Cancer Cell Biology Training Program

The frequent mutationaly activation of Ras proteins in human cancers (33%) has prompted considerable interest in developing anti-Ras inhibitors for cancer treatment. Ras is the founding member of a large superfamily of small GTPases, and recent studies have linked the abnormal activity of  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 (69 members). 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. The central  hypothesize of my studies is that the functions of Ect2 in cytokinesis are distinct from functions which promote Ect2-driven oncogenesis and that mislocalization may contribute to Ect2 activation in cancer. My studies will involve the evaluation of the consequences of an Ect2 deficiency in mouse development and aberrant Ect2 overexpression and altered regulation in CRC tumorigenicity, invasion and metastasis.