Abstract 4359: Several cancer types are associated with increased expression and activity of the ECT2 RhoGEF and decreased expression and activity of the DLC1 RhoGAP, leading to increased RhoA activity

Abstract

Abstract RhoA, which is a member of the Ras family of small GTPases, whose proteins cycle between an active GTP-bound form and an inactive GDP-bound form, frequently has high activity in advanced cancer. The RhoA protein is activated by RhoGEFs, which catalyze replacement of bound-GDP with bound-GTP, and inactivated by RhoGAPs, which hydrolyze bound-GTP to bound-GDP. In this study, we have used the The Cancer Genome Atlas (TCGA) and the NCI Clinical Proteomic Tumor Analysis Consortium (CPTAC) databases to examine the relationship between a specific RhoGEF, ECT2, and a specific RhoGAP, DLC1, and experimentally tested the biological relevance of some key findings. Using the TCGA dabase, we have found increased expression of the ECT2 RhoGEF frequently occurs in synchrony with decreased expression of the DLC1 RhoGAP in several tumor types, including lung adenocarcinoma, lung squamous cell carcinoma, and hepatocellular cancer. In lung adenocarcinoma, the combination of high ECT2 expression and low DLC1 expression level is more common in poorly differentiated tumors than in well differentiated ones. Using other publicly available datasets from NCBI Gene Expression Omnibus (GEO), the expression DLC1 and ECT2 was found to be cell cycle related, with higher DLC1 being observed exclusively in the G0 phase, while ECT2 was higher during the cell cycle, relative to G0, and peaked in the G2/M phase. In CPTAC, phosphorylation of a specific ECT2 amino acid (S861) is correlated with a poor prognosis in breast cancer. Consistent with this observation, experimental mutation of ECT2 S861 to A861 results in an ECT2 gene with loss-of-function. Point mutation of ECT2 and DLC1 were found at overall frequencies of 1.7% and 4.7%, respectively, in the tumors of the TCGA database. These cancer-associated mutations occur along the entire length of the ECT2 and DLC1 proteins, rather than being located primarily in the Rho-GEF domain of ECT2 or the Rho-GAP domain of DLC1, and experimental analysis of a subset of these mutants indicates that most of the ECT2 mutants are gain-of-function, while most of the DLC1 mutants are loss-of-function. Our results imply that ECT2 and DLC1 frequently act in concert, but in opposite directions, in cancer to increase RhoA activity. * Authors contributed equally to this abstract Citation Format: Dunrui Wang, Xiaolan Qian, Marian E. Durkin, Alexander G. Papageorge, Douglas R. Lowy. Several cancer types are associated with increased expression and activity of the ECT2 RhoGEF and decreased expression and activity of the DLC1 RhoGAP, leading to increased RhoA activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4359.