3.1 A sum of 56 candidate MPTDNRGs in PPI network were screen out
We screened out 3,314 DEGs-KIRCs, including 2,141 up-regulated and 1,173 down-regulated between KIRC and paracancerous samples from TCGA-KIRC dataset (Figure 1a, 1b). Next, the scores of MPTDNRGs were calculated in KIRC and paracancerous samples, revealing a significantly higher score in KIRC samples (P < 0.0001) (Figure 1c). Totally 408 DEGs-MPT, containing 267 up-regulated and 141 down-regulated were acquired from different scoring groups (Figure 1d, 1e). Ultimately, we identified 339 candidate MPTDNRGs by overlapping DEGs-KIRC and DEGs-MPT (Figure 1f). To uncover the biological roles and pathways linked to potential candidate MPTDNRGs, GO and KEGG enrichment analyses were performed (Figure 2a, 2b). To be more specific, the potential MPTDNRGs were correlated with biological processes including T cell differentiation and the control of T cell stimulation, as indicated in the biological process (BP) entries. They were also related to cellular components such as endocytic vesicles and their membranes, as listed in the cellular component (CC) entries. Their molecular functions, noted in the molecular function (MF) entries, included cytokine receptor activity and immune receptor activity, and they were enriched in KEGG pathways including rheumatoid arthritis. Moreover, to delve into the mutual influences of candidate MPTDNRGs at the protein level, a PPI network was constructed, which contained 339 candidate MPTDNRGs and 3,615 interaction pairs (Figure 2c). And to further identify key MPTDNRGs, we analyzed significant gene clusters within PPI network, and acquired 56 candidate MPTDNRGs with 1,314 interactions for subsequent analysis (Figure 2d).
3.2 IL2RA, CD7 and CXCL13 with high expression levels in KIRC samples were identified as key MPTDNRGs
We identified 19 genes with survival-related [hazard ratio (HR)≠1 and P < 0.05] (Figure 3a), and PH hypothesis test revealed that these 19 genes satisfied the hypothesis (P > 0.05). Then, 7 genes were further screened out (Lambdamin = 0.015), namely IL2RA, CD7, CXCL13, CTLA4, CD38, IL2RG and IL10RA (Figure 3b, 3c). Afterwards, IL2RA, CD7, CXCL13 and IL2RG were screened out by means of multivariate Cox analysis (HR≠1 and P < 0.05) (Figure 3d). Nevertheless, IL2RG exhibited a HR of less than 1 (HR = 0.69), contradicting the results of univariate Cox regression analysis (HR = 1.2). Accordingly, IL2RA, CD7 and CXCL13 were designated as key MPTDNRGs. And key MPTDNRGs exhibited high expression levels in KIRC samples from both TCGA-KIRC dataset and GSE40435 dataset (P < 0.0001) (Figure 3e, 3f).
3.3 A risk model was constructed according key MPTDNRGs
Consequently, a risk model was constructed by key MPTDNRGs, with RiskScore calculated as follows: = IL2RA*0.3233 + CD7*0.3673 + CXCL13*(-0.2197). In TCGA-KIRC dataset, the model was assessed through time-dependent ROC analysis, and AUC were 0.658, 0.614 and 0.625 at 1, 3 and 5 years, respectively (Figure 4a). These findings indicated the favorable efficacy of our risk model. Figure 4b, 4c illustrated distribution of samples in different risk groups. Clearly and unequivocally, high risk patients had significantly worst OS than low risk group (P = 0.00014) (Figure 4d). And we also carried out verification in E-MTAB-1980 dataset. Notably, the AUC were 0.810, 0.653 and 0.633 at 1, 3 and 5 years, respectively (Figure 4e). And likewise, high risk patients had significantly worst OS (P = 0.036) (Figure 4 f-h). The results were consistent with training cohort.
3.4 Only risk score and age were independent factors of prognosis
This research endeavored to determine if risk scores could act as a standalone predictor for the prognosis of patients with KIRC. As a consequence, we determined that risk scores, age, tumor grade, and stage are influential variables that affect the overall survival (OS) of KIRC patients (HR≠1 and P < 0.05) (Figure 5a). Nonetheless, the PH hypothesis test indicated that neither tumor grade nor stage fulfilled the required assumptions (P < 0.05). As a result, we proceeded with further analysis considering only risk score and age. Ultimately, we established that the risk score and age were the sole independent prognostic factors(HR≠1 and P < 0.05) (Figure 5b). Consequently, a nomogram was developed incorporating these two factors, risk score and age (Figure 5c). The calibration plots, which closely matched the reference line, suggested that the nomogram had a favorable predictive accuracy (Figure 5d). Furthermore, the decision curve analysis (DCA) at both 1 and 5 years showed that the nomogram had a clinical utility compared to using risk score and age in isolation (Figure 5e-g).
3.5 Different risk groups-related signaling pathways
Conducting GSEA aimed to provide a more profound understanding of the associated signaling pathways and the potential biological processes that characterize the distinct risk groups. The detail results of GSEA could be found in Additional file 2 Specifically, high risk group was mainly enriched in systemic lupus erythematosus, leishmania infection etc., and low risk group was mainly enriched in oxidative phosphorylation, valine leucine and isoleicine, etc. (Figure 6). GSEA uncovered distinct signaling pathways linked to various risk groups, thereby broadening our in-depth comprehension of KIRC.
3.6 Immune analysis of KIRC patients
The heatmap illustrated the scores of 28 immune cells (Figure 7a). Evidently, in high risk group, except for CD56bright natural killer cells, eosinophils and neutrophils, the proportion of 25 immune cells were significantly higher (P < 0.05) (Figure 7b). Then, we observed that the strongest correlation among differential immune cells was between T follicular helper cell and activated MDSC (r = 0.869 and P < 0.001) (Figure 7c-d). Further, the strongest correlation was observed between CD7 and activated CD8 T cells (r = 0.856, P < 0.001), exhibiting significantly higher expression in high risk group (P < 0.0001) (Figure 8a-c). Moving forward, we sought to determine if there existed any potential disparities in the levels of immune checkpoint expression across different risk categories. The results revealed that gene expression of 11 immune checkpoints was significantly higher in high risk group, like BTLA, CD274 and CTLA4 (P < 0.001) (Figure 8d). TIDE score was analyzed to access the potential for tumor immune evasion. Obviously, high risk group patients exhibited significantly higher TIDE score (P < 0.05) (Figure 8e). Additionally, the waterfall plot illustrated the top 20 mutations in tumor cells of different risk groups (Figure 8f, 8g). The results indicated that VHL and PBRM1 mutations were more prevalent in different risk groups. The higher frequency mutations in high risk group were frame shift del mutation and missense mutation, while the most common mutations in low risk group were nonsense mutation, missense mutation and frame shift del mutation.
3.7 Regulatory network of key MPTDNRGs
The ceRNA network showed that 3 mRNAs of the risk model could interact with 27 miRNAs, which could in turn interact with 36 lncRNAs. The complex interaction pairs were formed, such as CXCL13-hsa-miR-670-5p-AL121985.1, IL2RA-hsa-miR-6088-AL513497.1 (Figure 9a). A total of 25 TFs were predicted for key MPTDNRGs. Notably, IL2RA, CD7 and CXCL13 collectively predicted GATA2. CD7 and CXCL13 collectively predicted MAX and GATA3. CD7 and IL2RA collectively predicted USF2 (Figure 9b). The results indicated the regulatory mechanism for key MPTDNRGs in KIRC.
3.8 Verification of key MPTDNRGs expression
In the previous studies, we observed that IL2RA, CD7 and CXCL13 exhibited significantly higher expression levels in KIRC samples in both TCGA-KIRC and GSE40435 (P < 0.0001) (Figure 3e, 3f). This prompted us to further employ RT-qPCR techniques to validate the clinical expression levels of key MPTDNRGs in patients with KIRC. Remarkably, RT-qPCR revealed that both IL2RA and CD7 showed significantly higher expression in KIRC samples (P < 0.05), while CXCL13 also showed an up-regulation trend in KIRC (P = 0.0820), consistent with our previous findings (Figure 9c-e).