Induction of COX‐2 and PGE₂ biosynthesis by IL‐1β is mediated by PKC and mitogen‐activated protein kinases in murine astrocytes

Abstract

1 Interleukin-1 (IL-1) is an important mediator of immunoin¯ammatory responses in the brain. In the present study, we examined whether prostaglandin E 2 (PGE 2 ) production after IL-1b stimulation is dependent upon activation of protein kinases in astroglial cells. 2 Astrocyte cultures stimulated with IL-1b or the phorbol ester, PMA signi®cantly increased PGE 2 secretion. The stimulatory action of IL-1b on PGE 2 production was totally abolished by NS-398, a speci®c inhibitor of cyclo-oxygenase-2 activity, as well as by the protein synthesis inhibitor cycloheximide, and the glucocorticoid dexamethasone. Furthermore, IL-1b induced the expression of COX-2 mRNA. This occurred early at 2 h, with a maximum at 4 h and declined at 12 h. IL-1 b treatment also induced the expression of COX-2 protein as determined by immunoblot analysis. In that case the expression of the protein remained high at least up to 12 h. 3 Treatment of cells with protein kinase C inhibitors (H-7, bisindolylmaleimide and calphostin C) inhibited IL-1b stimulation of PGE 2 . In addition, PKC-depleted astrocyte cultures by overnight treatment with PMA no longer responded to PMA or IL-1. The ablation of the e ects of PMA and IL-1b on PGE 2 production, likely results from down-regulation of phorbol ester sensitive-PKC isoenzymes. Immunoblot analysis demonstrated the translocation of the conventional isoform cPKC-a from cytosol to membrane following treatment with IL-1b. 4 In addition, IL-1b treatment led to activation of extracellular signal-regulated kinase (ERK1/2) and p38 subgroups of MAP kinases in astroglial cells. Interestingly, the inhibition of ERK kinase with PD 98059, as well as the inhibition of p38 MAPK with SB 203580, prevented IL-1b-induced PGE 2 release. 5 ERK1/2 activation by IL-1b was sensitive to inhibition by the PKC inhibitor bisindolylmaleimide suggesting that ERK phosphorylation is a downstream signal of PKC activation. 6 These results suggest key roles for PKC as well as for ERK1/2 and p38 MAP kinase cascades in the biosynthesis of PGE 2 , likely by regulating the induction of cyclo-oxygenase-2, in IL-1b-stimulated astroglial cells.

Expression of interleukin‐1 receptors and their role in interleukin‐1 actions in murine microglial cells

“…these cultures (Figs 4-6) (see Parker et al 2002 for details). The activation of signaling pathways and subsequent release of inflammatory mediators in response to IL-1 has been described mainly in astrocytes (Molina-Holgado et al 2000). These observations suggest that responses of mixed glial cells to IL-1 are due mainly to activation of astrocytes via ligand binding to IL-1 receptors expressed on these cells (Fig.…”

“…These MAPKs are activated by IL-1 in glial cells Molina-Holgado et al 2000) and drive the transcription of genes for other inflammatory mediators such as IL-6 and prostaglandin-E 2 (PGE 2 ), resulting in their release.…”

Insulin-like growth factor-I induces cyclooxygenase-2 expression via PI3K, MAPK and PKC signaling pathways in human ovarian cancer cells☆

“…6D and 6E), indicating that PKC activation was important for IGF-I-mediated COX-2 transcriptional activation and mRNA stabilization. PKC was shown to regulate IL-1β-induced COX-2 expression through ERK1/2 activation in astrocytes (19). However, we found that pretreatment with the PKC inhibitor did not alter IGF-I-induced ERK1/2 activation in the cells (Fig.…”

“…PKC activity regulated COX-2 expression induced by inflammatory stimuli and stress signals (16,19,47,49,50). Activation of PKC promotes COX-2 gene transcription through the transcription factors NF-κB and C/EBP (16,50).…”

“…We further demonstrated that PKC was involved in both transcriptional and post-transcriptional regulation of COX-2 expression. It was observed that MAPK could be a downstream signal of PKC for regulating COX-2 expression (19,47). However, we found that in ovarian cancer cells, blockade of PKC activity did not inhibit IGF-I-induced ERK1/2 activation, suggesting that induction of COX-2 expression by PKC is independent of MAPK in human ovarian cancer cells.…”