gw-501516 and Carcinoma--Non-Small-Cell-Lung

We previously demonstrated that a selective agonist of peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta), GW501516, stimulated human non-small cell lung carcinoma (NSCLC) growth, partly through inhibition of phosphatase and tensin homolog deleted on chromosome 10 expression. Here, we show that GW501516 also decreases the phosphorylation of AMP-activated protein kinase alpha (AMPKalpha), a major regulator of energy metabolism. This was mediated through specific activation of PPARbeta/delta, as a PPARbeta/delta small interfering RNA inhibited the effect. However, AMPKalpha did not mediate the growth-promoting effects of GW501516, as silencing of AMPKalpha did not inhibit GW501516-induced cell proliferation. Instead, we found that GW501516 stimulated peroxisome proliferator-activated receptor coactivator gamma (PGC)-1alpha, which activated the phosphatidylinositol 3 kinase (PI3-K)/Akt mitogenic pathway. An inhibitor of PI3-K, LY294002, had no effect on PGC-1alpha, consistent with PGC-1alpha being upstream of PI3-K/Akt. Of note, an activator of AMPKalpha, 5-amino-4-imidazole carboxamide riboside, inhibited the growth-promoting effects of GW501516, suggesting that although AMPKalpha is not responsible for the mitogenic effects of GW501516, its activation can oppose these events. This study unveils a novel mechanism by which GW501516 and activation of PPARbeta/delta stimulate human lung carcinoma cell proliferation, and suggests that activation of AMPKalpha may oppose this effect.

Topics: Aminoimidazole Carboxamide; AMP-Activated Protein Kinases; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Cell Proliferation; Enzyme Activation; Heat-Shock Proteins; Humans; Lung Neoplasms; Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; Phosphatidylinositol 3-Kinases; Phosphorylation; PPAR delta; PPAR-beta; Ribonucleotides; RNA, Small Interfering; Signal Transduction; Thiazoles; Transcription Factors

Lung carcinoma remains one of the most common malignant tumors in the world despite recent advancements in the development of new chemotherapeutic agents for its treatment. Therefore, novel approaches for drug target discovery play an important role in the effort to help extend its dismal 5-year survival rate (<15%). Many mechanisms contribute to oncogenic transformation in carcinoma cells in the lung and recent evidence indicates that the overproduction of prostaglandin E(2) (PGE(2)), and the prostag-landin E(2) receptor subtype, EP4, promote the growth and progression of human nonsmall cell lung carcinoma (NSCLC), the most common lung carcinoma. Peroxisome proliferator-activated receptor beta/ delta (PPARbeta/delta), one of the nuclear hormone ligand-dependent transcription factors, has recently been reported to be involved in tumorigeniCity. We have shown that NSCLC cells express PPARbeta/delta protein and that treatment with a selective PPARbeta/delta agonist, GW501516, stimulated the expression of EP4 and induced NSCLC cell proliferation. In addition, this PPARbeta/delta agonist also induced EP4 promoter activity through the binding of C/EBP to the NF-IL6 site in the EP4 promoter. Therefore, PPARbeta/delta activation represents a novel molecular mechanism for regulating human cancer cell growth.

Topics: Blotting, Western; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Cell Proliferation; Dinoprostone; Electrophoretic Mobility Shift Assay; Humans; Lung Neoplasms; PPAR delta; PPAR-beta; Receptors, Prostaglandin E; Receptors, Prostaglandin E, EP4 Subtype; Thiazoles

Recent studies suggest that activation of peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) promotes cancer cell survival. We previously demonstrated that a selective PPARbeta/delta agonist, GW501516, stimulated human non-small cell lung carcinoma (NSCLC) cell growth. Here, we explore the mechanisms responsible for this effect. We show that GW501516 decreased phosphate and tensin homolog deleted on chromosome 10 (PTEN), a tumor suppressor known to decrease cell growth and induce apoptosis. Activation of PPARbeta/delta and phosphatidylinositol 3-kinase (PI3K)/Akt signaling was associated with inhibition of PTEN. GW501516 increased NF-kappaB DNA binding activity and p65 protein expression through activation of PPARbeta/delta and PI3K/Akt signals and enhanced the physical interactions between PPARbeta/delta and p65 protein. Conversely, inhibition of PI3K and silencing of p65 by small RNA interference (siRNA) blocked the effect of GW501516 on PTEN expression and on NSCLC cell proliferation. GW501516 also inhibited IKBalpha protein expression. Silencing of IKBalpha enhanced the effect of GW501516 on PTEN protein expression and on cell proliferation. It also augmented the GW501516-induced complex formation of PPARbeta/delta and p65 proteins. Overexpression of PTEN suppressed NSCLC cell growth and eliminated the effect of GW501516 on phosphorylation of Akt. Together, our observations suggest that GW501516 induces the proliferation of NSCLC cells by inhibiting the expression of PTEN through activation of PPARbeta/delta, which stimulates PI3K/Akt and NF-kappaB signaling. Overexpression of PTEN overcomes this effect and unveils PPARbeta/delta and PTEN as potential therapeutic targets in NSCLC.

Topics: Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Cell Proliferation; Down-Regulation; Humans; I-kappa B Proteins; Lung Neoplasms; NF-kappa B; NF-KappaB Inhibitor alpha; Phosphatidylinositol 3-Kinases; PPAR delta; PPAR-beta; PTEN Phosphohydrolase; Signal Transduction; Thiazoles; Transcription Factor RelA