Abstract LB-30: A functional analysis of the nuclear RhoGEF Ect2 in ovarian cancer

Abstract

Abstract Ect2 is a guanine nucleotide exchange factor (GEF) and activator of Rho family small GTPases. Ect2 regulates RhoA, Rac1, and Cdc42, thereby playing an important role in the control of cell proliferation, survival, and migration. Originally identified as an oncogene in vitro, the role of Ect2 in regulating migration makes it of particular interest in ovarian cancer, in which local invasion and ascites are prevalent. Notably, ECT2 is located on 3q26.1-3q26.2, the most frequent amplicon in ovarian cancer, and it has been found to be overexpressed at the mRNA level in ovarian tumors. We first explored the role of Ect2 in ovarian cancer by knocking it down using shRNA and assessing anchorage-independent growth and both random and directed migration in a panel of ovarian cancer cell lines. Our findings reveal that Ect2 expression is required for each of these functions. Interestingly, we found that Ect2 utilization of specific Rho GTPase substrates is highly context-dependent. In addition, to investigate the potential clinical importance of Ect2, we studied its expression and localization in primary epithelial ovarian cancers, using over 300 histological tumor and cyst samples incorporated into a tissue microarray (TMA). Ect2 is unusual among the RhoGEFs because of its localization. A critical regulator of cytokinesis, it is sequestered to the nucleus in interphase cells. It has been hypothesized that the overexpression and mislocalization of Ect2 into the cytoplasm leads to aberrant Rho activation and oncogenesis. Unexpectedly, our recently completed TMA data analysis suggests that malignant serous ovarian cancer is instead associated with nuclear Ect2, while benign disease is associated with mislocalized, cytosolic Ect2. We are currently exploring a possible nuclear mechanism to explain these findings. Although standard immunohistochemical analyses typically report only total protein levels, our new data reveal that unrestricted subcellular localization of Ect2 is likely to be more important than total protein levels for ovarian pathology. 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-30. doi:1538-7445.AM2012-LB-30