An Evolutionarily Conserved Function of Polycomb Silences the MHC Class I Antigen Presentation Pathway and Enables Immune Evasion in Cancer

Cancer Cell. 2019 Oct 14;36(4):385-401.e8. doi: 10.1016/j.ccell.2019.08.008. Epub 2019 Sep 26.

Abstract

Loss of MHC class I (MHC-I) antigen presentation in cancer cells can elicit immunotherapy resistance. A genome-wide CRISPR/Cas9 screen identified an evolutionarily conserved function of polycomb repressive complex 2 (PRC2) that mediates coordinated transcriptional silencing of the MHC-I antigen processing pathway (MHC-I APP), promoting evasion of T cell-mediated immunity. MHC-I APP gene promoters in MHC-I low cancers harbor bivalent activating H3K4me3 and repressive H3K27me3 histone modifications, silencing basal MHC-I expression and restricting cytokine-induced upregulation. Bivalent chromatin at MHC-I APP genes is a normal developmental process active in embryonic stem cells and maintained during neural progenitor differentiation. This physiological MHC-I silencing highlights a conserved mechanism by which cancers arising from these primitive tissues exploit PRC2 activity to enable immune evasion.

Keywords: EZH2; MHC class I; antigen presentation; bivalency; cancer; epigenetic repression; histone methyltransferase; immune evasion; immunotherapy; polycomb.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigen Presentation / drug effects
  • Antigen Presentation / immunology
  • Antineoplastic Agents, Immunological / pharmacology
  • Antineoplastic Agents, Immunological / therapeutic use
  • Antineoplastic Combined Chemotherapy Protocols / pharmacology*
  • Antineoplastic Combined Chemotherapy Protocols / therapeutic use
  • Cell Line, Tumor
  • DNA Methylation / immunology
  • Down-Regulation / drug effects
  • Down-Regulation / genetics
  • Down-Regulation / immunology
  • Drug Resistance, Neoplasm / genetics
  • Epigenetic Repression / drug effects
  • Epigenetic Repression / immunology
  • Female
  • Gene Expression Regulation, Neoplastic / drug effects
  • Gene Expression Regulation, Neoplastic / immunology*
  • Histocompatibility Antigens Class I / genetics*
  • Histocompatibility Antigens Class I / immunology
  • Histocompatibility Antigens Class I / metabolism
  • Histone Code / drug effects
  • Humans
  • Mice
  • Middle Aged
  • Neoplasms / drug therapy
  • Neoplasms / genetics
  • Neoplasms / immunology*
  • Neoplasms / pathology
  • Polycomb Repressive Complex 2 / antagonists & inhibitors
  • Polycomb Repressive Complex 2 / metabolism*
  • T-Lymphocytes / immunology
  • Tumor Escape / drug effects
  • Tumor Escape / genetics*
  • Xenograft Model Antitumor Assays

Substances

  • Antineoplastic Agents, Immunological
  • Histocompatibility Antigens Class I
  • Polycomb Repressive Complex 2