Purification and characterization of androgen binding protein from the rat epididymis

Studies on the role of glycosylation in the origin of the electrophoretic variants for rat corticosteroid-binding globulin

The glycoprotein corticosteroid-binding globulin (CBG) migrates as doublet bands in PAGE and SDS-PAGE, and as numerous bands in isoelectric focusing (IEF). This study deals with the origin of this heterogeneity. Desialation of rat CBG with neuraminidase does not abolish the doublet in either PAGE or SDS-PAGE, indicating that the doublet does not arise as a result of differences in sialic acid residues. Treatment of the separated upper and lower variants of native CBG with N-glycosidase F (PNGase-F) shows a differential pattern of deglycosylation over time indicating either differences in the number, type, or location of sugars attached to each of the variants. Rate of deglycosylation is quicker and more extensive for the upper variant when compared to the lower variant. PNGase-F treatment of 1% SDS-denatured CBG does not abolish the CBG doublet seen in SDS-PAGE, indicating that there is variation in the protein moiety. Sugars could not be detected on PNGase-F treated CBG using either wheat germ aglutinin horse radish peroxidase conjugate, concavilin-A HRP conjugate, or the digoxigenin glycan detection system. While the results clearly show differences in glycosylation between the CBG variants, differences in the protein moiety may also occur to give rise to the heterogeneity seen in CBG. The latter is supported by the fact that desialated CBG migrates as two bands in IEF. Migration in IEF is based solely on charge, and since only sialic acid residues are charged in N-linked glycosylation, any heterogeneity seen for the desialated glycoprotein must reside within the protein moiety itself. The presence of O-glycosylation containing an N-acetylgalactosamine with a beta 1-3 linkage to galactose could not be demonstrated using O-glycosidase. N-terminal blockage could not account for the variation, as both the upper and lower variants were able to be sequenced resulting in identical sequences for the first 13 amino acids. The data presented supports the hypothesis that the differences in the sugar as well as the protein moiety are responsible for the heterogeneity seen for CBG.

Genetic variations in human testosterone-estradiol binding globulin

The human testosterone-estradiol-binding globulin (hTeBG) is a plasma heterogeneous glycoprotein with high affinity for a number of circulating steroid hormones. The heterogeneity originates from differential glycosylation of a common protein precursor. Analysis of desialylated hTeBG by isoelectric focusing (IEF) has revealed that microheterogeneity could be partly attributed to variability in sialic acid content or rearrangement of amino acid composition. We have studied this possibility by the analysis of desialylated serum hTeBG by Western blotting of proteins previously separated on IEF-gels. Two distinct well-defined IEF patterns were identified. The most frequent consisted of two major IEF-bands of equal color intensity. The other pattern consisting of four IEF-bands was present in only 5.55% of the total serum samples analyzed. Family studies showed that these phenotypes were autosomally inherited with a simple Mendelian transmission and allele frequencies had an excellent agreement between the observed and expected phenotypes. Androgen affinity constants and serum concentrations of hTeBG variant were similar to those of normal hTeBG. Molecular analyses of each of the exons of hTeBG gene by denaturing gradient gel electrophoresis revealed the presence of a point mutation in exon 8. The studies presented herein confirm and extend previous reports on the existence of structural variants of hTeBG. In addition, the mutation reported in this study is probably the same as that recently identified within numerous ethnic groups throughout the world, thus further supporting the concept of a two allele gene worldwide concoding hTeBG.

Theobromine toxicity on Sertoli cells and comparison with cocoa extract in male rats

The target cell(s) of theobromine toxicity on rat testes and reproductive toxicity induced by pure theobromine and cocoa extract are evaluated in the present studies. Theobromine (500 mg/kg x 7 days) inhibited body weight gain in treated rats. Decreased cauda epididymal sperm reserve (38%), seminiferous tubule fluid (STF) volume (33%), lactate concentration in STF (22%), inhibition of binding activity of androgen binding protein (ABP, 21%) and reduced ABP content in STF were also observed in theobromine-treated animals. Cocoa extract containing an equivalent amount of theobromine did not produce significant toxicity in treated rats. Theobromine concentrations in serum and testes from pure theobromine-treated rats were 1.8- and 1.6-fold higher, respectively, than that in rats treated with cocoa extract. The results support Sertoli cells as the primary target cells of theobromine toxicity. The lower theobromine concentrations in serum and testes of cocoa extract-treated rats could account for the lower toxicity in these animals.

Structure, function, and regulation of androgen-binding protein/sex hormone-binding globulin

Despite over 20 years of research, the functions of ABP and SHBG remain elusive. The major reason for this lack of knowledge has been the unavailability of natural mutants with clinical defects for study. There is strong evidence that these binding proteins do act to modulate the gene regulatory actions of nuclear sex steroid receptors by controlling the availability of androgens and estrogens. In plasma, SHBG controls the metabolic clearance rate of sex steroids. In addition there is strong evidence that they have a much broader function. The identification of plasma membrane receptors in target tissues and the finding of homologous domains in several developmental proteins support other functions. Moreover, other experiments suggest the proteins may actually be hormones or growth factors. These findings are not compatible with a model that has the proteins only regulating free steroid hormone levels. Obviously, much more experimentation will be necessary to reveal the functions of ABP and SHBG. The recent discoveries have offered several clues to their functions and open new routes for study. These experiments, coupled with newly developed techniques, such as gene knockout by homologous recombination, make one optimistic that the functions of these unique proteins will be deciphered in the near future.

Evidence that human placenta is a site of sex hormone-binding globulin gene expression

The presence of an androgen-binding component in placenta was investigated in vitro using a tissue culture system of human placental explants. Explants of trophoblastic tissue from normal term placentas were kept in culture under appropriate conditions for at least 48 h in a serum-free medium. The existence of an androgen-binding protein was explored by binding assays, immunohistochemistry studies and Northern blot analyses of placental mRNA. Steady-state polyacrylamide gel electrophoresis and Scatchard plot analyses revealed the presence of a high affinity specific binding component for 5 alpha-dihydrotestosterone in cultured placenta. Immunohistochemical studies performed on intact placenta and on Percoll-gradient purified trophoblastic cells demonstrated the presence of specific immunoreactivity in the cytoplasm of syncytial cells. Northern blot analyses of placental mRNA showed a single hybridizable 32P-labeled human sex hormone-binding globulin (SHBG) cDNA band of approx. 1.6 kb which was identical in size to that obtained with liver mRNA. The results strongly suggest the placenta as an origin of SHBG and point out this tissue as an additional site of SHBG synthesis during pregnancy.

Human Sertoli cells in vitro: morphological features and androgen-binding protein secretion

Sertoli cells play a pivotal role in the regulation of spermatogenesis as they provide the anatomical basis of the blood-testis barrier. In the present paper we report some results of our studies on the ultrastructural features, the responsiveness to FSH, and the ability to secrete androgen-binding protein (ABP) of human Sertoli cells in vitro. The nucleus showed the characteristic foldings of the nuclear membrane, scattered chromatin, and a fibrillar nucleolus. In the cytoplasm Charcot-Boettcher crystals were present and active phagocytic activity was documented by the presence of vacuoles containing lipids and cellular debris. Human Sertoli cells in culture responded to FSH with a maximal rise in cAMP that was approx. 3-fold. This response to FSH is comparable to that reported for the adult rat but lower than that of the immature rat, and suggests that human as well as rat Sertoli cells could have a reduced response to FSH since sexual maturation was achieved. As no evidence has been reported on ABP secretion by human Sertoli cells in culture we evaluated the concentration of this protein in the Sertoli cell spent media. Human Sertoli cells in culture produced ABP and the response to FSH was dose-related. The Kd value of human ABP (hABP) was approx. 7.5 nM, being slightly higher than that of the rat ABP and an order of magnitude different from that of sex hormone-binding globulin (SHBG) present in human plasma. We also measured the association and dissociation rates of dihydrotestosterone-hABP complexes and the Kd/Ka ratio was very close to the value of Kd of the Scatchard analysis. The differences between hABP and SHBG may open the way to the selective measurement of ABP in many conditions of male infertility.

Lead acetate does not impair secretion of Sertoli cell function marker proteins in the adult Sprague Dawley rat

This study was conducted to determine the effects of lead on Sertoli cell function. Androgen binding protein and inhibin in testicular fluids and classical parameters of the hypothalamic-pituitary-gonadal axis were measured in adult male rats. For 10 wk, the rats were given water that contained 0.05%, 0.1%, 0.5%, and 1% lead acetate. Serum follicle-stimulating hormone, luteinizing hormone, and testosterone levels in all animals that ingested lead were normal at the middle and end of the experiment, as was the pituitary content of follicle-stimulating hormone and luteinizing hormone. Histologic examination revealed no disruption of spermatogenesis. Distribution of androgen binding protein in serum, seminiferous tubular fluid, and interstitial fluid was normal, as was the concentration of inhibin in interstitial fluid and seminiferous tubular fluid. However, a significant increase in epididymal androgen binding protein level and a decrease in seminal vesicle weight were observed in rats that ingested water containing 1% lead acetate. These results suggest that the effect of lead on spermatogenesis is not marked in adult Sprague Dawley rats, nor does Sertoli cell function appear to be affected adversely. Lead has been reported to alter in vitro metabolic function of Sertoli cells obtained from 16- to 21-d-old Sprague Dawley rats, and the Sertoli cells of juvenile animals may be more susceptible to lead than those of adult animals. The significant decrease in seminal vesicle weight and the abnormal epididymal androgen binding protein content indicate that lead could affect the male reproductive function in Sprague Dawley rats via its action on male accessory organs.

Partial purification of androgen binding protein from bull epididymis

An androgen binding protein (ABP), with an equilibrium dissociation constant of 4.2 nM and a molecular weight of about 100 kDa, has been purified from bull epididymal extracts using a four-step procedure. These preliminary results underline the main difficulties encountered in the purification of this protein present at a very low concentration (i.e. 50-fold less than in rat or rabbit epididymides). Ammonium sulfate precipitation is not a suitable step due to the formation, in presence of salt, of insoluble material leading to a loss of ABP. Lipids, particularly phospholipids, might be implicated in this phenomenon. Several steps, including anion exchange in batch followed by concentration, affinity chromatography and HPLC gel filtration allowed us to obtain a 7667-fold purified protein with a 9% yield.

Prolonged suppression of rat testis function by a depot formulation of Zoladex, a GnRH agonist

A sustained-release formulation of a potent gonadotropin-releasing hormone (GnRH) agonist, Zoladex (D-Ser(But),6 Aza Gly10-GnRH; ICI 118,630; goserelin), was administered subcutaneously (3.6 mg/depot) to male rats once every 28 days for 2-24 wk to determine the extent to which pituitary-testis function could be suppressed and whether suppression was maintained throughout the period of treatment. Administration of Zoladex resulted in sustained decreases in weight of the testis, epididymis, seminal vesicles and prostate gland. The decreases were apparent within 2 wk of initiating treatment. Patchy degeneration of the seminiferous tubules and atrophy of the Leydig cells were observed, but did not progress beyond the degree observed after 1 month of treatment. Serum and testis testosterone were markedly depressed after 2 wk of treatment, as was testis [125I]hCG binding. Serum gonadotropins were also reduced by treatment. Serum androgen binding protein (ABP) was elevated, testis ABP content remained unchanged, and epididymal ABP content was reduced. The changes are consistent with the hypothesis that this compound affects both the anterior pituitary gland and the testis. These findings indicate that depot delivery systems are a convenient way to administer GnRH analogs for sustained treatment schedules.

The action of calcitonin on the TM4 Sertoli cell line and on rat Sertoli cell-enriched cultures

The effects of synthetic salmon calcitonin on primary Sertoli cell-enriched cultures and on an established cell line (TM4 cells, derived from immature mouse Sertoli cells) were studied. Synthetic salmon calcitonin stimulated the conversion of [3H]adenine to [3H]cyclic AMP in both cell systems. In addition, this peptide stimulated the secretion of rABP in primary Sertoli cell-enriched cultures prepared from rat testis. Calcitonin also increased the total concentration of both androgen and estrogen receptors in TM4 cells. Because cAMP analogs decreased androgen and estrogen receptor concentrations, the effect of calcitonin on sex steroid receptors may not be mediated by its effect on cyclic AMP in these cells. The possibility that the action of synthetic salmon calcitonin on the receptors might be mediated by a change in cellular Ca2+ was investigated. Lowering extracellular Ca2+ concentrations from 1.5 mM to less than 0.01 mM markedly reduced the concentration of androgen and estrogen receptors; restoration of Ca2+ to 1.5 mM returned receptor levels to normal. When the receptor concentrations were decreased by lowering extracellular Ca2+ concentrations to 0.5 mM, treatment with the calcium ionophore, A23187, restored receptor levels to normal. Although the calcium channel blocker, verapamil, decreased receptor levels, calcitonin partially counteracted its effect. Trifluoperazine, an inhibitor of calmodulin, also diminished androgen and estrogen receptor, levels in the cytosol of TM4 cells. It was concluded that calcitonin stimulates the formation of cyclic AMP and the secretion of rABP by Sertoli cells. This peptide also increases the concentration of androgen and estrogen receptors, possibly by a mechanism that is, in part, Ca2+ -mediated. These results, along with those on Leydig cells, suggest that calcitonin could be a regulator of testicular function.

The androgen-binding protein gene is expressed in CD1 mouse testis

Androgen-binding protein (ABP) is a testicular Sertoli cell secretory protein that acts as a carrier of androgen in the male reproductive tract. ABP has been characterized from a wide range of animal species, including man, rabbit and rat. However, it has been widely accepted that mice do not produce testicular ABP. We have used immunological and molecular biological techniques to demonstrate that the ABP gene is expressed in the CD1 mouse. Steroid-binding, radioimmunoassay and immunocytochemical studies demonstrated that ABP is present in mouse testis and epididymis, but at 1/50 to 1/25 the level of rat epididymis. A 1.7 kilobase mRNA, homologous with rat ABP cDNA, was identified in mouse testis and Sertoli cells by Northern blot hybridization, but at a much lower level than in the rat. An ABP cDNA was isolated from a mouse testis cDNA library and encoded a protein (403 residues) with 89% of the amino acid residues identical to rat ABP, including a signal peptide. Our results indicate that ABP is expressed in the mouse and past failures to detect androgen-binding activity were due to the low level of ABP protein.

Localization of immunoreactive testibumin in the testis and epididymis of adult rats

Testibumin is a glycoprotein previously isolated from the spent media of primary Sertoli cell-enriched cultures prepared from 20-day-old rats. Immunoassayable testibumin is found in the highest concentrations in testis, epididymis and fluids of the male reproductive tract in adult rats. In the present study, light microscopy was used to show that immunostainable testibumin in paraffin sections of rat testis was localized along the base of the seminiferous epithelium and in finger-like projections from the base of the epithelium, corresponding to the position of the Sertoli cells. The immunostaining of Sertoli cells was shown to be specific since either purified testibumin or crude Sertoli cell-enriched culture medium could compete with antibody for binding sites in tissue sections. The observations using light microscopy were confirmed when Sertoli cells were examined by electron microscopy using a pre-embedding immunostaining technique. The epithelium of the epididymis also contained immunoreactive testibumin which was localized in the caput, corpus and cauda. Immunostainable testibumin was also localized in the corpora lutea of the rat ovary and in the epithelium of the uterine endometrium. These observations are consistent with previous reports that immunoreactive testibumin is present in these organs as demonstrated by radio-immunoassays. We conclude that (i) the immunolocalization of testibumin in Sertoli cells adds to a growing list of observations suggesting that it is made in this cell type; (ii) the other sites of testibumin synthesis in the male are uncertain but the ovary and uterus are possible sites in the female; (iii) electron microscopy following pre-embedding immunostaining and epitope selection can be used as an adjunct to conventional immunocytochemistry to localize proteins in Sertoli cells.

Structure of the rat androgen-binding protein gene

To study hormonal regulation of rat androgen-binding protein (ABP) we have cloned and sequenced the gene. A 5.3-kbp genomic DNA fragment was found to contain the entire coding region of the gene, which consists of 8 exons. The major site of transcription initiation in the testis was localized by primer extension and is located 36 bases upstream from the site of translation initiation. The gene does not contain a "TATA box" immediately upstream from the major start site. The sequence TACCTA occurs at residue -23, which is a functional TATA-like element in the SV40 major late gene. A sequence related to the cAMP response element is at residue -126 bp. Southern blot analysis of rat genomic DNA indicated a single gene for ABP in the rat. The existence of one gene supports the idea that sex steroid-binding protein (SBP) produced by fetal rat liver is coded by the same gene. The possibility that an alternate promoter region is active in the fetal liver is discussed.

The extracellular sex steroid-binding proteins of testis and liver. Structure-function studies

Though the existence of extracellular sex steroid-binding proteins has been known for a number of years, we are still only on the threshold of understanding their biological role. Through efforts such as those described above, we are beginning to examine the structure of these macromolecules and correlating them with present known functions. As our understanding of the function of these proteins evolves, we will be further able to ascribe structural domains.

Androgen binding protein in serum, testis and epididymis following treatment with the Leydig cell cytotoxic agent, ethylene dimethanesulphonate

Androgen binding protein (ABP) was measured in the serum, testes and epididymides of adult male rats after treatment with ethylene dimethanesulphonate (EDS), which has direct cytotoxic effects on Leydig cells and secondarily affects sperm production. Serum ABP increased to a maximum 7 days after treatment and remained elevated for most of the 63 days of observation. The ABP content of both the epididymides and testes declined and were low between 14 days and 21 days following treatment. By contrast, the concentration of ABP in these tissues was maintained after EDS treatment and was sometimes elevated. This divergence between ABP content and concentration was due to atrophy of the testes and epididymides after the decline in androgen secretion. The changes in serum and tissue ABP levels after EDS occurred earlier than those observed in adult hypophysectomized animals, possibly due to local paracrine influences that are lost secondarily to destruction of the Leydig cells. Testicular testosterone did not parallel ABP content as it fell dramatically 2 days after EDS and remained low for about 21 days before returning to near control values after 63 days. Testicular and epididymal sperm heads decreased in number after EDS, but were not clearly associated with the changes in ABP. The results confirm that androgens are important for the production of ABP and for the partitioning of this protein between the blood and the lumen of the reproductive tract.

Corticosteroid binding globulin, testosterone-estradiol binding globulin, and androgen binding protein belong to protein families distinct from steroid receptors

The cDNA nucleotide sequences and the deduced amino acid sequences of human corticosteroid binding globulin (hCBG), human testosterone-estradiol binding globulin (hTeBG), and rat androgen binding protein (rABP) were determined. Studies of the steroid binding sites suggest they are toward the carboxy-terminus in hTeBG and rABP and more central in hCBG. hCBG has remarkable sequence homology with members of a superfamily whose functions have diverged; these include thyroxine-binding protein, serine protease inhibitors, egg white proteins, and angiotensinogen. hTeBG and rABP have a 68% amino acid sequence identity. Hybridization studies suggest that hTeBG is probably even more closely related, if not identical, to hABP. The carboxy-terminal sequences of hTeBG and rABP are also similar to that of protein S, a vitamin-K-dependent clotting factor. There were no nucleotide or amino acid sequence homologies between hCBG, hTeBG, or rABP and other steroid binding proteins such as steroid receptors, albumin, alpha-fetoprotein, and vitamin D binding protein. We conclude that the "extracellular steroid binding proteins" and steroid receptors do not appear to have descended from a common ancestor.

Effect of sexual maturity on testicular injury subsequent to procarbazine administration in rats

The present study examined the effect of age on various aspects of Leydig cell and Sertoli cell function in Sprague-Dawley rats administered procarbazine. Procarbazine was administered intraperitoneally to Sprague-Dawley rats aged 14, 24, and 60 days in 3 weekly injections of 200 mg/kg. Animals were sacrificed 1 week after the last injection. Severe impairment of spermatogenesis was evident in all animals. Sertoli cell function, as assessed by total testicular ABP content, was not significantly different between procarbazine-treated animals and controls in any age group. On the other hand, procarbazine administration resulted in a 60% reduction in total intratesticular testosterone content in the 14-day-old rats but not in the 24- or 60-day-old animals. Serum testosterone was significantly reduced by 50% in the group of 14-day-old animals but not in the other age groups. Serum LH values were not significantly changed from control levels in any age group. Testicular content of Fe, Zn, Mn, and Cn were unaltered by procarbazine administration in any age group. Since serum LH and testicular cation content were not affected by procarbazine treatment, the significant decreases in serum and testicular testosterone in 14-day-old animals after procarbazine administration may indicate a direct age-dependent effect of procarbazine on Leydig cell function.

A minicolumn apparatus for androgen-binding protein measurement

An easy, rapid, and sensitive assay that permits measurements of androgen-binding protein (ABP) in tissue as well as in spent media from Sertoli cells is described; this method involves the specific binding of labeled dihydrotestosterone (DHT) to ABP. The apparatus holds 36 minicolumns loaded with a DEAE Bio-Gel matrix. A peristaltic pump is used for the free fraction elution, taking into account the extremely rapid rate of dissociation of the ABP-DHT complexes. This technique, which allows Scatchard plot analysis, has been used to measure the rates of association (5.15 X 10(5)M-1 S-1 and dissociation (21.32 X 10(-4) S-1; t 1/2 = 5.5 min): the ratio of these rate constants is in perfect agreement with equilibrium dissociation constants determined by Scatchard plot analysis (KD = 4-4.5 nM). The intraassay and interassay coefficients of variation are 5 and 8%, respectively. A good correlation (r = 0.98) is obtained with the standard method of steady-state polyacrylamide gel electrophoresis below a value of 250 micrograms cytosolic proteins/gel. This apparatus, which allows either the measurement of ABP in 12 samples (in triplicates) at a saturating concentration or the analysis of two Scatchard plots (each of 6 points), is also very useful for a rapid localization of ABP during chromatographic purification.

Evidence suggesting that germ cells influence the bidirectional secretion of androgen binding protein by the seminiferous epithelium demonstrated by selective impairment of spermatogenesis with busulphan

Androgen binding protein (ABP) was measured in the serum, testes and epididymides of adult rats up to 105 days after the induction of reversible impairment of spermatogenesis by a single injection of busulphan. This treatment decreased testicular and epididymal weights within 7-21 days after treatment, reaching a minimum at 63 days with partial recovery by 105 days. The testicular and epididymal content of sperm was unchanged up to 42 days after busulphan administration, was reduced considerably at 63 days and thereafter increased towards control values. The serum and testicular concentrations of testosterone were normal at all times after treatment, even though serum LH levels were increased at 42 and 63 days. Serum levels of FSH were also increased at 43 and 63 days after treatment. A biphasic pattern in the serum levels of ABP was observed. Concentrations were low up to 43 days post treatment when only the early germ cell types were depleted from the seminiferous epithelium and when the testicular and epididymal contents of ABP were normal. Serum levels of ABP increased as the more mature germ cells were depleted in numbers and the testicular and epididymal contents of ABP declined. It is concluded that bidirectional secretion of ABP into the interstitium (serum) and into the seminiferous tubular lumen by Sertoli cells is influenced considerably by the population of germ cells that are present in the seminiferous epithelium.

Rat androgen-binding protein: evidence for identical subunits and amino acid sequence homology with human sex hormone-binding globulin

The cDNA for rat androgen-binding protein (ABP) was previously isolated from a bacteriophage lambda gt11 rat testis cDNA library and its identity was confirmed by epitope selection. Hybrid-arrested translation studies have now demonstrated the identity of the isolates. The nucleotide sequence of a near full-length cDNA encodes a 403-amino acid precursor (Mr = 44,539), which agrees in size with the cell-free translation product (Mr = 45,000) of ABP mRNA. Putative sites of N-glycosylation and signal peptide cleavage were identified. Comparison of the predicted amino acid sequence of rat ABP with the amino-terminal amino acid sequence of human sex hormone-binding globulin revealed that 17 of 25 residues are identical. On the basis of the predicted amino acid sequence the molecular weight of the primary translation product, lacking the signal peptide, was 41,183. Hybridization analyses indicated that the two subunits of ABP are coded for by a single gene and a single mRNA species. Our results suggest that ABP consists of two subunits with identical primary sequences and that differences in post-translational processing result in the production of 47,000 and 41,000 molecular weight monomers.

Purification of androgen-binding protein from rat testis using high-performance liquid chromatography and physicochemical properties of the iodinated molecule

The androgen-binding protein (ABP) has been purified 87,500-fold from rat testis using 4 steps of HPLC, with a yield of 14%. The molecule was 99% pure with a specific activity estimated to 16,600 pmol/mg protein. The iodinated molecule was eluted in 2 peaks in Sephacryl S300 gel filtration with a molecular mass estimated to be 92,600 +/- 3300 and 50,300 +/- 4000 Da. The column isoelectrofocusing of 125I-ABP demonstrated 3 isoproteins isoelectric at pH 4.7, 4.9 and 5.3 and the sedimentation coefficient was estimated to be 4.7 S in sucrose gradient ultracentrifugation. The 125I-ABP had similar physiochemical properties to the non-labelled ABP of epididymis.

Rat testicular testibumin is a protein responsive to follicle stimulating hormone and testosterone that shares immunodeterminants with albumin

During a search for hormonally responsive products in media from Sertoli cell enriched cultures, a major follicle stimulating hormone responsive and testosterone-responsive protein was identified and designated CMB-1. The results of the present study indicate that this protein is related immunologically to rat albumin and rat alpha-fetoprotein (AFP) and is concentrated in the testis of the adult rat. CMB-1 was therefore termed testibumin. Testibumin was purified from Sertoli cell enriched cultures to apparent homogeneity by sequential high-performance liquid chromatography on anion-exchange, chromatofocusing, gel permeation, and hydroxylapatite columns. The purified protein consists of two concanavalin A (Con A) reactive forms: one which does not interact with Con A and the other which binds to this lectin and is eluted with methyl alpha-mannoside. Testibumin is a monomer with an apparent molecular weight of 69,000 and a pI ranging between 4.5 and 4.85. The heterogeneity of this protein was further demonstrated by crossed-immunoelectrophoresis and two-dimensional gel electrophoresis. A monospecific antiserum and highly purified testibumin were used to develop a specific radioimmunoassay which permitted studies of the hormonal responsiveness of Sertoli cell enriched culture and of the content of testibumin in the reproductive tract fluids in vivo. Even though testibumin was found in serum of both sexes, it was highly concentrated in the testicular and epididymal compartments in adult rats. This protein was compared to rat serum albumin and rat AFP immunologically. With the use of immunoblots, antiserum developed against testibumin showed partial cross-reactivity with albumin and AFP when these latter proteins were denatured and were present in amounts several orders of magnitude greater than testibumin. The extent of this cross-reactivity was then examined by comparing the ability of native and S-carboxymethylated albumin to compete with 125I-testibumin for binding to a monospecific testibumin antiserum. It was shown that the unfolded derivative of albumin showed partial cross-reactivity with testibumin. We conclude that testibumin is immunologically related to albumin and AFP as these latter proteins are related to one another and that testibumin is possibly the homologue of albumin in the seminiferous tubular compartment.

The effects of the indazole carboxylic acid derivative, tolnidamine, on testicular function: I. Early changes in androgen binding protein secretion in the rat

The indazole carboxylic acid derivative, tolnidamine, has marked antispermatogenic activity in several animal species. In this study, we assessed the effect of tolnidamine on rat Sertoli cell function both in vivo and in vitro, using androgen binding protein (rABP) as a marker. Groups of six male rats were killed 2, 4, 8, 16, 32, 64 hours and 5, 8, and 12 days following tolnidamine administration (250 mg/kg by oral gavage). There was a progressive reduction in both testicular and epididymal weights. Serum FSH levels did not change and LH showed a transient increase between 64 hours and 8 days. Except for an initial increase at 2 hours, there were no changes in serum testosterone. Epididymal rABP concentration and content declined as early as 8 hours, with the lowest values occurring at 5 and 12 days. By 16 hours, there was an increase in testicular rABP, which was also evident at 8 days and 12 days. Within 16 hours after tolnidamine, there was a rise in serum rABP, which persisted until the end of the experiment. When another indazole carboxylic acid derivative, lonidamine, was administered (250 mg/kg), similar changes were evident in epididymal and serum rABP at 32 hours, but the rapid decrease in testicular rABP suggested a different mechanism of action. In another experiment, single oral doses of tolnidamine (50, 100, 250, and 500 mg/kg) were administered to other groups of rats and the animals were killed after 24 hours and 5 days. With increasing doses of tolnidamine, there was a reduction in epididymal rABP concomitant with an increase in testis and serum rABP levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of testosterone-oestradiol-binding globulins from mammalian sera by anion-exchange high performance liquid chromatography

Testosterone-oestradiol-binding globulin (TeBG) has been isolated from serum or plasma of several species using procedures that yielded highly purified protein, but which required multiple and tedious chromatographic steps. In this report we describe a procedure for the isolation of TeBG which involves two chromatographic steps: androgen affinity chromatography followed by anion-exchange high performance liquid chromatography (anion-exchange HPLC). The purity of the final product was confirmed by silver staining following fractionation on sodium dodecyl sulphate-containing polyacrylamide gels. The size heterogeneity and specific binding activity of TeBGs purified from human, rabbit, or bull serum (or plasma) by this technique was indistinguishable from preparations obtained by conventional chromatography. The present technique shortened the entire purification procedure to about 5 working days and yielded milligram quantities of highly purified protein. Bases on our experience with serum or plasma from the human, rabbit, and bull, this approach should be suitable for isolation of TeBG from a wide range of species.

Rapid method for quantitation of androgen binding protein in Sertoli cell cultures and its use for measurement of binding kinetics

The accurate measurement of the kinetics of binding of 5 alpha-dihydrotestosterone to the Sertoli cell specific protein, androgen binding protein (ABP), has been frustrated by the extremely rapid rate of dissociation of the ABP-dihydrotestosterone complex. We describe a rapid and highly sensitive assay suitable for ABP quantitation which utilizes DEAE Bio-Gel and [3H]dihydrotestosterone. The assay has been used to accurately measure the rate of dissociation (8.25 X 10(-4) s-1, t1/2 14 min) and the rate of association (2.04 X 10(5) M s-1) of the binding of [3H]dihydrotestosterone to rat ABP. The ratio of these rate constants is in perfect agreement with the equilibrium dissociation constant determined by Scatchard analysis (4.0 nM). This multipoint assay is extremely rapid such that binding can be measured at equilibrium, it has high precision (coefficient of variation 3%), and is particularly useful at low protein concentrations (50 ng/ml); furthermore, the assay background of nonspecific 3H-binding is extremely low (0.2%). Since at such low protein concentrations a 10 point Scatchard analysis can be performed on 1 ml culture medium containing as little as 3 fmol ABP, the assay is suitable for monitoring changes in ABP secretion resulting from manipulations of cells in culture. The assay which utilizes DEAE Bio-Gel A is compared to five alternative methods: the standard method of steady state gel electrophoresis, Dextran-coated charcoal assay, hydroxylapatite assay, DEAE filter assay, and radioimmunoassay. The DEAE Bio-Gel assay has advantages over all of these alternative methods. In summary, this new assay is particularly useful for monitoring temporal changes in the secretion of ABP, and the method is equally effective in quantitating ABP in rat, rabbit and hamster Sertoli cell cultures.

The role of the carbohydrate moiety on the size heterogeneity and immunologic determinants of human testosterone-estradiol-binding globulin

Human testosterone-estradiol-binding globulin (hTeBG) has been purified to apparent homogeneity by several laboratories using procedures which, in most instances, were labor intensive. In this report, hTeBG was purified from pregnancy serum by a newly developed two step procedure involving sequential affinity chromatography and ion-exchange high performance liquid chromatography (ion-exchange HPLC). The purity of the final product was confirmed by silver stained SDS-polyacrylamide gel and reverse phase HPLC monitored at 206 nm. hTeBG purified by ion-exchange-HPLC maintained binding activity by Dextran coated charcoal (DCC) assay and size heterogeneity on SDS-polyacrylamide gels which were indistinguishable from those of the proteins purified by conventional chromatography. Removal of the carbohydrate moiety from the molecule by both enzymatic and chemical treatment reduced the apparent molecular size and eliminated lectin binding of hTeBG subunits. Deglycosylation did not, however, abolish or alter the distribution of the protomeric forms of this subunit. We conclude that hTeBG is a dimer whose monomer exhibits two protomeric forms which is not a result of carbohydrate heterogeneity. In addition, disialylated and deglycosylated hTeBG exhibited antigenic determinants identical to the native protein.

Demonstration of heavy and light protomers of human testosterone-estradiol-binding globulin

Human testosterone-estradiol-binding globulin (hTeBG) was purified from pregnancy serum by sequential ammonium sulfate precipitation, affinity chromatography, and hydroxylapatite chromatography. An overall purification of 2800-fold was achieved with a 27% total yield. Apparent homogeneity of the final product was shown by polyacrylamide gel electrophoresis with or without sodium dodecyl sulfate (SDS). The equilibrium dissociation constant (Kd) at 4 degrees C for 5 alpha-dihydrotestosterone (DHT) was estimated to be 1.94 +/- 0.95 X 10(-9) M. Analysis of the purified protein revealed microheterogeneity with regard to size on polyacrylamide gel in the presence of SDS and to charge on isoelectric focusing gels. The apparent molecular weight of native hTeBG determined by gradient gel electrophoresis was 115,000. SDS-polyacrylamide gel electrophoresis indicated that hTeBG is comprised of two molecular weight components of 53,000 and 46,000, which are designated as heavy (hTeBGH) and light (hTeBGL) protomers, respectively. Photolysis of purified hTeBG with [1,2-3H]17 beta-hydroxy-4,6-androstadien-3-one [( 3H]delta 6-testosterone) resulted in specific labeling of its binding sites. Analysis of photolabeled products by SDS-polyacrylamide gel electrophoresis revealed two radioactive products with electrophoretic mobilities identical to those of the hTeBGH and hTeBGL. The ratio of hTeBGH to hTeBGL was about 10:1. The H and the L protomers were separated and examined by peptide mapping using protease V8 and chymotrypsin. Comparison of the fragmentation patterns produced by these proteases revealed that hTeBGH and hTeBGL components were nearly identical. Removal of sialic acid or carbohydrate residues from hTeBG did not affect the presence of two molecular components. Isoelectric focusing of native hTeBG demonstrated three isoelectric variants with pIs at 4.75, 4.85 and 4.90. After treatment with neuraminidase and other glycosidases, only two isoelectric species were observed with more alkaline pIs. Although purified hTeBG appeared heterogeneous with regard to size and charge, it was remarkably homogeneous in its ability to absorb to Concanavalin A-Sepharose. We conclude that hTeBg, like the androgen binding proteins of the rabbit and rat, is a dimer whose monomer exhibits two protomeric forms.

Sertoli cells of adult rats in vitro. III. Purification of androgen-binding protein from the culture medium

A method giving a high yield for the isolation and purification of the androgen-binding protein (ABP) from the nutritional medium of cultured cells from adult rats is described.

Sertoli cells secrete both testis-specific and serum proteins

The secretions of the Sertoli cell were examined with two polyvalent antisera--one prepared against proteins in rat serum and the other against testis-specific proteins in rete testis fluid. These antisera detected 12 serum and 9 testis-specific proteins in rete testis fluid. To determine the origin of these proteins, primary cultures enriched in Sertoli cells were incubated with [35S]methionine, and the radiolabeled proteins in the medium were immunoprecipitated. Gel electrophoresis of the two immunoprecipitates resolved eight serum and nine testis-specific proteins. These two sets of proteins were specifically bound to their respective antiserum and were immunologically distinct. Medium from Sertoli cell cultures contained 10 times more of the testis-specific proteins than did cultures enriched for testicular myoid or interstitial cells. The concentration of the serum proteins in Sertoli cell medium was 5 and 10 times greater, respectively, than in myoid or interstitial cell preparations. The proteins from Sertoli cells were next characterized on two-dimensional gels. Seven of the proteins recognized by antiserum against serum proteins had identical molecular weights and isoelectric points as serum proteins. Three of these proteins were ceruloplasmin, transferrin, and glycoprotein 2. In addition to the proteins immunoprecipitated by the two antisera, more than 60 other proteins were detected on two-dimensional gels of the total secretory proteins. We conclude that the Sertoli cell secretes many proteins, some of which are specific to the testis and others of which are similar to serum proteins.

Heterogeneity in end-terminal sugars of rabbit and rat androgen binding protein (ABP)

The interaction between rabbit and rat androgen binding protein (ABP) and rabbit serum testosterone binding globulin (TeBG) with concanavalin A (Con A) was studied using affinity chromatography on Con A-Sepharose 4 B columns. When partly purified rat ABP, equilibrated with [3H]5 alpha-dihydrotesterone [3H]DHT was applied to Con A-Sepharose columns, approximately 50% of the ABP was retained by the column, whereas the remaining was eluted with the break-through protein fraction. A similar picture was found using partly purified rabbit ABP, or crude rabbit rete testis fluid. These studies indicate that both rat and rabbit ABP are glycoproteins, showing heterogeneity in their end-terminal sugars. When partly purified rabbit TeBG was examined by Con A-Sepharose affinity chromatography, the TeBG was completely retained by the column. The different elution patterns between rabbit ABP and rabbit TeBG indicate that these proteins, although showing identical physico-chemical and immunological properties (Weddington et al. 1975a,b), possess differences in their carbohydrate content.