Construction of WGCNA and Expression of SCAF1 in LIHC:
To identify gene modules associated with LIHC, we constructed a LIHC-related heatmap, where the turquoise module exhibited the strongest correlation with LIHC (Figure 1.a). Subsequently, we intersected VEGF-related genes, focal adhesion-related genes, and EMT-related genes with genes in the turquoise module, resulting in 20 genes identified through a Venn diagram (Figure 1.b). To select suitable hepatocellular carcinoma cell lines for subsequent experiments, we conducted Western blot experiments on three hepatocellular carcinoma cell lines and one normal cell line. The hepatocellular carcinoma cell lines Huh7, HCCLM3, and HepG2 were compared to the normal liver tissue cell line HL-7702 to determine the expression levels of SCAF1. We discovered that the expression level of SCAF1 was greatest in HCCLM3 (Figure 1.c), indicating that this cell line is suitable for subsequent experiments. To explore the expression of SCAF1 in LIHC, we obtained statistical information from the TCGA and ICGC websites and constructed box plots. The results consistently showed high expression of SCAF1 in LIHC (Supplementary Figure 1.a–b). Subsequently, to validate the above conclusions, we performed mRNA detection and WB experiments on SCAF1, demonstrating that LIHC tissues had greater levels of SCAF1 mRNA and protein expression than nearby tissues (Figure 1.e). Furthermore, to further verify the relationship between SCAF1 expression level and LIHC at the cellular level, we conducted HE staining and immunohistochemistry experiments on SCAF1 expression. The findings demonstrated that HCCLM3 cells expressed more SCAF1 than nearby tissues (Figure 1.f), further indicating the close association of high SCAF1 expression with LIHC.
Clinical Predictive Significance of SCAF1:
In order to investigate the relationship between clinical pathological characteristics and SCAF1, we observed changes in SCAF1 expression in LIHC samples with different clinical pathological features. The results showed that as clinical staging, pathological staging, and histological staging increased, the overall expression of SCAF1 also increased (Figure 2.a–c), indicating a close relationship between the clinical pathological characteristics of LIHC patients and SCAF1 expression. We also examined the effect of SCAF1 expression on patient prognosis and utilized the Kaplan-Meier survival technique to estimate the OS, DSS, and PFI of LIHC patients. The findings demonstrated that, in comparison to the low-expression group, the high-expression group of SCAF1 had reduced survival rates at each time (Figure 2. e–f), suggesting that high SCAF1 expression may be associated with a poor prognosis in LIHC patients. Furthermore, we created a prediction nomogram in which T stage was the most significant contributor to OS in order to reliably forecast the survival rate of LIHC patients (Figure 2.g). We created a prognosis ROC curve, where the AUC values for 1, 3, and 5 years were all larger than 0.5, to further assess the precision of gene prediction (Figure 2.h), confirming the high specificity and sensitivity of SCAF1 in predicting LIHC prognosis and suggesting that SCAF1 expression is a key factor affecting the prognosis of LIHC patients.
Potential Functions of SCAF1 in LIHC:
Given the significant upregulation of SCAF1 expression levels in LIHC, we aimed to study the regulatory mechanisms involving SCAF1 in LIHC. According to Figure 3.a–b's GSEA analysis, the elevated DEGs linked to SCAF1 were primarily enriched in pathways pertaining to adhesion junctions and angiogenesis. This suggests that there may be a correlation between the expression of SCAF1 and the levels of metastasis and angiogenesis in LIHC. In response to this conjecture, we carried out transwell assays to evaluate the effect of SCAF1 knockdown on the invasive migration of LIHC cells. We discovered that the SCAF1 knockdown group's HCCLM3 cells' capacity for migration and invasion was greatly diminished (Figure 3.c). Previous research has demonstrated that angiogenesis plays a major role in the invasion and migration processes of tumor cells [18]. Combining our predicted results, we confirmed through WB experiments and mRNA detection that knocking down SCAF1 could reduce the degree of VEGFA expression in LIHC (Figure 3.d), and there was a notable decrease in the cells' capacity to produce tubes in the angiogenesis experiment (Figure 3.e). Lowering SCAF1 may suppress the invasive migration of LIHC cells by altering key signals in the VEGF pathway (VEGFA).
Relationship between SCAF1 and the Immune Microenvironment:
Chemokines and their receptors, a superfamily of secreted small molecules, are closely associated with the development of LIHC [19]. Chemokines can regulate LIHC cells by affecting the expression of VEGF [20]. To explore the relationship between the SCAF1 gene in LIHC cells and chemokines, we used the TISIDB website to generate heatmaps for analysis, revealing that SCAF1 in LIHC cells was associated with multiple chemokines, including CCL19, CCL14, and CCL11, and there was a negative correlation found between the expression levels of SCAF1 and the three chemokines. Knocking down the expression of SCAF1 could upregulate the expression levels of CCL19, CCL14, and CCL11. This implies that SCAF1 may influence LIHC by controlling the expression of these three chemokines, which in turn influences the production of VEGF. Malignant tumor genesis, growth, and metastasis are all dependent on the tumor microenvironment (TME), which is made up of elements including VEGF and immune cells that have infiltrated the tumor [21, 22]. To further explore the ability of SCAF1 expression to regulate the tumor immune microenvironment and evaluate the relationship between immunity and VEGF, we scored SCAF1 for immunity, stroma, and estimate. We found that all three scores were negatively correlated with SCAF1 expression levels (Figures 5.a–c). Next, we investigated the connection between immune cell infiltration and SCAF1 expression in LIHC using the TIMER database. The findings demonstrated that elevated SCAF1 expression may raise the degree of immune cell infiltration, including B cells, CD8+ T cells, CD4+ T cells, neutrophils, macrophages, and dendritic cells. Subsequently, we investigated the connection between SCAF1 expression levels and immune cell surface markers. The results indicated that there was a positive correlation between SCAF1 expression levels and TAM, B cells, monocytes, Th1, Th2, and DC cell surface indicators (Figure 5.d-j). Combination therapy involving VEGF blockade therapy and immune checkpoint-targeted immunotherapy is becoming increasingly important and has become a first-line choice for various cancer treatments [23]. We then studied the correlation between immune checkpoints and SCAF1 in LIHC, and the outcomes demonstrated a negative correlation between the expression of SCAF1 and a number of immunological checkpoints, including CTLA-4 and PD-1(Supplementary Figure 1.c). Ultimately, we discovered that immunotherapy was not appropriate for individuals exhibiting elevated expression of SCAF1(Supplementary Figure 1.d–e). To investigate how tumor treatment affects VEGFA and SCAF1 expression, we performed principal component analysis and dimensionality reduction clustering on tissue cells, simulating tumor heterogeneity changes over time(Supplementary Figure 3.b–c). We arranged the expression levels of SCAF1 and cell types on the pseudo-time axis, and the results showed that as the pseudo-time axis progressed, the expression levels of SCAF1 increased (Supplementary Figure 3.d). The distribution of VEGFA and SCAF1 expression after immunotherapy is shown in Supplementary Figure 4.a–b, and after immunotherapy, the expression of VEGFA and SCAF1 was obviously downregulated, suggesting some mechanisms of immunotherapy.
Small molecule drugs targeting SCAF1:
Through network pharmacology analysis, we explored small-molecule drugs associated with the treatment of hepatocellular carcinoma (LIHC) and drugs targeting VEGFA. By searching the TCMSP database and cross-analyzing LIHC therapeutic molecules with drugs targeting VEGFA, we identified 16 small molecules (Figure 6.a). Using molecular docking techniques, we modeled the interactions between these small molecules and the SCAF1 protein. Genistein exhibited the strongest binding affinity with SCAF1, interacting with three amino acid residues of SCAF1 (85Glu, 84Thr, and 83Val) through hydrogen bonding, demonstrating stronger binding affinity compared to other molecules (Figure 6.b). Cell viability assays showed that cell proliferation significantly slowed down upon genistein treatment, while Western blot experiments demonstrated that genistein markedly downregulated the expression levels of SCAF1 and VEGFA (Figure 6.c–d). Furthermore, the migration and invasion capabilities of LIHC cells were markedly reduced upon genistein treatment (Figure 6.e). These findings suggest that genistein inhibits the occurrence and development of LIHC by suppressing the expression levels of SCAF1, thereby downregulating key molecules in the angiogenesis process.