Deregulation of mTORC1 in ccRCC

COI: REDD1 monoclonal antibody reported herein is now being sold by Bethyl laboratories. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Abstract mTORC1 is implicated in cell growth control and is extensively regulated. We previously reported that in response to hypoxia, mTORC1 is inhibited by REDD1. REDD1 is upregulated by HIF-1, and forced REDD1 expression is sufficient to inhibit mTORC1. REDD1-induced mTORC1 inhibition is TSC1/TSC2-dependent. In clear-cell renal cell carcinoma (ccRCC), VHL is frequently inactivated leading to constitutive activation of HIF-2 and/or HIF-1, which may be expected to upregulate REDD1 and inhibit mTORC1. However, mTORC1 is frequently activated in ccRCC and mTORC1 inhibitors are effective against this tumor type; a paradox herein examined. REDD1 was upregulated in VHL-deficient ccRCC by in silico microarray analyses, as well as qRT-PCR, western blot and immunohistochemistry. Vhl disruption in a mouse model was sufficient to induce Redd1. Using ccRCC-derived cell lines, we show that REDD1 upregulation in tumors is VHL-dependent, and that both HIF-1 and HIF-2 are, in a cell-type dependent manner, recruited to, and essential for, REDD1 induction. Interestingly, whereas mTORC1 is responsive to REDD1 in some tumors, strategies have evolved in others, such as mutations disrupting TSC1, to subvert mTORC1 inhibition by REDD1. Sequencing analyses of 77 ccRCCs for mutations in TSC1, TSC2 and REDD1, using PTEN as a reference, implicate the TSC1 gene, and possibly REDD1, as tumor suppressors in sporadic ccRCC. Understanding how ccRCCs become refractory to REDD1-induced mTORC1 inhibition should shed light into the molecular evolution of ccRCCs and may aid in patient selection for molecular targeted therapies. Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited.