Aging down‐regulates the transcription factor E2A, activation‐induced cytidine deaminase and Ig class switch in human B cells

Pax5 activity is enhanced in activated B cells and is essential for class switch recombination (CSR). We show that inhibitor of differentiation (Id)2 suppresses CSR by repressing the gene expression of activation-induced cytidine deaminase (AID), which has been shown to be indispensable for CSR. Furthermore, a putative regulatory region of AID contains E2A- and Pax5-binding sites, and the latter site is indispensable for AID gene expression. Moreover, the DNA-binding activity of Pax5 is decreased in Id2-overexpressing B cells and enhanced in Id2−/− B cells. The kinetics of Pax5, but not E2A, occupancy to AID locus is the same as AID expression in primary B cells. Finally, enforced expression of Pax5 induces AID transcription in pro–B cell lines. Our results provide evidence that the balance between Pax5 and Id2 activities has a key role in AID gene expression.

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Regulation of ϵ germline transcription and switch region mutations by IgH locus 3′ enhancers in transgenic mice

Blood ◽

10.1182/blood-2006-02-005355 ◽

2006 ◽

Vol 109 (1) ◽

pp. 159-167 ◽

Cited By ~ 9

Author(s):

Jurga Laurencikiene ◽

Vytas Tamosiunas ◽

Eva Severinson

Keyword(s):

B Cells ◽

Cytidine Deaminase ◽

Switch Region ◽

Endogenous Gene ◽

Class Switch ◽

Germline Transcription ◽

Igh Locus ◽

Activation Induced Cytidine Deaminase ◽

Switch Regions ◽

Transgenic Lines

Abstract Germline (GL) transcription is regulated by specific promoters and immunoglobulin heavy chain (IgH) 3′ locus enhancers and is necessary for Ig class-switch recombination (CSR). We have generated different transgenic lines containing the GL ϵ promoter, switch (S) ϵ region, and constant (C) ϵ region with or without the DNase I–sensitive regions (HS) 3A-HS1,2 or HS3B-HS4 3′ IgH enhancer pairs. The enhancerless construct was expressed in B cells activated by interleukin (IL)–4 and CD40, thus resembling regulation of the endogenous gene. Both enhancer-containing transgenes efficiently increased expression in B cells and were strongly up-regulated by stimuli. In addition, Sϵ regions of the transgene containing HS3B-HS4 were mutated in activated, sorted B cells. Such mutations are known to precede CSR and are dependent on activation-induced cytidine deaminase (AID). Our findings show that all elements necessary for recruitment of the recombination machinery are present in the transgene containing HS3 and HS4. These enhancers probably provide something more specific than mere increased accessibility of switch regions. We propose that transcription factors binding the enhancers help to target the recombination machinery to the switch regions.

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A/T mutagenesis in hypermutated immunoglobulin genes strongly depends on PCNAK164 modification

Journal of Experimental Medicine ◽

10.1084/jem.20070902 ◽

2007 ◽

Vol 204 (8) ◽

pp. 1989-1998 ◽

Cited By ~ 110

Author(s):

Petra Langerak ◽

Anders O.H. Nygren ◽

Peter H.L. Krijger ◽

Paul C.M. van den Berk ◽

Heinz Jacobs

Keyword(s):

B Cells ◽

Somatic Hypermutation ◽

Cytidine Deaminase ◽

Nuclear Antigen ◽

Translesion Dna Synthesis ◽

Class Switch ◽

Activation Induced Cytidine Deaminase ◽

Mismatch Recognition ◽

Proliferating Cell

B cells use translesion DNA synthesis (TLS) to introduce somatic mutations around genetic lesions caused by activation-induced cytidine deaminase. Monoubiquitination at lysine164 of proliferating cell nuclear antigen (PCNAK164) stimulates TLS. To determine the role of PCNAK164 modifications in somatic hypermutation, PCNAK164R knock-in mice were generated. PCNAK164R/K164R mutants are born at a sub-Mendelian frequency. Although PCNAK164R/K164R B cells proliferate and class switch normally, the mutation spectrum of hypermutated immunoglobulin (Ig) genes alters dramatically. A strong reduction of mutations at template A/T is associated with a compensatory increase at G/C, which is a phenotype similar to polymerase η (Polη) and mismatch repair–deficient B cells. Mismatch recognition, monoubiquitinated PCNA, and Polη likely cooperate in establishing mutations at template A/T during replication of Ig genes.

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Chronic lymphocytic leukemia B cells expressing AID display dissociation between class switch recombination and somatic hypermutation

Blood ◽

10.1182/blood-2002-10-3175 ◽

2003 ◽

Vol 101 (10) ◽

pp. 4029-4032 ◽

Cited By ~ 83

Author(s):

Pablo Oppezzo ◽

Françoise Vuillier ◽

Yuri Vasconcelos ◽

Gérard Dumas ◽

Christian Magnac ◽

...

Keyword(s):

B Cells ◽

Chronic Lymphocytic Leukemia ◽

Gene Product ◽

Mode Of Action ◽

Somatic Hypermutation ◽

Cytidine Deaminase ◽

Class Switch Recombination ◽

Lymphocytic Leukemia ◽

Class Switch ◽

Activation Induced Cytidine Deaminase

Abstract In B cells, somatic hypermutation (SHM) and class switch recombination (CSR) depend on the activation-induced cytidine deaminase (AID) gene product, although the precise mode of action of AID remains unknown. Because some chronic lymphocytic leukemia (CLL) B cells can undergo CSR without SHM, it constitutes a useful model to dissect AID function. In this work, we have studied AID expression, the presence of mutations in the preswitch μ DNA region, CSR, and the SHM in 65 CLL patients. Our results demonstrate that unmutated CLL B cells can constitutively express AID and that AID expression is associated with the presence of mutations in the preswitch region and in clonally related isotype-switched transcripts. They also demonstrate that in CLL without constitutive AID expression, AID induction on stimulation results in preswitch mutations and the CSR process. Our results show a dissociation between SHM and CSR in CLL and suggest that, in this disease, AID would require additional help for carrying out the SHM process.

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High expression of AID and active class switch recombination might account for a more aggressive disease in unmutated CLL patients: link with an activated microenvironment in CLL disease

Blood ◽

10.1182/blood-2009-12-257758 ◽

2010 ◽

Vol 115 (22) ◽

pp. 4488-4496 ◽

Cited By ~ 56

Author(s):

Florencia Palacios ◽

Pilar Moreno ◽

Pablo Morande ◽

Cecilia Abreu ◽

Agustín Correa ◽

...

Keyword(s):

B Cells ◽

Cytidine Deaminase ◽

Class Switch Recombination ◽

Lymphocytic Leukemia ◽

Small Subset ◽

Ki 67 ◽

Tissue Microenvironment ◽

Class Switch ◽

Activation Induced Cytidine Deaminase ◽

Progression Markers

Abstract Interaction of chronic lymphocytic leukemia (CLL) B cells with tissue microenvironment has been suggested to favor disease progression by promoting malignant B-cell growth. Previous work has shown expression in peripheral blood (PB) of CLL B cells of activation-induced cytidine deaminase (AID) among CLL patients with an unmutated (UM) profile of immunoglobulin genes and with ongoing class switch recombination (CSR) process. Because AID expression results from interaction with activated tissue microenvironment, we speculated whether the small subset with ongoing CSR is responsible for high levels of AID expression and could be derived from this particular microenvironment. In this work, we quantified AID expression and ongoing CSR in PB of 50 CLL patients and characterized the expression of different molecules related to microenvironment interaction. Our results show that among UM patients (1) high AID expression is restricted to the subpopulation of tumoral cells ongoing CSR; (2) this small subset expresses high levels of proliferation, antiapoptotic and progression markers (Ki-67, c-myc, Bcl-2, CD49d, and CCL3/4 chemokines). Overall, this work outlines the importance of a cellular subset in PB of UM CLL patients with a poor clinical outcome, high AID levels, and ongoing CSR, whose presence might be a hallmark of a recent contact with the microenvironment.

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