Apoptosis is the Primary Phenotype Evoked by p190RhoGAP Overexpression

p190RhoGAP (p190) is a RhoGTPase activator protein (GAP) that has been shown to regulate actin cytoskeletal dynamics via Rho‐dependent signaling pathways. By enhancing Rho‐mediated hydrolysis of RhoGTP to RhoGDP, p190 negatively regulates association of RhoGTP with its downstream effectors. The p190 gene is located on chromosome 19q13.3, which is mutated in several solid tumor types, suggesting its involvement in malignant transformation. Findings that p190 reduced the incidence of PDGF‐induced gliomas in mouse models further implicate it as a tumor suppressor. To gain insight into its mechanism of action, an overexpression approach was taken. Previous studies in our lab revealed that overexpression of p190 in epithelial cells led to a multi‐nucleated phenotype, suggesting that it negatively regulates mitosis. Chromatin condensation, an apoptotic marker, was also frequently observed. In contrast, overexpression of p190 in fibroblasts led to dendrite formation or chromatin condensation. To further elucidate which cellular processes p190 influenced most, both epithelial cells and fibroblasts were examined for the frequency of the three phenotypes in cells overexpressing p190. The most prominent phenotype in both cell types was apoptosis, as determined by TUNEL staining and caspase 3 cleavage. Real‐time microscopy in epithelials revealed that multi‐nucleation resulted in apoptosis, as did dendrite formation in fibroblasts. In conclusion, we found that overexpression of p190RhoGAP primarily resulted in apoptosis of both cell types, and that multi‐nucleation and dendrite formation appeared to be intermediate phenotypes leading to apoptosis in epithelial and fibroblastic cells, respectively. These results suggest that p190 may utilize different pathways in different cell types to mediate its anti‐tumor effects. National Institutes of Health CA39438 (SJP)