Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Stimulation of protein kinase C (PKC) by phorbol ester (PMA) was reported previously to increase total binding of the peptide in whole rat pituitary cells. The effect could be obtained in cells from intact, not from spayed animals, suggesting a different level of spontaneous phosphorylation in both conditions. In the present work, endogenous PKC was desensitized in pituitary cells sampled from intact or 3 weeks castrated male rats and maintained in primary culture. Desensitization was induced by overnight incubation with 1 microM PMA. The maximum number of plasma membrane LHRH receptors (Bmax) present on cells from in intact animals was higher (+ 98 +/- 9%) when binding was performed at 0.5 degrees C instead of 21 degrees C as already observed in non PKC-desensitized cells. PMA (100 nM) was ineffective to increase Bmax, suggesting effectiveness of enzyme desensitization. In contrast, ionomycin 1 microM increased Bmax (53 +/- 10%). This increment was inhibited by W7, a calmodulin inhibitor, with an IC50 = 1 +/- 0.35 10(-6) M. No temperature dependency of the Bmax was observed in cells from castrated rats as already shown in the absence of PKC desensitization. Under these conditions, a Bmax decrease of 34 +/- 6% and 36.5 +/- 7.5% respectively was observed in the presence of H7, a PKC inhibitor, or of W7 (IC50 = 1 +/- 0.5 10(-5) M and IC50 = 0.8 +/- 0.2 10(-6) M). We conclude that a Ca2+ calmodulin dependent protein kinase rather than PKC itself is responsible for unmasking LHRH receptors.
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PMID:A Ca2+ calmodulin dependent kinase rather than protein kinase C is involved in up-regulation of the LHRH receptor. 131 37

The natural gonadotropin-releasing hormone (GnRH) is secreted by hypothalamic neurons and acts at the level of anterior pituitary gonadotrophs releasing the peptides luteinizing hormone and follicle-stimulating hormone. GnRH is a decapeptide sensitive to peptidases, resulting in a short half-life. The synthesis of highly potent analogues of GnRH provides peptides with a longer half-life and a higher affinity to the GnRH-receptor. The presently available GnRH analogues for clinical use act initially as agonists by upregulating GnRH receptors in the pituitary. A few days after continuous application of GnRH analogues down-regulation of receptors and desensitization of the pituitary occur. In addition to receptor mechanisms, a number of postreceptor actions at the level of second messengers (protein kinase C, leukotriene and inositol phosphates) are responsible for the inhibition of adequate gonadotropin secretion. This paradoxical entire fertility action of the analogues is the basic principle for its clinical use, resulting in a reversible suppression of pituitary and thereby ovarian function.
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PMID:[Gonadotropin releasing hormone and analogs. Physiology and pharmacology]. 132 31

Gonadal steroids act at the pituitary to regulate gonadotropin-releasing hormone (GnRH) receptor number and the responsiveness of gonadotropes to GnRH and can act at post-receptor sites to modulate Ca(2+)-mediated and protein kinase C-mediated signal-transducing pathways. However, such effects have been seen in the mixed cell population of primary cell cultures and may involve indirect effects on cells other than gonadotropes. Here, steroid effects on a recently described gonadotrope-derived cell line (alpha T3-1 cells) have been assessed. In these cells estradiol, progesterone, testosterone and corticosterone all exerted trophic effects. Estradiol increased [3H]thymidine incorporation with an EC50 of 10(-12) to 10(-11) M and this effect was blocked by keoxifene, an estrogen receptor antagonist. Estradiol also reduced binding of [125I]buserelin (EC50 approximately 10(-11) M), an effect which appears to reflect a reduction in GnRH receptor number rather than a change in Kd. Estradiol also shifted the dose-response curve for GnRH-stimulated inositol phosphate (IP) accumulation rightward, increasing the EC50 for this GnRH effect by approximately 20-fold. Accordingly estradiol acts directly upon alpha T3-1 cells not only to reduce GnRH receptor number, but also to reduce the efficiency of coupling of residual GnRH receptors to second messenger generation.
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PMID:Estradiol regulates gonadotropin-releasing hormone receptor number, growth and inositol phosphate production in alpha T3-1 cells. 133 8

A series of novel gonadotropin releasing hormone (GnRH) and Somatostatin analogs have been developed in our laboratory and were screened for antiproliferative and signal transduction inhibitory effect. Our GnRH analog Folligen, had significant antitumor activity on DMBA induced mammary carcinomas in rats without blocking ovarian functions. The direct effect of Folligen and Buserelin has been compared on the human breast cancer cell line MDA-MB-231. Folligen was found to be more effective in inhibiting cell proliferation and significant differences were found in the signal transduction pathways activated by these analogs. Our novel Somatostatin analogs were screened for tyrosine kinase inhibition and for antiproliferative effect on human colon tumor cells and for growth hormone (GH) release inhibition in vitro and in vivo. The analog TT-2-50 was significantly more active inhibiting GH release in superfused rat pituitary cells and in vivo than native Somatostatin and it strongly inhibited tyrosine kinase and proliferation while it stimulated protein kinase C activity.
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PMID:Novel antitumor peptide hormones and their effect on signal transduction. 135 11

In cultured pituitary gonadotrophs, gonadotropin-releasing hormone (GnRH) caused dose-dependent and biphasic increases in cytoplasmic calcium concentration ([Ca2+]i) and LH release. Both extra- and intracellular calcium pools participate in GnRH-induced elevation of [Ca2+]i and LH secretion. The spike phase of the [Ca2+]i response represents the primary signal derived predominantly from the rapid mobilization of intracellular Ca2+. In contrast, the prolonged phase of the Ca2+ signal depends exclusively on Ca2+ entry from the extracellular pool. The influx of Ca2+ occurs partially through dihydropyridine-sensitive calcium channels. Both [Ca2+]i and LH responses to increasing concentrations of GnRH occur over very similar time scales, suggesting that increasing degrees of receptor occupancy are transduced into amplitude-modulated Ca2+ responses, which in turn activate exocytosis in a linear manner. However, several lines of evidence indicated the complexity over the relationship between Ca2+ signaling and LH exocytosis. In contrast to [Ca2+]i measurements in cell suspension, single cell Ca2+ measurements revealed the existence of a more complicated pattern of Ca2+ response to GnRH, with a biphasic response to high agonist doses and prominent oscillatory responses to lower GnRH concentrations, with a log-linear correlation between GnRH dose and the frequency of Ca2+ spiking. In addition, analysis of the magnitudes of the [Ca2+]i and LH responses of gonadotrophs to a wide range of GnRH concentrations in the presence and absence of extracellular Ca2+, and to K+ and phorbol ester stimulation, showed non-linearity between these parameters with amplification of [Ca2+]i-mediated exocytosis. Studies on cell depleted of protein kinase C under conditions that did not change the LH pool suggested the participation of protein kinase C in this amplification, especially during the plateau phase of the secretory response to GnRH.
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PMID:Calcium signaling and secretory responses in agonist-stimulated pituitary gonadotrophs. 137 99

We compared the ability of estradiol and progesterone to modulate gonadotropin-releasing hormone (GnRH) and protein kinase C (PKC)-mediated luteinizing hormone (LH) secretion. Long-term (48 h) treatment of rat pituitary cells with 1 nM estradiol enhanced GnRH and phorbol ester (TPA)-stimulated LH secretion. This positive effect was facilitated by additional short-term (4 h) treatment with progesterone (100 nM). However, long-term progesterone treatment, which inhibited GnRH-stimulated LH secretion, did not influence TPA-stimulated gonadotropin release. These steroid actions occurred without an effect on the total amount of LH in the cell cultures (total LH = LH secreted + LH remaining in the cell) and neither the secretagogues nor the steroids altered total LH. Since GnRH or TPA-induced LH secretion depends on Ca2+ influx into the gonadotroph, we also analyzed the effects of estradiol and progesterone under physiological extracellular Ca2+ concentrations and in the absence of extracellular Ca2+. The steroids were able to influence GnRH or TPA-induced LH secretion under both conditions. However, when TPA was used as stimulus in Ca(2+)-deficient medium the relative changes induced by estradiol and progesterone were more pronounced, possibly indicating that the extracellular Ca(2+)-independent component of PKC-mediated LH secretion is more important for the regulation of the steroid effects. It is concluded that estradiol and progesterone might mediate their modulatory actions on GnRH-stimulated LH secretion via an influence on PKC. This effect can occur independently from de novo synthesis of LH and Ca2+ influx into gonadotrophs.
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PMID:Modulatory actions of estradiol and progesterone on phorbol ester-stimulated LH secretion from cultured rat pituitary cells. 147 53

The impact of ethanol (EtOH) on male rodent reproduction has been well characterized for luteinizing hormone (LH) with suppression of LH release from the pituitary being reported. We have previously reported that acute ethanol (EtOH) exposure in vivo results in rapid and marked suppression of beta-LH gene expression and protein release from the pituitary. This suppression of beta-LH gene expression was unaccompanied by a change in the common alpha-subunit mRNA. To further explore the impact of ethanol on male rodent reproduction, we have expanded our studies to follicle stimulating hormone (FSH) and hypothalamic luteinizing hormone releasing hormone (LHRH) as well as of pituitary protein kinase C (PKC). Previously castrated male rats were acutely exposed to EtOH and a dramatic reduction in both serum FSH and LH levels was noted at 1.5 and 3 hr after treatment. These levels returned to saline injected control values at 6 and 24 hr. Despite the fall in serum FSH, there was no change in intrapituitary FSH content at any time point; this lack of pituitary FSH depletion in the face of a fall in serum levels is suggestive of impaired FSH release. In contrast to the fall in beta-LH steady-state mRNA levels seen previously and confirmed in the present studies, there was no change in beta-FSH steady-state mRNA at any time point suggesting that EtOH has dichotomous effects on the expression of these two gonadotropins. Pituitary PKC levels were also assessed and found to be unaffected by EtOH at any time point.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The effect of acute in vivo ethanol exposure on follicle stimulating hormone transcription and translation. 153 Jan 42

The priming effect of LHRH in vitro (which results in increased responsiveness of gonadotropes to both LHRH receptor-mediated and receptor-independent stimuli) is brought about by an unknown mechanism. The present results indicate that induction of the LHRH priming effect is inhibited in a concentration-dependent manner by the protein kinase C (PKC) inhibitors staurosporine, K252a, H7 and by the novel highly-selective PKC inhibitor, Ro 31-8220. In contrast, a range of other compounds that are relatively selective inhibitors of other kinases such as tyrosine kinases and Ca2+/calmodulin-dependent kinases were unable to prevent priming. The PKC inhibitors prevented priming without affecting initial LHRH-induced gonadotropin secretion. Thus, the priming-elicited increment in secretion was selectively removed, restoring hormone release to the level measured during an initial response to LHRH. Similar results were obtained on different days of the estrous cycle where the magnitude of the priming effect varies. Experiments on the time course of PKC inhibitor action revealed that the critical period was in the induction of the priming effect, not its expression. The PKC inhibitors had neither acute nor delayed effects on gonadotropin secretion induced by ionomycin. Staurosporine, K252a and Ro 31-8220 inhibited LHRH priming with identical potencies to their inhibition of phorbol ester-induced gonadotropin secretion. The reduced potency of H7 seen on LHRH priming compared to phorbol ester-induced gonadotropin release parallels results seen with this inhibitor on phorbol ester-induced secretion of growth hormone (Johnson and Mitchell (1989) Biochem. Soc. Trans. 17, 751-752) and on the pharmacological characteristics of PKCs partially purified from anterior pituitary tissue. In all aspects of this study, effects on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion appeared to be entirely similar.
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PMID:The priming effect of luteinizing hormone-releasing hormone (LHRH) but not LHRH-induced gonadotropin release, can be prevented by certain protein kinase C inhibitors. 163 16

The present study was undertaken to determine the effects of a protein kinase C inhibitor, staurosporine, on gonadotropin-releasing hormone agonist (GnRHa)-induced oocyte maturation and follicular prostaglandin (PG) production, and the response to direct activators of protein kinase C using rabbit mature follicle culture. Treatment of mature follicles with GnRHa (buserelin and leuprolide acetate) neither stimulated nor inhibited cAMP accumulation in both the follicle and oocyte. Exposure to staurosporine at 10(-6) M 60 or 15 min before GnRHa (buserelin) administration reduced significantly the meiotic maturation of follicle-enclosed oocytes induced by GnRHa at 10(-7) M. However, staurosporine addition coincident with the agonist or thereafter did not inhibit meiotic maturation. Staurosporine suppressed GnRHa-induced meiotic maturation in a dose-dependent manner, whereas hCG-stimulated oocyte maturation was not inhibited. Similarly, staurosporine administered 60 min before exposure to GnRHa suppressed GnRHa-stimulated PG production by mature follicles. The active phorbol esters, 10(-6) M 12-0-tetra-decanoyl phorbol 13-acetate (TPA) and 10(-6) M 4 beta-phorbol 12,13-didecanoate (4 beta-PDD) stimulated meiotic maturation whereas the biological inactive isomer, 4 alpha-PDD, did not. The kinetics of germinal versicle breakdown of follicle-enclosed oocytes in the presence of active phorbol esters paralleled that of GnRHa-treated oocytes. Furthermore, the concomitant addition of staurosporine at 10(-6) M to the culture medium inhibited significantly (p less than 0.05) TPA-induced meiotic maturation. These data demonstrate that GnRHa stimulated both the meiotic maturation of follicle-enclosed oocytes and follicular PG formation via a mechanism other than the cAMP-mediated process.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Protein kinase C mediates gonadotropin-releasing hormone agonist-induced meiotic maturation of follicle-enclosed rabbit oocytes. 163 39

The mechanisms of LH release and desensitization of the pituitary are still poorly known. We investigated the release of LH by dispersed rat pituitary cells, which were cultured with cytodex beads, packed into columns and superfused. The following results were obtained. 1) LH secretion was rapidly decreased by continuous infusion of 10(-8) M LHRH reaching the control level within 3-4 hours. The desensitization was also observed when the pulse amplitude of LHRH was more than 10(-7) M or when the pulse frequency was more than 4 times per hour. 2) Even after this continuous infusion of 10(-8) M LHRH, pituitary cells responded to 10(-6) M LHRH, 50 mM K+ and 3 mM 8-bromo-cAMP. 3) 3 mM 8-bromo-cAMP and 1 microM forskolin induced a significant increase in LH secretion. 4) 1 microM phorbol myristate acetate (PMA), 40 mu 1-oleoyl-2-acetylglycerol (OAG) and 20 microM Ca2+ ionophore (A-23187) caused a remarkable LH release. 5) 100 microM arachidonic acid (AA) caused a significant increase in LH release. However, the pretreatment with a lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA) abolished the LH response to AA. These results indicated that protein kinase A, protein kinase C and the Ca2(+)-AA system were involved in the mechanisms of LH secretion from the pituitary respectively, and the desensitization by LHRH was easily induced when the LHRH pulse frequency and pulse amplitude were not appropriate to pituitary stimulation.
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PMID:[Study on LH release and desensitization by means of a superfusion system with beads attached pituitary cells]. 169 60


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