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)

The cDNAs for human 5-hydroxytryptamine (5-HT)2C and 5-HT2A receptors were stably transfected separately into parent Chinese hamster ovary cells, and cell lines in which levels of transfected receptor protein expression and accumulation of inositol phosphates in response to 5-HT were comparable were chosen for study. The effect of activation of these receptors on 5-HT1B-like receptor-mediated responsiveness (i.e., inhibition of forskolin-stimulated cAMP accumulation) was studied. Activation of 5-HT2C receptors with 5-HT (0.1-100 microM) abolished the 5-HT1B-like response, which returned when 5-HT2C receptors were blocked with mesulergine (1 microM). Furthermore, the maximal response to 5-carboxytryptamine was reduced in a concentration-dependent manner by the 5-HT2A/5-HT2C-selective partial agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane. In contrast, activation of 5-HT2A receptors with either 5-HT or (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane did not alter the 5-HT1B-like response. The reduction of 5-HT1B-like responsiveness produced by 5-HT2C receptor activation was independent of protein kinase C activation and increases in the intracellular calcium concentration. Although 5-HT2A and 5-HT2C receptors are strikingly similar in structure and pharmacology, and the signal transduction systems coupled to these receptors have been thought to be similar, if not identical, these data provide the first evidence for fundamental differences in the signal transduction systems of these 5-HT2 receptor subtypes.
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PMID:Signal transduction differences between 5-hydroxytryptamine type 2A and type 2C receptor systems. 793 28

Serotonin (5-HT) contracts the guinea pig trachea through stimulation of the 5-HT2A receptor, a receptor generally linked with phosphoinositide (PI) hydrolysis. However, previous limited evidence suggested that 5-HT did not increase PI hydrolysis in guinea pig trachea. The present studies confirmed that the 5-HT2A receptor is not coupled to PI hydrolysis and investigated the calcium source and involvement of protein kinase C (PKC) in 5-HT-induced contraction in guinea pig trachea. In vitro experiments, which used an enriched tracheal muscle preparation, confirmed the inability of 5-HT (10(-10) to 10(-2) M) to increase PI hydrolysis. Short incubations (1-60 min) of the trachea with 5-HT (10(-4) M) to minimize possible 5-HT2A receptor desensitization did not increase PI hydrolysis, whereas carbamylcholine (10(-7) to 10(-3) M) and histamine (10(-7) to 10(-4) M) did. These results demonstrate that, unlike most other 5-HT2A receptors, the 5-HT2A receptor in guinea pig trachea is not coupled to PI hydrolysis. The L-type calcium channel antagonists nitrendipine (10(-6) and 10(-5) M) and diltiazem (5 x 10(-5) M) significantly blocked maximal tracheal contraction to 5-HT (45-60%) inhibition) but not to carbamylcholine. The maximal response to 5-HT in calcium-free buffer (0 calcium, 0.05 mM EGTA) was also inhibited by 56%. The residual contraction to 5-HT in the absence of extracellular calcium suggested that at least a portion of the nitrendipine-insensitive 5-HT contraction was due to the release of intracellular calcium. In support of this idea, ryanodine (3 x 10(-5) M), a compound known to deplete intracellular calcium stores, depressed maximal 5-HT contraction in the presence of either nitrendipine or diltiazem. Neither calphostin C (4 x 10(-8) and 10(-6) M) or staurosporine (10(-8) M), both putative PKC inhibitors, affected tracheal contraction to 5-HT. However, the PKC inhibitor bisindolylmaleimide (5 x 10(-6) M), which abolished contraction to phorbol 12,13-dibutyrate (10(-6) M), unlike calphostin C, inhibited contraction to 5-HT in both the absence and presence of nitrendipine. This finding suggests that PKC activation is involved in 5-HT contraction. Thus, the tracheal 5-HT2A receptor is unique in that activation of the receptor does not result in PI hydrolysis but increases calcium influx through L-type voltage-dependent calcium channels, calcium release from the sarcoplasmic reticulum and activation of a bisindolylmaleimide-sensitive PKC.
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PMID:Contractile serotonin-2A receptor signal transduction in guinea pig trachea: importance of protein kinase C and extracellular and intracellular calcium but not phosphoinositide hydrolysis. 796 3

Exposure of P11 cells to serotonin (5-HT) resulted in a transient increase in levels of 5-HT2A receptor mRNA. Exposure to 5-HT for as short a time as 1 min was sufficient to trigger a delayed increase in receptor mRNA. 5-HT-induced increases in receptor mRNA levels were not antagonized by the protein synthesis inhibitor cycloheximide. The increase in receptor mRNA levels was accompanied by a transient increase in the half-life of receptor mRNA; the rate of transcription of receptor mRNA was unchanged. Submaximal stimulation of phosphinositide hydrolysis by partial agonists or 6-fluoronorepinephrine, an alpha 1-adrenergic receptor agonist, also increased receptor mRNA levels. Exposure to phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C, mimicked these effects, whereas the protein kinase C inhibitor bisindolylmaleimide antagonized the effects of both 5-HT and PMA. When agonist-promoted increases in receptor mRNA were prevented, the rate of agonist-induced down-regulation was accelerated. These data suggest that levels of 5-HT2A receptor mRNA are regulated by phospholipase C-coupled receptors via a protein kinase C-dependent, post-transcriptional mechanism and indicate that agonist-promoted increases in levels of 5-HT2A receptor mRNA modulate receptor expression.
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PMID:Regulation of mRNA encoding 5-HT2A receptors in P11 cells through a post-transcriptional mechanism requiring activation of protein kinase C. 798 58

The effects of 5-hydroxytryptamine (5-HT)2A receptor activation on cAMP formation were studied in a cell line derived from embryonic rat cortex (A1A1). 5-HT (EC50 = 0.87 microM) amplified the amount of cAMP formed in response to 5'-N-ethylcarboxamidoadenosine (an adenosine A2 receptor agonist), cholera toxin, and forskolin after 15 min of coincubation in the presence of the phosphodiesterase inhibitor rolipram. This effect of 5-HT was blocked by 10 nM ketanserin as well as by 10 nM spiperone, indicating a response mediated by the 5-HT2A receptor subtype. Similarly, cAMP accumulation was enhanced by coincubation with the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) and the calcium ionophore A23187. After exposure to PMA for 24 hr (PKC-depleted cells), 5-HT and A23187 still enhanced cAMP formed in response to forskolin and 5'-N-ethylcarboxamidoadenosine, whereas the amplifying effects of PMA were abolished. Analysis by Western blots and PKC activity measurements revealed that, of three PKC isoforms detected in A1A1 cells (alpha, delta, and epsilon), only the calcium-independent isoform PKC-epsilon remained in membrane fractions after long term PMA treatment. In PKC-depleted cells, 5-HT-mediated amplification was greatly reduced after treatment with the calcium chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (acetoxymethyl)-ester or the calmodulin antagonists calmidazolium and N-(6-aminohexyl)-5-chloro-1-napthalenesulfonamide hydrochloride. In addition, 5-HT-mediated amplification of cAMP accumulation was reduced by the PKC inhibitor staurosporine in normal cells but was unaffected in PKC-depleted cells. In conclusion, these data suggest that 5-HT2A receptor activation can amplify cAMP formation in A1A1 cells by two distinct pathways coupled to the hydrolysis of inositol phosphates, i.e., PKC and calcium/calmodulin.
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PMID:5-Hydroxytryptamine type 2A receptors regulate cyclic AMP accumulation in a neuronal cell line by protein kinase C-dependent and calcium/calmodulin-dependent mechanisms. 819 Jan

Corticotropin-releasing factor (CRF), the key neuropeptide in the stress cascade, has major inhibitory actions on testicular function in addition to its known antireproductive effects at the central level (inhibition of sexual behavior and LH secretion). CRF is secreted by the Leydig cells of the testis and acts through high-affinity receptors at the Leydig cell membrane as a potent negative regulator of LH action, inhibiting gonadotropin-induced cAMP generation and androgen production. CRF is also a primary stimulus of beta-endorphin secretion by the Leydig cells, which in turn exerts paracrine inhibition of FSH action in the tubular compartment of the testis through high-affinity receptors in the Sertoli cells. CRF action in the Leydig cells involves a pertussis toxin-insensitive guanyl nucleotide regulatory unit. In contrast to CRF receptors in the brain, pituitary, and other peripheral tissues, those in the Leydig cell are not coupled to Gs. The inhibitory action of CRF in the Leydig cell is exerted through protein kinase C, at the level of the catalytic subunit of adenylate cyclase. The secretion of CRF by the Leydig cell is stimulated by LH, acting via release of serotonin (5HT) and autocrine activation of 5HT2 receptors. Serotonin acts on 5HT2 receptors in the Leydig cell to stimulate CRF secretion via a pertussis toxin insensitive G-protein and presumably through activation of phosphoinositide hydrolysis. The diversity of the biochemical responses to CRF and 5HT2 receptor activation (i.e., inhibition of adenylate cyclase at the cytoplasmic aspect of the cell membrane vs. stimulation of CRF release from secretion granules) may reflect the stimulation of different protein kinase C isoenzymes. The LH-->5HT-->CRF inhibitory loop serves to continuously buffer the stimulation of androgen production by gonadotropin. 5HT, the immediate stimulus of testicular CRF secretion, is released during stress and is locally increased in the testis in pathological conditions associated with impaired testicular function (i.e., orchitis, varicocele). Also, propranolol, the beta-adrenergic antagonist frequently used in the control of blood pressure in patients with hypertension and often associated with impotence, acts via a serotonergic mechanism to stimulate CRF secretion and causes marked inhibition of LH-induced cAMP production and steroidogenesis in cultured Leydig cells. These basic studies of 5HT and CRF are relevant to the pathogenesis of testicular dysfunction and for the development of antagonist therapies to block CRF production and its local antireproductive effects.
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PMID:Corticotropin-releasing factor: an antireproductive hormone of the testis. 838 38

Desensitization of serotonin 5-HT2 receptor-mediated enhancement of the N-methyl-D-aspartate (NMDA) depolarization was studied in rat cortical neurons. Serotonin and (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) induced long term desensitization. Staurosporine, a nonspecific protein kinase C inhibitor, potentiated the serotonin and DOI facilitation, suggesting acute desensitization was operative. In the case of DOI, long term desensitization was prevented by staurosporine. Activators of protein kinase C abolished the serotonin facilitation, an action prevented by staurosporine. Concanavalin A potentiated the facilitation at 100 microM, but not 30 microM serotonin, suggesting these receptors undergo dose dependent internalization. Calmodulin antagonists prevent long term desensitization induced by serotonin. The depolarization induced by NMDA alone was not altered by staurosporine, protein kinase C activators, concanavalin A or calmodulin antagonists. Serotonin at 100 microM, but not 30 microM, induced heterologous desensitization of phenylephrine and carbachol induced facilitation of the NMDA depolarization. We conclude that serotonin 5-HT2 receptors both induce and undergo several forms of desensitization.
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PMID:Multiple mechanisms of serotonin 5-HT2 receptor desensitization. 840 90

Previously it has been shown that excitatory effects of 5-hydroxytryptamine (5-HT) upon interneurons in the rat piriform cortex are mediated by 5-HT2A receptors. This receptor is linked to phosphoinositide turnover, and one consequence of stimulating this receptor is the activation of protein kinase C (PKC). In the present study, the effect of PKC inhibitors on the 5-HT excitation of piriform cortical interneurons was examined by extracellular recording in a rat brain slice preparation. Bath application of the selective PKC inhibitors, bisindolymalemide and chelerythrine, and the nonselective protein kinase inhibitor, H-7, all enhanced the excitatory effects of 5-HT. Two other nonselective protein kinase inhibitors, H-8 and HA 1004, which are 2.5-fold and 6.7-fold less potent than H-7 at inhibiting PKC, produced a slight or no enhancement, respectively, of the excitatory effect of 5-HT. Bisindolylmalemide, chelerytrine, and H-7 did not enhance the excitatory effects of norepinephrine or carbachol on the same interneurons. The PKC activator phorbol 12, 13-diacetate (PDA) decreased the excitatory effect of 5-HT; this decrease was rapidly reversed by H-7. As inhibitors of PKC selectively enhanced rather than blocked the excitation by 5-HT mediated by 5-HT2A receptors, we conclude that activation of PKC does not mediate the excitation by 5-HT of piriform cortical interneurons. Instead, we propose that PKC may have a negative feedback role in modulating the excitation by 5-HT of piriform cortical interneurons.
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PMID:Protein kinase C inhibitors enhance the 5-HT2A receptor-mediated excitatory effects of serotonin on interneurons in rat piriform cortex. 858 73

P11 cells were used as an in vitro model system to explore effects of exposure to 5-HT on levels of mRNA encoding 5-HT2A receptors. Exposure of cells to the agonist 5-HT resulted in a doubling of receptor mRNA levels. mRNA levels returned to control levels within 8-16 h. The stability of receptor mRNA transcripts was transiently increased, suggesting that a post-transcriptional process was responsible for the up-regulation of receptor mRNA. The 5-HT-induced increase in Levels on 5-HT2A receptor mRNA did not require de novo protein synthesis since the increase was not affected by prior treatment with the protein synthesis inhibitor cycloheximide. Results of studies in which the activity of protein kinase C was either increased with PMA or antagonized with bisindolylmaleimide indicated that protein phosphorylation was essential for increasing levels of 5-HT2A receptor mRNA. These findings suggest that PKC-dependent post-transcriptional and post-translational processes participate in regulating 5-HT2A receptor mRNA expression.
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PMID:Regulation of 5-HT2A receptor mRNA in P11 cells. 878

This study was undertaken to evaluate the effect of acute in vivo treatment with 1-(2,5-dimethoxy-4-iodo-phenyl)2-aminopropane (DOI), a selective 5-hydroxytryptamine 2A/2C (5HT2A/2C) receptor agonist, on the kinetic parameters of [3H]ketanserin binding to 5HT2A receptors and on the protein kinase C (PKC) activity in subcellular fractions of rat brain tissue. A single injection of DOI (10 mg/kg i.p.) downregulated (by 50%) 5HT2A receptor density in a cortical synaptosomal preparation assayed 24 h later. This effect was dose dependent, since a single injection of 5 mg/kg of DOI reduced the Bmax of [3H]ketanserin binding by 23% (without a change in Kd) and a single 1 mg/kg dose of DOI was without effect. Repeated doses of DOI (10 mg/kg for 3 days) further downregulated (by 63%) 5HT2A sites in cortical synaptosomes. A similar degree (50%) of downregulation of 5HT2A receptors by DOI (10 mg/kg) was seen in p-chloroamphetamine (PCA) lesioned rats, suggesting that the site of action of DOI in downregulation of 5HT2A receptors in rat brain is postsynaptic. An increase (by 38%) of PKC activity in the particulate fraction of the cortical synaptosomal preparation following a single injection of DOI (10 mg/kg) paralleled the decrease in 5HT2A receptor density, suggesting that 5HT2A sites may be downregulated as a result of phosphorylation of the receptor by activation of PKC after receptor stimulation with agonist. This possibility is further supported by the observation that three consecutive daily injections of DOI resulted in a significant decrease (by 19%) in cytosolic PKC activity and an increase (by 24%) of PKC activity in the particulate fraction. A single injection of DOI also induced a translocation of PKC activity from the cytosolic to the membrane fraction in PCA-lesioned rats. The present investigation has shown that downregulation of 5HT2A receptors in rat cerebral cortex by in vivo DOI treatment is accompanied by translocation of PKC activity from the cytosolic to the membrane fraction.
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PMID:Possible role of protein kinase C in regulation of 5-hydroxytryptamine 2A receptors in rat brain. 883 81

The aim of this study was to demonstrate that 5-HT activates electrolyte transport directly via 5-HT2A receptor in rat colonic crypt cells. Patch-clamp whole cell recording was performed in isolated crypts to measure the 5-HT-induced changes in electrogenic K+ and Cl- currents. Superfusing 5-HT (10 microM) in the bath solution increased both K+ and Cl- currents, which were antagonized by the presence of ketanserin (1 microM), a selective 5-HT2A antagonist, in the bath solution. Mesulergine (1 microM) a 5-HT2A and 5-HT2C antagonist, had no inhibitory effect. Strong chelation of the intracellular Ca2+ by 5 mM BAPTA inhibited 5-HT-induced currents. 5-HT also failed to activate K+ and C1- currents in the presence of GDPbetaS (0.5 mM) in the pipette solution. Intracellular administration of GTPgammaS (0.1 mM) mimicked the stimulatory effect of 5-HT, that was inhibited by 5 mM BAPTA. H-7 (0.05 mM), an inhibitor of protein kinase C, A, and G, did not affect the currents. These data indicate that a G protein-coupled pathway is involved in the activation of electrolyte secretion via 5-HT2A receptor.
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PMID:Serotonin activates electrolyte transport via 5-HT2A receptor in rat colonic crypt cells. 901 98


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