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.

• Keywords
• AID, ELOF1, RNA polymerase II, class switch recombination, somatic hypermutation, transcription,
• MeSH
• AICDA (Activation-Induced Cytidine Deaminase) MeSH
• B-Lymphocytes * immunology   metabolism   MeSH
• Cytidine Deaminase metabolism   genetics   MeSH
• Phosphoproteins * genetics   metabolism   MeSH
• Phosphorylation MeSH
• Transcription, Genetic MeSH
• Humans MeSH
• Mice, Knockout MeSH
• Mice MeSH
• DNA Repair MeSH
• Immunoglobulin Class Switching * MeSH
• RNA Polymerase II metabolism   genetics   MeSH
• Somatic Hypermutation, Immunoglobulin * MeSH
• Transcriptional Elongation Factors * genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• AICDA (Activation-Induced Cytidine Deaminase) MeSH
• Cytidine Deaminase MeSH
• Phosphoproteins * MeSH
• RNA Polymerase II MeSH
• Transcriptional Elongation Factors * 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.

• Keywords
• AID, Enhancer, Large tumor antigen, SV40, Somatic hypermutation, Tumorigenesis,
• MeSH
• AICDA (Activation-Induced Cytidine Deaminase) MeSH
• Antigens, Polyomavirus Transforming genetics   metabolism   MeSH
• Antigens, Viral, Tumor genetics   metabolism   MeSH
• B-Lymphocytes virology   metabolism   immunology   MeSH
• Cell Line MeSH
• Cytidine Deaminase * genetics   metabolism   MeSH
• Tumor Virus Infections genetics   virology   MeSH
• Carcinogenesis genetics   MeSH
• Humans MeSH
• Mutation MeSH
• Simian virus 40 * genetics   MeSH
• Polyomavirus Infections genetics   virology   MeSH
• Somatic Hypermutation, Immunoglobulin genetics   MeSH
• Enhancer Elements, Genetic * genetics   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• AICDA (Activation-Induced Cytidine Deaminase) MeSH
• Antigens, Polyomavirus Transforming MeSH
• Antigens, Viral, Tumor MeSH
• Cytidine Deaminase * 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 (Activation-Induced Cytidine Deaminase) MeSH
• Lymphocyte Activation MeSH
• Burkitt Lymphoma genetics   immunology   MeSH
• Cytidine Deaminase genetics   MeSH
• Transcription, Genetic MeSH
• Immunoglobulins genetics   metabolism   MeSH
• Chickens MeSH
• Humans MeSH
• Mutation genetics   MeSH
• Mutagenesis, Site-Directed MeSH
• B-Lymphocyte Subsets immunology   MeSH
• Avian Proteins genetics   metabolism   MeSH
• RNA Polymerase II genetics   metabolism   MeSH
• Antibody Diversity MeSH
• Somatic Hypermutation, Immunoglobulin MeSH
• Enhancer Elements, Genetic genetics   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• AICDA (Activation-Induced Cytidine Deaminase) MeSH
• Cytidine Deaminase MeSH
• Immunoglobulins MeSH
• Avian Proteins MeSH
• RNA Polymerase II MeSH