SIN1 encodes a protein that is highly similar to the yeast SIN1 protein, a stress-activated protein kinase. Recent studies have shown that it is identical to MIP1 for MEKK2 interacting protein 1. MAPKAP1 has also been shown to play a role in the TOR signaling process, a pathway that is involved in controlling cell growth and proliferation in response to environmental cues such as nutrients, growth factors and hormones. Within mTORC2, MAPKAP1 is required for complex formation and mTORC2 kinase activity. MAPKAP1 inhibits MAP3K2 by preventing its dimerization and autophosphorylation. It inhibits HRAS and KRAS signaling and enhances osmotic stress-induced phosphorylation of ATF2 and ATF2-mediated transcription. Multiple alternatively spliced isoforms of MAPKAP1 have been identified.