Potential therapeutic targets for bladder cancer: a proteome-wide Mendelian randomization study

Abstract

The incidence of bladder cancer (BCa) is increasing worldwide and the development of drug targets for BCa is necessary. We conducted a proteome-wide association study (PWAS) mainly using mendelian randomization (MR) to explore the causal proteins associated with BCa. Protein quantitative trait locis (pQTLs) were derived from two large proteome genome-wide association studies. After validation by multiple sensitivity analysis and two replication analyses, we identified five plasma proteins showed significant causal associations with BCa. Our study indicated that GSTM4 (OR = 0.81 (0.74-0.89), P = 5.14 × 10^-6, PPH4 = 0.89) emerged as the most reliable target. Besides, PSCA, LY6D, SLURP1 and GSTM1 also showed clear causal association but only failed in colocalization. We also performed several downstream analyses. Protein-protein interactions analysis found these causal targets came from glutathione S-transferase family or lymphocyte antigen-6 family. Phenome-wide MR analysis revealed PSCA may lead to peptic ulcer and local infections of skin and subcutaneous tissue. We then employed single-cell analysis, protein-protein interactions, and druggability evaluation. Phenome-wide MR analysis was to assess the possible side effects of these drug targets. Finally, the reliability of GSTM4 in BCa was confirmed via colony formation assay.

Keywords: Bladder cancer; biomarker; drug targets; mendelian randomization.

Figure 1

Overview of our study. MR: Mendelian randomization; PRESSO: Pleiotropy residual sum and outlier; PPH4: Posterior probability of hypothesis 4; PWAS: Proteome-wide association study.

Figure 2

Results of five significant proteins in PWAS. OR: Odds ratio; 95% CI: 95% confidence interval.

Figure 3

Single-cell type expression in bladder tumor tissues for the five significant targets identified by PWAS. A: A total of six cell types were identified. B, C: The expression of protein-coding genes in each cell type. D: GSTM4, LY6D and PSCA protein coding genes had evidence of enrichment in a cell type at average Log₂FC > 0.25 and FDR < 0.05.

Figure 4

Results of cross-cancer effect of these circulating targets.

Figure 5

Results of lifestyles that can affect selected circulating protein targets.

Figure 6

Colony formation assay showed that GSTM4 inhibited proliferation of bladder cancer cells. Colony numbers was counted and plotted. A, C: GSTM4 transfection in bladder cancer cells was detected using western blotting. B, D: The effects of overexpression of GSTM4 on proliferation were measured by colony formation assay in T24 and BIU cells. *P < 0.05, **P < 0.01, ***P < 0.001.