Isolation and characterization of mouse probasin: An androgen-regulated protein specifically expressed in the differentiated prostate

BACKGROUND. The development and growth of the prostate gland is regulated, in part, by a variety of steroid and polypeptide growth-factor hormones. As a consequence of hormone action, the prostate gland will produce a number of tissue-restricted gene products. Characterization of the regulation, exp ression, and function of genes encoding prostate-specific proteins is criti cal to our understanding of prostate biology. Probasin is a prostate-specif ic gene originally isolated from the rat and has been exploited as a marker of prostate differentiation and to elucidate androgen action. Furthermore, a number of transgenic mouse models of prostate cancer have been establish ed based on the regulatory elements derived from the rat probasin gene. in this report, we describe the isolation and characterization of the mouse pr obasin ortholog to further facilitate studies related to hormone action in the prostate and the generation and characterization of novel autochthonous models of prostate cancer. METHODS. Mouse probasin cDNA was isolated from a phage library, and the DNA sequence was determined. The predicted protein sequence was used to genera te specific oligonucleotide primers and antibodies. Probasin protein and RN A expression were examined by immunobloting, immunohistochemistry, and RT-P CR, in normal mouse prostate tissue and tumor tissues derived from the auto chthonous "transgenic adenocarcinoma of the mouse prostate" (TRAMP) model. Regulation of probasin expression in response to surgical castration and ho rmone supplementation was also characterized. RESULTS. Several points of evolutionary sequence conservation were identifi ed between mouse and rat probasin, especially in the 3' untranslated region . Specific polyclonal antibodies were generated to peptide fragments, and t he temporal and spatial pattern of probasin expression was examined. The ex pression of probasin was primarily localized to the apical membrane of diff erentiated secretory epithelium. Probasin mRNA and protein were absent from the poorly differentiated tissue of TRAMP tumors. Probasin was found to be androgen-regulated. in contrast to data from studies on rat probasin, no p ostcastration rebound of mouse probasin mRNA was observed. CONCLUSIONS. Probasin is a marker of differentiation and androgen action in the mouse prostate, and strong sequence conservation between mouse and rat probasin supports an essential role for this gene in the biology of the pr ostate gland. Isolation and characterization of mouse probasin will facilit ate further development and analysis of autochthonous mouse models of prost ate cancer. (C) 2000 Wiley-Liss, Inc.