The identification of DEGs in HCC
DEGs between HCC tumor and non-tumor samples were investigated of the GEO dataset (GSE45267, GSE45436, GSE60502, and GSE84402) by applying bioinformatics analysis. In total, 18 significantly upregulated genes and 67 significantly down-regulated genes were identified (including CFHR4) (Fig. 1) [24, 25].
The comparison of CFHR4 expression
The expression of CFHR4 in tumor samples was significantly lower than non-tumor samples in GSE45267, GSE45436, GSE60502, GSE84402, and TCGA-LIHC dataset (Fig. 2A-E)[5]. The immunohistochemistry and Western blot results of clinical samples confirmed that CFHR4 is under-expressed in HCC tissues, compared with normal tissues (Fig. 2F-G).
The correlation and GO/KEGG enrichment analysis results
The correlation between CFHR4 and CFHR4-correlated genes was identified (Fig. 3A). GO analysis results proved that CFHR4-correlated genes were significantly enriched in the drug-metabolic process, regulation of complement activation, steroid metabolic process, cytolysis, lipid transport at BP levels; organelle membrane, extracellular region, blood microparticle, endoplasmic reticulum membrane, extracellular space at CC levels, and oxygen binding, steroid hydroxylase activity, heme binding, aromatase activity, oxidoreductase activity, enzyme binding at MF levels. Additionally, the KEGG pathway enrichment of CFHR4 interactive genes showed that Retinol metabolism, Mineral absorption, Steroid hormone biosynthesis, Metabolic pathways, complement, and coagulation cascades, were the enriched pathways [5] (Fig. 3B-E).
The genomic mutation of CFHR4
The genomic mutation is closely associated with tumorigenesis[22]. The research showed about 7% of genetic alteration of CFHR4 in HCC, including amplification and missense mutation with unknown significance (Fig. 4A-B). In addition, missense mutation of CFHR4 resulted in the amino acid change, including Asparagine (N) 356 replaced by Isoleucine (I) and Lysine (K) 227 replaced by Asparagine (N) (Fig. 4C). The above results indicated that genetic alteration of CFHR4 could be found in HCC, which might play an important role in tumorigenesis of HCC [22].
The correlation of CFHR4 expression with the clinicopathological characteristics of HCC
Chi-square test was used to analyze the correlation between CFHR4 expression and clinicopathological factors (Table 3). Studies have shown that low CFHR4 expression was significantly associated with Age (P = 0. 026), BMI (P = 0.013), Race (P < 0.001), and Family history of cancer (P = 0.001), Histological grade (P < 0.001), TNM stage (P = 0. 048), and Serum AFP level (P < 0.001) [26–28]. (P < 0.05 *, P < 0.01 **, P < 0.001 ***)
The independent prognostic value of CFHR4 expression
The univariate analysis indicated that CFHR4 expression and TNM stage were directly correlated with OS in HCC. Furthermore, by Cox multivariate analysis, we found that low CFHR4 expression and TNM stage were confirmed as independent prognostic indicators influencing the prognosis of HCC patients (Fig. 5) [23].
The association between CFHR4 and survival
The results outlined that low expression of CFHR4 in tumor tissues was considerably associated with poor overall survival (OS, log rank P = 3.1e-07, HR = 0.41 (0.29–0.59), Fig. 6A) in patients with HCC. Moreover, a subgroup analysis revealed that the down-regulation of CFHR4 in tumor tissue was a risk factor for reduced 1-year OS (log rank P = 1.6e-08, HR = 0.25 (0.15–0.42), Fig. 6B), 3-year OS (log rank P = 1.1e-07, HR = 0.37 (0.25–0.54), Fig. 6C), 5-year OS (log rank P = 1.3e-07, HR = 0.39 (0.27–0.56), Fig. 6D), 5-year OS stage III-IV (log rank P = 0.00013, HR = 0.33 (0.18–0.60), Fig. 6E), 5-year relapse-free survival (RFS, log rank P = 5.5e-05, HR = 0.5 (0.36–0.71), Fig. 6F), and 5-year progression free survival (PFS, log rank P = 5.7e-07, HR = 0.47 (0.35–0.64), Fig. 6G) in HCC patients [5].
The diagnostic performance of CFHR4 mRNA Levels for the differentiation of HCC patients from healthy controls
The potential diagnostic utility of CFHR4 to differentiate between HCC and benign disease was assessed through generating a receiver operating characteristic (ROC) curve for CFHR4 expression. We found that the ROC area under the curve (AUC) of the CFHR4 was 0.72 (95% confidence interval (CI): 0.67–0.77) (Fig. 6H). However, we do not have a serum sample to verify our point, and considerable work needs to be done [24].
The correlation analysis between CFHR4 expression and tumor-infiltrating immune cells (TIICs)
We analyzed the correlation between CFHR4 expression and infiltrating immune cells (Monocyte, CD4 + T cells, Myeloid dendritic cells, CD8 + T cells, T cells regulatory (Tregs), Macrophages, Neutrophils, NK cells, Endothelial cells and Hematopoietic stem cells). The results showed that the expression of CFHR4 was positively correlated with the infiltration levels of Macrophages (r = 0.394, P = 3.07e-14), Neutrophils (r = 0.256, P = 1.51e-06), NK cells (r = 0.385, P = 5.35e-04), Endothelial cells (r = 0.397, P = 1.75e-14), and Hematopoietic stem cells (r = 0.366, P = 2.19 e-12) (Fig. 7A), and negatively correlated with Monocytes (r = -0.265, P = 6.12e-07), CD4 + T cells (r = -0.372, P = 9.66e-13), Myeloid dendritic cells (r = -0.366, P = 2.18e-12), CD8 + T cells (r = -0.329, P = 3.66e-10), and T cells regulatory (Tregs) (r = -0.239, P = 7.00 e-06) (Fig. 7B) [28].