RESUMO
Antibody diversification by somatic hypermutation, gene conversion, and class switch recombination is completely dependent on activation-induced cytidine deaminase (AID). A recent report showing induction of DNA mutations in Escherichia coli by overexpression of AID, Apobec-1, and related members of the RNA-editing cytidine deaminase family suggested that they may directly modify deoxycytidine in DNA in mammalian cells (DNA-editing model). We therefore examined whether Apobec-1 bona fide RNA-editing enzyme could show somatic hypermutation and class switching activities in murine B lymphocytes and fibroblasts. Unlike AID, Apobec-1 was unable to induce somatic hypermutation or class switching. The results force a reevaluation of the physiological significance of the DNA deaminase activities of AID and Apobec-1 in E. coli and in vitro.
Assuntos
Apolipoproteínas B/genética , Citidina Desaminase/genética , Edição de RNA/genética , Hipermutação Somática de Imunoglobulina/imunologia , Células 3T3 , Desaminase APOBEC-1 , Animais , Apolipoproteínas B/imunologia , Linfócitos B/imunologia , Linfócitos B/fisiologia , Linhagem Celular , Clonagem Molecular , Citidina Desaminase/imunologia , Escherichia coli/genética , Escherichia coli/imunologia , Genes Reporter , Proteínas de Fluorescência Verde , Proteínas Luminescentes/genética , Mamíferos , Camundongos , Mutagênese , Edição de RNA/imunologia , RNA Mensageiro/genética , Proteínas Recombinantes/imunologia , Hipermutação Somática de Imunoglobulina/genética , Transcrição GênicaRESUMO
Activation-induced cytidine deaminase (AID), a putative RNA-editing enzyme, is indispensable for somatic hypermutation (SHM), class switch recombination, and gene conversion of immunoglobulin genes, which indicates a common molecular mechanism for these phenomena. Here we show that ectopic expression of AID alone can induce hypermutation in an artificial GFP substrate in NIH 3T3 murine fibroblast cells. The frequency of mutations was closely correlated with the level of transcription of the target gene, and the distribution of mutations in NIH 3T3 cells was similar to those of SHM in B lymphocytes. These results indicate that AID is sufficient for the generation of SHM in an actively transcribed gene in fibroblasts, as well as B cells, and that any of the required cofactors must be present in these fibroblasts.
