Inhibition of IFN-γ-induced STAT1 activation by 15- deoxy-Δ^12,14-prostaglandin J₂

Abstract

bett. Inhibition of IFN-␥-induced STAT1 activation by 15-deoxy-⌬ 12,14 -prostaglandin J2. Am J Physiol Endocrinol Metab 284: E883-E891, 2003. First published January 7, 2003 10.1152/ajpendo.00515.2002The inhibitory actions of 15-deoxy-⌬ 12,14 -prostaglandin J2 (PGJ2) on inflammatory gene expression have been attributed to the ability of this prostaglandin to inhibit the activation of NF-B. In this study, we have identified an additional signaling pathway sensitive to inhibition by PGJ 2. We show that PGJ2 inhibits interferon (IFN)-␥-stimulated phosphorylation and DNAbinding activity of STAT1. The inhibitory actions on STAT1 phosphorylation are first apparent after a 1-to 2-h incubation and are maximal after a 6-h incubation with PGJ 2, and they correlate with the expression of heat shock protein (HSP)70 in islets. In previous studies, we have correlated the inhibitory actions of PGJ2 on inducible nitric oxide synthase (iNOS) expression and NF-B activation in response to IL-1 with the increased expression of HSP70. Using overexpression and antisense depletion, we provide evidence that HSP70 does not mediate the inhibitory actions of PGJ2 on IL-1-induced NF-B or IFN-␥-induced STAT1 activation or cytokine-stimulated iNOS expression by ␤-cells. Last, we show that the inhibitory actions of a short 6-h pulse with PGJ2 on IL-1 plus IFN-␥-stimulated iNOS expression and NO production by ␤-cells are persistent for extended periods (Յ48 h). These findings suggest that PGJ2 inhibits multiple cytokine-signaling pathways (IL-1 and IFN-␥), that the inhibitory actions are persistent for extended periods, and that increased HSP70 expression correlates with, but does not appear to mediate, the inhibitory actions of PGJ2 on IL-1 and IFN-␥ signaling in ␤-cells.interferon-␥; signal transducer and activator of transcription-1; peroxisome proliferator-activated receptor-␥ AUTOIMMUNE DIABETES IS CHARACTERIZED by islet inflammation followed by the selective destruction of insulinsecreting ␤-cells found in pancreatic islets of Langerhans (14). Cytokines released from inflammatory macrophages and T cells are believed to participate in ␤-cell damage during diabetes development (3, 35). Treatment of rat islets with IL-1 results in a timeand concentration-dependent inhibition of glucosestimulated insulin secretion that is followed by islet degeneration (8,22,29). The inhibitory and destructive actions of IL-1 on ␤-cell function correlate with the time-dependent expression of inducible nitric oxide synthase (iNOS) and production of nitric oxide and can be prevented by inhibitors of iNOS (10,12,36). Alone, interferon (IFN)-␥ does not appear to modulate ␤-cell function; however, IFN-␥ has been shown to both prime and potentiate the stimulatory actions of IL-1 on iNOS expression by rat islets (19,21). In addition, a combination of IL-1 and IFN-␥ is required to stimulate iNOS expression by mouse and human ␤-cells (6, 41). Nitric oxide, produced following iNOS expression, impairs ␤-cell function by inhibiting mitochondrial oxidative metabolism, a...

PPARγ is not required for the inhibitory actions of PGJ2on cytokine signaling in pancreatic β-cells

“…1). These findings confirm that the Q284P PPAR␥ mutant and the PPAR␥ antagonist GW-9662 are capable of inhibiting PPAR␥-mediated transcriptional activation in response to ligand stimulation at ligand concentrations that inhibit cytokine signaling in ␤-cells (25,37).…”

“…RINm5F or CV-1 cells were transiently transfected with 1 g of PPRE-luciferase and 0.5 g of the pCMV-SPORT-␤-galactosidase control plasmid using the Qiagen Superfect reagent according to the manufacturer's specifications and as described previously (1,37). After a 48-h transfection, experiments were initiated as indicated in the legends for Figs.…”

“…In a time-dependent manner, PGJ 2 stimulates the expression of heat shock protein (hsp) 70 that is first detectable after a 3-to 6-h incubation (37). Importantly, when islets express hsp 70 either in response to PGJ 2 treatment or after heat shock, IL-1-induced NF-B and IFN-␥-stimulated signal transducer and activator of transcription (STAT)1 activation are attenuated (25,32,37). Although the inhibitory actions of PGJ 2 on cytokine signaling correlate with elevated levels of hsp 70, antisense depletion of hsp 70 does not affect the inhibitory actions of PGJ 2 in ␤-cells (37).…”

“…In an effort to identify mechanisms to prevent cytokinemediated ␤-cell damage, we have shown that IL-1 fails to activate iNOS gene expression and NO production by RINm5F cells and rat islets treated simultaneously with the PPAR␥ agonist 15-deoxy-⌬ 12,14 -prostaglandin J 2 (PGJ 2 ) (25,37). We have also shown that PGJ 2 inhibits signaling cascades initiated by the proinflammatory cytokines IL-1␤ and IFN-␥ by a second mechanism that is associated with activation of a stress response.…”

“…We have also shown that PGJ 2 inhibits signaling cascades initiated by the proinflammatory cytokines IL-1␤ and IFN-␥ by a second mechanism that is associated with activation of a stress response. In a time-dependent manner, PGJ 2 stimulates the expression of heat shock protein (hsp) 70 that is first detectable after a 3-to 6-h incubation (37). Importantly, when islets express hsp 70 either in response to PGJ 2 treatment or after heat shock, IL-1-induced NF-B and IFN-␥-stimulated signal transducer and activator of transcription (STAT)1 activation are attenuated (25,32,37).…”