RESUMO
Class switch recombination (CSR) requires activation-induced deaminase (AID) to instigate double-stranded DNA breaks at the immunoglobulin locus. DNA breaks activate the DNA damage response (DDR) by inducing phosphorylation of histone H2AX followed by non-homologous end joining (NHEJ) repair. We carried out a genome-wide screen to identify CSR factors. We found that Usp22, Eny2, and Atxn7, members of the Spt-Ada-Gcn5-acetyltransferase (SAGA) deubiquitination module, are required for deubiquitination of H2BK120ub following DNA damage, are critical for CSR, and function downstream of AID. The SAGA deubiquitinase activity was required for optimal irradiation-induced γH2AX formation, and failure to remove H2BK120ub inhibits ATM- and DNAPK-induced γH2AX formation. Consistent with this effect, these proteins were found to function upstream of various double-stranded DNA repair pathways. This report demonstrates that deubiquitination of histone H2B impacts the early stages of the DDR and is required for the DNA repair phase of CSR.
Assuntos
Proteínas Mutadas de Ataxia Telangiectasia/metabolismo , Reparo do DNA , Proteína Quinase Ativada por DNA/metabolismo , Proteínas de Ligação a DNA/metabolismo , Histonas/metabolismo , Switching de Imunoglobulina/genética , Complexos Multiproteicos/metabolismo , Proteínas Nucleares/metabolismo , Ubiquitinação , Animais , Citidina Desaminase , Quebras de DNA de Cadeia Dupla , Reparo do DNA por Junção de Extremidades/efeitos da radiação , Reparo do DNA/efeitos da radiação , Endopeptidases/metabolismo , Recombinação Homóloga/efeitos da radiação , Camundongos , Interferência de RNA , Radiação Ionizante , Hipermutação Somática de Imunoglobulina/efeitos da radiação , Fatores de Transcrição/metabolismo , Ubiquitina Tiolesterase , Ubiquitinação/efeitos da radiaçãoRESUMO
Cellular DNA double-strand break-repair pathways have evolved to protect the integrity of the genome from a continual barrage of potentially detrimental insults. Inherited mutations in genes that control this process result in an inability to properly repair DNA damage, ultimately leading to developmental defects and also cancer predisposition. Here, we describe a patient with a previously undescribed syndrome, which we have termed RIDDLE syndrome (radiosensitivity, immunodeficiency, dysmorphic features and learning difficulties), whose cells lack an ability to recruit 53BP1 to sites of DNA double-strand breaks. As a consequence, cells derived from this patient exhibit a hypersensitivity to ionizing radiation, cell cycle checkpoint abnormalities, and impaired end-joining in the recombined switch regions. Sequencing of TP53BP1 and other genes known to regulate ionizing radiation-induced 53BP1 foci formation in this patient failed to detect any mutations. Therefore, these data indicate the existence of a DNA double-strand break-repair protein that functions upstream of 53BP1 and contributes to the normal development of the human immune system.
