ERN1 and cancer: On the other hand, hypoxic stress in cancer stimulates the inositol requiring enzyme 1α (IRE1)/XBP1 arm of the UPR to blunt immune elimination of cancer cells, by decreasing the expression of major histocompatibility complex 1 (MHC1) molecules in antigen-presenting dendritic cells, thereby weakening the function of CD8+ lymphocytes to kill cancer cells [45].