Somatic hypermutation (SHM) and class switch recombination (CSR) diversify immunoglobulin (Ig) genes and are initiated by the activation-induced deaminase (AID), a single-stranded DNA cytidine deaminase thought to engage its substrate during RNA polymerase II (RNAPII) transcription. Through a genetic screen, we identified numerous potential factors involved in SHM, including elongation factor 1 homolog (ELOF1), a component of the RNAPII elongation complex that functions in transcription-coupled nucleotide excision repair (TC-NER) and transcription elongation. Loss of ELOF1 compromises SHM, CSR, and AID action in mammalian B cells and alters RNAPII transcription by reducing RNAPII pausing downstream of transcription start sites and levels of serine 5 but not serine 2 phosphorylated RNAPII throughout transcribed genes. ELOF1 must bind to RNAPII to be a proximity partner for AID and to function in SHM and CSR, and TC-NER is not required for SHM. We propose that ELOF1 helps create the appropriate stalled RNAPII substrate on which AID acts.

• Klíčová slova
• AID, ELOF1, RNA polymerase II, class switch recombination, somatic hypermutation, transcription,
• MeSH
• AICDA (aktivací indukovaná cytidindeamináza) MeSH
• B-lymfocyty * imunologie   metabolismus   MeSH
• cytidindeaminasa metabolismus   genetika   MeSH
• fosfoproteiny * genetika   metabolismus   MeSH
• fosforylace MeSH
• genetická transkripce MeSH
• lidé MeSH
• myši knockoutované MeSH
• myši MeSH
• oprava DNA MeSH
• přesmyk imunoglobulinových tříd * MeSH
• RNA-polymerasa II metabolismus   genetika   MeSH
• somatická hypermutace imunoglobulinových genů * MeSH
• transkripční elongační faktory * genetika   metabolismus   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• myši MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• AICDA (aktivací indukovaná cytidindeamináza) MeSH
• cytidindeaminasa MeSH
• fosfoproteiny * MeSH
• RNA-polymerasa II MeSH
• transkripční elongační faktory * MeSH

Simian virus 40 (SV40) is a monkey virus with tumorigenic potential in rodents and is associated with several types of human cancers, including lymphomas. A related Merkel cell polyomavirus causes carcinoma in humans by expressing truncated large tumor antigen (LT), with truncations caused by APOBEC family of cytidine deaminase-induced mutations. AID (activation-induced cytidine deaminase), a member of the APOBEC family, is the initiator of the antibody diversification process known as somatic hypermutation and its aberrant expression and targeting is a frequent source of lymphomagenesis. In this study, we investigated whether AID could cause mutations in SV40 LT. We demonstrate that the SV40 enhancer has strong somatic hypermutation targeting activity in several cell types and that AID-induced mutations accumulate in SV40 LT in B cells and kidney cells and cause truncated LT expression in B cells. Our results argue that the ability of the SV40 enhancer to target somatic hypermutation to LT is a potential source of LT truncation events that could contribute to tumorigenesis in various cell types, thereby linking SV40 infection with malignant development through a novel mutagenic pathway.

• Klíčová slova
• AID, Enhancer, Large tumor antigen, SV40, Somatic hypermutation, Tumorigenesis,
• MeSH
• AICDA (aktivací indukovaná cytidindeamináza) MeSH
• antigeny transformující polyomavirové genetika   metabolismus   MeSH
• antigeny virové nádorové genetika   metabolismus   MeSH
• B-lymfocyty virologie   metabolismus   imunologie   MeSH
• buněčné linie MeSH
• cytidindeaminasa * genetika   metabolismus   MeSH
• infekce onkogenními viry genetika   virologie   MeSH
• karcinogeneze genetika   MeSH
• lidé MeSH
• mutace MeSH
• opičí virus SV40 * genetika   MeSH
• polyomavirové infekce genetika   virologie   MeSH
• somatická hypermutace imunoglobulinových genů genetika   MeSH
• zesilovače transkripce * genetika   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• AICDA (aktivací indukovaná cytidindeamináza) MeSH
• antigeny transformující polyomavirové MeSH
• antigeny virové nádorové MeSH
• cytidindeaminasa * MeSH

The Czech Republic, a part of the former Czechoslovakia, has been at the forefront of several research directions in virology, genetics and physiology [...].

• MeSH
• virologie * MeSH
• Publikační typ
• práce podpořená grantem MeSH
• úvodníky MeSH
• Geografické názvy
• Česká republika MeSH

Somatic hypermutation (SHM) drives the genetic diversity of Ig genes in activated B cells and supports the generation of Abs with increased affinity for Ag. SHM is targeted to Ig genes by their enhancers (diversification activators [DIVACs]), but how the enhancers mediate this activity is unknown. We show using chicken DT40 B cells that highly active DIVACs increase the phosphorylation of RNA polymerase II (Pol II) and Pol II occupancy in the mutating gene with little or no accompanying increase in elongation-competent Pol II or production of full-length transcripts, indicating accumulation of stalled Pol II. DIVAC has similar effect also in human Ramos Burkitt lymphoma cells. The DIVAC-induced stalling is weakly associated with an increase in the detection of ssDNA bubbles in the mutating target gene. We did not find evidence for antisense transcription, or that DIVAC functions by altering levels of H3K27ac or the histone variant H3.3 in the mutating gene. These findings argue for a connection between Pol II stalling and cis-acting targeting elements in the context of SHM and thus define a mechanistic basis for locus-specific targeting of SHM in the genome. Our results suggest that DIVAC elements render the target gene a suitable platform for AID-mediated mutation without a requirement for increasing transcriptional output.

• MeSH
• AICDA (aktivací indukovaná cytidindeamináza) MeSH
• aktivace lymfocytů MeSH
• Burkittův lymfom genetika   imunologie   MeSH
• cytidindeaminasa genetika   MeSH
• genetická transkripce MeSH
• imunoglobuliny genetika   metabolismus   MeSH
• kur domácí MeSH
• lidé MeSH
• mutace genetika   MeSH
• mutageneze cílená MeSH
• podskupiny B-lymfocytů imunologie   MeSH
• ptačí proteiny genetika   metabolismus   MeSH
• RNA-polymerasa II genetika   metabolismus   MeSH
• rozmanitost protilátek MeSH
• somatická hypermutace imunoglobulinových genů MeSH
• zesilovače transkripce genetika   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• AICDA (aktivací indukovaná cytidindeamináza) MeSH
• cytidindeaminasa MeSH
• imunoglobuliny MeSH
• ptačí proteiny MeSH
• RNA-polymerasa II MeSH

Secondary diversification of the Ig repertoire occurs through somatic hypermutation (SHM), gene conversion (GCV), and class switch recombination (CSR)-three processes that are initiated by activation-induced cytidine deaminase (AID). AID targets Ig genes at orders of magnitude higher than the rest of the genome, but the basis for this specificity is poorly understood. We have previously demonstrated that enhancers and enhancer-like sequences from Ig genes are capable of stimulating SHM of neighboring genes in a capacity distinct from their roles in increasing transcription. Here, we use an in vitro proteomics approach to identify E-box, MEF2, Ets, and Ikaros transcription factor family members as potential binders of these enhancers. ChIP assays in the hypermutating Ramos B cell line confirmed that many of these factors bound the endogenous Igλ enhancer and/or the IgH intronic enhancer (Eμ) in vivo. Further investigation using SHM reporter assays identified binding sites for E2A and MEF2B in Eμ and demonstrated an association between loss of factor binding and decreases in the SHM stimulating activity of Eμ mutants. Our results provide novel insights into trans-acting factors that dictate SHM targeting and link their activity to specific DNA binding sites within Ig enhancers.

• Klíčová slova
• AID, E2A, MEF2B, Ramos B cell line, Somatic hypermutation,
• MeSH
• geny pro imunoglobuliny MeSH
• kur domácí MeSH
• lidé MeSH
• somatická hypermutace imunoglobulinových genů fyziologie   MeSH
• transkripční faktory genetika   metabolismus   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH
• Názvy látek
• transkripční faktory MeSH