Novel link between prostaglandin E2 (PGE2) and cholinergic signaling in lung cancer: The role of c-Jun in PGE2-induced α7 nicotinic acetylcholine receptor expression and tumor cell proliferation

BACKGROUND Cyclooxygenase-2-derived prostaglandin E2 (PGE2) stimulates tumor cell growth and progression. α7 nicotinic acetylcholine receptor (nAChR) is a major mediator of cholinergic signaling in tumor cells. In the present study, we investigated the mechanisms by which PGE2 increases non-small cell lung cancer (NSCLC) proliferation via α7 nAChR induction. METHODS The effects of PGE2 on α7 nAChR expression, promoter activity, and cell signaling pathways were detected by Western blot analysis, real time reverse transcriptase polymerase chain reaction, and transient transfection assay. The effect of PGE2 on cell growth was determined by cell viability assay. RESULTS We found that PGE2 induced α7 nAChR expression and its promoter activity in NSCLC cells. The stimulatory role of PGE2 on cell proliferation was attenuated by α7 nAChR small interfering ribonucleic acids (siRNA) or acetylcholinesterase. PGE2-induced α7 nAChR expression was blocked by an antagonist of the PGE2 receptor subtype EP4 and by EP4 siRNA. Furthermore, PGE2 enhanced α7 nAChR expression via activation of c-Jun N-terminal kinase (JNK), phosphatidylinositol 3-kinase (PI3-K), and protein kinase A (PKA) pathways followed by increased c-Jun expression, a critical transcription factor. Blockade of c-Jun diminished the effects of PGE2 on α7 nAChR promoter activity and protein expression, and cell growth. CONCLUSION Our results demonstrate that PGE2 promotes NSCLC cell growth through increased α7 nAChR expression. This effect is dependent on EP4-mediated activation of JNK, PI3K, and PKA signals that induce c-Jun protein expression and α7 nAChR gene promoter activity. Our findings unveil a novel link between prostanoids and cholinergic signaling.