As shown in Figure 6, in this study, first, we together selected four NSCLC databases from GEO according to the screening principle which was described in the data source and preprocessing section; Second, we used GEO2R online tools to analyze the DEGs extracted from the four datasets respectively; Third, we applied Venn diagram software online to screen the common DEGs in these four datasets. In this part, we found that there were 162 DEGs in these four databases, including 41 up-regulated genes and 121 down-regulated genes in NSCLC tissues; Fourth, we analyzed all the 162 DEGs GO enrichment and KEGG pathways by using DAVID software. As shown in Table 3, the 162 DEGs were mainly enriched in ECM-receptor interaction, cell adhesion molecules, leukocyte transendothelial migration, protein digestion and absorption, PPAR signaling pathway, adrenergic signaling in cardiomyocytes and neuroactive ligand-receptor interaction to exert their biological function; Fifth, we constructed the PPI network of these 162 DEGs by applying the STRING database, then we discovered a significant modular containing 10 nodes through utilizing the Cytotype MCODE. These 10 core genes are ANLN, CCNA2, CDCA7, DEPDC1, DLGAP5, HMMR, KIAA0101, RRM2, TOP2A, and UBE2T; Last, we further analyzed the survival curve and the expression level between NSCLC tissues and normal lung tissues of these 10 core genes through Kaplan Meier plotter online database and GEPIA respectively. Taken together, we discovered that all the 10 genes were associated with poor prognosis in NSCLC, and they were all up-regulated DEGs.
ANLN (Anillin), an actin binding protein, is first found in Drosophila as a 124 kDa protein and plays an important role in cytokinesis (11). ANLN has higher expression levels in the brain, testis, and placenta, but lower expression levels in the heart, kidney, liver, pancreas, prostate, spleen and lung. Recently, ANLN has been identified as a prognostic biomarker in cervical cancer, breast cancer, pancreatic cancer, colorectal cancer, and bladder urothelial carcinoma. ANLN is also discovered overexpressing in the majority of the primary NSCLC and is involved in the metastasis of lung cancer (12). Pathway analysis demonstrated that ANLN participated in developmental processes through the regulation of nuclear division pathway (13).
CCNA2 (CyclinA2) belongs to a ubiquitously expressed member of the cyclin family and is expressed in almost all tissues in human (14). Evidence indicated that CCNA2 was up-regulated in many kinds of cancers, and as an oncogenic gene, CCNA2 also played an important role in regulating cancer cell growth and apoptosis, especially controlling the cell cycle at the G1/S and the G2/M transitions (15). CCNA2 can be used as a prognostic biomarker for colorectal cancer, ER+ breast cancer, esophageal squamous cell carcinoma and pancreatic etc. Resent study indicated that CCNA2 has higher expression in human NSCLC specimens than normal lung tissues, and could induce EMT and promote NSCLC metastasis via integrin αvβ3 signaling pathway (16). However, further research is needed to uncover the target gene of CCNA2.
CDCA7 (Cell division cycle-associated protein 7), also known as JPO1, is a new member of cell division cycle associated genes family (17). CDCA7 has been identified as a DNA-binding protein (18). MYC and E2F1 could bind to the promoter of CDCA7, thereby driving CDCA7 expression. Recently, CDCA7 was discovered as a critical regulator of lymphomagenesis and invasion (19), while overexpression of CDCA7 predicted poor prognosis in triple negative breast cancer and colorectal cancer (20, 21). Wang’s study indicated that CDCA7 was significantly overexpressed in LUAD compared with the normal lung tissues, and silencing CDCA7 could inhibit cell proliferation through G1 phase arrest and induction of apoptosis (22). In conclusion, CDCA7 can be considered as a therapeutic target for LUAD.
DEPDC1 (DEP domain containing 1), a highly conserved protein, plays important roles in many biological processes, for example, cell proliferation, cell cycle progression, cell apoptosis and signaling transduction etc (23). DEPDC1 was firstly reported to be highly overexpressed in bladder cancer and had a critical role in the development of the bladder cancer (24). Nowadays, DEPDC1 is considered as a novel oncoantigen which is upregulated in many kinds of cancers, including hepatocellular carcinoma, nasopharyngeal carcinoma, prostate cancer, breast cancer, and malignant glioma. DEPDC1 expression is also increased in LUAD and can be applied as a prognostic biomarker for NSCLC patients (25). Recently, DEPDC1 was found inducing apoptosis in A549 lung adenocarcinoma cells by the NF-κB signaling pathway (26). Further studies are needed to explore the mechanism of DEPDC1.
DLGAP5 (disc large homolog-associated protein 5), a mitotic spindle protein, can exert important biological function as a signaling molecule because it contains a guanylate-kinase-associated protein (GKAP) domain, which is highly conserved among many species and found in various eukaryotic signaling proteins (27). DLGAP5 overexpression could promote the proliferation potential of human cells, and the overexpression also been discovered in hepatocellular carcinoma, prostate cancer, colorectal cancer and adrenocortical carcinoma. Recently, studies also uncovered that DLGAP5 was highly overexpressed in the lung cancer tissues compared to corresponding normal lung tissues (28). Hence, DLGAP5 can be used as promising biomarker for early detection of lung cancer.
HMMR (Hyaluronan-mediated motility receptor), as an oncogene, is found highly up-regulated and plays important roles during the progression of human leukemias and solid tumors (29, 30). Tilghman’s work revealed that HMMR was overexpressed in glioblastoma (GBM) tumors where it supported the self-renewal and tumorigenic potential of GBM stem cells (31). Taken together, HMMR not only promotes the progression of tumor, but also maintains the cancer stem cell (CSC) stemness. Meanwhile, some other studies have developed HMMR with great value for prognostic prediction in NSCLC (32). But further research is needed to state the regulated mechanism of HMMR in NSCLC.
KIAA0101, also named as proliferating cell nuclear antigen (PCNA)-associated factor (PAF15), functions as an oncogene and is upregulated in various cancers, including breast cancer, esophageal cancer, hepatocellular carcinoma, ovarian cancer and lung cancer. KIAA0101 has been recently considered as a potential biomarker for recurrence and poor prognosis in tumor patients. Kato’s study discovered that KIAA0101 was overexpressed in the great majority of lung cancers, and KIAA0101 could be used as a specific target to treat lung cancer (33).
RRM2 (Ribonucleotide reductase M2 subunit), a small subunit of the ribonucleotide reductase complex, is a rate-limiting enzyme for dNTP producing and displays critical roles in many cellular processes such as cell proliferation, invasiveness, migration and angiogenesis (34). RRM2 has been reported overexpressing in various malignancies as a tumor driver, including breast cancer, gliomas, colorectal cancer, bladder cancer and NSCLC. Yang’s work found RRM2 was upregulated in NSCLC tumor and cell lines, and the aberrant upregulation predicted a poor prognosis (35). Mechanistically, they also revealed the vital role of LINC00667/miR-143-3p/RRM2 signal pathway in the NSCLC progression. In conclusion, RRM2 can be used as a therapeutic target for NSCLC.
TOP2A (Topoisomerase 2-alpha) encodes a nuclear enzyme which implicates in almost any processes of DNA metabolism, such as replication, transcription and chromosome segregation during interphase and mitosis (36). It has been reported that TOP2A has higher expression level in a variety of human cancers, including gastric cancer, bladder urothelial carcinoma, colon cancer and pancreatic cancer. Meanwhile, TOP2A also can be considered as the target for some of the most widely used chemotherapeutic drugs for human cancers treatment (37). But the role of TOP2A in progression of NSCLC has not been elucidated.
UBE2T (Ubiquitin-conjugating enzyme E2T, also named as HSPC150), a member of the E2 family, is firstly identified in a patient with Fanconi anemia (FA) (38). UBE2T takes part in main cellular processes such as cell cycle control, signal transduction and tumorigenesis through working with specific E3 ubiquitin ligase to active the degradation of relevant substrates (39). UBE2T has been also discovered overexpressed in prostate cancer, osteosarcoma, gastric cancer, hepatocellular carcinoma and lung cancer. But the mechanism of UBE2T to promote the progression of NSCLC is not clear now. Further studies are needed to clarify the relationship between UBE2T and NSCLC.