Mechanisms of prostaglandin E2-induced interleukin-6 release in astrocytes:: possible involvement of EP4-like receptors, p38 mitogen-activated protein kinase and protein kinase C

The expression of cyclooxygenase-2 (COX-2) and the synthesis of prostaglandin E2 (PGE(2)) as well as of cytokines such as interleukin-6 (IL-6) have all been suggested to propagate neuropathology in different brain disorders such as HIV-dementia, prion diseases, stroke and Alzheimer's disease. In this report, we show that PGE(2)-stimulated IL-6 release in U373 MG human astroglioma cells and primary rat astrocytes. PGE(2)-induced intracellular cAMP formation was mediated via prostaglandin E receptor 2 (EP2), but inhibition of cAMP formation and protein kinase A or blockade of EP1/EP2 receptors did not affect PGE(2)-induced IL-6 synthesis. This indicates that the cAMP pathway is not part of PGE(2)-induced signal transduction cascade leading to IL-6 release. The EP3/EP1-receptor agonist sulprostone failed to induce IL-6 release, suggesting an involvement of EP4-like receptors. PGE(2)-activated p38 mitogen-activated kinase (p38 MAPK) and protein kinase C (PKC). PGE(2)-induced IL-6 synthesis was inhibited by specific inhibitors of p38 MAPK (SB202190) and PKC (GF203190X). Although, up to now, EP receptors have only rarely been linked to p38 MAPK or PKC activation, these results suggest that PGE(2) induces IL-6 via an EP4-like receptor by the activation of PKC and p38 MAPK via an EP4-like receptor independently of cAMP.