Regulated localization of an AID complex with E2A, PAX5 and IRF4 at the Igh locus

Mol Immunol. 2016 Dec:80:78-90. doi: 10.1016/j.molimm.2016.10.014. Epub 2016 Nov 12.

Abstract

Activation-induced cytidine deaminase (AID) is the key mutagenic enzyme that initiates somatic hypermutation (SH) and class switch recombination (CSR) by deaminating cytosine to uracil. The targeting of AID and therefore SH and CSR to Ig genes is a central process of the immune system, but the trans-acting factors mediating the specific targeting have remained elusive. Here we show that defective calmodulin inhibition of the transcription factor E2A after activation of the B cell receptor (BCR) leads to reduced BCR, IL4 plus CD40 ligand stimulated CSR to IgE and instead CSR to other Ig classes. AID that initiates CSR is shown to be in a complex with the transcription factors E2A, PAX5 and IRF4 on key sequences of the Igh locus. Calmodulin shows proximity with each of them after BCR stimulation. BCR signaling reduces binding of the proteins to some of the target sites on the Igh locus, and calmodulin resistance of E2A blocks these reductions. AID binds directly to the bHLH domain of E2A and to the PD domain of PAX5. E2A, AID, PAX5 and IRF4 are components of a CSR complex that is redistributed on the Igh locus by BCR signaling through calmodulin binding.

Keywords: Activation-induced cytidine deaminase; Antibodies; Calmodulin; Class switch recombination; E2A; Transcription factors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • B-Lymphocytes / immunology
  • Basic Helix-Loop-Helix Transcription Factors / genetics*
  • Basic Helix-Loop-Helix Transcription Factors / immunology
  • Calmodulin / genetics
  • Calmodulin / immunology
  • Chromatin Immunoprecipitation
  • Cytidine Deaminase / genetics*
  • Cytidine Deaminase / immunology
  • Flow Cytometry
  • Genes, Immunoglobulin Heavy Chain / genetics*
  • Genes, Immunoglobulin Heavy Chain / immunology
  • Immunoglobulin Class Switching / genetics*
  • Immunoglobulin Class Switching / immunology
  • Interferon Regulatory Factors / genetics*
  • Interferon Regulatory Factors / immunology
  • Mice
  • PAX5 Transcription Factor / genetics*
  • PAX5 Transcription Factor / immunology
  • Real-Time Polymerase Chain Reaction
  • Somatic Hypermutation, Immunoglobulin / genetics
  • Somatic Hypermutation, Immunoglobulin / immunology
  • Transcriptional Activation

Substances

  • Basic Helix-Loop-Helix Transcription Factors
  • Calmodulin
  • Interferon Regulatory Factors
  • PAX5 Transcription Factor
  • Pax5 protein, mouse
  • Tcf3 protein, mouse
  • interferon regulatory factor-4
  • AICDA (activation-induced cytidine deaminase)
  • Cytidine Deaminase