Development of specific antibodies to rat insulin-like growth factor-binding proteins (IGFBP-2 to -6): analysis of IGFBP production by rat granulosa cells

Six insulin-like growth factor-binding proteins (IGFBPs) have been isolated and their cDNAs cloned in the rat and human species. The next step is to develop antibodies to each IGFBP. Toward this goal, we generated rabbit polyclonal antibodies to rat IGFBP-2, -4, -5, and -6, using synthetic peptide fragments of the IGFBPs. A rat IGFBP-3 polyclonal antibody was prepared in a previous study using the native protein. Western immunoblotting demonstrated that the IGFBP-2, -3, -4, -5, and -6 antibodies were highly specific for their respective antigens. The elicited antisera were used to study IGFBP production in primary cultures of rat granulosa cells grown in serum-free medium for 72 h. Ligand blotting with 125I-labeled IGF-I and IGF-II revealed two bands migrating at 29 and 24 kilodaltons (kDa) in the medium of untreated control cells, whereas no bands were detectable in medium from cells incubated with 100 ng/ml FSH. Western blotting of control medium with all of the IGFBP antibodies revealed that the IGFBP-4 antibody stained two bands at 28 and 24 kDa, and the IGFBP-5 antibody stained two bands at 30 and 29 kDa. By contrast, these bands were absent in medium from FSH-stimulated cells; instead, two lower molecular mass bands of 21.5 and 17.5 kDa were detected with the IGFBP-4 antibody, and a 21-kDa band was seen with the IGFBP-5 antibody. The same 21.5- and 17.5-kDa bands were seen when exogenously added IGFBP-4 was incubated with the FSH-conditioned medium, whereas untreated medium did not degrade the added IGFBP-4. Incubation with the conditioned medium also degraded exogenous IGFBP-5 to yield a 21-kDa band. By contrast, medium from control cells did not degrade the exogenous IGFBP-5. This finding indicates that FSH induced the production of a protease from granulosa cells that degraded IGFBP-4 and -5 in the culture medium. No IGFBPs were detectable in medium from control or FSH-treated cells using the IGFBP-2, -3, and -6 antibodies. Northern blotting analysis of the same control granulosa cell cultures revealed a 2.6-kilobase and a 6.0-kilobase transcript for IGFBP-4 and -5, respectively; however, the IGFBP-4 and -5 mRNAs were essentially undetectable in FSH-treated cell cultures. To determine the effects of the IGFBPs on steroidogenesis, dose-response experiments were performed with IGFBP-4 and -5.(ABSTRACT TRUNCATED AT 400 WORDS)

Structure of the rat insulin-like growth factor binding protein-4 gene

A family of six distinct insulin-like growth factor binding proteins (IGFBPs) have been isolated and their cDNA sequences characterized from rat and human species. Recently, the gene structures of the first three IGFBPs (IGFBP-1, -2 and -3) have also been determined. We now report the isolation of the rat IGFBP-4 gene and its genomic organization, as well as the DNA sequence of the promoter region. Rat IGFBP-4 gene spans at least 12 kilobases (kb) of the genomic sequence. It consists of four exons separated by three introns with approximate size of 6.4, 0.6 and 2.7 kb. A single transcriptional start site is located at 249 nucleotides upstream of the translational initiation ATG codon. The rat IGFBP-4 gene possesses a typical TATA box and a CAAT box, as well as multiple potential cis elements, including three cAMP responsive elements, three AP-1 binding sites and one progesterone receptor binding site in the 5' flanking region. The presence of these potential cis elements supports the tissue-specific expression of the IGFBP-4 gene.

Cloning of the rat insulin- like growth factor binding protein-5 gene and DNA sequence analysis of its promoter region

To understand the regulation of the insulin-like growth factor binding protein-5 (IGFBP-5) gene expression, we have cloned the IGFBP-5 gene from rat genomic libraries and determined its genomic organization as well as the DNA sequence at the 5' flanking region of the gene. The rat IGFBP-5 gene spans at least 17 kilobases (kb) of the genome and contains 4 exons interrupted by 3 introns of approximately 10, 0.6 and 0.7 kb, respectively. Southern blot analysis of the rat chromosome DNA revealed a single copy gene for IGFBP-5 in the haploid genome. Primer extension experiments demonstrated a single transcriptional start site located at 772 nucleotides 5' of the ATG translational start codon. In addition to a TATA box and a CAAT box, multiple putative cis-regulatory elements, including an AP-1, an AP-2 and a binding site for progesterone receptor are present in the promoter region. This finding suggests that the IGFBP-5 gene is one of those that are expressed in a tissue-specific manner.

Injection of anti-neuropeptide Y gamma-globulin into the hypothalamic paraventricular nucleus decreases food intake in rats

The effect of immunoneutralization of hypothalamic neuropeptide Y (NPY) on food intake was examined to clarify the involvement of NPY in the control mechanism of feeding behavior. Injection of anti-NPY gamma-globulin into the bilateral hypothalamic paraventricular nuclei of 24-h food-deprived rats significantly inhibited food intake for 1 h after the injection compared with rats that received normal rabbit gamma-globulin. This result suggests that NPY in the paraventricular nucleus plays a role in stimulating feeding behavior.

Localization of the heparin binding site of follistatin

To define the heparin-binding site of follistatin, the reduced and S-carboxymethylated recombinant human follistatin containing 288 amino acids was digested by Staphylococcus aureus V8. The digested product was subjected to sulfate cellufine column chromatography and the adsorbed peptide fragments eluted with a stepwise gradient of sodium chloride. The recovered column fractions were further purified by reversed-phase high-performance liquid chromatography (HPLC) and the HPLC peaks subjected to amino-terminal sequence analysis. All of the sulfate cellufine-retarded peptide fragments gave the same N-terminal amino acid sequence, which started at residue-68 of human follistatin, suggested that those fragments starting from residue-68 contain the heparin binding site. The multiple fragments might represent the oxidized, non-glycosylated or glycosylated forms of follistatin(68-113) resulting from the V8 digestion. A synthetic peptide corresponding to the region having the amino acid sequence 72-86 of follistatin was able to bind both heparin and sulfate cellufine, as well as compete with recombinant follistatin for binding to heparin. These findings further define the location of the heparin and heparan sulfate-binding site of follistatin at the basic amino acid-rich region comprising the amino acid sequence Lys75-Lys-Cys-Arg-Met-Asn-Lys-Lys-Asn-Lys-Pro-Arg86.

Expression of inhibin beta A and beta B, follistatin and activin-A receptor messenger ribonucleic acids in the rat seminiferous epithelium

The expression of inhibin beta A and beta B subunits, follistatin, and activin-A receptor messenger RNA (mRNAs) in different stages of rat seminiferous epithelial cycle was analyzed by in situ hybridization in order to understand their role in the regulation of spermatogenesis. Inhibin beta A mRNA was expressed in Sertoli cells in a highly stage-specific manner. The mRNA levels started to accumulate in Sertoli cells at stage VIII of the cycle and were highly expressed during stages IX-XI. Follistatin mRNA expression was identical to that of inhibin beta A, while inhibin beta B mRNA was maximally expressed in Sertoli cells at stages XIII-III. Low expression was found in stages VII-VIII. Activin-A receptor mRNA was localized mainly in spermatogenic cells. Maximal expression was seen in late primary spermatocytes at stages XIII-XIV and in early round spermatids at stages I-IV. A low even expression by Sertoli cells was also seen. Inhibin beta A and follistatin mRNAs were coexpressed in stage IX-XI Sertoli cells, suggesting close interplay between these molecules. The pattern of inhibin beta B mRNA expression was similar to that of inhibin alpha-mRNA. Localization of activin-A receptor mRNA in spermatogenic cells suggests that activin may influence meiotic divisions and early spermiogenesis.

Decrease in beta-subunit phosphotyrosine correlates with internalization and activation of the endosomal insulin receptor kinase

In a previous study, we showed that the rat hepatic insulin receptor (IR) kinase of endosomes (ENs) was transiently activated to levels exceeding those of plasma membrane (PM) receptors following insulin injection. Phosphatase treatment of EN receptors abolished IR kinase activation implicating beta-subunit autophosphorylation as a mediator of the activation process (Khan, M. N., Baquiran, G., Brule, C., Burgess, J., Foster, B., Bergeron, J. J. M., and Posner, B. I. (1989) J. Biol. Chem. 264, 12931-12940). In the present study, the phosphotyrosine (PY) content of the IR beta-subunit in PM and ENs was estimated by two different methods. In one method, direct in vivo labeling with 32Pi followed by receptor immunoprecipitation was carried out. In the second method, immunoblotting with antibodies against the submembrane domain of the IR beta-subunit, encompassing residue 960 (alpha 960), and with antibodies against PY (alpha PY) was used to determine the content of PY/beta-subunit in PM and ENs following injection of insulin. By both methods, it was found that the PY content of PM IR was significantly greater than that of IR in ENs. With doses of 1.5 micrograms of insulin/100 g body weight (50% receptor occupancy) or 15 micrograms/100 g body weight (receptor saturation), the PY/beta-subunit of PM IR attained a level 2.0 to 2.5-fold of that observed for the IR of ENs. Surprisingly, the IR of ENs incorporated 3 to 5 times more PY/beta-subunit than those of PM consequent to autophosphorylation. Exogenous IR kinase activity (poly(Glu:Tyr)) in PM changed only slightly with insulin dose. In contrast, EN receptors exhibited a dose-dependent increase in kinase activity coincident with the decrease in PY/beta-subunit levels. A comparison of the proportion of receptor and kinase activity immunoprecipitated by alpha PY both before and after autophosphorylation indicated that ENs but not PM contained a small population of lightly phosphorylated but highly activated receptors. Since Thr12-Lys (IR kinase residues 1142-1153) efficiently inhibited IR autophosphorylation of both PM and EN receptors, Tris phosphorylation of beta-subunit regulatory tyrosines was unlikely. These results may be explicable by a dephosphorylation-dependent activation of IR kinase, as seen with the src family of tyrosine kinases.

Regulation of pulsatile gonadotropin secretion by estrogen, inhibin, and follistatin (activin-binding protein) in ovariectomized rats

The following study was conducted to examine the effects of estrogen and polypeptides, given either alone or in combination, on pulsatile gonadotropin secretion. One week after ovariectomy, rats received s.c. injections of oil or various doses (0.5, 5, 20 micrograms) of estradiol benzoate (EB) followed 1 day later by i.v. administration of 60 micrograms purified porcine follistatin, 10 micrograms recombinant inhibin, or the appropriate vehicle. Four hours after injection of the nonsteroids, blood was collected at 10-min intervals for 2 h, and the effects on pulsatile hormone release were assessed. Administration of EB alone dose-dependently suppressed mean and trough (lowest point between two pulses) FSH levels and all parameters of pulsatile LH release. Both follistatin and inhibin at the doses employed suppressed mean FSH levels to an equivalent extent (40%). Follistatin, but not inhibin, suppressed FSH pulse amplitude, while neither polypeptide alone influenced FSH pulse frequency or any parameter of pulsatile LH release. The effects of follistatin and EB on mean FSH levels were additive at all EB doses, whereas the effects of inhibin and EB were additive only at the middle EB dose. Follistatin in combination with the lowest EB dose significantly suppressed mean LH levels. These studies are the first to demonstrate that combined treatment with estrogen and the nonsteroids follistatin and inhibin is more efficacious in suppressing FSH release than treatment with either agent alone, thereby indicating that both steroids and nonsteroids are probably important in the physiological regulation of FSH secretion in rats. The additive effects of these compounds on FSH secretion could form the basis for exploring novel contraceptive interventions.

Expression of insulin-like growth factor-binding protein-2 and -3 messenger ribonucleic acid in the porcine ovary: localization and physiological changes

Insulin-like growth factor-binding protein (IGFBP)-2 and -3 are the most prevalent IGFBPs in porcine follicular fluid, as determined on ligand blots, but little is known about the localization and regulation of their synthesis in vivo. This study was designed to investigate the localization and cyclic regulation of the mRNA for these two IGFBPs in the porcine ovary, RNA was extracted from whole ovaries morphologically classified as immature, preovulatory, and luteal. Northern hybridization analysis of this RNA showed no significant difference in the expression of IGFBP-2 mRNA in these ovaries (OD for preovulatory, luteal, and immature ovaries, 0.076 +/- 0.01, 0.071 +/- 0.01, and 0.10 +/- 0.008/micrograms RNA, respectively). IGFBP-3 mRNA was not different in immature and preovulatory ovaries, but was 10-fold greater (P less than 0.025) in luteal ovaries. Northern analysis of RNA extracted from ovaries also showed no significant change in IGFBP-2 mRNA on days (d) 11, 16, and 21 of the estrous cycle. IGFBP-3 mRNA tended to decrease between d11-16 with the onset of luteal regression and was significantly decreased in d21 preovulatory ovaries to 22% of the values in d11 ovaries. Granulosa, thecal, and luteal cells were also analyzed for IGFBP mRNA. IGFBP-2 mRNA was most abundant in granulosa cells, lower in thecal cells, and lowest in luteal cells. No IGFBP-3 mRNA could be detected in granulosa cells, and luteal cells expressed 15- to 63-fold greater levels than thecal cells. These results show that IGFBP-2 and -3 mRNAs are expressed in specific ovarian cell types and that their expression appears to be independently regulated during the reproductive cycle. This provides further evidence for the importance of these proteins as paracrine/autocrine regulators of ovarian function.

Gonadotropin and cAMP modulation of IGE binding protein production in ovarian granulosa cells

Porcine granulosa cells (GC) produce insulin-like growth factor (IGF) binding protein (BP)-3 and IGFBP-2 in culture. A gonadotropin, follicle-stimulating hormone (FSH), dramatically inhibited GC production of these IGFBPs in control cultures and in cultures stimulated by insulin plus epidermal growth factor (EGF) or IGF-I plus EGF. Stimulators of adenylate cyclase (forskolin, cholera toxin) and a derivative of adenosine 3',5'-cyclic monophosphate (cAMP), 8-bromoadenosine 3',5'-cyclic monophosphate, inhibited IGFBP synthesis in a manner similar to FSH. In contrast, the antagonist of cAMP action, (R)-p-adenosine 3',5'-cyclic phosphorothioate [(R)-p-cAMPS], significantly stimulated production of IGFBP-3 and IGFBP-2 compared with controls. This stimulatory effect of (R)-p-cAMPS was counteracted by cotreatment with FSH in a dose-dependent manner. Finally, treatment of GC cultures with FSH plus 3-isobutyl-1-methylxanthine resulted in a significant reduction in cellular content of mRNA coding for IGFBP-3 with no change in IGFBP-2 mRNA. In summary, agents that elevate intracellular cAMP were found to mimic the effects of FSH on IGFBP production.

Sensitive colorimetric bioassays for insulin-like growth factor (IGF) stimulation of cell proliferation and glucose consumption: use in studies of IGF analogs

We have established two in vitro bioassay systems for quantification of insulin-like growth factor (IGF) bioactivity. The first assay was used to quantitate mitogenic activity and the second was used to quantitate metabolic activity. Both assays use BALB/c 3T3 fibroblasts grown under serum-free conditions; detection of bioactivity in assays was performed colorimetrically and did not require the use of radioisotopes. The mitogenic bioassay, which requires 48 h for detection, quantitates changes in cell number and provides an index for determining the mitogenic activity of growth factors. Changes in cell number were measured by the enzymatic reduction of exogenously added MTT [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H tetrazolium bromide] to MTT-formazan by mitochondrial enzymes, which was directly correlated to cell number. The metabolic bioassay, which requires 22 h for detection, measures glucose consumption by detecting changes from the initial glucose concentration of conditioned medium after addition of various growth factors. When appropriate standards were established for these bioassays, they demonstrated a high level of reproducibility (coefficients of variation were 0.085-0.096 for the mitogenic bioassay and 0.120-0.191 for the metabolic bioassay). Both assays can be performed in 96-well microtiter plates, without the use of radioisotopes, or the limitations of conventional glucose, amino acid, or thymidine incorporation studies. In initial experiments for assay specificity, epidermal growth factor had no measurable effect in either assay. However, IGF-I, IGF-II, and insulin demonstrated effects on both metabolism and mitogenesis. In the case of the mitogenic bioassay, the maximum mitogenic activation by these growth factors was approximately 180% of control, and these factors demonstrated parallel sigmoidal dose-response curves, ranging from 0.02-2 ng/ml for IGF-I and from 2-200 ng/ml for both IGF-II and insulin. In the metabolic bioassay, in contrast to the mitogenic bioassay, insulin showed a dose-response curve whose shape was different from those of IGF-I and IGF-II. IGF-I and IGF-II stimulated glucose consumption in dose-dependent ranges of 0.02-3 ng/ml and 0.4-40 ng/ml, respectively. However, the dose-response effect of insulin was wider, ranging from 0.1-2000 ng/ml. When these assays were used to measure the bioactivity of IGF analogs, a des(1-3)-IGF-I, which has decreased affinity for IGF binding proteins, demonstrated activity equivalent to IGF-I, a [Leu27]IGF-II, which has markedly diminished affinity for the type 1 IGF receptor, exhibited approximately 0.07% of the potency of IGF-I and 1% of the potency of IGF-II.

Localization of insulin-like growth factor-binding protein-5 messenger ribonucleic acid in rat ovaries during the estrous cycle

To investigate the potential role of insulin-like growth factor-binding protein-5 (IGFBP-5) in ovarian physiology, we employed in situ hybridization and Northern analysis to localize IGFBP-5 mRNA in rat ovaries during the estrous cycle. By Northern analysis, the mRNA was abundant at all stages of the cycle. Two species of mRNAs were detected, with sizes of 6.0 and 1.8 kilobases, respectively. The relative amounts of the two transcripts changed throughout the cycle. By in situ hybridization, IGFBP-5 mRNA was expressed in only a few cell types: 1) granulosa cells of some atretic follicles, 2) some secondary interstitial cells, 3) some corpora lutea, and 4) the surface epithelium. The levels of message in both the granulosa and secondary interstitial cells changed over the cycle. At 1000 h on proestrus (before the LH/FSH surge), the message was expressed in only a few follicles. Interestingly, all were small atretic preantral (200-250 microns) follicles. At 2000 h on proestrus (after the LH/FSH surge), the IGFBP-5 mRNA was more abundant; now almost every atretic preantral follicle showed a strong hybridization signal. At 0200 and 1000 h on estrus, the mRNA appeared for the first time in granulosa cells of some atretic antral follicles and in secondary interstitial cells. Hence, virtually all atretic follicles, preantral and antral, now showed IGFBP-5 gene expression. In contrast to that on proestrus and estrus, the hybridization signal on diestrous days 1 and 2 was much less prominent and was found in only a few atretic preantral follicles. Throughout the cycle, IGFBP-5 mRNA was evident in some corpora lutea, but it was not particularly prominent. Abundant IGFBP-5 mRNA was evident in the surface epithelium, and no change was detected over the cycle. Dominant follicles were devoid of IGFBP-5 mRNA. In conclusion, this paper presents the first evidence that the IGFBP-5 gene is expressed in the adult rat ovary. The IGFBP gene is expressed in a cell-specific manner, e.g. in atretic granulosa, secondary interstitial cells, corpora lutea, and the surface epithelium, and the stage of the cycle significantly affected message levels, especially in atretic granulosa and secondary interstitial cells around estrous morning. These findings suggest that IGBP-5 may be an autocrine/paracrine regulator of ovarian physiology, particularly in relation to preantral follicle atresia.

Expression of messenger RNA for insulin-like growth factors and insulin-like growth factor binding proteins by experimental breast cancer and normal breast tissue in vivo

We report the expression of insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) by breast cancer cells and normal breast tissue in vivo. N-nitrosomethyl-urea (NMU)-induced rat mammary tumors synthesize mRNAs for IGF-II and IGFBP-2, -3, and -4. In contrast, normal lactating breast contains only IGFBP-2 and IGF-II messages; IGFBP-3 and -4 mRNAs are absent in this tissue. IGF-I and IGFBP-1 mRNAs are not expressed in either NMU tumors or in normal breast. This is the first report of in vivo expression of IGFBPs and IGF-II messages in breast tumors.

Cyclic changes in insulin-like growth factor-binding protein-4 messenger ribonucleic acid in the rat ovary

We have previously shown that the mRNA for insulin-like growth factor-binding protein-4 (IGFBP-4) is present in adult rat ovaries, being localized predominantly to granulosa cells of atretic follicles. Now we have considered the following questions. What class of atretic follicles expresses IGFBP-4 mRNA? How does IGFBP-4 mRNA expression change during the estrous cycle? In keeping with our earlier work, a strong hybridization signal for IGFBP-4 mRNA was present in subpopulations of follicles throughout the estrous cycle. In all cases, the hybridization signal was localized to granulosa cells. Among the various types of follicles, IGFBP-4 mRNA was present almost exclusively in atretic graafian (antral) follicles. Morphologically, the outer layer of granulosa cells was positive, while cells in the cumulus oophorous were negative. By Northern analysis and in situ hybridization, the levels of IGFBP-4 mRNA were found to change over the estrous cycle. At 1000 h on proestrus (before the LH/FSH surge), the hybridization signal was relatively weak, being restricted in some (but not all) atretic Graafian follicles. At 2000 h on proestrus, (after the LH/FSH surge), essentially all atretic Graafian follicles were strongly positive for the message. The pattern of hybridization was similar at 0200 h on estrus, but the signal was less intense. At 1000 h on estrus, the hybridization signal was variable, ranging from very strong to weak or undetectable in atretic follicles. At this stage, however, the highest levels of IGFBP-4 mRNA were measured by Northern analysis; interestingly, a strong signal became apparent in the stromal cells. On diestrous day 1, the message levels decreased, and the signal was restricted to some atretic follicles. On diestrous day 2, the hybridization signal was very weak. There was virtually no detectable IGFBP-4 mRNA in any healthy follicle. In summary, we found that IGFBP-4 mRNA is 1) not detected in healthy dominant follicles; 2) localized almost exclusively to atretic Graafian follicles, except on estrus when it also appears in stromal cells; 3) localized predominantly to the mural granulosa cells in atretic follicles; and 4) undergoes changes during the cycle, being most prominent around estrous morning. The possibility that IGFBP-4 plays a role in the cyclic destruction of cohort Graafian follicles at estrus, perhaps by mechanisms involving hormones, is discussed.

Melanotropic activity of gamma MSH peptides in melanoma cells

We studied the pigmentary activity of the peptides gamma 1, gamma 2 and gamma 3 melanocyte stimulating hormone (MSH), which differ in the structure of their C-termini, using hamster and mouse melanoma cell lines responsive to beta-MSH by increasing tyrosinase activity. Gamma 1-MSH alone or in combination with beta-MSH had no effect on either cell line. Gamma 2-MSH alone was biologically inactive but potentiated beta-MSH stimulation of tyrosinase activity. Gamma 3-MSH at high concentration (10 microM) induced tyrosinase activity and dendrite formation in the hamster melanoma line. When added together with beta-MSH, gamma 3-MSH partially inhibited the tyrosinase activity response to beta-MSH. Thus, gamma-MSH peptides have low intrinsic melanotropic activity in mammalian melanoma cells; the specific pigmentary responses appear to be affected by the structure of the C-terminal portion.

Attenuation of corticotropin releasing factor-induced hypotension in anesthetized rats with the CRF antagonist, alpha-helical CRF9-41; comparison with effect on ACTH release

The effect of pretreatment with the corticotropin releasing factor (CRF-41) antagonist, alpha-helical CRF(9-41), on the hypotensive response obtained on peripheral administration of CRF-41 has been assessed in anesthetized Wistar rats. A single IV bolus dose of rat CRF-41 (2 nmol, at 0 min) produced a hypotensive effect which was rapid in onset (-52 mmHg at +1 min) and sustained throughout the 60-min study period (-42, -40, -26 and -16 mmHg at +3, +10, +30 and +60 min, respectively). The antagonist [alpha CRF(9-41)] was administered in consecutive bolus doses of 12.5, 25 and 50 nmol at -15, -10 and -5 min, respectively. This had no effect on mean arterial blood pressure (MABP) or heart rate, nor did it change significantly the magnitude of the initial rapid fall in MABP when CRF-41 was administered (-45 mmHg at +1 min). However, following pretreatment with alpha CRF(9-41), MABP returned to control values within 3 min and the sustained period of hypotension was completely blocked. Administration of CRF-41 resulted in 44% and 142% increases in norepinephrine and epinephrine measured at +60 min. Pretreatment with the antagonist attenuated the rise in circulating catecholamine levels observed after CRF-41 administration. In comparison, pretreatment with the antagonist did not alter the ACTH response to CRF-41 at +1 and +3 min and only reduced ACTH levels by 28% (p less than 0.05), 43% (p less than 0.001) and 41% (p less than 0.01) at 10, 30 and 60 min, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Stage-specific cellular regulation of inhibin alpha-subunit mRNA expression in the rat seminiferous epithelium

To find out the local regulation of inhibin production and its possible paracrine role in the seminiferous epithelium, inhibin alpha mRNA levels were measured in sequential 1 mm segments of rat seminiferous tubules accurately staged by transillumination technique. Highest levels were found at stages XIV-I-IV of the cycle, and lowest at stages VI-VIIb of the cycle. When dividing spermatogonia were selectively destroyed by 3 Gy of high-energy X-irradiation, stage-specific inhibin alpha mRNA levels remained unchanged until 26 and 38 days after irradiation when stages VII and VIII of the cycle showed 6- and 4-fold increases during a selective reduction of pachytene spermatocyte and round spermatid numbers, respectively. The results suggest that these cells at a strictly stage-specific fashion have a paracrine inhibitory effect on Sertoli cell inhibin alpha gene expression. Inhibin alpha mRNA level also correlates closely to the follicle-stimulating hormone-stimulated cAMP production during the cycle of the seminiferous epithelium, but does not seem to have a correlation to spermatogonial DNA synthesis.

Solid phase synthesis of human growth hormone-releasing factor analogs containing a bicyclic beta-turn dipeptide

Three analogs derived from the N-terminal 29-residue fragment of human growth hormone-releasing factor (hGRF) which contained a bicyclic beta-turn dipeptide (BTD) at 7-8, 8-9, and 9-10 positions were synthesized by solid phase methodology to ascertain if the beta-turns are important for the biological activity of hGRF and also to show the applicability of the BTD unit to solid phase synthesis. All three analogs were obtained in good yield and purity indicating that the BTD unit can be used in the usual condition of solid phase synthesis. The capacity of these analogs to release growth hormone (GH) was tested in an in vitro bioassay using rat anterior pituitary cells. All three BTD-containing analogs showed the same maximal GH secretion with parallel dose-response curves to that of hGRF(1-29)NH2, except their relative potencies were very low.

Tissue-specific expression of four insulin-like growth factor-binding proteins (1, 2, 3, and 4) in the rat ovary

We investigated the possible presence of the mRNAs encoding four insulin-like growth factor-binding proteins (IGFBP-1, -2, -3, and -4) in the rat ovary. It has been demonstrated previously by Northern analysis that adult rat ovaries contain mRNA transcripts for IGFBP-2 and -3. Here we show by Northern analysis that adult rat ovaries contain mRNA for IGFBP-4, but the mRNA for IGFBP-1 was below the limit of detection. Using in situ hybridization, IGFBP-1 mRNA was not detected in any of the ovaries tested. The IGFBP-2 mRNA was localized specifically in thecal interstitial cells (TIC) and secondary interstitial cells of all ovaries. The IGFBP-2 signal was very strong in TIC of all Graafian follicles (healthy and atretic) and very strong in all secondary interstitial cells located in different regions of the ovary, but weak in TIC of preantral follicles. The IGFBP-3 hybridization signal was localized specifically to some corpora lutea. Here the hybridization single for IGFBP-3 was strong and distributed throughout the corpus luteum, strong but localized to only some luteal cells, or not detectable. The IGFBP-4 mRNA was localized almost exclusively to granulosa cells of atretic follicles. The intensity of the IGFBP-4 signals appeared to increase as the level of atresia increased. In some cases, IGFBP-4 signals were detected in the TIC, but they were weak and variable. These results show that the mRNAs for IGFBP-2, -3, and -4 are localized to the interstitial cells, corpora lutea, and atretic granulosa cells, respectively. The tissue-specific synthesis of IGFBP subtypes in specialized ovarian cells provides an excellent system to study the manner in which IGFBP synthesis is controlled and their potential role as an autocrine and paracrine factors.

Site-specific mutagenesis of human follistatin

Follistatin is a monomeric protein originally discovered in ovarian follicular fluid as a suppressor of pituitary follicle-stimulating hormone (FSH) secretion, and later identified as a binding protein for activin. To explore the role of the Asn-linked carbohydrate chains on the follistatin molecule in regard to the inhibition of FSH secretion and activin binding ability, site-specific mutations were introduced at either or both of the two potential Asn-linked glycosylation sites of human follistatin with 315 amino acids (hFS-315). The three types of follistatin mutants were expressed individually in Chinese hamster ovary cells. When tested for their ability to inhibit FSH secretion and to bind activin, each mutant was found to have a similar property as the non-mutated recombinant hFS-315, suggesting that glycosylation of the follistatin molecule has no effect in these functions. However, a two amino acid insertion in between the second and the third amino acid residues in hFS-315 caused the resulting compound to lose completely its inhibitory activity on FSH secretion from the pituitary as well as its binding ability to activin. This finding suggests that the amino-terminal region of the follistatin molecule is critical for both of these functions.

Characterization of an insulin-like growth factor binding protein (IGFBP-4) produced by the B104 rat neuronal cell line: chemical and biological properties and differential synthesis by sublines

A previous report from our laboratory described an approximately 30 kilodalton (kDa) insulin-like growth factor binding protein (IGFBP) that inhibited the binding of insulin-like growth factor I (IGF-I) by its receptor and was secreted by a subline of the B104 rat neuronal cell line. To better understand the biology of this IGFBP, it was purified from media conditioned by these B104 cells, and the chemical and biological properties of the protein were examined. The IGFBP existed as a 24 kDa form and a 28 kDa form when the conditioned media were analyzed by ligand blot. Deglycosylation studies indicated the 28 kDa species was the N-linked glycosylated form of the 24 kDa IGFBP. Multiple forms at both mol wts were found using two-dimensional electrophoresis, suggesting that there were posttranslational modifications in addition to glycosylation. The amino acid sequence of the 12 amino-terminal residues was identical to that of rat IGFBP-4. Increased synthesis of IGFBP-4 by the subline contrasted with neglible production by other B104 cells. Blot hybridization with rat IGFBP-4 complementary DNA showed differential expression of a 2.6 kilobase transcript among B104 cell lines that correlated with quantities of IGFBP-4 secreted in media. The difference persisted even when the cells were xenografted into athymic nude mice. Purified IGFBP-4 inhibited the binding of [125I]IGF-I by its receptor and blunted stimulation of [3H]thymidine incorporation by IGF-I. These findings suggest a role for IGFBP-4 in neural cell function and indicate the B104 cell lines may be a useful model for further examination of IGFBP-4 biology.

Cyclic changes in follistatin messenger ribonucleic acid and its protein in the rat ovary during the estrous cycle

The purpose of this research was to characterize the localization of follistatin mRNA and protein in the adult rat ovary during the 4-day estrous cycle. Analysis of ovarian sections using in situ hybridization and immunohistochemistry demonstrated the presence of follistatin messenger RNA (mRNA) and its protein in granulosa and luteal cells; no follistatin (message or protein) was detected in any of the other ovarian cell types. An important observation was that the intensity of follistatin signals changed during granulosa differentiation and the estrous cycle. During folliculogenesis, the first detectable hybridization signal appeared in the granulosa cells of secondary follicles, but the signal was weak. However, when a preantral follicle reached the early tertiary stage (beginning antrum formation), the message signal was very strong, being expressed in all granulosa cells of all such follicles (300-400 microns in diameter). In atretic follicles, follistatin mRNA was localized to granulosa cells, but only during the early stages. The above hybridization pattern of follistatin mRNA in prenatral and atretic follicles appeared constant throughout the estrous cycle. Interestingly, immunohistochemistry studies showed that the follistatin protein was detected only in certain follicles, being restricted to those which were healthy. On the morning of estrus, the follistatin protein was localized to a subpopulation of early tertiary follicles, presumably the dominant follicles selected to ovulate in the next cycle. As the dominant preovulatory follicles matured through diestrus and proestrus, the follistatin mRNA and protein signals appeared more intense in the granulosa cells. After ovulation, the hybridization and immunohistochemical signals continued to be strong in the newly formed corpora lutea on estrus morning. After luteolysis on diestrus-I, neither the follistatin message nor the protein was detectable in the corpora lutea. In conclusion, these results suggest that the follistatin message is present in all the granulosa cells of every developing follicle throughout the estrous cycle, but the follistatin protein appears to be present in only the selected dominant follicles. Accordingly, the possibility that follistatin might be an important regulatory molecule for selection/atresia should be considered.