Expression of a nuclear envelope protein recognized by the monoclonal antibody BU31 in lung tumours: relationship to Ki-67 antigen expression

The production of the murine monoclonal antibody BU31 is described. This antibody identifies a nuclear envelope protein which is expressed in some but not all cells, and which resembles statin, a protein reported to be expressed by non-proliferating cells. BU31 was applied onto frozen sections of a series of 78 lung tumours and the staining patterns were compared with those obtained with Ki-67. There was an inverse correlation between the proportion of tumour nuclei labelled with the two reagents (r = -0.61, 95 per cent confidence intervals -0.73 to -0.45). However, the four neuroendocrine neoplasms were BU31-negative. Squamous cell carcinomas often showed a peripheral distribution of the cells stained positively with Ki-67, whereas BU31 tended to label centrally situated cells. These observations are consistent with the concept that the antigen recognized by BU31 is expressed by non-proliferating cells in these tumours.

Hormonal regulation of insulin-like growth factor II and insulin-like growth factor binding protein expression by breast cancer cells in vivo: evidence for stromal epithelial interactions

Insulin-like growth factors (IGFs) I and II are potent mitogens for breast cancer cells. Their proliferative activity is likely to be influenced by their binding proteins (IGFBPs), a family of newly identified proteins. We report here on the in vivo hormonal regulation of mRNAs for IGF-II and IGFBPs in the N-nitrosomethylurea-induced rat mammary tumor, a well-established model of hormone-responsive mammary cancer. IGF-II mRNA levels tended to decrease in regressing tumors following ovariectomy, and they markedly increased upon reactivation of tumor growth with hormone repletion. Ovariectomy induced a drastic increase in IG-FBP-6 mRNA which was reversible with hormone repletion. Similar but more modest changes were observed with IGFBP-2 mRNA. In contrast, IGFBP-3 and IGFBP-4 mRNAs tended to decrease with ovariectomy and increase with hormone repletion. These latter effects, however, were modest, variable, and not statistically significant. In situ hybridization analysis revealed that IGF-II, IGFBP-5, and IGFBP-6 mRNAs were localized in the stromal component of the tumor, whereas IGFBP-2 mRNA was expressed by epithelial cells. We conclude that hormonal regulation of IGFBP expression is heterogeneous, thus suggesting divergent biological functions for these peptides. Our data also emphasize the importance of potential stromal-epithelial interactions in the control of breast cancer cell proliferation by IGFs.

Restraint changes pentobarbital-induced sleeping time in rats: evidence that arousal is modulated by brain corticotropin-releasing hormone and opioid in stress

The effect of restraint of different duration on sodium pentobarbital (PbNa)-induced sleeping time was examined in rats. 1 h-restraint significantly shortened PbNa (50 mg/kg b.wt., administered i.p. immediately after restraint)-induced sleeping time as reported previously, whereas 2 h-restraint significantly prolonged the sleeping time. Naloxone (1 mg/kg b.wt.) administered i.p. 15 min before the start of restraint further exaggerated the 1 h-restraint-caused shortening of PbNa-induced sleeping time, and it blocked the 2 h-restraint-caused prolongation of the sleeping time. SDZ202-250 (0.1 pmol and 0.5 pmol), a selective mu agonist, but not [D-Pen2-D-Pen5]enkephalin (0.1 pmol-1.0 nmol), a selective delta agonist, or U50488H (0.1 pmol-1.0 nmol), a selective kappa agonist, administered i.c.v. 15 min before the i.p. injection of PbNa significantly prolonged PbNa-induced sleeping time; its prolongation was blocked by naloxone. These results suggest that a mu receptor-binding opioid prolongs PbNa-induced sleeping time in stress. The 2 h-restraint-caused prolongation of PbNa-induced sleeping time was also blocked by alpha-helical CRH(9-41) (26 nmol), a corticotropin-releasing hormone (CRH) receptor antagonist, administered i.c.v. 15 min before the start of restraint. In conjunction with our previous findings that the i.c.v. administration of CRH shortens PbNa-induced sleeping time and the 1 h restraint-caused shortening of PbNa-induced sleeping time is blocked by the CRH receptor antagonist, the present results suggest that CRH may stimulate an opioid-specific sedative mechanism, thus causing the prolongation of PbNa-induced sleeping time in 2 h-restraint.(ABSTRACT TRUNCATED AT 250 WORDS)

Porcine ovarian granulosa cells secrete insulin-like growth factor-binding proteins-4 and -5 and express their messenger ribonucleic acids: regulation by follicle-stimulating hormone and insulin-like growth factor-1

Using ligand blotting, Western immunoblotting, and Northern analysis, we have characterized the insulin-like growth factor (IGF)-binding proteins (IGFBPs) produced by cultures of porcine granulosa cells. Ligand blot analysis of conditioned medium from untreated cultures of moderately differentiated granulosa cells (MDGCs; from 4-6-mm follicles) revealed mainly IGF-binding activity associated with IGFBP-2 (34 kDa) and IGFBP-3 (40/44-kDa doublet), which have previously been identified and characterized. In addition, these cultures secreted 30- and 22-kDa forms under some circumstances. The identification and regulation of these IGFBPs of lower molecular mass were the focus of the current studies. Treatment of these MDGCs with IGF-I dramatically stimulated the production (to a detectable level) of a 30-kDa IGFBP that was identified by immunoblotting with antiserum to IGFBP-5 but not antisera to IGFBP-1, -2, -3, -4, or -6. Production of IGFBP-5 was attenuated by concurrent treatment with FSH. IGFBP-5 mRNA in these cultures was correspondingly stimulated by IGF-I but unaffected by FSH. FSH increased the level of a minor 22-kDa IGFBP. Messenger RNAs for IGFBP-1, -4, and -6 were also examined but only IGFBP-4 mRNA was detectable, suggesting that the 22-kDa band was IGFBP-4. These results were compared to those in cultures of immature granulosa cells from 1-3-mm follicles, in which 22- and 30-kDa IGFBPs were readily detectable. An antiserum to IGFBP-4 precipitated the 22- and 30-kDa bands whereas deglycosylation shifted the 30-kDa IGFBP to 22 kDa, suggesting that both these bands represent glycosylation variants of IGFBP-4.(ABSTRACT TRUNCATED AT 250 WORDS)

Extrapituitary actions of gonadotropin-releasing hormone: stimulation of insulin-like growth factor-binding protein-4 and atresia

To understand how the intrinsic GnRH system functions in the ovary, we tested the effects of GnRH agonist (GnRH-a) on insulin-like growth factor-binding protein-4 (IGFBP-4) production, a novel marker of atresia. We also tested the ability of GnRH-a to stimulate atresia in vivo. When rat granulosa cells were cultured in defined medium for 2 days (controls), relatively large amounts of the 24,000 relative molecular mass IGFBP-4 accumulated in the medium. FSH (100 ng/ml) inhibited control IGFBP-4 protein levels and stimulated IGFBP-4 protease activity. GnRH-a increased (up to 4-fold) IGFBP-4 accumulation in the medium (ED50 = 1 x 10(-10) M), and the effect was blocked by a GnRH antagonist. Neither GnRH-a nor its antagonist had a detectable effect on protease activity. In coincubation experiments, GnRH-a effectively inhibited (ED50 = 3 x 10(-11) M) the FSH responses, and the effect of GnRH-a was blocked by GnRH antagonist. A 6-day time-course experiment showed that IGFBP-4 accumulation in control cultures remained constant for 2 and 4 days, after which it was undetectable. FSH (100 ng/ml) produced no measurable IGFBP-4 over the 6-day time course. The levels of IGFBP-4 increased markedly during the first 2 days of GnRH-a treatment, but were not significantly different from control levels on days 4 and 6. Similar results were obtained when cells were treated with FSH plus GnRH-a. Treating immature hypophysectomized estrogen-primed rats with GnRH-a in vivo caused a rapid and dramatic decrease (average, 60%) in the mitotic index of the granulosa cells of all preantral follicles (healthy and atretic) and increased pyknosis. These results demonstrate that 1) GnRH-a stimulates the expression of IGFBP-4 protein in rat granulosa cells in vitro; 2) GnRH-a abolishes the ability of FSH to inhibit IGFBP-4 expression and induce IGFBP-4 protease activity; and 3) GnRH-a stimulates atresia in preantral follicles in vivo. These results support the hypothesis that autocrine/paracrine secretion of ovarian GnRH might cause atresia by mechanisms involving increased IGFBP-4 synthesis.

Effect of growth hormone administration and treadmill exercise on serum and skeletal IGF-I in rats

Growth factors may be mediators of local and systemic factors that enhance bone formation. This study examined the effect of treadmill exercise and ovine growth hormone administration on levels of insulin-like growth factor I (IGF-I) in serum (ng/ml), long bone, and vertebrae and on bone formation rate. Forty female rats were divided into four groups: control; exercise (17 m/min, 1 h/day); growth hormone (0.05 mg.100 g-1.day-1); growth hormone plus exercise. After 9 wk of study, the serum levels of IGF-I were higher in the intervention groups than in the control group; however, the IGF-I concentration and the periosteal bone formation rate in the long bone were significantly higher only in the exercised rats. The IGF-I concentration and the cancellous bone formation rate in the vertebrae did not differ among the experimental groups. The vertebral and long bone formation rate were correlated with bone concentrations of IGF-I. Serum levels of IGF-I were also correlated with serum osteocalcin and the long bone formation but not with the vertebral bone formation. The association of bone formation with serum and bone IGF-I supports the suggestion that IGF-I is one of the growth factors that regulate bone formation, in particular as a mediator of the response of bone to exercise.

Insulin-like growth factor-binding protein-2: the effect of human chorionic gonadotropin on its gene regulation and protein secretion and its biological effects in rat Leydig cells

Human CG (hCG) and insulin-like growth factor-I (IGF-I) have synergistic effects on Leydig cell function. Leydig cells express high affinity IGF-I receptors. The number of IGF-I receptors and IGF-I receptor mRNA levels can be up-regulated by hCG. The most abundant mRNA species of the IGF binding proteins (IGFBPs) in rat Leydig cells is IGFBP-2. In the present study, we investigated the effect of hCG on IGFBP-2 transcription, mRNA accumulation, and protein production/secretion. Biological effects of IGFBP-2 on Leydig cells were also examined. Rat Leydig cells were purified from testes using centrifugal elutriation followed by Percoll gradient centrifugation. Cells were cultured for 24 h and then treated with or without hCG (10 ng/ml) for 6 h. The expression of IGFBP-2 mRNA was decreased by hCG in a dose-dependent manner, and at a concentration of 10 ng/ml the expression of IGFBP-2 mRNA was reduced by 50%. As early as 2 h after the addition of hCG, there was a significant decrease in IGFBP-2 mRNA accumulation. To evaluate the mechanism(s) responsible for decreased IGFBP-2 gene expression by hCG, the effect of hCG on the rate of transcription and stability of the mRNA was determined. Human CG (10 ng/ml) reduced the IGFBP-2 transcription rate by 32%/h in comparison with the control, while the half-life (t1/2) of mRNA remained unaltered (hCG-treated cells, 0.58 h; control cells, 0.51 h). IGFBP-2 with a molecular size of 33 kilodaltons was detected as a major band in the Western ligand blot.(ABSTRACT TRUNCATED AT 250 WORDS)

Local production and action of follistatin in human placenta

The aim of the present study was to investigate the possible production, localization, and action of follistatin in human placenta, fetal membranes (amnion, chorion), and maternal decidua. Four different experimental approaches were used: 1) Southern blot analysis following reverse polymerase chain reaction to identify follistatin messenger RNA (mRNA) in tissue homogenates; 2) immunohistochemistry to localize immunoreactive (ir-) follistatin in the various intrauterine tissues; 3) measurement by RIA of ir-follistatin levels in culture medium of placental cells; and 4) possible action of follistatin on human CG (hCG) and progesterone release from cultured placental cells. Placental and decidual cells collected during first trimester or at term gestation express follistatin mRNA; fetal membranes (amnion, chorion) at term also express follistatin mRNA. Immunoreactive follistatin is localized in syncytial cells of placental villi at term as well as in large decidual cells, in amnion epithelium, and in chorionic cells. The placental secretion of follistatin has been confirmed by the evidence of measurable levels of ir-follistatin in the medium of cultured placental cells at term; the release is time dependent and is not modified by the addition of forskolin or progesterone. The addition of increasing doses of recombinant human follistatin does not significantly influence the release of hCG or progesterone from cultured placental cells, whereas the activin A-induced hCG and progesterone release are completely reversed. The present data showed that 1) human placenta, fetal membranes, and decidua express follistatin mRNA; 2) ir-follistatin is localized and released from placental cells at term; and 3) follistatin has a functional role in the local control system regulating placental hormone production.

Novel anti-inflammatory undecapeptides that contain anisolyated glutamic acid derivatives

In various animal models of tissue injury, corticotropin-releasing factor (CRF) and related peptides inhibit swelling, edema and loss of protein from the vascular compartment. To search for smaller peptide segments of CRF that might retain anti-inflammatory activity, the authors tested peptides similar to the carboxy terminals of ovine (o) and human/rat (h/r) CRF. Also, because h/rCRF(35-39), -Arg-Lys-Leu-Met-Glu-, resembles Arg-Lys-Leu-Leu-Glu-, a sequence found in many intermediate filament proteins, analogous peptides were evaluated. Ovine CRF(21-41), -Met-Thr-Lys-Ala-Asp-Gln-Leu-Ala-Gln-Gln-Ala-His-Ser-Asn-Arg-Lys- Leu-Asp-Ile-Ala-NH2, its carboxy terminal carboxyl derivative, oCRF(21-41)-OH, and the fragments, oCRF(26-41) and oCRF(30-41), were inactive when assayed at 5 mg/kg i.v. on edema induced in the pentobarbital-anesthetized rat's hindpaw after immersion in 58 degrees C water for 1 min. Crude peptides, D-Leu-Ala-Thr-D-Tyr-Arg-Lys-Leu-Leu-Glu-Ile-D-Leu-NH2 and D-Ala-His-Ser-D-Asn-Arg-Lys-Leu-Leu-Glu-Ile-D-Leu-NH2, were found to have activity in this bioassay. Characterization of the structures within the crude mixture revealed that substitution of the glutamic acid residue with an anisolyated glutamic acid (2-amino-5-(methoxyphenyl)-5-oxopentanoic acid) derivative, designated as (A*), increased the overall potency. The glutamyl-anisole derivative was a by-product of the temperature-dependent Friedel-Crafts acylation reaction that occurs during hydrogen fluoride cleavage of glutamyl-containing peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

CRF and related peptides as anti-inflammatory agonists

The permeability of endothelial surfaces increases in response to injury. We have shown that vascular leakage in experimental models of tissue injury can be inhibited by CRF and by a novel class of peptides that we call mystixins. Binding sites for iodinated-Tyro-CRF have been revealed in mucous membranes, and immunoreactive CRF-like materials have been found in inflamed tissues. Perhaps the breakdown of cytoskeletal intermediate filaments after insult generates or exposes peptide domains similar to mystixins. Endogenous CRF-like or mystixin-like peptides, if activated or released locally in injured tissues, may function as agonists to counteract the immediate inflammatory response. If this is so, the peripheral actions of these peptides add a new dimension to the idea that CRF and related substances organize and regulate an organism's response to stress.

Insulin-like growth factor binding protein-3 gene expression is restricted to involuting corpora lutea in rat ovaries

There is evidence that insulin-like growth factor binding protein-3 (IGFBP-3) is a part of the intrinsic IGF system in rat CL. Here, we examined when during luteogenesis the IGFBP-3 gene is expressed. IGFBP-3 messenger RNA (mRNA) was characterized by Northern analysis and in situ hybridization techniques. Animals were selected at proestrus (P 1000 h and P 2000 h), estrus (E 0200 h and E 1000 h), diestrus I (DI 1100 h), and diestrus II (DII 1100 h), and in pregnancy (day 12, before luteolysis and day 21, during luteolysis). A single 2.6 kilobase IGFBP-3 transcript was identified at each stage of the estrous cycle; however, the amounts of message varied markedly, being most abundant at P 1000 h, least abundant at P 2000 h, E 0200 h, E 1000 h, and DI, and then more abundant at DII. Corroborating our earlier report, IGFBP-3 mRNA was limited solely to corpora lutea (CL). Newly-formed CL-I at E 0200 h and E 1000 h revealed no IGFBP-3 hybridization. This is the period of early luteinization when cells undergo hypertrophy and capillaries and lymphatics penetrate the granulosa lutein layer. At DI 1100 h, a few cells (12.2 +/- 3.4%) near the central cavity of the CL-I showed a positive hybridization signal for IGFBP-3; this period is commensurate with active luteinization when the vascular tissue develops a distinctly sinusoidal character and progesterone secretion by CL-I increases. At DII 1100 h, more cells in the central area were positive for IGFBP-3 (55.2 +/- 6.4%); this is the period of active luteolysis when P4 secretion has fallen to basal levels. At P 1000 h, a positive IGFBP-3 hybridization signal was detected in most CL-I cells (85.3 +/- 2.8%), and the signal was particularly intense in subtypes of endothelial cells lining venous sinusoids and/or lymphatics and some perivascular cells; this is the period when patches of pyknotic cells appear in the central area of CL-I. At P 2000 h, 45.9 +/- 1.6% of the CL-I cells showed a positive signal; however, the intensity of the signal was much weaker when compared to P 1000 h. During the next cycle, the CL-I become the CL of the second generation (CL-II), which show increased necrosis. Between estrus and diestrus II of the next cycle, a large number of the CL-II cells (approximately 75%) were positive for IGFBP-3 and the signal was very strong in some groups of cells.(ABSTRACT TRUNCATED AT 400 WORDS)

A retinoblastoma-binding protein related to a negative regulator of Ras in yeast

The growth suppression function of the retinoblastoma protein (Rb) is though to be mediated by Rb binding to cellular proteins. p48 is one of the major proteins that binds to a putative functional domain at the carboxy terminus of the Rb protein. Here we report the isolation of a full-length complementary DNA (RbAp48) encoding p48. Complex formation between p48 and Rb occurs in vitro and in vivo, and apparently involves direct interaction between the proteins. Like Rb, p48 is a ubiquitously expressed nuclear protein. RbAp48 share sequence homology with MSI1, a negative regulator of the Ras-cyclic AMP pathway in the yeast Saccharomyces cerevisiae. Furthermore, like MSI1, human RbAp48 suppresses the heat-shock sensitivity of the yeast ira1 strains and RAS2Val19 strains. Interaction with p48 may be one of the mechanisms for suppression of growth mediated by Rb.

Psychological stress increases arousal through brain corticotropin-releasing hormone without significant increase in adrenocorticotropin and catecholamine secretion

The effect of psychological and psychophysical stress on pentobarbital (PbNa)-induced sleeping time was examined in rats to clarify the influence of psychological stress on arousal. Psychological stress and electric footshock of 5-60 min duration significantly shortened PbNa-induced sleeping time, and the shortening was reversed by intracerebroventricular administration of a corticotropin-releasing hormone (CRH)-receptor antagonist. Electrical footshock and restraint significantly raised plasma adrenocorticotropin (ACTH) and catecholamine levels, whereas psychological stress did not significantly affect the plasma hormones levels. These results suggest that both psychological and psychophysical stress increase arousal through brain CRH. It is also concluded that expression of the central nervous system action of CRH, such as increasing arousal, is not necessarily accompanied by a significant increase in the secretion of ACTH and catecholamine in psychological stress.

Molecular heterogeneity of follistatin, an activin-binding protein. Higher affinity of the carboxyl-terminal truncated forms for heparan sulfate proteoglycans on the ovarian granulosa cell

Follistatin (FS), an activin-binding protein, is a monomer derived from two polypeptide core sequences of 315 (FS-315) and 288 (FS-288) amino acids originated from alternatively spliced mRNA. To define the structural heterogeneity of native FS, we purified six molecular forms of FS from porcine ovaries. Protein chemical analysis revealed that the structural differences among the six isoforms were caused by truncation of the carboxyl-terminal region and/or the presence of carbohydrate chains, resulting in the formation of FS-315, FS-288, and FS composed of 303 amino acids (FS-303) in various forms of glycosylation on the two potential Asn-linked glycosylation sites. The majority of FS isolated from porcine ovaries was FS-303, which may have been derived from FS-315 by proteolytic cleavage of the 12 COOH-terminal amino acids. All six molecular species have almost the same activin binding activity (Kd = 540-680 pM). By contrast, the COOH-terminal truncated form, FS-288, showed much higher affinity for the rat granulosa cell surface than FS-303, whereas FS-315 had no affinity. FS-288 bound to heparan sulfate-Sepharose CL-4B, but FS-315 did not, suggesting that the truncated forms of FS bind to heparan sulfate proteoglycans on the cell. COS cells transfected with the FS-288 DNA expressed the FS-288 protein, which adhered to the cell surface, but cells transfected with the FS-315 DNA secreted the expressed protein into the medium, which did not bind to the cell surface. In rat anterior pituitary culture, FS-288 (ED50 = 2 ng/ml) was more potent in suppressing follicle-stimulating hormone release than FS-303 (ED50 = 10 ng/ml) and FS-315 (ED50 = 20 ng/ml). These results suggest that cell-associated FS traps activin more tightly in the matrix, thereby more effectively blocking the activity of activin on heparan sulfate proteoglycans of the cell surface and that cell-associated FS plays an important role in controlling the various actions of activin in a paracrine or autocrine manner.

Differential control of activin, inhibin and follistatin proteins in cultured rat granulosa cells

Follistatin, activin and inhibin proteins are produced by granulosa cells, but the mechanisms controlling their production remain unclear. Here, we examined how the protein kinase A (PKA) and protein kinase C (PKC) pathways act and interact to regulate production of these proteins. Granulosa cells from immature rats were cultured with activators of the PKA pathway (100 ng/ml FSH, 10 microM forskolin) and/or activators of the PKC pathway (100 nM GnRH agonist, 100nM 2-0-tetradecanoyl-phorbol-13-acetate, TPA). Conditioned media were assayed for inhibin and activin by ligand blotting using recombinant human 125I-follistatin and for follistatin by double ligand blotting using cold activin plus 125I-follistatin. FSH and forskolin stimulated inhibin but not activin production. In contrast, GnRH and TPA stimulated activin, and to a lesser degree, inhibin production; significantly, this is the first demonstration of activin dimer production by granulosa cells. Activators of the PKA pathway antagonized the actions of PKC effectors and vice versa. All agents increased follistatin protein production, and the PKA and PKC activators interacted to generate further increases in follistatin production. These results show that the FSH-PKA signalling pathway favors formation of alpha beta inhibin dimers while the GnRH-PKC pathway favors formation of beta-subunit activin dimers. Both pathways act to increase follistatin protein production.

A 12-kilodalton N-glycosylated growth hormone-related peptide is present in human pituitary extracts

This study was designed to investigate whether N-linked glycosylation could account for the presence of glycosylated GH forms (G-GH) in human pituitary extracts. The study was carried out in commercially available pituitary GH preparations (pitGH). Recombinant GHs obtained from eu- or prokaryotic cells were used as controls. Radioiodinated GHs were incubated in tubes containing Concanavalin-A (Con-A) attached to a Sepharose 4B matrix. Pituitary G-GH forms were selectively displaced from Con-A by adding N-acetyl-D-glucosamine or methyl-alpha-D-mannopyranoside and electrophoresed. Autoradiographies of these gels identified a 12-kilodalton (12K) band as the glycosylated form. Due to the fact that this peptide was partially immunoprecipitated with an anti-GH serum and the absence of detectable PRL in the pitGH extracts, it would indicate that such a glycopeptide was GH related. Endoglycosidase-F treatment of pitGH extracts induced a decrease in the mol wt of that 12K peptide, as indicated by the changes observed in its mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This demonstrated that the sugar moieties were N-linked. When recombinant GHs were assayed by a similar method, no specific binding to Con-A was detected. NH2-terminal amino acid sequence analysis from the 12K band demonstrated that this band was composed by three peptides. Peptide 1 corresponds to the GH-N 102-119 sequence. Interestingly, peptide 2 exhibits GH-V 1-18 sequence, while peptide 3 seems to be a novel GH-related peptide. Taken together, these data suggest that the pituitary G-GH form found in human pituitary extracts is derived not from the "normal" GH-N gene, but, rather, from the GH-V gene or another unidentified gene. The potentially important pathophysiological implications of this finding need to be investigated.

Expression and regulation of insulin-like growth factor-binding protein-1, -2, -3, and -4 messenger ribonucleic acids in purified rat Leydig cells and their biological effects

The actions of insulin-like growth factor-I (IGF-I) are modified by binding proteins [IGF-binding proteins (IGFBPs)]. Previously, we reported that IGF-I enhances Leydig cell steroidogenesis and that IGF-I mRNA is expressed in Leydig cells. In the present study, we evaluated the expression and regulation of IGFBP-1, -2, -3, and -4 in purified rat Leydig cells and their biological effects. We found that none of the testicular crude interstitial cells, purified Leydig cells, or seminiferous tubules expressed IGFBP-1 mRNA. This indicated that IGFBP-1 mRNA is not expressed in the testis in detectable amounts. In contrast, large amounts of IGFBP-2 with a size of 1.8 kilobases (kb) were expressed in purified Leydig cells, and lesser amounts in crude interstitial cells. Small amounts of IGFBP-2 mRNA were expressed in seminiferous tubules, but none could be detected in liver. IGFBP-3 mRNA was predominantly expressed in purified Leydig cells, crude interstitial cells, and liver, while appreciable amounts were not found in seminiferous tubules. Liver had the highest amounts of IGFBP-4 mRNA, whereas purified Leydig cells and crude interstitial cells had lesser amounts. We next evaluated the pituitary dependency of IGFBP mRNAs in Leydig cells. Purified Leydig cells were isolated from 50-day-old rats 5 days after hypophysectomy. IGFBP-2, -3, and -4 mRNA levels in Leydig cells decreased 22%, 80%, and more than 90%, respectively, after hypophysectomy. In the liver, however, IGFBP-2 mRNA levels increased, and IGFBP-3 mRNA levels decreased, while IGFBP-4 remained unchanged. As expected, hypophysectomy caused decrements in large (7.0- to 7.5-kb; a 75% reduction) and small (0.8- to 1.2-kb; a 90% reduction) IGF-I mRNA levels in Leydig cells. Hypophysectomy also reduced IGF-I mRNA expression in liver. Finally, the effects of IGFBP-2, -3, and -4 on Leydig cell testosterone formation were investigated. hCG in a concentration of 10 ng/ml increased testosterone formation from 0.6 +/- 0.01 to 27.4 +/- 1.01 ng/10(6) cells.h. In the presence of IGF-I (10 ng/ml), testosterone formation was further increased to 58.6 +/- 1.6 ng/10(6) cells.h (P < 0.01). IGFBP-3 (0.1, 1, and 2.5 pmol/ml) caused a dose-dependent inhibition of IGF-I- plus hCG-induced testosterone formation. IGFBP-3 in a concentration of 2.5 pmol/ml completely neutralized the effects of IGF-I on Leydig cell steroidogenesis. IGFBP-4 had a lesser effect, while IGFBP-2 had no effect on IGF-I- plus hCG-induced testosterone formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased follistatin (activin-binding protein) gene expression in rat anterior pituitary tissue after ovariectomy may be mediated by pituitary activin

For lack of evidence to the contrary, it is now believed that the FSH-suppressing actions of follistatin are due to its ability to bind endogenous pituitary activin. Recent data have demonstrated a role for pituitary activin-B in mediating FSH hypersecretion after ovariectomy (OVX) and during the secondary FSH surge on estrus. Therefore, given that follistatin is produced within anterior pituitary tissue, and considering the potentially important function of follistatin to modulate activin bioactivity, we sought to gain insights into the regulation of follistatin gene expression in the anterior pituitary gland of adult female rats. At the termination of all in vivo investigations, rats were killed, trunk blood was collected for determination of serum LH and FSH levels by RIA, and pituitary tissue was collected, pooled (two or three glands per pool), and processed for determination of follistatin messenger RNA (mRNA) levels by a solution-hybridization RNase protection assay. In the first experiment, pituitary follistatin mRNA levels were significantly (P < 0.01) increased 3 weeks after OVX. Treatment of long-term ovariectomized rats with a Nal-Glu LHRH antagonist restored serum LH levels to precastration levels and suppressed serum FSH concentrations by 70%, but follistatin message levels were not altered. In contrast, treatment of castrated rats with recombinant human follistatin-288 selectively suppressed serum FSH levels (50%) and completely abolished OVX-induced increases in follistatin mRNA levels. Subsequent experiments revealed that OVX-induced increases in follistatin gene expression could be observed in pituitary tissue grafted underneath the kidney capsule of hypophysectomized rats. Furthermore, follistatin mRNA levels were significantly (P < 0.05) higher in pituitary glands taken from estrous rats during the secondary FSH surge (0200 h) than in glands obtained from rats on proestrous morning when serum FSH levels were basal. Because increased steady state follistatin mRNA levels in the latter two instances were associated with selective FSH hypersecretion, and such hypersecretion was previously shown to be dependent to a significant degree on pituitary activin, we next tested the hypothesis that increased pituitary follistatin gene expression is mediated by activin. Using cultures of dispersed pituitary cells, addition of recombinant human activin-A for 72 h increased follistatin mRNA levels 3-fold while enhancing only FSH secretion. Collectively, the present results demonstrate a coupling of follistatin gene expression in the anterior pituitary gland with changes in pituitary FSH secretion under conditions where LH secretion is unaltered. Viewed in the context of previous work, the data also suggest that changes in follistatin mRNA levels may be linked to activin signaling.

Stimulation of progesterone secretion by recombinant follistatin-288 in human granulosa cells

The effects of recombinant human follistatin (follistatin-288) on basal and hCG-stimulated progesterone secretion were examined in cultured human granulosa cells. Follistatin increased progesterone secretion in a dose-dependent manner. However, follistatin did not augment hCG- or cAMP-stimulated progesterone secretion. Time-course analysis revealed that follistatin increased progesterone secretion after 24 h of incubation. Follistatin also enhanced basal, but not hCG-stimulated, 20 alpha-hydroxyprogesterone accumulation, indicating that the increase in progesterone accumulation was not due to a blockade of the 20 alpha-hydroxylase metabolic pathway. In the presence of the phosphodiesterase inhibitor isobutylmethylxanthine, follistatin significantly increased intracellular cAMP accumulation to levels comparable to those induced by 1 IU/ml hCG. These results provide the first evidence of a stimulatory action of follistatin on progestin secretion in the human ovary, which is accompanied by an increased accumulation of intracellular cAMP levels. Follistatin may well be another potential regulator of steroid hormone production in human granulosa cells during the periovulatory period.

Human plasma free activin and inhibin levels during the menstrual cycle

The role of inhibin in gonadal function and reproduction has been confirmed by the measurement of plasma inhibin levels, but there has been no clinical data available on activin because of the lack of a good assay method. We measured plasma free activin levels during the normal menstrual cycle using a newly developed competitive protein binding assay with follistatin as the binding protein. Plasma inhibin levels were measured simultaneously using an alpha-subunit N-terminal fragment RIA with recombinant inhibin as the reference standard. Four normal women, aged 23-29 years, were investigated by obtaining plasma at 3-day intervals. Plasma inhibin levels showed some variation during the follicular phase, but a parallel rise in inhibin and progesterone was observed during the luteal phase. These findings confirmed those of previous studies. In contrast, plasma free activin levels did not show any substantial changes during the menstrual cycle. This study suggests that activin has no endocrine role in modulating the pituitary-gonadal axis during the normal menstrual cycle, while changes of inhibin reflect cyclic gonadal function and indicate an endocrine role for this protein in modulating gonadal activity.

Effects of estrous cycle stage and pregnancy on follistatin gene expression and immunoreactivity in rat reproductive tissues: progesterone is implicated in regulating uterine gene expression

Follistatin, a monomeric protein originally isolated from ovarian follicular fluid, is now believed to be a major local regulator of the multifaceted actions of activin by virtue of its activin-binding properties. In view of the ability of follistatin to stimulate progesterone production from granulosa cells and its presence in newly formed corpora lutea, the following study was conducted to determine the effects of cycle stage and pregnancy on follistatin gene expression and immunoreactivity in the rat ovary and uterus with the intent of gaining additional insights into the regulation of follistatin in these tissues. Decidua and placentas were also examined on days 15, 18, and 21 of pregnancy. Follistatin messenger RNA (mRNA) levels were quantified using a sensitive solution hybridization-RNase protection assay and values normalized to the amount of cyclophilin mRNA present in each sample. Levels of follistatin-like immunoreactivity (FLI) in serum and tissues were estimated using a homologous porcine follistatin RIA. Follistatin message levels in the ovary increased between proestrus and estrus with a return to proestrous values on both days of diestrus. In the nonpregnant uterus, mRNA levels on proestrus were similar to levels measured in uteri taken from hypophysectomized or ovariectomized rats. Interestingly, follistatin gene expression increased almost 3-fold between proestrus and estrus. An additional experiment demonstrated that this increase could be abated by treatment of proestrous rats with pentobarbital which blocks preovulatory rises in serum progesterone levels and could be restored by administration of progesterone to pentobarbital-treated proestrous rats. In pregnant rats, ovarian follistatin message levels on days 3 and 6 of pregnancy were identical to levels observed on day 2 of diestrus. However, an abrupt 4-fold increase in ovarian mRNA levels occurred between days 6 and 9 with a further 58% increase occurring by day 12. This marked increase in message levels was unaccompanied by changes in ovarian FLI levels. A precipitous decrease in transcript levels accompanied by a decline in FLI levels then followed with ovarian gene expression on days 15 through 21 being slightly higher than expression during the initial stages of gestation. Expression of the gene in the decidua and placenta did not vary between days 15 and 21 of pregnancy. Levels of FLI in serum also were invariant during the cycle and pregnancy.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural characterization of the rat insulin-like growth factor binding protein-6 gene

Recently a family of six distinct insulin-like growth factor binding proteins (IGFBPs) have been identified and the gene structures of the first five (IGFBP-1, -2, -3, -4 and -5) characterized. We now isolated the IGFBP-6 gene from a rat genomic library and determined its organization as well as the DNA sequence at the 5' flanking region of the gene. The rat IGFBP-6 gene spans 5.1 kb of the genomic sequence and contains four exons interrupted by three introns of approximately 2.4, 0.2 and 1.2 kb in length, respectively. Primer extension analysis and ribonuclease protection assay using RNA from rat lung tissues demonstrated two transcriptional start sites located at 85 and 82 nucleotides upstream of the ATG translational initiation codon. The promoter region of the rat IGFBP-6 gene is devoid of a TATA or a CAAT consensus sequence motif, but putative regulatory cis elements, including a Sp1, an estrogen receptor binding site and a retinoic acid responsive element, are present in the promoter region.

The expression of saporin, a ribosome-inactivating protein from the plant Saponaria officinalis, in Escherichia coli

We have isolated and sequenced genomic clones from the DNA of Saponaria officinalis using a cDNA probe that encodes proteins with high homology to saporin-6, one of the most potent of the ribosome-inactivating proteins that is currently used for the construction of immunotoxins and mitotoxins. Sequence differences in the clones suggest a multigene family of proteins. These data agree with observations of several different proteins with ribosome-inactivating protein activity and similar structure. Two of the genomic clones encode proteins that have identical sequences to two of the four isoforms of saporin-6. We have inserted the DNA from one genomic clone into an Escherichia coli expression system that encodes a signal sequence for export to the bacterial periplasmic space. Exportation is observed and the isolated gene product has ribosome-inactivation activity similar to the native protein. Sequence analysis shows differential processing of the remaining plant signal sequence. The majority of the expressed protein remains intracellular and this material also shows high specific activity and differential processing. Saporin as an immunotoxin in clinical trial and as a mitotoxin in experimental models has been extremely efficacious. These data indicate the ability to produce fusion proteins with saporin and cell-binding ligands for production of new reagents for further clinical and experimental use.