ERN1 and cancer: Recent studies have reported that in case of the accumulation of denatured proteins in the ER of cancer cells, the unfolded protein response (UPR) occurs, and that, as a result, the levels of CHOP related to cell death caused by ER stress, BIP, a chaperone in ER, and IRE1α and sXBP1 located upstream of CHOP and BIP, are elevated [19,26].