Prostaglandin E(2) stimulates normal bronchial epithelial cell growth through induction of c-Jun and PDK1, a kinase implicated in oncogenesis

BACKGROUND: Cyclooxygenase-2-derived prostaglandin E(2) (PGE(2)), a bioactive eicosanoid, has been implicated in many biological processes including reproduction, inflammation and tumor growth. We previously showed that PGE(2) stimulated lung cancer cell growth and progression through PGE(2) receptor EP2/EP4-mediated kinase signaling pathways. However, the role of PGE(2) in controlling lung airway epithelial cell phenotype remains unknown. We evaluated the effects of c-Jun and 3-phosphoinositede dependent protein kinase-1 (PDK1) in mediating epithelial cell hyperplasia induced by PGE(2). METHOD: The bronchial epithelial cell lines BEAS-2B and HBEc14-KT were cultured and then treated with PGE(2). PDK1 small interfering RNA (siRNA) and a PDK1 inhibitor, an antagonist of the PGE(2) receptor subtype EP4 and EP4 siRNA, c-Jun siRNA, and overexpressions of c-Jun and PDK1 have been used to evaluate the effects on cell proliferation. RESULTS: We demonstrated that PGE(2) increased normal bronchial epithelial cell proliferation through induction of PDK1, an ankyrin repeat-containing Ser/Thr kinase implicated in the induction of apoptosis and the suppression of tumor growth. PDK1 siRNA and a PDK1 inhibitor blocked the effects of PGE(2) on normal cell growth. The PGE(2)-induced PDK1 expression was blocked by an antagonist of the PGE(2) receptor subtype EP4 and by EP4 siRNA. In addition, we showed that induction of PDK1 by PGE(2) was associated with induction of the transcription factor, c-Jun protein. Silencing of c-Jun using siRNA and point mutations of c-Jun sites in the PDK1 gene promoter resulted in blockade of PDK1 expression and promoter activity induced by PGE(2). In contrast, overexpression of c-Jun induced PDK1 gene promoter activity and expression followed increased cell proliferation. CONCLUSION: PGE(2) increases normal bronchial epithelial cell proliferation through increased PDK1 gene expression that is dependent on EP4 and induction of c-Jun. Therewith, our data suggest a new role of c-Jun and PDK1 in mediating epithelial cell hyperplasia induced by PGE(2).