1. Identification of prognostic IRGs and irlncRNAs
We identified 1358 differentially expressed IRGs associated with KIRC using the limma package in the R language. Subsequently, the clinical data of KIRC and 1358 IRGs were analyzed and classified through WGCNA analysis using the R language
(Figure 1A). A total of 200 prognostic IRGs were obtained by univariate Cox analysis (p < 0.05). Then, we utilized co-expression analysis to obtain irlncRNAs that were coexpressed with IRGs (| r | > 0.6, p < 0.001). A total of 364 irlncRNAs were identified, of which 275 were distinguished as prognostic via univariate Cox analysis (p < 0.01).
2. Construction of the prognostic IRGs and irlncRNAs signature model
The previously acquired 200 IRGs and 275 irlncRNAs were used to construct the LASSO Cox regression model regarding the prognosis of KIRC (Figure 1B-1C). We integrated the expression profiles of 3 hub genes (AR, TREM1, PTX3) and 3 hub lncRNAs (HOTAIRM1, AC003092.1, DLGAP1-AS2) involved in model construction (Figure 2A). The risk score was calculated by multiplying the expression level of each gene or lncRNA and its corresponding coefficient. The 530 KIRC samples were divided into low- and high-risk groups based on the median risk score (Figure 2B-2D). KaplanMeier analysis showed that the long-term survival time of patients with KIRC in the high-risk group was shorter than that in the low (Figure 2E). ROC curve analysis showed that the AUC for 3-year survival was 0.718. (Figure 2F).
3. Model validation and clinical relationship assessment
Both univariate and multivariate Cox regression results showed that the tumor stage, tumor grade, and the risk score of this model were all associated with the prognosis of KIRC (Figure 2G). These results demonstrated that our model could be used as the independent prognostic factor for KIRC. The relationship between risk groups and clinicopathological characteristics noted that the risk score was correlated with survival status, tumor grade, and tumor stage but not with the age or gender of the patients (Table 1).
4. GO, KEGG, and PPI Analyses
We conducted differential gene expression analysis and obtained 503 DEGs, including 66 IRGs. Then, we performed GO and KEGG analysis of these DEGs (Figure 3A). To search for immune-related DEGs, we selected genes enriched via GO involved in the immune response, including B-cell activation, B-cell mediated immunity, T-cell activation, etc. Next, we constructed the PPI network for these selected immune-related DEGs using string and cytoscape software (Figure 3B). The number of nodes in the top 20 immune-related DRGs is shown in Figure 3C. Eventually, we selected a significant module from the MCODE plugin analysis that included the following genes: IL-6, CXCL1, CXCL13, CXCL8, CXCL2, CXCL6, PI3, NFKBIZ and TREM1 (Figure 3D).
5. Correlation between TREM1 expression and KIRC
We analyzed the clinical relationship between the nine immune-related DEGs and KIRC according to the ranking order obtained from the ENCODE results and selected the hub gene TREM1. The oncomine database analysis revealed that TREM1 was highly expressed in different types of cancer, including KIRC (Figure 4A). We further validated the relationship of TREM1 to KIRC using the TCGA database, and the results were similar to before (Figure 4B-4C). The TREM1 levels were gradually upregulated along with the tumor grades and stage 3 to stage 4 in KIRC (Figure 4D). Furthermore, the analysis of the clinical characteristics revealed that TREM1 was correlated with survival status, grade, and TNM stage in KIRC (Table 2). The survival analysis showed that KIRC patients with high TREM1 expression have a shorter survival time than those with low expression (Figure 4E). Univariate and multifactorial Cox regression results indicated that TREM1 is an independent prognostic factor for KIRC (Table 3).
6. Correlation of TREM1 with immune infiltration and their gene markers in
KIRC
The ESTIMATE results revealed that the presence of stromal cells and immune cells in the high-TREM1 expression group was more abundant than the group with the low expression (Figure 5A). The survival analysis showed a negative correlation between the immune score and survival time (Figure 5B). The CIBERSORT analysis results displayed higher contents of activated memory CD4+ T cells, monocytes, M0 and M2 macrophages, resting dendritic cells, activated resting mast cells, and neutrophils in the high-TREM1 expression group than in the low-TREM1 expression group. In contrast, a low expression of TREM1 yielded higher concentrations of CD8+ T cells, resting NK cells, activated NK cells, M1 macrophages, and resting mast cells (Figure 5C). In addition, the different abundances of the infiltrated immune cells between the high- and low-TREM1 expression groups were further confirmed through the correlation analysis conducted between the different marker subsets of immune cells and TREM1 (20). These findings validate that TREM1 is strongly linked with innate immunity since the major innate immune cell types such as dendritic cells, neutrophils, natural killer cells, and macrophages were strongly associated with TREM1 expression (Table 4) (21).
7. TREM-1 showed correlation IHC.
In the presence of TRME1, uniform cytoplasmic and membrane staining showed positive expression of TRME1. In benign tissues, TREM1 expression was very low, but high in tumor tissue areas. And TREM1 expression increased with increasing Fuhrman grade. OD values: Grade 3, vs Grade 1: 0.308vs0.199. (Figure 7).
8. Prediction of the function of TREM1
GSEA analysis showed that TREM1 was involved in various immune-related pathways, including B-cell receptor, JAK-STAT, NOD-like receptor, Toll-like receptor, and Tcell receptor signaling pathway (Figure 6A). Moreover, the string and GeneMANIA results showed that the function of TREM1 and its associated molecules (TYROBP, CD274, SFTPD, and VSIG4) were primarily related to the negative regulation of mononuclear cell, lymphocyte and leukocyte proliferation and the negative regulation of lymphocyte activation (Figure 6B-6C). These results indicate that TREM1 is closely related to immune infiltration.