3.1 BRD4 gene expression analysis in OC tissue
We used the Oncomine database to analyze the expression of BRD4 in tumor tissues and corresponding normal tissues. BRD4 expression was significantly increased in tumor tissues in patients with OC (Figure 1A, B). This suggests that BRD4 may play a role in the occurrence and development of OC.
3.2 Prognostic value of BRD4 in OC
The PrognoScan database was used to analyze the correlation between BRD4 (probes, ID: 202102_at and ID:12779) and the survival rate in OC. The cumulative survival rate of patients with high BRD4 expression was significantly lower than that of the low-expression group (Figure 2A, ID: 202102_at, P = 0.000538; Figure 2B, ID: 12779, P = 0.029596). Further, using the Kaplan-Meier Plotter database, we performed multivariate Cox regression analysis on the data related to BRD4 expression and OC patients. The cumulative overall survival (OS) of patients in the BRD4 high expression group was significantly lower than that of patients in the low expression group (Figure 2C, ID: 202102_at, P = 0.027; Figure 2D, 226054_at, P = 0.012). Patients in the BRD4 high expression group had significantly shorter progression-free survival (PFS) than those in the low expression group (Figure 2E, ID: 202102_at, P = 0.000247; Figure 2F, 226054_at, P = 0.0029). These results indicate that BRD4 is an important factor affecting the prognosis of patients with OC.
3.3 Subgroup analysis of the correlation between BRD4 expression and patient survival
To further understand the correlation between BRD4 expression and OC and the potential mechanism, we explored the relationship between BRD4 expression and clinical characteristics of OC patients using the Kaplan-Meier Plotter database (Table 1). High BRD4 expression was associated with poor OS of serous ovarian cancer (P < 0.05). In patients with early stage OC (stage 1-2), high BRD4 expression was significantly associated with poor prognosis (Table 1). Pathological registry analysis also showed that high expression of BRD4 was significantly associated with poor OS (Table 1), independent of the presence of TP53 mutation (P < 0.05). Most importantly, we found that after chemotherapy with various drugs, high expression of BRD4 was significantly associated with poor OS (P < 0.05). These results suggest that BRD4 may be an important factor that hinders chemotherapeutic treatment of OC.
3.4 Genomic changes of BRD4 in OC
Next, we used c-BioPortal to determine the type and frequency of BRD4 genome changes in OC based on sequencing data from OC patients in TCGA. Twenty-two percent of OC patients had BRD4 genome changes (Figure 3A). In addition, BRD4 CNV was significantly correlated with the OS and disease-specific survival (DSS) of OC patients (Figure 3B-C).
3.5 Analysis of BRD4 expression and immune infiltration level in OC
Lymphocyte infiltration is an independent predictor of cancer patient survival and lymph node metastasis . We evaluated the relationship between BRD4 expression and the degree of immune invasion in patients with OC tumors. First, we found that BRD4 expression was significantly positively correlated with tumor purity (r = 0.196, P = 1.47´10-5), indicating that BRD4 is related to tumor purity and is closely related to prognosis. We also found that BRD4 expression was positively correlated with the degree of infiltration by immune cells, including CD8+ T cells (P = 6.28´10-8), macrophages (P = 1.1´10-12), centrioles (P = 1.85´10-13), and dendritic cells (P = 1.30´10-9) (Figure 4). To further study the correlation between BRD4 and several types of infiltrating immune cells, we used the TIMER and GEPIA datasets to determine the correlation between BRD4 and different immune cell markers in OC. TIMER database analysis showed that BRD4 was significantly correlated with immune markers of macrophages, dendritic cells, and various effector T cells in OC (Table 2). GEPIA analysis results confirmed that BRD4 was significantly correlated with immune markers of macrophages, dendritic cells, and various effector T cells, as well as centrioles, in OC (Figure 5). Based on the above results, we believe that BRD4 expression is related to immune cell infiltration in OC and that BRD4 may play an important role in the immune evasion of OC cells.