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)

These studies describe the effect of protein kinase C (PKC) activation on the activity of voltage-sensitive L-type Ca2+ channels of GH3 pituitary cells. The rate of 45Ca2+ uptake was stimulated greater than 25-fold by depolarization in the presence of BAY K 8644; the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) reduced this response by 70% in a concentration-dependent fashion. Phorbol 12,13-dibutyrate (PDBu) inhibited depolarization-induced 45Ca2+ uptake within 1 min and caused a nearly maximal reduction after 1 h; its effects were rapidly reversible. TPA decreased the high K(+)-stimulated increase in intracellular free calcium ion concentration ([Ca2+]i) from 8.5- to 3.2-fold by 5 min and to 2.0-fold after 18 h without altering the peak [Ca2+]i response to the peptide hormone TRH. Ca2+ channel current, measured directly using the whole cell configuration of the patch-clamp technique, declined an average of 6.4% over 5 min for control cells and 28.9% when TPA was added to the bathing medium for 5 min. Treatment with 100 nM TPA for 24 h dramatically reduced peak current without shifting the peak of the current-voltage relationship. The mean peak Ca2+ channel current was reduced from 423 to 128 pA, although a few cells seemed completely resistant. To determine whether the effects of phorbol esters were due to the activation of PKC we tested the potency of several drugs to inhibit L-channel activity and to shift the affinity of the epidermal growth factor (EGF) receptor, an established PKC response.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Activation of protein kinase C reduces L-type calcium channel activity of GH3 pituitary cells. 131 2

In GH3 cells and other clonal rat pituitary tumor cells, TRH has been shown to mediate its effects on prolactin release via a rise of cytosolic Ca2+ and activation of protein kinase C. In this study, we examined the role of protein kinase C in TRH-stimulated prolactin release from female rat primary pituitary cell culture. Both TRH and PMA stimulated prolactin release in a dose-dependent manner. When present together at maximal concentrations, TRH and PMA produced an effect which was slightly less than additive. Pretreatment of rat pituitary cells with 10(-6) M PMA for 24 hrs completely down-regulated protein kinase C, since such PMA-pretreated cells did not release prolactin in response to a second dose of PMA. Interestingly, protein kinase C down-regulation had no effect on TRH-induced prolactin release from rat pituitary cells. In contrast, PMA-pretreated GH3 cells did not respond to a subsequent stimulation by either PMA or TRH. Pretreatment of rat pituitary cells with TRH (10(-7) M, 24 hrs) inhibited the subsequent response to TRH, but not PMA. Forskolin, an adenylate cyclase activator, stimulated prolactin release by itself and in a synergistic manner when incubated together with TRH or PMA. The synergistic effects of forskolin on prolactin release was greater in the presence of PMA than TRH. Down-regulation of protein kinase C by PMA pretreatment abolished the synergistic effect produced by PMA and forskolin but had no effect on those generated by TRH and forskolin. sn-1,2-Dioctanylglycerol (DOG) pretreatment attenuated the subsequent response to DOG and PMA but not TRH. The effect of TRH, but not PMA, on prolactin release required the presence of extracellular Ca2+. In conclusion, the mechanism by which TRH causes prolactin release from rat primary pituitary cells is different from that of GH3 cells; the former is a protein kinase C-independent process whereas the latter is at least partially dependent upon the activation of protein kinase C.
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PMID:PMA-sensitive protein kinase C is not necessary in TRH-stimulated prolactin release from female rat primary pituitary cells. 145 79

Endogenous phosphorylation of microtubule-associated proteins was examined in cultures of anterior pituitary cells from estradiol-treated rats. The cells were incubated for 1 h with 32P-orthophosphate and challenged for different times with removal of dopamine (DA), the addition of TRH in the presence of DA, or the transient removal of DA followed by addition of TRH. Microtubules were bundled by taxol followed by electrophoretic separation of the phosphorylated proteins and autoradiography. Within 10 s to 1 min of any of the treatments increased labeling of eight phosphoproteins (64, 80, 95, 110, 125, 155, 205 and 300 kDa) appeared in autoradiograms. The pattern of labeling in response to DA withdrawal was longer-lasting than that induced by TRH, whose effect disappeared by 10 min. The administration of TRH after a transient 10-min withdrawal of DA increased the magnitude and prolonged the duration of the effect of TRH. The 80-kDa microtubule-associated protein comigrated with the well characterized heat-stable, acid-soluble protein substrate for protein kinase C (PKC). The migration of the proteins following two-dimensional polyacrylamide gel electrophoresis and autoradiography was identical. Furthermore, the sequential extraction of microtubule-associated proteins followed by extraction of heat-stable, acid-soluble proteins showed a phosphoprotein of Mr 80 kDa. These observations suggest that the ubiquitous, heat-stable, acid-soluble 80-kDa phosphoprotein that is a specific substrate for PKC is associated with microtubules in lactotrophs. Furthermore, the levels of microtubule-associated phosphoprotein are increased following hormonal activation of PKC, although it is unclear whether this increase represents translocation of the phosphoprotein or phosphorylation of a previously associated protein.
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PMID:Hypothalamic regulation of microtubule-associated protein phosphorylation in lactotrophs. 150 62

We have reviewed the literature, which supports an important role for dopamine withdrawal in the regulation of PRL secretion. Concentrations of dopamine in the hypophyseal portal circulation are sufficient to occupy the majority of dopamine receptors (1) and tonically suppress PRL secretion (20-26). Brief escapes from dopaminergic regulation associated with the secretion of PRL have been observed (37-41). Therefore, dopamine regulates secretion of PRL both by occupancy of, as well as dissociation from, specific D2 dopamine receptors. The rapid off rate from its receptor (2) is consistent with signals transmitted through brief decreases in dopamine concentration. The removal of dopamine for 10 min results in increases in intracellular cAMP and presumably activation of protein kinase A (39, 138) as well as activation of phospholipase C (137, 138) and protein kinase C (136). The removal of dopamine results directly in the release of PRL (37-41). Furthermore, the brief removal of dopamine results in the long-term potentiation of the PRL-releasing action of TRH (38-40). The potentiating action of dopamine withdrawal appears to be mediated by the activation of protein kinase A since pretreatment with VIP, a hormone that signals via protein kinase A, also potentiates the action of TRH (39). TRH stimulates PRL release via Ca2+/protein kinase C (177-184). The potentiating action of dopamine removal is selective for the Ca2+/protein kinase C pathway since dopamine removal does not potentiate the PRL-secreting action of VIP (38, 87, 92). The action of TRH is potentiated up to 30 min after the return of dopamine and the suppression of PRL to basal levels (38). In Fig. 10, dopamine dissociation from its receptor or VIP association to its receptor are shown separated by a broken line to indicate that by the time the potentiation of the action of TRH is tested, either dopamine is again occupying its receptor or VIP is no longer present. Therefore, the effect of protein kinase A activation is remembered by the lactotroph. We hypothesize that the responsiveness of the cell to TRH is potentiated by the phosphorylation of proteins by protein kinase A. Two potential substrates for protein kinase A are voltage-dependent Ca2+ channels and protein phosphatase inhibitors that would prolong the action of protein kinase C. When TRH occupies its receptor, intracellular Ca2+ levels are increased first from intracellular stores and subsequently by extracellular Ca2+ influx (187-189). Intracellular Ca2+ is mobilized by increased levels of IP3(128). Extracellular Ca2+ enters the lactotroph via voltage-dependent Ca2+ channels (189, 190).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Dissociation of dopamine from its receptor as a signal in the pleiotropic hypothalamic regulation of prolactin secretion. 161 63

Previous reports have provided conflicting evidence as to whether the response to TRH desensitizes. Here we show that TRH stimulation of phosphoinositide (PPI) hydrolysis, measured as inositol phosphate accumulation in the presence of LiCl, desensitizes in rat pituitary GH3 cells and in rat glioma C6 cells stably transfected with mouse pituitary TRH receptor complementary DNA. In GH3 cells, the rate of stimulation by 1000 nM TRH of PPI hydrolysis was maximal initially and then decreased by 44 +/- 13% after 20 min. In an experimental paradigm in which PPI hydrolysis was measured by adding 20 mM LiCl at different times after TRH, desensitizations caused by 3, 10, and 1000 nM TRH were 33 +/- 5%, 41 +/- 6%, and 69 +/- 2%, respectively. In transfected C6 cells, TRH-induced desensitization of 76 +/- 9% was found. In GH3 cells, 1 microM phorbol myristate acetate (PMA), an activator of protein kinase C, inhibited the initial response to TRH by 75 +/- 6% and preexposure to PMA and TRH decreased the rate of PPI hydrolysis by 98 +/- 1% after 60 min. One hundred micromolar H-7 (1-(5-isoquinolinesulfonyl)-2-methyl piperazine), an inhibitor of protein kinases, abolished the effect of PMA but did not inhibit TRH-induced desensitization. Elevation of cytoplasmic free Ca2+ by K+ depolarization increased TRH stimulation of PPI hydrolysis. We conclude that TRH stimulation of PPI hydrolysis acutely desensitizes and that this effect is not specific to pituitary cells. TRH-induced desensitization, moreover, does not appear to be mediated by protein kinase C or by elevation of cytoplasmic free Ca2+.
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PMID:Thyrotropin-releasing hormone stimulation of phosphoinositide hydrolysis desensitizes. Evidence against mediation by protein kinase C or calcium. 165 82

We showed previously that TRH down-regulates TRH receptor (TRH-R) mRNA in GH3 cells by a mechanism that appears to be mediated by protein kinase C. Here we show that vasoactive intestinal peptide (VIP) down-regulates TRH-R mRNA and present evidence that this action is mediated by protein kinase A. In GH3 cells, VIP caused a time- and concentration-dependent decrease in TRH-R mRNA. This VIP effect was simulated by 8-(4-chlorophenylthio)-cAMP, forskolin, cholera toxin and 1-methyl-3-isobutylxanthine. When cells were incubated with agents that elevate cAMP and TRH or phorbol 12-myristate 13-acetate, the decrease in TRH-R mRNA was greater than with either agent alone. When cells were pre-incubated with H-7 [1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride], an inhibitor of protein kinases, the effects of VIP, TRH and phorbol 12-myristate 13-acetate were inhibited. We suggest that VIP, via protein kinase A, and TRH, via protein kinase C, dually regulate TRH-R mRNA.
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PMID:Evidence for dual regulation by protein kinases A and C of thyrotropin-releasing hormone receptor mRNA in GH3 cells. 165 32

The stimulation of TSH secretion by TRH involves the phosphatidylinositol second messenger pathway via activation of phospholipase C. This effect is mediated by a GTP-binding protein and leads to a mobilization of intracellular Ca2+ stores and an activation of protein kinase C. However, TRH stimulation also results in an influx of extracellular Ca2+. Since we have previously demonstrated that a non-TRH fragment of the prepro-TRH molecule, the connecting peptide PS4 (prepro-TRH 160-169), was able to potentiate the TRH-induced TSH release in a dose-dependent manner, we attempted to determine whether this potentiation might be due to a Ca(2+)-dependent phenomenon and whether a specific class of voltage-dependent Ca2+ channels, the L type Ca2+ channels, might be involved in the effect of PS4. This was studied by perifusing normal pituitary fragments with medium containing either the Ca2+ ionophore, ionomycin, and Co2+ ions, or organic compounds well known to block L-type Ca2+ channels, and by measuring the TSH response to a pulse of TRH (10 nM) in the presence or absence of PS4 (100 nM).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:A prepro-TRH connecting peptide (prepro-TRH 160-169) potentiates TRH-induced TSH release from rat perifused pituitaries by stimulating dihydropyridine- and omega-conotoxin-sensitive Ca2+ channels. 166 99

Adenosine is a potent paracrine/autocrine feedback inhibitor of cell activation in a variety of tissues. Adenosine action was studied in pituitary cells, in which spontaneous electrical activity causes characteristic oscillations of the cytosolic free Ca2+ concentration, [Ca2+]i. Cells of the GH3B6 rat pituitary tumor line were studied by microspectrofluorimetry using the Ca2+ probes indo-1 and fura-2, in part in combination with electrophysiological tight seal whole cell recordings, obtained with the novel approach of patch perforation. It was demonstrated that adenosine receptor activation by N6-(R-phenyl-isopropyl)-adenosine (PIA) caused a block of electrical activity and abolished the ensuing alterations in [Ca2+]i. PIA mimicked the inhibitory action of somatostatin. Adenosine effects are mediated by A1 receptors in these cells and are antagonized by IBMX, an adenosine receptor blocker. PIA also suppressed action potentials that were elicited by the activation of protein kinase C with the phorbol ester PMA, or during the second phase of TRH action. In contrast, no interference was notable on TRH-induced intracellular Ca2+ mobilization. In addition to the abolition of Ca2+ transients, PIA lowers basal [Ca2+]i in some cells. It is proposed that in addition to the inhibition of adenylate cyclase, A1 receptor action on [Ca2+]i is an important element in the control of excitable pituitary cells.
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PMID:Adenosine A1 receptor-induced inhibition of Ca2+ transients linked to action potentials in clonal pituitary cells. 168 Jul 18

In GH4C1 rat pituitary cells, 1,25-dihydroxycholecalciferol (1,25(OH)2D3) causes amplification of both the TRH-induced spike phase in cytosolic free calcium [( Ca2+]i) and the increase in [Ca2+]i induced by depolarization with K+. In the present study we investigated the actions of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on Ca2(+)-homeostasis in GH4C1 cells pretreated with 1,25(OH)2D3 for 24 h. In control and 1,25(OH)2D3-pretreated cells, incubation with TPA (0.1-300 nM) for 15 min in the presence of 45Ca2+ did not affect the basal uptake of 45Ca2+. However, if the cells were treated with 50 mM K+, TPA induced a time- and concentration-dependent decrease in depolarization-induced net 45Ca2+ uptake. A maximal decrease of 30-50% was observed with 100-300 nM TPA, 1,25(OH)2D3 pretreated cells being more responsive to the action of TPA than control cells. sn-1-Oleoyl-2-acetyl-glycerol, which mimics the action of TPA on protein kinase C (PKC), did not alter depolarization-induced uptake of 45Ca2+. Two agents which inhibit PKC activity, polymyxin B and K252A, did not prevent the effect of TPA on depolarization-induced uptake of 45Ca2+, whereas staurosporin totally inhibited the action of TPA. In Fura-2 loaded cells pretreated with 1,25(OH)2D3, incubation with 200 nM TPA for 9 min decreased the depolarization-induced spike and plateau phases of change in [Ca2+]i; only the spike phase was decreased in control cells. TPA did not affect basal [Ca2+]i in either group. Treatment with TPA for only 3 min decreased the TRH-induced spike in [Ca2+]i only in 1,25(OH)2D3 pretreated cells; however, after a 5-min treatment with TPA, the TRH-induced spike in [Ca2+]i was decreased in both control and 1,25(OH)2D3 pretreated cells. TPA did not affect the spike in [Ca2+] induced by 50 nM ionomycin. Na+/Ca2+ exchange was not altered by TPA, nor did TPA enhance efflux of 45Ca2+ from cells preloaded with 45Ca2+ for 2.5 h. We conclude that, in GH4C1 cells, TPA modulates plasma membrane calcium flux, probably via an inhibitory action on voltage-operated Ca2+ channels. This inhibitory action may be independent of activation of PKC, and 1,25(OH)2D3 pretreated cells are more responsive to the actions of TPA than are control cells. These results are consistent with our previous findings that 1,25(OH)2D3 enhances voltage-dependent Ca2+ channel activity in GH4C1 cells.
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PMID:12-O-tetradecanoyl-phorbol-13-acetate decreases influx of extracellular Ca2+ induced by depolarization in GH4C1 cells: effects of pretreatment with 1,25-dihydroxycholecalciferol. 169 Jun 36

Our previous studies demonstrated TRH stimulation of TSH beta gene expression in rat pituitary cell cultures and GH3 tumor cells in a transient expression assay. To begin to characterize the gene-proximal elements of the pathways involved in TRH stimulation of TSH beta gene transcription, we examined the effects of factors that increase intracellular calcium concentration, [Ca2+]i, or activate protein kinase C on TSH beta promoter activity in transfected GH3 cells. TPA, a tumor-promoting phorbol ester, stimulated a dose-dependent increase in TSH beta promoter activity at 8 h similar to TRH (2-3-fold). TPA did stimulate protein kinase C activation without [Ca2+] mobilization. The calcium ionophore ionomycin increased cytoplasmic free [Ca2+] by stimulating both calcium influx and release from internal stores without affecting protein kinase C. Ionomycin also stimulated a dose-dependent increase (2-fold) in TSH beta promoter activity at 8 h. However, the voltage-dependent Ca2+ channel agonist Bay K 8644, which increased influx of extracellular calcium, had little or no effect on TSH beta gene expression until 48 h (5-fold). Similar effects on prolactin/mRNA levels were observed in these cells. Effects of these factors were not additive, suggesting a common pathway(s) to stimulate gene expression. Inhibition of intracellular calcium mobilization by treatment with 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB-8) inhibited ionomycin effects on gene expression without affecting phorbol ester activity, and, conversely, inhibition of protein kinase C activity by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine dihydrochloride (H-7) or TPA desensitization blocked TPA effects without affecting ionomycin activity.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Thyrotropin-releasing hormone regulation of thyrotropin beta-subunit gene expression involves intracellular calcium and protein kinase C. 170 68


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