Figure 1 provided the research process of this study
Co-expression network construction to identify clinically significant modules
TCGA_PK_A4HP and TCGA_OR_A5JB were excluded from the subsequent study (Fig. 2(a)). Seventy-seven samples with were included in the analysis (Fig. 2(b)). In this research, the power of β = 4 (scale-free R^2 = 0.92) was determined as the soft thresholding to construct a scale-free network (Fig. 3).
We identified 23 modules (Fig. 4(a)) by using hierarchical average linkage clustering. Then we screened out modules related to the prognosis of ACC. Firstly, blue module was correlated with OS time (r = 0.35, p = 0.002, Fig. 4(b)) and OS (r = -0.61, p = 1e-08, Fig. 4(b)). Meanwhile, brown module was related with OS (r = 0.51, p = 4e-06, Fig. 4(b)) and OS time (r =-0.52, p = 3e-06, Fig. 4(b)). In addition, the MS (of OS time) of brown module ranked first among all modules, and the MS (of OS) of blue module was the highest in all modules (Fig. 4(d)). The relationship between MM and GS with OS time (cor = 0.77, p = 1.5e-180)/ OS (cor = 0.69, p = 1.9e-130) in brown module were significant too(Fig. 4(c)). The same results occurred in blue module (OS time: cor = 0.51, p = 9.7e-53; OS: cor = 0.71, p < 1e-200) (Fig. 4(c)). Consequently, we chose the blue and brown modules for further analysis.
GO Biological Processes and KEGG Analysis
We conducted GO and KEGG pathway enrichment analysis to explore the underlying function of genes in prognosis-related modules. On the basis of GO analysis, genes in the blue module were enriched in four BPs, including pattern specification process, regulation of membrane potential, embryonic organ morphogenesis and embryonic skeletal system development (Fig. 5(a)). As for the brown module, genes were enriched in 209 BPs (Supplementary Table S1). The top 10 terms were organelle fission, nuclear division, chromosome segregation, nuclear chromosome segregation, mitotic nuclear division, DNA replication, DNA conformation change, sister chromatid segregation, mitotic sister chromatid segregation and regulation of chromosome segregation (Fig. 5(c)). While in KEGG pathway enrichment analysis, genes in blue module were enriched in two KEGG pathways, including neuroactive ligand-receptor interaction and axon guidance (Fig. 5(b)). Meanwhile, genes in the brown module were enriched in six pathways, including cell cycle, oocyte meiosis, fanconi anemia pathway, progesterone-mediated oocyte maturation, DNA replication and homologous recombination (Fig. 5(d)).
Identification of hub genes
First, 1770 genes that reached the cutoff criterion (|GS|≥0.2) for both OS time and OS were selected (Fig. 6(a)). Then we got 16 genes from the blue module based on the screening criterion (|GS|≥0.2, |MM|≥0.8) (Fig. 6(b)). In the same way, we got 118 genes from the brown module (Fig. 6(c)). In all, 134 hub genes in key modules were screened out. Moreover, we tried to find hub genes associated with immunity. Therefore, two genes including BIRC5 (baculoviral IAP repeat containing 5) and PRLR (prolactin receptor), which were overlapping in WGCNA and IRGs gene lists, were eventually identified as immune-related prognosis biomarkers for further validation (Fig. 6(d)).
Hub Gene Validation
After screening out two biomarkers, we performed internal validation. At the beginning, according to the GEPIA, higher BIRC5 expression was significantly correlated with worse OS (Hazard ratio [HR] = 6.5, p = 6.5e-06, Fig. 7(a)) and DFS (HR = 3.3, p = 0.00054, Fig. 7(b)). Furthermore, we found that patients in high PRLR expression group had better OS (HR = 0.19, p = 7.2e-05, Fig. 7(e)) and DFS (HR = 0.29, p = 0.00039, Fig. 7(f)). Then we made a comparison of the mRNA expression of selected genes in ACC tumor tissue with normal tissue, the results revealed higher expression of BIRC5 (p < 0.05, Fig. 7(c)) in ACC samples compared with normal samples. It should be pointed out that although it was not significantly that PRLR expression in normal adrenal glands was higher than that in ACC tissues, there was still such a trend that the median expression of PRLR in normal adrenal glands was higher than that in ACC samples (Fig. 7(g)). Furthermore, the results also showed that patients with high BIRC5 expression (F = 6.06, p = 0.000981; Fig. 7(d)) had higher tumor stage. On the contrary, low expression of PRLR (F = 3.53, p = 0.0191; Fig. 7(h)) was significantly correlated to higher tumor stage.
On the other hand, we performed serious external validation. The results suggested that higher expression of BIRC5 was significantly related with worse OS (GSE10927: p = 0.033, Fig. 8(a); GSE19750: p = 0.0035, Fig. 8(b)) and EFS (Event-free survival) (GSE76019: p = 0.012, Fig. 8(c); GSE76021: p = 0.00012, Fig. 8(d)). Meanwhile, higher PRLR expression was significantly related with better OS (GSE10927: p = 0.039, Fig. 8(e); GSE19750: p = 0.039, Fig. 8(f)) and EFS (GSE76019: p = 0.031, Fig. 8(g); GSE76021: p = 0.041, Fig. 8(h)). On the basis of the Oncomine database, BIRC5 expression in ACC tissues is higher than that in normal adrenal glands (p = 0.01, Fig. 9(a)), and PRLR expression is higher in normal adrenal glands than that in ACC tissues (p = 1.59e-4, Fig. 9(b)). As shown in Fig. 10, BIRC5 was significantly correlated with ACC prognosis in one-way ANOVA (TCGA-ACC: p = 0.000003, F = 25.053; GSE76021: p = 0.000003, F = 35.021; GSE76019: p = 0.001, F = 13.624; Fig. 10(a)), spearman correlation analysis (TCGA-ACC: p = 0.000007, F = 0.483; GSE76021: p = 0.000001, F = 0.769; GSE76019: p = 0.001, F = 0.533; Fig. 10(b)) and distance correlation (TCGA-ACC: p = 2.2e-16, F = 0.508; GSE76021: p = 2.2e-16, F = 0.77848; GSE76019: p = 2.16e-11, F = 0.5595; GSE10927: p = 2.2e-16, F = 0.50755, Fig. 10(c)). PRLR was significantly correlated with ACC prognosis in one-way ANOVA (TCGA-ACC: p = 0.000003, F = 25.531; GSE76021: p = 0.028, Fig. 10(a)), spearman correlation analysis (TCGA-ACC: p = 0.000005, F = -0.49; Fig. 10(b)) and distance correlation (TCGA-ACC: p = 2.2e-16, F = 0.504; GSE76021: p = 0.000951, F = 0.45833; GSE76019: p = 0.0464, F = 0.33021; GSE10927: p = 2.2e-16, F = 0.50379, Fig. 10(c)). The results of ROC analysis indicated that BIRC5 (TCGA-ACC: AUC = 0.79, Fig. 11(a); GSE10927: AUC = 0.71, Fig. 11(b); GSE76019: AUC = 0.82, Fig. 11(c); GSE76021: AUC = 0.96, Fig. 11(d)) and PRLR (TCGA-ACC: AUC = 0.8, Fig. 11E; GSE10927: AUC = 0.71, Fig. 11(f); GSE76019: AUC = 0.69, Fig. 11(g); GSE76021: AUC = 0.72, Fig. 11(h)) both could significantly distinguish ACC samples from normal samples.
Relationship Between Gene Expression And TME
Varieties of immune cells in TME play an vital role in regulating anti-tumor response. Therefore, we conducted ssGSEA to determine the degree of alteration in the particular component of tumor infiltrating lymphocytes (TILs). Our study involved 28 immunophenotypes, including B cells, T cells, dendritic cells (DC) and other tumor-infiltrating lymphocytes. The results revealed that activated CD4 T cell and type 2 T helper cell were positively related with the expression levels of BIRC5 (Fig. 12(a)). And the level of CD56dim natural killer cell and type 17 T helper cell was positively related with PRLR expression (Fig. 12(c)). Pearson's correlation analysis suggested that the abundance of anti-tumor immune cells and pro-tumor immune cells was positively correlated in local environment (BIRC5: R = 0.9008, p < 0.001, Fig. 12(b); PRLR: R = 0.9008, p < 0.001, Fig. 12(d)).
Gene Set Enrichment Analysis
GSEA showed that BIRC5 was significantly enriched in KEGG pathways including cell cycle (nominal p < 0.001, n = 122, FDR < 25%, ES = -0.72, Fig. 13(a)). Meanwhile, we found that PRLR was significantly related to neuroactive ligand receptor interaction (nominal p = 0.002, n = 245, FDR = 19.1%, ES = -0.51, Fig. 13(b)).
On the other hand, we also used DSigDB to explore the drug pathways enriched in BIRC5 high expression samples. BIRC5 were mainly enriched in “resveratrol_mcf7_down” (size = 100, ES = -0.830, nominal p ≤ 0.001, FDR = 0.02340), “lucanthone_ctd_00006227” (size = 202, ES = -0.806, nominal p ≤ 0.001, FDR = 0.0447), “8-azaguanine_pc3_down” (size = 192, ES = -0.672, nominal p ≤ 0.001, FDR = 0.0356), “thioguanosine _mcf7_down” (size = 145, ES = -0.646, nominal p ≤ 0.001, FDR = 0.02331), “dasatinib_ctd_00004330” (size = 474, ES = -0.636, nominal p = 0.002, FDR = 0.04433), “monobenzone_pc3_down” (size = 196, ES = -0.627, nominal p ≤ 0.001, FDR = 0.0516) (Fig. 13(c)).