Liver cancer is the fourth leading cause of cancer-related deaths worldwide, with an estimated incidence rate of over one million cases per year, which seriously endangers human health (Bray et al., 2018; Llovet et al., 2018). Hepatocellular carcinoma (LIHC), accounting for 75–85% of cases, is the main pathological type of primary liver cancer (Bray et al., 2018). The majority of LIHC cases arise from hepatitis B and hepatitis C in hepatocytes (Zhang et al., 2004; Makarova et al., 2016). Additionally, the rising incidence of LIHC is due to a high rate of alcohol consumption and the occurrence of non-alcoholic fatty liver disease (Schütte et al., 2009; Gish et al., 2016). Although the development of various treatment technologies, including surgical resection, liver transplantation surgery, interventional therapy, chemotherapy, and radiotherapy, may reduce mortality to some extent, LIHC patients still bear a poor five-year survival rate of only 20–30% (Pang et al., 2008; Yang et al., 2009). Thus, there is an urgent need to deepen the understanding of LIHC tumorigenesis and develop new treatment and monitoring methods for early detection and prolong the survival of LIHC patients.

Dysregulation in any process of cell division may lead to malignancy (Collins and Garrett, 2005). Cell Division Cycle Associated (CDCA) family proteins, including eight respective members of CDCA1-8, function to regulate the cell cycle and proliferation, which play an important role in biological process. Previous studies have shown that the expression levels of all or part of CDCA family genes are significantly upregulated in lung cancer, breast cancer, renal cell cancer, etc. This high expression is usually associated with a poor prognosis. For example, CDCA genes are highly expressed in ovarian cancer tissues and act on the PLK pathway to promote tumor invasion and metastasis (Chen et al., 2020a; Chen et al., 2020b). CDCA7 can accelerate the proliferation of lung adenocarcinoma and non-small cell lung cancer by regulating the cell cycle (Wang et al., 2019). High mRNA expression of CDCA3/5/7/8 in breast cancer significantly reduced the survival rate of patients (Phan et al., 2018). These findings strongly suggest the potential role of CDCAs in the tumorigenesis and prognosis of patients. It is necessary and meaningful to understand the mechanism of action of CDCAs in LIHC. To date, however, there is no systematic and comprehensive analysis of CDCAs in LIHC.

To reveal the mechanism of LIHC tumorigenesis and to identify diagnostic and prognostic markers or therapeutic targets for LIHC patients, in the current study, the transcriptional levels of CDCA genes were investigated by Oncomine and GEPIA, and we found that CDCA1/3/5/8 expression levels were significantly increased in LIHC. We also evaluated the impact of CDCA1/3/5/8 on the prognosis of LIHC patients. Specifically, we analyzed the effect of CDCAs expression on the prognostic survival rate of LIHC patients, the correlation between CDCAs transcription and various clinical factors by Kaplan-Meier plotter, and the effect of genetic alterations of CDCAs on prognosis by cBioPortal. The relationship between CDCA1/3/5/8 and immune cell infiltration was analyzed using TIMER 2.0. In addition, the interaction network between CDCAs and neighboring genes was mapped using GeneMANIA.

With high mortality and poor prognosis, LIHC has become the fourth leading cause of cancer-related deaths worldwide (Bray et al., 2018). Most of the LIHC patients missed the best treatment period because of the untimely diagnosis. For others, even if they are temporarily cured, they have to face a very low prognostic survival rate and a very high risk of recurrence. Based on the characteristics of abnormal proliferation and uncontrolled growth of tumor cells. CDCA genes, which are responsible for regulating the cell cycle and proliferation, were selected as our research object to explore the mechanism of hepatocarcinogenesis. Through a series of bioinformatics analysis methods and the use of publicly accessible online databases, including Oncomine, Kaplan-Meier plotter, GEPIA, GeneMANIA, cBioPortal, and TIMER 2.0, we investigated the expression profiles of CDCA family genes in LIHC and corresponding normal tissues, and the effect of CDCAs expression on the survival of prognosis and immune cell infiltration. In addition, we also analyzed the expression correlation of CDCAs and screened the neighboring genes related to functional CDCAs.

We found that the expression levels of CDCA1/3/5/8 were significantly increased in LIHC, regardless of stage, sex, race, drinking behavior, and other clinical factors. CDCAs expression was significantly correlated with poor prognosis of OS, DSS, RFS, and PFS and was positively correlated with the infiltration of dendritic cells, B cells, and macrophages. We also found that the most relevant neighboring genes to CDCAs in LIHC were SGO2, NDC80, BIRC5, INCENP, and PLOD1. In general, our work suggests that CDCA1/3/5/8 has the potential to be a diagnostic gene in hepatocarcinogenesis and prognostic biomarkers for LIHC patients.

The CDCA family consists of eight independent individuals named CDCA1–8. To clarify the role of CDCAs in LIHC, multiple database analysis was performed, and CDCA1/3/5/8 was found to be highly expressed in LIHC tissue. Moreover, this active expression of CDCAs was observed in all stages of LIHC, indicating that CDCA1/3/5/8 has potential as a diagnostic gene for the occurrence and development of LIHC. Similarly, CDCA has been shown to be highly expressed in many other cancer types, such as breast cancer and lung cancer, indicating its wide applicability and functional conservation. However, there was no significant upregulation of CDCAs in leukemia, suggesting that it is necessary to distinguish the types of cancer when they were used as diagnostic genes.

According to previous reports, CDCA1, also known as Nuf2, is mainly responsible for regulating cell mitosis (Zhang et al., 2015). Downregulation of CDCA1 expression can inhibit the proliferation of tumor cells, while overexpression of CDCA1 is associated with poor prognosis (Hu et al., 2015). CDCA3 has been shown to promote cell proliferation and invasion through activation of the Ras signaling pathway or hypomethylation in gastric cancer cells (Zhang et al., 2019). CDCA5 plays important roles in migration, proliferation, apoptosis, and invasion of tumor cells by regulating sister chromatid segregation and cohesion (Xu et al., 2019). CDCA8 is an integral part of the chromosomal passenger complex, which is involved in mitosis and contributes to distant metastasis of cancer cells (Jeon et al., 2017). It is worth noting that the high expression of these four genes has been proven to reduce the prognostic survival rate of many cancer patients. This is consistent with the results of our study. In particular, there is a significant negative correlation between CDCAs and four common prognostic indices of OS, DSS, RFS, and PFS, and this correlation is applicable to different clinical factors, suggesting that high expression of CDCAs may be one of the causes of poor prognosis. These biomolecules have the potential to be prognostic biomarkers for LIHC patients.

However, in the presence of pathological conditions, such as hepatitis virus or vascular invasion, there was no correlation between CDCAs and OS, except for CDCA8, suggesting that we should consider the patient’s clinical condition when selecting the diagnostic gene. In addition, we found that the alteration frequency of CDCAs is extremely high, and the genetic alteration will reduce the prognosis survival of LIHC patients. The factors causing gene alteration should be avoided in the process of treatment, and the degree of an alteration should be properly considered when detecting expression and evaluating prognosis.

Dendritic cells are special antigen-presenting cells that play a major role in activating T lymphocytes with anti-tumor effects (Wculek et al., 2020). B cells can produce a kind of IgG antibody to recognize a certain antigen in tumor tissue, which can inhibit tumor growth (Li et al., 2009). Macrophages were divided into M1 macrophages and M2 macrophages. M1 macrophages are mainly related to the recognition and attack of tumor cells, while M2 macrophages are related to tumor progression and immunosuppression (Yang and Zhang, 2017; Shapouri et al., 2018). CDCAs showed a significant positive correlation with dendritic cells, B cells, and macrophages, indicating that CDCA-mediated hepatocarcinogenesis might mobilize the activity of these immune cells and make them play an anti-tumor role. When we further analyzed the relationship between CDCA1/3/5/8 expression and the biomarker genes of immune cells, we found a significant positive correlation between CDCAs expression and all test biomarkers of B cells and dendritic cells. However, for M1 macrophages and M2 macrophages, CDCAs were only related to some of macrophages biomarker genes, indicating that there is a certain specificity and selectivity in this interaction, which also provides some basis for immunotherapy in the future.

Although these four genes have some differences in function and target genes (pathways), they jointly regulate the cell division cycle to promote the proliferation and invasion of tumor cells. The Pearson correlation coefficients of these four genes were all greater than 0.85. GeneMANIA analysis showed twenty neighboring genes to CDCAs, and the functions of these genes are also related to cell cycle regulation. For example, SGO1 is considered to play a major role in recruiting the chromosomal passenger complex to chromosomes (Bonner et al., 2020); SGO2 is a pericentromeric protein that associates with cohesin at centromeres and regulates chromosomal segregation during meiosis (El et al., 2017). SGO1/2 functions as an essential protector for centromeric cohesion and is required for accurate chromosome segregation during mitosis and meiosis (Dudas et al., 2011). PLOD1 has been reported to function in extracellular matrix formation and is involved in various diseases, including cancer (Wang et al., 2018). The NDC80 complex, including the main elements of NDC80, SPC24, and SPC25, is highly expressed in various tumors and cooperatively promotes the invasion and metastasis of tumor cells (Alushin et al., 2012; Umbreit et al., 2012). BIRC5 is a negative regulatory protein that inhibits tumor cell apoptosis and promotes cell proliferation (Cho et al., 2020; Shi et al., 2020).

These proteins are more or less involved in the development of tumors, which explains the mechanism of CDCA-mediated hepatocarcinogenesis to a certain extent. This also screened out some targets for future research on new therapeutic methods. However, the specific roles of CDCAs in tumorigenesis and development, as well as their interaction with target proteins need to be further verified. The same shortcomings run through our research because the results were based on big data mining and analysis, which inevitably led to some false-positive results. An important purpose was to provide researchers with a more instructive research idea and tried to make our findings point out a direction for future research. Although we mined the data as comprehensively as possible and had obtained some meaningful conclusions, the relevant results still require further experimental and clinical verification.