Expression study of three secretory proteins (prostatic secretory protein of 94 amino acids, probasin, and seminal vesicle secretion II) in dysplastic and neoplastic rat prostates.

BACKGROUND

Prostatic secretory protein of 94 amino acids (PSP94), probasin, and seminal vesicle secretion II (SVSII) are the three major proteins secreted by the lateral lobe of the rat prostate gland. Among these proteins, rodent PSP94 but not probasin and SVSII has a human homologue and it is also a major secretory protein of the human prostate, in addition to prostatic acid phosphatase and prostate-specific antigen.

METHODS

In this study, we examined and compared the mRNA expression of these three secretory markers in three rat models of prostate cancer including the sex steroid-induced dysplasia (prostatic intraepithelial neoplasia or PIN) in Noble (Nb) rat model, an androgen-independent Nb rat prostatic tumor (AIT) and Dunning rat prostatic adenocarcinomas (both androgen-dependent and -independent) by in situ hybridization (ISH), reverse transcriptase-polymerase chain reaction (RT-PCR), and immunohistochemistry.

RESULTS

The transcripts for the three markers were highly expressed in the secretory epithelium of normal lateral prostate (LP). Their hybridization signals became reduced in the epithelial cells in the low-grade PINs and significantly weakened or lost in the high-grade PINs induced in the LP. Interestingly, we observed that some dysplastic cells located at the basal compartment of the PIN lesions, and nests of outpouching epithelial cells in the vicinity of PINs, expressed positive hybridization signals of three markers. In the adenocarcinoma, signals of probasin but not PSP94 and SVSII were detected. No hybridization signals were detected in both Dunning and AIT tumors. By RT-PCR, transcripts for these proteins were still detected but significantly reduced in the Dunning tumors, whereas in the AIT tumor, only SVSII transcripts were detected. Immunohistochemistry of PSP94 also showed a reduced staining in the PIN lesions, but no immunoreactivity was seen in the rat prostatic tumors.

CONCLUSIONS

The mRNA expression of the three prostatic secretory markers were decreased in the hormone-induced PINs and in two rat prostatic tumors, indicating that the androgen-regulated secretory differentiation was impaired during the development of the premalignant lesion and further reduced in advanced tumors. The abnormal expression pattern of these secretory markers and androgen receptor (AR) in the basal compartment of the PIN lesions suggests that there is a population of cell types with secretory phenotype appearing in the basal cell layer during the early malignant transformation of the prostatic epithelium.