In previous years, Ras, a small GTPase oncogene has been a focus in cancer research because it is one of the most commonly mutated genes associated with all human cancers (33%). Ras is the founding member of a large superfamily of small GTPases, and recent studies have linked the abnormal activity implicated Ras superfamily proteins, in particular, the Ras homologous (Rho) GTPases to tumorigenesis. However, unlike Ras, Rho GTPases are not mutated directly in cancer, but instead their abnormal activity has been linked to their abnormal expression and/or regulation. Perhaps the most significant mechanism that has emerged in which aberrant activity of Rho GTPase is the result of abnormalities in activating proteins called RhoGEFs (guanine nucleotide exchange factors). My studies are focused on one RhoGEF, Ect2 (Epithelial cell transforming sequence 2). Ect2 is a member of the human Dbl family of RhoGEFs. Previous studies indicate that Ect2 is essential in normal mammalian cytokinesis. In contrast, abnormal overexpression of Ect2 has been observed in many cancers, and a recent study demonstrated a critical role for Ect2 in lung carcinoma cell line growth and tumorigenicity. We have found that Ect2 expression is elevated in colorectal carcinoma (CRC) patient tumor tissue, APCmin mice with spontaneous intestinal adenomas, and human CRC cell lines. There is evidence that Ect2, which is present in the nucleus of normal cells, is mislocalized into the cytoplasm in lung and brain cancers. This mislocalization may lead to inappropriate Rho activation in the cytoplasm. In addition to its RhoGEF catalytic domain, Ect2 is comprised of multiple addition domains. How Ect2 becomes aberrantly activated in cancer and whether the mechanisms of Ect2 function in normal and neoplastic cells are distinct, are poorly understood and the focus of my studies. We hypothesize that the functions of Ect2 in cytokinesis are distinct from functions which promote oncogenesis and that mislocalization may contribute to Ect2 activation in cancer. These studies will require my application of a very diverse repertoire of experimental techniques, foster my development into an independent researcher and establish my abilities to do basic and translational cancer research.
Like the Ras oncoprotein, aberrant Rho (Ras homologous;e.g., RhoA, Rac1 and Cdc42) small GTPase signal transduction is also implicated in human oncogenesis. However, whereas direct mutation of Ras leads to its activation, indirect mechanisms lead to Rho activation. Our preliminary findings identified overexpression of Ect2, a guanine nucleotide exchange factor (RhoGEF) and Rho activator, in colorectal cancer (CRC). While Ect2 has been implicated in normal cell cytokinesis, we hypothesize that the aberrant overexpression and mislocalization of Ect2 promotes CRC tumorigenic, invasive and metastatic growth. We propose studies cell culture and mouse model studies to address the role and mechanism of Ect2 in normal and neoplastic cellular function. There is emerging interest that RhoGEFs may be an important new class of protein targets for cancer drug discovery. Our studies will provide validation for Ect2 importance in CRC and eludicate mechanisms of Ect2 activation and oncogenesis for therapeutic intervention. Significance of studying colorectal cancer: CRC is the 3rd leading cause of cancer deaths in the US and while there are a number of targeted therapeutic options available for CRC (e.g., bevacizumab and cetuximab) there is still a dire need for new and improved molecularly-targeted therapies.
|Cook, D R; Rossman, K L; Der, C J (2014) Rho guanine nucleotide exchange factors: regulators of Rho GTPase activity in development and disease. Oncogene 33:4021-35|