Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P51812 (mitogen-activated protein)
 10,636 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The classical paradigm for G protein-coupled receptor (GPCR) signal transduction involves the agonist-dependent interaction of GPCRs with heterotrimeric G proteins at the plasma membrane and the subsequent generation, by membrane-localized effectors, of soluble second messengers or ion currents. Termination of GPCR signals follows G protein-coupled receptor kinase (GRK)- and beta-arrestin-mediated receptor uncoupling and internalization. Here we show that these paradigms are inadequate to account for GPCR-mediated, Ras-dependent activation of the mitogen-activated protein (MAP) kinases Erk1 and -2. In HEK293 cells expressing dominant suppressor mutants of beta-arrestin or dynamin, beta2-adrenergic receptor-mediated activation of MAP kinase is inhibited. The inhibitors of receptor internalization specifically blocked Raf-mediated activation of MEK. Plasma membrane-delimited steps in the GPCR-mediated activation of the MAP kinase pathway, such as tyrosine phosphorylation of Shc and Raf kinase activation by Ras, are unaffected by inhibitors of receptor internalization. Thus, GRKs and beta-arrestins, which uncouple GPCRs and target them for internalization, function as essential elements in the GPCR-mediated MAP kinase signaling cascade.
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PMID:Essential role for G protein-coupled receptor endocytosis in the activation of mitogen-activated protein kinase. 942 17

The Ras-dependent activation of mitogen-activated protein (MAP) kinase pathways by many receptors coupled to heterotrimeric guanine nucleotide binding proteins (G proteins) requires the activation of Src family tyrosine kinases. Stimulation of beta2 adrenergic receptors resulted in the assembly of a protein complex containing activated c-Src and the receptor. Src recruitment was mediated by beta-arrestin, which functions as an adapter protein, binding both c-Src and the agonist-occupied receptor. beta-Arrestin 1 mutants, impaired either in c-Src binding or in the ability to target receptors to clathrin-coated pits, acted as dominant negative inhibitors of beta2 adrenergic receptor-mediated activation of the MAP kinases Erk1 and Erk2. These data suggest that beta-arrestin binding, which terminates receptor-G protein coupling, also initiates a second wave of signal transduction in which the "desensitized" receptor functions as a critical structural component of a mitogenic signaling complex.
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PMID:Beta-arrestin-dependent formation of beta2 adrenergic receptor-Src protein kinase complexes. 998 59

We investigated the role of arrestins in the trafficking of human alpha2-adrenergic receptors (alpha2-ARs) and the effect of receptor trafficking on p42/p44 MAP kinase activation. alpha2-ARs expressed in COS-1 cells demonstrated a modest level of agonist-mediated internalization, with alpha2c > alpha2b > alpha2a. However, upon coexpression of arrestin-2 (beta-arrestin-1) or arrestin-3 (beta-arrestin-2), internalization of the alpha2b AR was dramatically enhanced and redistribution of receptors to clathrin coated vesicles and endosomes was observed. Internalization of the alpha2c AR was selectively promoted by coexpression of arrestin-3, while alpha2a AR internalization was only slightly stimulated by coexpression of either arrestin. Coexpression of GRK2 had no effect on the internalization of any alpha2-AR subtype, either in the presence or absence of arrestins. Internalization of the alpha2b and alpha2c ARs was inhibited by coexpression of dominant negative dynamin-K44A. However, alpha2-AR-mediated activation of either endogenous or cotransfected p42/p44 mitogen-activated protein (MAP) kinase was not affected by either dynamin-K44A or arrestin-3. Moreover, activation of p42/p44 MAP kinase by endogenous epidermal growth factor, lysophosphatidic acid, and beta2-adrenergic receptors was also unaltered by dynamin-K44A. In summary, our data suggest that internalization of the alpha2b, alpha2c, and to a lesser extent alpha2a ARs, is both arrestin- and dynamin-dependent. However, endocytosis does not appear to be required for alpha2-adrenergic, epidermal growth factor, lysophosphatidic acid, or beta2-adrenergic receptor-mediated p42/p44 MAP kinase activation in COS-1 cells.
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PMID:Role of arrestins in endocytosis and signaling of alpha2-adrenergic receptor subtypes. 1019 13

Agonist-promoted internalization of some G protein-coupled receptors has been shown to mediate receptor desensitization, resensitization, and down-regulation. In this study, we investigated whether opioids induced internalization of the human and rat kappa opioid receptors stably expressed in Chinese hamster ovary cells, the potential mechanisms involved in this process and its possible role in activation of mitogen-activated protein (MAP) kinase. Exposure of the human kappa receptor to the agonists U50,488H, U69,593, ethylketocyclazocine, or tifluadom, but not etorphine, promoted receptor internalization. However, none of these agonists induced significant internalization of the rat kappa opioid receptor. U50, 488H-induced human kappa receptor internalization was time- and concentration-dependent, with 30-40% of the receptors internalized following a 30-min exposure to 1 microM U50,488H. Agonist removal resulted in the receptors gradually returning to the cell surface over a 60-min period. The antagonist naloxone blocked U50, 488H-induced internalization without affecting internalization itself, while pretreatment with pertussis toxin had no effect on U50, 488H-induced internalization. In contrast, incubation with sucrose (0.4-0.8 M) significantly reduced U50,488H-induced internalization of the kappa receptor. While co-expression of the wild type GRK2, beta-arrestin, or dynamin I had no effect on kappa receptor internalization, co-expression of the dominant negative mutants GRK2-K220R, beta-arrestin (319-418), or dynamin I-K44A significantly inhibited receptor internalization. Whether receptor internalization is critical for MAP kinase activation was next investigated. Co-expression of dominant negative mutants of beta-arrestin or dynamin I, which greatly reduced U50,488H-induced internalization, did not affect MAP kinase activation by the agonist. In addition, etorphine, which did not promote human kappa receptor internalization, was able to fully activate MAP kinase. Moreover, U50,488H or etorphine stimulation of the rat kappa receptor, which did not undergo internalization, also effectively activated MAP kinase. Thus, U50,488H-induced internalization of the human kappa opioid receptor in Chinese hamster ovary cells occurs via a GRK-, beta-arrestin-, and dynamin I-dependent process that likely involves clathrin-coated pits. In addition, internalization of the kappa receptor is not required for activation of MAP kinase.
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PMID:U50,488H-induced internalization of the human kappa opioid receptor involves a beta-arrestin- and dynamin-dependent mechanism. Kappa receptor internalization is not required for mitogen-activated protein kinase activation. 1020 34

After activation, agonist-occupied G protein-coupled receptors are phosphorylated by G protein-coupled receptor kinases and bind cytosolic beta-arrestins, which uncouple the receptors from their cognate G proteins. Recent studies on the beta2-adrenergic receptor have demonstrated that beta-arrestin also targets the receptors to clathrin-coated pits for subsequent internalization and activation of mitogen-activated protein kinases. We and others have previously shown that muscarinic acetylcholine receptors (mAChRs) of the m1, m3, and m4 subtype require functional dynamin to sequester into HEK-293 tsA201 cells, whereas m2 mAChRs sequester in a dynamin-independent manner. To investigate the role of beta-arrestin in mAChR sequestration, we determined the effect of overexpressing beta-arrestin-1 and the dominant-negative inhibitor of beta-arrestin-mediated receptor sequestration, beta-arrestin-1 V53D, on mAChR sequestration and function. Sequestration of m1, m3, and m4 mAChRs was suppressed by 60-75% in cells overexpressing beta-arrestin-1 V53D, whereas m2 mAChR sequestration was affected by less than 10%. In addition, overexpression of beta-arrestin-1 V53D as well as dynamin K44A significantly suppressed m1 mAChR-mediated activation of mitogen-activated protein kinases. Finally, we investigated whether mAChRs sequester into clathrin-coated vesicles by overexpressing Hub, a dominant-negative clathrin mutant. Although sequestration of m1, m3, and m4 mAChRs was inhibited by 50-70%, m2 mAChR sequestration was suppressed by less than 10%. We conclude that m1, m3, and m4 mAChRs expressed in HEK-293 tsA201 cells sequester into clathrin-coated vesicles in a beta-arrestin- and dynamin-dependent manner, whereas sequestration of m2 mAChRs in these cells is largely independent of these proteins.
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PMID:Regulation of muscarinic acetylcholine receptor sequestration and function by beta-arrestin. 1021 3

Agonist-promoted internalization (endocytosis) of G-protein-coupled receptors (GPCRs), including all three opioid receptor types (mu, delta and kappa), has been shown to occur via the clathrin endosomal pathway in response to receptor phosphorylation and the actions of the proteins, beta-arrestin and dynamin. Many members of the GPCR family stimulate mitogen-activated protein kinases (MAPK or ERK) activity and, in several cases, it appears that MAPK activation is dependent on receptor internalization. We have reinvestigated the question of whether internalization is obligatory for MAPK activation by opioid receptors, using cell lines expressing the cloned mu or delta receptor. Morphine, which is known to activate both mu and delta receptors, does not induce their rapid internalization into clathrin-coated endosomes. However, morphine produced a robust stimulation of MAPK in both cell lines, as demonstrated by the appearance of phosphorylated MAPK. Moreover, pre-exposure of cells to the internalization inhibitors, concanavalin A or hypertonic sucrose, totally blocked DAMGO mu-selective agonist) and DTLET (delta-selective agonist)-mediated receptor internalization, yet neither treatment affected MAPK phosphorylation induced by these peptides. Our results provide evidence that receptor internalization is not an obligatory requirement for MAPK activation by mu and delta opioid receptors. Hypotheses are presented to explain the seemingly contradictory results obtained from different laboratories.
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PMID:mu and delta-opioid receptor agonists induce mitogen-activated protein kinase (MAPK) activation in the absence of receptor internalization. 1088 53

We examined the pathway of prostaglandin E(2) (PGE(2))-induced internalization of the prostaglandin EP4 receptor in HEK 293 cells. Co-expression of dominant negative beta-arrestin (319-418) or dynamin I (K44A) with the EP4 receptor reduced internalization. The activated receptor co-localized with GFP-arrestin 2 and GFP-arrestin 3, confirming the requirement for beta-arrestins in internalization. Inhibition of clathrin-coated vesicle-mediated internalization resulted in inhibition of sequestration, whereas inhibition of caveola-mediated internalization had no effect. PGE(2) stimulation of the EP4 receptor resulted in rapid mitogen-activated protein (MAP) kinase activation. Examination of an internalization-resistant mutant and co-expression of mutant accessory proteins with EP4 revealed that MAP kinase activation proceeds independently of internalization.
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PMID:Agonist-induced internalization and mitogen-activated protein kinase activation of the human prostaglandin EP4 receptor. 1147 Feb 76

beta-Arrestins are cytosolic proteins that mediate homologous desensitization of G protein-coupled receptors (GPCRs) by binding to agonist-occupied receptors and by uncoupling them from heterotrimeric G proteins. The recent finding that beta-arrestins bind to some mitogen-activated protein (MAP) kinases has suggested that they might also function as scaffolds for GPCR-stimulated MAP kinase activation. To define the role of beta-arrestins in the regulation of ERK MAP kinases, we examined the effect of beta-arrestin overexpression on ERK1/2 activation and nuclear signaling in COS-7 cells expressing angiotensin II type 1a receptors (AT1aRs). Expression of either beta-arrestin1 or beta-arrestin2 reduced angiotensin-stimulated phosphatidylinositol hydrolysis but paradoxically increased angiotensin-stimulated ERK1/2 phosphorylation. The increase in ERK1/2 phosphorylation in beta-arrestin-expressing cells correlated with activation of a beta-arrestin-bound pool of ERK2. The beta-arrestin-dependent increase in ERK1/2 phosphorylation was accompanied by a significant reduction in ERK1/2-mediated, Elk1-driven transcription of a luciferase reporter. Analysis of the cellular distribution of phospho-ERK1/2 by confocal immunofluorescence microscopy and cellular fractionation revealed that overexpression of beta-arrestin resulted in a significant increase in the cytosolic pool of phospho-ERK1/2 and a corresponding decrease in the nuclear pool of phospho-ERK1/2 following angiotensin stimulation. beta-Arrestin overexpression resulted in formation of a cytoplasmic pool of beta-arrestin-bound phospho-ERK, decreased nuclear translocation of phospho-ERK1/2, and inhibition of Elk1-driven luciferase transcription even when ERK1/2 was activated by overexpression of cRaf-1 in the absence of AT1aR stimulation. These data demonstrate that beta-arrestins facilitate GPCR-mediated ERK activation but inhibit ERK-dependent transcription by binding to phospho-ERK1/2, leading to its retention in the cytosol.
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PMID:beta-Arrestin scaffolding of the ERK cascade enhances cytosolic ERK activity but inhibits ERK-mediated transcription following angiotensin AT1a receptor stimulation. 1177 2

Arrestins play an important role in regulating the function of G protein-coupled receptors including receptor desensitization, internalization, down-regulation, and signaling via nonreceptor tyrosine kinases and mitogen-activated protein kinases. Previous studies have revealed that arrestins themselves are also subject to regulation. In the present study, we focused on identifying potential mechanisms involved in regulating the function of arrestin-3. Using metabolic labeling, phosphoamino acid analysis, and mutagenesis studies, we found that arrestin-3 is constitutively phosphorylated at Thr-382 and becomes dephosphorylated upon beta(2)-adrenergic receptor activation in COS-1 cells. Casein kinase II (CKII) appears to be the major kinase mediating arrestin-3 phosphorylation, since 1) Thr-382 is contained within a canonical consensus sequence for CKII phosphorylation and 2) wild type arrestin-3 but not a T382A mutant is phosphorylated by CKII in vitro. Functional analysis reveals that mutants mimicking the phosphorylated (T382E) and dephosphorylated (T382A or T382V) states of arrestin-3 promote beta(2)-adrenergic receptor internalization and bind clathrin, beta-adaptin, and Src to comparable levels as wild type arrestin-3. This suggests that the phosphorylation of arrestin-3 does not directly regulate interaction with endocytic (clathrin, beta-adaptin) or signaling (Src) components and is in contrast to arrestin-2, where phosphorylation appears to regulate interaction with clathrin and Src. However, additional analysis reveals that arrestin-3 phosphorylation may regulate formation of a large arrestin-3-containing protein complex. Differences between the regulatory roles of arrestin-2 and -3 phosphorylation may contribute to the different cellular functions of these proteins in G protein-coupled receptor signaling and regulation.
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PMID:Regulation of arrestin-3 phosphorylation by casein kinase II. 1187 51

Over the past decade, it has become apparent that many G-protein-coupled receptors (GPCRs) generate signals that control cellular differentiation and growth, including stimulation of Ras family GTPases and activation of mitogen-activated protein (MAP) kinase pathways. The mechanisms that GPCRs use to control the activity of MAP kinases vary between receptor and cell type but fall broadly into one of three categories: signals initiated by classical G protein effectors, e.g., protein kinase (PK)A and PKC, signals initiated by cross-talk between GPCRs and classical receptor tyrosine kinases, e.g., "transactivation" of epidermal growth factor (EGF) receptors, and signals initiated by direct interaction between beta-arrestins and components of the MAP kinase cascade, e.g., beta-arrestin "scaffolds". While each of these pathways results in increased cellular MAP kinase activity, emerging data suggest that they are not functionally redundant. MAP kinase activation occurring via PKC-dependent pathways and EGF receptor transactivation leads to nuclear translocation of the kinase and stimulates cell proliferation, while MAP kinase activation via beta-arrestin scaffolds primarily increases cytosolic kinase activity. By controlling the spatial and temporal distribution of MAP kinase activity within the cell, the consequences of GPCR-stimulated MAP kinase activation may be determined by the mechanism by which they are activated.
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PMID:Activation and targeting of mitogen-activated protein kinases by G-protein-coupled receptors. 1205 42


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