Comparative study of androgen binding in rat submandibular gland and prostate

Abstract

A comparative study of androgen binding in the cytosol and nuclear extract of the rat submandibular gland (SMG) and ventral prostate (VP) was investigated by using methyltrienolone (R1881), testosterone (T) and dihydrotestosterone (DHT) as the labeled ligands. The 3H-labeled steroid was incubated with the cytosol or nuclear KCl extract in a Tris-HCl buffer (pH 7.4) at 4 degrees C for 20 h. A sephacryl S-200 column chromatography showed a single binding peak in the nuclei and two critical peaks on the binding in the cytosol of SMG. The eluation patterns of SMG were similar to those of the nuclei and cytosol from rat VP. The binding proteins were recovered predominantly in the cytosol as 150-200 kDa mol wt and in the nuclei as 14-20 Kda mol wt. The cytosol and nuclei of rat SMG and VP have a common androgen binding subunit of the molecular weight of 14-20 kDa. R1881 bound to cytosolic protein with a higher affinity than DHT in SMG and VP. The amount of the R1881 specific binding in the cytosol of male SMG was similar to that of VP, and the DHT specific binding in the male SMG cytosol was about 1/3 of the binding in the cytosol of VP. R1881, DHT and T suppressed the 3H-R1881 binding completely in the cytosol of rat VP. Whereas, in the cytosol of rat SMG, the 3H-R1881 binding was slightly suppressed by R1881 at low concentrations and effectively suppressed by R1881 at higher concentrations. DHT and T were weak inhibitors to the 3H-R1881 binding in SMG, and E2 was almost ineffective on the binding in male SMG and VP. DHT bound specifically to the nuclear extract protein in VP. The DHT specific binding was not so significant as T and R1881 in the nuclei of SMG. However, the T binding in the male nuclei was strikingly augmented by simultaneous adding of T and DHT to the incubation medium. Such androgen binding augmentation was not shown in VP. This means that the nuclear 14-20 kDa protein in SMG have an ability to bound a large amount of androgen, whose character is far different from the androgen binding mechanisms in VP, and that transformed binding protein is androgen dependent in the nuclei of rat SMG. These results demonstrated that rat SMG and VP had the same of similar molecular weight of androgen binding protein in the cytosol and nuclei. However, the protein in the nuclei of SMG had a marked different character from VP.