In situ hybridization study of PSP94 (prostatic secretory protein of 94 amino acids) expression in human prostates

BACKGROUND. The prostatic secretory protein of 94 amino acids (PSP94), also named beta-microseminoprotein, is one of the major proteins secreted by th e human prostate. However, its value as a prognostic marker for prostate ca ncers is still under debate. The aim of the present study was to examine th e expression pattern of this protein in fetal, pubertal, and aged human pro states. METHODS. Nonisotopic in situ hybridization using a digoxigenin-labeled ribo probe for PSP94 and immunohistochemistry were used to demonstrate the expre ssion of PSP94 in different regions or zones of fetal, pubertal, and adult human prostates. Its localization pattern was also compared with those of t wo other major secretory proteins, prostate-specific antigen (PSA) and pros tatic acid phosphatase (PAP), by immunohistochemistry. RESULTS. PSP94 mRNA and its protein were localized to the secretory epithel ium of normal pubertal and adult human prostates. No hybridization signal a nd immunoreactivity of PSP94 were seen in fetal prostates at 6-7 months of gestation, whereas some glandular cells were positive to PSA and PAP immuno stainings. In the adult prostates, PSP94 expression was intense in the acin i in the peripheral zone, less intense in the transition zone, and variable in the central zone. Such a zonal expression pattern was more apparent in the pubertal prostates. However, no obvious differential expression pattern was observed in the immunohistochemistry of PAP and PSA, which showed a un iform staining of the secretory epithelia of the acini in all anatomic zone s. The hybridization signals and immunoreactivity of PSP94 became reduced o r lost in premalignant prostatic intraepithelial neoplastic lesions and dif ferent grades of prostatic carcinomas. CONCLUSIONS. Fetal prostates at 6-7 months of gestation already synthesize PSA and PAP hut not PSP94. The delayed expression of PSP94 appears to corre late with the development of the prostate gland. A differential expression pattern of PSP94 is demonstrated in different anatomical zones, showing tha t this protein is more expressed and synthesized in the acini in the periph eral zone than in the central and transition zones. However, such a zonal p attern is not seen in the immunohistochemistry of PSA and PAP. The present study also shows that PSP94 is downregulated in different grades of prostat e cancers. (C) 1999 Wiley-Liss, Inc.