Negative regulator of the mechanistic target of rapamycin complex 1 (mTORC1), an evolutionarily conserved central nutrient sensor that stimulates anabolic reactions and macromolecule biosynthesis to promote cellular biomass generation and growth (PubMed:17277771, PubMed:17386266, PubMed:17510057, PubMed:29236692). In absence of insulin and nutrients, AKT1S1 associates with the mTORC1 complex and directly inhibits mTORC1 activity by blocking the MTOR substrate- recruitment site (PubMed:29236692). In response to insulin and nutrients, AKT1S1 dissociates from mTORC1 (PubMed:17386266, PubMed:18372248). Its activity is dependent on its phosphorylation state and binding to 14-3-3 (PubMed:16174443, PubMed:18372248). May also play a role in nerve growth factor-mediated neuroprotection (By similarity). {ECO:0000250|UniProtKB:Q9D1F4, ECO:0000269|PubMed:16174443, ECO:0000269|PubMed:17277771, ECO:0000269|PubMed:17386266, ECO:0000269|PubMed:17510057, ECO:0000269|PubMed:18372248, ECO:0000269|PubMed:29236692}. This is the function of AKT1S1 (AKT1 substrate 1, ENSG00000204673).