ARTC1-mediated VAPB ADP-ribosylation regulates calcium homeostasis

Mono-ADP-ribosylation(MARylation)is a post-translational modification that regulates a variety of biological processes,including DNA damage repair,cell proliferation,metabolism,and stress and immune responses.In mammals,MARylation is mainly catalyzed by ADP-ribosyltransferases(ARTs),which consist of two groups:ART cholera toxin-like(ARTCs)and ART diphtheria toxin-like(ARTDs,also known as PARPs).The human ARTC(hARTC)family is composed of four members:two active mono-ADP-ARTs(hARTC1 and hARTC5)and two enzymatically inactive enzymes(hARTC3 and hARTC4).In this study,we systematically examined the homology,expression,and localization pattern of the hARTC family,with a particular focus on hARTC1.Our results showed that hARTC3 interacted with hARTC1 and promoted the enzymatic activity of hARTC1 by stabilizing hARTC1.We also identified vesicle-associated membrane protein-associated protein B(VAPB)as a new target of hARTC1 and pinpointed Arg50 of VAPB as the ADP-ribosylation site.Furthermore,we demonstrated that knockdown of hARTC1 impaired intracellular calcium homeostasis,highlighting the functional importance of hARTC1-mediated VAPB Arg50 ADP-ribosylation in regulating calcium homeostasis.In summary,our study identified a new target of hARTC1 in the endoplasmic reticulum and suggested that ARTC1 plays a role in regulating calcium signaling.