Modulation of unfolded protein responses, apoptosis, and autophagy by coronavirus accessory proteins. Schematic diagram showing the three arms of UPR signaling pathways and the correlated apoptosis and autophagy pathways regulated by accessory proteins. Accessory proteins modulating the pathway are shown in red. Abbreviations: PERK, PKR-like ER protein kinase; IRE1, inositol-requiring enzyme 1; ATF6, activating transcription factor 6; GRP78, glucose-regulated protein, 78 kDa; eIF2α, eukaryotic initiation factor 2 subunit α; ATF4, activating transcription factor 4; CRE, cAMP response element; CHOP, C/EBP-homologous protein; PP1, protein phosphatase 1; GADD34, growth arrest and DNA damage inducible 34; UPRE, unfolded protein response element; ERSE, ER stress response element; XBP, X-box-binding protein; JNK, c-Jun N-terminal kinases; Bcl-2, B-cell lymphoma 2/XL; Bcl-xL, Bcl-2-like protein 1; S1/2P, site-1/2 protease; FADD, Fas associated via death domain; BaX, Bcl2-associated X; Bid, BH3-interacting domain.