Identification of Differentially Expressed Proteins in Direct Expressed Prostatic Secretions of Men with Organ-confined Versus Extracapsular Prostate Cancer

University of Toronto, Canada
Molecular &amp Cellular Proteomics (Impact Factor: 6.56). 09/2012; 11(12). DOI: 10.1074/mcp.M112.017889
Source: PubMed


Current protocols for the screening of prostate cancer cannot accurately discriminate clinically indolent tumors from more aggressive ones. One reliable indicator of outcome has been the determination of organ-confined versus non-organ-confined disease but even this determination is often only made following prostatectomy. This underscores the need to explore alternate avenues to enhance outcome prediction of prostate cancer patients. Fluids that are proximal to the prostate, such as expressed prostatic secretions (EPS), are attractive sources of potential prostate cancer biomarkers as these fluids likely bath the tumor. Direct-EPS samples from 16 individuals with extracapsular (n = 8) or organ-confined (n = 8) prostate cancer were used as a discovery cohort, and were analyzed in duplicate by a 9-step MudPIT on a LTQ-Orbitrap XL mass spectrometer. A total of 624 unique proteins were identified by at least two unique peptides with a 0.2 % false discovery rate. A semi-quantitative spectral counting algorithm identified 133 significantly differentially expressed proteins in the discovery cohort. Integrative data mining prioritized 14 candidates, including two known prostate cancer biomarkers: prostate-specific antigen and prostatic acid phosphatase, which were significantly elevated in the direct-EPS from the organ-confined cancer group. These and five other candidates (SFN, MME, PARK7, TIMP1, TGM4) were verified by Western blotting in an independent set of direct-EPS from patients with biochemically recurrent disease (n = 5) versus patients with no evidence of recurrence upon follow-up (n = 10). Lastly, we performed proof-of-concept SRM-MS-based relative quantification of the five candidates using unpurified heavy isotope-labeled synthetic peptides spiked into pools of EPS-urines from men with extracapsular and organ-confined prostate tumors. This study represents the first efforts to define the direct-EPS proteome from two major sub-classes of prostate cancer using shotgun proteomics and verification in EPS-urine by SRM-MS.

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Available from: Thomas Kislinger, Jan 07, 2014
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    • "Readily accessible biological fluids are the preferred sources of cancer biomarkers and MS-based analysis of biological fluids has identified KLKs in seminal plasma (KLK2–3, KLK11) [42], expressed prostatic secretions (KLK1–3, KLK11, KLK13) [43] [44], urine (KLK1, KLK3, KLK11, and KLK13) [45] [46] [47], serum (KLK1–3, KLK5–8, KLK11–15) [48], and ascites (KLK5–8, KLK10–11) [49] [50]. Proteomic methods can be substituted for currently employed methods of detection of known markers and will be applied to identify and detect novel markers in the future. "
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    • "Our group has also aimed to develop a proteomics-based platform for the discovery and subsequent verification of prostate cancer-related proteins [71,75,88]. Specifically focusing our attention on prostate-proximal fluids, we have recently identified over 100 protein candidates that are differentially expressed when patients with organ-confined and extraprostatic tumors are compared [88]. A small number of these candidates were also found to be expressed differentially in urinary EPS from patients with recurrent disease (identified on the basis of elevated post-prostatectomy PSA levels) when assayed by stable isotope dilution-SRM-MS. "
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