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Query: EC:3.1.26.9 (ribonuclease)
 6,589 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of hCG, 8-bromo-cAMP, 4 beta-phorbol 12 beta-myristate 13 alpha-acetate, and forskolin on insulin-like growth factor-I (IGF-I) receptor gene expression of Leydig cells were studied. The treatment of purified Leydig cells with hCG caused a dose-dependent increase in [125I]IGF-I binding to Leydig cells without changes in binding affinity, indicating that the increased binding was due to increased receptor numbers and not to increased affinity. The minimal time required for hCG to induce IGF-I binding was 6 h, and it had reached a plateau at 16 h. 8-Bromo-cAMP (1 mM) increased IGF-I binding about 2-fold, and forskolin (10 microM) increased binding about 51%. Using the ribonuclease protection assay, we found that hCG and 8-bromo-cAMP could increase IGF-I receptor mRNA expression as early as 2 h before the increase in IGF-I binding. The induction by hCG was over 3.5-fold at 4 h and decreased to about 2-fold at 6 h. 4 beta-Phorbol 12 beta-myristate 13 alpha-acetate had a very small effect on IGF-I receptor mRNA levels (1.5-fold increase at 2 h and no changes at 4 and 6 h). In conclusion, IGF-I receptors can be up-regulated by hCG, 8-bromo-cAMP, and forskolin. The up-regulation of IGF-I receptor number is associated with transient increases in IGF-I receptor mRNA levels. This could be a mechanism by which hCG and IGF-I interact to enhance Leydig cell steroidogenesis.
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PMID:Human chorionic gonadotropin up-regulates insulin-like growth factor-I receptor gene expression of Leydig cells. 165 15

This article presents a detailed overview of the conceptual and technical considerations involved in the measurement of insulin-like growth factor-I (IGF-I) mRNAs in leukocytes. Two different quantitative techniques that take advantage of the in vitro synthesis of antisense and sense synthetic IGF-I RNA, respectively, are described: the ribonuclease protection assay (commonly referred to as solution hybridization) and competitive RT-PCR. We have improved the ribonuclease protection assay by constructing tandem, cassette riboprobes to generate multigene antisense RNAs of varying sizes. This approach permits the simultaneous quantitation of two or more mRNAs in a single RNA sample, one of which can serve as an internal standard for comparison of IGF-I transcripts among various treatments. The second approach of competitive RT-PCR represents an improvement in previous technologies by cloning a competing IGF-I sequence into an RNA expression vector. The resulting synthetic sense competitor IGF-I RNA (1.1 kb) serves as an internal standard during both the reverse transcription and amplification steps. We have used both the ribonuclease protection assay and competitive RT-PCR to define the macrophage as the major cellular source of leukocyte-derived IGF-I and to characterize these macrophage-derived mRNAs as being derived almost exclusively from exon 1. In addition, these techniques have allowed us to study the ontogeny of IGF-I expression in differentiating bone marrow macrophages and show that hematopoietic progenitors are induced to express abundant IGF-I transcripts as they differentiate into macrophages in the presence of CSF-1. These techniques can be readily adapted for measuring steady-state transcripts for a variety of leukocyte-derived hormones.
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PMID:Theoretical and functional aspects of measuring insulin-like growth factor-I mRNA expression in myeloid cells. 784 52

Autocrine expression of polypeptide growth factors may be important in the growth regulation of cancer cells. Different growth factor activities have been identified in a variety of tumors. This article describes a case of malignant ascites in a patient recently treated for breast cancer. The use of growth factor mRNA expression as a factor to differentiate between breast and ovarian origins of cancer cells contained in malignant ascites was examined. Expression of insulin-like growth factor-I (IGF-I), IGF-II, and transforming growth factor alpha mRNA was examined by ribonuclease protection assay. The tumor cells expressed IGF-II and transforming growth factor alpha, but not IGF-I mRNA. This pattern of growth factor expression is compatible with a breast cancer primary of the malignant cells contained in the ascites fluid. Therefore, IGF-I mRNA expression may be useful in distinguishing between adenocarcinomas of breast or ovarian origins.
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PMID:Case report: use of insulin-like growth factor-I gene expression to distinguish between breast and ovarian cancer. 814 Nov 35

The effects of feed restriction and refeeding on ovarian and hepatic insulin-like growth factor-I (IGF-I) gene expression, systemic and ovarian IGF-I concentrations and on associated metabolic changes were measured in prepubertal gilts. Eleven pairs of littermate gilts (70.7 +/- 4.7 kg) were placed on a maintenance level of feeding for 7 days (days 1-7). On day 8, littermates were either fed at a maintenance level of energy or fed to appetite for a further 6 days. Blood samples were taken on day 13 (07.00-16.00 h) to determine plasma insulin and IGF-I, and on day 14 (02.00-06.00 h) to determine plasma GH levels. Following slaughter on day 14, one ovary from each animal was retained to measure follicular fluid IGF-I and oestradiol concentrations. The remaining ovary and a sample of liver were retained for IGF-I mRNA analysis using a ribonuclease protection assay. Six days of refeeding significantly increased plasma IGF-I (P < 0.005) and basal insulin (P < 0.05) but there was no effect on plasma GH. Ovarian follicular volume and diameter were significantly larger after refeeding (P < 0.05), with no effect on follicular fluid oestradiol concentrations. Mean follicular fluid IGF-I concentrations were unaffected by treatment. However, the relationships between individual follicular IGF-I concentrations, absolute follicular fluid IGF-I contents and follicle volume were affected by feeding level (P < 0.05). Regression analysis of the same data also revealed that at this stage of maturity, small follicles had greater follicular fluid concentrations of IGF-I than larger follicles. Refeeding increased the amount of IGF-I mRNA in hepatic but not ovarian tissue. We conclude that there is differential regulation of the IGF-I gene in porcine hepatic and ovarian tissues, and that ovarian factors other than, or as well as, IGF-I are involved in the regulation of ovarian responses to refeeding.
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PMID:Ovarian and hepatic insulin-like growth factor-I gene expression and associated metabolic responses in prepubertal gilts subjected to feed restriction and refeeding. 825 87

Osteoblast-enriched (Ob) cultures isolated from fetal rat bone synthesize insulin-like growth factor-I (IGF-I), which functions as a locally acting growth and differentiation factor in the skeleton. Consistent with prior studies demonstrating that IGF-I production is enhanced in bone by agents that induce cAMP, prostaglandin E2 (PGE2) stimulates both cAMP synthesis and IGF-I mRNA in Ob cells. However, little is known about how cAMP regulates IGF-I expression in this or any other cell system. In rat tissues, multiple mechanisms influence levels of IGF-I mRNA, including transcription from two promoters, differential RNA splicing and stability, and alternative RNA polyadenylation. To determine how cAMP influences IGF-I gene expression in Ob cultures, we examined the responses of these cells to treatment with PGE2. PGE2 rapidly enhanced the accumulation of both large and small IGF-I transcripts, with increases in IGF-I mRNA detected within 2 h of treatment and persisting for 24 h. Analysis of precursor RNA by a highly specific and sensitive ribonuclease protection assay demonstrated a rise in nascent IGF-I mRNA within 30 min of exposure to PGE2, with a peak stimulation of 4-fold above control levels seen by 2 h and levels remaining elevated for up to 24 h. IGF-I transcripts in Ob cells were directed only by promoter 1, the more 5' of the two rat IGF-I gene promoters. As additionally assessed using the RNA polymerase II inhibitor 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole, PGE2 treatment had little effect on IGF-I mRNA stability. In aggregate, these studies show that in fetal rat Ob cultures, PGE2 enhances IGF-I gene expression primarily through transcriptional mechanisms that are limited to a single IGF-I gene promoter. Ob cells, therefore, may be an excellent model for determining how cAMP regulates IGF-I gene transcription.
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PMID:Prostaglandin E2 rapidly stimulates insulin-like growth factor-I gene expression in primary rat osteoblast cultures: evidence for transcriptional control. 839 6

Hemopoietic cells have been reported to synthesize insulin-like growth factor-I (IGF-I) messenger RNA (mRNA), but the relative contribution of specific cell lineages that express these transcripts remains unknown. Reverse transcription and amplification of complementary DNA (cDNA) by the polymerase chain reaction were used to characterize full-length IGF-I mRNA transcripts in murine hemopoietic cells. The identity of transcripts encoding the entire prepropeptide was confirmed by restriction endonuclease digestion, Southern blotting, cloning, and Sanger sequencing. Abundance of IGF-I mRNA transcripts was assessed both by Northern blotting and sensitive ribonuclease protection assays followed by quantification with Phosphor-Imager analysis. Whereas IGF-I cDNA transcripts could be detected in a variety of leukocytes after polymerase chain reaction amplification, IGF-I mRNA was negligible or nondetectable in T and B cell lines and in those tissues containing a predominance of these cell types (e.g. spleen and thymus) by Northern blotting and ribonuclease protection assays. In contrast, elicited peritoneal macrophages, a macrophage cell line, microglia, and bone marrow macrophages differentiated in vitro expressed abundant IGF-I mRNA transcripts, whereas neither a premyeloid cell line nor freshly isolated bone marrow cells expressed significant transcripts. The 5'-identity of macrophage IGF-I transcripts was established using an exon 2-derived IGF-I cDNA probe. All protected transcripts were foreshortened, indicating transcript initiation exclusively within exon 1, characteristic of extra-hepatic IGF-I mRNA. However, at the 3'-end, both IGF-I Ea (lacking exon 5) and IGF-I Eb (containing exon 5) mRNA transcripts were evident, with the Eb product being detected at levels similar to those present in hepatic cellular RNA. A large molecular size (26 kilodaltons) prepro-IGF-I peptide was also detected in macrophage cell lysates by Western blotting. Collectively, our observations show that: 1) among hemopoietic cells, myeloid rather than lymphoid cells are the major source of IGF-I; 2) macrophage IGF-I mRNA consists of class I Ea and Eb transcripts; 3) these transcripts are translated into protein; and 4) expression of IGF-I is directly associated with differentiation of bone marrow macrophages.
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PMID:Murine macrophages express abundant insulin-like growth factor-I class I Ea and Eb transcripts. 840 86

GH appears to play an important metabolic role during late pregnancy and in lactation maintenance. In this study, pregnant (days 8, 15, and 20 of gestation) and postpartum (days 3 and 8 postpartum, including lactating and nonlactating dams) Wistar rats were used to investigate pituitary GH gene expression and hormone secretion, and the potential alterations of the major signals regulating GH secretion and action [somatostatin (SS) and GH-releasing hormone (GHRH), GH receptor (GH-R), and insulin-like growth factor-I (IGF-I)]. GH and SS messenger RNA (mRNA) were quantitated by Northern blot, and both IGF-I and GH-R mRNA were analyzed by the ribonuclease protection assay technique. Pituitary IR-GH content and GH mRNA increased at midpregnancy. IR-GH content was decreased in lactating rats. Plasma GH levels progressively increased during pregnancy, whereas no significant alterations were shown during lactation. Elevated GH levels persisted during lactation. Levels at this time were higher in nonsuckling compared with suckling dams. Liver GH-R mRNA progressively decreased during pregnancy, but it remained unchanged during lactation. Plasma IGF-I and liver IR-IGF-I constantly decreased during pregnancy, and no significant modifications were seen either in suckling or in nonsuckling animals. IGF-I mRNA accumulation in the liver decreased during pregnancy. After delivery, a progressive decrease of liver IGF-I mRNA occurred. At the hypothalamic level, a progressive increase in the IR-SS content was found during pregnancy, with no SS mRNA modification. After delivery, a higher hypothalamic IR-SS content was found in lactating than in nonlactating rats, with no changes in SS mRNA levels. Hypothalamic IR-IGF-I also showed a progressive increase during pregnancy with no significant alterations during lactation. Hypothalamic IR-GHRH presented a nonsignificant mild increase during pregnancy with no modifications during lactation. In the pituitary, IR-IGF-I content progressively increased during gestation, reaching its highest concentration at day 20. During lactation, pituitary IGF-I did not change. In summary, our data show that the mechanisms of the increase in plasma GH levels occurring during pregnancy include an increase in GH gene expression in the pituitary, a decrease in SS secretion from the hypothalamus, an increase in IR-IGF-I content in the hypothalamus and in the pituitary, and a significant decrease in circulating IGF-I. Plasma and liver IR-IGF-I and IGF-I mRNA in the liver decreased throughout gestation due to a lower GH-R gene expression in the liver. This state of GH resistance with a higher GH/IGF-I ratio could be important in providing supplementary nutrients to the fetus. During lactation, GH and its regulatory machinery did not show important modifications.
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PMID:Regulation of growth hormone (GH) gene expression and secretion during pregnancy and lactation in the rat: role of insulin-like growth factor-I, somatostatin, and GH-releasing hormone. 923 98

Down-regulation of the progesterone receptor (PR) by its ligand has been demonstrated in breast cancer cell lines and in the rat uterus. However, in the stromal cells of endometrium, reduction of the PR level is not apparent in the luteal phase of the menstrual cycle. The purpose of this study was to determine the effect of progestin on PR and PR mRNA in isolated human endometrial stromal cells. Western blot analysis showed that progesterone or medroxyprogesterone acetate increased the two isoforms, PR-A and PR-B, in stromal cells but reduced them in glandular epithelial cells. Progestin increased the PR-A and PR-B mRNA by 2- to > 10-fold in the stromal cells of 12 specimens measured by solution hybridization-ribonuclease protection assay. A time study showed that the increase in PR mRNA required at least a 2- to 3-day incubation with progestin and that the high mRNA levels were maintained or increased slightly beyond 10 days of progestin incubation. The stimulatory effect of progestin was inhibited by RU-486 and by cycloheximide, suggesting that the up-regulation requires ligand binding to PR and de novo protein synthesis. Progestin also increased the stability of PR mRNA in endometrial stromal cells. These results demonstrated for the first time that progestin exerts an up-regulation of PR by increasing the steady-state level of PR mRNA specifically in human endometrial stromal cells. The up-regulation of PR by progestin may be mediated in part by progestin-induced endometrial stromal cell factors such as estrogen and insulin-like growth factor-I, both of which stimulated the PR-A and PR-B mRNA in stromal cells.
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PMID:Regulation of progesterone receptor messenger ribonucleic acid by progestin in human endometrial stromal cells. 940 41

The immortalized GT1-7 cell line synthesizes and secretes GnRH, the key hormone of reproduction. However, GT1-7 cells lack the normal inputs from neurotransmitters, growth factors, and steroids, which are involved in the maturation and maintenance of GnRH neurons in the brain. We examined the effects of the neurotrophic factor insulin-like growth factor-I (IGF-I) on GnRH gene expression and the mechanism for these changes. Initially, effects of IGF-I on GnRH gene expression were determined by ribonuclease protection assay. In time-course experiments, IGF-I treatment caused significant increases in nuclear GnRH primary transcript levels, an index of GnRH gene transcription, 4 and 8 h after initiation of IGF-I treatment. GnRH messenger RNA (mRNA) levels in the cytoplasm were stimulated by IGF-I at 24 h of treatment. IGF-I also affected GT1-7 cell morphology, with an increase in process extension and cell-cell contacts. In contrast, GnRH peptide levels in the medium were initially stimulated and then suppressed by IGF-I, indicating an uncoupling of biosynthesis and secretion. The increase in GnRH mRNA levels induced by IGF-I is probably caused by a transcriptional mechanism, as evidenced by the increase in GnRH primary transcript levels before a change in GnRH mRNA levels, as well as our finding of a similar GnRH mRNA half-life for both control and IGF-I-treated cells. Interestingly, GT1-7 cells themselves were observed to express IGF-I immunoreactivity, suggesting the possibility of autoregulation by this neurotrophic factor. It is concluded that IGF-I is an important modulator of GnRH gene expression and release in the GT1-7 cell line. The reported stimulatory effects of IGF-I in vivo, and its hypothesized role in the development of GnRH neurons in the brain, suggest that IGF-I may make the GT1-7 cells line more like a mature GnRH neuron, as a model for future studies.
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PMID:Insulin-like growth factor-I effects on gonadotropin-releasing hormone biosynthesis in GT1-7 cells. 949 46

Insulin-like growth factor-I (IGF-I) plays an essential role in reproductive function. Leydig cells express specific IGF-I receptors, and IGF-I enhances human chorionic gonadorphin (hCG)-induced testosterone formation. In the present study, we evaluate the effect of IGF-I on the gene expression and protein levels of steroidogenic acute regulatory protein (StAR), the rate-limiting step in steroidogenesis. StAR mRNA is expressed in rat Leydig cells as two major transcripts of 3.8 and 1.7 kb. StAR mRNA levels (both 3.8 and 1.7 kb) were markedly induced about 20-fold by hCG (10 ng/mL). Concomitant addition of IGF-I (50 or 100 ng/mL) and hCG (10 ng/mL) resulted in significant increases in StAR and cytochrome P450 side-chain cleavage (P450scc) mRNA levels, whereas lower doses of IGF-I (1 or 10 ng/ mL) had small effects. Synergistic effects of IGF-I and hCG on StAR mRNA levels were confirmed by ribonuclease protection assay (RPA). IGF-I (100 ng/mL) enhanced hCG- and 20 OH-cholesterol + hCG-induced testosterone formation, whereas the conversions of pregnenolone, 17-OH pregnenolone, dehydroepiandrosterone, and androstenedione to testosterone were not affected. This suggests that the major effect of IGF-I is at the steps of StAR and P450scc, whereas other steroidogenic enzymes are not affected. To evaluate whether increased StAR mRNA levels induced by IGF-I and hCG are associated with increased StAR protein levels, we carried out Western blot analyses. Basal StAR protein levels were low after 24 h in culture. hCG (10 ng/mL) increased StAR protein by 4.5-fold. In the presence of IGF-I (100 ng/mL), hCG-induced StAR protein levels were further increased. In conclusion, our present study demonstrated that IGF-I enhances Leydig cell steroidogenesis by upregulating hCG-induced StAR gene expression and protein production.
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PMID:Upregulation of human chorionic gonadotrophin-induced steroidogenic acute regulatory protein by insulin-like growth factor-I in rat Leydig cells. 966 48


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