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

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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Different isoforms of BSAP regulate expression of AID in normal and chronic lymphocytic leukemia B cells

Blood ◽

10.1182/blood-2004-09-3644 ◽

2005 ◽

Vol 105 (6) ◽

pp. 2495-2503 ◽

Cited By ~ 29

Author(s):

Pablo Oppezzo ◽

Gérard Dumas ◽

Ana Inés Lalanne ◽

Béatrice Payelle-Brogard ◽

Christian Magnac ◽

...

Keyword(s):

B Cells ◽

Chronic Lymphocytic Leukemia ◽

Somatic Hypermutation ◽

Cytidine Deaminase ◽

Lymphocytic Leukemia ◽

Interleukin 4 ◽

Class Switch ◽

Activation Induced Cytidine Deaminase ◽

Complete Form ◽

Lower Expression

Abstract Activation-induced cytidine deaminase (AID) is key to initiating somatic hypermutation (SHM) and class switch recombination (CSR), but its mode of action and regulation remains unclear. Since Pax-5 and Id-2 transcription factors play an opposing role in AID regulation, we have studied the expression of Pax-5, Id-2, and prdm-1 genes in 54 chronic lymphocytic leukemia (CLL) B cells. In 21 cases, presence of AID is constantly associated with high expression of the complete form of the Pax-5 gene (Pax-5a) and lower expression of the Id-2 and prdm-1 transcripts. In 33 cases, the absence of AID expression and CSR is associated with a reduction of Pax-5a and the appearance of a spliced form with a deletion in exon 8 (Pax-5/Δ-Ex8). Stimulation with CD40L+interleukin 4 (IL-4) induces CSR, the presence of AID transcripts, up-regulation of Pax-5a and down-regulation of Pax-5/Δ-Ex8, and Id-2 and prdm-1 transcripts. Pax-5a and Pax-5/Δ-Ex8 are translated into 2 isoforms of the B-cell–specific activator protein (BSAP) and both are able to bind the AID-promoter region. Overall, these results suggest that Pax-5/Δ-Ex8 could play an important role in the control of its own transcription and indirectly in AID expression and CSR.

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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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Activation-induced cytidine deaminase in chronic lymphocytic leukemia B cells: expression as multiple forms in a dynamic, variably sized fraction of the clone

Blood ◽

10.1182/blood-2003-05-1585 ◽

2003 ◽

Vol 102 (9) ◽

pp. 3333-3339 ◽

Cited By ~ 95

Author(s):

Emilia Albesiano ◽

Bradley T. Messmer ◽

Rajendra N. Damle ◽

Steven L. Allen ◽

Kanti R. Rai ◽

...

Keyword(s):

B Cells ◽

Chronic Lymphocytic Leukemia ◽

Somatic Hypermutation ◽

Splice Variants ◽

Cytidine Deaminase ◽

Prognostic Indicator ◽

Lymphocytic Leukemia ◽

Leukemic Cells ◽

Activation Induced Cytidine Deaminase

AbstractThe degree of somatic mutation of immunoglobulin variable (Ig V) region genes is an important prognostic indicator of clinical course and outcome in B-cell chronic lymphocytic leukemia (B-CLL), although the reason for this association remains unclear. Furthermore, some B-CLL cells continue to acquire Ig V gene mutations after the transforming event. Because activation-induced cytidine deaminase (AID) is an essential component of the canonical somatic hypermutation process in healthy B cells, its expression in B-CLL is potentially relevant to the disease. We detected full-length AID transcripts and 3 splice variants by conventional reverse transcription polymerase chain reaction (RT-PCR) in approximately 40% of the cases examined. More sensitive real-time quantitative PCR detected AID transcripts in virtually all B-CLL samples tested, although the range of transcript levels was very large between different cases and varied within individual cases over time. Limiting dilution assays revealed that AID expression was restricted to a small fraction of the leukemic cells in the blood. However, this small fraction is not unique in its ability to express AID, because in vitro stimulation of B-CLL cells with appropriate stimuli significantly increased the fraction of AID-expressing cells. These data suggest that AID-mediated DNA alterations may occur in a variably sized, minor subset of B-CLL cells at any given time.

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High expression of activation-induced cytidine deaminase (AID) and splice variants is a distinctive feature of poor-prognosis chronic lymphocytic leukemia

Blood ◽

10.1182/blood-2002-09-2906 ◽

2003 ◽

Vol 101 (12) ◽

pp. 4903-4908 ◽

Cited By ~ 108

Author(s):

Helen McCarthy ◽

William G. Wierda ◽

Lynn L. Barron ◽

Candy C. Cromwell ◽

Jing Wang ◽

...

Keyword(s):

B Cells ◽

Chronic Lymphocytic Leukemia ◽

Somatic Hypermutation ◽

Splice Variants ◽

Cytidine Deaminase ◽

Lymphocytic Leukemia ◽

High Expression ◽

Variable Regions ◽

Normal Peripheral Blood ◽

Activation Induced Cytidine Deaminase

AbstractIn chronic lymphocytic leukemia (CLL), analysis of immunoglobulin heavy chain variable regions for somatic hypermutation identifies 2 prognostic subsets, mutated and unmutated. Investigators have postulated that unmutated and mutated CLL arises from malignant transformation of pre– and post–germinal center (GC) B cells, respectively. Alternatively, unmutated cases may arise from B cells stimulated by T-cell–independent antigens or from GC B cells with inactive somatic hypermutation. Activation-induced cytidine deaminase (AID), a protein essential for somatic hypermutation, is expressed by GC B cells in which this process occurs. We investigated AID mRNA expression in 20 CLL cases. In 8 cases we detected high expression of wild-type AID mRNA and 2 splice variants; in 12 cases and 5 normal peripheral blood B-cell samples we detected no expression using standard conditions. Of 8 CLL cases that highly expressed AID, 7 were unmutated, suggesting that this subset may arise from GC-experienced B cells with inactive somatic hypermutation, and may predict prognosis.

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AID from bony fish catalyzes class switch recombination

Journal of Experimental Medicine ◽

10.1084/jem.20051378 ◽

2005 ◽

Vol 202 (6) ◽

pp. 733-738 ◽

Cited By ~ 78

Author(s):

Vasco M. Barreto ◽

Qiang Pan-Hammarstrom ◽

Yaofeng Zhao ◽

Lennart Hammarstrom ◽

Ziva Misulovin ◽

...

Keyword(s):

B Cells ◽

Catalytic Domain ◽

Somatic Hypermutation ◽

Cytidine Deaminase ◽

Class Switch Recombination ◽

Adaptive Immune System ◽

Bony Fish ◽

Class Switching ◽

Class Switch ◽

Switch Regions

Class switch recombination was the last of the lymphocyte-specific DNA modification reactions to appear in the evolution of the adaptive immune system. It is absent in cartilaginous and bony fish, and it is common to all tetrapods. Class switching is initiated by activation-induced cytidine deaminase (AID), an enzyme expressed in cartilaginous and bony fish that is also required for somatic hypermutation. Fish AID differs from orthologs found in tetrapods in several respects, including its catalytic domain and carboxy-terminal region, both of which are essential for the switching reaction. To determine whether evolution of class switch recombination required alterations in AID, we assayed AID from Japanese puffer and zebra fish for class-switching activity in mouse B cells. We find that fish AID catalyzes class switch recombination in mammalian B cells. Thus, AID had the potential to catalyze this reaction before the teleost and tetrapod lineages diverged, suggesting that the later appearance of a class-switching reaction was dependent on the evolution of switch regions and multiple constant regions in the IgH locus.

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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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