UC San Diego

The small GTPase Rheb has been found to be overexpressed in some tumors, and its overexpression is thought to promote tumor growth by maintaining activation of the mTORC1 protein complex in the nutrient deficient tumor environment. At this time, the mechanism that leads to increased Rheb levels in tumor cells is unknown. In this proposal we characterized the functional elements of the Rheb promoter. We cloned a 1360 base pair region of the human Rheb promoter and tested its activity using luciferase reporter assays. We then generated several 5' truncations. The 5' truncation data pointed to a region between -316 and -113 where a significant activity decrease could be associated with the presence of an important Rheb promoter core element. Further investigation using 5'RACE PCR led us to the discovery of a putative transcriptional start site in the context of an Initiator element (Inr) 101 nucleotides upstream of the translational start site. Unfortunately, mutational analysis of the Inr failed to demonstrate that it served as the main transcriptional start site