Uptake of androgens by intact and detergent-treated nuclei from the rat ventral prostate

5 alpha-Reductase type 1 is localized to the outer nuclear membrane

The subcellular distribution of the two isozymes of 5 alpha-reductase has been controversial. To resolve this issue which could provide clues about the respective functions of the two isozymes, two antisera were generated, one which was specific for the Type 1 5 alpha-reductase and one which recognized both isozymes. In COS cells transfected separately with the Type 1 or Type 2 cDNA, both isozymes were detected on Western blots at an M(r) of 26,000. Subfractionation of the COS cells resulted in the partitioning of both isozymes between the crude nuclear and cytosolic fractions, while cytoimmunofluorescence localized both reductases to the nuclear periphery. In rat liver homogenate, the 5 alpha-reductase was also detected at M(r) 26,000. The 5 alpha-reductase immunoreactivity was increased after castration of the animals with no further effect when castrated animals were treated with androgens. Although the rat liver expresses only the Type 1 5 alpha-reductase, the 5 alpha-reductase was distributed about equally between crude nuclear and cytosolic subfractions; this distribution could be shifted to the cytosolic fractions with harsher homogenization procedures. Further extensive subfractionation and extraction studies identified the rat liver Type 1 5 alpha-reductase as an integral membrane protein present in the outer nuclear membrane of the nuclear envelope and in rough endoplasmic reticulum. Thus, the subfractionation and cytoimmunofluorescence studies are consistent with the localization of the Type 1 5 alpha-reductase to the outer nuclear membrane of the nuclear envelope which is continuous with and indistinguishable from the endoplasmic reticulum. This study is the first to localize rat liver Type 1 5 alpha-reductase to the nuclear envelope to which the prostatic 5 alpha-reductase activity previously had been localized. We conclude that, contrary to previous tissue distribution studies, but consistent with investigations in transfected cells, both isozymes are similarly localized to the nuclear periphery.

Evaluation of biopsy techniques for androgen receptor assay in human prostatic tissue

Androgen receptors were assayed in nuclei prepared from human benign hypertrophic prostate tissue obtained at retropubic prostatectomy by transurethral resection (TURP) and by cold punch resection. Androgen receptor was not detected in 70% of the transurethrally resected samples, and in those cases where receptors were observed they showed no correlation with enucleated samples. However, androgen receptors were detected in all cold punch resected samples and enucleated tissue with similar concentrations evident in samples from the same gland. These results suggest that prostate specimens collected by TURP are not suitable for androgen receptor analysis, whereas the technique of cold punch resection yields prostate samples that are more reliable for a correct evaluation of androgen receptor content.

Androgen interactions with intact nuclear envelopes from the rat ventral prostate

Intact nuclear envelopes containing nuclear pore complexes have been prepared from the rat ventral prostate. The polypeptide profile of the nuclear envelopes from the rat prostate resembled that of nuclear envelopes prepared from the male rat liver. Isolation of the nuclear envelopes after incubation of purified nuclei with radioactive dihydrotestosterone results in labelling of the membrane. More dihydrotestosterone is bound after incubations at 22 degrees C for 18 h than at 2 degrees C for 18 h or 22 degrees C for 2 h. Scatchard analysis revealed a class of binding sites with an apparent Kd of 46 nM. Dihydrotestosterone, testosterone, cyproterone acetate and methyltrienolone were effective as competitors of labelled dihydrotestosterone binding to the nuclear envelopes, while estradiol did not compete. Castration of the rats 24, 48 and 96 h prior to preparation of nuclei resulted in loss of androgen binding to the membranes. Extraction with 0.6 M NaCl resulted in the loss of 72% of the androgen binding.

Nuclear androgen binding sites in the male rat. I. Unoccupied sites in the prostate

A study was made of unoccupied androgen binding sites in the nuclei of ventral prostate glands of male rats. They were measured at 0 degrees C by comparing specific binding of 1 nM [3H]DHT to salt extract of purified nuclei during the first hour with specific binding during both hours. This method was dependent upon demonstrated completion of uptake into unoccupied binding sites within the first hour and linearity of exchange with occupied binding sites during both hours. Unoccupied binding sites were not artefactual. They did not increase if tissue concentration was diluted prior to homogenization, while they decreased if homogenization was delayed after the tissue was minced. They could be occupied, both in vitro (if precharged with at least 1 nM unlabeled DHT) or in vivo, by administering testosterone propionate subcutaneously or by infusing testosterone into the jugular vein. Exposure to a high concentration of unoccupied prostatic cytosolic binding sites (608.4 fmol from castrated rats) as compared to low concentration (29.3 fmol from intact rats) during homogenization had little effect upon nuclear unoccupied binding site concentrations (2.16 fmol/mg DNA vs 2.41 fmol/mg DNA, respectively). In individual rats, concentration of unoccupied nuclear androgen binding sites was 4.61 +/- 1.05 fmol/mg DNA, while total binding site concentration (measured with 10 nM [3H]DHT for 24h at 12 degrees C) was 866 +/- 103 fmol/mg DNA. Unoccupied nuclear binding sites reached their highest concentration in animals 4 months old (15.09 fmol/mg DNA) when animals 21 days through 720 days of age were studied. By use of association and dissociation rates of binding, it was determined that the apparent Kd of nuclear binding sites was 1.11 X 10(-12) M. There were no observed differences between unoccupied and occupied binding sites in steroid specificity or in sedimentation rate in an 8-24% glycerol density gradient. Although no physiological importance can be attributed as yet to unoccupied nuclear androgen binding sites in the prostate, they do provide a convenient comparison with putative androgen binding sites in the nuclei of testicular and epididymal germ cells.

Androgenic control of acetate incorporation into phospholipids and triacylglycerols in rat ventral prostate

To obtain information about androgenic hormone actions on the synthesis of lipids from [1-14C]acetate in rat ventral prostate, in vitro and in vivo experiments have been carried out. The time course of incorporation of labelled acetate was studied. Also different solubilization media of androgenic hormones was investigated. We have selected Tween-80. Results for in vitro experiments, show that increasing concentrations of testosterone and dihydro-testosterone correspond to an increase in the incorporation of labelled acetate into phospholipids and a decrease in the incorporation into triacylglycerols. In vivo experiments of incorporation of [1-14C]acetate have also been carried out and show a similar pattern to the situation found in our in vitro experiments.

Characterization of androgen uptake by purified nuclei from an androgen-dependent and two androgen-independent cell lines of the Shionogi mouse mammary carcinoma

Properties of androgen uptake by nuclei prepared from an androgen-dependent tumour cell line occurred after 2 h incubation at 20 degrees C; 2. Nuclei from three tumour cell lines displayed similar affinity for DHT but the two androgen-independent cell lines had less than one-quarter the number of uptake sites; 3. Loss of label from nuclei which had been pre-incubated with [3H]-DHT for 18 h at 20 degrees C was greater from the AD cell line nuclei than from the androgen-independent cell lines; 4. Whole cell contamination of the nuclear preparations did not contribute to specific DHT uptake.