scholarly journals In vivo and in vitro studies of immunoglobulin gene somatic hypermutation

2001 ◽  
Vol 356 (1405) ◽  
pp. 21-28 ◽  
Author(s):  
Julian E. Sale ◽  
Mats Bemark ◽  
Gareth T. Williams ◽  
Christopher J. Jolly ◽  
Michael R. Ehrenstein ◽  
...  
Keyword(s):  
Somatic Hypermutation ◽  
Class Switch Recombination ◽  
Variable Region ◽  
Immunoglobulin Gene ◽  
Immunoglobulin Genes ◽  
Class Switch ◽  
Immunoglobulin Repertoire ◽  
Genetic Events

Following antigen encounter, two distinct processes modify immunoglobulin genes. The variable region is diversified by somatic hypermutation while the constant region may be changed by class–switch recombination. Although both genetic events can occur concurrently within germinal centre B cells, there are examples of each occurring independently of the other. Here we compare the contributions of class–switch recombination and somatic hypermutation to the diversification of the serum immunoglobulin repertoire and review evidence that suggests that, despite clear differences, the two processes may share some aspects of their mechanism in common.

scholarly journals Regulation of class switch recombination and somatic mutation by AID phosphorylation

2008 ◽  
Vol 205 (11) ◽  
pp. 2585-2594 ◽  
Author(s):  
Kevin M. McBride ◽  
Anna Gazumyan ◽  
Eileen M. Woo ◽  
Tanja A. Schwickert ◽  
Brian T. Chait ◽  
...  
Keyword(s):  
Somatic Mutation ◽  
Somatic Hypermutation ◽  
Cytidine Deaminase ◽  
Point Mutations ◽  
Class Switch Recombination ◽  
Variable Region ◽  
Dna Breaks ◽  
Class Switching ◽  
Class Switch

Activation-induced cytidine deaminase (AID) is a mutator enzyme that initiates somatic mutation and class switch recombination in B lymphocytes by introducing uracil:guanine mismatches into DNA. Repair pathways process these mismatches to produce point mutations in the Ig variable region or double-stranded DNA breaks in the switch region DNA. However, AID can also produce off-target DNA damage, including mutations in oncogenes. Therefore, stringent regulation of AID is required for maintaining genomic stability during maturation of the antibody response. It has been proposed that AID phosphorylation at serine 38 (S38) regulates its activity, but this has not been tested in vivo. Using a combination of mass spectrometry and immunochemical approaches, we found that in addition to S38, AID is also phosphorylated at position threonine 140 (T140). Mutation of either S38 or T140 to alanine does not impact catalytic activity, but interferes with class switching and somatic hypermutation in vivo. This effect is particularly pronounced in haploinsufficient mice where AID levels are limited. Although S38 is equally important for both processes, T140 phosphorylation preferentially affects somatic mutation, suggesting that posttranslational modification might contribute to the choice between hypermutation and class switching.

scholarly journals A new class of errant DNA polymerases provides candidates for somatic hypermutation

2001 ◽  
Vol 356 (1405) ◽  
pp. 47-51 ◽  
Author(s):  
Brigette Tippin ◽  
Myron F. Goodman
Keyword(s):  
Somatic Hypermutation ◽  
Dna Polymerases ◽  
Variable Region ◽  
Affinity Maturation ◽  
Immunoglobulin Genes ◽  
New Class ◽  
Eukaryotic Dna ◽  
Factor Governing

The mechanism of somatic hypermutation of the immunoglobulin genes remains a mystery after nearly 30 years of intensive research in the field. While many clues to the process have been discovered in terms of the genetic elements required in the immunoglobulin genes, the key enzymatic players that mediate the introduction of mutations into the variable region are unknown. The recent wave of newly discovered eukaryotic DNA polymerases have given a fresh supply of potential candidates and a renewed vigour in the search for the elusive mutator factor governing affinity maturation. In this paper, we discuss the relevant genetic and biochemical evidence known to date regarding both somatic hypermutation and the new DNA polymerases and address how the two fields can be brought together to identify the strongest candidates for further study. In particular we discuss evidence for the in vitro biochemical misincorporation properties of human Rad30B/Pol ι and how it compares to the in vivo somatic hypermutation spectra.

scholarly journals Human PMS2 deficiency is associated with impaired immunoglobulin class switch recombination

2008 ◽  
Vol 205 (11) ◽  
pp. 2465-2472 ◽  
Author(s):  
Sophie Péron ◽  
Ayse Metin ◽  
Pauline Gardès ◽  
Marie-Alexandra Alyanakian ◽  
Eamonn Sheridan ◽  
...  
Keyword(s):  
Somatic Hypermutation ◽  
Cytidine Deaminase ◽  
Class Switch Recombination ◽  
Dna Breaks ◽  
Gene Encoding ◽  
Class Switch ◽  
Double Strand Dna Breaks ◽  
Switch Regions

Immunoglobulin (Ig) class switch recombination (CSR) deficiencies are rare primary immunodeficiencies characterized by the lack of switched isotype (IgG/IgA/IgE) production. In some cases, CSR deficiencies can be associated with abnormal somatic hypermutation. Analysis of CSR deficiencies has helped reveal the key functions of CSR-triggering molecules, i.e., CD40L, CD40, and effector molecules such as activation-induced cytidine deaminase and uracil N-glycosylase. We report a new form of B cell–intrinsic CSR deficiency found in three patients with deleterious, homozygous mutations in the gene encoding the PMS2 component of the mismatch repair machinery. CSR was found partially defective in vivo and markedly impaired in vitro. It is characterized by the defective occurrence of double-strand DNA breaks (DSBs) in switch regions and abnormal formation of switch junctions. This observation strongly suggests a role for PMS2 in CSR-induced DSB generation.

scholarly journals Cernunnos influences human immunoglobulin class switch recombination and may be associated with B cell lymphomagenesis

2012 ◽  
Vol 209 (2) ◽  
pp. 291-305 ◽  
Author(s):  
Likun Du ◽  
Roujun Peng ◽  
Andrea Björkman ◽  
Noel Filipe de Miranda ◽  
Cornelia Rosner ◽  
...  
Keyword(s):  
B Cell ◽  
Cell Lymphoma ◽  
Class Switch Recombination ◽  
B Cell Lymphoma ◽  
Dominant Negative ◽  
Dominant Negative Effect ◽  
End Joining ◽  
Class Switch

Cernunnos is involved in the nonhomologous end-joining (NHEJ) process during DNA double-strand break (DSB) repair. Here, we studied immunoglobulin (Ig) class switch recombination (CSR), a physiological process which relies on proper repair of the DSBs, in B cells from Cernunnos-deficient patients. The pattern of in vivo generated CSR junctions is altered in these cells, with unusually long microhomologies and a lack of direct end-joining. The CSR junctions from Cernunnos-deficient patients largely resemble those from patients lacking DNA ligase IV, Artemis, or ATM, suggesting that these factors are involved in the same end-joining pathway during CSR. By screening 269 mature B cell lymphoma biopsies, we also identified a somatic missense Cernunnos mutation in a diffuse large B cell lymphoma sample. This mutation has a dominant-negative effect on joining of a subset of DNA ends in an in vitro NHEJ assay. Translocations involving both Ig heavy chain loci and clonal-like, dynamic IgA switching activities were observed in this tumor. Collectively, our results suggest a link between defects in the Cernunnos-dependent NHEJ pathway and aberrant CSR or switch translocations during the development of B cell malignancies.

scholarly journals Clinical, Immunological, and Functional Characterization of Six Patients with Very High IgM Levels

2020 ◽  
Vol 9 (3) ◽  
pp. 818 ◽  
Author(s):  
Vera Gallo ◽  
Emilia Cirillo ◽  
Rosaria Prencipe ◽  
Alessio Lepore ◽  
Luigi Del Vecchio ◽  
...  
Keyword(s):  
B Cell ◽  
Somatic Hypermutation ◽  
Functional Characterization ◽  
Class Switch Recombination ◽  
Pathogenic Mutation ◽  
Potential Candidate ◽  
Class Switch ◽  
Potential Candidate Gene ◽  
Very High

Very high IgM levels represent the hallmark of hyper IgM (HIGM) syndromes, a group of primary immunodeficiencies (PIDs) characterized by susceptibility to infections and malignancies. Other PIDs not fulfilling the diagnostic criteria for HIGM syndromes can also be characterized by high IgM levels and susceptibility to malignancies. The aim of this study is to characterize clinical phenotype, immune impairment, and pathogenic mechanism in six patients with very high IgM levels in whom classical HIGM syndromes were ruled out. The immunological analysis included extended B-cell immunophenotyping, evaluation of class switch recombination and somatic hypermutation, and next generation sequencing (NGS). Recurrent or severe infections and chronic lung changes at the diagnosis were reported in five out of six and two out of six patients, respectively. Five out of six patients showed signs of lymphoproliferation and four patients developed malignancies. Four patients showed impaired B-cell homeostasis. Class switch recombination was functional in vivo in all patients. NGS revealed, in one case, a pathogenic mutation in PIK3R1. In a second case, the ITPKB gene, implicated in B- and T-cell development, survival, and activity was identified as a potential candidate gene. Independent of the genetic basis, very high IgM levels represent a risk factor for the development of recurrent infections leading to chronic lung changes, lymphoproliferation, and high risk of malignancies.

scholarly journals Apex2 is required for efficient somatic hypermutation but not for class switch recombination of immunoglobulin genes

2009 ◽  
Vol 21 (8) ◽  
pp. 947-955 ◽  
Author(s):  
Z. Sabouri ◽  
I.-m. Okazaki ◽  
R. Shinkura ◽  
N. Begum ◽  
H. Nagaoka ◽  
...  
Keyword(s):  
Somatic Hypermutation ◽  
Class Switch Recombination ◽  
Immunoglobulin Genes ◽  
Class Switch

scholarly journals LMP1 signaling can replace CD40 signaling in B cells in vivo and has unique features of inducing class-switch recombination to IgG1

Blood ◽  
2008 ◽  
Vol 111 (3) ◽  
pp. 1448-1455 ◽  
Author(s):  
Julia Rastelli ◽  
Cornelia Hömig-Hölzel ◽  
Jane Seagal ◽  
Werner Müller ◽  
Andrea C. Hermann ◽  
...  
Keyword(s):  
B Cells ◽  
B Cell ◽  
Cell Function ◽  
Somatic Hypermutation ◽  
Class Switch Recombination ◽  
Cd40 Ligand ◽  
Barr Virus ◽  
Class Switch ◽  
Epstein Barr

AbstractThe Epstein-Barr virus (EBV) protein LMP1 is considered to be a functional homologue of the CD40 receptor. However, in contrast to the latter, LMP1 is a constitutively active signaling molecule. To compare B cell–specific LMP1 and CD40 signaling in an unambiguous manner, we generated transgenic mice conditionally expressing a CD40/LMP1 fusion protein, which retained the LMP1 cytoplasmic tail but has lost the constitutive activity of LMP1 and needs to be activated by the CD40 ligand. We show that LMP1 signaling can completely substitute CD40 signaling in B cells, leading to normal B-cell development, activation, and immune responses including class-switch recombination, germinal center formation, and somatic hypermutation. In addition, the LMP1-signaling domain has a unique property in that it can induce class-switch recombination to IgG1 independent of cytokines. Thus, our data indicate that LMP1 has evolved to imitate T-helper cell function allowing activation, proliferation, and differentiation of EBV-infected B cells independent of T cells.

scholarly journals The ubiquitous octamer-binding protein(s) is sufficient for transcription of immunoglobulin genes.

1990 ◽  
Vol 10 (3) ◽  
pp. 982-990 ◽  
Author(s):  
D G Johnson ◽  
L Carayannopoulos ◽  
J D Capra ◽  
P W Tucker ◽  
J H Hanke
Keyword(s):  
B Cell ◽  
Protein S ◽  
Cell Types ◽  
In Vitro Transcription ◽  
Immunoglobulin Gene ◽  
Immunoglobulin Genes ◽  
Specific Expression ◽  
Specific Regulation

All immunoglobulin genes contain a conserved octanucleotide promoter element, ATGCAAAT, which has been shown to be required for their normal B-cell-specific transcription. Proteins that bind this octamer have been purified, and cDNAs encoding octamer-binding proteins have been cloned. Some of these proteins (referred to as OTF-2) are lymphoid specific, whereas at least one other, and possibly more (referred to as OTF-1), is found ubiquitously in all cell types. The exact role of these different proteins in directing the tissue-specific expression of immunoglobulin genes is unclear. We have identified two human pre-B-cell lines that contain extremely low levels of OTF-2 yet still express high levels of steady-state immunoglobulin heavy-chain mRNA in vivo and efficiently transcribe an immunoglobulin gene in vitro. Addition of a highly enriched preparation of OTF-1 made from one of these pre-B cells or from HeLa cells specifically stimulated in vitro transcription of an immunoglobulin gene. Furthermore, OFT-1 appeared to have approximately the same transactivation ability as OTF-2 when normalized for binding activity. These results suggest that OTF-1, without OTF-2, is sufficient for transcription of immunoglobulin genes and that OTF-2 alone is not responsible for the B-cell-specific regulation of immunoglobulin gene expression.

scholarly journals Mlh1 Can Function in Antibody Class Switch Recombination Independently of Msh2

2003 ◽  
Vol 197 (10) ◽  
pp. 1377-1383 ◽  
Author(s):  
Carol E. Schrader ◽  
Joycelyn Vardo ◽  
Janet Stavnezer
Keyword(s):  
B Cells ◽  
Somatic Hypermutation ◽  
Class Switch Recombination ◽  
Variable Region ◽  
Class Switch ◽  
Switch Regions ◽  
Substitution Mutations ◽  
Antibody Class ◽  
Variable Region Genes ◽  
Mmr Proteins

Mismatch repair proteins participate in antibody class switch recombination, although their roles are unknown. Previous nucleotide sequence analyses of switch recombination junctions indicated that the roles of Msh2 and the MutL homologues, Mlh1 and Pms2, differ. We now asked if Msh2 and Mlh1 function in the same pathway during switch recombination. Splenic B cells from mice deficient in both these proteins were induced to undergo switching in culture. The frequency of switching is reduced, similarly to that of B cells singly deficient in Msh2 or Mlh1. However, the nucleotide sequences of the Sμ-Sγ3 junctions resemble junctions from Mlh1- but not from Msh2-deficient cells, suggesting Mlh1 functions either independently of or before Msh2. The substitution mutations within S regions that are known to accompany switch recombination are increased in Msh2- and Mlh1 single-deficient cells and further increased in the double-deficient cells, again suggesting these proteins function independently in class switch recombination. The finding that MMR functions to reduce mutations in switch regions is unexpected since MMR proteins have been shown to contribute to somatic hypermutation of antibody variable region genes.

53BP1 Is Targeted to Sites of DNA Breaks within the Immunoglobulin Heavy Chain Locus and Promotes Class Switch Recombination.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2379-2379
Author(s):  
John Manis ◽  
Nicole Walsh ◽  
Phil Carpenter ◽  
Shilpee Dutt
Keyword(s):  
Dna Damage ◽  
B Cells ◽  
Dna Damage Response ◽  
Cellular Response ◽  
Somatic Hypermutation ◽  
Class Switch Recombination ◽  
Dna Breaks ◽  
Class Switch ◽  
Damage Response

Abstract The maintenance of genomic integrity relies on the cellular response to chromosomal damage from both exogenous (e.g. ionizing radiation) and endogenous (e.g. oxidative stress) sources. Various members of the DNA damage-sensing pathway including ATM, H2AX, 53BP1, and MDC1 are necessary to orchestrate the repair of DNA breaks. B cells undergo several programmed DNA alterations during their development: V(D)J recombination, Somatic Hypermutation (SHM), and Class Switch Recombination (CSR). We have previously shown that 53BP1 is relatively dispensable for V(D)J recombination and SHM. In contrast, class switch recombination is largely blocked to all isotypes indicating that regulated DNA breaks in B cells are regarded differentially by the DNA damage response machinery. 53BP1 is thought to promote the joining of DNA ends during CSR thus preventing translocations that could potentially lead to lymphoma. To better understand the damage response to CSR induced DNA breaks, a chromatin immunoprecipitation strategy and a combined immunofluorescence/FISH method was used to examine the components that assemble at IgH switch (S) regions during CSR. H2AX was found at S regions specifically targeted to undergo CSR after in vitro stimulation of B cells, and to a lesser degree, at adjacent S regions that were not activated for a switch event. H2AX was also found at S regions in switch activated 53BP1-deficient B cells. In contrast, 53BP1 was found primarily at S regions specifically targeted for CSR, and not at the adjacent S regions. Moreover, the localization of 53BP1 to S regions appeared to be in part, independent of DNA breaks, and potentially reliant on specialized DNA structures that are generated during CSR. These findings support a differential role for the various components of the DNA damage response program during CSR and have implications for understanding mechanisms of lymphomagenesis.

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