ADP-ribosyltransferases, an update on function and nomenclature

ADP-ribosylation, a modification of proteins, nucleic acids and metabolites, confers broad functions, including roles in stress responses elicited for example by DNA damage and viral infection and is involved in intra- and extracellular signaling, chromatin and transcriptional regulation, protein biosynthesis and cell death. ADP-ribosylation is catalyzed by ADP-ribosyltransferases, which transfer ADP-ribose from NAD+ onto substrates. The modification, which occurs as mono- or poly-ADP-ribosylation, is reversible due to the action of different ADP-ribosylhydrolases. Importantly, inhibitors of ADP-ribosyltransferases are approved or are being developed for clinical use. Moreover, ADP-ribosylhydrolases are being assessed as therapeutic targets, foremost as anti-viral drugs and for oncological indications. Due to the development of novel reagents and major technological advances that allow the study of ADP-ribosylation in unprecedented detail, an increasing number of cellular processes and pathways are being identified that are regulated by ADP-ribosylation. In addition, characterization of biochemical and structural aspects of the ADP-ribosyltransferases and their catalytic activities have expanded our understanding of this protein family. This increased knowledge requires that a common nomenclature be used to describe the relevant enzymes. Therefore, in this viewpoint, we propose an updated and broadly supported nomenclature for mammalian ADP-ribosyltransferases that will facilitate future discussions when addressing the biochemistry and biology of ADP-ribosylation. This is combined with a brief description of the main functions of mammalian ADP-ribosyltransferases to illustrate the increasing diversity of mono- and poly-ADP-ribose mediated cellular processes.