MicroRNA-181 a regulates epithelial-mesenchymal transition by targeting PTEN in drug-resistant lung adenocarcinoma cells

Chemoresistance is an inevitable occurrence in lung adenocarcinoma, which has been associated with decreased expression of the phosphatase and tensin homolog deleted on chromosome ten (PTEN). Therefore, it is important to identify novel molecular mechanisms to suppress chemoresistance in lung adenocarcinoma cells. Paclitaxeland cisplatin-resistant A549 lung carcinoma cell derivatives were developed by longterm serial culture. The metastatic properties of the cells were assessed using wound-healing assays, migration assays, invasion assays, morphological examination, and western blot analysis/ RT-PCR of genes associated with the epithelial-mesenchymal transition (EMT). To identify novel regulators of EMT in A549 cells, differentially expressed miRNAs in drug-resistant cells were identified by microarray analysis. The role of miR181a was established by transfection with specific mimic and inhibitor followed by functional assays. Luciferase assays were performed to assess the ability of miR-181a to target the PTEN promoter, and regulation of PTEN expression by miR-181a was assessed by western blot analysis and RT-PCR. Paclitaxeland cisplatin-resistant A549 cells acquired metastatic properties and EMT phenotype and had reduced PTEN expression as compared to sensitive cells. miR-181a was identified as a differentially expressed miRNA in drug-resistant A549 cells, and miR-181a mimic and inhibitor were shown to affect migration, invasion, morphology and expression of EMT-associated genes. PTEN was identified as a direct target of miR-181a. Our findings demonstrate that miR-181a expression in lung adenocarcinoma is associated with EMT progression, potentially through targeting of PTEN. Regulation of miR-181a may provide a novel strategy for overcoming resistance to paclitaxel and cisplatin in lung adenocarcinoma. Introduction Lung adenocarcinoma is a highly malignant disease with aggressive clinical behavior. In 2013, lung cancer was predicted to account for 26% of all female cancer deaths and 28% of all male cancer deaths (1). Patients diagnosed with lung adenocarcinoma usually survive only a few months, even with the assistance of individualized treatment strategies, including surgery combined with radiation and chemotherapy. The high mortality is mainly accounted for by drug resistance during chemotherapy treatment. Thus, to achieve better treatment outcome in lung adenocarcinoma patients, it is of the utmost importance to explore the mechanisms of drug resistance and to identify novel methods to overcome drug resistance. Paclitaxel and cisplatin, as first-line treatment for patients suffering from lung adenocarcinoma, improves survival with manageable toxicity (2,3). However, tumor cells acquire resistance to paclitaxel/cisplatin, which causes eventual failure to prolong the survival of lung adenocarcinoma patients. There is abundant evidence that chemoresistance is associated with the acquisition of EMT phenotypic of cancer cells (4). The serial process of EMT involves epithelial cells switching to mesenchymal phenotypic cells. The epithelial cell-cell junctions become disassembled, and the expression of epithelial markers, including E-cadherin and β-catenin, is reduced, while the motility and invasion potential is increased, and mesenchymal properties, such as the high expression of molecular markers vimentin, Snail, Slug, Twist, Zinc-finger E-boxbinding homeobox1 (ZEB1) and ZEB2, become apparent (5-8). Additionally, EMT is often associated with the loss of expression of the phosphatase and tensin homolog deleted on chromosome ten (PTEN), an inhibitor of the phosphatidylinositol 3-kinase/ Akt pathway (9). Mutation or reduced expression of PTEN is frequently observed in lung cancer, though the mechanism of PTEN loss is not well understood (10,11). MicroRNAs (miRNAs) have been see as key post-transcriptional level regulators of gene expression (12). Involvement of miRNAs has been demonstrated in tumorigenesis, metastasis, embryonic development, metabolism and other pathological and normal physiological (13,14). PTEN has been shown to be a tumor suppressor gene in human hepatocellular carcinoma, and miRNA-21 has been shown to regulate the expression of PTEN (14). MicroRNA-492 expression promotes the progression of hepatic cancer by targeting PTEN (15). The PTEN MicroRNA-181a regulates epithelial-mesenchymal transition by targeting PTEN in drug-resistant lung adenocarcinoma cells HAIHUI LI1,2, PEI ZHANG3, XIAOJIN SUN3, YIMING SUN3, CHAO SHI2, HAO LIU3 and XUEGANG LIU1,2 1Shandong University, Jinan, Shandong; 2Department of Thoracic Surgery, The First Affiliated Hospital of Bengbu Medical College, Bengbu, Anhui; 3Faculty of Pharmacy, Bengbu Medical College, Bengbu, Anhui, P.R. China Received June 12, 2015; Accepted August 4, 2015 DOI: 10.3892/ijo.2015. 3144 Correspondence to: Professor Hao Liu, Faculty of Pharmacy, Bengbu Medical College, Bengbu, Anhui, P.R. China E-mail: liuhao6886@foxmail.com Professor Xuegang Liu, Shandong University, Jinan, Shandong,