Histidine triad nucleotide-binding protein 1 (HINT1) is a member of the histidine triad (HIT) protein family, a group of small nucleotide-binding and -hydrolyzing proteins. HINT1 interacts with several diverse proteins and has been suggested to have tumor suppressive activities. HINT1 catalyzes the hydrolysis of adenosine 5’-monophoramidate substrates such as AMP-morpholidate, but its enzymatic function does not appear to play a role in its tumor suppression. Recent experiments demonstrate that HINT1 forms a complex with POSH and JNK in vivo, inhibiting AP-1 activity and the phosphorylation of c-Jun, and this action could contribute to the tumor suppressor activity of HINT1. Other studies raise the possibility of HINT1 as a candidate gene for schizophrenia.