Clinicopathological characteristics of HCC patients and top ten PCGs
A flow diagram illustrating the process of the present study is shown in Figure 1. The study included a total of 370 HCC patients, and their clinicopathological characteristics, as obtained in the TCGA dataset, were previously reported (27). Several factors, including clinical factors, hepatitis B virus (HBV) status, tumor stage, and radical resection, were correlated to the OS (all P ≤ 0.05). The top ten PCGs of LINC01116-related by Pearson correlation are as follows: SOX2, BEND6, TMSB15A, PLAU, OLFML2B, NTNG1, SLC17A7, NTRK1, MRC2 and SLC7A3 (all correlation ≥ 0.800, all P< 1E-80, Table 1). Following Pearson correlation analysis, the genes associated with LINC01116 are shown in Supplementary Table 1.
Analysis of differential expressions and diagnostic potential
Differential expressions analysis using the MERAV database indicated that LINC01116, BEND6, PLAU, OLFML2B, SLC17A7, and SLC7A3 were significantly different from LINC01116 (Figure S1 A, C, E, F, H, K), while the others were not. Differential expression analysis showed that LINC01116 and OLFML2B were differentially expressed, with higher expression in tumor tissues (P=0.045, 0.019, Figure 2A, F). In terms of the diagnostic potentials of the various genes, only LINC01116, TMSB15A, PLAU, OLFML2B, and MRC2 were found to have the potential of aiding in HCC diagnosis (all AUC≥0.700, all P≤0.05, Figure 3A, D-F, J).
Survival analysis and conjoint analysis
Survival analysis of LINC01116 and PCGs were performed using the univariate Cox hazard regression model. The model showed that LINC01116 and OLFML2B have prognostic significance (crude P= 0.044, 0.024, respectively. Table 2, Figure 4 A, F). We then conducted a multivariate cox regression model using prognosis-related clinical factors and these genes. Multivariate analysis revealed that LINC01116 and TMSB15A have prognostic significance (adjusted P=0.046, 0.003, respectively, Table 2). Further, conjoint analysis for LINC01116 and TMSB15A was performed and showed distinguished survival among groups a, b, and c (crude P= 0.032, adjusted P= 0.002, Table 3, Figure 4L).
Construction of predictive model using risk scores and nomogram
A risk score model was constructed using LINC01116, TMSB15A expressions, and HBV status, and tumor stage and radical resection via a multivariate cox hazard model (Figure 5A, Table 4). The identified elements of risk score include risk score rank, survival status, and heatmap of the expression of LINC01116 and TMSB15A. Risk scores were divided into low and high-risk groups at median cutoff. A Kaplan-Meier plot was drawn using low and high-risk groups (crude P=0.030, Figure 5B, Table 2). After that, time-dependent ROC curves were drawn at 1-5 year, which revealed similar prediction results (Figure 5C). A nomogram was constructed using the expressions of LINC01116, TMSB15A and HBV status, and tumor stage and radical resection based on the different points of each factor (Figure 6). Tumor stage I, radical resection, without HBV infection, low expression of LINC01116, and high expression of TMSB15A indicated lower points, which therefore suggested a better OS prediction at 1, 3-, and 5-years (Figure 6A). Internal validations were conducted using C-index for predicted and actual OS status (Figure 6B).
Exploration of molecular mechanisms via GSEA
We explored the potential molecular mechanisms of LINC01116 and TMSB15A that could be involved in HCC prognosis. We then analyzed gene ontology (GO) terms and the Kyoto encyclopedia of genes and genomes (KEGG) pathways to identify the specific mechanisms. Specifically, LINC01116 enriched in several GO terms, including cellular response to vascular endothelial growth factors stimulus, mesenchymal morphogenesis, dendritic cell differentiation, vascular endothelial growth factor receptor signaling pathway, vasculogenesis, and integrin-mediated signaling pathway. (Figure 7A-H). The enriched KEGG pathways participate in focal adhesion, cell adhesion molecular cams, chemokine signaling, TGF-β signaling, notch signaling, B cell receptor signaling, pathways in cancer, and MAPK signaling (Figure 7I-P). TMSB15A was enriched in GO terms involved in negative regulation of endothelial cell proliferation, blood vessel endothelial cell migration, stem cell division, mesenchyme development, and vasculogenesis. (Figure S2 A-H). TMSB15A was enriched in KEGG pathways involved in drug metabolism, other enzymes, peroxisome, propanoate metabolism, and steroid hormone biosynthesis (Figure S2 I-L).
Identification of candidate target drugs and interaction networks of LINC01116
Using |fold change|≥2 and P≤0.05, we identified a total of 171 up-regulated and 37 down-regulated genes. We then used these DEGs to construct interaction networks, including KEGG pathways and diseases (Figure 8). This interactive network was associated with metabolic diseases, peptide hormone metabolism, NODAL signaling, regulation of beta-cell development, WNT ligand biogenesis and trafficking, antimicrobial peptides, PI3K/AKT signaling in cancer, and signaling by the insulin receptor. After that, candidate target drugs were generated via the cMAP database using these DEGs and listed as follows: Thiamine, Cromolyn, Rilmenidine, Chlorhexidine, Sulindac_sulfone, Chloropyrazine, and Meprylcaine (Figure 9, Table 5). Two dimensional (2D) structures of these drugs are shown in Figure 9A-G. Our results show that the drugs have potential clinical significance, are negatively related to the expression of LINC01116, with its high expression indicating a poor outcome (Figure 9H).
Immune infiltration and promoter methylation analysis of PCGs
Due to the unavailability of LINC01116 in TIMER and UALCAN, only PCGs were conducted in the analysis of immune infiltration and methylation. The analysis of immune infiltration revealed that all the four PCGs (MRC2, OLFML2B, PLAU, TMSB15A) were negatively associated with the purity (all P<0.001, r<0, Figure 10). Meanwhile, all the four PCGs were positively associated with specific cell types, including B cell, CD8+ T cell, CD4+ T cell, macrophage, neutrophil, and dendritic cells (all P<0.050, r>0). Then, SCNA analysis indicated that all of the four genes were partially associated with SCNA among B cell, CD8+ T cell, CD4+ T cell, macrophage, neutrophil, and dendritic cells (Figure 11). Specifically, MRC2 and OLFML2B showed significance in arm-level gain and high amplification; PLAU showed significance in arm-level deletion, while TMSB15A exhibited significance in arm-level deletion and gain.
Analysis of promoter methylation demonstrated that MRC2, OLFML2B, and PLAU revealed differential and high methylation levels in primary tumors compared with normal (all P<0.001, Figure 12A, E, I). However, no significant differences were observed in TMSB15A (Figure 12M). Methylation analysis by gender demonstrated that MRC2, OLFML2B, and PLAU have differential and high methylation in HCC tissues of both male and female populations compared with healthy tissues (all P<0.050, Figure 12B, F, J). However, TMSB15A showed differential methylation between males and females (Figure 12N). Methylation analysis by race suggested that MRC2, OLFML2B, and PLAU have differential significance between normal and other races, including Caucasian, African-American, and Asian (Figure 12C, G, K). However, TMSB15A showed a difference between the Caucasian and Asian populations (Figure 12O). Methylation analysis by tumor grade suggested that MRC2, OLFML2B, and PLAU have differential significance between normal and tumor grades 1-3 (Figure 12D, H, L) while TMSB15A showed no difference between normal tissues and tumor grade (Figure 12P).
Construction of ceRNA network and validations of clinical significance by oncomine database
A ceRNA network was constructed based on negative regulation relationship with LINC01116 (Figure 13). Specifically, LINC01116 was connected with miR-423-3P, miR-1908-5P, miR-744-5P, miR-1180-3P, miR-671-5P, GSK3B, FOXM1, TNIP2, PA2G4, BCL2L11, NKIRAS2, EEF1A2, TLE3. Then, validation by the Oncomine database suggested that OLFML2B, PLAU, and MRC2 have differential expressions and diagnostic potentials for HCC in the two datasets (all P<0.050, all AUC>0.700, Figure S3 C-H, K-P). However, TMSB15A showed diagnostic potentials in only one dataset (Figure S3 A-B, I-J).