Littérature scientifique sur le sujet « TYROSINE KINASE ASSAY »

Abstract A large percentage of cancer cases present without knowledge of the causative genetic events. Tyrosine kinases are frequently implicated in the pathogenesis of cancer, but identification of specific tyrosine kinases as cancer targets has been a slow process. Tyrosine kinases are thought to play a causative role in acute myeloid leukemia (AML), based in part on the high percentage of cases with phosphorylation of STAT5—a marker for activity of tyrosine kinase signaling. However, known abnormalities in tyrosine kinases in AML are restricted to internal tandem duplications of FLT3 or genetic aberrations in FLT3, c-KIT, and a few other genes. Thus, the specific tyrosine kinases that form the basis for targeted intervention have remained unclear in the majority of AML patients. Here, we report a novel assay by which cells from AML patients are functionally screened with RNAi to elucidate tyrosine kinase targets amenable to therapeutic intervention. Methods: To determine targets necessary for viability of malignant cells, we screened cell lines as well as primary cells from AML patients by electroporating siRNAs individually targeting each member of the tyrosine kinase family. Four days later, we determined the cell viability and tabulated sensitivity of the cells to any individual tyrosine kinase. Where possible, results were confirmed by treating samples with small-molecule inhibitors with activity against the genes identified by the assay. In addition, the mechanism of oncogenesis was investigated for each positive result. Results: We demonstrate that siRNA screening can identify tyrosine kinase targets containing activating mutations in JAK3 (A572V) in CMK cells (Figure 1) and c-KIT (V560G) in HMC1.1 cells. In addition, this assay identifies targets that do not contain mutations, such as JAK1 (Figure 1) and the focal adhesion kinases, yet are still crucial to the survival of the cells. We have also used this assay to determine sensitivity of numerous primary AML samples to inhibition of individual tyrosine kinases. Candidate targets found in primary samples include FLT1, PDGFR, JAK1/3, JAK2, CSF1R, ROR1, and EPHA5. Studies using small-molecule kinase inhibitors have confirmed sensitivity of specific samples to inhibition of target genes identified by the assay. Finally, the mechanism of oncogenesis and its relation to the gene target has been established in select samples with genetic abnormalities ranging from point mutations and insertional mutations to evidence of chromosomal rearrangements. Conclusions: We demonstrate that RNAi functional screening can determine sensitivity to individual tyrosine kinases, both in cell lines and in primary samples. For the first time, this technique offers the potential to match specific therapies for targeted intervention with individual patients based on a functional assay. Figure 1. CMK cells were transfected with an siRNA library individually targeting each member of the tyrosine kinase family, N-RAS, K-RAS, and non-specific controls. Cell viability was determined by an MTS assay 4 days later. Each bar represents an individual kinase with values shown as percent mean ± s.e.m (n = 3) (normalized to non-specific controls). Figure 1. CMK cells were transfected with an siRNA library individually targeting each member of the tyrosine kinase family, N-RAS, K-RAS, and non-specific controls. Cell viability was determined by an MTS assay 4 days later. Each bar represents an individual kinase with values shown as percent mean ± s.e.m (n = 3) (normalized to non-specific controls).

We present a novel homogeneous in vitro assay format and apply it to the quantitative determination of the enzymatic activity of a tyrosine kinase. The assay employs a short peptidic substrate containing a single tyrosine and a single probe attached via a cysteine side chain. The structural flexibility of the peptide allows for the dynamic quenching of the probe by the nonphosphorylated tyrosine side chain. The probe responds with changes in its fluorescence lifetime depending on the phosphorylation state of the tyrosine. We use this effect to directly follow the enzymatic phosphorylation of the substrate, without having to resort to additional assay components such as an antibody against the phosphotyrosine. As an example for the application of this assay principle, we present results from the development of an assay for Abelson kinase (c-Abl) used for compound profiling. Adjustments in the peptide sequence would make this assay format suitable to a wide variety of other tyrosine kinases.

The authors present a fluorescence lifetime—based kinase binding assay that identifies and characterizes compounds that bind to the adenosine triphosphate (ATP)—binding pocket of a range of tyrosine and serine/threonine kinases. The assay is based on displacement of an Alexa Fluor® 647 conjugate of staurosporine from the ATP-binding site of a kinase, which is detected by a change in the fluorescence lifetime of the probe between the free (displaced) and kinase-bound states. The authors screened 257 kinases for specific binding and displacement of the Alexa Fluor® 647-staurosporine probe and found that approximately half of the kinases tested could potentially be assayed with this method. They present inhibitor binding data against 4 selected serine/threonine kinases and 4 selected tyrosine kinases, using 6 commonly used kinase inhibitors. Two of these kinases were chosen for further studies, in which inhibitor binding data were compared to inhibition of kinase activity using 2 separate activity assay formats. Rank-order potencies of compounds were similar, but not identical, between the binding and activity assays. It was postulated that these differences could be caused by the fact that the assays are measuring distinct phenomena, namely, activity versus binding, and in a purified recombinant kinase preparation, there can exist a mixture of active and nonactivated kinases. To explore this possibility, the authors compared binding affinity for the probe using 2 kinases in their respective nonactivated and activated (phosphorylated) forms and found a kinase-dependent difference between the 2 forms. This assay format therefore represents a simple method for the identification and characterization of small-molecule kinase inhibitors that may be useful in screening a wide range of kinases and may be useful in identifying small molecules that bind to kinases in their active or nonactivated states. ( Journal of Biomolecular Screening 2007:828-841)

Suitable assay conditions for the detection of cytosolic protein-tyrosine kinase activities in crude extracts of various rat tissues have been determined. Cytosolic protein-tyrosine kinases showed common characteristics including substrate specificity and divalent cation requirement. Using (Val5) angiotensin II and Mn2+ rather than a src-related synthetic peptide, E11G1, and Mg2+, we obtained higher activities of cytosolic protein-tyrosine kinases. Among various rat tissues tested, spleen, bone marrow, thymus, small intestine, appendix and lung, in decreasing order of total activity, contained high activities of cytosolic protein-tyrosine kinases. These results suggest that the enzyme activities in lymphatic organs and in organs closely related to cell proliferation are high. The assay system described allows the precise measurement of cytosolic protein-tyrosine kinase activity in various rat tissues, both normal and malignant.

Despite vast improvements in our understanding of cancer genetics, a large percentage of cancer cases present without knowledge of the causative genetic events. Tyrosine kinases are frequently implicated in the pathogenesis of numerous types of cancer, but identification and validation of tyrosine kinase targets in cancer can be a time-consuming process. We report the establishment of an efficient, functional screening assay using RNAi technology to directly assess and compare the effect of individually targeting each member of the tyrosine kinase family. We demonstrate that siRNA screening can identify tyrosine kinase targets containing activating mutations in Janus kinase (JAK) 3 (A572V) in CMK cells and c-KIT (V560G) in HMC1.1 cells. In addition, this assay identifies targets that do not contain mutations, such as JAK1 and the focal adhesion kinases (FAK), that are crucial to the survival of the cancer cells. This technique, with additional development, might eventually offer the potential to match specific therapies with individual patients based on a functional assay.

In the last few years, fluorescence polarization (FP) has been applied to the development of robust, homogeneous, high throughput assays in molecular recognition research, such as ligand-protein interactions. Recently, this technology has been applied to the development of homogeneous tyrosine kinase assays, since there are high-affinity anti-phosphotyrosine antibodies available. Unlike tyrosine kinases, application of FP to assay development for serine/threonine kinases has been impeded because of lack of high-affinity anti-phosphoserine/threonine antibodies. In the present study, we report the discovery of a high-affinity, monoclonal anti-phosphoserine antibody, 2B9, with a Kd of 250 ± 34 pM for a phosphoserine-containing peptide tracer, fluorescein-RFARKGS(PO4)LRQKNV. Our data suggest that 2B9 is selective for fluorescein-RFARKGS(PO4)LRQKNV. The antibody and tracer have been used for the development of a competitive FP assay for protein kinase C (PKC) in 384-well plates. Phosphatidylserine, which enhances the kinase activity of PKC in a Ca2+-dependent manner and has a structure similar to that of phosphoserine, did not interfere with binding of the peptide tracer to the antibody in the FP assay. The data indicate that the FP assay is more sensitive and robust than the scintillation proximity assay for PKC. The FP assay developed here can be used for rapid screening of hundreds of thousands of compounds for discovery of therapeutic leads for PKC-related diseases.

Abstract Abstract 708 Aberrantly activated tyrosine kinases and their associated signaling pathways are critical to leukemogenesis and primary acute myeloid leukemia (AML) cell viability. While aberrant kinase activation has been confirmed in a significant percentage of AML, constitutive phosphorylation of STAT5, a marker of tyrosine kinase activation, is present in the majority of AML samples indicating that as yet unidentified tyrosine kinases can be aberrantly activated and contribute to leukemogenesis. Efforts to identify activating tyrosine kinase mutations using high-throughput sequencing have identified low frequency mutations of uncertain functional significance. Because these studies failed to detect additional high-frequency kinase mutations, the identity and mechanism of tyrosine kinase activation may be unique in many AMLs. To avoid the imitations of high-throughput sequencing, we have developed a functional assay that can rapidly and simultaneously identify therapeutic targets while providing therapeutic options. Methods: To rapidly identify activated kinase pathways in individual, primary AML samples, we have developed a small-molecule inhibitor array which includes 90 small-molecule, cell-permeable inhibitor compounds including a core of 36 tyrosine kinase inhibitors that covers the majority of the tyrosine kinome. Many of the inhibitors are available for clinical use or are in clinical development. In this assay, inhibitors were placed in 96-well plates at four serial dilutions to allow IC50 calculations. Three days after adding primary AML cells to each well, we performed an MTS cell viability assay to evaluate the effect of each inhibitor on cell viability. Because most inhibitors affect multiple kinases, we compared target specificities of compounds that decrease primary AML cell viability with those that have no effect to identify potential targets. Results: In preliminary proof-of-principal experiments, we tested leukemia cell lines with known activating tyrosine kinase mutations and Ba/F3 cell lines expressing activated tyrosine kinases. Appropriate inhibitor sensitivity profiles were obtained in CMK cells which depend on a JAK3 A572V mutation for viability, MKPL-1 cells with an activating CSF1R translocation, and in a Ba/F3 line expressing JAK2 V617F. In addition to the primary target, downstream targets were frequently identified; MKPL-1 cells also showed sensitivity to phosphoinositol 3-kinase and NFKB inhibitors. Thus, not only primary targets but the downstream signaling pathways critical to leukemic cell viability can be highlighted using this assay. To date, we have analyzed approximately 150 primary leukemia and lymphoma samples. In some cases, targets could be identified by comparison of overlapping kinase specificities for compounds that decreased leukemic cell viability and subtraction of possible kinase targets inhibited by compounds that had no effect on viability. However, many cases exhibited complex, often unique, inhibitor sensitivity profiles that complicated target identification. Comparison with sensitivity profiles for known aberrantly activated kinases was useful when available. Accordingly, additional leukemia cell lines and Ba/F3 lines that depend on a single aberrantly activated tyrosine kinase for viability are being evaluated. Automated scripts that correlate the leukemic cell inhibitor sensitivity with the inhibitor target specificity are also in preparation. Conclusions: These preliminary data demonstrate that the small-molecule inhibitor functional assays can rapidly identify disease causing genes, provide insights into their mechanism of action, and suggest therapeutic options. The distinct patterns of tyrosine kinase sensitivity in these samples support the hypothesis that tyrosine kinases and related pathways contributing to leukemogenesis in each patient may be different and that targeted therapy will be most effective when administered on an individualized basis. Disclosures: Druker: OHSU patent #843 - Mutate ABL Kinase Domains: Patents & Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents & Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding.

Protein kinases, a class of enzymes that phosphorylate certain tyrosine, serine, and threonine residues, play an important role in cellular functions and are important targets in drug discovery research. Thus, it is of interest to develop a simple assay that can be used to measure protein kinase activity toward specific substrates and is suitable for the high throughput screening (HTS) of potential kinase inhibitors. The scintillation proximity concept has been successfully applied for measuring specific kinase activity using surfaces passively coated with a peptide substrate. In this study, we evaluated kinase assay performance on three ScintiStrip platforms: unmodified surface, streptavidin-coated surface, and streptavidin covalently attached to surface. The high affinity of streptavidin toward biotin-linked peptide substrates makes it a unique platform for measuring specific incorporation of radiolabeled phosphate into selected substrates of specific enzymes in the presence of others. Therefore, this assay may be used with cell extracts containing impure kinases as well as with purified enzymes. The scope of this assay was demonstrated with purified tyrosine kinases (e.g., p60c-src kinase) and A431 cell extracts. This scintillation proximity assay is universal, simple, rapid, accurate, and can be adapted for use with robotics for HTS.

ABSTRACT Members of the Eph family of receptor tyrosine kinases exhibit a striking degree of amino acid homology, particularly notable in the kinase and membrane-proximal regions. A mutagenesis approach was taken to address the functions of specific conserved tyrosine residues within these catalytic and juxtamembrane domains. Ligand stimulation of wild-type EphB2 in neuronal NG108-15 cells resulted in an upregulation of catalytic activity and an increase in cellular tyrosine phosphorylation, accompanied by a retraction of neuritic processes. Tyrosine-to-phenylalanine substitutions within the conserved juxtamembrane motif abolished these responses. The mechanistic basis for these observations was examined using the highly related EphA4 receptor in a continuous coupled kinase assay. Tandem mass spectrometry experiments confirmed autophosphorylation of the two juxtamembrane tyrosine residues and also identified a tyrosine within the kinase domain activation segment as a phosphorylation site. Kinetic analysis revealed a decreased affinity for peptide substrate upon substitution of activation segment or juxtamembrane tyrosines. Together, our data suggest that the catalytic and therefore biological activities of Eph receptors are controlled by a two-component inhibitory mechanism, which is released by phosphorylation of the juxtamembrane and activation segment tyrosine residues.

Cholecystokinin (CCK) is the major pancreatic secretagogue and acinar cell mitogen. This study was performed to determine by which effector systems CCK regulates tyrosine kinases, phosphatidylinositol (PtdIns) 3-kinase, and phospholipase D (PLD) activities. Pancreatic acini loaded with [3H]myristic acid or [3H]inositol were used to assay PLD and PtdIns 3-kinase. G protein activation with NaF increased particulate and crude cytosolic tyrosine kinase and PLD activities. PLD activation was pertussis toxin sensitive. Inhibition of phospholipase C (PLC) slightly reduced caerulein-stimulated particulate tyrosine kinase and blocked crude cytosolic tyrosine kinase activity without affecting caerulein-induced PLD activity. Ca2+ is an important factor in caerulein stimulation of tyrosine kinase and PLD activities. Protein kinase C and tyrosine kinase inhibition abolished caerulein-activated particulate and crude cytosolic tyrosine kinase and PtdIns 3-kinase activities without any effect on PLD. Wortmannin inhibited PLD and PtdIns 3-kinase activation. Caerulein-induced amylase secretion was partially reduced by tyrosine kinase inhibition, with no effect from wortmannin. Caerulein can stimulate a pertussis toxin-insensitive G protein, leading to particulate tyrosine kinase activation and a Ca(2+)-sensitive cytosolic tyrosine kinase through PLC activation. However, PLD activation by caerulein is pertussis toxin sensitive, cytosolic Ca2+ sensitive, and independent of previous PLC and tyrosine kinase activation.

With the advent of Tyrosine kinase inhibitors (TKI) as a therapy for Chronic myeloid Leukemia (CML), the patients now enjoy a life expectancy close to that of the general population. But some patients do get unresponsive to the TKI treatment over time due to several mutations in the kinase domain of the BCR-ABL fusion protein, which further leads to activation of multiple signaling cascades within the leukemic cell, helping it survive and proliferate. This project validates and optimizes a new method of In situ PLA that incorporates the usage of different padlocks and template oligos. Multiple cross-reactivity tests and interaction assays in multiple cancer cell lines will further optimize this system as a robust multiplex protein-protein interaction detection tool. Proteins associated with the MAP-K, PI3-K, and Jak-STAT signaling pathways were the main detection targets.

A number of reports have demonstrated the importance of the CUB domaincontaining protein 1 (CDCP1) in facilitating cancer progression in animal models and the potential of this protein as a prognostic marker in several malignancies. CDCP1 facilitates metastasis formation in animal models by negatively regulating anoikis, a type of apoptosis triggered by the loss of attachment signalling from cell-cell contacts or cell-extra cellular matrix (ECM) contacts. Due to the important role CDCP1 plays in cancer progression in model systems, it is considered a potential drug target to prevent the metastatic spread of cancers. CDCP1 is a highly glycosylated 836 amino acid cell surface protein. It has structural features potentially facilitating protein-protein interactions including 14 N-glycosylation sites, three CUB-like domains, 20 cysteine residues likely to be involved in disulfide bond formation and five intracellular tyrosine residues. CDCP1 interacts with a variety of proteins including Src family kinases (SFKs) and protein kinase C ä (PKCä). Efforts to understand the mechanisms regulating these interactions have largely focussed on three CDCP1 tyrosine residues Y734, Y743 and Y762. CDCP1-Y734 is the site where SFKs phosphorylate and bind to CDCP1 and mediate subsequent phosphorylation of CDCP1-Y743 and -Y762 which leads to binding of PKCä at CDCP1-Y762. The resulting trimeric protein complex of SFK•CDCP1•PKCä has been proposed to mediate an anti-apoptotic cell phenotype in vitro, and to promote metastasis in vivo. The effect of mutation of the three tyrosines on interactions of CDCP1 with SFKs and PKCä and the consequences on cell phenotype in vitro and in vivo have not been examined. CDCP1 has a predicted molecular weight of ~90 kDa but is usually detected as a protein which migrates at ~135 kDa by Western blot analysis due to its high degree of glycosylation. A low molecular weight form of CDCP1 (LMWCDCP1) of ~70 kDa has been found in a variety of cancer cell lines. The mechanisms leading to the generation of LMW-CDCP1 in vivo are not well understood but an involvement of proteases in this process has been proposed. Serine proteases including plasmin and trypsin are able to proteolytically process CDCP1. In addition, the recombinant protease domain of the serine protease matriptase is also able to cleave the recombinant extracellular portion of CDCP1. Whether matriptase is able to proteolytically process CDCP1 on the cell surface has not been examined. Importantly, proteolytic processing of CDCP1 by trypsin leads to phosphorylation of its cell surface-retained portion which suggests that this event leads to initiation of an intracellular signalling cascade. This project aimed to further examine the biology of CDCP1 with a main of focus on exploring the roles played by CDCP1 tyrosine residues. To achieve this HeLa cells stably expressing CDCP1 or the CDCP1 tyrosine mutants Y734F, Y743F and Y762F were generated. These cell lines were used to examine: • The roles of the tyrosine residues Y734, Y743 and Y762 in mediating interactions of CDCP1 with binding proteins and to examine the effect of the stable expression on HeLa cell morphology. • The ability of the serine protease matriptase to proteolytically process cell surface CDCP1 and to examine the consequences of this event on HeLa cell phenotype and cell signalling in vitro. • The importance of these residues in processes associated with cancer progression in vitro including adhesion, proliferation and migration. • The role of these residues on metastatic phenotype in vivo and the ability of a function-blocking anti-CDCP1 antibody to inhibit metastasis in the chicken embryo chorioallantoic membrane (CAM) assay. Interestingly, biochemical experiments carried out in this study revealed that mutation of certain CDCP1 tyrosine residues impacts on interactions of this protein with binding proteins. For example, binding of SFKs as well as PKCä to CDCP1 was markedly decreased in HeLa-CDCP1-Y734F cells, and binding of PKCä was also reduced in HeLa-CDCP1-Y762F cells. In contrast, HeLa-CDCP1-Y743F cells did not display altered interactions with CDCP1 binding proteins. Importantly, observed differences in interactions of CDCP1 with binding partners impacted on basal phosphorylation of CDCP1. It was found that HeLa-CDCP1, HeLa-CDCP1-Y743F and -Y762F displayed strong basal levels of CDCP1 phosphorylation. In contrast, HeLa-CDCP1-Y734F cells did not display CDCP1 phosphorylation but exhibited constitutive phosphorylation of focal adhesion kinase (FAK) at tyrosine 861. Significantly, subsequent investigations to examine this observation suggested that CDCP1-Y734 and FAK-Y861 are competitive substrates for SFK-mediated phosphorylation. It appeared that SFK-mediated phosphorylation of CDCP1- Y734 and FAK-Y861 is an equilibrium which shifts depending on the level of CDCP1 expression in HeLa cells. This suggests that the level of CDCP1 expression may act as a regulatory mechanism allowing cells to switch from a FAK-Y861 mediated pathway to a CDCP1-Y734 mediated pathway. This is the first time that a link between SFKs, CDCP1 and FAK has been demonstrated. One of the most interesting observations from this work was that CDCP1 altered HeLa cell morphology causing an elongated and fibroblastic-like appearance. Importantly, this morphological change depended on CDCP1- Y734. In addition, it was observed that this change in cell morphology was accompanied by increased phosphorylation of SFK-Y416. This suggests that interactions of SFKs with CDCP1-Y734 increases SFK activity since SFKY416 is critical in regulating kinase activity of these proteins. The essential role of SFKs in mediating CDCP1-induced HeLa cell morphological changes was demonstrated using the SFK-selective inhibitor SU6656. This inhibitor caused reversion of HeLa-CDCP1 cell morphology to an epithelial appearance characteristic of HeLa-vector cells. Significantly, in vitro studies revealed that certain CDCP1-mediated cell phenotypes are mediated by cellular pathways dependent on CDCP1 tyrosine residues whereas others are independent of these sites. For example, CDCP1 expression caused a marked increase in HeLa cell motility that was independent of CDCP1 tyrosine residues. In contrast, CDCP1- induced decrease in HeLa cell proliferation was most prominent in HeLa- CDCP1-Y762F cells, potentially indicating a role for this site in regulating proliferation in HeLa cells. Another cellular event which was identified to require phosphorylation of a particular CDCP1 tyrosine residue is adhesion to fibronectin. It was observed that the CDCP1-mediated strong decrease in adhesion to fibronectin is mostly restored in HeLa-CDCP1-Y743F cells. This suggests a possible role for CDCP1-Y743 in causing a CDCP1-mediated decrease in adhesion. Data from in vivo experiments indicated that HeLa-CDCP1-Y734F cells are more metastic than HeLa-CDCP1 cells in vivo. This indicates that interaction of CDCP1 with SFKs and PKCä may not be required for CDCP1-mediated metastasis formation of HeLa cells in vivo. The metastatic phenotype of these cells may be caused by signalling involving FAK since HeLa-CDCP1- Y734F cells are the only CDCP1 expressing cells displaying constitutive phosphorylation of FAK-Y861. HeLa-CDCP1-Y762F cells displayed a very low metastatic ability which suggests that this CDCP1 tyrosine residue is important in mediating a pro-metastatic phenotype in HeLa cells. More detailed exploration of cellular events occurring downstream of CDCP1-Y734 and -Y762 may provide important insights into the mechanisms altering the metastatic ability of CDCP1 expressing HeLa cells. Complementing the in vivo studies, anti-CDCP1 antibodies were employed to assess whether these antibodies are able to inhibit metastasis of CDCP1 and CDCP1 tyrosine mutants expressing HeLa cells. It was found that HeLa- CDCP1-Y734F cells were the only cell line which was markedly reduced in the ability to metastasise. In contrast, the ability of HeLa-CDCP1, HeLa- CDCP1-Y743F and -Y762F cells to metastasise in vivo was not inhibited. These data suggest a possible role of interactions of CDCP1 with SFKs, occurring at CDCP1-Y734, in preventing an anti-metastatic effect of anti- CDCP1 antibodies in vivo. The proposal that SFKs may play a role in regulating anti-metastatic effects of anti-CDCP1 antibodies was supported by another experiment where differences between HeLa-CDCP1 cells and CDCP1 expressing HeLa cells (HeLa-CDCP1-S) from collaborators at the Scripps Research Institute were examined. It was found that HeLa-CDCP1-S cells express different SFKs than CDCP1 expressing HeLa cells generated for this study. This is important since HeLa-CDCP1-S cells can be inhibited in their metastatic ability using anti-CDCP1 antibodies in vivo. Importantly, these data suggest that further examinations of the roles of SFKs in facilitating anti-metastatic effects of anti-CDCP1 antibodies may give insights into how CDCP1 can be blocked to prevent metastasis in vivo. This project also explored the ability of the serine protease matriptase to proteolytically process cell surface localised CDCP1 because it is unknown whether matriptase can cleave cell surface CDCP1 as it has been reported for other proteases such as trypsin and plasmin. Furthermore, the consequences of matriptase-mediated proteolysis on cell phenotype in vitro and cell signalling were examined since recent reports suggested that proteolysis of CDCP1 leads to its phosphorylation and may initiate cell signalling and consequently alter cell phenotype. It was found that matriptase is able to proteolytically process cell surface CDCP1 at low nanomolar concentrations which suggests that cleavage of CDCP1 by matriptase may facilitate the generation of LWM-CDCP1 in vivo. To examine whether matriptase-mediated proteolysis induced cell signalling anti-phospho Erk 1/2 Western blot analysis was performed as this pathway has previously been examined to study signalling in response to proteolytic processing of cell surface proteins. It was found that matriptase-mediated proteolysis in CDCP1 expressing HeLa cells initiated intracellular signalling via Erk 1/2. Interestingly, this increase in phosphorylation of Erk 1/2 was also observed in HeLa-vector cells. This suggested that initiation of cell signalling via Erk 1/2 phosphorylation as a result of matriptase-mediated proteolysis occurs by pathways independent of CDCP1. Subsequent investigations measuring the flux of free calcium ions and by using a protease-activated receptor 2 (PAR2) agonist peptide confirmed this hypothesis. These data suggested that matriptase-mediated proteolysis results in cell signalling via a pathway induced by the activation of PAR2 rather than by CDCP1. This indicates that induction of cell signalling in HeLa cells as a consequence of matriptase-mediated proteolysis occurs via signalling pathways which do not involve phosphorylation of Erk 1/2. Consequently, it appears that future attempts should focus on the examination of cellular pathways other than Erk 1/2 to elucidate cell signalling initiated by matriptase-mediated proteolytic processing of CDCP1. The data presented in this thesis has explored in vitro and in vivo aspects of the biology of CDCP1. The observations summarised above will permit the design of future studies to more precisely determine the role of CDCP1 and its binding partners in processes relevant to cancer progression. This may contribute to further defining CDCP1 as a target for cancer treatment.

Neurotrophins and their receptors are key molecules in the development of the
nervous system. Neurotrophin-3 binds preferentially to its high-affinity receptor
NTRK3, which exists in two major isoforms in humans, the full-length kinaseactive
form (150 kDa) and a truncated non-catalytic form (50 kDa). The two
variants show different 3'UTR regions, indicating that they might be differentially
regulated at the post-transcriptional level. In this work we explore how
microRNAs take part in the regulation of full-length and truncated NTRK3,
demonstrating that the two isoforms are targeted by different sets of microRNAs.
We analyze the physiological consequences of the overexpression of some of the
regulating microRNAs in human neuroblastoma cells. Finally, we provide
preliminary evidence for a possible involvement of miR-124 - a microRNA with no
putative target site in either NTRK3 isoform - in the control of the alternative
spicing of NTRK3 through the downregulation of the splicing repressor PTBP1.
Las neurotrofinas y sus receptores constituyen una familia de factores cruciales
para el desarrollo del sistema nervioso. La neurotrofina 3 ejerce su función
principalmente a través de una unión de gran afinidad al receptor NTRK3, del cual
se conocen dos isoformas principales, una larga de 150KDa con actividad de tipo
tirosina kinasa y una truncada de 50KDa sin dicha actividad. Estas dos isoformas
no comparten la misma región 3'UTR, lo que sugiere la existencia de una
regulación postranscripcional diferente. En el presente trabajo se ha explorado
como los microRNAs intervienen en la regulación de NTRK3, demostrando que las
dos isoformas son reguladas por diferentes miRNAs. Se han analizado las
consecuencias fisiológicas de la sobrexpresión de dichos microRNAs utilizando
células de neuroblastoma. Finalmente, se ha estudiado la posible implicación del
microRNA miR-124 en el control del splicing alternativo de NTRK3 a través de la
regulación de represor de splicing PTBP1.

has been significant progress in the development of new technologies and methodologies to characterize gene expression. The fluorescent-based real-time reverse transcription (RT) polymerase chain reaction (PCR) is an important tool used for clinical and molecular research, biotechnology and as a diagnostic test. Insulin-like growth factors (IGF-1 and IGF-2) and insulin are ubiquitously expressed and play important roles in the regulation of cell growth, differentiation and the maintenance of cell differentiation in mammals. The IGF system (IGF-1, IGF-2, IGF -1 receptor, IGF-2 receptor and six IGF-binding proteins) and insulin are consequently essential to most aspects of male and female reproduction. IGF-1 is produced in multiple tissues but predominately in the liver, from where it enters the circulation. Insulin is secreted by β-cells of the pancreas’ islets of Langerhans. Both IGF-1 and insulin polypeptides bind to specific cell surface receptors. These receptors are members of the superfamily known as tyrosine protein kinases, and are composed of two α and two β subunits linked by disulfide bonds to form an αβ–αβ heterotetramer. The α subunits include ligand binding sites, whereas the β subunits contain tyrosine kinase activity. The aim of this project was to develop real-time RT-PCR assays for quantification of equine insulin-like growth factor-1 receptor (IGF-1R) and insulin receptor (INS-R) mRNA. The assays were developed using stallion testicular tissue samples, obtained by excisional biopsy, from three horse breeds (Friesan, Thoroughbred and Warmblood). The assays developed were efficient, sensitive and had a broad linear range of detection (seven logs for IGF-1R and six logs for INS-R). The assays worked well in our hands and were both sensitive and specific for the detection of equine IGF-1R and INS-R mRNA in a variety of equine tissues.
Dissertation (MMedVet)--University of Pretoria, 2011.
Production Animal Studies
Unrestricted

La leucemia mieloide cronica (CML) è un tumore del sangue che colpisce ogni anno più di 4500 pazienti negli Stati Uniti e più di 7500 in Europa. La CML è causata da un riarrangiamento cromosomico che si traduce nella creazione di BCR/ABL1, una chinasi costituticamente attiva. L'attività incontrollata di questa chinasi determina l'accumulo di cellule mieloidi immature e la riduzione dei globuli rossi e piastrine nel sangue. Questi cambiamenti compromettono la funzione del sistema immunitario, di erogazione di ossigeno e coagulazione. Questa malattia rimane spesso silenziosa per molti anni in fase cronica (CP), ma se non trattata, procede alla fase più aggressiva e meno curabile, la fase blastica (BP). L'intervento con un regime terapeutico efficace nel più breve tempo possibile è quindi di fondamentale importanza. L'odierno approccio clinico prevede l'individuazione di mutazioni del dominio di BCR-ABL1 chinasi solo nei pazienti con una prima risposta inadeguata agli inibitori tirosin chinasici (Resistenza primaria). La mancanza di risposta iniziale può essere rilevata solo dopo un minimo di 3-12 mesi dalla diagnosi.La capacità di capire come i pazienti rispondono ai farmaci al momento della diagnosi, con una semplice analisi del sangue periferico potrebbe aiutare i medici a prescrivere trattamenti su misura per il paziente diminuendo l'insorgenza di future resistenze ai farmaci. Il test che proponiamo si basa sull'utilizzo di un peptide sintetico con elevata specificità per BCR-ABL1. Il test utilizza anticorpi per rilevare la fosforilazione del peptide che avviene usando lisati di sangue periferico o midollo osseo.
Chronic Myelogenous Leukemia (CML) is a blood cancer that affects each yearmore than 4500 patients in USA and more than 7500 in Europe. CML is caused byan acquired chromosomal rearrangement that results in the creation of BCR-ABL1, an abnormally active kinase. The uncontrolled activity of this kinasedetermines the accumulation of immature myeloid cells and the reduction of redblood cells and platelets in the blood stream. These changes compromise thefunction of immune system, oxygen delivery and coagulation. This diseaseremains often silent for many years in a so-called chronic phase (CP), but if leftuntreated, it proceeds to the more aggressive and least treatable accelerating(AP) and blastic phases (BP). Intervening with an effective therapeutic regimenin the shortest time possible is therefore of paramount importance.The standard clinical approach prescribes the detection of BCR-ABL1 kinasedomain mutations only in patients with an inadequate initial response to TKIs(primary resistance). The lack of initial response can be detected only after aminimum of 3-12 months from the diagnosis.The ability to understand how patients respond to drugs at diagnosis with asimple analysis of peripheral blood would help clinicians to prescribe morepatient-tailored treatments decreasing the insurgence of future drug resistance.The test assay we are proposing is based on an immobilized syntheticallyoptimized peptide with a high specificity for BCR-ABL1. The test uses antibodiesto detect the occurred peptide phosphorylation from appropriately preparedperipheral blood or bone marrow cell lysates.

"Bone marrow tyrosine kinase in chromosome X (BMX) is a major member of the TEC family kinases and has been implicated in tumorigenecity, motility, proliferation and differentiation. BMX is highly overexpressed in prostate cancer and it is involved in the adaptive compensatory mechanism of castrate-resistance prostate cancer to androgen deprivation therapy. Besides, it suppresses a core component of the intrinsic apoptotic pathway, granting tumor cells the ability to escape apoptosis induced by chemotherapeutic drugs. BMX knockout mouse have a normal lifespan, without an obvious altered phenotype, suggesting that therapies based on BMX inhibition, may have limited side effects. We developed a series of BMX-IN-1 analogues that showed an increased inhibitory capacity when compared to BMX-IN-1. Since crystallographic information is essential to understand the molecular basis of BMX inhibition by covalent inhibitors we establish a baculovirus-insect expression system protocol for the production of the recombinant human BMX. Here we report the full biochemical and biophysical characterization of human BMX alone and in complex with different covalent ligands.(...)"

BACKGROUND: Activating mutations of FGFR3 are frequently identified in superficial urothelial carcinoma (UC) and increased expression of FGFR1 and FGFR3 are common in both superficial and invasive UC. METHODS: The effects of inhibition of receptor activity by three small molecule inhibitors (PD173074, TKI-258 and SU5402) were investigated in a panel of bladder tumour cell lines with known FGFR expression levels and FGFR3 mutation status. RESULTS: All inhibitors prevented activation of FGFR3, and inhibited downstream MAPK pathway signalling. Response was related to FGFR3 and/or FGFR1 expression levels. Cell lines with the highest levels of FGFR expression showed the greatest response and little or no effect was measured in normal human urothelial cells or in UC cell lines with activating RAS gene mutations. In sensitive cell lines, the drugs induced cell cycle arrest and/or apoptosis. IC(50) values for PD173074 and TKI-258 were in the nanomolar concentration range compared with micromolar concentrations for SU5402. PD173074 showed the greatest effects in vitro and in vivo significantly delayed the growth of subcutaneous bladder tumour xenografts. CONCLUSION: These results indicate that inhibition of FGFR1 and wild-type or mutant FGFR3 may represent a useful therapeutic approach in patients with both non-muscle invasive and muscle invasive UC.