Somatic Hypermutation of Immunoglobulin Genes is Linked to Transcription

Storb, Ursula; Peters, Andrew; Klotz, Emily; Kim, N.; Sui, Hong; Kage, Karen; Rogerson, Brian J.; Martin, Terence E.

doi:10.1007/978-3-642-71984-4_2

Cited by 40 publications

(36 citation statements)

References 26 publications

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“…It is also possible that SHM could be triggered by an abasic site that stalls replication, thus recruiting an inaccurate polymerase for extension by several nucleotides before accurate replication resumes (see ref. 41 for discussion of the role of abasic sites in SHM). Thus, damage to G-C base pairs might lead to mutations at G-C pairs and concomitantly recruit enzymes for SHM at A-T base pairs.…”

Section: Discussionmentioning

confidence: 99%

Correlation of somatic hypermutation specificity and A-T base pair substitution errors by DNA polymerase η during copying of a mouse immunoglobulin κ light chain transgene

Pavlov

Rogozin

Galkin

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

118

110

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To test the hypothesis that inaccurate DNA synthesis by mammalian DNA polymerase (pol ) contributes to somatic hypermutation (SHM) of Ig genes, we measured the error specificity of mouse pol during synthesis of each strand of a mouse Ig light chain transgene. We then compared the results to the base substitution specificity of SHM of this same gene in the mouse. The in vitro and in vivo base substitution spectra shared a number of common features. A highly significant correlation was observed for overall substitutions at A-T pairs but not for substitutions at G-C pairs. Sixteen mutational hotspots at A-T pairs observed in vivo were also found in spectra generated by mouse pol in vitro. The correlation was strongest for errors made by pol during synthesis of the non-transcribed strand, but it was also observed for synthesis of the transcribed strand. These facts, and the distribution of substitutions generated in vivo, support the hypothesis that pol contributes to SHM of Ig genes at A-T pairs via short patches of low fidelity DNA synthesis of both strands, but with a preference for the non-transcribed strand.H igh affinity antibodies result from somatic hypermutation (SHM) of Ig genes followed by selection. The SHM process introduces base substitutions at a very high rate into DNA encoding the variable regions of immunoglobulins (1-4). Although the mechanism for introducing these sequence changes is currently unknown, several features of SHM specificity offer clues to the DNA transactions that might be involved. For example, SHM primarily occurs in two highly mutable DNA sequence motifs (5-9). One is the RGYW sequence (the underlined G is mutated, R ϭ A or G, Y ϭ T or C, and W ϭ A or T), which is found in SHM substitution spectra in equal proportions in both DNA strands. The other is the WA motif, where substitutions are more likely in one strand than the other (5, 7-10). A clue to the origins of the substitutions in the WA motif is the observation that their type and location correlates with the base substitution error specificity of human DNA polymerase when copying a bacterial gene sequence in a model system in vitro (8). Based on that correlation and additional considerations of the two mutable motifs (11), we suggested that errors at A-T base pairs by pol may contribute to as much as one third of somatic mutations in Ig genes, preferentially during synthesis of the non-transcribed strand. This hypothesis is supported by the observation that XP-V patients lacking active polymerase have a lower proportion of somatic substitutions at A-T base pairs in Ig genes (12). Because pol error specificity does not correlate with substitutions in the RGYW sequence motif, and because those substitutions are distributed equally on both strands, we further suggested that SHM may involve more than one DNA transaction and more than one DNA polymerase (8). This finding is consistent with the two-phase model of SHM proposed earlier (9, 13). Other DNA polymerases suggested to participate in SHM include pol (14-16), pol (17, 18) ...

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Section: Discussionmentioning

confidence: 99%

Correlation of somatic hypermutation specificity and A-T base pair substitution errors by DNA polymerase η during copying of a mouse immunoglobulin κ light chain transgene

Pavlov

Rogozin

Galkin

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

118

110

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“…However, other explanations exist that could account for this differential mutation of the V versus C regions without the requirement of B cell-specific cis-acting sequences. One possibility is that the mutator associates with the RNA polymerase II complex to produce mutations during the initiation phase, but eventually falls off this complex during the elongation phase (30,31). Another possibility is that mutation depends on the availability of single-stranded DNA (see below) and that there is more single-stranded DNA in the V region than in the C region, caused by (i) stable RNA-DNA hybrids in the V region as a result of transcription that leaves the nontranscribed strand single-stranded, (ii) a higher RNA polymerase II density in the V region than in the C region, or (iii) transcription inducing stable secondary DNA structures in the V region with single-stranded loops of DNA (6).…”

Section: Discussionmentioning

confidence: 99%

Somatic hypermutation of the AID transgene in B and non-B cells

Martín

Scharff

2002

Proc. Natl. Acad. Sci. U.S.A.

150

109

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Somatic hypermutation (SHM) of the Ig genes is required for affinity maturation of the humoral response to foreign antigens. Activation-induced cytidine deaminase (AID), which is specifically expressed in germinal center centroblasts, is indispensable for this process. Expression of AID is sufficient to activate SHM in hybridomas, non-B cells, and Escherichia coli, suggesting that it initiates the mutational process by deaminating DNA. However, the cisacting sequences that are responsible for targeting AID activity to the variable (V) region of Ig genes are unknown. Here we show that expression of AID in B cell lines (i.e., Burkitt's lymphoma Ramos and hybridoma P1-5) not only causes hypermutation of Ig sequences, but also of the AID transgene itself. Because it is possible that B cell-specific transacting factors bind to and recruit the ''mutator'' to the AID transgene, we tested whether the AID transgene can mutate in non-B cells. Indeed, we show that expression of AID in Chinese hamster ovary cells causes SHM of both the Ig and AID transgenes. These data suggest that high transcription rates alone may predispose any gene to mutation by AID but do not preclude that there are specific B cell factors that account for the extremely high rate of V mutation in vivo and its targeting to the V region.A ffinity maturation of the antibody response is mediated by somatic hypermutation (SHM) of the antibody genes with subsequent selection of B cell clones that produce higher affinity antibodies to the immunizing antigen. SHM causes point mutations and occasional deletions and insertions at very high rates of Ϸ10 Ϫ3 bp per generation and occurs during the centroblast stage of B cell differentiation. The mutations are restricted to the variable region (V region) that encodes the antibody binding site and to sequences that are Ϸ1.5 kb downstream from the Ig promoter. Some of these mutations increase the affinity of the antibody so that it can neutralize viruses and toxins and inactivate pathogenic organisms.Mice and humans with mutations in activation-induced cytidine deaminase (AID) have defects in SHM (1, 2), class-switch recombination (1), and gene conversion (3, 4). Based on the sequence similarity of AID to the RNA-editing enzyme APOBEC-1 (5), it was postulated that AID might function by editing a specific message that results in the production of an altered protein that subsequently causes mutation (6). However, the higher than expected number of transition mutations in V regions (7) raises the possibility that AID might be a DNAspecific cytidine deaminase that converts C to U nucleotides directly in the DNA of the V region. In fact, we recently showed that AID induced the P1-5 hybridoma to exclusively mutate G⅐C bp, and most of these mutations were transition mutations (8). With the finding that AID can induce SHM in non-B cells (9) and Escherichia coli (4), it is more likely that AID is a DNA-specific cytidine deaminase.The mechanism for targeting of SHM to the V region of Ig genes is not known. Interestingly, SHM h...

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“…For example, somatic joining of the V, D, and J gene segments, mediated by the RAGs, occurs during early B cell development (1). In addition, somatic hypermutation (SHM) 4 of the rearranged V(D)J sequence, mediated by the activation-induced deaminase gene (AID), occurs in activated B cells in response to antigenic challenge (2). The combinatory effects of SHM and the selection for B cells expressing Ig with a higher affinity for Ag leads to affinity maturation (3).…”

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confidence: 99%

“…Accumulating evidence has identified a connection between SHM and transcription (4). For example, the expression levels of transgenes strongly correlate with the levels of mutation (5)(6)(7).…”

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confidence: 99%

Roles of the Ig κ Light Chain Intronic and 3′ Enhancers inIgkSomatic Hypermutation

Inlay

Gao

Odegard

et al. 2006

The Journal of Immunology

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Somatic hypermutation (SHM) of the rearranged Ig genes is required for the affinity maturation of Abs. SHM is almost exclusively targeted to the rearranged Ig loci, but the mechanism of this gene-specific targeting remains unclear. The Ig κ L chain locus contains multiple enhancers, including the MAR/intronic (iEκ) and 3′ enhancers (3′Eκ). Previous transgenic studies indicate that both κ enhancers are individually necessary for SHM of Igk. In contrast, later studies of Ag-selected Vκ genes in 3′Eκ−/− mice found no absolute requirement for 3′Eκ in κ SHM. To address the roles of the two κ enhancers in SHM in a physiological context, we analyzed SHM of the endogenous Igk in mice with a targeted deletion of either iEκ or 3′Eκ in Peyer’s patch germinal center B cells. Our findings indicate that, although 3′Eκ is quantitatively important for SHM of Igk, iEκ is not required for κ SHM. In addition, a reduction of κ mRNA levels is also detected in activated 3′Eκ−/− B cells. These findings suggest that iEκ and 3′Eκ play distinct roles in regulating Igk transcription and SHM.

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Somatic Hypermutation of Immunoglobulin Genes is Linked to Transcription

Cited by 40 publications

References 26 publications

Correlation of somatic hypermutation specificity and A-T base pair substitution errors by DNA polymerase η during copying of a mouse immunoglobulin κ light chain transgene

Correlation of somatic hypermutation specificity and A-T base pair substitution errors by DNA polymerase η during copying of a mouse immunoglobulin κ light chain transgene

Somatic hypermutation of the AID transgene in B and non-B cells

Roles of the Ig κ Light Chain Intronic and 3′ Enhancers inIgkSomatic Hypermutation

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