- The endoplasmic reticulum (ER) is responsible for folding, modifying and trafficking a large portion of the cellular proteome. When misfolded or unfolded proteins accumulate, the ER experiences stress, activating the unfolded protein response (UPR). Among the three UPR sensors—IRE1, ATF6 and PERK—PERK (PKR‑like ER kinase) plays a unique role by rapidly adjusting protein synthesis to reduce the burden on the ER. Through its kinase activity and downstream transcriptional programmes, PERK coordinates adaptive responses that restore proteostasis or, under severe stress, initiate apoptosis.
- PERK is a type I transmembrane protein with a luminal domain that senses misfolded proteins and a cytosolic kinase domain that mediates signalling. Under non‑stress conditions, PERK remains inactive through association with the ER chaperone BiP/GRP78. When misfolded proteins accumulate, BiP dissociates, allowing PERK to oligomerise and undergo trans‑autophosphorylation. This activation triggers its primary function: phosphorylation of the translation initiation factor eIF2α.
- Phosphorylation of eIF2α leads to global attenuation of protein synthesis, reducing the influx of nascent polypeptides into the ER. This translational pause is essential for preventing further accumulation of misfolded proteins and giving the ER time to recover. Despite the reduction in global translation, specific mRNAs containing upstream open reading frames (uORFs) are preferentially translated. Among these, ATF4 is the most important.
- ATF4 is a transcription factor that activates genes involved in amino‑acid metabolism, antioxidant defence, autophagy and stress adaptation. Through ATF4, PERK signalling intersects with the oxidative stress response, enhancing cellular resilience against ROS. ATF4 also induces genes that support redox balance, mitochondrial function and metabolic homeostasis, linking ER stress to broader cellular physiology.
- Under prolonged or severe ER stress, PERK signalling shifts from adaptive to apoptotic. Persistent ATF4 activation induces CHOP, a transcription factor that downregulates anti‑apoptotic proteins and sensitises mitochondria to stress. CHOP promotes cell death when recovery is no longer possible, preventing dysfunctional or potentially malignant cells from compromising tissue integrity. This duality—protective under moderate stress, apoptotic under severe stress—makes PERK a critical decision‑making node in the UPR.
- PERK signalling is tightly integrated with other UPR branches. Crosstalk with IRE1 coordinates transcriptional reprogramming and RNA degradation. Interaction with ATF6 ensures balanced induction of chaperones and ER‑associated degradation (ERAD). PERK also interfaces with the proteostasis network and autophagy, forming a unified system that preserves cellular integrity under stress.
- Dysregulation of PERK contributes to numerous diseases. In neurodegenerative disorders such as Alzheimer’s, Parkinson’s and ALS, chronic PERK activation impairs protein synthesis and contributes to neuronal dysfunction. In diabetes, PERK signalling influences insulin production and β‑cell survival. In cancer, tumour cells often exploit PERK to tolerate high secretory demand and proteotoxic stress, making PERK an attractive therapeutic target.
- In summary, PERK is a central ER stress sensor that regulates translational control, metabolic adaptation and apoptosis. Through eIF2α phosphorylation, ATF4 induction and CHOP‑mediated cell‑death pathways, PERK orchestrates adaptive responses that restore proteostasis or eliminate irreparably damaged cells. Its pivotal role in ER biology, metabolism and disease makes PERK a major focus of modern cell‑stress research.
