Abstract
Epidemiologic studies have shown that vast majority of lung cancers (85-90%) are causally linked to tobacco smoking. Although much information has been gained about the effects of smoking on various signaling pathways, little is known about how deregulation of miRNAs leads to activation of oncogenes and inhibition of tumor suppressor genes in non-small cell lung cancer (NSCLC). Our previous study showed that smoking inhibits TGF-β-induced tumor suppressor functions through downregulation of Smad3 in lung cancer cells. In order to understand the upstream mechanism of downregulation of Smad3 by smoking, we performed miRNA microarray analyses after treating human lung adenocarcinoma A549 and immortalized peripheral lung epithelial HPL1A cells with cigarette smoke condensate (CSC). We identified miR-216b as being upregulated in CSC treated cells. MiR-216b overexpression decreases Smad3 protein expression by binding to its 3'-UTR, and attenuates transforming growth factor beta (TGF-β) signaling and target gene expression. MiR-216b increases B-cell lymphoma 2 (BCL-2) expression and promotes chemoresistance of NSCLC cells by decreasing apoptosis. Increased acetylation of histones H3 and H4 in miR-216b gene promoter plays a role in CSC induced miR-216b expression. Taken together, these results suggest that smoking-mediated upregulation of miR-216b increases NSCLC cell growth by downregulating Smad3 and inhibiting TGF-β-induced tumor suppressor function, and induces resistance to platinum-based therapy.