The EP₃ receptor stimulates ceramide and diacylglycerol release and inhibits growth of primary keratinocytes

Primary human keratinocytes (PHKs) are known to express the EP₃ subtype of prostaglandin E₂ receptor. To better understand the role of EP₃ receptors in regulating epidermal function, we characterized their expression, localization, and signaling effects in human skin. Three different splice variants of the EP₃ receptor (EP_3A1, EP_3C, and EP_3D) were found to be expressed. Immunohistochemical analysis of human skin demonstrated that EP₃ receptors were most prominently expressed in the basal and lower spinous layers of the epidermis. The EP₃ receptor agonist sulprostone was then used to examine EP₃ receptor-dependent keratinocyte signaling pathways and functional effects. We observed that sulprostone inhibits keratinocyte growth at doses between 0.02 and 2 nM and induces sn- 1,2-diacylglycerol (DAG) and ceramide production. Concurrent expression of the cell-cycle inhibitory protein p21^WAF1 also occurred. These data suggest that EP₃ receptors produce epidermal growth inhibition through the action of DAG and ceramide second messengers.