Regulated localization of an AID complex with E2A, PAX5 and IRF4 at the Igh locus.
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.
Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden.
Jannek
J
Hauser
Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden.
Christine
C
Grundström
Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden.
Ramesh
R
Kumar
Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden. Electronic address: Thomas.Grundstrom@umu.se.
Thomas
T
Grundström
D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000276:immunology; D002147:Calmodulin / Q000235:genetics / Q000276:immunology; D047369:Chromatin Immunoprecipitation; D003564:Cytidine Deaminase / Q000235:genetics* / Q000276:immunology; D005434:Flow Cytometry; D050438:Genes, Immunoglobulin Heavy Chain / Q000235:genetics* / Q000276:immunology; D017578:Immunoglobulin Class Switching / Q000235:genetics* / Q000276:immunology; D050835:Interferon Regulatory Factors / Q000235:genetics* / Q000276:immunology; D051379:Mice; D051757:PAX5 Transcription Factor / Q000235:genetics* / Q000276:immunology; D060888:Real-Time Polymerase Chain Reaction; D027041:Somatic Hypermutation, Immunoglobulin / Q000235:genetics / Q000276:immunology; D015533:Transcriptional Activation; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D000099218:Interferon Regulatory Factor-4
D051792:Basic Helix-Loop-Helix Proteins; D002147:Calmodulin; D003564:Cytidine Deaminase; D050835:Interferon Regulatory Factors; D051757:PAX5 Transcription Factor; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D000099218:Interferon Regulatory Factor-4; C497282:Pax5 protein, mouse; C075668:Tcf3 protein, mouse
Activation-induced cytidine deaminase; Antibodies; Calmodulin; Class switch recombination; E2A; Transcription factors