HIF-mediated Suppression of DEPTOR Confers Resistance to mTOR Kinase Inhibition in Renal Cancer

Mechanistic target of rapamycin (mTOR) is a fundamental regulator of cell growth, proliferation, and metabolism. mTOR is activated in renal cancer and accelerates tumor progression. Here, we report that the mTOR inhibitor, DEP domain-containing mTOR-interacting protein (DEPTOR), is strikingly suppressed in clear cell renal cell carcinoma (ccRCC) tumors and cell lines. We demonstrate that DEPTOR is repressed by both hypoxia-inducible factors, HIF-1 and HIF-2, which occurs through activation of the HIF-target gene and transcriptional repressor, BHLHe40/DEC1/Stra13. Restoration of DEPTOR- and CRISPR/Cas9-mediated knockout experiments demonstrate that DEPTOR is growth inhibitory in ccRCC. Furthermore, loss of DEPTOR confers resistance to second-generation mTOR kinase inhibitors through deregulated mTORC1 feedback to IRS-2/PI3K/Akt. This work reveals a hitherto unknown mechanism of resistance to mTOR kinase targeted therapy that is mediated by HIF-dependent reprograming of mTOR/DEPTOR networks and suggests that restoration of DEPTOR in ccRCC will confer sensitivity to mTOR kinase therapeutics.