Seung Un Seo1,6, Seon Min Woo1,6, Min Wook Kim2, Eun-Woo Lee2,3,*, Kyoung-jin Min4,* and Taeg Kyu Kwon1,5,*
1Department of Immunology, School of Medicine, Keimyung University, Daegu 42601, South Korea. 2Metabolic Regulation Research Center, Korea Research Institute of Bioscience and Biotechnology (KRIBB), Daejeon 34141, South Korea. 3Department of Functional Genomics, University of Science and Technology (UST), Daejeon 34141, South Korea. 4New Drug Development Center, Daegu-Gyeongbuk Medical Innovation Foundation (DGMIF), Daegu 41061, South Korea. 5Center for Forensic Pharmaceutical Science, Keimyung University, Daegu 42601, South Korea. 6These authors contributed equally: Seung Un Seo, Seon Min Woo.
Raptor plays a critical role in mTORC1 signaling. High expression of Raptor is associated with resistance of cancer cells to PI3K/mTOR inhibitors. Here, we found that OTUB1-stabilized Raptor in a non-canonical manner. Using biochemical assays, we found that the tyrosine 26 residue (Y26) of OTUB1 played a critical role in the interaction between OTUB1 and Raptor. Furthermore, non-receptor tyrosine kinases (Src and SRMS kinases) induced phosphorylation of OTUB1 at Y26, which stabilized Raptor. Interestingly, phosphorylation of OTUB1 at Y26 did not affect the stability of other OTUB1-targeted substrates. However, dephosphorylation of OTUB1 destabilized Raptor and sensitized cancer cells to anti-cancer drugs via mitochondrial reactive oxygen species-mediated mitochondrial dysfunction. Furthermore, we detected high levels of phospho-OTUB1 and Raptor in samples of patients with renal clear carcinoma. Our results suggested that regulation of OTUB1 phosphorylation may be an effective and selective therapeutic target for treating cancers via down-regulation of Raptor.