Signal transduction pathways for epidermal growth factor stimulated cyclooxygenase-2 induction in astrocytes

Cyclooxygenase-2 (COX-2) derived prostaglandins (PGs) are pathophysiological mediators in various disease states. Recently, we have demonstrated the rapid, epidermal growth factor receptor (EGFR)-dependent induction of COX-2 and PGE2 synthesis in astrocytes following optic nerve injury and in culture. We have now investigated the signal transduction pathways activated by EGFR to accomplish the expression of COX-2 in primary optic nerve astrocytes. When astrocytes were exposed to EGF, marked, rapid gene expression of COX-2 was observed. Activation of EGFR caused an increase in the phosphorylation of extracellular signal-regulated kinase (ERK), p38 MAPK (p38) and c-Jun NH (2)-terminal kinase (JNK). Furthermore, U0126, an ERK pathway inhibitor, and SB203580, a p38 MAPK inhibitor, diminished EGF-induced COX-2 expression; whereas, a JNK inhibitor did not suppress COX-2 expression by EGF. Using inhibitors of several other signaling cascades, we found that, unlike epithelial and cancer cells, NF-κB, PI 3-kinase/Akt and PKC were not signaling pathways for EGFR-dependent induction of COX-2 in optic nerve astrocytes. Taken together, these data suggest that ERK and p38 are key components of the intracellular signaling switch that transduces EGFR activation into COX-2 induction and PGE2 biosynthesis in optic nerve astrocytes.