Identification of prognostically relevant pyroptosis -associated lncRNAs
Figure 1 illustrates the flow chart of our research program. We first screened 33 pyroptosis-related genes and extracted the gene expression data in TCGA-LIHC database. Then, we used Pearson correlation analysis to identify 785 lncRNAs associated with pyroptosis. Subsequently, we identified 172 differentially expressed lncRNAs associated with pyroptosis in tumor samples and non-tumor samples. We used univariate Cox regression to screen 15 lncRNAs associated with prognosis (Figure 2), and they were all associated with poor prognosis (HR>1).
Establishment and verification of pyroptosis-related lncRNA prognostic signature for HCC
In the training set, four prognostic lncRNAs (AL357079.1, SNHG4, AL163953.1 and AL442125.2) associated with pyroptosis were identified from the 15 lncRNAs characterized above to build a model for predicting HCC prognosis. Risk score formula is as follows: Risk score = AL357079.1 expression * 0.090679 + SNHG4 expression * 0.332627 + AL163953.1 expression * 0.045756 + AL442125.2 expression * 0.777904, where the coefficients for each lncRNA were obtained from the LASSO regression model.
The high-risk group had greater expression of four pyroptosis-related lncRNAs, poorer patient living conditions (Figure 3A), and significantly shorter OS (Figure 4A). We use the same grouping method in the testing set and the findings are similar to the training set (Figure 3B, Figure 4B). Notably, the AUC values of the ROC curves for the training and testing sets OS were 0.746 (Figure 4C) and 0.740 (Figure 4D) respectively, indicating good specificity and sensitivity of the constructed signature.
Independent prognostic analysis of the pyroptosis-related lncRNA signature
Next, we performed uni-Cox and multi-Cox regression analyses on the constructed signature. Uni-Cox regression analysis identified Stage, T classification and risk score as independently factors of HCC prognosis (Figure 5A-B). In contrast, multi-Cox regression analysis identified only the risk score as an independently factor for HCC prognosis (Figure 5C-D).
Based on the clinicopathological and identified model, we constructed a nomogram (C-index: 0.71) to predict HCC patient prognosis at 1, 2, and 3 years (Figure 5E).
Differences in gene mutation and immune infiltration
Somatic cell variant analysis revealed the top 20 mutated genes and the top five were TP53, CTNNB1, TTN, MUC16 and MUC4. The most frequent type of mutation was missense mutation. Interestingly, we found that TP53 was more prone to mutation in the high-risk group (Figure 6).
The composition of immune cell subpopulations is associated with the anti-tumor effect of immunotherapy in the tumor microenvironment. We plotted immune cell histogram and heatmap of HCC patients. The result showed that M0, M1, M2, CD8T and CD4T resting cells significantly infiltrated in hepatocellular carcinoma cell (Figure 7A). Moreover, we found that M0 macrophage was correlated significantly and negatively with CD8T cell (Figure 7B). The macrophages M0 infiltration in the high-risk group was significantly increased. Conversely, the proportion of Monocytes, Mast cells resting, T cells CD8 as well as NK cells resting infiltration in the low-risk group was significantly increased (Figure 7C).
Differences in the response to chemotherapy and small molecule drugs
Because of the survival differences between the two groups, we hypothesized that their sensitivity to chemotherapeutic agents was different. Therefore, we further analyzed the different outcomes of the two groups of HCC patients in terms of response to chemotherapy (Figure 8A). Low-risk group patients had lower 50% inhibitory concentrations (IC50) and greater drug sensitivity to gemcitabine, Adriamycin and mitomycin C. In contrast, high-risk group patients were more sensitive to sorafenib. In conclusion, the signature we constructed provides direction for the development of chemotherapy strategies for HCC patients.
We screened 395 DEGs between the two groups according to the prognostic model and analyzed them using the CMAP database. Eight small molecule drugs, including SC-560, anisomycin and vancomycin, were screened, suggesting that they may be potential drug targets for the high-risk group patients (Figure 8B).
Identification of biological pathways of pyroptosis-related lncRNA signature
We show 20 GO-enriched pathways and 10 KEGG-enriched pathways (Figure 9A, B). The most enriched pathway for GO analysis was cell-cell adhesion, and the most enriched pathway for KEGG analysis was calcium signaling pathway. In addition, pathways including epithelial cell differentiation, cell adhesion molecules, and gap junction also showed different levels of enrichment. Based on these enriched pathways, we identified seven PPI functional groups and characterized the pathway for each functional group (Figure 9C). Wnt/β-catenin signaling pathway plays an essential role in MCODE1 (Figure 9D).