Prostate alpha-protein: subunit structure, polyamine binding, and inhibition of nuclear chromatin binding of androgen-receptor complex

Ductal heterogeneity in rat dorsal-lateral prostate

Given the lobar complexity of the rat prostate at the morphological level, differences in secretory protein expression were investigated in individual prostatic ducts that constitute the subdivisions of the dorsal-lateral prostate, ie., the dorsal prostate, lateral prostate type 1 and lateral prostate type 2. For this purpose, individual prostatic ducts were microdissected from these prostatic lobes, photographed, and secretions subsequently collected from individual prostatic ducts and analyzed by Western blot for the expression of DP-1 and probasin, two major proteins expressed in rat the dorsal-lateral prostate. Many individual glands constituting the dorsal prostate, lateral prostate type 1 and lateral prostate type 2 co-express DP-1 and probasin, but at vastly different levels. DP-1 is a major secretory protein of the dorsal prostate and lateral prostate type 1, while probasin is the major secretory protein of the lateral prostate type 2. A small percentage of individual ducts of the dorsal prostate, lateral prostate type 1 and lateral prostate type 2 express either DP-1 or probasin. However, most of the individual prostatic ducts constituting the dorsal prostate and lateral prostate type 1 express DP-1 at high levels and probasin at low levels. Conversely, most of the individual prostatic glands that constitute the lateral prostate type 2 express probasin at high levels and DP-1 at low levels. This study emphasizes the morphological and functional heterogeneity within the prostate gland.

Electrophoretic modification of sperm plasma membrane by ventral prostate secretion in golden hamsters

Plasma membrane proteins were extracted either from epididymal spermatozoa after incubation with ventral prostate gland secretion or from spermatozoa recovered from uteri of females mated with surgically treated males belonging to the following groups: TX (excision of all accessory sex glands, ASG), VPX (bilateral excision of ventral prostate), VP (bilateral excision of all ASG except the ventral prostate), and SH (sham-operated). Incubation of spermatozoa with ventral prostatic secretion resulted in an 11-fold increase in glycoprotein content of the plasma membrane, but total protein concentration remained unchanged. The in vivo study indicated that interactions of ASG secretions and spermatozoa were complicated by the presence of uterine secretions. Glycoprotein content was reduced in the presence of ventral prostatic secretions. SDS-PAGE profiles showed that both uterine and ASG secretions could modify proteins on the sperm surface. Enrichment of a 25-kD subunit was apparently effected by uterine secretions and further promoted by combined secretions of the ampullary gland, coagulating gland, dorsolateral prostate, and seminal vesicle, but was reduced by the ventral prostate. A number of other protein subunits appeared to be specifically modified by the ventral prostate, while other ASG secretions were also shown to alter the effects of the ventral prostate on the sperm surface.

Prostatein C3-mRNA: a sensitive marker of androgen-responsiveness in prostate explant cultures

Prostatein is an androgen-dependent protein which is secreted by the rat ventral prostate. To determine if prostatein or its mRNA were responsive to androgen in vitro, prostate explants were cultured in media containing 0 or 25 nM dihydrotestosterone (DHT), estradiol (E2), or cortisol (F). Prostatein concentrations in medium were measured by radioimmunoassay at 2 and 4 days and in homogenates at 4 days. They were not changed significantly by any of these steroids. The concentration of the mRNA for the C3-subunit of prostatein was determined by dot hybridization at 0, 2, 4, 6, and 8 days. It was decreased significantly by 2 days when compared with explants cultured in the presence of DHT and significant differences persisted through 8 days. In conclusion, quantitation of the mRNA for the C3-subunit of prostatein in short-term cultures of ventral prostate explants appears to be more sensitive to changes in androgen concentration than does measurement of prostatein, per se. Prostatein C3-mRNA may be a useful marker for in vitro studies of androgen agonists and antagonists.

An immunohistochemical technique for localization and semiquantitation of estramustine-binding protein (EMBP) in rat and human prostate

An immunohistochemical technique for determination of "estramustine-binding protein" (EMBP) in rat prostate is described. The localization and staining intensity of this protein were correlated to prostatic morphological structures in intact animals and at different time intervals after androgen deprivation by castration. EMBP was found almost exclusively in epithelial cells, while the fibromuscular stroma seemed to be negative. Intracellularly, immunostaining was confined to the cytoplasm, but was absent in nuclei. In intact rats, acinar lumina demonstrated heavy immunostaining, indicating secretion of EMBP. Orchiectomy caused a diminution of EMBP expression as well as secretion, suggesting that EMBP synthesis is under androgenic regulation. Human benign hyperplastic and cancerous prostatic specimens were also examined. All human specimens examined so far exhibited positive epithelial staining although of varying intensity. Therefore, this immunohistochemical technique may be used for studying the correlation of EMBP with tumor malignancy grade and for clinical investigations of how various treatments affect EMBP expression in prostatic carcinomas.

Suppression of steroid receptor-chromatin interaction by inhibitors present in ammonium sulfate-fractionated rat testicular androgen receptor preparations

Tritiated androgen receptor complex was partially purified by ammonium sulfate precipitation at 15 to 37% saturation from rat testicular or prostatic cytosols. A greater amount of prostatic tritiated androgen receptor complex bound to rat Sertoli cell chromatin than tritiated testicular androgen receptor complex. However, the testicular androgen receptor complex was more potent in competing for binding of either tritiated androgen receptor complex preparation to the Sertoli cell chromatin. Combining equal amounts of tritiated testicular and prostatic androgen receptor complexes resulted in lower binding than that observed with tritiated prostatic androgen receptor complex alone, while doubling the concentration of tritiated prostatic androgen receptor complex led to a 2-fold increase in binding. It is conceivable that the partially purified testicular androgen receptor complex preparations contain factor(s) that inhibit the binding interaction of tritiated androgen receptor complex with chromatin, while there is no evidence for the presence of such inhibitors in tritiated prostatic androgen receptor complex preparations. Fractionation of testicular cytosol on DEAE-cellulose yielded a flow-through fraction with inhibitory activity and a bound fraction containing tritiated androgen receptor complex that was eluted with 0.3 M KCl and also showed inhibitory activity. These factors also inhibited the binding of tritiated estradiol receptor complex to chromatin. They were non-dialyzable and their inhibitory effect was abolished after heating at 60 C for 30 minutes. It is concluded that ammonium sulfate-fractionated rat testicular androgen receptor complex preparations contain inhibitors of steroid receptor-chromatin interaction. The inhibitory factors can be fractionated into two distinct fractions by DEAE-cellulose column chromatography. They are nondialyzable and heat-labile. The precise chemical nature of the postulated inhibitor(s) remains to be determined.

Androgen-regulated expression of secretory protein synthesis in mouse ventral prostate

Two proteins of molecular weights 25 and 12 kDa (p25 and p12 respectively), whose expression is regulated by testosterone, were identified in mouse ventral prostate. An antiserum raised to mouse ventral prostate secretion was used to demonstrate that p25 corresponds to the major secretory glycoprotein in mouse prostatic fluid. This antiserum does not cross-react with the major secretory proteins of the rat ventral prostate. Western blot analysis of mouse ventral prostate proteins using the prostatic secretion antiserum demonstrates that p12 and p25 are detectable at 3 weeks of age, but the maximum level of both proteins is not attained until 5 weeks of age. In addition, synthesis of p25 was also observed in prostate tissue derived from differentiated embryonic urogenital sinus tissue growing as implants under the renal capsule of syngeneic male hosts.

Purification and characterization of a steroid-binding sialoglycoprotein from rat ventral prostate

An androgen-dependent sialoglycoprotein was purified from the secretion of rat ventral prostate by chromatofocusing and DEAE-Sepharose column chromatography. It showed a native molecular weight of 47,000 and consisted of two dissimilar subunits with molecular weights of 20,000 and 18,000. However, each subunit contained a common peptide with molecular weight of 16,000. It also contained 442 +/- 62 micrograms sialic acids per milligram protein and bound pregnenolone with a binding affinity of 1.2 microM-1. Its amino acid composition was similar to those of other known prostatic steroid-binding proteins. Hence, we propose that it is the sialylated form of rat prostatic steroid-binding protein.

Testicular cytosol factors inhibit the binding of steroid-receptor complexes to chromatin

Testicular and prostatic androgen-receptor complexes as well as uterine estradiol-receptor complexes, partially purified by ammonium sulfate precipitation (15-37%), were bound to germ cell chromatin. At equivalent concentrations, less testicular androgen-receptor complexes bound to chromatin than did the other two steroid-receptor complexes. Addition of a partially purified testicular androgen-receptor preparation with prostatic androgen-receptor or uterine estradiol-receptor preparation to the binding interaction mixture reduced the binding of either of the latter two steroid-receptor complexes to chromatin. These data suggest the presence of inhibitory factor(s) in the testicular receptor preparations. Testicular cytosols were fractionated by ammonium sulfate precipitation into fractions A (15-37% saturation), B (37-50%) and C (50-75%). All fractions inhibit binding of these steroid-receptor complexes to chromatin. Fractions A and B appear to be heat labile, while fraction C was more stable. Further fractionation of A and C fractions on DEAE cellulose yielded A1 and C1 (filtrates) as well as A2 and C2 (0.3 M NaCl eluents), respectively. Subfractions A1, A2, and C2 contained inhibitory factors for the binding of steroid-receptor complexes to chromatin while C1 showed no effect. These data demonstrated that testicular cytosol contains a variety of inhibitory factors which affect the binding of both androgen-receptor and estradiol-receptor complexes to chromatin.

Characterization of the androgen-dependent 22Kdalton glycoprotein from rat ventral prostate

Oxidation by molecular oxygen converted the 22Kdalton glycoprotein from rat ventral prostate into a 34K species and this reaction could be reversed by thiol reducing reagent. Measurement of the level of the 22Kdalton glycoprotein in prostatic cytosol by the radial immunodiffusion technique showed that changes in the 22Kdalton glycoprotein concentration in response to androgen withdrawal and replacement were slow in comparison to androgen regulated levels of mRNA coding for the protein. (3) Charcoal absorption steroid binding assays of the 22Kdalton glycoprotein revealed that the protein did not bind testosterone, estradiol, progesterone or corticosterone. These results indicate that the 22Kdalton glycoprotein is metabolically stable, not steroid-binding, and exists as an oligomer through disulfide crosslinking.

Two-dimensional characterization of prostatic acid phosphatase, prostatic specific antigen and prostate binding protein in expressed prostatic fluid

Specimens of pooled prostatic fluid, collected by rectal massage from men under 50 years of age with no apparent prostatic disorders, were subjected to two-dimensional gel electrophoresis to study the composition of its proteins. In a preliminary study, a total of 57 major protein groups were detected. In the present study, we attempted to identify, in the two-dimensional gels, those that are related to prostate-associated proteins, i.e., prostatic acid phosphatase (PAP), prostatic specific antigen (PSA), and prostate binding protein (PBP). Individual proteins were recognized by the procedure of Western Blot using specific antisera with peroxidase-antiperoxidase as the staining reagent. Each protein spot in the two-dimensional gel was expressed, along the abscissa, by its isoelectric point (pI) and, along the ordinate, by the molecular weight (MW). PAP consisted of a train of more than ten protein spots that occupied an area in the gel from pI 7.0, MW 45,000 to pI 6.0, MW 50,000. Four protein spots with a MW of 34,000 and a pI range of 8.2-8.8 were identified as PSA. PBP was observed as having three protein spots that were located at pI 5.6-6.6 with a single MW of 15,000. For PAP and PSA, additional protein spots with lower MWs also stained positively with the specific antisera, suggestive of the presence of degradative products of these proteins. Following the removal of the serum-related proteins by an extensive absorption with anti-human serum antibody by affinity chromatography, the prostatic fluid contained 27 major groups of non-serum proteins. These non-serum proteins in the prostatic fluid included PAP, PSA, PBP, and their related smaller molecular species. These results indicate that the prostatic fluid contains PAP, PSA, PBP and that their presence and the patterns of their distribution in the two-dimensional gels should be considered as the characteristic property of the prostatic secretions.

Regulation of prostatic steroid binding protein mRNAs by testosterone

Testosterone regulates the expression of prostatic steroid binding protein by stimulating the accumulation of C1, C2 and C3 mRNA. We have used intervening sequence RNA probes to quantitate the primary transcript and a processed intermediate for C1 and C3 in nuclear RNA. Both C1 and C3 primary transcript concentration declined by about 100-fold 3 days after castration and were induced by testosterone within 1 h. In view of the magnitude and kinetics of the response we conclude that testosterone acts primarily within the cell nucleus to increase steady-state levels of nuclear RNA.

Multiple gene action determining a mouse salivary protein phenotype: identification of the structural gene for androgen binding protein (Abp)

A novel variation in electrophoretic phenotype is described for a mouse salivary androgen binding protein (Abp). Crosses show that the variation is inherited in an autosomal codominant manner and protein characterization studies show that the variant Abp differs in isoelectric point from the common form of the protein. Those observations suggest that the variation involves the structural gene for the mouse salivary Abp. The genetic studies also show that the electrophoretic mobility of the variant Abp can be influenced by the sex-limited saliva pattern (Ssp) gene. The SspS allele alters the electrophoretic mobility of Abp in males at puberty or in females which have received exogenous testosterone [Karn, R.C., Dlouhy, S.R., Springer, K.R., Hjorth, J.P., and Nielsen, J.T. (1982). Biochem Genet. 20:493]. This study shows that Abp and Ssp are distinct genes which are not closely linked and that SspS is trans active in F1 (Abpa/Abpb, SspS/SspF) males.

Immunochemical characterization of the androgen-dependent spermine-binding protein of the rat ventral prostate

A solid-phase radioimmunoassay was developed to measure the level of the androgen-dependent spermine-binding protein (SBP) in the cytosol fraction of the rat ventral prostate during endocrine manipulation. The concentration of SBP and immunologically cross-reacting material (CRM) in the ventral prostate was at least 5000 times higher than the level of CRM detected in rat serum or cytosol from other rat tissues. Cytosol from the ventral prostate of intact rats was separated by DEAE-cellulose chromatography into three major fractions of CRM. One of these fractions corresponded to the elution position of SBP. Cytosol prepared from rats 48 h after castration lacked SBP and one of the two other fractions of CRM. This loss coincided with an increase in CRM in the remaining fraction. No significant difference was detected in the total level of CRM when intact and 48 h-castrated rats were compared. Injection of rats with 5 alpha-dihydrotestosterone (DHT) immediately after castration prevented these changes in the profile of CRM. Several proteins cross-reacting with antibodies to purified SBP were detected in cytosol by using an immunoblot procedure. The highest-Mr band corresponded to SBP. The effect of short- and long-term castration and subsequent DHT treatment on CRM was studied by using the immunoblot technique. Short-term castration (2 days) led to the disappearance of CRM coinciding with SBP (Mr 35 000-38 000) and an increase in smaller forms of CRM (Mr 24 000 and 22 000). Injection of rats with DHT 2 days after castration led to the reappearance of CRM corresponding to SBP, which returned to normal levels within 4 to 5 days of treatment. Long-term castration (up to 14 days) led to a gradual disappearance of all CRM; subsequent DHT treatment led to the reappearance of all forms of CRM and normal levels were attained within 5 days. We have identified SBP and the various forms of CRM as a secretory product of the rat ventral prostate by immunohistochemical staining and by DEAE-cellulose fractionation of prostatic fluid. Prostatic fluid is rich in proteolytic activity and these proteinases may be responsible for processing SBP to small forms of CRM.

Biochemistry of the nonhuman primate prostate and seminal vesicles. II. Molecular weights of soluble proteins

The molecular weights of the soluble proteins from cranial and caudal prostate and seminal vesicle tissues of several species of nonhuman primates were separated by electrophoresis. The tissues of animals belonging to the genus Macaca were found to be similar and are compared to those of other species. The molecular weights of these proteins are discussed with regard to known concentrations of prostate and seminal vesicle proteins.

Amino acid sequence homology between rat prostatic steroid binding protein and rabbit uteroglobin

Using a computer program designed to detect evolutionary relationships between proteins, I find that the polypeptide chain of rabbit uteroglobin has amino acid sequence homology with the C1 and C2 polypeptide chains of rat prostatic steroid binding protein. Using this finding I suggest several interesting approaches for studying the biology of these proteins.

Reduction of prostatic binding protein-messenger ribonucleic acid sequences in rat prostate by castration

Messenger RNA coding for the three subunits of prostatic binding protein was isolated from polysomal RNA of rat ventral prostate by oligo (dT)-cellulose affinity chromatography and purified by repeated sedimentations through sucrose gradients under denaturing conditions. The purified mRNA migrated as a 9S peak in sucrose gradient centrifugation and hybridized with its cDNA within 2 log Rot units. In a cell-free reticulocyte lysate system, the mRNA directed the synthesis of three polypeptides of 12000, 9000, and 8000 daltons. These translation products were identified as the subunits of prostatic binding protein by immunoreaction with antibodies to this protein. Quantitation of prostatic binding protein-mRNA sequences in normal and castrated rats by hybridization with the cDNA probe showed that 3-day castration reduced the prostatic binding protein-mRNA sequences to less than 2% of the normal level. Similar hybridization was performed by using the cDNA to determine the level of prostatic binding protein coding sequences in polysomal poly(A) RNA following castration. The results showed a first-order rate constant of 3.92 X 10-2 h-1 for reduction of prostatic binding protein-mRNA sequences in polysomes. The period of castration required to reduce the level of these sequences to 50% of the normal level was calculated to be 17.6 h.

Androgen transport proteins: physical properties, hormonal regulation, and possible mechanism of TeBG and ABP action

The physical properties and hormonal regulation of testosterone estradiol binding globulin (TeBG) and androgen binding protein (ABP) are reviewed. Brief mention is made of prostatic binding protein. The discussion focuses on the mechanism of action for these proteins in androgen secretion, transport, and absorption and androgen binding models. Speculations are presented for the functional significance of these proteins.

Estramustine binding in rat, baboon and human prostate measured by high pressure liquid chromatography

High pressure liquid chromatography (HPLC) was used to determine 3H-estramustine (estradiol-17 beta 3N-bis-[2-chlorethyl] carbamate), 3H-17 beta-hydroxy-5 alpha-androstan-3-one (3H-dihydrotestosterone or 3H-DHT), 3H-estradiol-17 beta (3H-E2) and 3H-3 beta-hydroxy-5-pregnen-20-one (3H-pregnenolone) binding in 50(2) microliter of cytosol utilizing a column which separates proteins in the molecular weight range of 2,000 to 70,000 daltons. The rat prostate contains a protein in considerable concentration and with the highest affinity for estramustine (375,000 dpm 3H-estramustine per mg. cytosol protein) among the substances tested. Operationally, we have named this protein "estramustine binding protein" (EBP), though it is very likely similar to other previously described prostatic proteins (e.g., alpha-protein, prostatein, prostatic binding protein). The sensitivity of the HPLC method disclosed EBP-like proteins, but in much lesser concentrations, in some of the other tissues tested. The concentration of these proteins in the human and baboon prostates was much lower (average for the baboon cranial lobe 4800 dpm/mg cytosol protein, with a somewhat higher value for the caudal lobe) than that in the rat gland. The amount of the EBP-like protein was higher in prostatic cancer than in that of benign prostatic hypertrophy (BPH) (range 9350--25,900 vs. 2200--18,900 dpm/mg cytosol protein). In the human, the highest value was found in one normal prostate tested (106,000 dpm/mg cytosol protein).