SLAP controls mTORC2 integrity via UBE3C-mediated non-degradative mLST8 ubiquitination to suppress colorectal tumorigenesis.

The mechanistic target of rapamycin complex 2 (mTORC2) signaling pathway, which regulates cell growth and migration, exhibits oncogenic function in colorectal cancer (CRC). mTORC2 signaling is primarily activated by a complex assembly of mTOR, RICTOR, SIN1, and mLST8; however, the mechanisms by which dysregulation of this pathway contributes to its oncogenic function remain elusive. Here, we show that the Src-Like Adaptor Protein (SLAP), a negative regulator of tyrosine kinase signaling receptors, controls mTORC2 integrity to mediate its tumor-suppressive function in CRC. Mechanistically, SLAP interacts with mLST8 and facilitates its non-degradative ubiquitination at lysines 86 and 215, thereby reducing the integrity of mTORC2 and mTORC2-AKT signaling. The E3 ubiquitin ligase UBE3C was identified as a novel SLAP interactor involved in this ubiquitination process. Functionally, SLAP inhibition of CRC cell growth and invasion was dependent upon mTORC2 signaling inhibition. In immunodeficient mice CRC xenografts, SLAP depletion enhanced mTORC2 activity and sensitized CRC cells to mTOR catalytic inhibitors. Together, our findings reveal a previously unrecognized SLAP-UBE3C-mLST8 axis that regulates mTORC2 integrity and suggest a potential therapeutic avenue for targeting mTORC2 in CRC.