Proteomic Characterization of Primary and Metastatic Prostate Cancer Reveals Reduced Proteinase Activity in Aggressive Tumors
Abstract BackgroundProstate cancer (PCa) is a heterogeneous group of tumors with variable clinical courses. Clinically, it is critical to separate and treat aggressive PCa (AG) from non-aggressive PCa (NAG). Although recent genomic studies have identified a spectrum of molecular abnormalities associated with PCa, it is still challenge to separate AG from NAG. To better understand the functional consequence of PCa progression and the unique features of AG from NAG, we studied proteomic signatures of primary AG, NAG and metastatic PCa.Methodes39 PCa and 10 benign prostate controls in discovery cohort and 57 PCa in independent-collected validation cohort were analyzed using data-independent acquisition (DIA) SWATH–MS platform. Proteins with the highest variances (top 500 proteins) were annotated for the pathway enrichment analysis. Functional analysis of differentially expressed proteins in NAG and AG was performed. Data was further validated using validation cohort, as well as by comparison with TCGA mRNA expression and immnunochemistry on PCa tissue microarray (TMA).Results4,415 proteins were identified in the tumor and benign control tissues, including 158 up-regulated and 116 down-regulated proteins in AG tumors. A functional analysis of tumor-associated proteins revealed the reduced expression of several proteinases, including dipeptidyl peptidase 4 (DPP4), carboxypeptidase E (CPE) and prostate specific antigen (KLK3) in AG and metastatic PCa. A targeted analysis using SWATH data further identified that the reduced expression of DPP4 was associated with the accumulation of DPP4 substrates in AG tumors, including the reduced ratio of DPP4 cleaved peptide to intact substrate peptide. Findings were further validated using independent-collected cohort, by comparison with TCGA mRNA data, and the immunochemical stains of our tumor microarray (TMA).ConclusionsOur study is the first large-scale proteomics analysis of PCa tissue using DIA SWATH-MS platform. It not only provides an interrogative proteomic signature of PCa subtypes, but also indicates critical roles of certain proteinases, especially DPP4, in PCa progression. The spectrum map and protein profile generated in the study can be used to investigate potential biological mechanisms involved in the PCa progression as well as for the development of a clinical assay to distinguish aggressive from indolent PCa.