Supplementary Figure 2A-B from Nicotine Stimulates PPARβ/δ Expression in Human Lung Carcinoma Cells through Activation of PI3K/mTOR and Suppression of AP-2α
ARTICLE ABSTRACT
We previously showed that nicotine stimulates non–small cell lung carcinoma (NSCLC) cell proliferation through nicotinic acetylcholine receptor (nAChR)–mediated signals. Activation of peroxisome proliferator–activated receptor β/δ (PPARβ/δ) has also been shown to induce NSCLC cell growth. Here, we explore the potential link between nicotine and PPARβ/δ and report that nicotine increases the expression of PPARβ/δ protein; this effect was blocked by an α7 nAChR antagonist (α-bungarotoxin), by α7 nAChR short interfering RNA, and by inhibitors of phosphatidylinositol 3-kinase (PI3K; wortmannin and LY294002) and mammalian target of rapamycin (mTOR; rapamycin). In contrast, this effect was enhanced by PUN282987, an α7 nAChR agonist. Silencing of PPARβ/δ attenuated the stimulatory effect of nicotine on cell growth, which was overcome by transfection of an exogenous PPARβ/δ expression vector. Of note, nicotine induced complex formation between α7 nAChR and PPARβ/δ protein and increased PPARβ/δ gene promoter activity through inhibition of AP-2α as shown by reduced AP-2α binding using electrophoretic gel mobility shift and chromatin immunoprecipitation assays. In addition, silencing of Sp1 attenuated the effect of nicotine on PPARβ/δ. Collectively, our results show that nicotine increases PPARβ/δ gene expression through α7 nAChR–mediated activation of PI3K/mTOR signals that inhibit AP-2α protein expression and DNA binding activity to the PPARβ/δ gene promoter. Sp1 seems to modulate this process. This study unveils a novel mechanism by which nicotine promotes human lung carcinoma cell growth. [Cancer Res 2009;69(16):6445–53]
