Abstract

We recently identified and characterized a protease present in rat serum which is capable of generating des(1–3)IGF-I. In this study, we have investigated the effects of GH deficiency and replacement on the activity of this protease in rat serum and tissue extracts. Protease activity was significantly higher in sera from hypophysectomized (hypox) rats than sham-operated rats (P<0·001) and GH treatment of hypox rats (human GH, 100 μg/100 g body weight i.p. for 10 days) significantly reduced the levels towards normal. The addition of IGF-I to hypox rat serum to achieve IGF-I concentrations comparable with or greater than that seen in normal rat serum had no effect on the measured protease activity. Protease activity was also detected in tissue extracts. The level of protease activity in the various tissues from sham-operated rats demonstrated the following order: liver>testes>heart> skeletal muscle>lung>thymus>kidney>brain>spleen. In all tissue extracts examined, except that from the lung, the levels of protease activity were higher in extracts from hypox rats compared with sham-operated rats. The largest differences between tissue extracts from hypox and shamoperated rats were seen in spleen (4-fold higher), kidney (2·27-fold), testes (1·55-fold) and heart (1·31-fold). In the liver, kidney and testes, GH treatment significantly reduced protease activity. Since the pattern of serum IGF-binding proteins (IGFBPs) differ in hypox rats compared with normal rats, we determined whether these changes could result in enhanced serum binding of des(1–3)IGF-I. Sera from hypox, GH-treated hypox and sham-operated rats were incubated with either ¹²⁵I-IGF-I or ¹²⁵I-des(1–3)IGF-I and analyzed by Sephacryl S-200 chromatography. Under the conditions used, ¹²⁵I-des(1–3)IGF-I was recovered exclusively in the 7·5 kDa peak when incubated with serum from sham-operated rats. After incubation with sera from hypox or GH-treated hypox rats approximately 20% of the ¹²⁵I-des(1–3)IGF-I was recovered in the 50 kDa peak with the remaining radioactivity recovered as free peptide. These observations suggest that the generation of des(1–3)IGF-I may be inversely regulated by GH and may represent yet another site of GH regulation of IGF-I action. The changes in the pattern of serum IGFBPs which occur in GH deficiency are unlikely to negate the enhanced generation of des(1–3)IGF-I by increasing binding capacity for this IGF-I variant.

Journal of Endocrinology (1995) 146, 141–148

We have recently identified in serum an acid protease which is capable of generating des(1-3)IGF-I from intact IGF-I. Here we have utilized a synthetic substrate with the sequence, biotin-G-P-E-T-L-C-BSA which contains the N-terminal sequence of IGF-I, to investigate the levels of this protease activity in streptozotocin-diabetic rats. Protease activity, quantified in terms of the amount of the biotin label lost, was determined in serum and hepatic extracts from normal control rats, diabetic rats and insulin-treated diabetic rats. Both the serum protease activity and protease activity in hepatic extracts were significantly increased in diabetic rats compared with control rats (P<0.02 and P<0.005). Following acute administration of insulin, a rapid and marked reduction in serum protease activity was observed; with an approximately 50% reduction apparent at 30 min (P<0.001). Chronic insulin treatment of diabetic rats also significantly reduced the serum and hepatic protease activity to the levels seen in control rats. A positive correlation between protease activity and serum glucose level was observed (r=0.58, P<0.005). The abundance of Spi 2.1 mRNA, a serine protease inhibitor, capable of inhibiting the IGF-I protease activity in vitro, was significantly decreased in the liver of diabetic rats and insulin treatment of diabetic rats did not normalize Spi 2.1 mRNA levels. These data suggest that the conversion of IGF-I to the more active des(1-3)IGF-I variant may be enhanced in diabetic animals. Since serum IGF-I levels are reduced in diabetic rats, increased des(1-3)IGF-I-generating protease activity would enhance the functional activity of the circulating IGF-I.

ABSTRACT

While prostaglandin F_2α (PGF_2α) has been thought to be a natural luteolysin in non-primates, a luteolytic effect in the human corpus luteum is less evident. We therefore investigated the action of PGF_2α on monolayer cultures of human luteal cells obtained from mid-luteal phase corpora lutea.

PGF_2α increased basal and human chorionic gonadotrophin (hCG)-stimulated progesterone production by human cultured luteal cells. A potent tumour-promoting phorbol ester, phorbol 12-myristate-13-acetate (PMA), also stimulated progesterone production by cultured human luteal cells.

Although human luteal cells were incubated for 24 h with PMA, hCG was still able to stimulate the production of progesterone by PMA-pretreated cells. However, PMA pretreatment blocked the ability of PGF_2α to stimulate progesterone production. It is possible that the luteotrophic effect of PGF_2α may be mediated, in part, by the activation of protein kinase C.

Addition of PGF_2α to suspensions of human luteal cells preincubated with myo-[2-³H]inositol promoted an increase in labelled inositol phosphates. PGF_2α also rapidly increased intracellular free Ca²⁺ in human luteal cells loaded with the fluorescent Ca²⁺ probe, fura-2.

We conclude that PGF_2α and PMA stimulate progesterone production and that PGF_2α increases the intracellular free calcium and inositol phosphates of human cultured luteal cells in the mid-luteal phase.

Journal of Endocrinology (1992) 133, 451–458

Accumulating evidence indicates that menaquinone-4 (MK-4), a vitamin K(2) with four isoprene units, inhibits osteoclastogenesis in murine bone marrow culture, but the reason for this inhibition is not yet clear, especially in human bone marrow culture. To clarify the inhibitory mechanism, we investigated the differentiation of colony-forming-unit fibroblasts (CFU-Fs) and osteoclasts in human bone marrow culture, to learn whether the enhancement of the differentiation of CFU-Fs from progenitor cells might relate to inhibition of osteoclast formation. Human bone marrow cells were grown in alpha-minimal essential medium with horse serum in the presence of MK-4 until adherent cells formed colonies (CFU-Fs). Colonies that stained positive for alkaline phosphatase activity (CFU-F/ALP(+)) were considered to have osteogenic potential. MK-4 stimulated the number of CFU-F/ALP(+) colonies in the presence or absence of dexamethasone. The stimulation was also seen in vitamin K(1) treatment. These cells had the ability to mineralize in the presence of alpha-glycerophosphate. In contrast, both MK-4 and vitamin K(1) inhibited 1,25 dihydroxyvitamin D(3)-induced osteoclast formation and increased stromal cell formation in human bone marrow culture. These stromal cells expressed ALP and Cbfa1. Moreover, both types of vitamin K treatment decreased the expression of receptor activator of nuclear factor kappaB ligand/osteoclast differentiation factor (RANKL/ODF) and enhanced the expression of osteoprotegerin/osteoclast inhibitory factor (OPG/OCIF) in the stromal cells. The effective concentrations were 1.0 microM and 10 microM for the expression of RANKL/ODF and OPG/OCIF respectively. Vitamin K might stimulate osteoblastogenesis in bone marrow cells, regulating osteoclastogenesis through the expression of RANKL/ODF more than through that of OPG/OCIF.

ABSTRACT

A rat oestrogen receptor-β-galactosidase fusion protein was expressed using a pEX2/rat oestrogen receptor cDNA construct. Scatchard analysis of [³H]oestradiol-17β binding to the cell lysate revealed that the fusion protein had functional binding sites specific for oestradiol with a dissociation constant of 1·49 nmol/l. The relative molecular weight (M _r) of the fusion protein was determined as 180 000 by immunoblot analysis of the cell lysate employing a monoclonal antibody to the human oestrogen receptor.

The protein was isolated by means of SDS-PAGE and subsequent electroblotting. By immunization with the purified materials on nitrocellulose membrane, a polyclonal antibody to the rat oestrogen receptor was raised in a rabbit. Binding of [³H]oestradiol to the oestrogen receptor from the rat uterus was inhibited by the antibody in a dose-dependent manner. The antibody was also able to recognize the oestrogen receptor occupied by [³H]oestradiol. Thus, the antibody could react with both forms of the receptor molecule, either occupied or unoccupied by the hormone. In immunoblot analysis of the cytosol fraction of the rat uterus, a single band of M _r 67 000, the size of the oestrogen receptor, was detected by the antibody. Moreover, when the antibody was applied to immunohistochemical examination of paraffin-embedded pituitary and brain sections of the rat, immunostaining was observed in cells of the anterior pituitary and in neurones in specific regions of the brain. The immunoreactivity was restricted exclusively to cell nuclei in both tissues.

These results demonstrate that the polyclonal antibody obtained in the present study was specific to the oestrogen receptor, and that it would be a powerful tool to detect and analyse the receptors in various target tissues for oestrogen.

Journal of Endocrinology (1992) 135, 333–341

ABSTRACT

The present studies were carried out to investigate the effect of several growth factors on human endometrial stromal cells.

In human endometrial stromal cells, bombesin and bradykinin provoked an increase in intracellular free Ca²⁺ and in labelled inositol phosphates when pre-incubated with [³H]myoinositol. Some or possibly all of the initial increase in intracellular free Ca²⁺ represented a mobilization of Ca²⁺ from intracellular stores and the second phase of the response depended on Ca²⁺ influx from the extracellular medium.

[³H]Thymidine was added to human cultured endometrial stromal cells with bombesin, bradykinin, epidermal growth factor (EGF), prostaglandin F_2α, vasopressin and platelet-derived growth factor. Bombesin, bradykinin and EGF stimulated the incorporation of [³H]thymidine into DNA in quiescent cells.

In conclusion, bombesin and bradykinin are growth factors which activate phospholipase C in human endometrial stromal cells, while EGF stimulates DNA synthesis without the activation of phospholipase C.

Journal of Endocrinology (1991) 131, 313–318

Abstract

Arachidonate 12-lipoxygenase, which oxygenates positions 12 and 13 of arachidonic and linoleic acids, is present in porcine anterior pituitary cells. Colocalization of the 12-lipoxygenase with various pituitary hormones was examined by immunohistochemical double-staining using antibodies against 12-lipoxygenase and various anterior pituitary hormones. Under light microscopy, approximately 7% of the cells producing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were positive for 12-lipoxygenase, whereas the enzyme was detected in less than 2% of the cells producing thyrotrophin, prolactin, growth hormone (GH), and adrenocorticotrophin. In an attempt to examine the participation of 12-lipoxygenase metabolites in pituitary hormone release, we incubated the primary culture of porcine anterior pituitary cells with 12-hydroperoxy-arachidonic acid or 13-hydroperoxy-linoleic acid. Significant stimulation of LH and FSH release by these hydroperoxides was observed at 10 μm in a time-dependent manner. At doses around 10 μm these compounds produced responses of similar magnitude to 1 nm gonadotrophin-releasing hormone (GnRH), but higher concentrations (30 μm) of the compounds were required for GH release. In contrast, 12-hydroxy-arachidonic and 13-hydroxy-linoleic acids were almost ineffective. Furthermore, the gonadotrophin release by 1 nm GnRH was inhibited by nordihydroguaiaretic acid (a lipoxygenase inhibitor) with an IC₅₀ of about 5 μm. Thus, the hydroperoxy (but not hydroxy) products of 12-lipoxygenase may be involved in the release of pituitary hormones especially LH and FSH.

Journal of Endocrinology (1996) 148, 33–41

ABSTRACT

Immunohistochemical localization of 17α-hydroxylase/C17-20 lyase (P-450_17α,lyase) and aromatase cytochrome P-450 (P-450_arom) in polycystic ovary (PCO) syndrome was studied using specific polyclonal antibodies which had been raised against the corresponding enzymes. In the majority of follicles that were atretic and smaller than 7 mm in diameter, theca interna cells showed high P-450_17α,lyase immunoreaction, while small numbers of granulosa cells showed little P-450_arom immunoreaction. In some atretic follicles that were larger than 11 mm in diameter, the hyperplastic theca interna cell layer showed high immunoreaction to P-450_17α,lyase, while the poorly proliferated granulosa cell layer showed a mixture of weak and negative immunoreaction to P-450_arom. No immunoreaction to P-450_17α,lyase or P-450_arom was recognized in PCO stroma. These findings suggest that the theca interna cells and the granulosa cells from PCOs show abnormal steroidogenic function, while the localization of P-450_17α,lyase and P-450_arom in PCOs was essentially identical to that in the normal ovary. Theca interna cells in PCO atretic follicles are the main site of excess androgen production.

Journal of Endocrinology (1993) 139, 503–509

Cytokines and steroid hormones use different sets of signal transduction pathways, which seem to be unrelated. Interleukin-6 (IL-6) uses JAK tyrosine kinase and STAT (signal transducer and activator of transcription) transcription factor. Glucocorticoid binds glucocorticoid receptor (GR), which is a member of the steroid receptor superfamily. We have studied the crosstalk between the IL-6-JAK-STAT and glucocorticoid-nuclear receptor pathways. IL-6 and glucocorticoid synergistically activated the IL-6 response element on the rat alpha2-macroglobulin promoter (APRE)-driven luciferase gene. The exogenous expression of GR enhanced the synergism. The exogenous expression of dominant negative STAT3 completely abolished the IL-6 plus glucocorticoid-induced activation of the APRE-luciferase gene. Tyrosine phosphorylation of STAT3 stimulated by IL-6 alone was not different from that by IL-6 plus glucocorticoid. The protein level of STAT3 was also not increased by glucocorticoid stimulation. The time course of STAT3 tyrosine phosphorylation by IL-6 plus glucocorticoid was not different from that by IL-6 alone. The synergism was studied on the two other IL-6 response elements, the junB promoter (JRE-IL-6) and the interferon regulatory factor-1 (IRF-1) promoter (IRF-GAS) which could be activated by STAT3. The synergistic activation by glucocorticoid on the IL-6-activated JRE-IL-6 and the IRF-GAS-driven luciferase gene was not detected. Glucocorticoid did not change the mobility of IL-6-induced APRE-binding proteins in a gel shift assay. These results suggest that the synergism was through the GR and STAT3, and the coactivation pathway which was specific for APRE was the target of glucocorticoid.

In this study we describe a novel mutation of the thyroid peroxidase (TPO) gene that resulted in a total iodide organification defect. TPO activity and thyroxine formation in thyroglobulin in the thyroid gland of the patient were below the limits of detection. However, TPO mRNA was detectable at a similar size and concentration as compared with normal thyroid tissues when measured by Northern blot analysis. Sequence analysis of the TPO gene showed the presence of two mutations, a missense mutation in exon 7 and C insertion in exon 14. These mutations were heterozygous and located in different alleles. The latter mutation has already been reported as one of the mutations of the TPO gene resulting in total iodide organification defect. The former mutation was further analysed by mRNA transfection studies in which mutated mRNA was transfected to CHO-K1 cells by electroporation. The results of transfection studies showed that the cells transfected with mutated mRNA expressed similar size TPO molecules to those of cells transfected with wild-type mRNA but that they lacked TPO activity. The two mutations of the TPO gene resulting in the total iodide organification defect in the patient cosegregated from her parents.