Apurinic/apyrimidinic endonuclease 2 regulates the expansion of germinal centers by protecting against activation-induced cytidine deaminase-independent DNA damage in B cells

J Immunol. 2014 Jul 15;193(2):931-9. doi: 10.4049/jimmunol.1400002. Epub 2014 Jun 16.

Abstract

Activation-induced cytidine deaminase (AID) initiates a process generating DNA mutations and breaks in germinal center (GC) B cells that are necessary for somatic hypermutation and class-switch recombination. GC B cells can "tolerate" DNA damage while rapidly proliferating because of partial suppression of the DNA damage response by BCL6. In this study, we develop a model to study the response of mouse GC B cells to endogenous DNA damage. We show that the base excision repair protein apurinic/apyrimidinic endonuclease (APE) 2 protects activated B cells from oxidative damage in vitro. APE2-deficient mice have smaller GCs and reduced Ab responses compared with wild-type mice. DNA double-strand breaks are increased in the rapidly dividing GC centroblasts of APE2-deficient mice, which activate a p53-independent cell cycle checkpoint and a p53-dependent apoptotic response. Proliferative and/or oxidative damage and AID-dependent damage are additive stresses that correlate inversely with GC size in wild-type, AID-, and APE2-deficient mice. Excessive double-strand breaks lead to decreased expression of BCL6, which would enable DNA repair pathways but limit GC cell numbers. These results describe a nonredundant role for APE2 in the protection of GC cells from AID-independent damage, and although GC cells uniquely tolerate DNA damage, we find that the DNA damage response can still regulate GC size through pathways that involve p53 and BCL6.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / genetics
  • Apoptosis / immunology
  • B-Lymphocytes / immunology*
  • B-Lymphocytes / metabolism
  • Cell Cycle / genetics
  • Cell Cycle / immunology
  • Cell Proliferation
  • Cells, Cultured
  • Cytidine Deaminase / deficiency
  • Cytidine Deaminase / genetics
  • Cytidine Deaminase / immunology*
  • DNA Breaks, Double-Stranded
  • DNA Damage*
  • DNA-(Apurinic or Apyrimidinic Site) Lyase
  • DNA-Binding Proteins / immunology
  • DNA-Binding Proteins / metabolism
  • Endonucleases / deficiency
  • Endonucleases / genetics
  • Endonucleases / immunology*
  • Flow Cytometry
  • Germinal Center / immunology*
  • Germinal Center / metabolism
  • Immunoglobulin Class Switching / genetics
  • Immunoglobulin Class Switching / immunology
  • Lymphocyte Activation / genetics
  • Lymphocyte Activation / immunology
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Inbred Strains
  • Mice, Knockout
  • Multifunctional Enzymes
  • Oxidative Stress / immunology
  • Proto-Oncogene Proteins c-bcl-6
  • Reactive Oxygen Species / immunology
  • Reactive Oxygen Species / metabolism
  • Somatic Hypermutation, Immunoglobulin / genetics
  • Somatic Hypermutation, Immunoglobulin / immunology
  • Tumor Suppressor Protein p53 / deficiency
  • Tumor Suppressor Protein p53 / genetics
  • Tumor Suppressor Protein p53 / immunology

Substances

  • Bcl6 protein, mouse
  • DNA-Binding Proteins
  • Multifunctional Enzymes
  • Proto-Oncogene Proteins c-bcl-6
  • Reactive Oxygen Species
  • Tumor Suppressor Protein p53
  • Apex2 protein, mouse
  • Endonucleases
  • AICDA (activation-induced cytidine deaminase)
  • Cytidine Deaminase
  • DNA-(Apurinic or Apyrimidinic Site) Lyase