CHAC1 (ChaC, cation transport regulator homolog 1 (E. coli)) is a 264 amino acid cytoplasmic protein that belongs to the ChaC family. Induced by chemical activators of the unfolded protein response (UPR) pathway, including DTT, tunicamycin and thapsigargin, CHAC1 is a pro-apoptotic member of this pathway and may mediate the pro-apoptotic effects of the ATF4-ATF3-DDIT3/CHOP cascade. Overexpression of CHAC1 may lead to an increase in apoptosis, while suppression of CHAC1 results in subdued apoptosis.