Our study consisted of 3 stages. We first compared the mRNA and protein expression levels of CDC45 in HCC tissues as well as normal tissues using various databases. We then investigated the prognostic value of CDC45 expression in HCC and found that patients with elevated CDC45 expression had advanced clinicopathological parameters and inferior survival. In the second stage, we assessed CDC45 expression at the protein level in our TMA and conducted a survival analysis based on a distinct comparison of the expression of CDC45. In the third stage, significantly involved DEGs of CDC45 were screened, and corresponding functional annotations were performed.
Transcriptional Levels Of CDC45 In Patients With HCC
We first compared the transcriptional levels of CDC45 expression between tissues from HCC and control (normal liver tissue) in three datasets. In the GEPIA database, 369 HCC and 160 normal tissues were used for the analysis, and the results showed that the CDC45 mRNA level was higher in HCC tissues than in normal tissues (Fig. 1a). CDC45 expression was also significantly higher in HCC tissues than in normal tissues in the Oncomine database (Fig. 1b). To further confirm the results, we analysed the expression of CDC45 in the GSE76427 dataset from the GEO database and obtained the results as above (Fig. 1c). In addition, the IHC results from the Human Protein Atlas showed that CDC45 staining was not detected in normal liver tissues(Fig. 1d,f), even if there were exsit tumour tissue that not detect CDC45 staining, a result showed that the medium levels of expression were observed in HCC tumour tissues (Fig. 1e,g).Taken together, these data indicated that CDC45 was upregulated at the transcriptional but unclear at proteomic levels in HCC tissues compared with normal tissues.
CDC45 mRNA expression correlated with advanced clinicopathological parameters and poor prognosis in HCC patients
Using the UALCAN analysis, we found significantly elevated CDC45 mRNA expression in HCC samples compared to normal samples. As shown in Fig. 2a, CDC45 mRNA expression in HCC samples was notably correlated with advanced clinical stage (P < 0.01). Similarly, the results shown in Fig. 2b suggested that CDC45 mRNA expression was significantly correlated with pathological grade (P < 0.01). Subsequently, the survival analysis using GEPIA showed that higher CDC45 expression was significantly correlated with shorter OS (Fig. 2c, P < 0.001) and disease-free survival (DFS) (Fig. 2d, P < 0.01) in 364 HCC patients. Overall, the upregulation of CDC45 expression levels was significantly associated with advanced clinicopathological parameters and poor prognosis in HCC patients.
Validation of CDC45 expression in HCC and adjacent normal tissues
After confirming the correlation between mRNA expression of CDC45 and prognosis of HCC patients in the bioinformatics database, we further detected the protein expression levels in our TMA. IHC staining was used to detect the CDC45 protein expression levels in HCC tumour samples and matched adjacent normal tissues from 56 HCC patients (Fig. 3a). CDC45 staining was observed mainly in the cytoplasm. Compared to adjacent normal liver tissues, the expression of CDC45 was significantly decreased in HCC tissues (P < 0.0001, Fig. 3b).
Association Of CDC45 Expression With Clinical Characteristics
We then explored the relationship between CDC45 expression levels and the clinicopathological features of HCC patients. Among the clinicopathological parameters, CDC45 expression was positively correlated with tumour size (P = 0.034) and microvascular invasion (P = 0.046). However, the correlation between CDC45 expression and other clinical parameters (including sex, age, tumour number, Edmondson grade, metastasis, vessel invasion, hepatitis B surface (HBs) antigen, and cirrhosis) was not significant (P > 0.05; Table 1). These findings suggested that low CDC45 expression is associated with worse overall disease condition.
Clinical significance of CDC45 expression in the prognosis of HCC
The Kaplan–Meier survival curve indicated that CDC45 expression was significantly associated with OS in HCC patients (P = 0.019; Fig. 3c). In all HCC patients, the OS was shorter in patients with low CDC45 expression than in patients with high CDC45 expression. Additionally, we used Cox regression to analyse the prognostic factors of HCC. A univariate Cox regression revealed that tumour size (P = 0.007), metastasis (P < 0.001), microvascular invasion (P = 0.022), Edmondson grade (P < 0.001) and vessel invasion (P = 0.011) were independent prognostic factors in patients with HCC. A multivariate Cox regression analysis revealed that distant metastases (P < 0.001) and Edmondson grade (P = 0.013) were independent prognostic factors for patients with HCC (Table 2). Consistent with the results of the Kaplan–Meier analysis, both the univariate (P = 0.022) and multivariate (P = 0.035) Cox regression analyses showed that CDC45 expression was significantly associated with the prognosis of HCC.
Table 2
Univariate and multivariate Cox regression survival analyses
Parameters | Univariate analyses | | Multivariate analyses |
Hazard ratio (95% CI) | P-value | Hazard ratio (95% CI) | P-value |
CDC45 expression | 0.558 (0.338–0.920) | 0.022 | | 0.509 (0.271–0.957) | 0.035 |
Size | 1.965 (1.201–3.213) | 0.007 | | 1.157 (0.614–2.177) | 0.652 |
Metastasis | 5.075 (2.673–9.636) | 0.000 | | 6.533 (2.916–14.635) | 0.000 |
Microvascular invasion | 1.879 (1.097–3.219) | 0.022 | | 1.015 (0.374–2.753) | 0.977 |
Vessel invasion | 2.035 (1.174–3.525) | 0.011 | | 1.636 (0.602–4.440) | 0.334 |
Edmondson grade | 2.696 (1.655–4.392) | 0.000 | | 2.082 (1.166–3.715) | 0.013 |
CI, confidence interval. |
Identification of DEGs and functional annotations as well as predicted signalling pathways
To further investigate the biological roles of CDC45 in HCC, the genes from the GSE76427 dataset were divided into two groups according to the median value of CDC45 expression to screen the DEGs between the low and high CDC45 expression groups. The screening criteria are discussed in the Materials and methods section). As shown in Fig. 4a, there were 233 upregulated and 167 downregulated DEGs. Specifically, the top 20 significant DEGs with positive and negative correlations are shown in the heat map in Fig. 4b. Subsequently, 400 involved DEGs were subjected to GO annotation and KEGG pathway analyses. The top 30 GO terms with the highest gene enrichment are shown in Fig. 4c. The related genes were significantly involved in eukaryote division, including organelle fission, nuclear division, chromosome segregation and mitotic nuclear division, and were markedly involved in the regulation of the cell cycle phase transition and DNA replication. Moreover, the KEGG analysis showed that most of the involved significant pathways included the cell cycle, DNA replication, drug metabolism and metabolism of xenobiotics by cytochrome P450, chemical carcinogenesis, meiosis and fatty acid degradation signalling (Fig. 4d). The detailed functional annotations, KEGG analysis information and percentage of each term are illustrated in additional file 1.
To further explore the interplay among the DEGs, we constructed a PPI network based on the STRING online database and Cytoscape software. As illustrated in Fig. 5a, the network contains 400 nodes and 1,622 edges. Clustering analysis of the PPI network was then carried out using Cytotype MCODE, and the top three significant modules were selected based on the degree of importance. Module 1 contains 43 nodes and 683 edges (Fig. 5b); module 2 contains 13 nodes and 39 edges (Fig. 5c); and module 3 contains 19 nodes and 58 edges (Fig. 5d). Submodule analysis information is shown in additional file 2.