The first insights into the TRE17 oncogene: A potential link between actin remodeling and vesicular trafficking

The TRE17 oncogene was identified by virtue of its transforming abilities in fibroblasts, however its molecular interactions and cellular functions have remained unexplored. TRE17 contains a TBC domain that is homologous to the yeast proteins Msb3 and Msb4, which function in a pathway with Cdc42p in regulating polarized actin remodeling and secretion. This suggested that perhaps TRE17 functions downstream of Rho GTPases in mammalian cells and regulating similar activities. Thus, my thesis work has focused on providing the first insights into this novel oncogene, including its cellular localization, interactions with G-proteins, and the regulation of actin remodeling and vesicular trafficking.;I demonstrate that TRE17 localizes to the plasma membrane and to an Arf6-dependent tubular recycling endosome. This localization is dynamic and requires the integrity of the cytoskeleton. A truncated TRE17 allele induces the formation of peripheral membrane protrusions and enlarged vesicular and vacuolar structures within the cytosol, indicating this may be a hyperactive allele of TRE17.;I also show that TRE17 is regulated by the Rho GTPases Rac1 and Cdc42. TRE17 indirectly associates with these G-proteins in a GTP-dependent manner, and the activation of Rac or Cdc42 induces the recruitment of TRE17 to the plasma membrane. Downstream of these GTPases, TRE17 stimulates actin remodeling at the cell cortex and dynamic membrane protrusions.;Further, I demonstrate that TRE17 regulates the small GTPase Arf6. TRE17 directly associates with Arf6 in a GDP-dependent manner via TRE17's TBC domain. This association stimulates Arf6 activation, possibly by acting as a chaperone to recruit inactive Arf6 to the plasma membrane. TRE17 also regulates the trafficking of Arf6-dependent cargo, such as the beta1-integrin and MHC I; and cell spreading, a process that depends on the coordinate regulation of actin remodeling and vesicular trafficking.;Together, these results suggest that TRE17 functions downstream of Rho GTPases to regulate actin remodeling as well as vesicular trafficking via the Arf6-dependent pathway. Since deregulation of these processes lead to the acquisition of a more migratory and invasive phenotype in cancer cells, these studies not only provide insight into the normal function of TRE17, but also into how it may contribute to tumorigensis.