Prostaglandin E2 stimulates human lung carcinoma cell growth through induction of integrin-linked kinase: the involvement of EP4 and Sp1.

Cyclooxygenase-2-derived prostaglandin E(2) (PGE(2)) stimulates tumor cell growth and progression. However, the mechanisms by which PGE(2) increases tumor growth remain incompletely understood. In studies performed in non-small cell lung carcinoma (NSCLC) cells, we found that PGE(2) stimulates the expression of integrin-linked kinase (ILK). ILK small interfering RNA (siRNA) inhibited the mitogenic effects of PGE(2). In view of its perceived importance, we turned our attention to the mechanisms involved in PGE(2)-induced ILK expression and found that this effect was blocked by an antagonist of the PGE(2) receptor subtype EP4 and by EP4 siRNA. Furthermore, we showed that PGE(2) induction of ILK was associated with phosphorylation of extracellular signal-regulated kinase and phosphatidylinositol 3-kinase/Akt, which were abrogated by ILK siRNA. Transient transfection, gel mobility shift assays, and chromatin immunoprecipitation experiments showed that PGE(2) induced ILK promoter activity and increased Sp1, although it had no effect on nuclear factor-kappaB and AP-2 DNA-binding activity. Blockade of Sp1 abrogated the effect of PGE(2) on expression of ILK and promoter activity and on cell growth. In summary, our observations show that PGE(2) increases NSCLC cell growth through increased ILK expression, which is dependent on EP4 signaling and on induction of Sp1 protein and Sp1 DNA-binding activity in the ILK promoter. These studies suggest a novel molecular mechanism by which PGE(2) stimulates NSCLC cell growth and unveils a new molecular target for the development of therapies against NSCLC.