PARP16 is a tail-anchored endoplasmic reticulum protein required for the PERK and IRE1α-mediated unfolded protein response

Poly(ADP-ribose) polymerases (PARPs) (also known as ADP-ribosyl transferase D proteins) modify acceptor proteins with ADP-ribose modifications of varying length (reviewed in refs 1–3). PARPs regulate key stress response pathways, including DNA damage repair and the cytoplasmic stress response(2,3,4,5,6). Here, we show that PARPs also regulate the unfolded protein response (UPR) of the endoplasmic reticulum (ER). Human PARP16/ARTD15 is a tail-anchored ER transmembrane protein required for activation of the functionally related ER stress sensors PERK and IRE1α during the UPR. The third identified ER stress sensor, ATF6, is not regulated by PARP16. Similar to other PARPs that function during stress, PARP16 enzymatic activity is up-regulated during ER stress when it (ADP-ribosyl)ates itself, PERK and IRE1α. (ADP-ribosyl)ation by PARP16 is sufficient for activating PERK and IRE1α in the absence of ER stress, and is required for PERK and IRE1 α activation during the UPR. Modification of PERK and IRE1α by PARP16 increases their kinase activities and the endonuclease activity of IRE1α. Interestingly, the C-terminal luminal tail of PARP16 is required for PARP16 function during ER stress, suggesting that it transduces stress signals to the cytoplasmic PARP catalytic domain.