Separation of Mutational and Transcriptional Enhancers in Ig Genes

Kothapalli, Naga Rama; Collura, Kaitlin M.; Norton, Darrell D.; Fugmann, Sebastian D.

doi:10.4049/jimmunol.1101568

Cited by 20 publications

(32 citation statements)

References 30 publications

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“…These studies imply that transcription driven by any promoter might support SHM. This notion is consistent with later studies suggesting that the level of transcription is not necessarily correlated with the level of mutations [80, 81]. It has been long proposed that the mutator enzyme (now known as AID) may associate with RNAP II to mediate SHM [82].…”

Section: Cis Regulatory Elements In Shm Targetingsupporting

confidence: 88%

Generation and repair of AID-initiated DNA lesions in B lymphocytes

Chen

Wang

2014

Front. Med.

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Activation-induced deaminase (AID) initiates the secondary antibody diversification process in B lymphocytes. In mammalian B cells, this process includes somatic hypermutation (SHM) and class switch recombination (CSR), both of which require AID. AID induces U:G mismatch lesions in DNA that are subsequently converted into point mutations or DNA double stranded breaks during SHM/CSR. In a physiological context, AID targets immunoglobulin (Ig) loci to mediate SHM/CSR. However, recent studies reveal genome-wide access of AID to numerous non-Ig loci. Thus, AID poses a threat to the genome of B cells if AID-initiated DNA lesions cannot be properly repaired. In this review, we focus on the molecular mechanisms that regulate the specificity of AID targeting and the repair pathways responsible for processing AID-initiated DNA lesions.

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Section: Cis Regulatory Elements In Shm Targetingsupporting

confidence: 88%

Generation and repair of AID-initiated DNA lesions in B lymphocytes

Chen

Wang

2014

Front. Med.

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“…Importantly, this DIVAC ( div ersification ac tivator) region includes, but is not limited to, the defined IgL enhancer, which was previously shown not to be required for SHM in the IgL locus (9, 29). The identity of the functionally critical elements, however, is in dispute (9, 25), and thus far, no specific collection of DNA binding sites has been identified that can explain DIVAC function (24, 27). …”

Section: Introductionmentioning

confidence: 99%

“…Intriguingly, all of the studies of the DT40 IgL locus have narrowed in on regions containing E boxes (9, 25, 28). The E box motif is defined by the consensus sequence CANNTG, and serves as a binding site for class I helix-loop-helix DNA binding proteins, or E proteins, which have well characterized roles in B and T lymphocyte development (30).…”

Section: Introductionmentioning

confidence: 99%

A Critical Context-Dependent Role for E Boxes in the Targeting of Somatic Hypermutation

McDonald

Alinikula

Buerstedde

et al. 2013

The Journal of Immunology

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Secondary B cell repertoire diversification occurs by somatic hypermutation (SHM) in germinal centers following antigen stimulation. In SHM, activation-induced cytidine deaminase (AID) mutates the variable region of the immunoglobulin (Ig) genes to increase the affinity of antibodies. Although somatic hypermutation (SHM) acts primarily at Ig loci, low levels of off-target mutation can result in oncogenic DNA damage, illustrating the importance of understanding SHM targeting mechanisms. A candidate targeting motif is the E box, a short DNA sequence (CANNTG) found abundantly in the genome and in many SHM target genes. Using a reporter assay in chicken DT40 B cells, we previously identified a 1928-bp portion of the chicken IgL locus capable of supporting robust SHM. Here, we demonstrate that mutation of all 20 E boxes in this fragment reduces SHM targeting activity by 90%, and that mutation of subsets of E boxes reveals a functional hierarchy in which E boxes within "core" targeting regions are of greatest importance. Strikingly, when the sequence and spacing of the 20 E boxes is preserved but surrounding sequences are altered, SHM targeting activity is eliminated. Hence, while E boxes are vital SHM targeting elements, their function is completely dependent on their surrounding sequence context. These results suggest an intimate cooperation between E boxes and other sequence motifs in SHM targeting to Ig loci and perhaps also in restricting mistargeting to certain non-Ig loci.

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“…In mice, deletion of this region in the Igh locus diminishes Pol II and ablates Spt5 and AID recruitment (8, 31). In DT40 cells, deletions in this region in the Igλ locus modulate transcription and reduce mutagenesis (32–34). Thus, a definitive role for the 3′ enhancer region in transcription and mutation is unclear at this time.…”

Section: Discussionmentioning

confidence: 99%

Topoisomerase I deficiency causes RNA polymerase II accumulation and increases AID abundance in immunoglobulin variable genes

et al. 2015

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Activation-induced deaminase (AID) is a DNA cytosine deaminase that diversifies immunoglobulin genes in B cells. Recent work has shown that RNA Polymerase II (Pol II) accumulation correlates with AID recruitment. However, a direct link between Pol II and AID abundance has not been tested. We used the DT40 B-cell line to manipulate levels of Pol II by decreasing topoisomerase I (Top1), which relaxes DNA supercoiling in front of the transcription complex. Top1 was decreased by stable transfection of a short hairpin RNA against Top1, which produced an accumulation of Pol II in transcribed genes, compared to cells transfected with sh-control RNA. The increased Pol II density enhanced AID recruitment to variable genes in the λ light chain locus, and resulted in higher levels of somatic hypermutation and gene conversion. It has been proposed by another lab that AID itself might directly suppress Top1 to increase somatic hypermutation. However, we found that in both AID+/+ and AID−/− B cells from DT40 and mice, Top1 protein levels were identical, indicating that the presence or absence of AID did not decrease Top1 expression. Rather, our results suggest that the mechanism for increased diversity when Top1 is reduced is that Pol II accumulates and recruits AID to variable genes.

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Separation of Mutational and Transcriptional Enhancers in Ig Genes

Cited by 20 publications

References 30 publications

Generation and repair of AID-initiated DNA lesions in B lymphocytes

Generation and repair of AID-initiated DNA lesions in B lymphocytes

A Critical Context-Dependent Role for E Boxes in the Targeting of Somatic Hypermutation

Topoisomerase I deficiency causes RNA polymerase II accumulation and increases AID abundance in immunoglobulin variable genes

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