In the current clinical diagnosis and treatment, the continuous increase of serum alpha-fetoprotein (AFP) is often used as an important indicator of liver cancer, but the increase of AFP is also common in some other liver diseases, such as cirrhosis , indicating that the specificity and sensitivity of AFP for the diagnosis of liver cancer is not enough. Therefore, biomarkers with higher specificity and sensitivity are needed to diagnose early HCC and effectively judge the future survival of HCC patients. At present, many new and more effective biomarkers are being discovered and applied in clinics. For example, silencing DUSP21 significantly inhibited cell proliferation, colony formation, and tumorigenicity of HCC cells in vivo. DUSP21 plays a significant role in maintaining hepatocellular carcinoma cell proliferation, therefore it could be a potential therapeutic target for liver cancer . High expression of cholesterol esterase (SOAT1) was associated with the worst prognostic risk. By inhibiting the cholesterol esterification enzyme SOAT1, cholesterol levels on the cytoplasmic membrane can be reduced, effectively inhibiting tumour cell proliferation and migration . Therefore, in our study, DEGs and WGCNA were used for the biological analysis of HCC in TCGA and GEO databases. As a result, 73 genes were obtained; PPI and Cytoscape were used for further analysis of Overlapping genes to obtain 10 Hub genes. Namely, CDK1, TOP2A, DLGAP5, CDC20, ASPM, CEP55, TPX2, KIF11, KIF20A, CCNA2. Combining the enrichment of OS, DFS and KEGG pathways of 10 genes, ultimately we found that high expression of CDK1, CDC20 and CCNA2 was significantly associated with OS in HCC patients.
Cyclin Dependent Kinase 1 (CDK1) is the protein-encoding gene for a protein that is a member of the Serine/threonine-protein Kinase family. The protein is a catalytic subunit of a highly conserved protein kinase complex called the M-phase promoting factor (MPF), which is required for the G1/S and G2/M phase transitions of the eukaryotic cell cycle. It was found that miR-582-5p was down-regulated in hepatocellular carcinoma tissues and up-regulation of miR-582-5p inhibited cell proliferation and blocked the cell cycle in G0/G1 phase. miR-582-5p directly inhibited the expression of CDK1 and AKT3, and indirectly inhibited the expression of cyclinD1, thereby regulating HCC . Experiments have also confirmed that dihydroartemisinin (DHA) can reduce the expression level of CDK1, thereby inhibiting the proliferation of liver cancer cells . At present, CDK1 is highly expressed in various tumour tissues to varying degrees, and it has been proved that CDK1 can play an important role in lung cancer , breast cancer , pancreatic cancer , colorectal cancer  and so on by regulating the cell cycle. In the present study, high CDK1 expression was strongly associated with poor prognosis in HCC patients. KEGG pathway also showed that CDK1 was mainly involved in cell cycle, Oocyte meiosis, Cellular Senescence, P53 signalling Pathway and other signalling pathways. Studies have found that CCNB1/CDK1 can mediate mitochondria, coordinate ATP output, and provide biological energy for cell G2/M transformation, thus interrupting the cell replication cycle [15, 16]. Therefore, CDK1 plays an essential role in the cell cycle and cell proliferation.
Anaphase Promoting Complex (APC) was activated by cell division cycle 20 (CDC20) and CDH1 to form two different E3 ubiquitin ligase complexes sub-complexes, APCCdc20 and APCCdh1. CDC20 is an oncogenic factor and CDH1 is a tumour suppressor factor . It is currently believed that the APCCdc20 complex can disrupt the ubiquitination of downstream cell cycle regulators securin and cyclin B  and regulate the activity of downstream pluripotent related transcription factors SOX2 to promote the invasion and renewal of glioma stem cells . The degree of CDC20 expression has now been found to correlate significantly with tumour prognosis, with higher CDC20 expression associated with lower 5-year survival rates for patients. Studies have shown that the expression level of CDC20 increases in non-small cell lung cancer (NSCLC), resulting in the more significant pleural invasion of cancer cells, while the growth rate of lung cancer cells is significantly slowed down after the expression level of CDC20 is down-regulated . In our study, the high expression of CDC20 also predicted the poor prognosis of HCC patients, and CDC20 was mainly enriched in cell cycle, oocyte meiosis and other pathways. A related study found that CDC20 was overexpressed in 68% of hepatocellular carcinoma tissues , that overall survival was lower in HCC patients with high CDC20 expression, and that CDC20 was predictive of prognosis in HCC patients . In addition, numerous studies have found that anti-mitotic agents such as paclitaxel can inhibit APCCdc20, and CDC20 gene knockout can lead to a checkpoint-independent mitotic block, which can effectively kill cancer cells [23, 24]. All of these suggest that CDC20 is a potential target for the treatment of HCC.
The CCNA2 gene encodes a protein that belongs to a family of highly conserved cell cycle proteins, whose members function to regulate the cell cycle. CCNA2 binds and activates cyclin-dependent kinase 2, thereby facilitating the G1/S and G2/M transitions. Studies have shown that p53-P21-DREAM-CDE /CHR pathway can down-regulate the CCNA2 gene, thereby blocking the G2/M cell cycle and controlling the growth of cancer cells . This article also found that high CCNA2 expression was significantly associated with the prognosis of HCC patients and that the proliferation of hepatocellular carcinoma cells could be inhibited by drugs that inhibit the FXR-miR-22-CCNA2 signalling pathway . The current studies have found that CCNA2 is highly expressed in all types of tumours. For example, E2F1 can promote the proliferation of triple-negative breast cancer (TNBC) through up-regulation of CCNA2 . miR-545 can inhibit proliferation by inhibiting CCNA2 expression in osteosarcoma cells . In addition, the high expression of CCNA2 has been reported in lung cancer , gastric cancer , ovarian cancer  and esophageal cancer .
Multiple bioinformatics methods were used to jointly screen out potential targets for HCC. This study indicated that the high expression of CDK1, CDC20 and CCNA2 was negatively correlated with the survival rate of HCC patients, and these targets are mainly involved in regulating the cell cycle and thus controlling the proliferation of tumour cells. These newly discovered potential targets may provide new ideas and new research directions for the treatment of HCC and have important clinical significance. However, our study also had many limitations. First, the sample size we selected was not large enough for a specific analysis of subtypes in HCC, which may lead to inaccurate hub genes screening and insufficient coverage. Secondly, the reliability of Hub genes has not been verified experimentally in this paper, and the specific mechanism of hub genes regulating HCC is not fully understood, which needs further exploration in the future.