In recent years, more and more studies have shown that H2AFY is differentially expressed and plays corresponding biological functions in multiple tumour types, including HCC, lung cancer, prostate cancer, acute myeloid leukaemia (AML), melanoma, and colon cancer(15, 26–30). According to previously published studies, the role of H2AFY in tumours is very complex and it is very challenging to study H2AFY in tumours. H2AFY has been reported to function in HCC stemness, in highly differentiated HCC, and steatosis-related HCC, but the clinical application value of H2AFY has not yet been reported. Therefore, this study focused on the exploration of the relationship between H2AFY and the clinical characteristics of HCC, and clarified the correlation between H2AFY and the prognosis of HCC patients.
Here, we conducted a preliminary study on the expression of H2AFY in patients with HCC using gene expression profile data and clinical feature data in the TCGA database. Compared with normal liver tissues, the expression level of H2AFY in HCC is higher, and as age, clinical stage, histological grade, T stage and HCC progress, the expression level of H2AFY in HCC shows a gradually increasing trend. The results of the survival analysis and logistic regression were also consistent with the above results, which suggests that the patients with high expression of H2AFY had lower survival and a poor prognosis. The results of the multivariate Cox analysis suggested that H2AFY was an independent risk factor for HCC, and the ROC curve suggested the potential value of H2AFY in the diagnosis of HCC. Therefore, H2AFY may play an important role in the development of HCC, and H2AFY is helpful for diagnostic and prognostic analyses of HCC patients.
Our analysis results based on the TCGA database showed that H2AFY was highly expressed in HCC, which suggests that H2AFY may promote the occurrence and development of HCC. However, most studies have suggested that H2AFY plays a role in tumour suppression(15, 21), which seems to contradict our results. However, some studies have reported that H2AFY has a carcinogenic role (13, 20, 31). Actually, H2AFY has two different splice variants (MacroH2A1.1 and MacroH2A1.2), which are quite different in function. Different expression rates of the two isoforms of H2AFY in tumours may lead to different outcomes, which we believe may provide part of the explanation.
The expression ratio of MacroH2A1.1 and MacroH2A1.2, the two isoforms of H2AFY, may be of great significance. MacroH2A1.1 acts as a tumour suppressor by inhibiting cell proliferation, migration, and invasion, while the function of MacroH2A1.2 is largely dependent on the type of cancer(18, 32). In differentiated and proliferating cells, MacroH2A1.1 and MacroH2A1.2 have obvious expression differences: MacroH2A1.1 is primarily found in differentiated cells, while MacroH2A1.2 is mainly found in proliferating cells(33, 34).
Most studies have confirmed that MacroH2A1.1 exerts anti-cancer effects(12, 13). MacroH2A1.1 plays an anticancer role in prostate cancer and reduces tumour malignancy(26). Macroh2a1.1 can inhibit Epithelial Mesenchymal Transition (EMT)(35). The unbalanced expression of H2AFY isoforms, especially the reduction in MacroH2A1.1, will lead to the impaired differentiation of red blood cells, and will eventually lead to anaemia in myelodysplastic syndrome (MDS) patients(36). In colon cancer patients, MacroH2A1.1 mRNA expression was decreased, while MacroH2A1.2 mRNA expression was up-regulated. MacroH2A1.1 expression was negatively correlated with disease severity and survival, while MacroH2A1.2 did not show that same characteristic(30). However, sometimes MacroH2A1.1 also shows the opposite effect, and in one study, high expression of MacroH2A1.1 was associated with poor prognosis in triple-negative breast cancer(37). Compared with MacroH2A1.1, MacroH2A1.2 has a more complex role in tumours. MacroH2A1.2 is overexpressed in tumour cells, and its macro domain interacts with HER-2 to promote the proliferation and carcinogenicity of cancer cells(31). In tumour xenografts, MacroH2A1.2 increased the invasiveness, growth and migration of cancer cells(13). In both in vivo and in vitro experiments, reducing the expression level of MacroH2A1.2 could promote the progression of melanoma by increasing the expression of the CDK8 oncogene(29).
Three known splicing factors have been described for H2AFY, including splicing factor MBNL1, the protein-coding gene QKI, and the RNA helicases Ddx5 and Ddx17(12, 38). The former two promote the expression of MacroH2A1.1, while the latter are beneficial to the expression of MacroH2A1.2. These splicing factors can produce two alternative transcripts. At the same time, some studies have shown that the two isoforms may have similar domains and that both isoforms are responsible for X chromosome inactivation(39).
Based on previous studies, we hypothesized that there might be a competitive association between the two isoforms of H2AFY. MacroH2A1.1 has cancer-inhibiting properties, while MacroH2A1.2 has cancer-promoting characteristics, and both of them jointly regulate the occurrence and development of tumours. Therefore, we attempted to further determine the expression levels of the two H2AFY isoforms in HCC. Unfortunately, we were unable to retrieve the respective expression data of the two isoforms of H2AFY from the TCGA database. However, our study raises the possibility that in patients with HCC, the diagnosis and prognosis of HCC may be assessed based on the total expression of H2AFY alone, rather than the expression of the H2AFY isoform.
We conducted an enrichment analysis of H2AFY by GSEA. The analysis results showed that H2AFY may be correlated with fatty acid metabolism, pathways in cancer, MAPK signalling pathway, melanoma, prostate cancer, acute myeloid leukaemia, and colorectal cancer, among others. Previous studies have confirmed the reliability of our analysis results. For example, H2AFY has a significant correlation with lipid metabolism-related HCC(40), as it can also alter the lipid metabolism of HCC cells and allow tumour cells to be more adaptable to the changing microenvironment(23). Some evidence indicates that H2AFY is a new fusion gene companion for MECOM gene in patients with AML and may promote the development of AML, but the exact mechanism is unclear(28). H2AFY has also been reported in melanoma, prostate cancer and colorectal cancer(26, 29, 30).