br Acknowledgments br Introduction Lung cancer is a common b

Acknowledgments
Introduction Lung cancer is a common but extremely perilous cancer, with approximately 733,000 new incidences reported annually in China [1]. Lung cancer ranks highest in the causes of tumor-related mortality, accounting for approximately one quarter of all cancer deaths [2]. Non-small cell lung cancer (NSCLC) accounts for approximately 85% of lung cancers, and lung adenocarcinoma (LAD) is a subtype of NSCLC [3]. Despite the improvements in lung cancer treatment that have been achieved in recent decades, there are still several obstacles to improving the survival rate, such as late diagnosis, chemotherapy resistance and a high metastatic rate [[4], [5], [6]]. Therefore, developing novel targets and biomarkers for lung cancer and investigating the underlying molecular mechanisms are essential and urgent. As short, noncoding RNA molecules, microRNAs (miRNAs) are believed to serve as key regulators of transcription and to participate in tumorigenesis by targeting oncogenes or tumor suppressors [7]. MiR-21 has been implicated in multiple malignancy-related processes and facilitates the progression of various malignancies, such as cervical cancer [8], gastric cancer [9] and renal cancer [10]. MiR-21 is a biomarker for early-stage NSCLC, as its expression is remarkably upregulated in NSCLC tissues [11]. MiR-21 overexpression also distinctively suppresses cellular apoptosis in NSCLC [12]. Through modulating EZH2, miR-21 upregulation enhances the proliferation and chemo/radio therapy resistance of lung cancer cells [13]. Therefore, the dysregulation of miR-21 is very likely to influence the progression of LAD. WW and C2 domain containing 1 (WWC1, also called KIBRA) is a gene localized on the positive strand of chromosome 5q34, and this gene is predominantly expressed in the kidney and Telatinib [14]. KIBRA participates in the regulation of important intracellular transport processes and the establishment of cell polarity [15]. However, the association between KIBRA and human cancers remains unclear. Moleirinho et al. reported that the reduced expression of KIBRA was correlated with a more aggressive subtype of breast cancer and a worse prognosis [16], indicating that KIBRA may be an anti-oncogene. The Hippo signaling pathway regulates various cellular processes, such as growth control, cellular polarity and contact inhibition [17], and this pathway was shown to be crucially important in not only lung development but also lung tumorigenesis [18]. In metastatic lung cancer, cell migration and invasion were shown to be suppressed by knocking down Yap1 and Taz, the Hippo mediators [19]. The oncogene RASSF7 inhibited the Hippo signaling pathway in NSCLC and upregulated the expression of proteins associated with cell viability and invasion [20]. Previous studies have indicated that KIBRA is an upstream regulator of this pathway [14]. Considering the close relationship between KIBRA and the Hippo signaling pathway, we believed that they both greatly influence the development of LAD. Therefore, using bioinformatics analysis, we not only identified KIBRA as the hub gene which is downregulated in LAD but also revealed the suppression of the Hippo signaling pathway in LAD. With elevated expression levels, miR-21 promoted LAD progression by targeting KIBRA. These discoveries implied that in LAD, the Hippo signaling pathway was of great importance. Moreover, miR-21 and KIBRA may be potential targets/biomarkers for LAD treatment.
Material and methods
Results
Discussion The significantly altered genes and pathways in LAD tissues were identified through bioinformatics analysis. KIBRA was the hub gene of the black module screened by WGCNA, and the Hippo signaling pathway was the distinctively suppressed pathway identified by GSEA. MiR-21 was shown to target KIBRA and to be upregulated in LAD, promoting the growth and metastasis of LAD cells. MiR-21 was also demonstrated to suppress the Hippo signaling pathway in LAD through targeting KIBRA.