Cascade profiling of the ubiquitin-proteasome system in cancer

Abstract : In this work we describe a systematic approach for screening of ubiquitin-proteasome system (UPS) based on cascade organization. We have evaluated the effect of RNAi knockdown of individual UPS components on viability of PCa cells with major focus on TMPRSS:ERG-positive cell line, VCaP, as a model of prevalent phenotype of prostate cancer. Seven genes have been identified to be particularly important for the functioning of PCa cells. Among them, UBE2U was the strongest hit. This thesis provides the first evidence for UBE2U involvement in prostate carcinogenesis and describes initial characterization of UBE2U as a potential drug-target.The prevalence of the components of CRL/NEDD8 pathway in the hits (four out of seven) suggested the importance of neddylation for PCa biology. Two of these hits, CUL2 and RBX1, being specific to TMPRSS2:ERG-positive cells, are potentially ERG-dependent. We have also revealed the crucial role of CRL-exchange factor CAND1, in particular, when the neddylation is compromised. Knockdown of CAND1 induces apoptosis in VCaP cells that is further potentiated by neddylation-specific inhibitor MLN4924. CAND1 is, therefore, a novel potential drug target. Furthermore, we have demonstrated that the inhibition of CRL/NEDD8 pathway in prostate cancer cells has a complex outcome that strongly depends on cellular context. MLN4924 inhibitor induced apoptosis in all tested cell lines, though TMPRSS2:ERG positive cells were significantly more resistant. We have demonstrated that the increased resistance of VCaP cells reflects the plasticity of cancer cells ensured by sophisticated interaction network ERG:NF-kB:c-Myc:Wnt/β-cat:AR. We found that partial inhibition of neddylation triggered transcriptional reprogramming of VCaP cells leading to cell quiescence and inhibition of proliferation-dependent apoptosis. This was a result of re-activation of AR program and induction of differentiation-like state. We conclude that CRL/NEDD8 pathway regulates cancer transcriptional network that underlies cancer cells plasticity. This knowledge would help to find better treatments for TMPRSS2:ERG-positive cancers.Finally, we observed that neddylation inhibition changed membrane properties and morphology of VCaP cells. This was accompanied by dose-dependent changes in the level and the localization of several membrane-associated proteins, including occludin, N-cadherin, paxillin and FAK. We thus conclude that CRL/NEDD8 pathway might be involved in sorting/trafficking of membrane proteins. This part of the work requires further investigation, as understanding of the underlying mechanisms is of general importance and may uncover a new role of CRL/NEDD8 pathway in regulation of cellular functions.General conclusions:1.We have obtained a comprehensive dataset on the involvement of all human E1-E2 UPS components in the regulation of viability of PCa cells, represented by five different cell lines.2.Our work has revealed new potential drug targets for PCa treatment: UBE2U and CAND1.3.We have demonstrated the role of CRL/NEDD8 pathway in the regulation of cancer cell plasticity and morphology.
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Anastasiia Rulina. Cascade profiling of the ubiquitin-proteasome system in cancer. Agricultural sciences. Université Grenoble Alpes, 2015. English. ⟨NNT : 2015GREAV028⟩. ⟨tel-01321321⟩

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