title: Ultraviolet light suppresses IFN-gamma-induced IL-7 gene expression in murine keratinocytes by interfering with IFN regulatory factors.
abstract: UV light is a potent stimulus for keratinocytes to release several cytokines. Recently, UV light was shown to inhibit keratinocyte release of IL-7, a growth factor for dendritic epidermal T cells. Since to date IL-7 is the only keratinocyte-derived cytokine down-regulated by UV light, we addressed the molecular mechanisms involved. IFN-gamma treatment of the murine keratinocyte cell line Pam 212 resulted in an up-regulation of IL-7 mRNA, while IL-7 transcripts were suppressed in cells exposed to UV before IFN-gamma. Because IFN-gamma induces IL-7 via activation of an IFN-stimulated response element (ISRE) located in the 5' upstream region of the IL-7 gene, bandshift assays were performed using the ISRE sequence from the IL-7 gene. Nuclear extracts from untreated cells revealed two bands, a slower migrating band identified by supershift analysis as IFN regulatory factor-2 (IRF-2), a transcriptional repressor, and a more rapidly migrating band identified as IRF-1, a transcriptional activator. IFN-gamma significantly induced IRF-1 binding, whereas UV treatment plus IFN-gamma decreased IRF-1 binding, suggesting that UV light suppresses IFN-gamma-induced expression of IL-7 by interfering with IRF-1. Chloramphenicol transferase assay confirmed functional relevance, showing that the minimal promoter sequence for the ISRE explicitly responded to IFN-gamma, which was suppressed by UV irradiation. Northern blot analysis using an IRF-1 cDNA probe revealed that UV light reduced IFN-gamma-induced IRF-1 mRNA. This study demonstrates that UV light can inhibit cytokine activities by interference with transcriptional activators. This newly described ability of UV light may contribute to its immunosuppressive properties.
authors.affiliation: Ludwig Boltzmann Institute for Cell Biology and Immunobiology of the Skin, Department of Dermatology, University of Münster, Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Aragane
authors.forename: A
authors.initials: A
authors.lastname: Schwarz
authors.forename: T A
authors.initials: TA
authors.lastname: Luger
authors.forename: K
authors.initials: K
authors.lastname: Ariizumi
authors.forename: A
authors.initials: A
authors.lastname: Takashima
authors.forename: T
authors.initials: T
authors.lastname: Schwarz
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000235:genetics / Q000276:immunology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D050856:Interferon Regulatory Factor-1; D007371:Interferon-gamma / Q000494:pharmacology*; D015851:Interleukin-7 / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology*; D015603:Keratinocytes / Q000276:immunology* / Q000528:radiation effects; D051379:Mice; D010750:Phosphoproteins / Q000235:genetics / Q000276:immunology*; D014466:Ultraviolet Rays
chemical_list: D004268:DNA-Binding Proteins; D050856:Interferon Regulatory Factor-1; D015851:Interleukin-7; C494258:Irf1 protein, mouse; D010750:Phosphoproteins; D007371:Interferon-gamma