Nowadays, LUAD is one of the most important subtypes of non-small cell lung cancer, which still has the characteristics of high incidence and extreme mortality[17]. The main reason is lacking effective biomarkers that can accurately identify the diagnosis of LUAD patients at present[18]. Therefore, we conducted a comprehensive analysis of the datasets selected from the GEO database using bioinformatics methods to screen candidate genes for the diagnosis and prognosis of LUAD patients, and explored the correlation between the immune cells infiltration and the expression levels of these genes in the LUAD tissues in this study.
First, the three GSE datasets obtained from the GEO database were utilized to screen the DEGs, and a total of 156 common up-regulated genes and 434 common down-regulated genes were found. Subsequently, 156 common up-regulated genes were submitted to Metascape for the analysis of GO and pathway enrichment. Biological processes (BP), molecular functions (MF) and cellular components (CC) are fully included in this GO analysis. Subsequently, the PPI network was constructed based on common up-regulated genes using Metascape and the MCODE plug-in was used to screen out seven important subnetworks in the PPI network, namely MCODE 1, MCODE 2, MCODE 3, MCODE 4, MCODE 5, MCODE 6 and MCODE 7[19]. MCODE 1 contains the largest number of key genes, which are AURKB, CDC20, CDCA5, CDCA8, CENPF, KNTC1 and CCNB2, respectively. Next, GEPIA2 and UALCAN databases were used to analyze the expression levels of the above candidate genes in LUAD tissues and normal lung tissues and found that the expression levels of hub genes in tumor tissues were all significantly higher than in normal tissues, expect KNTC1. In addition, the analysis of the Kaplan-Meier Plotter database found that these key genes with high expression levels showed worse prognosis in patients with LUAD. Further, we explored the correlation of these candidate genes with the infiltration of six immune cells in patients with LUAD in order to look forward to providing new insight in tumor immunotherapy.
AURKB (Aurora Kinase B) is a protein coding gene that acts as a key regulator of mitosis[20]. Many existing studies have confirmed that AURKB is a crucial carcinogenic factor in different kinds of carcinoma. For example, AURKB was found to be expressed at higher levels in renal cell carcinoma tissues than in normal kidney tissues, suggesting that it may regulate renal cell carcinoma progression by modulating the intestinal immune network for IgA production and signaling pathways involving cytokine-cytokine receptor interactions[21]. Furthermore, AURKB was overexpressed in gastric cancer and was strongly linked to clinicopathologic features of the disease. Silenced AURKB may decrease the invasive and migratory capacities of gastric cancer cells by disrupting the VEGFA/Akt/mTOR and Wnt/-catenin/Myc pathways[22]. Additionally, AURKB activation was attributed to acquired resistance to EGFR TKIs, suggesting that AURKB might be a target in NSCLC patients who were advancing to anti-EGFR treatment but did not have resistance mutations[23].
CDC20 (Cell Division Cycle 20) appears to act as a regulatory protein interacting with several other proteins at multiple points in the cell cycle[24]. Min Shi et al. found that CDC20 played a crucial role in the development of hepatocellular carcinoma by governing PHD3 protein[25]. Besides, Yang Gao et al. found that targeting CDC20 radiosensitized colorectal cancer cells through mitochondrial-dependent apoptotic signaling[26]. Thus, Qin Zhang et al. found that CDC20 combined with CD44 or β-catenin could serve as an important indicator for the prognosis of patients with prostate cancer[27]. Further, Huan Deng et al. found that CDC20 was upregulated in LUSC at the mRNA and protein levels[28]. However, little research has been done on the effects of CDC20 on LUAD, and the mechanism of action remains unclear.
CDCA5 (Cell Division Cycle Associated 5) is another protein-coding gene involved in DNA repair[29]. CDCA5 promoted the progression of bladder cancer via dysregulating mitochondria-mediated apoptosis, cell cycle regulation, and activation of the PI3k/AKT/mTOR pathway[30]. Additionally, CDCA5 aided in the development of esophageal squamous cell carcinoma. and may be an interesting target for esophageal squamous cell carcinoma immunotherapy[31]. Moreover, CDCA5 phosphorylation and activation by mitogen-activated protein kinase were critical for human lung cancer[32].
CDCA8 (Cell Division Cycle Associated 8) is a component of the chromosomal passenger complex, which is required for mitosis and cell division to occur[33]. According to current literatures, increased CDCA8 expression in ovarian cancer tissues probably played a critical role in the development of ovarian cancer and it most likely functioned in carcinogenesis through the PLK1 pathway[34]. Besides, CDCA8 was involved in the construction of meiotic spindles and chromosomal segregation during human oocyte meiosis[35]. Meanwhile, CDCA8 overexpression accelerated the development of cutaneous melanoma and resulted in a worse prognosis[36]. Additionally, aurora kinase B-mediated phosphorylation and activation of CDCA8 played a major role in human lung cancer[37]. Moreover, miR-133b suppressed lung adenocarcinoma cell proliferation, motility, and invasion by targeting CDCA8[38].
CENPF is a gene that encodes a protein that is involved in the centromere-kinetochore complex association[39]. A current study indicated that overexpression of CENPF in breast cancer was associated with a poor prognosis and tumor bone metastases by controlling parathyroid hormone-related peptide (PTHrP) production via activating PI3K-AKT-mTORC1[40]. Besides, the HnRNPR-CCNB1/CENPF axis was involved in the proliferation and metastasis of gastric cancer[41]. Additionally, silencing CENPF substantially reduced LUAD cell tumor development in an experimental xenograft lung cancer model using naked mice armpits of the right forelimb. However, there was no sufficient studies on the mechanism of CENPF in LUAD[42].
KNTC1 encodes a protein participating in the processes that guarantee correct chromosomal segregation during cell division[43]. A recent study indicated that silencing KNTC1 with shRNA inhibited cell viability and caused apoptosis in esophageal squamous cell carcinoma[44]. Moreover, relevant bioinformatics publications demonstrated that KNTC1 was associated with a poor outcome in patients with hepatocellular carcinoma and cervical cancer[45, 46]. However, there has been no research on the mechanism of action of KNTC1 in patients with LUAD.
CCNB2 (Cyclin B2) is a member of the cyclin family, more precisely the B-type cyclins that can interact with p34cdc2, and was a critical component of the cell cycle regulation mechanism[47]. In vitro and in vivo, CCNB2 promoted the proliferation of triple-negative breast cancer cells[48]. As validated by a comprehensive bioinformatics study, CCNB2 was a promising therapeutic target for ovarian cancer[49]. Additionally, miR-335-5p targeting CCNB2 could disrupt the cell cycle and increase lung adenocarcinoma metastasis[50]. Moreover, CCNB2 had been discovered as a marker of immune checkpoint inhibitor (ICI) responsiveness in NSCLC and overexpression of CCNB2 was a poor prognostic indicator in Chinese patients with NSCLC[51, 52].
The findings of our research were acquired through data mining online database using bioinformatics techniques. The limitations of this study included the absence of specific in vitro or in vivo experiments to validate the significance of the selected hub genes in LUAD patients. Additionally, the results of our study may include partial bias owing to the issue of data quantity and quality. As a result, we will further verify experimental evidence of function for these potential genes as soon as possible in the future.