Oncohistone Mutations Occur at Functional Sites of Regulatory ADP-Ribosylation

Abstract

Recent studies have identified cancer-associated mutations in histone genes that lead to the expression of mutant versions of core histones called oncohistones. Many oncohistone mutations occur at Asp and Glu residues, two amino acids known to be ADP-ribosylated (ADPRylated) by PARP-1. We screened 25 Glu or Asp oncohistone mutants for their effects on cell growth in breast and ovarian cancer cells. Ectopic expression of six mutants of three different core histones (H2B, H3, and H4) altered cell growth in at least two different cell lines. Two of these sites, H2BD51 and H4-D68, were indeed sites of ADPRylation in wild-type (unmutated) histones, and mutation of these sites inhibited ADPRylation. Mutation of H2B-D51 dramatically altered chromatin accessibility at enhancers and promoters, as well as gene expression outcomes, whereas mutation of H4-D68 did not. Additional biochemical, cellular, proteomic, and genomic analyses demonstrated that ADPRylation of H2B-D51 inhibits p300-mediated acetylation of H2B at many Lys residues. In breast cancer cell xenografts in mice, H2B-D51A promoted tumor growth, but did not confer resistance to the cytotoxic effects of PARP inhibition. Collectively, these results demonstrate that functional Asp and Glu ADPRylation sites on histones are mutated in cancers, allowing cancer cells to escape the growth-regulating effects of post-translational modifications via distinct mechanisms.

Chemoenzymatic and Synthetic Approaches To Investigate Aspartate- and Glutamate-ADP-Ribosylation

“…ADPr has been reported to target multiple sites on nucleosome-incorporated histones, including serine, aspartate, and glutamate residues. ,, Many fundamental questions remain regarding the molecular mechanisms through which known nucleosome ADPr sites trigger distinct biochemical signaling outputs. We recently employed semisynthetic, full-length ADP-ribosylated histones to show that H2BS6- and H3S10-poly-ADPr convert nucleosomes into potent substrates for the ATP-dependent chromatin remodeler ALC1 .…”

Beyond the Usual Suspects: Examining the Role of Understudied Histone Variants in Breast Cancer

“…One might hypothesize that because this mutation occurs in the acidic patch of H2B, a region in histones known as the ‘landing dock’ for chromatin remodelers [ 164 ], it might affect their binding and thereby affect the balance between active and repressive chromatin states. Another recent study shows that the expression of the onco-histone H2B D51A/N significantly enhanced cell proliferation in breast cancer [ 165 ]. H2B D51 is an ADP-ribosylation site that is essential for p300-mediated acetylation inhibition of several lysine residues on H2B.…”

“…Therefore, the loss of ADP-ribosylation on H2B D51A/N mutations might disrupt the acetylation pattern on H2B, leading to significant changes in chromatin accessibility at enhancers and promoters, along with alterations in gene expression patterns. Notably, mutation of D51 to A was associated with accelerated breast tumor formation in mouse xenografts [ 165 ]. These discoveries imply that both the presence and the specific mutations of these variants play crucial roles in organizing chromatin structure, which in turn influences patterns of gene expression.…”