Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.24 (mitogen-activated protein kinase)
 95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It has been known for some time that chronic treatment of neuronal cells and tissues with opioids, contrary to their acute effect, leads to an increase in cAMP accumulation. This phenomenon, defined as adenylyl cyclase superactivation, has been implicated in opiate addiction, yet the mechanism by which it is induced remains unclear. Here, we show that this phenomenon can be reproduced and studied in COS-7 cells cotransfected with adenylyl cyclase type V and mu-opioid receptor cDNAs. These cells display acute opioid inhibition of adenylyl cyclase activity, whereas prolonged exposure to the mu-agonist morphine or [-Ala2, N-methyl-Phe4, Gly-ol5]enkephalin leads to a time-dependent superactivation of adenylyl cyclase. This superactivated state is reversible, because it is gradually lost following agonist withdrawal. Adenylyl cyclase superactivation can be prevented by pertussis toxin pretreatment, indicating the involvement of Gi/o proteins, or by cotransfection with the carboxyl terminus of beta-adrenergic receptor kinase or with alpha-transducin (scavengers of Gbetagamma dimers), indicating a role for the G protein betagamma dimers in adenylyl cyclase superactivation. However, contrary to several other Gbetagamma-dependent signal transduction mechanisms (e.g. the extracellular signal-regulated kinase 2/MAP kinase pathway), adenylyl cyclase superactivation is not affected by the Ras dominant negative mutant N17-Ras.
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PMID:Chronic opioid treatment induces adenylyl cyclase V superactivation. Involvement of Gbetagamma. 870 9

To examine whether the mitogen-activated protein kinase (MAPK) cascade and phospholipase A2 (PLA2) are involved in the signal transduction mechanism of the opioid receptor, the delta-, mu-, and kappa-opioid receptors were stably expressed from cDNA in Chinese hamster ovary cells. Activation of the delta-, mu-, and kappa-receptors by agonists induced a rapid and transient increase in MAPK activity accompanied by reduced electrophoretic mobility of the 42-kDa isoform of MAPK (p42), probably owing to phosphorylation. The opioid receptor-mediated increase in MAPK activity was suppressed not only by pretreatment with genistein, a tyrosine protein kinase inhibitor, but also by prolonged exposure to phorbol 12-myristate 13-acetate and pretreatment with GF 109203X, a selective protein kinase C (PKC) inhibitor, suggesting the involvement of PKC as well as tyrosine protein kinase. Furthermore, stimulation of the delta-, mu-, and kappa-receptors with opioid agonists in the presence of A23187, a calcium ionophore, resulted in an increase in arachidonate release, suggesting that PLA2 is activated by the opioid receptors when the intracellular Ca2+ concentration is elevated. Both MAPK activation and increase in arachidonate release mediated by the opioid receptors were abolished by pretreatment with pertussis toxin, suggesting that these responses are mediated by Gi or Go types of GTP-binding regulatory proteins.
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PMID:Functional coupling of the delta-, mu-, and kappa-opioid receptors to mitogen-activated protein kinase and arachidonate release in Chinese hamster ovary cells. 875 40

The mitogen-activated protein (MAP) kinase of Chinese hamster ovary cells (CHO mu66 cell line) transfected to express mu-opioid receptors was markedly activated by mu agonists. The rank order of effectiveness of agonists was approximately the same as the rank order of their binding affinities to the mu receptor. The delta and kappa receptor-specific agonists cyclic[D-Pen2, D-Pen5]enkephalin and U69,593 showed a very weak stimulatory effect. The mu agonist-stimulated MAP kinase activity peaked at approximately 4-8 min and lasted almost 1 hr. The stimulatory effect of mu agonists was antagonized by the opioid receptor antagonist naltrexone and inhibited by pretreatment of cells with pertussis toxin. This opioid-induced activation of MAP kinase activity may have a role in the long term effects of opioids.
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PMID:The stimulatory effect of opioids on mitogen-activated protein kinase in Chinese hamster ovary cells transfected to express mu-opioid receptors. 879 99

Rat-1 fibroblasts were transfected with a cDNA encoding the mouse delta opioid receptor. Two separate clones, D2 (which expressed some 6 pmol of the receptor/mg of membrane protein) and DOE (which expressed some 0.2 pmol/mg of membrane protein), were examined in detail. With membranes from both clones, the opioid agonist [D-Ala2]leucine enkephalin (DADLE) caused stimulation of high-affinity GTPase activity and of the binding of guanosine 5'-[gamma-[35S]thio]triphosphate, and inhibition of forskolin-amplified adenylate cyclase activity. DADLE also induced phosphorylation and activation of both the p42MAPK (42 kDa isoform) and p44MAPK (44 kDa isoform) members of the mitogen-activated protein kinase (MAP kinase) family. All of these effects of DADLE were prevented in both clones by pretreatment of the cells with pertussis toxin. The maximal response that could be produced by DADLE in direct assays of G-protein activation were substantially greater in clone D2 than in clone DOE, but in both clones essentially full phosphorylation of both p42MAPK and p44MAPK could be achieved. EC50 values for DADLE stimulation of GTPase activity and for activation of p44MAPK were substantially lower in clone D2 than in clone DOE. Moreover, in both clones the EC50 value for DADLE stimulation of p44MAPK was substantially lower than that for stimulation of GTPase activity, and the Hill coefficients for agonist activation of p44MAPK (h > 1) displayed marked co-operativity whereas those for G-protein activation did not (h 0.8-1.0). DADLE activation of p44MAPK showed more sustained kinetics in clone D2 than in clone DOE. By contrast, lysophosphatidic acid, acting at an endogenously expressed G-protein-coupled receptor, also activated p44MAPK in both clones in a pertussis toxinsensitive manner, but both the kinetics and the concentration-response curve for activation of p44MAPK by this ligand were similar. As with other systems, maintained cellular levels of a cAMP analogue prevented the effects of both G-protein-coupled receptors on activation of p44MAPK. These results demonstrate for the first time that an opioid receptor, at least when expressed in Rat-1 fibroblasts, is able to initiate activation of the MAP kinase cascade in a G1-dependent manner, and show that only a very small proportion of the cellular G1 population is required to be activated to result in full phosphorylation of the p42MAPK and p44MAPK MAP kinases.
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PMID:Agonist activation of p42 and p44 mitogen-activated protein kinases following expression of the mouse delta opioid receptor in Rat-1 fibroblasts: effects of receptor expression levels and comparisons with G-protein activation. 894 92

Morphine sulfate causes immunomodulatory and immunosuppressive effects in human. In this study, the signaling pathway involved in these morphine effects was studied. Addition of morphine sulfate to human CEMx174 lymphocytic cells resulted in increased expression of mitogen-activated protein kinase cascade proteins. Morphine enhanced the cellular levels of ERK1 (44 kDa), ERK2 (42 kDa), a 54-kDa ERK, MEK1 (45 kDa), and MEKK (78 kDa). A time-dependent increase in the activated (Thr and Tyr dually phosphorylated) state of ERK1 and ERK2 was also observed. Naloxone, a morphine antagonist, reversed the observed morphine effects, implicating a micro opioid receptor-mediated process. These findings suggest that mitogen-activated protein kinases are important intermediates in signal transduction pathways initiated by morphine receptors in immune cells.
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PMID:Induction and activation of mitogen-activated protein kinases of human lymphocytes as one of the signaling pathways of the immunomodulatory effects of morphine sulfate. 934 Nov 10

Opioid receptor-like 1 (ORL1) receptor, a member of the superfamily of G-protein-coupled receptors has significant primary sequence homology to the mu-, delta- and kappa-opioid receptors. The ORL1 receptor is selectively activated by the recently discovered peptide nociceptin. To probe the functional homology amongst these receptors, a Chinese hamster ovary (CHO) cell line expressing the human ORL1 receptor has been characterized. Nociceptin inhibited forskolin-stimulated increases in intracellular cAMP with an IC50 of 70 pM. Stimulation by nociceptin caused a 2-fold increase in the rate of [35S]GTPgammaS binding to membranes derived from CHO cells expressing the ORL1 receptor. Following incubation with nociceptin mitogen-activated protein kinase activity was increased by 2-fold in cells expressing the ORL1 receptor. In non-transfected CHO cells, nociceptin had no effect on cAMP accumulation, the rate of [35S]GTPgammaS binding or mitogen-activated protein kinase activity. Human ORL1 receptors expressed in CHO cells selectively bound [125I][Tyr14]nociceptin with a Kd of 2.1 pM and a Bmax of 2.6 pmol/mg protein. Similar to opioid receptors, nociceptin binding to the ORL1 receptor was altered by Na+, GTPgammaS and dithiothreitol. Na+ increased the Kd of nociceptin binding to the ORL1 receptor. GTPgammaS decreased the apparent Bmax of [125I][Tyr14]nociceptin binding but had no effect on the Kd of the remaining sites. Pretreatment with dithiothreitol inhibited nociceptin binding to the ORL1 receptor. Nociceptin binding was insensitive to low nanomolar concentrations of opioid receptor-selective agonists and antagonists. However, high micromolar levels of opioid receptor-selective agents inhibited the binding. Morphine, naloxone, naltrindole, nor-Binaltorphimine and CTAP (D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2) inhibited nociceptin binding to ORL1 receptor with Ki values of 36, 24, 0.4, 8 and 28 microM, respectively. These results imply that ORL1 is a G-protein-coupled receptor with functional as well as structural homology to opioid receptors. In addition, opioid receptor ligands may serve as starting templates for the development of ORL1 specific ligands.
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PMID:Nociceptin activation of the human ORL1 receptor expressed in Chinese hamster ovary cells: functional homology with opioid receptors. 938 38

Many chemoattractants cause chemotaxis of leukocytes by stimulating a structurally distinct class of G protein-coupled receptors. To identify receptor functions required for chemotaxis, we studied chemotaxis in HEK293 cells transfected with receptors for nonchemokine ligands or for interleukin 8 (IL-8), a classical chemokine. In gradients of the appropriate agonist, three nonchemokine Gi-coupled receptors (the D2 dopamine receptor and opioid mu and delta receptors) mediated chemotaxis; the beta2-adrenoreceptor and the M3-muscarinic receptor, which couple respectively to Gs and Gq, did not mediate chemotaxis. A mutation deleting 31 C-terminal amino acids from the IL-8 receptor type B quantitatively impaired chemotaxis and agonist-induced receptor internalization, but not inhibition of adenylyl cyclase or stimulation of mitogen-activated protein kinase. To probe the possible relation between receptor internalization and chemotaxis, we used two agonists of the mu-opioid receptor. Morphine and etorphine elicited quantitatively similar chemotaxis, but only etorphine induced receptor internalization. Overexpression of two betagamma sequestering proteins (betaARK-ct and alphat) prevented IL-8 receptor type B-mediated chemotaxis but did not affect inhibition of adenylyl cyclase by IL-8. We conclude that: (i) Nonchemokine Gi-coupled receptors can mediate chemotaxis. (ii) Gi activation is necessary but probably not sufficient for chemotaxis. (iii) Chemotaxis does not require receptor internalization. (iv) Chemotaxis requires the release of free betagamma subunits.
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PMID:Receptors induce chemotaxis by releasing the betagamma subunit of Gi, not by activating Gq or Gs. 940 40

The effect of nociceptin/orphanin FQ (N/OFQ), an endogenous ligand for the newly identified opioid receptor-like (ORL1) receptor, on mitogen-activated protein kinase (MAPK) was investigated in Chinese hamster ovary cells stably expressing ORL1 receptor. N/OFQ rapidly stimulated phosphorylation and activity of MAPK (p42 and p44 isoforms) in a concentration-dependent manner. The p42 isoform was preferentially activated by N/OFQ. Maximal activation (5.4 +/- 1.2-fold of basal for p42 isoform) was achieved after a 1-min exposure of cells to 100 nM N/OFQ. The activation was blocked completely by pretreatment with pertussis toxin, but was not reversed by naloxone. U-73122, a phospholipase C-specific inhibitor, significantly inhibited phospholipase C activity, as well as MAPK activation stimulated by N/OFQ. Furthermore, N/OFQ-stimulated MAPK activation was suppressed by a protein kinase C-specific inhibitor, chelerythrine. The results demonstrate that N/OFQ can effectively stimulate MAPK by the activation of ORL1 receptor and pertussis toxin-sensitive G proteins, and that phospholipase C, as well as protein kinase C, is critically involved in these processes.
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PMID:Nociceptin/orphanin FQ activates mitogen-activated protein kinase in Chinese hamster ovary cells expressing opioid receptor-like receptor. 948 55

The mu-opioid receptor mediates not only the beneficial painkilling effects of opiates like morphine but also the detrimental effects of chronic exposure such as tolerance and dependence. Different studies have linked tolerance to opioid receptor desensitization. Agonist activation of the mu-opioid receptor stimulates a mitogen-activated protein kinase (MAPK) activity, but the functional significance of this pathway remains unclear. We have focused on the MAPK signaling cascade to study mu-opioid receptor desensitization. We report that inhibition of the MAPK pathway blocks desensitization of mu-opioid receptor signaling as well as the loss of receptor density due to internalization. Our results suggest that a feedback signal emanating from the MAPK cascade is required for mu-opioid receptor desensitization.
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PMID:A mitogen-activated protein kinase pathway is required for mu-opioid receptor desensitization. 957 95

The recently identified 17-amino acid peptide nociceptin (orphanin FQ) is the endogenous ligand for the opioid receptor-like-1 (ORL-1) receptor. A physiologic role for nociceptin (OFQ) activation of the ORL-1 receptor (OFQR) may be to modulate opioid-induced analgesia. The molecular mechanism by which nociceptin (OFQ) and ORL-1 (OFQR) modify opioid-stimulated effects, however, is unclear. Both ORL-1 (OFQR) and opioid receptors mediate pertussis toxin (PTX)-sensitive signal transduction, indicating these receptors are capable of coupling to Gi/Go proteins. This study determines that nociceptin stimulates an intracellular signaling pathway, leading to activation of mitogen-activated protein (MAP) kinase in CHO cells expressing ORL-1 receptor (OFQR). Nociceptin (OFQ)-stimulated MAP kinase activation was inhibited by PTX or by expression of the carboxyl terminus of beta-adrenergic receptor kinase (betaARKct), which specifically blocks Gbetagamma-mediated signaling. Expression of the proline-rich domain of SOS (SOS-PRO), which inhibits SOS interaction with p21ras, also attenuated nociceptin (OFQ)-stimulated MAP kinase activation. The phosphatidylinositol 3-kinase (PI-3K) inhibitors wortmannin and LY294002 reduced nociceptin (OFQ)-stimulated MAP kinase activation, whereas inhibition of protein kinase C (PKC) activity by bisindolylmaleimide I or cellular depletion of PKC had no effect. In a similar manner, in cells expressing mu-opioid receptor, [D-Ala2,N-Me-Phe4,Gly-ol]-enkephalin (DAMGO; a mu-opioid receptor-selective agonist) stimulated PTX-sensitive MAP kinase activation that was inhibited by wortmannin, LY294002, betaARKct expression, or SOS-PRO expression but not affected by inhibition of PKC activity. These results indicate that both ORL-1 (OFQR) and mu-opioid receptors mediate MAP kinase activation via a signaling pathway using the betagamma-subunit of Gi, a PI-3K, and SOS, independent of PKC activity. In cells expressing both ORL-1 (OFQR) and mu-opioid receptors, pretreatment with nociceptin decreased subsequent nociceptin (OFQ)- or DAMGO-stimulated MAP kinase activation. In contrast, pretreatment of cells with DAMGO decreased subsequent DAMGO-stimulated MAP kinase but had no effect on subsequent nociceptin (OFQ)-stimulated MAP kinase activation. These results demonstrate that nociceptin (OFQ) activation of ORL-1 (OFQR) can modulate mu-opioid receptor signaling in a cellular system.
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PMID:Nociceptin (ORL-1) and mu-opioid receptors mediate mitogen-activated protein kinase activation in CHO cells through a Gi-coupled signaling pathway: evidence for distinct mechanisms of agonist-mediated desensitization. 972 27


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