Prostasomes and prostate cancer

INTRODUCTION & OBJECTIVES: Prostasomes (prostate secretory vesicles in human seminal plasma) are characterised by a very complex mosaic of proteins at their surface. A recent proteomic analysis has identified 139 proteins that can be divided into the following categories: enzymes, transport/structural, GTPproteins, chaperone proteins, signal transduction proteins, and unnotated proteins. Since phosphorylationidephosphorylation of proteins plays a critical role in regulating cell proliferation and malignant transformation, prostasome protein phosphorylation is likely to reflect neoplastic prostate transformation. The aim of this study was to analyze prostasomes isolated from patients affected by prostate cancer and to determine whether they present biochemical features which could be regarded as a prostate cancer marker. MATERIAL & METHODS: Specimens of macroscopically neoplastic and microscopically healthy tissues were taken from 30 pts who underwent radical prostatectomy. Samples were then divided in two parts and, while one was kept frozen at -70°C in 5mM Tris-HCl, pH 7.6 and protease inhibitor cocktails until histological response, the other was histologically analyzed. Enzyme activities were determined either by spectrophotometry or by HPLC. Immunodetection was performed by WB analysis with the appropriate primary antibody. RESULTS: Enzyme activities and immunodetection of prostasome proteins from prostate cancer tissues did not show significant differences when compared to controls (prostasomes isolated from ejaculates of healthy donors), therefore no enzyme activity could be regarded as neoplastic marker. Immunoblots of PSA, localized at the surface of prostasomes, was detected as a doublet at approx. 30 KDa and in agreement with already published results. Patterns of phosphorylated tyrosine residues showed the existence of three bands of 50, 40; and 27 KDa in prostasomes from healthy tissues whereas prostate cancer samples showed bands of 50, 40, and 20 KDa. No serine-phosphorylated proteins were visible in healthy tissues whereas prostate cancer samples showed a 20KDa band. CONCLUSIONS: The serine phosphorylation pattern of prostasomes is different in normal and neoplastic prostate tissues. This finding provides a potential tool for prostate cancer diagnosis