Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.6.1.1 (adenylate cyclase)
 19,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The maturation of ovarian granulosa cells is dependent upon the pituitary gonadotropin FSH, the actions of which are mediated via specific plasma membrane receptors. To study the regulation of ovarian FSH receptor expression at the mRNA level, we used a specific cRNA probe to evaluate changes in FSH receptor transcripts in cultured granulosa cells. Granulosa cells obtained from immature estrogen-treated rats contained two predominant FSH receptor mRNA transcripts (7.0 and 2.5 kilobases), the levels of which declined in a time-related manner during a 2-day culture period. However, inclusion of FSH (30 ng/ml) in the culture medium prevented the decline in FSH receptor mRNA levels. Compared to controls, treatment of granulosa cells for 48 h with FSH (1-100 ng/ml) increased FSH receptor mRNA levels in a dose-dependent manner (ED50, 4.5 ng/ml), with a maximal 5.9 +/- 0.7-fold increase observed in response to 30 ng/ml FSH. The stimulatory actions of FSH were mimicked by the adenyl cyclase activator forskolin (0.1-30 microM), suggesting the involvement of cAMP in FSH receptor gene transcription and/or mRNA stability. Incubation of granulosa cells for 48 h with epidermal growth factor (EGF; 0.3-10 ng/ml), basic fibroblast growth factor (bFGF; 1-30 ng/ml), or insulin-like growth factor-I (IGF-I; 1-30 ng/ml) did not affect basal FSH receptor mRNA levels, whereas the highest doses of EGF and bFGF, but not IGF-I, completely suppressed the stimulatory effects of FSH (30 ng/ml) on its own receptor mRNA levels. Similarly, GnRH (10-1000 nM) attenuated the actions of FSH on its receptor mRNA levels in a dose-dependent manner (ID50, 8 nM). The inhibitory effects of GnRH (100 nM) were reversed by cotreatment with a GnRH antagonist ([Ac-D-Phe1,D-pCl-Phe2,D-Trp3,6]GnRH; 100 nM), indicating that the actions of GnRH are mediated via specific GnRH receptors. These data indicate that treatment of granulosa cells with FSH increases the levels of two FSH receptor mRNA transcripts. However, this positive feedback system, which may lead to an amplification of FSH action, is tightly regulated by the inhibitory actions of EGF, bFGF, and GnRH. Thus, the use of cultured rat granulosa cells provides a model system to analyze the hormonal regulation of FSH receptor gene expression in the ovary.
 ...
PMID:Hormonal regulation of follicle-stimulating hormone receptor messenger ribonucleic acid levels in cultured rat granulosa cells. 131 Dec 35

Somatostatin, a cyclic tetradecapeptide, is both a hypothalamic hormone and a paracrine peptide, with effects on many tissues. Despite the fact that somatostatin can inhibit various cellular events in a number of cell lines, somatostatin is a constituent of medium defined for optimal growth of FRTL5, a line of differentiated and nontransformed rat thyroid follicular cells. In the present study we have evaluated the role of somatostatin in the control of DNA synthesis in FRTL5 cells and have investigated the mechanisms of somatostatin interaction with pathways stimulated by TSH and insulin-like growth factor-I (IGF-I). Somatostatin inhibits TSH-stimulated DNA synthesis and cell proliferation in FRTL5 cells. Maximal effects are observed at somatostatin concentrations of 0.1-10 ng/ml, and the effects are diminished at somatostatin concentrations above 10 ng/ml. Somatostatin also inhibits (Bu)2cAMP-stimulated DNA synthesis, suggesting that the loci of somatostatin action are both proximal and distal to activation of adenylate cyclase. Somatostatin also inhibits DNA synthesis stimulated by insulin-like growth factor-I (IGF-I), a pleiotropic growth factor that works through non-cAMP-dependent pathways. The somatostatin analog octreotide is more potent than native somatostatin in inhibiting DNA synthesis stimulated by either TSH or IGF-I. Somatostatin does not alter TSH or IGF-I binding to FRTL5, demonstrating that somatostatin affects the postreceptor signal transduction pathways stimulated by these factors. We conclude that 1) the use of somatostatin in hormone-supplemented medium for FRTL5 is unnecessary and may inhibit cell growth; 2) somatostatin can inhibit the direct effects of IGF-I on peripheral tissues in addition to its ability to interfere with IGF-I synthesis by inhibiting the synthesis and release of pituitary GH; and 3) somatostatin is a useful tool for dissecting the pathways involved in mediating differentiated function and growth of FRTL5 cells.
 ...
PMID:Somatostatin inhibits deoxyribonucleic acid synthesis induced by both thyrotropin and insulin-like growth factor-I in FRTL5 cells. 197 59

Adenosine inhibits TSH-stimulated [3H]thymidine incorporation into DNA in FRTL5 thyroid follicular cells by both inhibiting cAMP generation and acting at a locus beyond adenylate cyclase. On the other hand, adenosine markedly potentiates DNA synthesis in FRTL5 stimulated by insulin-like growth factor-I (IGF-I). The mechanisms of this latter effect are unknown, but require the coincubation of adenosine and IGF-I and not mediated by an increase in intracellular cAMP concentration. Adenosine increases the maximal response of FRTL5 to [3H]thymidine incorporation stimulated by IGF-I and increases the sensitivity of FRTL5 to IGF-I. These effects of adenosine are reflected by an increase in nuclear labeling as well as by an increase in [3H]thymidine incorporation into DNA. Adenosine also plays a role as an autocrine growth factor in FRTL5, since adenosine deaminase increases the response of these cells to TSH. The effects of adenosine on both TSH- and IGF-I-stimulated DNA synthesis are shared by guanosine and inosine, although with different potencies for the various guanine nucleosides. Inosine potentiates IGF-I-stimulated DNA synthesis, but inhibits TSH-stimulated DNA synthesis only weakly. Adenosine interacts with multiple receptors and with multiple postreceptor pathways in FRTL5 to produce divergent effects on the control of cell replication by two growth factors (TSH and IGF-I) that act through different postreceptor pathways.
 ...
PMID:Adenosine has divergent effects on deoxyribonucleic acid synthesis in FRTL5 cells: inhibition of thyrotropin-stimulated and potentiation of insulin-like growth factor-I-stimulated thymidine incorporation. 247 35

The present study shows that pretreatment of BAC cells with insulin or insulin-like growth factor-I (IGF-I) enhances the cAMP response to maximal concentrations of ACTH and cholera toxin. However, the effects of IGF-I at a nanomolar concentration (50 ng/ml) were higher than for insulin at the same concentration but similar for insulin at a micromolar concentration (10 micrograms/ml). We have investigated whether the effects of the two peptides can be related to some modifications of the guanine nucleotide regulatory binding protein Gs. Insulin enhanced Gs as observed by ADP ribosylation and immunoblotting but the effects were approximately the same at nanomolar and micromolar concentrations; again, the effects of IGF-I (50 ng/ml) were higher. These results indicate that both IGF-I and insulin increase the Gs complex of adenylate cyclase, but IGF-I is more potent than insulin at physiological concentrations.
 ...
PMID:Insulin-like growth factor-I and insulin increase the stimulatory guanine nucleotide binding protein (Gs) in cultured bovine adrenal cells. 255 33

Numerous reports have appeared in the literature indicating phenotypic heterogeneity among cells of the osteoblastic lineage. This diversity may be due to either certain stages of differentiation or a subspecialization of already terminally differentiated osteoblasts. To obtain answers to this question, we report on studies undertaken to clone bone cell populations from 1 day postnatal rat calvaria which express well defined differences in phenotype. To achieve this goal, we have used the soft agarose cloning technique which previously has almost exclusively been applied to clone cells of neoplastic origin. The reason for being able to employ this method is based on the fact that bone cells can be induced by transforming growth factor-beta to reversibly acquire the transformed phenotype, an event expressed by anchorage-dependent bone cells to form progressively growing colonies in soft agarose. Individual colonies, harvested from agarose, were expanded to clonal bone cell populations. Characterizing 48 cell clones by detection of osteoblastic cell markers such as alkaline phosphatase activity, PTH- and prostaglandin-E2-induced adenylate cyclase activity, osteocalcin mRNA synthesis, as well as collagen synthesis, 7 subsets of osteoblastic cell types were identified. Each subset was found to express a distinct phenotype, indicated by the absence or presence of osteoblastic cell markers. Some clones, previously found not to exhibit any osteoblastic traits, developed PTH responsiveness when treated with insulin-like growth factor-I/transforming growth factor-beta, suggesting that these clones may originate from the osteoprogenitor cell pool. While most clonal cell populations were characterized as fully functional osteoblastic cells, some clones expressed merely 1, 2, or 3 osteoblastic markers, which suggests that they may represent stages of differentiation along the osteogenic pathway. In addition, other subclones displayed the capacity to synthesize osteocalcin and showed PTH and prostaglandin-E2 responsiveness, but were found to be devoid of alkaline phosphatase activity. Others expressed all osteoblastic cell markers except PTH responsiveness. The phenotypic constellation of the latter suggests that these cell clones may represent mature osteoblast-like cells, which, perhaps due to environmental circumstances present at the time of isolation, have become altered in accordance with the physiological requirements of the tissue.
 ...
PMID:Evidence for heterogeneity of the osteoblastic phenotype determined with clonal rat bone cells established from transforming growth factor-beta-induced cell colonies grown anchorage independently in semisolid medium. 267 79

Estradiol (E2) replacement therapy effectively prevents or delays postmenopausal bone loss, but the mode of E2 action on bone is still unknown. Recently, the presence of E2 receptors was described for bone-derived cells. In this study we examined the estrogen responsiveness of osteoblastic cells using the experimentally immortalized calvarial cell lines RCT-1 and RCT-3 as well as primary cultures of calvarial and trabecular bone cells. E2 treatment reduced PTH-stimulated adenylate cyclase activity by 20-30% in RCT cells; the maximum effect was observed after treatment with 1 nM E2 for 4 h or longer. In trabecular cells E2 decreased PTH-stimulated adenylate cyclase activity by 60-80%. After a lag period of at least 48 h, E2 treatment (0.01-10 nM) increased cell number and [3H]thymidine incorporation in both RCT-3 cells and primary cultures of trabecular cells to 20-60% above control values. Half-maximal effects were observed at about 1 nM E2. Antibodies against insulin-like growth factor-I (IGF-I) inhibited the E2-induced proliferation in a dose-dependent manner without affecting basal growth. Furthermore, E2 treatment increased the steady state levels of IGF-I mRNA 2- to 2.5-fold in calvarial and RCT-3 cells compared to control levels. In addition, E2 (10 nM) increased the level of collagen mRNA more than 2-fold and opposed the suppression of collagen mRNA produced by PTH treatment. The E2 effects were specific to 17 beta-E2, since they were not observed with the biologically less active stereoisomer 17 alpha-E2 and were blocked by the E2 antagonist tamoxifen (1 microM). Thus, for osteoblastic cells in culture, E2 can directly stimulate proliferation as well as collagen and IGF-I mRNA while decreasing PTH responsiveness; these effects could explain the anabolic and anticatabolic effects of E2 on bone.
 ...
PMID:Estradiol effects on proliferation, messenger ribonucleic acid for collagen and insulin-like growth factor-I, and parathyroid hormone-stimulated adenylate cyclase activity in osteoblastic cells from calvariae and long bones. 275 78

The ovarian granulosa cell has recently been shown to be a site of insulin-like growth factor-I (IGF-I) production, reception, and action. In large measure, IGF-I action (in the rat) appears contingent upon its ability to synergize with FSH, a major promoter of granulosa cell differentiation. It is the objective of the in vitro studies reported herein to elucidate the cellular mechanism(s) whereby IGF-I amplifies FSH hormonal action, placing special emphasis on the potential role of the putative intracellular second messenger cAMP in this regard. Basal FSH binding (115.7 +/- 2.1 fmol/mg cell protein) to rat granulosa cells cultured under serum-free conditions remained unchanged after 72 h of treatment with IGF-I (50 ng/ml) by itself (107.1 +/- 1.0 fmol/mg cell protein). In contrast, treatment with FSH (20 ng/ml) resulted in a significant (P less than 0.05) decrease in FSH binding capacity (but not affinity) relative to controls in either the absence or presence of IGF-I. Whereas treatment with FSH resulted in a substantial increase in forskolin-stimulatable adenylate cyclase activity (10 +/- 1.7% conversion of [3H] ATP to [3H]cAMP), concurrent treatment with IGF-I resulted in 2.2-fold enhancement of FSH action. This IGF-I effect proved dose dependent with an apparent median effective dose of 3.6 +/- 0.8 ng/ml, a concentration in keeping with its granulosa cell receptor binding affinity. Significantly, however, IGF-I proved capable of enhancing Bt2cAMP-stimulated progesterone accumulation suggesting that IGF-I may be also acting at site(s) distal to cAMP generation. Taken together, these and previous studies indicate that nanomolar concentrations of exogenously added IGF-I may be interacting with the FSH transduction signal at multiple cellular site(s) to effect amplification of FSH action.
 ...
PMID:Insulin-like growth factor-I as an amplifier of follicle-stimulating hormone action: studies on mechanism(s) and site(s) of action in cultured rat granulosa cells. 283 Oct 34

Treatment of cultured rat astrocytes with insulin increased (Na+ + K+)-ATPase activity expressed per protein or DNA by 1.6- to 2.1-fold, but did not affect Mg(2+)-ATPase and adenylate cyclase activities. Insulin treatment increased protein and DNA contents under the conditions, while it did not cause morphological differentiation as determined by a microscopic inspection. Insulin-like growth factor-I (IGF-I) had a similar effect on the enzyme activity in astrocytes: the effect of insulin was observed at supraphysiological concentrations, while that of IGF-I was observed at physiological concentrations. Insulin and IGF-I both stimulated DNA synthesis at the concentrations that caused an increase in enzyme activity. The effect was blocked by tyrosine kinase inhibitors such as genistein and herbimycin A and by cycloheximide. Western blot analysis showed that alpha 1 and alpha 2 isoforms of (Na+ + K+)-ATPase were present in cultured astrocytes and that insulin and IGF-I increased the content of the alpha 1 isoform but did not that of the alpha 2 isoform. Two components of ouabain inhibition were observed in the enzyme purified partially from cultured astrocytes, and treatment of the cells with IGF-I increased the ratio of the low-affinity component of the inhibition, indicating a selective increase in the activity of the alpha 1 isoform. These results indicate that insulin increases (Na+ + K+)-ATPase activity through an activation of IGF-I receptors and the increase is due to the selective induction of the alpha 1 isoform in cultured astrocytes.
 ...
PMID:Selective induction of alpha 1 isoform of (Na+ + K+)-ATPase by insulin/insulin-like growth factor-I in cultured rat astrocytes. 823 54

The effects of insulin-like growth factor-I (IGF-I) and IGF-II on the human osteoblast cell-line OHS-4 were investigated. Both IGF-I and IGF-II stimulated cell proliferation at nanomolar concentrations and alkaline phosphatase activity was decreased in a dose-dependent manner with either IGF-I or IGF-II. The production of the bone-specific protein osteocalcin was not influenced by either IGF-I or IGF-II. However, they acted synergistically with 1,25-dihydroxy-vitamin D3 at concentrations ranging from 10 to 100 nmol/l. Neither IGF-I nor IGF-II had an effect on either the basal or the parathyroid hormone-stimulated level of adenylate cyclase activity, and likewise they had no effect on phosphodiesterase activity. Binding and cross-linking experiments confirmed the presence of both type-I and type-II IGF receptors on the OHS-4 cells. The present study shows that IGF-I and IGF-II have similar effects on the parameters studied in these osteoblastic cells. They influenced both proliferation and differentiation markers.
 ...
PMID:Comparison of the effects of insulin-like growth factors-I and -II on the human osteosarcoma cell line OHS-4. 842 72

Insulin-like growth factor-I (IGF-I) is a potent mitogen in many cell systems. In cultured rat granulosa cells, however, IGF-I is known to be an inducer of differentiation. The present study was conducted to identify the factor which determines the direction of IGF-I action: either DNA synthesis or LH receptor expression. When granulosa cells were incubated with IGF-I in the presence of various concentrations of follicle-stimulating hormone (FSH), DNA synthesis as assessed by [3H]thymidine incorporation was increased only in the presence of low doses of FSH. The stimulatory effect of FSH on DNA synthesis was observed in a very narrow range of FSH concentration between 2 and 10 ng/ml. At higher concentrations, FSH had little effect on DNA synthesis but instead induced expression of receptors for luteinizing hormone (LH), a marker of granulosa cell differentiation. At 5 ng/ml, FSH elicited maximal stimulation of DNA synthesis and simultaneously induced LH receptor expression to some extent. In these cells, DNA synthesis peaked at 36 h but expression of LH receptor occurred later than 36 h, peaking at 60 h. The ability of IGF-I to stimulate DNA synthesis was enhanced by the long term pretreatment with FSH: when FSH was added from the beginning and IGF-I was added after 36 h or later, IGF-I-mediated DNA synthesis was approximately twice as great, and was accompanied by a two-fold increase in the number of bromodeoxyuridine-labeled nuclei. Under these conditions, LH receptor expression was reduced to approximately 50%. Finally when cells were incubated for 12 h with or without FSH, washed extensively with the medium and then IGF-I was added, DNA synthesis was augmented only in FSH-primed cells. Forskolin, an activator of adenylate cyclase, reproduced the effect of FSH. These results indicate that, in the presence of FSH, IGF-I has the ability to induce both DNA synthesis and differentiation and that FSH determines the action of IGF-I on promotion of either growth or differentiation. Furthermore, priming with FSH renders granulosa cells responsive to IGF-I in terms of DNA synthesis.
 ...
PMID:Growth of differentiation: determination by FSH of the action of insulin-like growth factor-I in cultured rat granulosa cells. 873 47


1 2 Next >>