Lung adenocarcinoma is the most common type of lung cancer with 80% incidence of all lung cancers (20), which is closely related with metastasis and poor prognosis. Histopathology is necessary for cancer diagnosis, while it is inadequacy for predicting disease progresssion and prognosis of lung adenocarcinoma (21). The gene expression profile analysis based on microarray data facilitates the discovery of biomarkers for patient survival prediction in lung adenocarcinoma. Here, in this paper, we utilized the lncRNA/mRNA expression profiles of NSCLC cells to identify the biomarkers for predicting metastasis and prognosis of lung adenocarcinoma patients.
PPI network was constructed for genes with differential expression. Our data showed that CCNB1 and TTK were the significant nodes in PPI network and both of the genes were clustered in module A. CCNB1 encoding cyclin B1 protein is a member of conserved cyclin family that plays a regulatory role in cell cycle (22). The function and pathway analysis showed that CCNB1 was involved in cell cycle related biological processes, such as cell cycle checkpoint and chromosome segregation, which was according to the previous report (23). The genetic polymorphisms of CCNB1 was found to be related with the susceptibility, progression, and survival of breast cancer in Han Chinese (23). CCNB1 has been proposed to be the marker for predicting prognosis of patients with ER+ breast cancer (24). In addition, the down-regulation of CCNB1 is closely related impaired cell proliferation and tumor growth of colorectal cancer (25). Besides, the previous gene expression profiling analysis showed that cell cycle genes such as CCNB1 were altered at the early stage of lung adenocarcinoma (26). Previous evidences have showed that CCNB1 expression is associated with tumor progression and prognosis of lung adenocarcinoma (27, 28). Our survival analysis also showed CCNB1 was a prognosis associated gene and was expected to be a biomarker for predicting prognosis of lung adenocarcinoma.
TTK (threonine and tyrosine kinase), also known as Mps1 (monopolar spindle1), is the core component of spindle assembly checkpoint, which plays a key role in chromosomes allocation. TTK has been found to be overexpressed in several types of human cancers, such as glioma, breast cancer, and colon cancer (29). It is reported that TTK protein was significantly up-regulated in liver tumor tissues compared with adjacent normal hepatic tissues (30). TTK expression inhibition by TTK siRNA significantly suppressed the liver tumor growth and the spread of tumor cells. Targeting TTK has been proposed to be an adjunct therapy for liver cancer. In addition, TTK has been found to be specially overexpressed in triple-negative breast cancer, a aggressive subtype of breast cancer (31). The expression of TTK has been determined to evaluate the prognosis of colon and breast cancer (32, 33). Although the role of TTK in cancers has been widely reported, the studies about TTK in lung adenocarcinoma are limited. In this paper, TTK was found to be a prognosis associated gene and prominently enriched in cell cycle checkpoint, chromosome segregation. We suggested that TTK was involved in cell proliferation and may be the biomarker for predicting the prognosis of lung adenocarcinoma.
In addition, lncRNA-mRNA interaction network showed that CCNB1 was a target for lncRNA SNHG12 which was the most significant node in lncRNA-mRNA network. A recent study suggested that SNHG12 mediated oxygen-glucose deprivation and induced reoxygenation damage in neurons underlying ischaemic stroke. Our function enrichment analysis showed that SNHG12 was closely related with GO:0055114~oxidation-reduction process and hsa00010:Glycolysis/Gluconeogenesis pathway. Our findings may explain the role of SNHG12 in ischaemic stroke, which suggested that our findings were significant. Besides, SNHG12 was also involved in GO:0006260~DNA replication and GO:0000082~G1/S transition of mitotic cell cycle, which suggested that SNHG12 could regulate the cell proliferation. Recent evidences show that lncRNA SNHG12 promotes proliferation and metastasis of osteosarcoma and papillary thyroid carcinoma (34, 35), which was consistent with our findings. The oncogenic role of lncRNA SNHG12 is also determined in cervical cancer (36) and prostate cancer (37). However, the prognostic role in lung adenocarcinoma has been reported rarely. In this paper, survival analysis showed that lncRNA SNHG12 was closely associated with prognosis. Thus, we suggested lncRNA SNHG12 as a biomarker for prognosis of lung adenocarcinoma.
In conclusion, the mRNA and lncRNA expression profile revealed the differential expressed mRNAs and lncRNAs based on microarray data. TTK and CCNB1 were differentially expressed in high metastatic lung adenocarcinoma cells and they were the significant nodes in PPI network. LncRNA SNHG12 was identified to be the differentially expressed lncRNA in lung adenocarcinoma cells and was a core node in coexpression network. TTK , CCNB1 and lncRNA SNHG12 were proposed to be the biomarker for the metastasis and prognosis of lung adenocarcinoma.