Thomas A. Bicsak

Chemical and biological characterization of the inhibin family of protein hormones.

Publisher Summary This chapter discusses the chemical and biological characterization of the inhibin family of protein hormones, which is a family of peptides isolated from the follicular fluid or rete testis fluid on the basis of their ability to inhibit the secretion of the follicle-stimulating hormone (FSH) by cultured rat anterior pituitary cells. It also reviews the possible roles of inhibin and fibre-reinforced plastic (FRP)/activin in placenta, brain, and bone marrow. Inhibin-related dimers are broadly distributed anatomically and have powerful activities in several biological systems where inhibin and FRP/activin often exhibit opposite effects. While the physiologic roles of inhibin to regulate FSH secretion in the female rat and immature male rat are strongly supported, the significance of these hormones within the gonad, brain, placenta, and bone marrow have yet to be placed in in vivo context. Although the panoply of functions of inhibin and FRP/activin are certainly incompletely understood at this time, this family has already demonstrated a powerful mechanism for the generation of signal diversity whereby differential subunit association can result in the generation of dimers with opposing biological actions in multiple tissues.

Hormonal regulation of inhibin production by cultured Sertoli cells

The hormonal regulation of inhibin production by cultured rat Sertoli cells was examined using a specific radioimmunoassay (RIA) which detects the N-terminal portion of the porcine inhibin alpha chain. FSH, but not hCG or prolactin caused a dose-dependent increase in inhibin production (EC50 for FSH = 2.4 ng/ml); both secreted and intracellular levels of inhibin were increased, but the secreted form represented one-half to two-thirds of the total. The FSH-stimulated production of inhibin was augmented by addition of a phosphodiesterase inhibitor, and could be mimicked by cholera toxin, forskolin, or dibutyryl cAMP, all of which are known to increase intracellular cAMP levels. Inclusion of either dihydrotestosterone or estradiol in the cultures had no effect on inhibin production, both in the presence and absence of FSH. Examination of the conditioned media from forskolin-treated Sertoli cells by gel filtration chromatography revealed a single peak of bioactive and immunoreactive inhibin, at a molecular weight of approximately 32,000, similar to that observed for the porcine and bovine follicular fluid inhibins. Thus, FSH activated the cAMP pathway to stimulate Sertoli cell production of inhibin which in turn suppresses pituitary FSH release to form a closed-loop feedback system.

Granulosa cells as hormone targets : the role of biologically active follicle-stimulating hormone in reproduction

Publisher Summary This chapter describes that with recent advances in cellular and molecular biology, significant progress has been made to elucidate the effect of diverse hormones at the ovarian granulosa cells. Follicle-stimulating hormone (FSH) is the primary regulator of granulosa cell differentiation. The mechanisms by which FSH induces the expression of multiple genes associated with feedback actions, ovulation, steroidogenesis, and other differentiated functions are studied. The chapter highlights the reception, action, and local synthesis of various growth factors and further explains the paracrine and autocrine roles of these growth factors in the modulation of FSH actions at the granulosa cells. The granulosa cell aromatase bioassay (GAB) allows measurement of serum levels of bioactive FSH in diverse species. The characterization of bioactive FSH molecules secreted by eukaryotic cell lines transfected with human FSH genes provides clinically useful reagents for stimulating follicle maturation and spermatogenesis.

Insulin-like growth factor binding protein measurement: Sodium dodecyl sulfate-stable complexes with insulin-like growth factor in serum prevent accurate assessment of total binding protein content by ligand blotting

The possibility that sodium dodecyl sulfate (SDS)-stable complexes of insulin-like growth factor I (IGF-I) and its binding proteins (IGF-BP) exist in rat serum has been examined by using SDS-polyacrylamide gel electrophoresis (PAGE) followed by both [125I]IGF-I ligand blotting and immunoblotting with antisera directed against either IGF-BP3 or IGF-I. While ligand blotting of rat serum only revealed free IGF-BP subunits (Mr approximately 50, 35, and 30 kDa), immunoblotting with either the IGF-BP3 antiserum or IGF-I antiserum revealed major immunoreactive bands with higher molecular weights (greater than 110, approximately 100, and approximately 84 kDa). The IGF-BP3 antiserum also stained the 50-kDa form of the serum IGF-BP. Specifically stained protein bands were identified by comparison with control immunoblots incubated with normal rabbit serum. Treating the serum with 0.1 N HCl prior to electrophoresis reduced the amount of high molecular weight IGF-BP3 immunoreactive species, with a concomitant increase in the amount of the 50-kDa form. A similar result was obtained if the samples were boiled prior to electrophoresis. These data indicate that not all IGF-BP/IGF complexes may dissociate under normal SDS-PAGE conditions. Therefore, data obtained by using ligand blotting alone may underestimate the amount of total IGF-BP present, especially if the mixture being analyzed also contains large amounts of IGF.

Purification of nonspecific protease-free collagenase from clostridium histolyticum

The collagenase (EC 3.4.24.3) produced by the bacterium Clostridium histolyticum has been purified free from nonspecific protease contaminants by a two-step procedure. The crude culture medium is chromatographed over heparin-Sepharose and Sephacryl S-200, and the resulting preparation has no activity versus noncollagenous proteins or N alpha-benzoyl-L-arginine ethyl ester, yet cleaves native thermally reconstituted collagen fibrils quite efficiently (specific activity, 3000 units/mg). The purification described may be useful for those investigators requiring substantially purified collagenase for applications such as cell culture or collagen quantitation in protein mixtures.

Neuroendocrine regulation of oocyte tissue plasminogen activator.

Publisher Summary This chapter discusses the characterization of oocyte tissue-type plasminogen activator (tPA) activity under a number of physiological and possibly pathological conditions. In combination with the fibrin autograph, it provides a complete analysis of the PA activity in oocytes or in any other system that contains a PA. Even samples that contain both urokinase (uPA) and tPA can be quantitated using this method, although the total PA activity should be expressed in units of uPA activity. Because the extreme sensitivity of the two-step enzymatic cascade allows the present chromogenic substrate assay to determine tPA activity in a small number of oocytes, this assay should provide the unique opportunity to study the neuroendocrine regulation of oocyte functions. Future quantitative analysis of secreted tPA from fertilized oocytes or early embryos may also serve as the basis for noninvasive monitoring of the well-being of these cells.

Rat granulosa cells produce a novel trypsin-like protease in response to gonadotropin treatment

Rat ovaries produce a novel ovarian trypsin-like protease that is regulated during follicular development. The protease extracted from the ovaries of immature gonadotropin-treated female rats was unstable to denaturation, but was recoverable after non-denaturing electrophoresis. The activity was inhibited by synthetic serine protease inhibitors but not by aprotinin or soybean trypsin inhibitor, thus distinguishing the enzyme from pancreatic trypsin. Treatment with pregnant mares serum gonadotropin (PMSG) significantly increased the levels of enzyme in the ovarian granulosa cells (Control, 0.0027 units/10(6) cells; PMSG-treated, 0.0062 units/10(6) cells) which was also secreted by these cells. The novel enzyme described here may be important for matrix remodelling during follicular growth.

Chemical and kinetic characterization of tadpole back skin collagenase

The purified collagenase from tadpole (Rana catesbiana) back skin was studied with respect to its activation energy using soluble and fibrillar type I collagen, as well as a synthetic peptide substrate, DNP-Pro-Gln-Gly-Ile-Ala-Gly-Gln-D-Arg. The activation energy appeared to be independent of the nature of the substrate, ranging between 28 and 35 kcal/mol. The peptide was cleaved at the Gly-Ile bond and proved to be a poor substrate (kcat/Km, 1.21 h-1 microM-1) when compared with native type I collagen in solution (kcat/Km, 40.6 h-1 microM-1), consistent with the enzymes low activity versus gelatin [T. A. Bicsak and E. Harper (1984) J. Biol. Chem. 259, 13145]. The amino acid composition of the collagenase was shown to be high in glycine and glutamic acid, and the preparation was shown not to be contaminated with collagen by digestion with bacterial collagenase. The enzyme was not inhibited by iodoacetic acid or 2-hydroxy-5-nitrobenzyl bromide, suggesting the lack of essential cysteinyl and tryptophanyl residues, but was inhibited by micromolar concentrations of ZnCl2, consistent with the presence of essential histidine(s). Ethoxyformic anhydride irreversibly inhibited the collagenase suggesting the presence of essential lysyl residues.

Naturally Occurring Antihormones: Secretion of FSH Antagonists by Women Treated with a GnRH Analog

Follicle-stimulating hormone (FSH) is a glycoprotein essential for gonadal development and steroidogenesis. Recent studies suggest that deglycosylation of FSH results in the formation of antagonistic proteins that are capable of binding to gonadal receptors but that are devoid of bioactivity. Treatment of hypogonadal women with an antagonist of gonadotropin-releasing hormone substantially decreased serum FSH bioactivity with minimal changes in immunoreactivity. Chromatofocusing and size fractionation of the serum samples indicated the secretion of immunoreactive FSH isoforms that are devoid of bioactivity but that are capable of blocking FSH action in ovarian granulosa cells. These findings provide the first demonstration of naturally occurring circulating antihormones. These FSH antagonists may play an important role in the physiology and pathophysiology of the gonads.