IRE1 Pathway: Activated IRE1 splices XBP1 mRNA, leading to the production of a potent transcription factor that upregulates genes involved in protein folding, ER-associated degradation (ERAD), and lipid biosynthesis. PERK Pathway: PERK phosphorylates eIF2α, reducing general protein synthesis and selectively translating ATF4, which activates genes involved in antioxidant responses, amino acid metabolism, and apoptosis. ATF6 Pathway: ATF6 is transported to the Golgi apparatus where it is cleaved, releasing an active fragment that enters the nucleus to upregulate genes encoding ER chaperones and components of the ERAD machinery.
