Disruption of mutually negative regulatory feedback loop between interferon-inducible p202 protein and the E2F family of transcription factors in lupus-prone mice.
Studies have identified IFN-inducible Ifi202 gene as a lupus susceptibility gene (encoding p202 protein) in mouse models of lupus disease. However, signaling pathways that regulate the Ifi202 expression in cells remain to be elucidated. We found that steady-state levels of Ifi202 mRNA and protein were high in mouse embryonic fibroblasts (MEFs) from E2F1 knockout (E2F1(-/-)) and E2F1 and E2F2 double knockout (E2F1(-/-)E2F2(-/-)) mice than isogenic wild-type MEFs. Moreover, overexpression of E2F1 in mouse fibroblasts decreased expression of p202. Furthermore, expression of E2F1, but not E2F4, transcription factor in mouse fibroblasts repressed the activity of 202-luc-reporter in promoter-reporter assays. Interestingly, the E2F1-mediated transcriptional repression of the 202-luc-reporter was independent of p53 and pRb expression. However, the repression was dependent on the ability of E2F1 to bind DNA. We have identified a potential E2F DNA-binding site in the 5'-regulatory region of the Ifi202 gene, and mutations in this E2F DNA-binding site reduced the E2F1-mediated transcriptional repression of 202-luc-reporter. Because p202 inhibits the E2F1-mediated transcriptional activation of genes, we compared the expression of E2F1 and its target genes in splenic cells from lupus-prone B6.Nba2 congenic mice, which express increased levels of p202, with age-matched C57BL/6 mice. We found that increased expression of Ifi202 in the congenic mice was associated with inhibition of E2F1-mediated transcription and decreased expression of E2F1 and its target genes that encode proapoptotic proteins. Our observations support the idea that increased Ifi202 expression in certain strains of mice contributes to lupus susceptibility in part by inhibiting E2F1-mediated functions.
Panchanathan
Ravichandran
R
Department of Environmental Health, University of Cincinnati, 3223 Eden Avenue, Cincinnati, OH 45267, USA.
Xin
Hong
H
Choubey
Divaker
D
D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D004195:Disease Models, Animal; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D050703:E2F2 Transcription Factor / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D050704:E2F4 Transcription Factor / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D004622:Embryo, Mammalian / Q000276:immunology / Q000473:pathology; D005347:Fibroblasts / Q000276:immunology / Q000473:pathology; D005786:Gene Expression Regulation / Q000235:genetics / Q000276:immunology*; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000276:immunology*; D008180:Lupus Erythematosus, Systemic / Q000235:genetics / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D018345:Mice, Knockout; D041681:NIH 3T3 Cells; D010750:Phosphoproteins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology*; D016160:Retinoblastoma Protein / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D013154:Spleen / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000276:immunology / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D050687:E2F1 Transcription Factor; D050703:E2F2 Transcription Factor; D050704:E2F4 Transcription Factor; C493754:E2f1 protein, mouse; C484940:E2f2 protein, mouse; C493763:E2f4 protein, mouse; C092537:Ifi202b protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53