.127.21.4701.

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The secreted protein sonic hedgehog (Shh) is required to establish patterns of cellular growth and differentiation within ventral regions of the developing CNS. The expression of Shh in the two tissue sources responsible for this activity, the axial mesoderm and the ventral midline of the neural tube, is regulated along the anteroposterior neuraxis. Separate cis-acting regulatory sequences have been identified which direct Shh expression to distinct regions of the neural tube, supporting the view that multiple genes are involved in activating Shh transcription along the length of the CNS. We show here that the activity of one Shh enhancer, which directs reporter expression to portions of the ventral midbrain and diencephalon, overlaps both temporally and spatially with the expression of Sim2. Sim2 encodes a basic helix-loop-helix (bHLH-PAS) PAS domain containing transcriptional regulator whose Drosophila homolog, single-minded, is a master regulator of ventral midline development. Both vertebrate and invertebrate Sim family members were found sufficient for the activation of the Shh reporter as well as endogenous Shh mRNA. Although Shh expression is maintained in Sim2(−)(/)(−) embryos, it was determined to be absent from the rostral midbrain and caudal diencephalon of embryos carrying a dominant-negative transgene that disrupts the function of bHLH-PAS proteins. Together, these results suggest that bHLH-PAS family members are required for the regulation of Shh transcription within aspects of the ventral midbrain and diencephalon.

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21

Hirose, K., M. Morita, M. Ema, J. Mimura, H. Hamada, H. Fujii, Y. Saijo, O. Gotoh, K. Sogawa y Y. Fujii-Kuriyama. "cDNA cloning and tissue-specific expression of a novel basic helix-loop-helix/PAS factor (Arnt2) with close sequence similarity to the aryl hydrocarbon receptor nuclear translocator (Arnt)." Molecular and Cellular Biology 16, n.º 4 (abril de 1996): 1706–13. http://dx.doi.org/10.1128/mcb.16.4.1706.

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We isolated mouse cDNA clones (Arnt2) that are highly similar to but distinct from the aryl hydrocarbon receptor (AhR) nuclear translocator (Arnt). The composite cDNA covered a 2,443-bp sequence consisting of a putative 2,136-bp open reading frame encoding a polypeptide of 712 amino acids. The predicted Arnt2 polypeptide carries a characteristic basic helix-loop-helix (bHLH)/PAS motif in its N-terminal region with close similarity (81% identity) to that of mouse Arnt and has an overall sequence identity of 57% with Arnt. Biochemical properties and interaction of Arnt2 with other bHLH/PAS proteins were investigated by coimmunoprecipitation assays, gel mobility shift assays, and the yeast two-hybrid system. Arnt2 interacted with AhR and mouse Sim as efficiently as Arnt, and the Arnt2-AhR complex recognized and bound specifically the xenobiotic responsive element (XRE) sequence. Expression of Arnt2 successfully rescued XRE-driven reporter gene activity in the Arnt-defective c4 mutant of Hepa-1 cells. RNA blot analysis revealed that expression of Arnt2 mRNA was restricted to the brains and kidneys of adult mice, while Arnt mRNA was expressed ubiquitously. In addition, whole-mount in situ hybridization of 9.5-day mouse embryos showed that Arnt2 mRNA was expressed in the dorsal neural tube and branchial arch 1, while Arnt transcripts were detected broadly in various tissues of mesodermal and endodermal origins. These results suggest that Arnt2 may play different roles from Arnt both in adult mice and in developing embryos. Finally, sequence comparison of the currently known bHLH/PAS proteins indicates a division into two phylogenetic groups: the Arnt group, containing Arnt, Arnt2, and Per, and the AhR group, consisting of AhR, Sim, and Hif-1alpha.

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Button, Emily L., David C. Bersten y Murray L. Whitelaw. "HIF has Biff – Crosstalk between HIF1a and the family of bHLH/PAS proteins". Experimental Cell Research 356, n.º 2 (julio de 2017): 141–45. http://dx.doi.org/10.1016/j.yexcr.2017.03.055.

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23

Kinoshita, K. "Altered DNA binding specificity of Arnt by selection of partner bHLH-PAS proteins". Nucleic Acids Research 32, n.º 10 (2 de junio de 2004): 3169–79. http://dx.doi.org/10.1093/nar/gkh637.

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Wiesener, M. S., H. Turley, W. E. Allen, C. Willam, K. U. Eckardt, K. L. Talks, S. M. Wood et al. "Induction of Endothelial PAS Domain Protein-1 by Hypoxia: Characterization and Comparison With Hypoxia-Inducible Factor-1α". Blood 92, n.º 7 (1 de octubre de 1998): 2260–68. http://dx.doi.org/10.1182/blood.v92.7.2260.

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Abstract Hypoxia results in adaptive changes in the transcription of a range of genes including erythropoietin. An important mediator is hypoxia-inducible factor-1 (HIF-1), a DNA binding complex shown to contain at least two basic helix-loop-helix PAS-domain (bHLH-PAS) proteins, HIF-1α and aryl hydrocarbon nuclear receptor translocator (ARNT). In response to hypoxia, HIF-1α is activated and accumulates rapidly in the cell. Endothelial PAS domain protein 1 (EPAS-1) is a recently identified bHLH-PAS protein with 48% identity to HIF-1α, raising the question of its role in responses to hypoxia. We developed specific antibodies and studied expression and regulation of EPAS-1 mRNA and protein across a range of human cell lines. EPAS-1 was widely expressed, and strongly induced by hypoxia at the level of protein but not mRNA. Comparison of the effect of a range of activating and inhibitory stimuli showed striking similarities in the EPAS-1 and HIF-1α responses. Although major differences were observed in the abundance of EPAS-1 and HIF-1α in different cell types, differences in the inducible response were subtle with EPAS-1 protein being slightly more evident in normoxic and mildly hypoxic cells. Functional studies in a mutant cell line (Ka13) expressing neither HIF-1α nor EPAS-1 confirmed that both proteins interact with hypoxically responsive targets, but suggest target specificity with greater EPAS-1 transactivation (relative to HIF-1α transactivation) of the VEGF promoter than the LDH-A promoter.

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25

Wiesener, M. S., H. Turley, W. E. Allen, C. Willam, K. U. Eckardt, K. L. Talks, S. M. Wood et al. "Induction of Endothelial PAS Domain Protein-1 by Hypoxia: Characterization and Comparison With Hypoxia-Inducible Factor-1α". Blood 92, n.º 7 (1 de octubre de 1998): 2260–68. http://dx.doi.org/10.1182/blood.v92.7.2260.2260_2260_2268.

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Hypoxia results in adaptive changes in the transcription of a range of genes including erythropoietin. An important mediator is hypoxia-inducible factor-1 (HIF-1), a DNA binding complex shown to contain at least two basic helix-loop-helix PAS-domain (bHLH-PAS) proteins, HIF-1α and aryl hydrocarbon nuclear receptor translocator (ARNT). In response to hypoxia, HIF-1α is activated and accumulates rapidly in the cell. Endothelial PAS domain protein 1 (EPAS-1) is a recently identified bHLH-PAS protein with 48% identity to HIF-1α, raising the question of its role in responses to hypoxia. We developed specific antibodies and studied expression and regulation of EPAS-1 mRNA and protein across a range of human cell lines. EPAS-1 was widely expressed, and strongly induced by hypoxia at the level of protein but not mRNA. Comparison of the effect of a range of activating and inhibitory stimuli showed striking similarities in the EPAS-1 and HIF-1α responses. Although major differences were observed in the abundance of EPAS-1 and HIF-1α in different cell types, differences in the inducible response were subtle with EPAS-1 protein being slightly more evident in normoxic and mildly hypoxic cells. Functional studies in a mutant cell line (Ka13) expressing neither HIF-1α nor EPAS-1 confirmed that both proteins interact with hypoxically responsive targets, but suggest target specificity with greater EPAS-1 transactivation (relative to HIF-1α transactivation) of the VEGF promoter than the LDH-A promoter.

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Gradin, K., J. McGuire, R. H. Wenger, I. Kvietikova, M. L. fhitelaw, R. Toftgård, L. Tora, M. Gassmann y L. Poellinger. "Functional interference between hypoxia and dioxin signal transduction pathways: competition for recruitment of the Arnt transcription factor." Molecular and Cellular Biology 16, n.º 10 (octubre de 1996): 5221–31. http://dx.doi.org/10.1128/mcb.16.10.5221.

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Hypoxia-inducible factor 1 alpha (HIF-1 alpha) and the intracellular dioxin receptor mediate hypoxia and dioxin signalling, respectively. Both proteins are conditionally regulated basic helix-loop-helix (bHLH) transcription factors that, in addition to the bHLH motif, share a Per-Arnt-Sim (PAS) region of homology and form heterodimeric complexes with the common bHLH/PAS partner factor Arnt. Here we demonstrate that HIF-1 alpha required Arnt for DNA binding in vitro and functional activity in vivo. Both the bHLH and PAS motifs of Arnt were critical for dimerization with HIF-1 alpha. Strikingly, HIF-1 alpha exhibited very high affinity for Arnt in coimmunoprecipitation assays in vitro, resulting in competition with the ligand-activated dioxin receptor for recruitment of Arnt. Consistent with these observations, activation of HIF-1 alpha function in vivo or overexpression of HIF-1 alpha inhibited ligand-dependent induction of DNA binding activity by the dioxin receptor and dioxin receptor function on minimal reporter gene constructs. However, HIF-1 alpha- and dioxin receptor-mediated signalling pathways were not mutually exclusive, since activation of dioxin receptor function did not impair HIF-1 alpha-dependent induction of target gene expression. Both HIF-1 alpha and Arnt mRNAs were expressed constitutively in a large number of human tissues and cell lines, and these steady-state expression levels were not affected by exposure to hypoxia. Thus, HIF-1 alpha may be conditionally regulated by a mechanism that is distinct from induced expression levels, the prevalent model of activation of HIF-1 alpha function. Interestingly, we observed that HIF-1 alpha was associated with the molecular chaperone hsp90. Given the critical role of hsp90 for ligand binding activity and activation of the dioxin receptor, it is therefore possible that HIF-1 alpha is regulated by a similar mechanism, possibly by binding an as yet unknown class of ligands.

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Ward, M. P., J. T. Mosher y S. T. Crews. "Regulation of bHLH-PAS protein subcellular localization during Drosophila embryogenesis". Development 125, n.º 9 (1 de mayo de 1998): 1599–608. http://dx.doi.org/10.1242/dev.125.9.1599.

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The Drosophila Single-minded and Tango basic-helix-loop-helix-PAS protein heterodimer controls transcription and embryonic development of the CNS midline cells, while the Trachealess and Tango heterodimer controls tracheal cell and salivary duct transcription and development. Expression of both single-minded and trachealess is highly restricted to their respective cell lineages, however tango is broadly expressed. The developmental control of subcellular localization of these proteins is investigated because of their similarity to the mammalian basic-helix-loop-helix-PAS Aromatic hydrocarbon receptor whose nuclear localization is dependent on ligand binding. Confocal imaging of Single-minded and Trachealess protein localization indicate that they accumulate in cell nuclei when initially synthesized in their respective cell lineages and remain nuclear throughout embryogenesis. Ectopic expression experiments show that Single-minded and Trachealess are localized to nuclei in cells throughout the ectoderm and mesoderm, indicating that nuclear accumulation is not regulated in a cell-specific fashion and unlikely to be ligand dependent. In contrast, nuclear localization of Tango is developmentally regulated; it is localized to the cytoplasm in most cells except the CNS midline, salivary duct, and tracheal cells where it accumulates in nuclei. Genetic and ectopic expression experiments indicate that Tango nuclear localization is dependent on the presence of a basic-helix-loop-helix-PAS protein such as Single-minded or Trachealess. Conversely, Drosophila cell culture experiments show that Single-minded and Trachealess nuclear localization is dependent on Tango since they are cytoplasmic in the absence of Tango. These results suggest a model in which Single-minded and Trachealess dimerize with Tango in the cytoplasm of the CNS midline cells and trachea, respectively, and the dimeric complex accumulates in nuclei in a ligand-independent mode and regulates lineage-specific transcription. The lineage-specific action of Single-minded and Trachealess derives from transcriptional activation of their genes in their respective lineages, not from extracellular signaling.

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Kim, Seon-Hee, Gyu-Seok Oh, Woon-Mok Sohn, Kihyun Lee, Hyun-Jong Yang y Young-An Bae. "Molecular characteristics and induction profiles of hypoxia-inducible factor-1αand other basic helix–loop–helix and Per–Arnt–Sim domain-containing proteins identified in a carcinogenic liver flukeClonorchis sinensis". Parasitology 146, n.º 2 (2 de agosto de 2018): 176–86. http://dx.doi.org/10.1017/s0031182018001245.

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AbstractClonorchis sinensis(C. sinensis), a trematode parasite that invades the hypoxic hepatobiliary tract of vertebrate hosts requires a considerable amount of oxygen for its sexual reproduction and energy metabolism. However, little is known regarding the molecular mechanism ofC. sinensisinvolved in the adaptation to the hypoxic environments. In this study, we investigated the molecular structures and induction patterns of hypoxia-inducible factor-1α(HIF-1α) and other basic helix–loop–helix and Per–Arnt–Sim (bHLH–PAS) domain-containing proteins such as HIF-1β, single-minded protein and aryl hydrocarbon receptor, which might prompt adaptive response to hypoxia, inC. sinensis. These proteins possessed various bHLH–PAS family-specific domains. Expression ofC. sinensis HIF-1α(CsHIF-1α) was highly induced in worms which were either exposed to a hypoxic condition or co-incubated with human cholangiocytes. In addition to oxygen, nitric oxide and nitrite affected theCsHIF-1αexpression depending on the surrounding oxygen concentration. Treatment using a prolyl hydroxylase-domain protein inhibitor under 20%-oxygen condition resulted in an increase in the CsHIF-1αlevel. Conversely, the otherbHLH–PASgenes were less responsive to these exogenous stimuli. We suggest that nitrite and nitric oxide, as well as oxygen, coordinately involve in the regulation of HIF-1αexpression to adapt to the hypoxic host environments inC. sinensis.

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Chang, Wai Hoong y Alvina G. Lai. "Genome-wide analyses of the bHLH superfamily in crustaceans: reappraisal of higher-order groupings and evidence for lineage-specific duplications". Royal Society Open Science 5, n.º 3 (marzo de 2018): 172433. http://dx.doi.org/10.1098/rsos.172433.

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The basic helix-loop-helix (bHLH) proteins represent a key group of transcription factors implicated in numerous eukaryotic developmental and signal transduction processes. Characterization of bHLHs from model species such as humans, fruit flies, nematodes and plants have yielded important information on their functions and evolutionary origin. However, relatively little is known about bHLHs in non-model organisms despite the availability of a vast number of high-throughput sequencing datasets, enabling previously intractable genome-wide and cross-species analyses to be now performed. We extensively searched for bHLHs in 126 crustacean species represented across major Crustacea taxa and identified 3777 putative bHLH orthologues. We have also included seven whole-genome datasets representative of major arthropod lineages to obtain a more accurate prediction of the full bHLH gene complement. With focus on important food crop species from Decapoda, we further defined higher-order groupings and have successfully recapitulated previous observations in other animals. Importantly, we also observed evidence for lineage-specific bHLH expansions in two basal crustaceans (branchiopod and copepod), suggesting a mode of evolution through gene duplication as an adaptation to changing environments. In-depth analysis on bHLH-PAS members confirms the phenomenon coined as ‘modular evolution’ (independently evolved domains) typically seen in multidomain proteins. With the amphipod Parhyale hawaiensis as the exception, our analyses have focused on crustacean transcriptome datasets. Hence, there is a clear requirement for future analyses on whole-genome sequences to overcome potential limitations associated with transcriptome mining. Nonetheless, the present work will serve as a key resource for future mechanistic and biochemical studies on bHLHs in economically important crustacean food crop species.

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Coban, Mathew A., Patrick R. Blackburn, Murray L. Whitelaw, Mieke M. van Haelst, Paldeep S. Atwal y Thomas R. Caulfield. "Structural Models for the Dynamic Effects of Loss-of-Function Variants in the Human SIM1 Protein Transcriptional Activation Domain". Biomolecules 10, n.º 9 (12 de septiembre de 2020): 1314. http://dx.doi.org/10.3390/biom10091314.

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Single-minded homologue 1 (SIM1) is a transcription factor with numerous different physiological and developmental functions. SIM1 is a member of the class I basic helix-loop-helix-PER-ARNT-SIM (bHLH–PAS) transcription factor family, that includes several other conserved proteins, including the hypoxia-inducible factors, aryl hydrocarbon receptor, neuronal PAS proteins, and the CLOCK circadian regulator. Recent studies of HIF-a-ARNT and CLOCK-BMAL1 protein complexes have revealed the organization of their bHLH, PASA, and PASB domains and provided insight into how these heterodimeric protein complexes form; however, experimental structures for SIM1 have been lacking. Here, we describe the first full-length atomic structural model for human SIM1 with its binding partner ARNT in a heterodimeric complex and analyze several pathogenic variants utilizing state-of-the-art simulations and algorithms. Using local and global positional deviation metrics, deductions to the structural basis for the individual mutants are addressed in terms of the deleterious structural reorganizations that could alter protein function. We propose new experiments to probe these hypotheses and examine an interesting SIM1 dynamic behavior. The conformational dynamics demonstrates conformational changes on local and global regions that represent a mechanism for dysfunction in variants presented. In addition, we used our ab initio hybrid model for further prediction of variant hotspots that can be engineered to test for counter variant (restoration of wild-type function) or basic research probe.

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Korkalainen, Merja, Jere Lindén, Jouko Tuomisto y Raimo Pohjanvirta. "Effect of TCDD on mRNA expression of genes encoding bHLH/PAS proteins in rat hypothalamus". Toxicology 208, n.º 1 (marzo de 2005): 1–11. http://dx.doi.org/10.1016/j.tox.2004.11.003.

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Moffett, P., M. Reece y J. Pelletier. "The murine Sim-2 gene product inhibits transcription by active repression and functional interference." Molecular and Cellular Biology 17, n.º 9 (septiembre de 1997): 4933–47. http://dx.doi.org/10.1128/mcb.17.9.4933.

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The Drosophila single-minded (Dsim) gene encodes a master regulatory protein involved in cell fate determination during midline development. This protein is a member of a rapidly expanding family of gene products possessing basic helix-loop-helix (bHLH) and hydrophobic PAS (designated a conserved region among PER, ARNT [aryl hydrocarbon receptor nuclear translocator] and SIM) protein association domains. Members of this family function as central transcriptional regulators in cellular differentiation and in the response to environmental stimuli such as xenobiotics and hypoxia. We have previously identified a murine member of this family, called mSim-2, showing sequence homology to the bHLH and PAS domains of Dsim. Immunoprecipitation experiments with recombinant proteins indicate that mSIM-2 associates with the arnt gene product. In the present work, by using fine-structure mapping we found that the HLH and PAS motifs of both proteins are required for optimal association. Forced expression of GAL4/mSIM-2 fusion constructs in mammalian cells demonstrated the presence of two separable repression domains within the carboxy terminus of mSIM-2. We found that mSIM-2 is capable of repressing ARNT-mediated transcriptional activation in a mammalian two-hybrid system. This effect (i) is dependent on the ability of mSIM-2 and ARNT to heterodimerize, (ii) is dependent on the presence of the mSIM-2 carboxy-terminal repression domain, and (iii) is not specific to the ARNT activation domain. These results suggest that mSIM-2 repression activity can dominantly override the activation potential of adjacent transcription factors. We also demonstrated that mSIM-2 can functionally interfere with hypoxia-inducible factor 1alpha (HIF-1alpha)/ARNT transcription complexes, providing a second mechanism by which mSIM-2 may inhibit transcription.

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Pecenova, L. y Robert Farkas. "Multiple functions and essential roles of nuclear receptor coactivators of bHLH-PAS family". Endocrine Regulations 50, n.º 3 (1 de julio de 2016): 165–81. http://dx.doi.org/10.1515/enr-2016-0019.

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Abstract Classical non-peptide hormones, such as steroids, retinoids, thyroid hormones, vitamin D3 and their derivatives including prostaglandins, benzoates, oxysterols, and bile acids, are collectively designated as small lipophilic ligands, acting via binding to the nuclear receptors (NRs). The NRs form a large superfamily of transcription factors that participate virtually in every key biological process. They control various aspects of animal development, fertility, gametogenesis, and numerous metabolic pathways, and can be misregulated in many types of cancers. Their enormous functional plasticity, as transcription factors, relates in part to NR-mediated interactions with plethora of coregulatory proteins upon ligand binding to their ligand binding domains (LBD), or following covalent modification. Here, we review some general views of a specific group of NR coregulators, so-called nuclear receptor coactivators (NRCs) or steroid receptor coactivators (SRCs) and highlight some of their unique functions/roles, which are less extensively mentioned and discussed in other reviews. We also try to pinpoint few neglected moments in the cooperative action of SRCs, which may also indicate their variable roles in the hormone-independent signaling pathways.

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Zhou, Y. D., M. Barnard, H. Tian, X. Li, H. Z. Ring, U. Francke, J. Shelton, J. Richardson, D. W. Russell y S. L. McKnight. "Molecular characterization of two mammalian bHLH-PAS domain proteins selectively expressed in the central nervous system". Proceedings of the National Academy of Sciences 94, n.º 2 (21 de enero de 1997): 713–18. http://dx.doi.org/10.1073/pnas.94.2.713.

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35

Annunziata, Rossella, Andrés Ritter, Antonio Emidio Fortunato, Alessandro Manzotti, Soizic Cheminant-Navarro, Nicolas Agier, Marie J. J. Huysman et al. "bHLH-PAS protein RITMO1 regulates diel biological rhythms in the marine diatomPhaeodactylum tricornutum". Proceedings of the National Academy of Sciences 116, n.º 26 (6 de junio de 2019): 13137–42. http://dx.doi.org/10.1073/pnas.1819660116.

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Periodic light–dark cycles govern the timing of basic biological processes in organisms inhabiting land as well as the sea, where life evolved. Although prominent marine phytoplanktonic organisms such as diatoms show robust diel rhythms, the mechanisms regulating these processes are still obscure. By characterizing aPhaeodactylum tricornutumbHLH-PAS nuclear protein, hereby named RITMO1, we shed light on the regulation of the daily life of diatoms. Alteration of RITMO1 expression levels and timing by ectopic overexpression results in lines with deregulated diurnal gene expression profiles compared with the wild-type cells. Reduced gene expression oscillations are also observed in these lines in continuous darkness, showing that the regulation of rhythmicity by RITMO1 is not directly dependent on light inputs. We also describe strong diurnal rhythms of cellular fluorescence in wild-type cells, which persist in continuous light conditions, indicating the existence of an endogenous circadian clock in diatoms. The altered rhythmicity observed in RITMO1 overexpression lines in continuous light supports the involvement of this protein in circadian rhythm regulation. Phylogenetic analysis reveals a wide distribution of RITMO1-like proteins in the genomes of diatoms as well as in other marine algae, which may indicate a common function in these phototrophs. This study adds elements to our understanding of diatom biology and offers perspectives to elucidate timekeeping mechanisms in marine organisms belonging to a major, but under-investigated, branch of the tree of life.

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Emmons, R. B., D. Duncan, P. A. Estes, P. Kiefel, J. T. Mosher, M. Sonnenfeld, M. P. Ward, I. Duncan y S. T. Crews. "The spineless-aristapedia and tango bHLH-PAS proteins interact to control antennal and tarsal development in Drosophila". Development 126, n.º 17 (1 de septiembre de 1999): 3937–45. http://dx.doi.org/10.1242/dev.126.17.3937.

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The Drosophila spineless (ss) gene encodes a basic-helix-loop-helix-PAS transcription factor that is required for proper specification of distal antennal identity, establishment of the tarsal regions of the legs, and normal bristle growth. ss is the closest known homolog of the mammalian aryl hydrocarbon receptor (Ahr), also known as the dioxin receptor. Dioxin and other aryl hydrocarbons bind to the PAS domain of Ahr, causing Ahr to translocate to the nucleus, where it dimerizes with another bHLH-PAS protein, the aryl hydrocarbon receptor nuclear translocator (Arnt). Ahr:Arnt heterodimers then activate transcription of target genes that encode enzymes involved in metabolizing aryl hydrocarbons. In this report, we present evidence that Ss functions as a heterodimer with the Drosophila ortholog of Arnt, Tango (Tgo). We show that the ss and tgo genes have a close functional relationship: loss-of-function alleles of tgo were recovered as dominant enhancers of a ss mutation, and tgo-mutant somatic clones show antennal, leg, and bristle defects almost identical to those caused by ss(−) mutations. The results of yeast two-hybrid assays indicate that the Ss and Tgo proteins interact directly, presumably by forming heterodimers. Coexpression of Ss and Tgo in Drosophila SL2 cells causes transcriptional activation of reporters containing mammalian Ahr:Arnt response elements, indicating that Ss:Tgo heterodimers are very similar to Ahr:Arnt heterodimers in DNA-binding specificity and transcriptional activation ability. During embryogenesis, Tgo is localized to the nucleus at sites of ss expression. This localization is lost in a ss null mutant, suggesting that Tgo requires heterodimerization for translocation to the nucleus. Ectopic expression of ss causes coincident ectopic nuclear localization of Tgo, independent of cell type or developmental stage. This suggests that the interaction of Ss and Tgo does not require additional signals, unlike the ligand-dependent interaction of Ahr and Arnt. Despite the very different biological roles of Ahr and Arnt in insects and mammals, the molecular mechanisms by which these proteins function appear to be largely conserved.

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Freeman, Samuel L., Hanna Kwon, Nicola Portolano, Gary Parkin, Umakhanth Venkatraman Girija, Jaswir Basran, Alistair J. Fielding et al. "Heme binding to human CLOCK affects interactions with the E-box". Proceedings of the National Academy of Sciences 116, n.º 40 (16 de septiembre de 2019): 19911–16. http://dx.doi.org/10.1073/pnas.1905216116.

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The circadian clock is an endogenous time-keeping system that is ubiquitous in animals and plants as well as some bacteria. In mammals, the clock regulates the sleep–wake cycle via 2 basic helix–loop–helix PER-ARNT-SIM (bHLH-PAS) domain proteins—CLOCK and BMAL1. There is emerging evidence to suggest that heme affects circadian control, through binding of heme to various circadian proteins, but the mechanisms of regulation are largely unknown. In this work we examine the interaction of heme with human CLOCK (hCLOCK). We present a crystal structure for the PAS-A domain of hCLOCK, and we examine heme binding to the PAS-A and PAS-B domains. UV-visible and electron paramagnetic resonance spectroscopies are consistent with a bis-histidine ligated heme species in solution in the oxidized (ferric) PAS-A protein, and by mutagenesis we identify His144 as a ligand to the heme. There is evidence for flexibility in the heme pocket, which may give rise to an additional Cys axial ligand at 20K (His/Cys coordination). Using DNA binding assays, we demonstrate that heme disrupts binding of CLOCK to its E-box DNA target. Evidence is presented for a conformationally mobile protein framework, which is linked to changes in heme ligation and which has the capacity to affect binding to the E-box. Within the hCLOCK structural framework, this would provide a mechanism for heme-dependent transcriptional regulation.

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Lavista-Llanos, Sofía, Lázaro Centanin, Maximiliano Irisarri, Daniela M. Russo, Jonathan M. Gleadle, Silvia N. Bocca, Mariana Muzzopappa, Peter J. Ratcliffe y Pablo Wappner. "Control of the Hypoxic Response in Drosophila melanogaster by the Basic Helix-Loop-Helix PAS Protein Similar". Molecular and Cellular Biology 22, n.º 19 (1 de octubre de 2002): 6842–53. http://dx.doi.org/10.1128/mcb.22.19.6842-6853.2002.

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ABSTRACT In mammalian systems, the heterodimeric basic helix-loop-helix (bHLH)-PAS transcription hypoxia-inducible factor (HIF) has emerged as the key regulator of responses to hypoxia. Here we define a homologous system in Drosophila melanogaster, and we characterize its activity in vivo during development. By using transcriptional reporters in developing transgenic flies, we show that hypoxia-inducible activity rises to a peak in late embryogenesis and is most pronounced in tracheal cells. We show that the bHLH-PAS proteins Similar (Sima) and Tango (Tgo) function as HIF-α and HIF-β homologues, respectively, and demonstrate a conserved mode of regulation for Sima by oxygen. Sima protein, but not its mRNA, was upregulated in hypoxia. Time course experiments following pulsed ectopic expression demonstrated that Sima is stabilized in hypoxia and that degradation relies on a central domain encompassing amino acids 692 to 863. Continuous ectopic expression overrode Sima degradation, which remained cytoplasmic in normoxia, and translocated to the nucleus only in hypoxia, revealing a second oxygen-regulated activation step. Abrogation of the Drosophila Egl-9 prolyl hydroxylase homologue, CG1114, caused both stabilization and nuclear localization of Sima, indicating a central involvement in both processes. Tight conservation of the HIF/prolyl hydroxylase system in Drosophila provides a new focus for understanding oxygen homeostasis in intact multicellular organisms.

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Wang, Feng, Shengli Shi, Ruixue Zhang y Oliver Hankinson. "Identifying target genes of the aryl hydrocarbon receptor nuclear translocator (Arnt) using DNA microarray analysis". Biological Chemistry 387, n.º 9 (1 de septiembre de 2006): 1215–18. http://dx.doi.org/10.1515/bc.2006.150.

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Abstract The aryl hydrocarbon receptor nuclear translocator (Arnt) is a basic helix-loop-helix (bHLH) protein that also contains a Per-Arnt-Sim (PAS) domain. In addition to forming heterodimers with many other bHLH-PAS proteins, including the aryl hydrocarbon receptor (AhR) and hypoxia-inducible factors 1α, 2α and 3α, Arnt can also form homodimers when expressed from its cDNA in vitro or in vivo. However, target genes of the Arnt/Arnt homodimer remain to be identified. In this study, we have elucidated the profile of genes responsive to the reintroduction of Arnt expression in an Arnt-deficient mouse hepatoma cell line (c4), using DNA microarray analysis. The expression of 27 genes was upregulated by 1.5-fold or more in c4 cells infected with a retroviral vector expressing mouse Arnt, while no genes were found to be downregulated. Among the upregulated genes, BCL2/adenovirus E1B 19 kDa-interacting protein 1 (NIP3), serine (or cysteine) proteinase inhibitor, clade E, member 1 (PAI1), and N-myc downstream regulated-like (NDR1), were confirmed to be induced by Arnt using real-time PCR. We also found that the 5′ promoter region of 15 out of 20 upregulated genes contain the type 2 E-box 5′-CACGTG-3′ Arnt/Arnt binding sequence, consistent with the notion that they represent target genes for Arnt.

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Dardente, Hugues, Erin E. Fortier, Vincent Martineau y Nicolas Cermakian. "Cryptochromes impair phosphorylation of transcriptional activators in the clock: a general mechanism for circadian repression". Biochemical Journal 402, n.º 3 (26 de febrero de 2007): 525–36. http://dx.doi.org/10.1042/bj20060827.

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CLOCK and BMAL1 [brain and muscle ARNT (arylhydrocarbon receptor nuclear translocator)-like protein 1] are central components of the molecular clock in mammals and belong to the bHLH (basic helix–loop–helix)/PAS [PER (Period)/ARNT/SIM (single-minded)] family. Features of their dimerization have never been investigated. Here, we demonstrate that PAS domain function requires regions extending over the short PAS core repeats. Strikingly, while deleting PAS core repeats does not overtly affect dimerization, it abolishes the transcriptional activity of the heterodimer. Interestingly, these deletions also abolish co-dependent phosphorylation of CLOCK and BMAL1, suggesting a link between the phosphorylation status of the heterodimer and its transactivation potential. We demonstrate that NPAS2 (neuronal PAS domain protein 2) and BMAL2 also undergo similar posttranslational modifications, thereby establishing the mechanism proposed for CLOCK–BMAL1 as a common feature of transcriptional activators in the circadian clock. The discovery of two novel splice variants of BMAL2 confirms the crucial role of the PAS domain and further strengthens the view that co-dependent phosphorylation is of functional significance. In agreement with this, we demonstrate that CRY1–2 (cryptochromes 1–2) affect transactivation and phosphorylation of transcriptional activators of the clock. Furthermore, CRY proteins stabilize the unphosphorylated forms of BMAL1(BMAL2) thereby shifting the phosphorylated/unphosphorylated ratio towards a predominantly unphosphorylated (transcriptionally inactive) form. In contrast, PER proteins, which are weak repressors, are without effect. From these results, we propose a general mechanism for the inhibition of CLOCK(NPAS2)–BMAL1(BMAL2) circadian transcriptional activation by CRY1–2.

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Deng, Jiao, Lijuan Wang, Lan Zhang, Chaojie Yang, Juan Huang, Liwei Zhu, Qingfu Chen, Ziye Meng, Fang Cai y Taoxiong Shi. "Tartary Buckwheat (Fagopyrum tataricum) FtTT8 Inhibits Anthocyanin Biosynthesis and Promotes Proanthocyanidin Biosynthesis". International Journal of Molecular Sciences 24, n.º 24 (11 de diciembre de 2023): 17368. http://dx.doi.org/10.3390/ijms242417368.

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Tartary buckwheat (Fagopyrum tataricum) is an important plant, utilized for both medicine and food. It has become a current research hotspot due to its rich content of flavonoids, which are beneficial for human health. Anthocyanins (ATs) and proanthocyanidins (PAs) are the two main kinds of flavonoid compounds in Tartary buckwheat, which participate in the pigmentation of some tissue as well as rendering resistance to many biotic and abiotic stresses. Additionally, Tartary buckwheat anthocyanins and PAs have many health benefits for humans and the plant itself. However, little is known about the regulation mechanism of the biosynthesis of anthocyanin and PA in Tartary buckwheat. In the present study, a bHLH transcription factor (TF) FtTT8 was characterized to be homologous with AtTT8 and phylogenetically close to bHLH proteins from other plant species. Subcellular location and yeast two-hybrid assays suggested that FtTT8 locates in the nucleus and plays a role as a transcription factor. Complementation analysis in Arabidopsis tt8 mutant showed that FtTT8 could not recover anthocyanin deficiency but could promote PAs accumulation. Overexpression of FtTT8 in red-flowering tobacco showed that FtTT8 inhibits anthocyanin biosynthesis and accelerates proanthocyanidin biosynthesis. QRT-PCR and yeast one-hybrid assay revealed that FtTT8 might bind to the promoter of NtUFGT and suppress its expression, while binding to the promoter of NtLAR and upregulating its expression in K326 tobacco. This displayed the bidirectional regulating function of FtTT8 that negatively regulates anthocyanin biosynthesis and positively regulates proanthocyanidin biosynthesis. The results provide new insights on TT8 in Tartary buckwheat, which is inconsistent with TT8 from other plant species, and FtTT8 might be a high-quality gene resource for Tartary buckwheat breeding.

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Bernardo, Travis J. y Edward B. Dubrovsky. "Molecular Mechanisms of Transcription Activation by Juvenile Hormone: A Critical Role for bHLH-PAS and Nuclear Receptor Proteins". Insects 3, n.º 1 (22 de marzo de 2012): 324–38. http://dx.doi.org/10.3390/insects3010324.

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Richardson, Vicki M., Michael J. Santostefano y Linda S. Birnbaum. "Daily Cycle of bHLH-PAS Proteins, Ah Receptor and Arnt, in Multiple Tissues of Female Sprague–Dawley Rats". Biochemical and Biophysical Research Communications 252, n.º 1 (noviembre de 1998): 225–31. http://dx.doi.org/10.1006/bbrc.1998.9634.

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Bae, Kiho, Choogon Lee, David Sidote, Keng-yu Chuang y Isaac Edery. "Circadian Regulation of a Drosophila Homolog of the Mammalian Clock Gene: PER and TIM Function as Positive Regulators". Molecular and Cellular Biology 18, n.º 10 (1 de octubre de 1998): 6142–51. http://dx.doi.org/10.1128/mcb.18.10.6142.

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ABSTRACT The Clock gene plays an essential role in the manifestation of circadian rhythms (≅24 h) in mice and is a member of the basic helix-loop-helix (bHLH) PER-ARNT-SIM (PAS) superfamily of transcription factors. Here we report the characterization of a novelDrosophila bHLH-PAS protein that is highly homologous to mammalian CLOCK. (Similar findings were recently described by Allada et al. Cell 93:791–804, 1998, and Darlington et al., Science 280:1599–1603, 1998.) Transcripts from this putative Clockortholog (designated dClock) undergo daily rhythms in abundance that are antiphase to the cycling observed for the RNA products from the Drosophila melanogaster circadian clock genes period (per) and timeless(tim). Furthermore, dClock RNA cycling is abolished and the levels are at trough values in the absence of either PER or TIM, suggesting that these two proteins can function as transcriptional activators, a possibility which is in stark contrast to their previously characterized role in transcriptional autoinhibition. Finally, the temporal regulation of dClock expression is quickly perturbed by shifts in light-dark cycles, indicating that this molecular rhythm is closely connected to the photic entrainment pathway. The isolation of a Drosophila homolog ofClock together with the recent discovery of mammalian homologs of per indicate that there is high structural conservation in the integral components underlying circadian oscillators in Drosophila and mammals. Nevertheless, because mammalian Clock mRNA is constitutively expressed, our findings are a further example of striking differences in the regulation of putative circadian clock orthologs in different species.

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Whitelaw, M. L., J. A. Gustafsson y L. Poellinger. "Identification of transactivation and repression functions of the dioxin receptor and its basic helix-loop-helix/PAS partner factor Arnt: inducible versus constitutive modes of regulation". Molecular and Cellular Biology 14, n.º 12 (diciembre de 1994): 8343–55. http://dx.doi.org/10.1128/mcb.14.12.8343-8355.1994.

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Gene regulation by dioxins is mediated via the dioxin receptor, a ligand-dependent basic helix-loop-helix (bHLH)/PAS transcription factor. The latent dioxin receptor responds to dioxin signalling by forming an activated heterodimeric complex with a specific bHLH partner, Arnt, an essential process for target DNA recognition. We have analyzed the transactivating potential within this heterodimeric complex by dissecting it into individual subunits, replacing the dimerization and DNA-binding bHLH motifs with heterologous zinc finger DNA-binding domains. The uncoupled Arnt chimera, maintaining 84% of Arnt residues, forms a potent and constitutive transcription factor. Chimeric proteins show that the dioxin receptor also harbors a strong transactivation domain in the C terminus, although this activity was silenced by inclusion of 82 amino acids from the central ligand-binding portion of the dioxin receptor. This central repression region conferred binding of the molecular chaperone hsp90 upon otherwise constitutive chimeras in vitro, indicating that hsp90 has the ability to mediate a cis-repressive function on distant transactivation domains. Importantly, when the ligand-binding domain of the dioxin receptor remained intact, the ability of this hsp90-binding activity to confer repression became conditional rather than irreversible. Our data are consistent with a model in which crucial activities of the dioxin receptor, such as dimerization with Arnt and transactivation, are conditionally repressed by the central ligand- and-hsp90-binding region of the receptor. In contrast, the Arnt protein appears to be free from any repressive activity. Moreover, within the context of the dioxin response element (xenobiotic response element), the C terminus of Arnt conferred a potent, dominating transactivation function onto the native bHLH heterodimeric complex. Finally, the relative transactivation potencies of the individual dioxin receptor and Arnt chimeras varied with cell type and promoter architecture, indicating that the mechanisms for transcriptional activation may differ between these two subunits and that in the native complex the transactivation pathway may be dependent upon cell-specific and promoter contexts.

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46

Whitelaw, M. L., J. A. Gustafsson y L. Poellinger. "Identification of transactivation and repression functions of the dioxin receptor and its basic helix-loop-helix/PAS partner factor Arnt: inducible versus constitutive modes of regulation." Molecular and Cellular Biology 14, n.º 12 (diciembre de 1994): 8343–55. http://dx.doi.org/10.1128/mcb.14.12.8343.

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Gene regulation by dioxins is mediated via the dioxin receptor, a ligand-dependent basic helix-loop-helix (bHLH)/PAS transcription factor. The latent dioxin receptor responds to dioxin signalling by forming an activated heterodimeric complex with a specific bHLH partner, Arnt, an essential process for target DNA recognition. We have analyzed the transactivating potential within this heterodimeric complex by dissecting it into individual subunits, replacing the dimerization and DNA-binding bHLH motifs with heterologous zinc finger DNA-binding domains. The uncoupled Arnt chimera, maintaining 84% of Arnt residues, forms a potent and constitutive transcription factor. Chimeric proteins show that the dioxin receptor also harbors a strong transactivation domain in the C terminus, although this activity was silenced by inclusion of 82 amino acids from the central ligand-binding portion of the dioxin receptor. This central repression region conferred binding of the molecular chaperone hsp90 upon otherwise constitutive chimeras in vitro, indicating that hsp90 has the ability to mediate a cis-repressive function on distant transactivation domains. Importantly, when the ligand-binding domain of the dioxin receptor remained intact, the ability of this hsp90-binding activity to confer repression became conditional rather than irreversible. Our data are consistent with a model in which crucial activities of the dioxin receptor, such as dimerization with Arnt and transactivation, are conditionally repressed by the central ligand- and-hsp90-binding region of the receptor. In contrast, the Arnt protein appears to be free from any repressive activity. Moreover, within the context of the dioxin response element (xenobiotic response element), the C terminus of Arnt conferred a potent, dominating transactivation function onto the native bHLH heterodimeric complex. Finally, the relative transactivation potencies of the individual dioxin receptor and Arnt chimeras varied with cell type and promoter architecture, indicating that the mechanisms for transcriptional activation may differ between these two subunits and that in the native complex the transactivation pathway may be dependent upon cell-specific and promoter contexts.

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47

Beischlag, Timothy V., Song Wang, David W. Rose, Joseph Torchia, Suzanne Reisz-Porszasz, Khurshid Muhammad, Walter E. Nelson, Markus R. Probst, Michael G. Rosenfeld y Oliver Hankinson. "Recruitment of the NCoA/SRC-1/p160 Family of Transcriptional Coactivators by the Aryl Hydrocarbon Receptor/Aryl Hydrocarbon Receptor Nuclear Translocator Complex". Molecular and Cellular Biology 22, n.º 12 (15 de junio de 2002): 4319–33. http://dx.doi.org/10.1128/mcb.22.12.4319-4333.2002.

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ABSTRACT The aryl hydrocarbon receptor complex heterodimeric transcription factor, comprising the basic helix-loop-helix-Per-ARNT-Sim (bHLH-PAS) domain aryl hydrocarbon receptor (AHR) and aryl hydrocarbon receptor nuclear translocator (ARNT) proteins, mediates the toxic effects of TCDD (2,3,7,8 tetrachlorodibenzo-p-dioxin). The molecular events underlying TCDD-inducible gene activation, beyond the activation of the AHRC, are poorly understood. The SRC-1/NCoA-1, NCoA-2/GRIP-1/TIF-2, and p/CIP/AIB/ACTR proteins have been shown to act as mediators of transcriptional activation. In this report, we demonstrate that SRC-1, NCoA-2, and p/CIP are capable of independently enhancing TCDD-dependent induction of a luciferase reporter gene by the AHR/ARNT dimer. Furthermore, injection of anti-SRC-1 or anti-p/CIP immunoglobulin G into mammalian cells abolishes the transcriptional activity of a TCDD-dependent reporter gene. We demonstrate by coimmunoprecipitation and by a reporter gene assay that SRC-1 and NCoA-2 but not p/CIP are capable of interacting with ARNT in vivo after transient transfection into mammalian cells, while AHR is capable of interacting with all three coactivators. We confirm the interactions of ARNT and AHR with SRC-1 with immunocytochemical techniques. Furthermore, SRC-1, NCoA-2, and p/CIP all associate with the CYP1A1 enhancer region in a TCDD-dependent fashion, as demonstrated by chromatin immunoprecipitation assays. We demonstrate by yeast two-hybrid, glutathione S-transferase pulldown, and mammalian reporter gene assays that ARNT requires its helix 2 domain but not its transactivation domain to interact with SRC-1. This indicates a novel mechanism of action for SRC-1. SRC-1 does not require its bHLH-PAS domain to interact with ARNT or AHR, but utilizes distinct domains proximal to its p300/CBP interaction domain. Taken together, these data support a role for the SRC family of transcriptional coactivators in TCDD-dependent gene regulation.

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Fahim, Ammad, Zaira Rehman, Muhammad Faraz Bhatti, Amjad Ali, Nasar Virk, Amir Rashid y Rehan Zafar Paracha. "Structural insights and characterization of human Npas4 protein". PeerJ 6 (14 de junio de 2018): e4978. http://dx.doi.org/10.7717/peerj.4978.

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Npas4 is an activity dependent transcription factor which is responsible for gearing the expression of target genes involved in neuro-transmission. Despite the importance of Npas4 in many neuronal diseases, the tertiary structure of Npas4 protein along with its physico-chemical properties is limited. In the current study, first we perfomed the phylogenetic analysis of Npas4 and determined the content of hydrophobic, flexible and order-disorder promoting amino acids. The protein binding regions, post-translational modifications and crystallization propensity of Npas4 were predicted through different in-silico methods. The three dimensional model of Npas4 was predicted through LOMET, SPARSKS-X, I-Tasser, RaptorX, MUSTER and Pyhre and the best model was selected on the basis of Ramachandran plot, PROSA, and Qmean scores. The best model was then subjected to further refinement though MODREFINER. Finally the interacting partners of Npas4 were identified through STRING database. The phylogenetic analysis showed the human Npas4 gene to be closely related to other primates such as chimpanzees, monkey, gibbon. The physiochemical properties of Npas4 showed that it is an intrinsically disordered protein with N-terminal ordered region. The post-translational modification analyses indicated absence of acetylation and mannosylation sites. Three potential phosphorylation sites (S108, T130 and T136) were found in PAS A domain whilst a single phosphorylation site (S273) was present in PAS B domain. The predicted tertiary structure of Npas4 showed that bHLH domain and PAS domain possess tertiary structures while the rest of the protein exhibited disorder property. Protein-protein interaction analysis revealed NPas4 interaction with various proteins which are mainly involved in nuclear trafficking of proteins to cytoplasm, activity regulated gene transcription and neurodevelopmental disorders. Moreover the analysis also highlighted the direct relation to proteins involved in promoting neuronal survival, plasticity and cAMP responsive element binding protein proteins. The current study helps in understanding the physicochemical properties and reveals the neuro-modulatory role of Npas4 in crucial pathways involved in neuronal survival and neural signalling hemostasis.

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Aitola, Marjo, Christine M. Sadek, Jan-Åke Gustafsson y Markku Pelto-Huikko. "Aint/Tacc3 Is Highly Expressed in Proliferating Mouse Tissues During Development, Spermatogenesis, and Oogenesis". Journal of Histochemistry & Cytochemistry 51, n.º 4 (abril de 2003): 455–69. http://dx.doi.org/10.1177/002215540305100407.

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Aint was originally identified on the basis of its interaction in vitro with the aryl hydrocarbon nuclear receptor translocator (Arnt). Arnt is a common heterodimerization partner in the basic helix-loop–helix (bHLH)-PER-ARNT-SIM (PAS) protein family and is involved in diverse biological functions. These include xenobiotic metabolism, hypoxic response, and circadian rhythm. In addition, Arnt has a crucial role during development. Aint is a member of a growing family of transforming acidic coiled-coil (TACC) proteins and is the murine homologue of human TACC3. Here we report the spatiotemporal expression of Tacc3 mRNA and protein in embryonic, postnatally developing, and adult mouse tissues using in situ hybridization and immunocytochemistry. Tacc3 mRNA was highly expressed in proliferating cells of several organs during murine development. However, the only adult tissues expressing high levels were testis and ovary. Immunocytochemistry revealed that Tacc3 is a nuclear protein. Our results suggest that Tacc3 has an important role in murine development, spermatogenesis, and oogenesis.

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50

Lafleur, Véronique N., Silvia Halim, Peter J. Ratcliffe y David R. Mole. "Abstract 677: Bi-directional crosstalk between the HIF and AHR transcription factors in clear cell kidney cancer". Cancer Research 82, n.º 12_Supplement (15 de junio de 2022): 677. http://dx.doi.org/10.1158/1538-7445.am2022-677.

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Abstract Hypoxia is a key feature of the solid tumour microenvironment, in which it is associated with poor prognosis and resistance to therapy. Hypoxia-inducible factor (HIF) is the central mediator of cellular responses to hypoxia and drives a transcriptional program with central roles in tumorigenesis. Clear cell renal cell cancers (ccRCC) exhibit the most direct and profound upregulation of the HIF pathway - through bi-allelic inactivation of the VHL tumour suppressor, a ubiquitin ligase that targets HIF-alpha subunits for degradation under normal oxygenated conditions. HIF-alpha proteins are members of the bHLH-PAS family and interact with HIF-1beta (also known as ARNT) to form functional heterodimers binding chromatin. However, the aryl hydrocarbon receptor (AHR), another bHLH-PAS protein that dimerises with HIF-1beta, is also up-regulated in ccRCC, raising the possibility of crosstalk between these two transcriptional pathways. Previous studies support an antagonistic relationship between HIF and AHR, with evidence of a context-dependent and gene-specific crosstalk. Here, we investigate the pan-genomic and precise relationship between the HIF and AHR transcription factors in ccRCC. Using immunoprecipitation, we show direct competition for HIF-1beta binding between the HIF-alpha and AHR proteins in renal cancer cell lines. Pan-genomic analysis of HIF-1alpha, HIF-2alpha, HIF-1beta and AHR chromatin binding by ChIP-seq analysis reveals a widespread competitive interaction between HIF and AHR. In RCC4 cells, this interaction is bidirectional, with induction of HIF leading to a reduction in AHR binding, while induction of AHR reduces binding of both HIF-1alpha and HIF-2alpha to chromatin. However, this competition is diminished at sites bound by both HIF and AHR, indicating a cooperative interaction between the two transcription factors in cis. Thus, while the HIF-alpha and AHR proteins compete for the common binding partner HIF-1beta, they appear to form a cooperative interaction when bound to neighbouring sites on chromatin. Linking these findings to changes in gene expression by RNA-seq analysis, we show the global downstream effects of the competition between HIF and AHR, but also reveal a degree of overlap and cooperativity between their transcriptional programs. Furthermore, we provide evidence of this antagonistic relationship in ccRCC tumours (TCGA database), in which we observe a negative correlation between HIF and AHR target gene expression. These findings shed light on the complex crosstalk between the HIF and AHR transcriptional pathways, which encompasses both a widespread inhibitory interaction and specific cooperative events and highlight a role for AHR in modifying the HIF transcriptional output in ccRCC. Citation Format: Véronique N. Lafleur, Silvia Halim, Peter J. Ratcliffe, David R. Mole. Bi-directional crosstalk between the HIF and AHR transcription factors in clear cell kidney cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 677.

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