Expression Pattern of GSDMB in Pan-Cancer Perspective
The complete working set contained 33 types of cancer of which the mRNA expression pattern of GSDMB were evaluated. As showed in Fig. 1, in comparison to normal tissues, GSDMB was significantly up regulated in 12 out of 33 cancer types and down regulated in 15 out of 33 cancer types. The data demonstrated that the mRNA expression of GSDMB was expressed in an abnormal way throughout different types of cancers.
Upregulated mRNA and Protein Expression of GSDMB in ccRCC Patients
In order to establish the mRNA as well as protein expression of GSDMB in ccRCC, data on GSDMB expression found in TCGA, GEO and HPA were analyzed. Fig. 2A showed the unpaired data analysis indicating that the levels of mRNA expression of GSDMB in ccRCC (n=539) were significantly greater compared to that of surrounding normal tissues (n=72) (1.93±0.968 vs 0.895±0.613, P<0.001). Subsequent paired data analyses demonstrated that the levels of mRNA expression of GSDMB in ccRCC tissues (n=72) were significantly greater in comparison to that of surrounding healthy tissues (n=72) (Fig. 2B, 1.238 ±0.585 vs 0.895±0.613, P<0.001), which was also validated in GEO database (GSE53757) (Fig. 2C, 159.474 ± 66.165 vs 107.306 ±47.003, P<0.001) (Fig. 2C). We conducted analysis on CPTAC via UALCAN to show throughput analysis of GSDMB protein expression. The results indicated that the protein expression of GSDMB in ccRCC (n=110) was significantly greater compared to that of healthy tissues (n=84) (Fig. 2D). As showed in Fig. 2E and 2F, immunohistochemical staining from HPA demonstrated GSDMB protein was also up regulated in ccRCC tissue. These findings suggest that the mRNA as well as protein expression of GSDMB is up regulated in ccRCC.
Relationships Between GSDMB mRNA Levels and Clinical Pathological Features of ccRCC Patients
Dunn’s test and Kruskal-Wallis test were conducted to assess the relation among GSDMB mRNA expression and clinical pathological features of ccRCC samples. Table 1 showed the baseline features of ccRCC patients which were retrieved after accessing the TCGA database. As showed in Fig. 3A-L, higher levels of GSDMB expression were identified in patients with high T stage (Fig. 3A), and patients with high pathologic stage (Fig. 3B). Besides, the GEO database also demonstrated that GSDMB were up regulated in patients with high T stage (Fig. 3C). Nonetheless, statistically significant differences were not observed among the levels of GSDMB expression and diverse clinical pathological features, including gender (Fig. 3D), age (Fig. 3E), serum calcium (Fig. 3F), hemoglobin (Fig. 3G), laterality (right or left) (Fig. 3H), histologic grade (Fig. 3I), N stage (Fig. 3J), M stage (Fig. 3K) or primary therapy outcome (Fig. 3L). Overall, these outcomes suggested that GSDMB is associated with high T stage, which additionally suggests that GSDMB may have a role as biomarker of poor prognosis in ccRCC.
Differential RNA-Seq levels of GSDMB as a potential biomarker to differentiate between ccRCC and normal samples
To assess the effectiveness of GSDMB in distinguishing ccRCC from normal samples, the ROC curve analysis was performed. The ROC curve analysis in Fig. 4A demonstrated that GSDMB was associated with an AUC value of 0.820 (95%CI: 0.772–0.869). Based on a cutoff value of 1.062, LIMK1 showed a sensitivity, specificity, as well as accuracy of 75.0, 77.2, and 76.9%, respectively. Furthermore, the positive predictive value was 30.5% while the negative predictive value was 95.9%. These results showed that GSDMB may be a valuable biomarker for the differentiation between ccRCC and normal tissues.
High mRNA expression of GSDMB is correlated to poor OS and disease specific survival (DSS)
Kaplan-Meier curves were carried out to examine the correlation between mRNA expression of GSDMB and OS, DSS in ccRCC patients. Fig. 4B and 4C showed the OS and DSS of ccRCC patients that had a high level of GSDMB was significantly shorter compared to that of a low-level of GSDMB (hazard ratio (HR)=1.98 (1.45-2.71), P <0.001; HR=1.92(1.30-2.85), P=0.001). Besides, A subgroup analysis was performed on T1, T2, T3, T4, respectively (Fig. 4D-G). It showed that GSDMB correlates with high T stage and unfavourable prognosis. Taken together, these results demonstrated that an elevated mRNA expression of GSDMB may have a role as a biomarker associated with poor prognosis in ccRCC.
Increased expressions of GSDMB associated with poor prognosis in various stages of cancer
The results of the Kaplan-Meier survival analysis indicated that ccRCC patients with a high level of GSDMB expression were associated with a poorer prognosis in comparison to patients with a low level of GSDMBexpression in the following categories of various stages of cancer : T (T1 & T2, P = 0.014; T3 & T4, P = 0.008), N (N0, P = 0, N1; P =0.405), M (M0, P=0; M1, P=0.028), and pathologic stage (I&II; P=0.009; III&IV, P=0.011) (Fig. 5A). These findings indicate that the GSDMB’s expression level can influence the prognosis of ccRCC patients in various pathological stages.
Construction and verification of a nomogram on the basis of GSDMB expression
In order to present an useful quantitative model that can assist clinicians in establishing the correct prognosis of ccRCC patients, we constructed a nomogram which combined the clinical features of patients that were independently correlated to survival through multivariate analysis (M stage, age, histologic grade and GSDMB; Fig. 5B). A point scale was used to appoint the locations of these variables in the nomogram according to the multivariate Cox analysis as follows: we used a straight line to identify the number of points for the variables in the nomogram, and the total number of the points appointed to every variable was rescaled on a scope between 0 and 100. The different locations of the variables were summed and then listed as the total number of points. Vertical lines were drawn from the axis of total points downwards to the outcome axis to identify the expected survival of ccRCC patients after 1, 3, and 5 years.’ The C-index of the nomogram was 0.774 with 1000 bootstrap replicates. The bias-corrected line, which was visualized in the calibration plot was nearing the ideal curve (also referred to as the 45-degree line), which represents a fair agreement between the observed and predicted values (Fig. 5C). Taken together, the results have shown that the nomogram is a superior model capable of establishing long-term survival (1, 3, and 5 years) in ccRCC patients than individual prognostic factors.
Identifiying DEGs in high and low GSDMB expression groups
The DSEeq2 package in R (|logFC|>2, modified P-value < 0.05) was used to analyze the data from TCGA and 1331 DEGs were detected in the high level of GSDMB expression group and low level of GSDMB expression group, among these 1197 were up regulated and 134 down regulated genes in the high expression group (Fig. 6A). Fig. 6B showed the heatmap of the ten most significant DEGs in the high level and low level GSDMB expression groups.
PPI networks and functional annotations
In order to build PPI networks and functional annotations, the STRING database, GO, and KEGG analyses was conducted. A network of GSDMB and its associated 10 co-expression genes are presented in Fig. 7A. Moreover, Fig. 7B shows that the alterations in the biological process of GSDMB were related to cytokine-cytokine receptor interaction. Functional annotations have shown that these types of genes were most likely associated with the palmitoyltransferase complex. Fig. 7C–G show the correlation analyses between GSDMB expression and co-expressed genes in ccRCC from TCGA.
Correlation analysis of GSDMB expression and immune cell infiltration in ccRCC
The potential relation between the expression of GSDMB and the six different types of tumor infiltrating immune cells was analyzed via the TIMER database. Fig. 8A showed that GSDMB expression was correlated to tumor purity (r=−0.04, P=3.89e-01); B cells (r=−0.055, P=2.42e-01); CD8+ T cells (r=0.009, P=8.53e-01); CD4+ T cells (r = 0.291, P = 1.90e-1); macrophages (r = -0.037, P = 4.31e-1); neutrophils (r = 0.144, P =2.04e-03); and dendritic cells (r = 0.011, P = 8.13e-1). The relation between GSDMB expression and 28 different kinds of TILs as identified in the TISIDB database was also evaluated. Fig. 8B showed the associations between expression of GSDMB and the 28 different types of TILs throughout human cancers. Fig. 8C-8M shows that GSDMB expression was associated to an abundance of activated B cells (r=0.286, P=2.11e-11); eosinophil (r=0.211, P=9.48e-7); activated CD8 T cells (r=0.215, P=5.92e-7); activated CD4 T cells (r=0.202, P=2.72e-6); immature B cells (r=0.181, P=2.66e-5); myeloid derived suppressor cells (MDSC) (r=0.193, P=7.42e-5); monocyte cells (r=-0.31, P=3.21e-13); gamma delta T cells (Tgd) (r=-0.152, P=0.000441); natural killer cells (NK) (r=-0.147, P=0.000652); type 17 T helper cells (Th17) (r=0.135, P=0.00172) and regulatory T cells (Treg) (r=-0.109, P=0.0114). These findings demonstrated that GSDMB may have a distinct function in immune infiltration in ccRCC.