FIG. 4.

Inactivation of proapoptotic pathways and activation of prosurvival pathways contribute to cancer cell survival. Cancer cells are subjected to ER stress because of intrinsic factors such as high glucose metabolic rate and extrinsic factors such as nutrient and oxygen deprivation in the tumor microenvironment. This leads to the induction of the GRPs, and, coupled with mutations as a result of tumorigenesis that often inactivate the proapoptotic pathways, shifts the balance to the prosurvival branches of the UPR.