HSPA5

HSPA5, also known as GRP78/BiP, encodes an endoplasmic reticulum (ER)-resident Hsp70 family chaperone that maintains protein folding, assembly, and quality control within the ER lumen^[1][2]. Mechanistically, HSPA5 functions as a central regulator of the unfolded protein response (UPR) by interacting with the ER stress sensors PERK, IRE1, and ATF6, thereby coordinating cellular adaptation to proteotoxic stress^[3][4]. Under basal conditions, HSPA5 binds and suppresses these UPR transducers, whereas accumulation of unfolded or misfolded proteins promotes HSPA5 dissociation and activation of downstream stress-signaling pathways^[3][4]. Consequently, HSPA5 contributes to restoration of proteostasis through regulation of protein folding, ER-associated degradation, autophagy, and survival-associated stress responses^[1][5]. Disease studies further demonstrate that dysregulated HSPA5 expression is linked to cancer, neurodegeneration, viral infection, and inflammatory disorders, highlighting its broad relevance to cellular stress adaptation and disease pathogenesis^[2][6][7][8]. In experimental models, genetic depletion of HSPA5 disrupts UPR homeostasis and causes degeneration of Purkinje cells, establishing an essential role in neuronal survival and normal tissue function^[9][10]. Compared with other cytosolic Hsp70 family members, HSPA5 is distinguished by its predominant ER localization and specialized function in ER protein quality control and stress signaling^[1][2]. For research applications, HSPA5 has emerged as a therapeutic target, and pharmacological modulation of its activity is widely used to investigate ER stress, UPR signaling, and disease-associated proteostasis mechanisms^[6].