Citrullination of histone H3 interferes with HP1-mediated transcriptional repression

PLoS Genet. 2012 Sep;8(9):e1002934. doi: 10.1371/journal.pgen.1002934. Epub 2012 Sep 13.

Abstract

Multiple Sclerosis (MS) is an autoimmune disease associated with abnormal expression of a subset of cytokines, resulting in inappropriate T-lymphocyte activation and uncontrolled immune response. A key issue in the field is the need to understand why these cytokines are transcriptionally activated in the patients. Here, we have examined several transcription units subject to pathological reactivation in MS, including the TNFα and IL8 cytokine genes and also several Human Endogenous RetroViruses (HERVs). We find that both the immune genes and the HERVs require the heterochromatin protein HP1α for their transcriptional repression. We further show that the Peptidylarginine Deiminase 4 (PADI4), an enzyme with a suspected role in MS, weakens the binding of HP1α to tri-methylated histone H3 lysine 9 by citrullinating histone H3 arginine 8. The resulting de-repression of both cytokines and HERVs can be reversed with the PADI-inhibitor Cl-amidine. Finally, we show that in peripheral blood mononuclear cells (PBMCs) from MS patients, the promoters of TNFα, and several HERVs share a deficit in HP1α recruitment and an augmented accumulation of histone H3 with a double citrulline 8 tri-methyl lysine 9 modifications. Thus, our study provides compelling evidence that HP1α and PADI4 are regulators of both immune genes and HERVs, and that multiple events of transcriptional reactivation in MS patients can be explained by the deficiency of a single mechanism of gene silencing.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Chromosomal Proteins, Non-Histone* / genetics
  • Chromosomal Proteins, Non-Histone* / metabolism
  • Citrulline / metabolism
  • Endogenous Retroviruses / genetics
  • Endogenous Retroviruses / metabolism
  • Female
  • Gene Expression Regulation / drug effects
  • HEK293 Cells
  • Histones* / genetics
  • Histones* / metabolism
  • Humans
  • Hydrolases* / genetics
  • Hydrolases* / metabolism
  • Immunity, Innate / genetics
  • Interleukin-8 / genetics
  • Interleukin-8 / metabolism
  • Leukocytes, Mononuclear / drug effects
  • Lymphocyte Activation / genetics
  • MCF-7 Cells
  • Male
  • Middle Aged
  • Multiple Sclerosis* / genetics
  • Multiple Sclerosis* / metabolism
  • Ornithine / analogs & derivatives
  • Ornithine / pharmacology
  • Protein-Arginine Deiminase Type 4
  • Protein-Arginine Deiminases
  • T-Lymphocytes / metabolism
  • Tumor Necrosis Factor-alpha / genetics
  • Tumor Necrosis Factor-alpha / metabolism

Substances

  • CXCL8 protein, human
  • Chromosomal Proteins, Non-Histone
  • Histones
  • Interleukin-8
  • N-alpha-benzoyl-N5-(2-chloro-1-iminoethyl)-L-ornithine amide
  • Tumor Necrosis Factor-alpha
  • heterochromatin-specific nonhistone chromosomal protein HP-1
  • Citrulline
  • Ornithine
  • Hydrolases
  • PADI4 protein, human
  • Protein-Arginine Deiminase Type 4
  • Protein-Arginine Deiminases

Grant support

This work was supported in part by the Agence National pour la Recherche, by the Fondation pour la Recherche Medicale, and by the ARSEP foundation. PS received support from the Sandwich Fellowship Program of the French Embassy in India and from the Institut National de la Santé et de la Recherche Médicale. TC, AM-L, and TP were supported by the Aase and Ejnar Danielsen Foundation and the Danish MS Society. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.