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Liu F, Austin DA, Webster NJG. Gonadotropin-releasing hormone-desensitized LbetaT2 gonadotrope cells are refractory to acute protein kinase C, cyclic AMP, and calcium-dependent signaling. Endocrinology 2003; 144:4354-65. [PMID: 12960037 DOI: 10.1210/en.2003-0204] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Sustained exposure of gonadotropes to GnRH causes a pronounced desensitization of gonadotropin release, but the mechanisms involved are poorly understood. It is known that desensitization is associated with decreased GnRH receptor and Gq/11 levels in alphaT3-1 cells, but it is not known whether downstream signaling is impaired. We have shown previously that chronic stimulation of signaling via expression of an active form of Galphaq causes GnRH resistance in LbetaT2 cells. In this study we investigated whether chronic GnRH treatment could down-regulate protein kinase C (PKC), cAMP, or Ca2+-dependent signaling in LbetaT2 cells. We found that chronic GnRH treatment desensitizes cells to acute GnRH stimulation not only by reducing GnRH receptor and Gq/11 expression but also by down-regulating PKC, cAMP, and calcium-dependent signaling. Desensitization was observed for activation of ERK and p38 MAPK and induction of c-fos and LHbeta protein expression. Activation of individual signaling pathways was able to partially mimic the desensitizing effect of GnRH on ERK, p38 MAPK, c-fos, and LHbeta but not on Gq/11. Chronic stimulation with phorbol esters reduced GnRH receptor expression to the same extent as chronic GnRH. Sustained GnRH also desensitized PKC signaling by down-regulating the delta, epsilon, and theta isoforms of PKC. We further show that chronic GnRH treatment causes heterologous desensitization of other Gq-coupled receptors.
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Affiliation(s)
- Fujun Liu
- Department of Medicine, University of California San Diego Cancer Center, San Diego, California 92093, USA
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2
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Abstract
We have studied signaling mechanisms that stimulate exocytosis and luteinizing hormone secretion in isolated male rat pituitary gonadotropes. As judged by reverse hemolytic plaque assays, phorbol-12-myristate-13-acetate (PMA) stimulates as many gonadotropes to secrete as does gonadotropin-releasing hormone (GnRH). However, PMA and GnRH use different signaling pathways. The secretagogue action of GnRH is not very sensitive to bisindolylmaleimide I, an inhibitor of protein kinase C, but is blocked by loading cells with a calcium chelator, 1,2-bis-(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. The secretagogue action of PMA is blocked by bisindolylmaleimide I and is not very sensitive to the intracellular calcium chelator. GnRH induces intracellular calcium elevations, whereas PMA does not. As judged by amperometric measurements of quantal catecholamine secretion from dopamine- or serotonin-loaded gonadotropes, the secretagogue action of PMA develops more slowly (in several minutes) than that of GnRH. We conclude that exocytosis of secretory vesicles can be stimulated independently either by calcium elevations or by activation of protein kinase C.
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Affiliation(s)
- J Billiard
- Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA
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3
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Harris D, Reiss N, Naor Z. Differential activation of protein kinase C delta and epsilon gene expression by gonadotropin-releasing hormone in alphaT3-1 cells. Autoregulation by protein kinase C. J Biol Chem 1997; 272:13534-40. [PMID: 9153199 DOI: 10.1074/jbc.272.21.13534] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The effect of gonadotropin-releasing hormone (GnRH) upon protein kinase C (PKC) delta and PKCepsilon gene expression was investigated in the gonadotroph-derived alphaT3-1 cell line. Stimulation of the cells with a stable analog [D-Trp6]GnRH (GnRH-A) resulted in a rapid elevation of PKCepsilon mRNA levels (1 h), while PKCdelta mRNA levels were elevated only after 24 h of incubation. The rapid elevation of PKCepsilon mRNA by GnRH-A was blocked by pretreatment with a GnRH antagonist or actinomycin D. The PKC activator 12-O-tetradecanoylphorbol-13-acetate (TPA), but not the Ca2+ ionophore ionomycin, mimicked the rapid effect of GnRH-A upon PKCepsilon mRNA elevation. Additionally, the rapid stimulatory effect of GnRH-A was blocked by the selective PKC inhibitor GF109203X, by TPA-mediated down-regulation of endogenous PKC, or by Ca2+ removal. Interestingly, serum-starvation (24 h) advanced the stimulation of PKCdelta mRNA levels by GnRH-A and the effect could be detected at 1 h of incubation. The rapid effect of GnRH-A upon PKCdelta mRNA levels in serum-starved cells was mimicked by TPA, but not by ionomycin, and was abolished by down-regulation of PKC or by Ca2+ removal. Preactivation of alphaT3-1 cells with GnRH-A for 1 h followed by removal of ligand and serum resulted in elevation of PKCdelta mRNA levels after 24 h of incubation. Western blot analysis revealed that GnRH-A and TPA stimulated (within 5 min) the activation and some degradation of PKCdelta and PKCepsilon. We conclude that Ca2+ and PKC are involved in GnRH-A elevation of PKCdelta and PKCepsilon mRNA levels, with Ca2+ being necessary but not sufficient, while PKC is both necessary and sufficient to mediate the GnRH-A response. A serum factor masks PKCdelta but not PKCepsilon mRNA elevation by GnRH-A, and its removal exposes preactivation of PKCdelta mRNA by GnRH-A which can be memorized for 24 h. PKCdelta and PKCepsilon gene expression evoked by GnRH-A is autoregulated by PKC, and both isotypes might participate in the neurohormone action.
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Affiliation(s)
- D Harris
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel
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4
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Naor Z, Shacham S, Harris D, Seger R, Reiss N. Signal transduction of the gonadotropin releasing hormone (GnRH) receptor: cross-talk of calcium, protein kinase C (PKC), and arachidonic acid. Cell Mol Neurobiol 1995; 15:527-44. [PMID: 8719039 DOI: 10.1007/bf02071315] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
1. The decapeptide neurohormone gonadotropin releasing hormone (GnRH) is the first key hormone of the reproductive system. Produced in the hypothalamus, GnRH is released in a pulsatile manner into the hypophysial portal system to reach the anterior pituitary and stimulates the release and synthesis of the gonadotropin hormones LH and FSH. GnRH, a Ca2+ mobilizing ligand, binds to its respective binding protein, which is a member of the seven transmembrane domain receptor family and activates a G-protein (Gq). 2. The alpha subunit of Gq triggers enhanced phosphoinositide turnover and the elevation of multiple second messengers required for gonadotropin release and biosynthesis. 3. The messenger molecules IP3, diacylglycerol, Ca2+, protein kinase C, arachidonic acid and leukotriene C4 cross-talk in a complex networks of signaling, culminating in gonadotropin release and gene expression.
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Affiliation(s)
- Z Naor
- Department of Biochemistry, Tel Aviv University, Ramat Aviv, Israel
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5
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Ben-Menahem D, Shraga-Levine Z, Mellon PL, Naor Z. Mechanism of action of gonadotropin-releasing hormone upon gonadotropin alpha-subunit mRNA levels in the alpha T3-1 cell line: role of Ca2+ and protein kinase C. Biochem J 1995; 309 ( Pt 1):325-9. [PMID: 7542447 PMCID: PMC1135837 DOI: 10.1042/bj3090325] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Addition of [D-Trp6]gonadotropin-releasing hormone (GnRHa) to alpha T3-1 cells induced a very rapid response upon gonadotropin alpha-subunit mRNA which was detected after 30-60 min and was abolished by pretreatment with actinomycin D. A similar response was obtained with the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA), or the Ca2+ ionophore, ionomycin. GnRHa (10 nM) also stimulated a secondary rise in alpha-subunit mRNA levels between 12 and 24 h of incubation. No additivity was obtained (at 60 min) upon the combined addition of GnRHa and PMA, GnRHa and ionomycin, or PMA and ionomycin. The effect of GnRHa upon alpha-subunit mRNA was blocked by the PKC inhibitors staurosporine or GF 109203X. Down-regulation of endogenous PKC activity resulted in inhibition of the stimulatory effect of gonadotropin-releasing hormone (GnRH), PMA and ionomycin. Removal of extra-cellular Ca2+ abolished the effect of GnRHa and PMA upon alpha-subunit mRNA levels. Interestingly PMA and ionomycin had no effect on alpha-subunit mRNA levels at 24 h of incubation; however, the combined addition of the drugs mimicked the late phase of GnRHa (10 nM) action. The data provide evidence that PKC and Ca2+ are involved in mediating the early and the late responses of GnRHa upon alpha-subunit mRNA elevation and that differential cross-talk exists between the messengers.
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Affiliation(s)
- D Ben-Menahem
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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6
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Marantz Y, Reiss N, Przedecki F, Naor Z. Involvement of protein phosphatases in gonadotropin releasing hormone regulated gonadotropin secretion. Mol Cell Endocrinol 1995; 111:7-11. [PMID: 7649355 DOI: 10.1016/0303-7207(95)03540-n] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The role of persistent protein phosphorylation upon gonadotropin releasing hormone (GnRH) stimulated luteinizing hormone (LH) release was investigated by the use of the selective inhibitors of protein phosphatase type 1 (PP1) and 2A (PP2A), okadaic acid (OA) and calyculin A. Pre-incubation of cultured rat pituitary cells with OA (24 h) or calyculin A (30 min) resulted in inhibition of GnRH-stimulated LH release with significant inhibition being detected at 10 nM and 30 nM for OA and calyculin A, respectively. The inactive OA analog norokadone and the protein tyrosine phosphatase inhibitor vanadyl hydroperoxide had no significant effect on GnRH-induced LH release. The stimulatory effects of the protein kinase C (PKC) activator 12-O-tetradecanoylphorbol 13-acetate (TPA, 50 ng/ml) or the Ca2+ ionophore, ionomycin (1 micron), upon LH release were also abolished by pretreatment with OA (10-20 nM) or calyculin A (30 nM). Stimulation of LH release by high K+ (28 mM) or residual LH release stimulated by GnRH in Ca(2+)-free medium were also blocked by OA. These observations indicate that protein dephosphorylation is involved positively in GnRH-stimulated LH release. The site of action of the protein phosphatases PP1 and PP2A is most likely downstream to Ca2+ elevation and PKC activation by GnRH.
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Affiliation(s)
- Y Marantz
- Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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7
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Stojilkovic SS, Catt KJ. Expression and signal transduction pathways of gonadotropin-releasing hormone receptors. RECENT PROGRESS IN HORMONE RESEARCH 1995; 50:161-205. [PMID: 7740156 DOI: 10.1016/b978-0-12-571150-0.50012-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- S S Stojilkovic
- Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
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Abayasekara DR, Michael AE, Webley GE, Flint AP. Mode of action of prostaglandin F2 alpha in human luteinized granulosa cells: role of protein kinase C. Mol Cell Endocrinol 1993; 97:81-91. [PMID: 8143907 DOI: 10.1016/0303-7207(93)90213-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
It is well documented that prostaglandin F2 alpha (PGF2 alpha) inhibits progesterone production in luteal cells, but its mode of action is uncertain. It has recently been suggested that PGF2 alpha acts by activating the calcium and phospholipid-dependent protein kinase, protein kinase C (PKC). This hypothesis has been tested by comparing the site and mode of action of PGF2 alpha, a PGF2 alpha analogue (cloprostenol) and the PKC activator phorbol myristate acetate (4 beta PMA) in human granulosa-lutein cells. PGF2 alpha and cloprostenol exerted similar concentration-dependent inhibitory actions on gonadotrophin-stimulated cyclic AMP (cAMP) accumulation and progesterone production by human granulosa-lutein cells. The similarity in the actions of PGF2 alpha and cloprostenol in human granulosa-lutein cells suggests that they can be used interchangeably to study the role of PGF2 alpha in the regulation of steroidogenesis in the human ovary. Gonadotrophin-stimulated cAMP accumulation and progesterone production was also concentration-dependently inhibited by 4 beta PMA. In addition, cloprostenol and 4 beta PMA also inhibited dibutyryl cAMP-stimulated progesterone production, suggesting that these compounds inhibit LH action at sites before and after the generation of cAMP. The pre-cAMP site of action can be localised to the stimulatory G-protein (Gs) as both compounds inhibited cholera toxin-stimulated cAMP accumulation without affecting forskolin-stimulated cAMP accumulation. The post cAMP site of action can be localised to actions on cholesterol side chain cleavage enzyme, as both cloprostenol and 4 beta PMA inhibited 22R hydroxycholesterol-supported progesterone production without affecting pregnenolone-supported progesterone production. The finding that cloprostenol and 4 beta PMA interact with the steroidogenic cascade in a similar manner is indicative of a shared common mediator of their actions in human granulosa-lutein cells, i.e. PKC. The inhibitory actions of PGF2 alpha and 4 beta PMA on hLH-stimulated progesterone production were abolished in the presence of the PKC inhibitor, staurosporine. In addition, in PKC-depleted cells (achieved by exposure to 4 beta PMA for 20 h) the inhibitory actions of PGF2 alpha and 4 beta PMA were abolished. These results support the hypothesis that the inhibitory actions of PGF2 alpha are mediated by PKC in human granulosa-lutein cells.
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Affiliation(s)
- D R Abayasekara
- Institute of Zoology, Zoological Society of London, Regent's Park, UK
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9
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Taragnat C, Durand P. Functional heterogeneity of gonadotrophs in the ovine fetus: analysis by reverse hemolytic plaque assay. Mol Cell Endocrinol 1993; 96:7-17. [PMID: 8276141 DOI: 10.1016/0303-7207(93)90089-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Stimulation of sheep fetal gonadotrophs with 10(-7) M luteinizing hormone releasing hormone (LHRH) for 3 h in culture wells increased luteinizing hormone (LH) release over basal values. Using the reverse hemolytic plaque assay (RHPA), we demonstrated that this increase was due to a recruitment of LH-secreting cells. During gestation, the percentage of LH-containing cells able to release and the mean size of plaques were the highest at around 100-130 days and were usually lower in females than in males. In an attempt to delineate the involvement of protein kinase C (PKC) in LH release, cells were treated with an activator of PKC, phorbol 12-myristate 13-acetate (PMA). Stimulation of cells with 10(-6) M PMA for 3 h enhanced LH release in culture wells 2- to 3-fold more than did 10(-7) M LHRH. This increase was a consequence of an enhanced number of LH-secreting cells and, in males only, of an enhancement of the mean plaque size. The percentage of LH-secreting cells among LH-containing cells and the plaque areas were maximal between 110 and 120 days of gestation in both sexes. They were usually lower in females than in males. Stimulation of cells with LHRH plus PMA enhanced LH release in culture wells in an additive manner when compared to either factor alone in both sexes and at all fetal ages. This additive effect reflected an increase in the number of secreting cells. Under these conditions, plaque sizes were larger than the plaque sizes obtained with PMA alone in males and in females in late gestation. In conclusion, our results show that LHRH stimulated LH secretion from sheep fetal cells by recruiting secreting cells when compared to controls. Both 100-120 days of gestation and were higher in males than in females. Results following treatment of cells with PMA, either alone or in combination with LHRH, suggest that these two secretagogues act on two different subpopulations of gonadotrophs and probably through different pathways.
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Affiliation(s)
- C Taragnat
- Station de Physiologie de la Reproduction des Mammifères Domestiques, URA-CNRS 1291, Institut National de la Recherche Agronomique, Nouzilly, France
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Roseng L, Rivedal E, Sanner T. Effect of protein kinase C inhibitors on TPA-induced inhibition of gap junctional intercellular communication and induction of transformed morphology in Syrian hamster embryo cells. Toxicol In Vitro 1993; 7:637-44. [DOI: 10.1016/0887-2333(93)90098-p] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/1992] [Revised: 02/15/1993] [Indexed: 10/27/2022]
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Dan-Cohen H, Sofer Y, Schwartzman ML, Natarajan RD, Nadler JL, Naor Z. Gonadotropin releasing hormone activates the lipoxygenase pathway in cultured pituitary cells: role in gonadotropin secretion and evidence for a novel autocrine/paracrine loop. Biochemistry 1992; 31:5442-8. [PMID: 1610790 DOI: 10.1021/bi00139a004] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The formation and role of arachidonic acid (AA) and its metabolites during gonadotropin releasing hormone- (GnRH-) induced gonadotropin secretion were investigated in primary cultures of rat pituitary cells. Prelabeled cells ([3H]AA) responded to GnRH challenge with increased formation (about 2-fold) of the leukotrienes LTC4, LTD4, and LTE4 as well as 5- and 15-eicosatetraenoic acids (5- and 15-HETE) as identified by HPLC. Formation of leukotrienes and 15-HETE was further verified by specific radioimmunoassays. No significant increase in the formation of 12-HETE or of the cyclooxygenase products prostaglandin E (PGE) and thromboxane A2 by GnRH was noticed. Addition of physiological concentrations of LTC4 enhanced basal LH release, while subphysiological concentrations of LTC4 (10(-15)-10(-12) M) inhibited GnRH-induced LH release by about 35% (p less than 0.02). Using specific lipoxygenase inhibitors L-656,224 and MK 886, we found inhibition of GnRH-induced LH release by about 40% at concentrations known to specifically inhibit the 5-lipoxygenase pathway. The peptidoleukotriene receptor antagonist ICI 198,615 inhibited LTC4- and LTE4-induced LH release and surprisingly also the effect of GnRH on LH release by 40%. The data strongly suggest a role for AA and its lipoxygenase metabolites in the on/off reactions of GnRH upon LH release. The data also present a novel amplification cycle in which newly formed leukotrienes become first messengers and establish an autocrine/paracrine loop.
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Affiliation(s)
- H Dan-Cohen
- Department of Biochemistry, Tel Aviv University, Israel
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12
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Conn PM, Hawes BE, Janovick JA. Selection of models for the study of GnRH stimulated gonadotropin release prejudices the assignment of roles for mediators and modulators of hormone action. Mol Cell Endocrinol 1992; 84:C33-7. [PMID: 1316852 DOI: 10.1016/0303-7207(92)90025-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- P M Conn
- Department of Pharmacology, University of Iowa College of Medicine, Iowa City 52242-1109
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13
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Kurscheid-Reich D, Hegemann L, Wohlfeil S. Effect of protein kinase inhibitors on ACTH-stimulated aldosterone production in rat zona glomerulosa cells. Life Sci 1992; 51:1157-63. [PMID: 1325591 DOI: 10.1016/0024-3205(92)90518-t] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
In order to obtain further evidence for the involvement of protein kinases in the short-term ACTH-stimulated aldosterone synthesis in rat zona glomerulosa cells, the effects of three different compounds with protein kinase inhibitory properties were investigated. Staurosporine, H-7 and trifluoperazine inhibited ACTH-stimulated aldosterone release in a dose-dependent manner. While the inhibitory effect of H-7 was reversible upon washing of the cells with inhibitor-free medium, the inhibition was maintained in cells treated with staurosporine or trifluoperazine. In contrast to the stimulated production, basal release of aldosterone even at the highest drug concentrations tested was not completely inhibited. We thus conclude that protein kinases may play a crucial role in short-term ACTH-stimulated aldosterone production in rat glomerulosa cells.
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Affiliation(s)
- D Kurscheid-Reich
- Yale University, School of Medicine, Dept. Internal Medicine, New Haven, CT 06510-8056
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14
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Leigh AJ, Wilson CA, Edger MJ, Tipping KE, Patel M, Chapman AJ, Whitehead SA. Stimulation of luteinizing hormone-Beta messenger ribonucleic Acid and post-translational modification of luteinizing hormone isoforms by second messengers mediating the action of gonadotrophin-releasing hormone. J Neuroendocrinol 1991; 3:605-11. [PMID: 19215530 DOI: 10.1111/j.1365-2826.1991.tb00325.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Abstract Several second messenger systems have been implicated in mediating the action of gonadotrophin-releasing hormone on the pituitary gonadotrophs and numerous studies have shown that activation of these systems induces luteinizing hormone (LH) secretion. However, it is not known how gonadotrophin-releasing hormone or the second messenger systems induce de novo LH biosynthesis and post-translational modification of the hormone. In these experiments hemipituitary glands have been perifused with drugs which activate second messengers or stimulate protein kinase C directly. The LH secretory responses have been correlated with measurements of common a and LHbeta mRNA and the molecular species of LH which were present in the pituitary perifusate after exposure to the drugs. Gonadotrophin-releasing hormone (50 ng/ml, 42 nM), with and without the presence of extracellular Ca(2+), the Ca(2+) ionophore, A23187 (10 muM), and phorbol 12-myristate (1 muM) all stimulated an increase in LHbeta mRNA compared with controls and the appearance of a different isoform of LH to that found stored in and released from the unstimulated pituitary gland. Phospholipase C was without effect on LHbeta mRNA levels and showed minimal efficacy in inducing the appearance of the different LH isoform.
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Affiliation(s)
- A J Leigh
- Departments of Obstetrics and Gynaecology St George's Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK
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Koch B, Lutz-Bucher B. Inhibition of protein kinase C activity in cultured pituitary cells attenuates both cyclic AMP-independent and -dependent secretion of ACTH. Mol Cell Endocrinol 1991; 77:57-65. [PMID: 1667763 DOI: 10.1016/0303-7207(91)90058-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The present study examines the effect of reduction of protein kinase C (PKC) activity, as induced by either phorbol ester (PMA) down-regulation or staurosporine inhibition, on the secretion of ACTH from cultured anterior pituitary (AP) cells. Short-term (3 h) exposure of cells to 5 nM PMA resulted in almost complete desensitization to both PMA and vasopressin (AVP), while there was only a minor incidence on the effect of corticotropin-releasing factor (CRF). In contrast, long-term (12-24 h) exposure of cells to PMA, as well as pretreatment with staurosporine, dramatically reduced the stimulatory influence of CRF. This was shown not to be due to a decline in ACTH cells' stores, nor to the toxicity of phorbol ester or to a negative autofeedback of ACTH. Pretreatment of corticotrophs with PMA failed to dampen the CRF-induced cyclic AMP formation, while it caused a decline in the effects of forskolin and 8-bromoadenosine cyclic AMP. Stimulated ACTH secretion subsequent to either veratridine- or high K(+)-induced cell depolarization was likewise decreased. We conclude that in corticotrophs the stimulatory action of not only AVP, but also of that of CRF on ACTH secretion strongly relies on PKC activity. In the case of CRF, however, this may not be a primary consequence of receptor occupation, as evidence suggests an indirect relationship which may involve PKC regulation of Ca2+ channels and/or the ion's intracellular messenger function.
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Affiliation(s)
- B Koch
- Institut de Physiologie, URA CNRS 309, Strasbourg, France
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