Regulation of Rictor Protein Expression in Colorectal Cancer Cells

Colorectal cancer (CRC) is the second most common cause of cancer deaths in the United States with 146,970 new cases and 49,920 deaths estimated in 2009. Dysregulation of the phosphatidylinosito/-3 (PI3K)/Akt signaling pathway contributes to tumorigenesis by promoting cell proliferation and inhibiting apoptosis" Akt requires phosphorylation on two sites for full activation, After activated by P/3K, PDK1 phosphorylates Akt at Thr308. Mammalian Target of Rapamycin Complex 2 (mTORC2) phosphorylates Akt at Ser473 and inhibition of mTORC2 by knockdown of rietor, a component of mTORC2, results in Akt inaetivationand tumor growth inhibition, However, little is known about upstream signaling pathways regulating mTORC2 assembly and activity. Our preliminary data demonstrate that rictor protein level is elevated in human primary CRC cells and liver metastatic CRC cells, Knockdown of rictor inhibits anchorage independent CRC growth" In addition, we have found that inhibition of PP2A increases, while protein phosphatase activators decrease, rictor protein expression" Moreover, we show rictor is rapidly degraded by the ubiquitinproteasome pathway. Based on our findings, the central hypothesis of this proposal is that rictor phosphorylation contributes to its stabilization and mTORC2 assembly" The long-term goal of our studies is to better understand the upstream signaling pathways regulating mTORC2 assembly and activity and to establish elements of these pathways as novel targets for more specific therapies for CRC growth and metastasis" To examine our hypothesis and address the long-term goal, we have designed experiments with the following Specific Aims: 1) to determine the role of PP2A in controlling rictor protein degradation; 2) to assess the roles of protein phosphatases in rapamycin-mediated mTORC2 dissociation; 3) to identify the regions in rietor protein responsible for rietor protein proteolysis and ubiquitination" To investigate the regulation of mTORC2 components is crucial to the development of targeted drugs for the treatment of CRC that exhibit dysregulation of PI3K1Akt pathway.