RESUMEN
One important mechanism of cross-regulation by opposing cytokines is inhibition of signal transduction, including inhibition of Janus kinase-STAT signaling by suppressors of cytokine signaling. We investigated whether IFN-gamma, a major activator of macrophages, inhibited the activity of IL-10, an important deactivator. Preactivation of macrophages with IFN-gamma inhibited two key anti-inflammatory functions of IL-10, the suppression of cytokine production and of MHC class II expression. Gene expression profiling showed that IFN-gamma broadly suppressed the ability of IL-10 to induce or repress gene expression. Although IFN-gamma induced expression of suppressor of cytokine signaling proteins, IL-10 signal transduction was not suppressed and IL-10 activation of Janus kinases and Stat3 was preserved. Instead, IFN-gamma switched the balance of IL-10 STAT activation from Stat3 to Stat1, with concomitant activation of inflammatory gene expression. IL-10 activation of Stat1 required the simultaneous presence of IFN-gamma. These results demonstrate that IFN-gamma operates a switch that rapidly regulates STAT activation by IL-10 and alters macrophage responses to IL-10. Dynamic regulation of the activation of different STATs by the same cytokine provides a mechanism by which cells can integrate and balance signals delivered by opposing cytokines, and extends our understanding of cross-regulation by opposing cytokines to include reprogramming of signaling and alteration of function.
Asunto(s)
Interferón gamma/farmacología , Interleucina-10/metabolismo , Interleucina-10/fisiología , Transducción de Señal/inmunología , Adyuvantes Inmunológicos/farmacología , Adyuvantes Inmunológicos/fisiología , Línea Celular , Células Cultivadas , Proteínas de Unión al ADN/biosíntesis , Proteínas de Unión al ADN/metabolismo , Proteínas de Unión al ADN/fisiología , Sinergismo Farmacológico , Regulación de la Expresión Génica/inmunología , Humanos , Mediadores de Inflamación/antagonistas & inhibidores , Mediadores de Inflamación/fisiología , Interferón gamma/fisiología , Interleucina-10/antagonistas & inhibidores , Lipopolisacáridos/antagonistas & inhibidores , Lipopolisacáridos/farmacología , Activación de Macrófagos/inmunología , Factor de Transcripción STAT1 , Factor de Transcripción STAT3 , Transactivadores/biosíntesis , Transactivadores/metabolismo , Transactivadores/fisiología , Factor de Necrosis Tumoral alfa/antagonistas & inhibidores , Factor de Necrosis Tumoral alfa/biosíntesis , Regulación hacia Arriba/inmunologíaRESUMEN
Recent reports suggest that a novel mechanism of glucocorticoid (GC) immunosuppressive action is inhibition of signaling by IL-2 and IL-12, cytokines that use the Janus kinase-STAT signaling pathway. We investigated whether GCs could also block activation of Janus kinase-STAT signaling by IFN-gamma, a potent proinflammatory cytokine. Addition of dexamethasone to PBMC cultures resulted in a dramatic inhibition of IFN-gamma activation of STAT1. Several days of exposure to GCs were required for inhibition of IFN-gamma signaling to become apparent, and the underlying mechanism was down-regulation of STAT1 expression. GCs suppressed the expression of STAT1 mRNA, but did not affect STAT1 protein stability. STAT1 expression and IFN-gamma signaling were preferentially suppressed in macrophages. GCs did not act directly on macrophages, but worked indirectly by regulating macrophage-lymphocyte interactions that control STAT1 expression. GCs inhibited IFN-gamma-inducible gene expression, thus demonstrating the physiological significance of inhibition of signal transduction. Our results identify a novel level of regulation of IFN-gamma signaling, whereby GCs control the amplitude of IFN-gamma signaling by regulating STAT1 expression. These results suggest that inhibition of IFN-gamma signaling contributes to the immunosuppressive action of GCs.
Asunto(s)
Dexametasona/farmacología , Regulación hacia Abajo/efectos de los fármacos , Regulación hacia Abajo/inmunología , Inmunosupresores/farmacología , Interferón gamma/antagonistas & inhibidores , Interferón gamma/fisiología , Proteínas de la Leche , Transducción de Señal/efectos de los fármacos , Transducción de Señal/inmunología , Antiinflamatorios/farmacología , Células Cultivadas , Quimiocina CXCL10 , Quimiocinas CXC/antagonistas & inhibidores , Quimiocinas CXC/biosíntesis , Quimiocinas CXC/genética , Proteínas de Unión al ADN/antagonistas & inhibidores , Proteínas de Unión al ADN/biosíntesis , Proteínas de Unión al ADN/genética , Regulación de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica/inmunología , Humanos , Factor 1 Regulador del Interferón , Interferón gamma/genética , Interferón gamma/metabolismo , Leucocitos Mononucleares/efectos de los fármacos , Leucocitos Mononucleares/inmunología , Leucocitos Mononucleares/metabolismo , Receptores de Lipopolisacáridos/biosíntesis , Receptores de Lipopolisacáridos/sangre , Monocitos/efectos de los fármacos , Monocitos/inmunología , Monocitos/metabolismo , Fosfoproteínas/antagonistas & inhibidores , Fosfoproteínas/biosíntesis , Fosfoproteínas/genética , ARN Mensajero/antagonistas & inhibidores , ARN Mensajero/biosíntesis , Factor de Transcripción STAT1 , Factor de Transcripción STAT5 , Factores de Tiempo , Transactivadores/antagonistas & inhibidores , Transactivadores/biosíntesis , Transactivadores/genéticaRESUMEN
A general paradigm in signal transduction is ligand-induced feedback inhibition and the desensitization of signaling. We found that subthreshold concentrations of interferon-gamma (IFN-gamma), which did not activate macrophages, increased their sensitivity to subsequent IFN-gamma stimulation; this resulted in increased signal transducer and activator of transcription 1 (STAT1) activation and increased IFN-gamma#150;dependent gene activation. Sensitization of IFN-gamma signaling was mediated by the induction of STAT1 expression by low doses of IFN-gamma that did not effectively induce feedback inhibition. IFN-gamma signaling was sensitized in vivo after IFN-gamma injection, and STAT1 expression was increased after injection of lipopolysaccharide and in rheumatoid arthritis synovial cells. These results identify a mechanism that sensitizes macrophages to low concentrations of IFN-gamma and regulates IFN-gamma responses in acute and chronic inflammation.