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Regulation of ATM-Dependent DNA Damage Responses in Breast Cancer by the RhoGEF Net1
Annual summary 1 Apr 2012-31 Mar 2013
TEXAS UNIV HEALTH SCIENCE CENTER AT HOUSTON
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The Neuroepithelioma transforming gene 1 Net1 is a RhoA specific guanine nucleotide exchange factor GEF that is frequently overexpressed in human cancer, including breast cancer. We have previously reported that DNA damage activates Net1 to control RhoA and p38 MAPK mediated cell survival pathway in response to ionizing radiation IR. However, others have shown that Net1 activation contributes to RhoB-mediated cell death after IR. Thus, the role of Net1 in controlling IR responses and cell survival is controversial. With the completion of the first year of this fellowship, we have found that the Net1A isoform is specifically required for DNA double-strand break DSB-induced signaling and DNA repair. Depletion of Net1A in human breast cancer cells reduced IR-stimulated ATM activation and signaling to its substrates Chk2 and H2AX. In addition, suppression of Net1A expression adversely affected cell survival after IR. Moreover, we observed that overexpression of the Net1A isoform significantly reduced H2AX foci formation after IR, which required the unique N-terminal region of Net1A. Importantly, this effect did not require Rho GTPase activation by Net1A, and was not recapitulated by overexpression of RhoA or RhoB. Net1A was also found to co-immunoprecipitate with the DNA-PK complex in an IR-regulated manner. Taken together, our current data suggests a model in which Net1A functions as a non-catalytic binding protein to control DNA damage response signaling and DNA repair to affect cell survival after IR.
APPROVED FOR PUBLIC RELEASE