Discovery of PWAS in prostate cancer
The FUSION pipeline was used to integrate the PCa GWAS findings with human blood proteomes for the PWAS of PCa. Based on the 9084-master analyzed sample size derived from the ARIC database, the PWAS identified 16 genes (MSMB, PLG, CHMP2B, ATF6B, EGF, TAPBP, GAS1, MMP7, SERPINA3, AIF1, PRDX3, DKK3, PSAPL1, MINPP1, ANGPTL4, and CTSS), whose protein levels were associated with prostate cancer at P < 0.05 (Fig. 2). After Bonferroni correction threshold of P < 0.05/number, where Microseminoprotein-beta (MSMB), Plasminogen (Plg), CHMP2B, Activating transcription factor 6 (ATF6), Epidermal Growth Factor (EGF), Tapasin Binding Protein (TAPBP), Growth Arrest Specific Gene 1 (GAS1) and matrix metalloproteinase 7 (MMP7) were more significantly associated with prostate cancer.
Expression of these genes in different cell types of PCa
We investigated whether risk genes identified by PWAS are enriched in specific prostate cell types. Using human single-cell RNA-seq data from a cell-type database, we identified enriched causal genes expressed specifically in eight cell types (Fig. 3). TAPBP, ATF6B, CHMP2B, MSMB were expressed in a higher proportion of malignant cells, while TAPBP was expressed in a higher proportion and level in various immune cells.
TWAS identified four genes associated with PCa
We combined prostate cancer GWAS data with the human prostate transcriptome to perform transcriptome-wide association analysis (TWAS) of prostate cancer using FUSION. Expression of 4 out of 8 genes (CHMP2B, ATF6B, TAPBP, GAS1) in blood was associated with PCa (Table 1). This suggests that the combined evidence from PWAS and TWAS suggests a role in the pathogenesis of prostate cancer.
Table 1
TWAS identified four genes associated with Pca
gene | P value |
CHMP2B | 3.66E-04 |
ATF6B | 1.68E-04 |
TAPBP | 3.72E-03 |
GAS1 | 3.85E-01 |
8 genes associated with prostate cancer were validated by MR using prostate pQTL.
Most of the analyzed proteins could only be detected using a single SNP; therefore, MR estimation was mainly based on the Wald ratio method. We further identified the above eight proteins, and these biomarkers revealed significant evidence of association in prostate cancer GWAS (Table 2). We further analyzed their odds ratios and showed that among them, ATF6B, CHMP2B, GAS1, and MMP7 were the risk factors for the occurrence of PCa, while EGF, MSMB, PLG, TAPBP were protective factors (Fig. 4).
Table 2
Candidate genes identified by Mendelian randomization.
Gene | nsnps | IVW | MR Egger pval | Weighted median pval |
OR | ORLower | ORUpper | Pval |
ATF6B | 11 | 1.2966 | 1.0964 | 1.5334 | 0.002397 | 0.630797082 | 0.000124905 |
CHMP2B | 21 | 1.1427 | 1.0800 | 1.2091 | 3.63E-06 | 0.160124428 | 2.18935E-05 |
EGF | 12 | 0.8494 | 0.7963 | 0.9061 | 7.21E-07 | 0.020274016 | 2.29141E-05 |
GAS1 | 4 | 1.2076 | 1.0588 | 1.3773 | 0.004923 | 0.774952735 | 0.096094973 |
MMP7 | 20 | 1.0962 | 1.0434 | 1.1517 | 0.000265 | 0.49333611 | 0.010928317 |
MSMB | 7 | 0.7767 | 0.6945 | 0.8688 | 9.74E-06 | 0.327374195 | 0.000347019 |
PLG | 23 | 0.8492 | 0.8066 | 0.8940 | 4.61E-10 | 0.017827813 | 2.70502E-07 |
TAPBP | 24 | 0.8942 | 0.8620 | 0.9276 | 2.35E-09 | 0.004858965 | 1.9132E-07 |
Co-localization between prostate cancer risk genes and pQTL in the prostate gland
Prostate cancer PWAS associations may arise from coincidental overlap between pQTL and loci that are in linkage disequilibrium with prostate cancer GWAS loci, or from the concurrent occurrence of a variant associated with protein expression, which is a protein quantitative trait locus (pQTL), and PCa. Statistical co-localization analyses for each gene report the probability of GWAS and pQTL sharing a causal variant, referred to as Hypothesis 4 (H4) and PP4/(PP3 + PP4) ≥ 0.75. Based on H4 ≥ 75% and PP4/(PP3 + PP4) ≥ 0.75, the analysis revealed three of the eight genes that provided evidence of genetic co-localization (MSMB, TAPBP, and EGF) (Table 3). This suggests that these three proteins play an important role in the pathophysiology of prostate cancer. TAPBP showed positive results in all of the above analyses, so its relationship with PCa needs to be further explored.
Table 3
Candidate genes identified by Bayesian colocalization.
Gene | nsnps | PP.H3.abf | PP.H4.abf |
MSMB | 596 | 0.000521504 | 0.99947791 |
TAPBP | 5290 | 0.022416109 | 0.96049176 |
EGF | 2841 | 0.079297104 | 0.88166609 |
CHMP2B | 3177 | 0.99938787 | 0.00060374 |
GAS1 | 3039 | 0.063961688 | 0.46131011 |
MMP7 | 2986 | 0.39553352 | 0.02078762 |
PLG | 811 | 0.994315549 | 0.00565747 |
Enrichment Analysis of the genes in PCa
In addition, we utilized the overrepresentation analysis (ORA) algorithm to decipher the role of TAPBP across different PCa cohorts. The GO results illustrated that TAPBP participated in cell adhesion, response to stimulus and nuclear division in BP; extracellular exosome, extracellular organelle and centromeric region in CC; and signaling receptor binding, protein − containing complex binding, and cell adhesion molecule binding in MF (Fig. 5A). KEGG analysis revealed that TAPBP might be involved in cell cycle, and p53 signaling pathway (Fig. 5B). GSEA and hallmark analysis also confirmed that TAPBP mainly participated in immune response, antigen processing and presentation, T cell receptor signaling pathway and Tnfa signaling via nfkb (Fig. 5C, D). Through the above finding, we found that TAPBP were involved in the immune response and cell cycle.
Mutation landscape between subtypes
The detailed genomic landscape difference between subgroups is depicted in Fig. 6A,
which indicates that the low TAPBP led to a high mutation frequency of speckle type BTB/POZ protein, SPOP, gain of 8q24.21 and 11q13.2 chromosome, and loss of 19q13.2 and 19q13.2 chromosome.
Drug sensitivity analysis
We harnessed three comprehensive drug sensitivity databases, GDSC, CTRP, and PRISM, to detect the relationship between TAPBP expression and therapy sensitivity or resistance. As Fig. 6B illustrated, high FDX1 expression displayed a consensus result of therapy resistance to Amuvatinib, Trichostatin, Pilaralisib, EHT − 1864, and Panobinostat in the GDSC database; MK − 2206, neuronal differentiation inducer III, lomeguatrib, BRD − A02303741:carboplatin (1:1 mol/mol), and necrostatin − 7 in the CTRP database; broxaterol, albuterol, GSK1904529A, pimobendan, thiamphenicol, eprinomectin, etc., in the PRISM database.
Potential prostate cancer-causing proteins with clinical associations
In furtherance of the understanding of the clinical association of TAPBP, a number of specific prostate cancer clinical indicators were used to correlate studies with it. As the most commonly used PCa screening indicator, PSA was first used for analysis. We found that the expression levels of TAPBP were not significantly associated with normal PSA (Fig. 7A). Biopsy is the gold standard for PCa diagnosis, and Gleason score is usually used to determine the benignity or malignancy of biopsied tissue. Our study found that as the Gleason score increased, the expression level of TAPBP decreased (Fig. 7B). Correspondingly TAPBP were more expressed overall in normal tissues than in tumor tissues (Fig. 7C). Further analysis of the relationship between PCa TNM staging and the expression of TAPBP showed a negative correlation between the relative expression of TAPBP and TNM staging (Fig. 7D, E, F), and showed lower expression in metastatic tumors (Fig. 7G). Tumor mutational burden (TMB), as an emerging biomarker, has received increasing attention for its role in predicting the efficacy of tumor immunotherapy. High GWAS scores are associated with low TMB (Fig. 7H).