PGE2 induces c-fos expression by a cAMP-independent mechanism in glomerular mesangial cells

Prostanoids induce expression of several immediate-early genes, but the molecular mechanisms underlying these responses remain poorly characterized. We studied induction of the proto-oncogene c-fos by PGE2 in mesangial cells as a model of gene regulation by prostanoids. PGE2 induced marked and transient accumulation of c-fos mRNA. Addition of exogenous 8-bromo-cAMP or forskolin failed to induce c-fos mRNA, suggesting that activation of an EP2 receptor linked to adenylate cyclase did not account for induction of c-fos by PGE2. These data contrast with previous experiments in NIH 3T3 cells in which PGE2 induced c-fos by a cAMP-dependent mechanism. Depletion of protein kinase C blocked induction of c-fos mRNA by PGE2, whereas a protein tyrosine kinase inhibitor had no effect. We further showed that PGE2 induces the c-fos gene by increasing the transactivating capacity of the serum-response element. Transient transfections with a CAT fusion gene driven by an AP-1 cis-element demonstrated that although PGE2 markedly induced c-fos, PGE2 did not increase AP-1-driven transcriptional responses. Electrophoretic gel mobility shift assays revealed that PGE2 failed to increase binding of AP-1 complexes to a consensus AP-1 DNA sequence. Taken together, these experiments provide evidence for a cAMP-independent, protein kinase C-dependent pathway linking a PGE2 receptor on the plasma membrane to transcriptional activation in the nucleus. Regulation of gene transcription by PGE2 probably involves c-fos induction without concomitant activation of AP-1.