PGE₂ stimulates human brain natriuretic peptide expression via EP₄ and p42/44 MAPK

Brain natriuretic peptide (BNP) produced by cardiac myocytes has antifibrotic and antigrowth properties and is a marker of cardiac hypertrophy. We previously showed that prostaglandin E₂ (PGE₂) is the main prostaglandin produced in myocytes treated with proinflammatory stimuli and stimulates protein synthesis by binding to its EP₄ receptor. We hypothesized that PGE₂, acting through EP₄, also regulates BNP gene expression. We transfected neonatal ventricular myocytes with a plasmid encoding the human BNP (hBNP) promoter driving expression of a luciferase reporter gene. PGE₂ increased hBNP promoter activity 3.5-fold. An EP₄ antagonist reduced the stimulatory effect of PGE₂ but not an EP₁ antagonist. Because EP₄ signaling can involve adenylate cyclase, cAMP, and protein kinase A (PKA), we tested the effect of H-89, a PKA inhibitor, on PGE₂ stimulation of the hBNP promoter. H-89 at 5 μM decreased PGE₂ stimulation of BNP promoter activity by 100%. Because p42/44 MAPK mediates the effect of PGE ₂ on protein synthesis, we also examined the role of MAPKs in the regulation of BNP promoter activity. PGE₂ stimulation of the hBNP promoter was inhibited by a MEK1/2 inhibitor and a dominant-negative mutant of Raf, indicating that p42/44 MAPK was involved. In contrast, neither a p38 MAPK inhibitor nor a JNK inhibitor reduced the stimulatory effect of PGE₂. Involvement of small GTPases was also studied. Dominant-negative Rap inhibited PGE₂ stimulation of the hBNP promoter, but dominant-negative Ras did not. We concluded that PGE₂ stimulates the BNP promoter mainly via EP₄, PKA, Rap, and p42/44 MAPK.