Epigenetics of the antibody response

Li, Guideng; Zan, Hong; Xu, Zhenming; Casali, Paolo

doi:10.1016/j.it.2013.03.006

Cited by 81 publications

(86 citation statements)

References 124 publications

(193 reference statements)

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“…The recruitment may occur through a combination of chromatin modifications, protein modifications, and the help of molecular chaperones. It is known that when the Ig locus undergoes SHM and CSR, the local chromatin undergoes epigenetic modifications (50), and a protein factor may recruit UNG2 to these chromatin tags. Alternatively, since the action of AID requires transcription of target genes (51), UNG may be recruited to the transcript elongation complexes.…”

Section: Discussionmentioning

confidence: 99%

Genomic Uracil Homeostasis during Normal B Cell Maturation and Loss of This Balance during B Cell Cancer Development

Shalhout

Haddad

Sosin

et al. 2014

Molecular and Cellular Biology

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d Activation-induced deaminase (AID) converts DNA cytosines to uracils in immunoglobulin genes, creating antibody diversification. It also causes mutations and translocations that promote cancer. We examined the interplay between uracil creation by AID and its removal by UNG2 glycosylase in splenocytes undergoing maturation and in B cell cancers. The genomic uracil levels remain unchanged in normal stimulated B cells, demonstrating a balance between uracil generation and removal. In stimulated UNG ؊/؊ cells, uracil levels increase by 11-to 60-fold during the first 3 days. In wild-type B cells, UNG2 gene expression and enzymatic activity rise and fall with AID levels, suggesting that UNG2 expression is coordinated with uracil creation by AID. Remarkably, a murine lymphoma cell line, several human B cell cancer lines, and human B cell tumors expressing AID at high levels have genomic uracils comparable to those seen with stimulated UNG ؊/؊ splenocytes. However, cancer cells express UNG2 gene at levels similar to or higher than those seen with peripheral B cells and have nuclear uracil excision activity comparable to that seen with stimulated wild-type B cells. We propose that more uracils are created during B cell cancer development than are removed from the genome but that the uracil creation/excision balance is restored during establishment of cell lines, fixing the genomic uracil load at high levels. When B lymphocytes are activated through antigen presentation, they acquire hypermutations in the immunoglobulin (Ig) genes, facilitating affinity maturation of antibodies. An enzyme, activation-induced deaminase (AID), initiates these events by converting cytosines in DNA to uracil (1-4). The introduction of this rare base into DNA leads to a very high frequency of base substitution mutations in the Ig variable domain (known as somatic hypermutations [SHMs]; reviewed in references 5 and 6). Generation of uracils is also the first step in the creation of strand breaks in the switch regions of Ig genes, leading to the replacement of the constant domain with other domains such as ␥, in a process called class-switch recombination (CSR; reviewed in reference 7). AID also binds near the transcription start sites of a large number of actively transcribed genes (8) and mutates a number of additional genes, including those encoding BCL-6, MYC, PAX-5, and PIM1 (9-12). The uracils generated by AID are thought to be removed by the nuclear form of the uracil-DNA glycosylase, UNG2, creating abasic sites that are repaired by error-prone copying mechanisms causing hypermutations (13,14). Another uracil-DNA glycosylase, SMUG1, is normally considered the backup enzyme for UNG2 (15), but overproduction of SMUG1 is required for it to complement an UNG Ϫ/Ϫ mutant during CSR (16). Additionally, DNA mismatch repair (MMR) also plays a role in shaping the mutation spectrum in SHM (17).There is a strong connection between expression of AID and cancers in animals. Constitutive expression of AID in mice causes T cell cancers (18). Many human...

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Section: Discussionmentioning

confidence: 99%

Genomic Uracil Homeostasis during Normal B Cell Maturation and Loss of This Balance during B Cell Cancer Development

Shalhout

Haddad

Sosin

et al. 2014

Molecular and Cellular Biology

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“…Epigenetic marks/changes are induced in B cells by signals triggered by CD40, Toll-like receptors (TLRs) and cytokine receptors to regulate CSR/SHM and plasma cell differentiation (5, 6, 26–34). They inform the antibody response to exogenous (e.g., microbial) antigens in healthy subjects or self-antigens in autoimmune patients (5).…”

Section: Introductionmentioning

confidence: 99%

“…They inform the antibody response to exogenous (e.g., microbial) antigens in healthy subjects or self-antigens in autoimmune patients (5). miRNAs also cross-regulate with DNA methylation and histone modifications (35).…”

Section: Introductionmentioning

confidence: 99%

MicroRNAs in lupus

2014

Self Cite

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Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by the production of an array of pathogenic autoantibodies, including high-affinity anti-dsDNA IgG antibodies, which plays an important role in disease development and progression. Lupus preferentially affects women during their reproductive years. The pathogenesis of lupus is contributed by both genetic factors and epigenetic modifications that arise from exposure to the environment. Epigenetic marks, including DNA methylation, histone post-translational modifications and microRNAs (miRNAs), interact with genetic programs to regulate immune responses. Epigenetic modifications influence gene expression and modulate B cell functions, such as class switch DNA recombination (CSR), somatic hypermutation (SHM) and plasma cell differentiation, thereby informing the antibody response. Epigenetic dysregulation can result in aberrant antibody responses to exogenous antigens or self-antigens, such as chromatin, histones and dsDNA in lupus. miRNAs play key roles in the post-transcriptional regulation of most gene-regulatory pathways and regulate both the innate and the adaptive immune responses. In mice, dysregulation of miRNAs leads to aberrant immune responses and development of systemic autoimmunity. Altered miRNA expression has been reported in human autoimmune diseases, including lupus. The dysregulation of miRNAs in lupus could be the result of multiple environmental factors, such as sex hormones and viral or bacterial infection. Modulation of miRNA is a potential therapeutic strategy for lupus.

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“…Furthermore, a role of histone modifications, associated with KMT2D and KDM6A function, has been clearly demonstrated in the immune response [14,15].…”

Section: Introductionmentioning

confidence: 98%