EC:2.7.11.13 - FACTA Search

Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Target Concepts:

Query: EC:2.7.11.13 (protein kinase C)
49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Static incubation with tumor-promoting 4 beta-phorbol esters, activators of the Ca2(+)- and phospholipid-dependent protein kinase C enzyme (PKC), caused dose-dependent increases in gonadotropin (GTH) and growth hormone (GH) secretion in primary cultures of dispersed goldfish pituitary cells. The estimated half-maximal effective doses (ED50) for stimulating GTH and GH release were 0.35 +/- 0.17 and 0.32 +/- 0.13 nM 12-O-tetradecanoyl phorbol 13 acetate (TPA), 3.71 +/- 1.30 and 1.37 +/- 0.76 nM 4 beta-phorbol 12,13-dibutyrate, 6.90 +/- 4.84 and 1.89 +/- 0.25 nM 4 beta-phorbol 12,13-dibenzoate, and 455 +/- 258 and 311 +/- 136 nM 4 beta-phorbol 12,13-diacetate, respectively. In contrast, treatments with up to 10 microM of the inactive 4 alpha-phorbol 12,13-didecanoate ester did not alter GTH and GH release. Additions of the synthetic diacylglycerol, dioctanoyl glycerol, also enhanced GTH and GH secretion in a dose-dependent manner and with ED50s of 1.73 +/- 0.83 and 1.73 +/- 1.19 microM, respectively. The GTH and GH responses to stimulation by TPA were attenuated by incubation with Ca2(+)-depleted medium containing EGTA or by treatment with the Ca2+ channel blocker verapamil. Coincubation with the PKC inhibitor H7 reduced the GTH and GH responses to TPA. As in previous studies, additions of salmon gonadotropin-releasing hormone (sGnRH) or chicken GnRH-II (cGnRH-II) induced GTH and GH release; these hormone responses to sGnRH and cGnRH-II were also decreased by the addition of H7. These results indicate that activation of PKC may stimulate GTH and GH release in goldfish and suggest that sGnRH and cGnRH-II actions on goldfish pituitary GTH and GH secretion are also mediated, at least partially, by PKC.
...
PMID:Possible involvement of protein kinase C in gonadotropin and growth hormone release from dispersed goldfish pituitary cells. 190 52

Previous studies have shown that, in goldfish, the gonadotropin (GTH) response to salmon GTH-releasing hormone (sGnRH) is partly mediated by arachidonic acid (AA) metabolism via the lipoxygenase enzyme system, whereas protein kinase C (PKC) participates in both sGnRH- and chicken (c)GnRH-II-induced GTH secretion. In this study, the interactions between AA- and PKC-dependent pathways in mediating the long-term GnRH stimulation of GTH release were further investigated using dispersed goldfish pituitary cell cultures in static incubation. Treatments with AA or the PKC activator tetradecanoylphorbol acetate (TPA) increased GTH release. The GTH responses to AA and TPA were additive. The lipoxygenase inhibitor nordihydroguairetic acid (NDGA) and the PKC inhibitor H7 selectively reduced AA- and TPA-stimulated GTH release, respectively. These findings suggest that the GTH responses to stimulation by AA- and PKC-dependent signaling pathways are independent of one another. In other experiments, the GTH response to cGnRH-II was unaffected by NDGA but was abolished by H7. In contrast, sGnRH-induced GTH release was attenuated by NDGA and H7. Furthermore, in the presence of both NDGA and H7, the GTH response to sGnRH was abolished. These data suggest that sGnRH stimulation of GTH secretion involves both AA- and PKC-dependent mechanisms; in contrast, cGnRH-II action is not dependent on AA metabolism. The pathway by which AA might be mobilized in response to a GnRH challenge was also investigated by pharmacological manipulations. The diacylglcerol (DG) lipase inhibitor, U-57908, did not decrease sGnRH- and cGnRH-II-induced GTH secretion. On the other hand, the phospholipase A2 (PLA2) inhibitors, bromophenacyl bromide (BPB), chloroquine, and quinacrine, reduced sGnRH-elicited, but not cGnRH-II-stimulated GTH release. The addition of AA reversed the inhibitory action of BPB on sGnRH-elicited GTH release. In addition, the GTH response to AA was additive to the cGnRH-II-induced, but not the sGnRH-elicited GTH release. Together, these findings indicate that sGnRH-induced AA mobilization probably involves activation of PLA2 but not DG lipase. These results also support the hypothesis that the AA signaling component is much less important in mediating the long-term cGnRH-II-stimulated GTH secretion, as compared to sGnRH-elicited GTH release.
...
PMID:Interactions between protein kinase C and arachidonic acid in the gonadotropin response to salmon and chicken gonadotropin-releasing hormone-II in goldfish. 819 33

We have previously shown that the abilities of the two native goldfish GnRHs, salmon GnRH (sGnRH) and chicken GnRH II (cGnRH II), to stimulate gonadotropin (GtH) secretion and elevate intracellular Ca2+ levels are mimicked by the protein kinase C (PKC) stimulators, 1,2-dioctanoylglycerol (DiC8) and 12-O-tetradecanoyl phorbol-13-acetate (TPA). The ability of PKC inhibitors to attenuate GnRH-stimulated GtH secretion was also demonstrated. In the present study, the involvement of PKC was examined through the reduction of cellular PKC levels by prolonged preincubation of the cells with TPA (TPA desensitization). TPA pretreatment reduced the levels of PKC in fish pituitary cells as measured by immunoblotting (Western blot). Pretreatment of dispersed goldfish pituitary cells in static culture with TPA abolished the GtH responses to sGnRH, cGnRH II and ionomycin, and drastically reduced TPA- and DiC8-stimulated GtH release, but had no major effect on forskolin-induced GtH release. TPA pretreatment also reduces the cell content of GtH in goldfish pituitary cells. Interestingly, treatment with all of the pharmacological secretagogues tested led to a decrease in cellular contents of GtH, however, the two native GnRHs had no such effect. In rapid column perifusion experiments (1-min fractions), the GtH responses induced by both native GnRHs were characterized by an initial acute increase in hormone secretion followed by a 'plateau' phase which is smaller in magnitude relative to the initial phase. TPA pretreatment of perifused cells greatly reduced both the peak and plateau phases of sGnRH- and cGnRHII-stimulated GtH secretion;TPA-induced GtH release is also greatly attenuated.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Downregulation of protein kinase C levels leads to inhibition of GnRH-stimulated gonadotropin secretion from dispersed pituitary cells of goldfish. 826 51

In goldfish, gonadotropin (GTH-II) responses to the two endogenous GnRHs, salmon-GnRH and chicken-GnRH-II, are mediated by activation of protein kinase C (PKC) and voltage-sensitive Ca2+ channels. In this study, we investigated the role of extracellular Na+, voltage-dependent Na+ channels, and the plasma membrane Na+/H+ exchanger in mediating GnRH-stimulated GTH-II release from dispersed goldfish pituitary cells. Perifusion with Na+-depleted medium reduced the GTH-II response to both GnRHs and the response to the protein kinase C activator, phorbol 12-myristate 13-acetate. Conversely, increasing Na+ influx with veratridine (100 microM) stimulated GTH-II release in the presence and in the absence of extracellular Ca2+. However, the voltage-sensitive Na+ channel blocker, tetrodotoxin (1 microM), did not affect GnRH- stimulated GTH-II release, and the GnRHs did not affect voltage-sensitive Na+ currents. In contrast, the Na+/H+ antiport inhibitors, amiloride or its analog, DMA, reduced GTH-II responses to the GnRHs and phorbol 12-myristate 13-acetate. The Na+/H+ antiport inhibitors did not affect voltage-sensitive Ca2+ or Na+ currents or the GTH-II release response to the Ca2+ ionophore, ionomycin. These findings indicate that extracellular Na+ and the Na+/H+ exchanger are involved in the mediation of GnRH-stimulated GTH-II release. In addition, Na+ entry may modulate GTH-II release independent of extracellular Ca2+.
...
PMID:Involvement of extracellular sodium in agonist-induced gonadotropin release from goldfish (Carassius auratus) gonadotrophs. 877 Sep 7

In the goldfish, it has been proposed that gonadotropin (GTH) release induced by GTH-releasing hormone (GnRH) involves Ca2+ entry through voltage-sensitive Ca2+ channels (VSCC), protein kinase C (PKC) activation, and arachidonic acid (AA) metabolism, but not cyclic AMP (cAMP) action. However, cAMP appears to mediate GnRH action in other teleosts. In this study, the relative importance of PKC and cAMP in mediating GnRH action in goldfish was studied using primary cultures of dispersed pituitary cells. Consistent with an involvement of PKC in GnRH action, the GTH responses to the PKC activating tetradecanoyl phorbol acetate (TPA), salmon (s)GnRH, and chicken (c)GnRH-II were inhibited by two selective PKC inhibitors, calphostin C, and staurosporine. Furthermore, GTH release responses induced by sGnRH or cGnRH-II were not additive to responses stimulated by the PKC-activating diglyceride DiC8, in either long-term static incubation or acute perifusion experiments. In static incubation studies, the GTH responses to sGnRH and DiC8 were potentiated by the VSCC agonist Bay K 8644, suggesting that VSCC participates in both PKC and GnRH action. Concentrations of K+ < 100 mM did not elicit GTH secretion when tested alone, but were effective in stimulating GTH release in the presence of subthreshold doses of DiC8 or TPA. This suggests that minimal activation of PKC greatly enhances the effectiveness of Ca2+ influx to increase GTH secretion. Taken together, these results indicate that PKC is an important mediator of GnRH-induced, VSCC-dependent GTH release. In contrast to the involvement of PKG, cAMP-dependent mechanisms showed no evidence of direct participation in GnRH-induced GTH release in goldfish. In static incubation studies, the GTH responses to sGnRH and cGnRH-II were not affected by H89, a cAMP-dependent protein kinase (PKA) inhibitor. Furthermore, the GTH release stimulated by cAMP was additive to the response to sGnRH, cGnRH-II, DiC8, TPA, or AA. However, compared to the response to forskolin or TPA alone, combinations of forskolin and TPA resulted in a potentiated increase in GTH release. The acute GTH response to forskolin was also enhanced by DiC8. Thus, cAMP-dependent mechanisms may constitute an independent pathway that interacts positively with GnRH-dependent mechanisms in the regulation of GTH release.
...
PMID:Interactions between signaling pathways in mediating GnRH-stimulated GTH release from goldfish pituitary cells: protein kinase C, but not cyclic AMP is an important mediator of GnRH-stimulated gonadotropin secretion in goldfish. 880 63

In goldfish, growth hormone (GH) release is stimulated by dopamine via D1 receptors and cAMP-dependent mechanisms and by gonadotropin-releasing hormone (GnRH) through a protein kinase C (PKC) pathway; in addition, both D1 and GnRH actions require extracellular Ca2+. In this study, the involvement of arachidonic acid (AA) and calmodulin (CaM) in mediating the GH responses to D1 and GnRH stimulation was examined using primary cultures of dispersed goldfish pituitary cells. In 2-hr static incubation experiments, the phospholipase A2 inhibitor bromophenacylbromide (BPB; 50 microM) decreased the GH responses to the D1 agonist SKF38393 (1 microM), the adenylate cyclase activator forskolin (10 microM), and the cAMP analog 8Br-cAMP (1 mM), but not the responses to salmon (s)GnRH (100 nM), chicken (c)GnRH-II (100 nM), and AA (50 microM). Similarly, the phospholipase A2 inhibitor quinacrine (50 microM) and an inhibitor of AA metabolism, nordihydroguaiaretic acid (NDGA; 50 microM), reduced the GH responses to SKF38393, forskolin, and 8Br-cAMP. The response to the dopamine agonist apomorphine (1 microM) was also decreased by NDGA. The GH responses to AA did not add to those of forskolin or SKF38393, but were additive to responses to sGnRH and the PKC activator tetradecanoyl phorbol acetate (TPA; 100 nM). In perifusion experiments, treatment with BPB reduced the acute GH response to 1 microM SKF38393, 10 microM forskolin, or 1 mM 8Br-cAMP. Taken together, these results suggest that mobilization and metabolism of AA mediate both acute and prolonged GH responses to D1, but not GnRH. The involvement of AA probably occurs distal to D1-induced cAMP generation. Two-hour static incubation with 10 nM to 10 microM KN62, a CaM-dependent kinase II inhibitor, decreased the GH response to 100 nM sGnRH or cGnRH-II. KN62 (1 microM) similarly decreased the GH response to 1 mu M SKF38393, 10 microM forskolin, 1 mM 8Br-cAMP, or 100 nM TPA. In perifusion studies, KN62 (1 microM) also reduced the acute GH response to 5 min pulses of 100 nM sGnRH, 100 nM cGnRH-II, or 1 microM SKF38393. These results indicate that CaM mediates the acute, as well as the prolonged, GH responses to GnRH and dopamine. The involvement of CaM likely occurs distal to cAMP and PKC.
...
PMID:Role of arachidonic acid and calmodulin in mediating dopamine D1- and GnRH-stimulated growth hormone release in goldfish pituitary cells. 886 Mar 13

To analyze the multihormonal control mechanisms of GTH secretion in the eel, primary culture of pituitary cells from control or estradiol-treated female silver eels, a treatment known to stimulate in vivo GTH synthesis, was developed. Dispersed eel pituitary cells obtained by enzymatic (trypsin/DNAse) and mechanical dispersion were cultured in Earles M199, at 18 degrees. Immunoreactive GTH (ir-GTH) cells were characterized by the immunoperoxidase method, using antiserum to carp GTH beta subunit. Ir-GTH cells from control silver eels were small and represented 14% of the dispersed pituitary cells. In contrast, ir-GTH cells from estradiol-treated eels were larger (cell area x 2.5) and represented a higher proportion (21%) of the pituitary cells. Intracellular and medium contents of GTH were measured by radioimmunoassay for the GTH beta subunit. In vivo estradiol-treatment increased more than 100-fold the GTH content of cell cultures. GTH release, studied over 1 to 4 hr, was undetectable in cultures from normal eels. In contrast, GTH release was low (less than 2% of cell content) but measurable in cultures from estradiol-treated eels. Subsequent experiments examined effects of various secretagogues on GTH release from primary cultures of pituitary cells from estradiol-pretreated eels. GTH release was significantly increased (x1.5 to x3 basal release) by 10(-6) M GnRH-A as well as by both native GnRHs in the eel (mammalian GnRH, mGnRH, and chicken GnRH-II, cGnRH-II), at the same concentration. Lower GnRH concentrations had no significant effect, indicating a low sensitivity of gonadotrophs to GnRH, likely to be related to their immature state at the silver stage. The similar efficacy of mGnRH and cGnRH-II suggested that the pituitary GnRH receptor had a low specificity toward various molecular forms, in the eel as in the other nonmammalian species. The protein kinase C (PKC) activator (phorbol ester: PMA) also stimulated GTH secretion, with a maximal effect at 10(-8) M, indicating that the PKC pathway was functional. In contrast, a depolarizing agent (50 mM KCl) had no significant effect on GTH release, suggesting lack of a functional voltagesensitive calcium channel (VSCC) secretory pathway. Perifusion experiments on whole pituitary confirmed the lack of effect of KCl on gonadotrophs from E2-pretreated eels and indicated that an additional in vivo treatment with GnRH agonist and dopamine antagonist could induce the differentiation of a functional VSCC pathway. These characteristics of the transduction mechanisms may be related to the immature state of the eel gonadotrophs at the silver stage.
...
PMID:Primary cultures of dispersed pituitary cells from estradiol-pretreated female silver eels (Anguilla anguilla L.): immunocytochemical characterization of gonadotropic cells and stimulation of gonadotropin release. 892 61

In goldfish, gonadotropin-releasing hormone (GnRH) stimulation of growth hormone (GH) release has been shown to involve extracellular Ca2+ entry through voltage-sensitive Ca2+ channels and the activation of protein kinase C (PKC). In this study, the possible involvement of extracellular Na+ in mediating the GH response to GnRH was examined using dispersed pituitary cells. Perifusion with Na(+)-depleted medium reversibly reduced the acute GH response to 5-min pulses of either 10 nM salmon (s)GnRH or 10 nM chicken (c)GnRH-II. Similarly, replacement of normal medium with Na(+)-depleted medium attenuated the long-term GH release response to sGnRH and cGnRH-II under static incubation conditions. These results suggest that GnRH-induced GH release requires the presence of extracellular Na+. Treatment with 5-min pulses of the Na(+)-channel agonist veratridine (10 microM) increased GH release in an extracellular Ca(2+)-dependent manner, presumably due to activation of voltage-sensitive Ca2+ channels resulting from the depolarizing effect of increased Na+ influx. On the other hand, Na+ entry through tetrodotoxin (TTX)-sensitive, voltage-dependent Na+ channels is not involved in GnRH-induced GH release. Application of 250 nM TTX, which abolished the voltage-sensitive Na+ currents in identified goldfish somatotropes, did not affect the acute GH responses to 5-min pulses of sGnRH and cGnRH-II. The possible participation of Na+/H+ antiport in mediating the extracellular Na(+)-dependent GnRH action on GH release was then examined. In static incubation experiments, sGnRH- and cGnRH-II-induced GH secretion were reduced by inhibitors of the Na+/H+ antiport, amiloride and dimethylamiloride (DMA). Likewise, the GH response to the PKC activator, tetradecanoyl phorbol acetate, was attenuated by treatment with Na(+)-depleted medium, amiloride, and DMA. The inhibitory actions of amiloride and DMA were selective as these drugs did not affect the GH response elicited by the Ca2+ ionophore ionomycin and the voltage-sensitive Ca2+ channel agonist, Bay K 8644. Taken together, these results indicate that extracellular Na+ and the Na+/H+ exchanger are involved in the mediation of GnRH-stimulated GH release in goldfish. Furthermore, this dependence on Na+ and Na+/H+ antiport probably occurs distal to the activation of PKC by GnRH.
...
PMID:Extracellular sodium dependence of GnRH-stimulated growth hormone release in goldfish pituitary cells. 908 72

Previous studies have demonstrated that growth hormone (GH) release in goldfish is under the stimulatory control of gonadotropin-releasing hormone (GnRH) and dopamine and the inhibitory control of somatostatin (SRIF). GnRH stimulation is mediated through protein kinase C (PKC)- and calcium-dependent mechanisms, whereas dopamine D1 receptor activation increases GH secretion through cyclic (c) AMP-dependent intracellular signal transduction pathways. In this study, the mechanisms of SRIF inhibition on GH secretion were examined using primary cultures of dispersed goldfish pituitary cells in static incubation. Application of 1 microM SRIF inhibited the GH-release responses to 100 nM salmon GnRH, 100 nM chicken GnRH-II, and 1 microM SKF38393, a D1 agonist. These results indicate that inhibitory action of SRIF on stimulated GH release is direct, at the level of the pituitary cells. Addition of SRIF reduced the GH release responses to two activators of PKC (100 microM dioctanoyl glycerol and 100 nM tetradecanoyl phorbol acetate) and to two ionophores (10 microM A23187 and 10 microM ionomycin). Similarly, SRIF abolished the GH responses to an activator of adenylate cyclase (10 microM forskolin), a membrane-permeant cAMP analog (1 mM 8-bromo-cAMP), and a voltage-sensitive calcium channel agonist (1 microM Bay K 8644). Taken together, these observations indicate that the inhibitory actions of SRIF on D1- and GnRH-stimulated GH release can be exerted at sites distal to cAMP production and PKC activation, respectively. SRIF also exerts its effect at sites distal to calcium mobilization. Since SRIF inhibition was more effective against Bay K 8644-induced response than against ionophore-induced GH response, an inhibitory action at the level of extracellular calcium entry through voltage-sensitive channels is also possible.
...
PMID:Somatostatin inhibition of growth hormone release in goldfish: possible targets of intracellular mechanisms of action. 940 21

Overnight preincubation of goldfish pituitary cell culture with testosterone (T) enhanced the gonadotropin (GTH)-II responses to GTH-releasing hormone (GnRH). In this study, the involvement of GnRH signal transduction components and the requirement for T metabolism in mediating this direct, pituitary cell action of T were examined using cultured pituitary cells from both male and female goldfish. Each sets of related experiments were done in at least two different stages of the gonadal reproductive cycle and similar effects were observed. Overnight treatment with 10 nM T increased GTH-II responses to maximal stimulatory doses (100 nM) of either salmon (s)GnRH or chicken (c)GnRH-II, but not the total cellular GTH-II contents measured prior to and after a 2-h GnRH challenge. T increased the efficacy and sensitivity of the GTH-II response to stimulation by a protein kinase C (PKC) activator, tetradecanoyl phorbol acetate (TPA) without altering the ED50 of the dose-response curve. In T-treated cells, addition of a PKC inhibitor attenuated GTH-II responses to 100 nM doses of sGnRH, cGnRH-II, or TPA. T did not affect the GTH-II release stimulated by high concentrations of the Ca2+ ionophore ionomycin (100 microM) and the voltage-sensitive Ca2+ channel (VSCC) agonist Bay K 8644 (10 microM); similarly, the sensitivity of the GTH-II response to ionomycin and Bay K 8644 was also unaltered. Taken together, these data suggest that T potentiates GnRH-stimulated GTH-II release by enhancing the effectiveness of PKC-dependent pathways, but not by increasing the total Ca2+-sensitive GTH-II pool, the sensitivity of the release response to increases in intracellular Ca2+, or the amount of available GTH-II. However, the VSCC agonist nifedipine reduced sGnRH- and cGnRH-II-elicited GTH-II release in T-treated as well as in non-T-treated cells, suggesting that VSCC dependence is still present in the GnRH-induced response following exposure to T. Since total cGnRH-II binding to pituitary cells was not increased by T, increases in GnRH receptor capacity are unlikely following T treatment. The ability of T to increase GnRH-stimulated GTH-II secretion was not mimicked by 11-ketotestosterone or dihydrotestosterone, but was abolished by coincubation with an aromatase inhibitor. When viewed together, these observations suggest that aromatization of T may be required for the pituitary action of T on GnRH-induced GTH-II release.
...
PMID:In vitro action of testosterone in potentiating gonadotropin-releasing hormone-stimulated gonadotropin-II secretion in goldfish pituitary cells: involvement of protein kinase C, calcium, and testosterone metabolites. 970 78

1 2 3 Next >>