Negative regulator of the mTORC1 and mTORC2 signaling pathways. Inhibits the kinase activity of both complexes (By similarity). Part of the mammalian target of rapamycin complex 1 (mTORC1) which contains MTOR, MLST8, RPTOR, AKT1S1/PRAS40 and DEPTOR. Part of the mammalian target of rapamycin complex 2 (mTORC2) which contains MTOR, MLST8, PROTOR1, RICTOR, MAPKAP1 and DEPTOR. Interacts (via PDZ domain) with MTOR; interacts with MTOR within both mammalian target of rapamycin complexes mTORC1 and mTORC2 (By similarity). Interacts (via PDZ domain) with MINAR1 (via N-terminus) (By similarity). Interacts with SIK3 (By similarity). At postnatal day 1 (P1), in cartilage growth plate, primarily expressed in resting and proliferating chondrocytes. This expression pattern is maintained at least until P21 (at protein level). Phosphorylation weakens interaction with MTOR within mTORC1 and mTORC2. Ubiquitinated; ubiquitination leads to proteasomal degradation. Extended N-terminus.