The fast-growing business of Serine ADP-ribosylation.

ADP-ribosylation (ADPr) is a widespread post-translational modification (PTM) spanning all kingdoms of life. It is employed by bacteria and viruses in their war against the host, and by eukaryotes to regulate many physiological processes, across almost all cellular compartments. PARP1, the founding member of the PARP family, is an early sensor of single- and double-strand breaks and catalyzes ADPr to mediate DNA damage repair. The recent discovery of Serine-ADPr and the PARP1 accessory factor HPF1 has brought a momentous change to the field. Bolstered by innovative ways to study ADPr, new and exciting research directions are rapidly emerging. In this review we explore our understanding of the HPF1/PARP1-mediated ADPr signaling pathway in DNA damage. We focus on the mechanistic steps leading to Serine-ADPr and its relevance in the DNA damage response. We discuss important technological advances that have enabled a nuanced study of Serine-ADPr, and conclude with an overview of the role of PARP inhibitors in cancer therapy.