title: Aiolos controls gene conversion and cell death in DT40 B cells.
abstract: The Ikaros family transcription factor Aiolos is important for B cell function, since B cells of Aiolos-null mutant mice exhibit an activated phenotype, enhanced B-cell receptor (BCR) signalling response and develop a systemic lupus erythematosus (SLE) type autoimmune disease. Aiolos has also been reported to interact with anti-apoptotic Bcl-2 and Bcl-x(L) in T cells, but whether Aiolos regulates cell death has not been studied in B cells. Here we show that the disruption of Aiolos in the DT40 B cell line induces a cell death sensitive phenotype, as the Aiolos(-/-) cells are more prone to apoptosis by nutritional stress, BCR cross-linking, UV- or gamma-irradiation. Furthermore, the Aiolos(-/-) cells have defective Ig gene conversion providing evidence that Aiolos is needed for the somatic diversification of the BCR repertoire. The re-expression of DNA-binding isoform Aio-1 was able to restore the gene conversion defect of the Aiolos-deficient cells, whereas the introduction of dominant negative isofom Aio-2 had no effect on gene conversion, thus demonstrating the functional importance of alternative splicing within Ikaros family. Although the Aiolos(-/-) cells exhibit reduced expression of activation-induced cytidine deaminase (AID), ectopic AID overexpression did not restore the gene conversion defect in the Aiolos(-/-) cells. Our findings indicate that Aiolos may regulate gene conversion in an AID independent manner.
authors.affiliation: Turku Graduate School of Biomedical Sciences, University of Turku, Turku, Finland. elli.narvi@utu.fi
authors.forename: E
authors.initials: E
authors.lastname: Narvi
authors.forename: K-P
authors.initials: KP
authors.lastname: Nera
authors.forename: P
authors.initials: P
authors.lastname: Terho
authors.forename: L
authors.initials: L
authors.lastname: Mustonen
authors.forename: J
authors.initials: J
authors.lastname: Granberg
authors.forename: O
authors.initials: O
authors.lastname: Lassila
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology*; D016923:Cell Death / Q000235:genetics*; D002478:Cells, Cultured; D002642:Chick Embryo; D043525:Cytosine Deaminase / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics; D005434:Flow Cytometry; D016044:Fusion Proteins, bcr-abl; D005785:Gene Conversion / Q000235:genetics*; D005786:Gene Expression Regulation; D020868:Gene Silencing; D051740:Ikaros Transcription Factor; D051379:Mice; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D015534:Trans-Activators / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; C491396:Ikzf3 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D051740:Ikaros Transcription Factor; D011505:Protein-Tyrosine Kinases; D016044:Fusion Proteins, bcr-abl; D043525:Cytosine Deaminase