Cloning and Characterization of the 5(alpha)-Reductase Type 2 Promoter in the Rat Epididymis

Steroid 5(alpha) -reductase converts testosterone to the more potent androgen, dihydrotestosterone. The molecular mechanisms responsible for maintaining high concentrations of the 5(alpha)-reductase type 2 mRNA in the caput epididymidis and for regulating its region-specific expression are unknown. To gain insight into its transcriptional regulation, the cloning and characterization of the 5ʹ upstream region of 5(alpha) -reductase type 2 were undertaken. Sequential deletion analysis was done to map the 2243-base pair (bp) cloned 5ʹ upstream region, and the constructs were transfected into epididymal PC1 cells and prostatic PC3 cells. In both cell lines, regulatory elements and the minimal promoter were mapped to the 485-bp region upstream of the start codon. Primer extension and 5ʹ RACE identified one transcriptional start site at 33-bp upstream of the start codon. Using electrophoretic mobility shift assay, a specific band was observed in the –68- to –32-bp region in the presence of nuclear extracts. Supershift and mutational studies confirmed the binding of SP1 and, to a lesser extent, SP3 to the two potential SP1 binding sites and the preference of these proteins to one binding site over the other. SP1 and SP3 were both predominantly immunolocalized to the principal cells of the epididymis and follow distinct distribution patterns in this tissue. These results provide a framework crucial in the further investigation of the transcriptional regulation of 5(alpha)reductase type 2 in the rat epididymis.