Localization of type 5 17beta-hydroxysteroid dehydrogenase, 3beta-hydroxysteroid dehydrogenase, and androgen receptor in the human prostate by in situ hybridization and immunocytochemistry.

An important source of androgens in the human prostate are those synthesized locally from the inactive adrenal precursor dehydroepiandrosterone (DHEA) and its sulfated derivative DHEA-S. Three beta-HSD (hydroxysteroid dehydrogenase) converts DHEA into androstenedione (4-dione), whereas type 5 17beta-HSD catalyzes the reduction of 4-dione into testosterone in the human prostate and other peripheral intracrine tissues. In the present study, we have used two complementary approaches, namely in situ hybridization and immunocytochemistry, to identify the cells that contain the type 5 17beta-HSD messenger RNA and enzyme in human benign prostatic hyperplasia (BPH). Localization of 3beta-HSD and of the androgen receptor (AR) was also investigated by immunostaining in the same tissue. To find out whether there are any differences between BPH and normal prostate tissue, the localization of type 5 17beta-HSD was reexamined by immunocytochemistry in the normal human prostate samples and also in normal prostate epithelial cell line (PrEC). The in situ hybridization results obtained with a tritiated uridine triphosphate (3H-UTP)-labeled type 5 17beta-HSD riboprobe are in agreement with the immunostaining data obtained with a specific antibody to the enzyme. The immunostaining results obtained from normal prostate tissue and BPH were found to be similar. Thus, in the glandular epithelium, basal cells highly express the messenger RNA and the enzyme, whereas luminal cells show a much lower and variable level of expression. In the stroma and walls of blood vessels, fibroblasts and the endothelial cells lining the blood vessels show positive staining. Similar results are observed when the cellular distribution of 3beta-HSD is investigated. AR immunoreactivity, however, shows a different distribution because, in the epithelium, most of the nuclei of basal cells are negative, whereas the majority of nuclei of the luminal cells show positive staining. A strong reaction for AR is also found in most stromal cell nuclei and in the nuclei of most endothelial cells, as well as in some other cells of the walls of blood vessels. In conclusion, human type 5 17beta-HSD, as well as 3beta-HSD, are highly expressed, not only in the basal epithelial cells and stromal fibroblasts but also in the endothelial cells and fibroblasts of the blood vessels. AR, on the other hand, is highly expressed in the luminal cells. The present data suggest that DHEA is transformed in the basal cells of the glandular epithelium into 4-dione by 3beta-HSD and then into testosterone by type 5 17beta-HSD, whereas dihydrotestosterone is synthesized in the luminal cells after diffusion of testosterone from the underlying layer of basal cells. The potential role of androgen formation and action in blood vessels is unknown and opens new avenues of investigation for a better understanding of the multiple roles of androgens.