STAT4, STAT5A, STAT5B, and STAT6 expression are lower, and STAT1 expression is higher in BRCA tissues
To investigate the difference of STATs expression between BRCA tumor and normal tissue, seven STAT family members have been detected. The levels of STAT expression in cancer and normal samples were compared (Fig. 1). The findings demonstrated that STAT4, STAT5A, STAT5B, and STAT6 expression levels were decreased in breast cancer tissues while STAT1 expression levels considerably increased (p < 0.01). To validate the preceding findings, Fig. 2 illustrates a comparison of STAT family expression levels in BRCA and normal tissues. A significant decrease in STAT4, STAT5A, STAT5B, and STAT6 expression levels was observed in BRCA tissues compared to normal tissues (p < 0.001), while STAT1 and STAT2 expression levels were remarkably higher in BRCA tissues (p < 0.001) and (p < 0.05), respectively. As a result, in BRCA tissues, STAT1 expression was higher than in adjacent normal tissue, while STAT4, STAT5A, STAT5B, and STAT6 were down-regulated.
Genomic alterations of the STATs family and gene and protein network
In BRCA samples, we assessed the types and frequencies of STATs using the cBioPortal database. It was found that STATs family members rarely mutated (less than five times), indicating that they were highly conserved (Fig. 3A). GeneMANIA and STRING programs were used to generate the STATs family's gene-gene and protein-protein interaction network. We discovered that the STATs family interacted with 20 potential target genes and 11 potential target proteins (Fig. 3BC). Then, we used “correlation analysis” by (bc-GenExMiner v4.7) for seven members of the STATs family, we found STAT1 was positively correlated STAT2 (r = 0.41, p < 0.0001) and STAT4 (r = 0.47, p < 0.0001), STAT5A was positively correlated STAT5B (r = 0.46, p < 0.0001) (Fig. 3D).
Association of STATs expression and clinicopathological characteristics in BRCA patients
Our study examined the correlation between the expression of STATs and various clinical characteristics of BRCA patients, such as age, pathologic stage, radiation therapy, and TNM stage. The expression of STATs was higher in the ≤ 60-compared with > 60 group, especially STAT4 (p < 0.01). The distribution of STAT1, STAT2, STAT3, STAT5A, and STAT6 was not significantly different (Fig. 4). The expression of STAT family members in patients was also examined in relation to tumor stage. Interestingly, STAT1 was significantly high in stage1/2/3/4 than that in normal. However, the expression of STAT4/5A/5B/6 was significantly low in stage1/2/3/4 than that in normal (Fig. 5). In terms of TNM stages, the transcriptional levels of STATs were associated with the TNM stages of the patients. We discovered strongly positive associations between STAT1, STAT4, STAT5A, STAT5B, and STAT6 expression and TNM stages. The expression levels of STAT4, STAT5A, STAT5B, and STAT6 were marked lower in T1-T4, N0-N3, and M0-M1 than in normal tissues, while the expression level of STAT1 was higher inversely (Fig. 6, Fig. 7, and Fig. 8).
Prognostic value of mRNA expression of STATs in BRCA patients
Next, BRCA prognosis was examined based on STATs family expression. Kaplan-Meier analyses were used to test the effect of STATs on clinical outcomes. Figure 9 shows that high STAT4 expression is related to better OS (HR = 0.59, p = 0.002), DSS (HR = 0.59, p = 0.018), and PFI (HR = 0.55, p < 0.001) than those for the low-STAT4 group. However, in terms of OS, DSS, and PFI, STAT1/2/3/5A/5B/6 expression levels showed no significant correlation.
For the purpose of comprehending the predictive relevance of STAT4 expression in breast cancer, we used the Cox proportional hazard regression model. Additionally, the outcomes were displayed as forest plots (Fig. 10). As shown in Fig. 10A, STAT4 expression were significantly linked with the probability of mortality were patient age (p < 0.001), T stage (p = 0.012), N stage (p < 0.001), M stage (p < 0.001), and pathologic stage III and stage IV (p < 0.001). An analysis of multivariate Cox regression was performed to determine whether STAT4 expression is an independent predictor of BRCA and to assess STAT4's ability to predict clinical outcomes. STAT4 was a significant good prognostic factor for OS (HR = 0.648, p = 0.025), with similar findings for and PFI (HR = 0.498, p = 0.011) (Fig. 10C). Despite the fact that it had no significant predictive ability for DSS (Fig. 10B). In multivariate Cox regression analysis, the clinical stage, particularly the clinical N and M stages, exhibited predictive advantages for clinical outcomes. Additionally, we provided Kaplan-Meier analyses for OS, DSS, and PFI in male sex, age > 60 years, N stages, and M stages (Fig. 11). In all of the investigations, the groups with high STAT4 expression experienced noticeably improved clinical outcomes.
The prognostic nomogram was created using all statistically relevant prognostic variables in each multivariate Cox regression analysis, and the calibration curve was created to gauge the effectiveness of the nomogram (Fig. 12). The nomogram to predict OS, with a C-index of 0.660, contained clinical N and M stages as well as STAT4. Clinical N and M stages, a nomogram was created to predict DSS, STAT4 had a C-index of 0.705. A predictive nomogram for PFI was created using clinical stage, clinical N and M stages, and STAT4, and it had a C-index of 0.631. Except for the 5-year prediction of OS and DSS, all three nomograms of 1, 3, and 5-year clinical results were perfectly predicted by the calibration curves.
Overall, our findings indicated that STAT4 was a favorable prognostic factor and an independent prognostic marker in BRCA.
Correlation between STATs mRNA expression and immune cell infiltration in BRCA tumors
For a deeper understanding of STAT's suggestive role, it is necessary to investigate the types of immune cells infiltrating BRCA patients. Based on the ssGSEA method, STATs and immune cell infiltration were investigated using Spearman's analysis. As shown in Fig. 13 and Fig. 14, STAT1 expression correlated strongly with tumor-infiltrating immune cells, including aDCs (r = 0.686, p < 0.001), Macrophages (r = 0.424, p < 0.001), T cells (r = 0.502, p < 0.001), Th1 cells (r = 0.549, p < 0.001), and Treg cells (r = 0.534, p < 0.001). aDC and STAT2 expression exhibited a substantial positive association (r = 0.403, p < 0.001), T helper cells (r = 0.392, p < 0.001), T central memory cells (r = 0.392, p < 0.001), and T cells (r = 0.366, p < 0.001). The expression of STAT3 was inversely correlated with that of aDC, B cells, CD8 T cells, cytotoxic cells, and DCs. More specifically, Statistically, STAT4 expression was positively correlated with T cells (r = 0.822, p < 0.001), cytotoxic cells (r = 0.746, p < 0.001), B cells (r = 0.691, p < 0.001), Th1 cells (r = 0.686, p < 0.001), and aDC (r = 0.642, p < 0.001). A moderately positive correlation was found between STAT5A/5B/6 expression and the number of CD8 + T cells, NK cells, and T helper cells.
To evaluate the therapeutic potential of STATs-based therapy for breast cancer, the association between STATs mRNA expression and immune checkpoints (PD-1/PD-L1 and CTLA-4) in breast cancer tumors was further investigated in-depth (Fig. 15) [18]. STAT1 expression was positively correlated with CD274 (PD-1) (r = 0.720, p < 0.001), PDCD1 (r = 0.500, p < 0.001), and CTLA-4 (r = 0.620, p < 0.001), Furthermore, PD-1 and STAT4 expression were significantly correlated (r = 0.690, p < 0.001), PDCD1 (r = 0.760, p < 0.001), and CTLA-4 (r = 0.770, p < 0.001). The expression of STAT3, STAT5A, and STAT5B, however, did not correlate with PD-1/PD-L1 and CTLA-4. Based on the combined findings, STATs may influence immune cells in the tumor microenvironment of BRCA.