Abstract
Prostaglandin E~2~ (PGE~2~) has been shown to have a strong cytoprotective effect, inhibiting apoptosis. In the present study, we evaluated whether PGE~2~ has a protective effect on cigarette smoke extract (CSE)‐induced apoptosis in human lung fibroblasts. Apoptosis was assessed by various methods, including DNA content analysis. CSE (15%–20%) led to apoptosis and induced imbalance in favor of pro‐ over anti‐apoptotic protein expression and activated caspases. PGE~2~ blocked CSE‐induced apoptosis and modulated the balance of pro‐ and anti‐apoptotic proteins and decreased the activation of caspases. This anti‐apoptotic effect was mediated via EP~2~ receptor activation as the EP~2~ agonist butaprost mimicked PGE~2~ activity and siRNA for the EP~2~ receptor blocked it. An adenylyl cyclase inhibitor was found to abolish the PGE~2~‐mediated cytoprotective effect. Correspondingly, c‐AMP analogs blocked CSE‐induced apoptosis. Consistently, the protein kinase A (PKA) inhibitor KT‐5720 abolished PGE~2~‐mediated protection. PGE~2~ and butaprost phosphorylated Bad and KT‐5720 blocked phosphorylation. These results suggest that PGE~2~ inhibits CSE‐induced apoptosis via EP~2~ receptor activation and activation of PKA, which leads to an alteration in the balance between pro‐ and anti‐apoptotic factors. Through such a mechanism, PGE~2~ may alter survival of cells in the smoke‐exposed lungs, thus affecting the pathogenesis of cigarette smoke‐induced disease. J. Cell. Physiol. 210: 99–110, 2007. © 2006 Wiley‐Liss, Inc.