The Role of the Tumor Suppressor, p190RhoGAP, in Apoptosis and Cytokinesis

p190RhoGAP (p190) is a RhoGTPase activating protein which regulates a variety of biological events by enhancing Rho-mediated hydrolysis of RhoGTP to RhoGDP. Multiple lines of evidence suggest that p190 can function as a tumor suppressor, although its mechanism of action remains unknown. p190 has also been implicated in the apoptotic process as both protein and mRNA levels are upregulated upon apoptotic initiation in rat prostate cells undergoing apoptosis. To gain insights into its mechanism of action as a tumor suppressor, an overexpression approach was taken. Previous studies revealed that overexpression of p190 in epithelial transformed cells led to a multinucleated phenotype. Chromatin condensation, a marker of apoptosis, was also frequently observed. In contrast, overexpression of p190 in non-transformed fibroblasts led to a dendrite-like phenotype, in addition to chromatin condensation. Work presented in this dissertation revealed that the primary phenotype of p190 overexpression is apoptosis, which occurs in a caspaseand Rho-dependent manner. p190 overexpression also preferentially induced multinucleation in transformed cells and dendrite-like formation in non-transformed cells, indicating that the secondary phenotypes are determined by transformation status and may act as intermediate phenotypes in the p190-apoptotic pathway. Preliminary data revealed that the NF-B pathway may be responsible for the differential response to p190 overexpression and that apoptosis may proceed through a JNK-Bim/Mcl-1 pathway regardless of transformation ii status. Finally, we show that p190 conferred docetaxel sensitivity to breast cancer cells through its down regulation of Rho. In addition to apoptosis, p190 regulates progression through cytokinesis. Previous work demonstrated that p190 overexpression induces multinucleation as a result of decreased RhoGTP levels at the cleavage furrow. This study demonstrates that p190 overexpression inhibited myosin II activation, which is required for completion of cytokinesis. p190 overexpression also reduced anillin localization to the cleavage furrow, and silencing of anillin prevented p190 localization to the cleavage furrow. Further studies revealed that p190 and anillin physically interact and regulate the localization of each other in a contractility-dependent manner. Together the data from this study further define the role of p190 in cytokinesis and clarify p190's role as a tumor suppressor.

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