The PD-L1 Promoter Methylation Predicts Gene And Protein Expression Levels in Urothelial Carcinoma

We aimed to clarify the role of PD-L1 promoter methylation in bladder cancer by analyzing PD-L1 methylation and mRNA expression in FFPE samples, along with PD-L1 mRNA and protein levels in urine samples from bladder urothelial carcinoma patients. We analyzed PD-L1 promoter methylation in 43 bladder urothelial carcinoma tissue samples and 41 non-malignant bladder tissues using methylation-sensitive high-resolution melting analysis to assess two CpG islands (cg15837913, cg19724470). PD-L1 mRNA expression in tissues and urine samples, along with PD-L1 protein levels in urine, were evaluated. The bladder urothelial carcinoma group showed significantly higher methylation rates for cg19724470 and cg15837913 compared to controls (P = 0.016, P = 0.049 respectively). In the patient group, tissue PD-L1 mRNA expression was 15.22 times higher and urinary PD-L1 mRNA expression 6.56 times higher in the cg19724470 unmethylated group compared to the methylated group. Urinary PD-L1 protein concentration was twice as high in the cg19724470 unmethylated group compared to the methylated group. In the patients, tissue PD-L1 mRNA expression was 4.58 times higher and urinary PD-L1 mRNA expression 2.58 times higher in the cg15837913 unmethylated group compared to the methylated group. Moreover, the urinary PD-L1 protein concentration was 1.7 times higher in the cg15837913 unmethylated group than in the methylated group (P = 0.036). A positive correlation was observed between tissue PD-L1 mRNA and both urine PD-L1 mRNA and protein levels and between urine PD-L1 mRNA and protein levels. This study suggests that PD-L1 methylation may be a key epigenetic regulator influencing PD-L1 expression and disease pathogenesis in bladder urothelial carcinoma.