Identification of Hub Genes
A total of 750 DEGs were identified from the GEPIA database, and 1,881 DEGs were identified from Oncomine. Sixty-nine common genes were screened out using the Venn diagram (Fig. 1 A). We then performed GO and pathway enrichment analyses for the common genes using Metascape. The results showed that these common genes were involved in 20 main GO terms and pathways, of which the top five were mitotic cell cycle, cGMP-PKG signaling pathway, extracellular matrix organization, muscle contraction, and response to hydrogen peroxide (Fig. 1 B). Finally, a PPI network of DEGs was constructed using the STRING and Cytoscape software, containing 69 nodes and 83 edges (Fig. 1 C). One significant module was identified using MCODE. This module contained 11 genes, Aurora-A kinase (AURKA), BIRC5, CENPA, CKS1B, ECT2, MYBL2, NUF2, RRM2, TK1, TPX2, and UBE2C, which were considered to be hub genes (Fig. 1 D).
Prognosis-related Hub Genes
The association between the expression of 11 hub genes and overall survival was evaluated using the R survival package. High expression of three genes (AURKA, BIRC5, CKS1B) was related to an unfavorable prognosis (Fig. 2 A–K). We further validated the prognostic value of the three genes in BLCA using the PROGgenesV2, PrognoScan, and OSblca databases. Our results showed that BLCA patients with higher expression levels of the three hub genes exhibited poorer OS, DFS, and DSS, indicating that the three hub genes may be associated with unfavorable prognosis (Table 1). In summary, our data suggested that the three key genes could serve as biomarkers of poor prognosis.
Association between Three Key Genes andClinical Parameters in BLCA
A previous study reported that the OS of BLCA patients was significantly associated with clinical characteristics, including TNM stage, smoking history, lymph invasion, and histological type (29). The three hub genes identified here were associated with various clinical characteristics including age, histological subtype, molecular subtype, nodal metastasis status, sample type, smoking, cancer stage, and TP53 mutation status (Table 2). Most importantly, overexpression of the three hub genes was positively correlated with histological subtypes (Fig. 3 A–C). The expression of the three hub genes was higher in the basal squamous and neuronal subtypes than in the luminal subtype (Fig. 3 D–F). BLCA patients with TP53 mutations also showed high expression of the three hub genes (Fig. 3 G–I). Taken together, these results suggest that increased expression of the three key genes might predict poor prognosis in patients with BLCA.
CD8+ T Cell Infiltration Predicts Poor Prognosis in BLCA
The TIMER and TISIDB databases were used to explore the relationship between the three prognosis-related genes and tumor-infiltrating immune cells. The three genes were positively associated with levels of infiltrating CD8+ T cells, neutrophils, and dendritic cells. Expression of BIRC5 was negatively correlated with infiltration of B cells (Table 3, Fig. 4 A–F). High levels of infiltration of CD8+ T cells were associated with poor prognosis (Fig. 4 G). These results suggest that these genes may affect prognosis via regulation of CD8+ T cells.
Three Key Genes Correlated with Immunotherapy Response
Previous studies have suggested that TMB and PD-L1 expression are correlated with response to atezolizumab in mUC (17). Our results indicated that the three key genes were associated with TMB in multiple cancers, including adrenocortical carcinoma, BLCA, and breast invasive carcinoma (Fig. 5 A–C). We further discovered that the expression levels of the three hub genes were positively correlated with infiltration of PD-L1 (CD274) expression (Fig. 5 D–F). Finally, our results showed that the three hub genes exhibited a significant difference in expression between responders and non-responders to atezolizumab in urothelial cancer via TISIDB analysis (Table 4). Taken together, these results suggest that the impact of the three hub genes on response to immunotherapy in BLCA may be associated with TMB and PD-L1 expression. The three key genes may thus represent a promising immunotherapeutic target. Finally, we found that the three prognosis-related genes had the highest expression levels in the C2 (IFN-gamma dominant) subtype and the lowest in the C3 (inflammatory) subtype (Fig. 5 G–I).
Drug–Gene Interaction Network
Drugs targeting three key genes were collected from the DrugBank database. AURKA and 18 other targets were correlated with 15 drugs. BIRC5 and two targets were related to 15 drugs. CKS1B and another three targets interacted with three drugs (Fig. 6 A–C). Our results may contribute to the development of new targets for BLCA immunotherapy.