Investigating Poly(ADP-ribose) Polymerase 1 (PARP1) Epigenetic Crosstalks and Regulation by Oncohistone Mutations

Abstract

Histone post-translational modifications (PTMs) are critical players in regulating various cellular processes. When this epigenetic machinery goes awry, it can dysregulate many molecular pathways to lead to human disease. One particular chromatin effector often implicated in cancer is Poly(ADP-ribose) polymerase 1 (PARP1), which is best known for its role in DNA damage repair. PARP1 adds ADP-ribosyl groups onto a host of substrates, including serine residues on histone H3. Recent studies have highlighted the interplay between histone ADP-ribosylation (ADPr) and other neighboring PTMs, better known as “crosstalks.” To further investigate the effect of local epigenetic and protein sequence contexts on PARP1 activity, this study assessed ADPr on reconstituted chromatin substrates containing modified residues or oncohistone mutants in vitro. These oncohistone mutants are potential drivers in cancer and inhibit chromatin effectors that directly interact with the mutated residue. They are suspected to affect other enzymes as well. Furthermore, epigenetic crosstalks involving ADPr were assessed in cells subject to DNA damage. As new oncohistones have been recently identified in patient tumors, a library screen was also performed to identify potential modulators of PARP1 activity. We found that phosphorylation at H3S10 and the mutant H3.3K9M significantly blocked PARP1 activity on histone substrates in vitro. Top hits from the oncohistone library screen also suggest that mutants important for DNA-histone contacts interfere with PARP1 activity, emphasizing the importance of DNA engagement for ADP-ribosylation. This work expands on the understanding of how PARP1 is regulated by chromatin context, both through PTMs and mutations, and how aberrations in its activity can be linked to oncogenesis.