Role of the E-3 ligase CHIP in the negative regulation of the transcription factor TAp63

Stephen Armstrong
The p53 family of tumor suppressors is an important group of transcription factors preventing the development of cancer by targeting cell-cycle arrest and apoptosis mediator proteins for transcription. The most studied, p53, is frequently inactivated in carcinomas by mutation or genetic silencing, while the other two members TAp63 (transactivation domaincontaining p63) and TAp73 are rarely mutated, but rather are regulated at the protein level. The most common regulation method for TAp63 is
more » ... od for TAp63 is post-translational modification, and one of the most prominent ways to negatively regulate expression and function of TAp63 is by ubiquitination followed by proteasome-mediated degradation. Ubiquitination of TAp63 is carried out by an E-3 ligase enzyme that is able to catalyze the attachment of a small peptide called ubiquitin to a target substrate. Poly-ubiquitin chains are required in order for the proteasome to recognize a substrate, and there are many E-3 ligases that can catalyze the attachment of poly-ubiquitin chains to the TAp63 protein. These include the primary regulator of TAp63, Itch/AIP4. In this study, we identify and characterize another primary regulator of TAp63, the E-3 ligase CHIP, which is a key mediator of ubiquitination during the heat shock response. We observed that CHIP is able to bind to TAp63, facilitating the attachment of polyubiquitin chains. The over-expression of CHIP in carcinoma cells results in a reduction in TAp63 protein expression, accompanied by oncogenic effects including an increase in cell survival, and a decrease in apoptosis and cell cycle arrest. Knockdown of endogenous CHIP results in an increase in TAp63 expression accompanied by tumor suppressive effects including a decrease in cell survival and migration, and an increase in apoptosis and cell cycle arrest. CHIP expression is negatively correlated with TAp63 expression in various carcinoma cell lines, and invasive prostate carcinoma patient tissue samples. This research supports an oncogenic role for iii CHIP in the negative regulation of TAp63 expression and function, and provides a possible therapeutic target for carcinoma treatment in the future. iv Preface This thesis is an original work by Stephen Armstrong. The research project, of which this is a part, received research ethics approval from the Health Research Ethics Board -Biomedical Panel (University of Alberta) for the use of prostate tissue samples. Project Name: Detection of p53 family members and related regulatory factors in prostate cancer
doi:10.7939/r37w67b33 fatcat:zpdkiv3revbinkpnaw7bvx2ng4