title: IFN-epsilon mediates TNF-alpha-induced STAT1 phosphorylation and induction of retinoic acid-inducible gene-I in human cervical cancer cells.
abstract: Retinoic acid inducible gene-I (RIG-I) plays important roles during innate immune responses to viral infections and as a transducer of cytokine signaling. The mechanisms of RIG-I up-regulation after cytokine stimulation are incompletely characterized. It was previously reported that IFN-gamma induces the expression of RIG-I in endothelial cells. In this study, we characterized the mechanism of type I IFN-mediated up-regulation of RIG-I in HeLa cells and found that, in addition to type I IFN, TNF-alpha, a cytokine that regulates innate immune responses, induced expression of RIG-I. To investigate whether TNF-alpha- and type I IFN-mediated up-regulations of RIG-I were causally related, we studied the kinetics of these responses. Our results were consistent with a model in which TNF-alpha functioned upstream of type I IFNs. The ability of TNF-alpha to up-regulate RIG-I required protein synthesis, expression of functional type I IFNRs, and STAT1 signaling. We also found that IFN-epsilon was the only IFN isoform expressed constitutively in HeLa cells and that its expression was up-regulated in response to stimulation with TNF-alpha. The mechanism of up-regulation involved stabilization of IFN-epsilon mRNA in the absence of transcriptional activation. Silencing the expression of IFN-epsilon attenuated STAT1 expression and phosphorylation and inhibited RIG-I expression, providing additional support for the participation of IFN-epsilon upstream of STAT1. Our findings support a sequential mechanism whereby TNF-alpha leads to stabilization of IFN-epsilon mRNA, increased IFN-epsilon synthesis, engagement of type I IFNRs, increased STAT1 expression and phosphorylation, and up-regulation of RIG-I expression. These findings have implications for our understanding of the immune responses that follow cytokine stimulation.
authors: Huntsman Cancer Institute, University of Utah, Salt Lake City, Utah 84112, USA.
authors: Tomoh
authors: T
authors: Matsumiya
authors: Stephen M
authors: SM
authors: Prescott
authors: Diana M
authors: DM
authors: Stafforini
mesh_terms: D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000378:metabolism*; D005260:Female; D006367:HeLa Cells; D006801:Humans; D007372:Interferons / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D011971:Receptors, Immunologic; D017471:Receptors, Interferon / Q000145:classification / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects; D002583:Uterine Cervical Neoplasms / Q000235:genetics / Q000378:metabolism*
chemical_list: C524005:IFNE protein, human; D012333:RNA, Messenger; D011971:Receptors, Immunologic; D017471:Receptors, Interferon; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D014409:Tumor Necrosis Factor-alpha; D007372:Interferons; C452820:RIGI protein, human; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases