PERK

Protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is one of four known kinases that respond to cellular stress by deactivating the eukaryotic initiation factor 2 α (eIF2α) or other signal transduction cascades. PERK is highly expressed in pancreatic beta-cells and is essential in the beta-cell's development, differentiation and function.

PERK is a type I ER membrane protein containing a stress-sensing domain facing the ER lumen, a transmembrane segment, and a cytosolic kinase domain. Increase in unfolded proteins in the ER causes release of ER chaperones from the stress-sensing domain of PERK, which results in its activation via oligomerization and autophosphorylation at multiple serine, threonine, and tyrosine residues. Upon activation, PERK phosphorylates eIF2α at serine 51, rendering it an inhibitor of the ribosome translation initiation complex, consequently reducing overall protein synthesis. The reduction in translation reduces the ER burden, providing time for the cell to process or degrade the accumulated unfolded proteins to restore ER homeostasis. Although global protein synthesis is decreased, there is specific increased translation of certain mRNAs, such as ATF4, which modulate cellular survival pathways and enhance UPR function. Interfering with PERK function in cancer cells may limit their ability to thrive under hypoxia or nutrient deprived conditions and lead to apoptosis or tumor growth inhibition.