Cigarette smoke mediates epigenetic repression of miR-487b during pulmonary carcinogenesis
Sichuan Xi, … , Leandro Mercedes, David S. Schrump
Sichuan Xi, … , Leandro Mercedes, David S. Schrump
Published February 15, 2013
Citation Information: J Clin Invest. 2013;123(3):1241-1261. https://doi.org/10.1172/JCI61271.
View: Text | PDF
Research Article Oncology

Cigarette smoke mediates epigenetic repression of miR-487b during pulmonary carcinogenesis

Abstract

MicroRNAs are critical mediators of stem cell pluripotency, differentiation, and malignancy. Limited information exists regarding microRNA alterations that facilitate initiation and progression of human lung cancers. In this study, array techniques were used to evaluate microRNA expression in normal human respiratory epithelia and lung cancer cells cultured in the presence or absence of cigarette smoke condensate (CSC). Under relevant exposure conditions, CSC significantly repressed miR-487b. Subsequent experiments demonstrated that miR-487b directly targeted SUZ12, BMI1, WNT5A, MYC, and KRAS. Repression of miR-487b correlated with overexpression of these targets in primary lung cancers and coincided with DNA methylation, de novo nucleosome occupancy, and decreased H2AZ and TCF1 levels within the miR-487b genomic locus. Deoxy-azacytidine derepressed miR-487b and attenuated CSC-mediated silencing of miR-487b. Constitutive expression of miR-487b abrogated Wnt signaling, inhibited in vitro proliferation and invasion of lung cancer cells mediated by CSC or overexpression of miR-487b targets, and decreased growth and metastatic potential of lung cancer cells in vivo. Collectively, these findings indicate that miR-487b is a tumor suppressor microRNA silenced by epigenetic mechanisms during tobacco-induced pulmonary carcinogenesis and suggest that DNA demethylating agents may be useful for activating miR-487b for lung cancer therapy.

Authors

Sichuan Xi, Hong Xu, Jigui Shan, Yongguang Tao, Julie A. Hong, Suzanne Inchauste, Mary Zhang, Tricia F. Kunst, Leandro Mercedes, David S. Schrump

×

Figure 6

miR-487b functions as a tumor suppressor in lung cancer cells.

Options: View larger image (or click on image) Download as PowerPoint
miR-487b functions as a tumor suppressor in lung cancer cells. (A) Effec...
(A) Effects of miR-487b expression on in vitro proliferation of Calu-6 and H841 lung cancer cells. (B) Matrigel invasion assays demonstrating that overexpression of miR-487b inhibited, whereas knockdown of miR-487b enhanced, invasion of Calu-6 and H841 lung cancer cells. miR-487b significantly inhibited CSC-induced invasion of lung cancer cells. The effects of miR-487b knockdown on invasion of DMSO-treated cells were comparable to these observed in vector controls exposed to CSC. *P < 0.05; **P < 0.01. (C) Cell count assays demonstrating effects of miR-487b on proliferation of lung cancer cells overexpressing SUZ12, BMI1, WNT5A, MYC, or KRAS. miR-487b had no effects on proliferation induced by cyclin D1, which is not targeted by miR-487b. +P < 0.05; ++P < 0.01 vs. control. *P < 0.05; **P < 0.01 vs. miR-487b. (D) Matrigel assays demonstrating effects of miR-487b on invasive potential of lung cancer cells following overexpression of the 5 miR-487 targets. miR-487b had no effects on invasion induced by cyclin D1. +P < 0.05; ++P < 0.01 vs. control. *P < 0.05; **P < 0.01 vs miR-487b. (E) Specificity of effects of miR-487b expression on invasion potential of lung cancer cells mediated by MYC and KRAS. miR-487b failed to inhibit invasion induced by overexpression of MYC and KRAS lacking full 3′ UTR sequences.