Abstract LB-152: PIK3CA mutation spectrum in urothelial carcinoma reflects cell context-dependent signalling and phenotypic outputs

Abstract

Abstract Activating p110α mutations are frequently observed in urothelial carcinoma (UC). Their specific effects in urothelial cells and the reason for the large excess of helical domain mutations relative to kinase domain mutations have not been studied. Thus we investigated the phenotypic consequences of hotspot and UC-specific rare PIK3CA mutations in immortalized normal human urothelial cells (NHUC) and mouse fibroblasts (NIH3T3). Our results show that in NHUC, all PIK3CA mutants activate the AKT pathway. The potency of AKT downstream activation by helical and kinase domain mutants was related to the frequency of mutation occurrence in UC (E545K>E542K>H1047R). In NIH3T3, the H1047R kinase domain mutant induced significantly higher levels of AKT activation relative to helical domain mutant forms and this was reflected in their abilities to promote anchorage-independent growth. In NHUC, only E542K and E545K helical domain mutant forms conferred a significant proliferative advantage at confluence and in nutrient limiting conditions. Both types of mutant forms induced NHUC cell motility, though no significant differences were found between helical and kinase domain mutant forms. Our findings indicate that the cellular consequences of mutant PIK3CA are both cell type- and mutation-specific. This provides a rationale for the observed PIK3CA mutation spectrum in UC and suggests that helical domain mutations may confer a selective advantage in the urothelium in vivo by overcoming normal contact-mediated inhibitory signals and allowing nutrient-independent proliferation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-152. doi:1538-7445.AM2012-LB-152