Cyclooxygenase-2-derived prostaglandin E2 (PGE2) stimulates tumor cell growth and progression. However, the mechanisms by which PGE2 increases tumor growth remain incompletely understood. We investigated non-small cell lung carcinoma cells (NSCLC) H1838 and H1792 and demonstrated that PGE2 stimulates the expression of integrin-linked kinase (ILK). ILK siRNA inhibited the mitogenic effects of PGE2. In view of its perceived importance, we turned our attention to the mechanisms involved in PGE2-induced ILK expression and found that this effect was blocked by an antagonist of the PGE2 receptor subtype EP4 (AH23848) and by EP4 siRNA. Furthermore, we found that PGE2 induction of ILK was associated with phosphorylation of ERK and activation of the PI3-K/Akt/mTOR-raptor/p70S6K/4E-BP1 pathways, which were abrogated by ILK siRNA. Transient transfection, gel mobility shift assays, and chromatin immunoprecipitation (ChIP) experiments showed that PGE2 induced ILK promoter activity and increased the Sp1-DNA binding activity, while it had no effect on NF-κB and AP-2 binding activity. Blockade of Sp1 abrogated the effect of PGE2 onexpression of ILK protein and promoter activity, and reduced cell growth. Finally, overexpression of ILK enhanced the effect of PGE2 on Sp1 expression, DNA binding activity, and on cell growth. In summary, our observations demonstrate that PGE2 acts on EP4 and increases NSCLC cell growth through activation of ILK signals. PGE2 induction of ILK is dependent on induction of Sp1-DNA binding activity in the ILK promoter. These studies suggest a novel molecular mechanism by which PGE2 stimulates NSCLC cell growth and unveils a new molecular target for the development of strategies against NSCLC.

99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA