Growth regulation of primary human keratinocytes by prostaglandin E receptor EP₂ and EP₃ subtypes

We examined the contribution of specific EP receptors in regulating cell growth. By RT-PCR and northern hybridization, adult human-keratinocytes express mRNA for three PGE₂ receptor subtypes associated with cAMP signaling (EP₂, EP₃, and small amounts of EP₄). In actively growing, non-confluent primary keratinocyte cultures, the EP₂ and EP₄ selective agonists, 11- deoxy PGE₁ and I-OH PGE₁, caused complete reversal of indomethacin-induced growth inhibition. The EP₃/EP₂ agonist (misoprostol), and the EP₁/EP₂ agonist (17-phenyl trinor PGE₂), showed less activity. Similar results were obtained with agonist-induced cAMP formation. The ability of exogenous dibutyryl cAMP to completely reverse indomethacin-induced growth inhibition support the conclusion that growth stimulation occurs via an EP₂ and/or EP₄ receptor-adenylyl cyclase coupled response. In contrast, activation of EP₃ receptors by sulprostone, which is virtually devoid of agonist activity at EP₂ or EP₄ receptors, inhibited bromodeoxyuridine uptake in indomethacin- treated cells up to 30%. Although human EP₃ receptor variants have been shown in other cell types to markedly inhibit cAMP formation via a pertussis toxin sensitive mechanism, EP₃ receptor activation and presumably growth inhibition was independent of adenylyl cyclase, suggesting activation of other signaling pathways.