251
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Schmitt JM, Stork PJS. Galpha and Gbeta gamma require distinct Src-dependent pathways to activate Rap1 and Ras. J Biol Chem 2002; 277:43024-32. [PMID: 12221082 DOI: 10.1074/jbc.m204006200] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The Src tyrosine kinase is necessary for activation of extracellular signal-regulated kinases (ERKs) by the beta-adrenergic receptor agonist, isoproterenol. In this study, we examined the role of Src in the stimulation of two small G proteins, Ras and Rap1, that have been implicated in isoproterenol's signaling to ERKs. We demonstrate that the activation of isoproterenol of both Rap1 and Ras requires Src. In HEK293 cells, isoproterenol activates Rap1, stimulates Rap1 association with B-Raf, and activates ERKs, all via PKA. In contrast, the activation by isoproterenol of Ras requires Gbetagamma subunits, is independent of PKA, and results in the phosphoinositol 3-kinase-dependent activation of AKT. Interestingly, beta-adrenergic stimulation of both Rap1 and ERKs, but not Ras and AKT, can be blocked by a Src mutant (SrcS17A) that is incapable of being phosphorylated and activated by PKA. Furthermore, a Src mutant (SrcS17D), which mimics PKA phosphorylation at serine 17, stimulates Rap1 activation, Rap1/B-Raf association, and ERK activation but does not stimulate Ras or AKT. These data suggest that Rap1 activation, but not that of Ras, is mediated through the direct phosphorylation of Src by PKA. We propose that the beta(2)-adrenergic receptor activates Src via two independent mechanisms to mediate distinct signaling pathways, one through Galpha(s) to Rap1 and ERKs and the other through Gbetagamma to Ras and AKT.
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Affiliation(s)
- John M Schmitt
- Vollum Institute, and the Department of Cell and Developmental Biology, Oregon Health Sciences University, Portland, Oregon 97201, USA
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252
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McCole DF, Keely SJ, Coffey RJ, Barrett KE. Transactivation of the epidermal growth factor receptor in colonic epithelial cells by carbachol requires extracellular release of transforming growth factor-alpha. J Biol Chem 2002; 277:42603-12. [PMID: 12202486 DOI: 10.1074/jbc.m206487200] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have shown previously that the muscarinic agonist, carbachol (CCh), transactivates the epidermal growth factor receptor (EGFr) via calmodulin, Pyk-2, and Src kinase activation. EGFr phosphorylation causes extracellular signal-regulated kinase (ERK) activation and inhibits CCh-stimulated chloride secretion across intestinal epithelial cells. Here we investigated whether CCh-stimulated EGFr transactivation involves EGFr ligand release. Pre-incubation of T(84) cell monolayers with a neutralizing antibody to the EGFr ligand binding domain decreased CCh-induced phosphorylation of EGFr and ERK. CCh-stimulated efflux of (86)Rb+ from T(84) cell monolayers, which parallels changes in chloride secretion, was potentiated by anti-EGFr pre-incubation. Anti-EGFr did not reduce CCh-stimulated Pyk-2 phosphorylation. Co-incubation with the Src kinase inhibitor PP2 and anti-EGFr had an additive inhibitory effect on CCh-induced ERK phosphorylation greater than either inhibitor alone. CCh caused the basolateral release of transforming growth factor alpha (TGF-alpha) into T(84) cell bathing media. A metalloproteinase inhibitor, WAY171318, reduced CCh-induced phosphorylation of ERK and completely blocked EGFr phosphorylation and TGF-alpha release. We conclude that CCh-stimulated EGFr transactivation and subsequent ERK activation, a pathway that limits CCh-induced chloride secretion, is mediated by metalloproteinase-dependent extracellular release of TGF-alpha and intracellular Src activation. These findings have important implications for our understanding of the role of growth factors in regulating epithelial ion secretion.
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Affiliation(s)
- Declan F McCole
- Department of Medicine, University of California, School of Medicine, San Diego, California 92103, USA
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253
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Lefkowitz RJ, Pierce KL, Luttrell LM. Dancing with different partners: protein kinase a phosphorylation of seven membrane-spanning receptors regulates their G protein-coupling specificity. Mol Pharmacol 2002; 62:971-4. [PMID: 12391258 DOI: 10.1124/mol.62.5.971] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- Robert J Lefkowitz
- Department of Medicine, Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA.
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254
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Friedman J, Babu B, Clark RB. Beta(2)-adrenergic receptor lacking the cyclic AMP-dependent protein kinase consensus sites fully activates extracellular signal-regulated kinase 1/2 in human embryonic kidney 293 cells: lack of evidence for G(s)/G(i) switching. Mol Pharmacol 2002; 62:1094-102. [PMID: 12391272 DOI: 10.1124/mol.62.5.1094] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Stimulation of the beta(2)-adrenergic receptor (beta(2)AR) in human embryonic kidney (HEK) 293 cells causes a transient activation of Extracellular Signal-Regulated Kinase (ERK) 1/2. One of the mechanisms proposed for this activation is a PKA-mediated phosphorylation of the beta(2)AR that switches receptor coupling from G(s) to G(i) and triggers internalization of the receptor. To examine these phenomena, we characterized agonist activation of ERK1/2 in HEK293 cells by the endogenous beta(2)AR and in HEK293 cells stably overexpressing either the wild-type beta(2)AR or a substitution mutant beta(2)AR (PKA(-)) that lacks the cyclic AMP-dependent protein kinase (PKA) consensus phosphorylation sites (S261A, S262A and S345A, S346A). As the baseline, we established that epinephrine stimulation of the endogenous beta(2)AR in HEK293 cells (20-30 fmol/mg) caused a rapid and transient activation of ERK1/2 with an EC(50) of 5 to 6 nM. In contrast, the potency of epinephrine stimulation of ERK1/2 in cells stably overexpressing WTbeta(2)AR and PKA(-) (2-4 pmol of beta(2)AR/mg) was increased by over 100-fold relative to HEK293 cells, the EC(50) values being 20 to 60 pM. The nearly identical 100-fold shift in EC(50) for ERK1/2 activation in the PKA(-) and WTbeta(2)AR relative to that in the HEK293 showed that the PKA(-) are fully capable of activating ERK1/2. We also found maximal activation of ERK1/2 in the overexpressing cell lines at concentrations of epinephrine that cause no internalization (i.e., the EC(50) for internalization was 75 nM). Pertussis toxin pretreatment caused only a weak inhibition of epinephrine activation of ERK1/2 in the HEK293 (7-16%) and no inhibition in the PKA(-) cells. Finally we found that the Src family kinase inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (10 microM) caused a >90% inhibition of epinephrine or forskolin activation of ERK1/2 in both cell lines. Our results indicate that the dominant mechanism of beta(2)AR activation of ERK1/2 does not require PKA phosphorylation of the beta(2)AR, receptor internalization or switching from activation of G(s) to G(i) but clearly requires activation of a Src family member that may be downstream of PKA.
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Affiliation(s)
- Jacqueline Friedman
- Department of Integrative Biology and Pharmacology, the University of Texas Health Science Center at Houston Medical School, Houston, Texas 77225, USA
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255
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Wang Y, Pennock S, Chen X, Wang Z. Endosomal signaling of epidermal growth factor receptor stimulates signal transduction pathways leading to cell survival. Mol Cell Biol 2002; 22:7279-90. [PMID: 12242303 PMCID: PMC139821 DOI: 10.1128/mcb.22.20.7279-7290.2002] [Citation(s) in RCA: 208] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In spite of intensified efforts to understand cell signaling from endosomes, there is no direct evidence demonstrating that endosomal signaling is sufficient to activate signal transduction pathways and no evidence to demonstrate that endosomal signaling is able to produce a biological outcome. The lack of breakthrough is due in part to the lack of means to generate endosomal signals without plasma membrane signaling. In this paper, we report the establishment of a system to specifically activate epidermal growth factor (EGF) receptor (EGFR) when it endocytoses into endosomes. We treated cells with EGF in the presence of AG-1478, a specific EGFR tyrosine kinase inhibitor, and monensin, which blocks the recycling of EGFR. This treatment led to the internalization of nonactivated EGF-EGFR complexes into endosomes. The endosome-associated EGFR was then activated by removing AG-1478 and monensin. During this procedure we did not observe any surface EGFR phosphorylation. We also achieved specific activation of endosome-associated EGFR without using monensin. By using this system, we provided original evidence demonstrating that (i) the endosome can serve as a nucleation site for the formation of signaling complexes, (ii) endosomal EGFR signaling is sufficient to activate the major signaling pathways leading to cell proliferation and survival, and (iii) endosomal EGFR signaling is sufficient to suppress apoptosis induced by serum withdrawal.
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Affiliation(s)
- Yi Wang
- Department of Cell Biology and Signal Transduction Research Group, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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256
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Ehses JA, Pelech SL, Pederson RA, McIntosh CHS. Glucose-dependent insulinotropic polypeptide activates the Raf-Mek1/2-ERK1/2 module via a cyclic AMP/cAMP-dependent protein kinase/Rap1-mediated pathway. J Biol Chem 2002; 277:37088-97. [PMID: 12138104 DOI: 10.1074/jbc.m205055200] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The gastrointestinal hormone, glucose-dependent insulinotropic polypeptide (GIP), is one of the most important regulators of insulin secretion following ingestion of a meal. GIP stimulates insulin secretion from the pancreatic beta-cell via its G protein-coupled receptor activation of adenylyl cyclase and other signal transduction pathways, but there is little known regarding subsequent protein kinase pathways that are activated. A screening technique was used to determine the relative abundance of 75 protein kinases in CHO-K1 cells expressing the GIP receptor and in two pancreatic beta-cell lines (betaTC-3 and INS-1 (832/13) cells). This information was used to identify kinases that are potentially regulated following GIP stimulation, with a focus on GIP regulation of the ERK1/2 MAPK pathway. In CHO-K1 cells, GIP induced phosphorylation of Raf-1 (Ser-259), Mek1/2 (Ser-217/Ser-221), ERK1/2 (Thr-202 and Tyr-204), and p90 RSK (Ser-380) in a concentration-dependent manner. Activation of ERK1/2 was maximal at 4 min and was cAMP-dependent protein kinase-dependent and protein kinase C-independent. Studies using a beta-cell line (INS-1 clone 832/13) corroborated these findings, and it was also demonstrated that the ERK1/2 module could be activated by GIP in the absence of glucose. Finally, we have shown that GIP regulation of the ERK1/2 module is via Rap1 but does not involve Gbetagamma subunits nor Src tyrosine kinase, and we propose that cAMP-based regulation occurs via B-Raf in both CHO-K1 and beta-cells. These results establish the importance of GIP in the cellular regulation of the ERK1/2 module and identify a role for cAMP in coupling its G protein-coupled receptors to ERK1/2 activity in pancreatic beta-cells.
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Affiliation(s)
- Jan A Ehses
- Department of Physiology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada
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257
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Martin S, Navarro V, Vincent JP, Mazella J. Neurotensin receptor-1 and -3 complex modulates the cellular signaling of neurotensin in the HT29 cell line. Gastroenterology 2002; 123:1135-43. [PMID: 12360476 DOI: 10.1053/gast.2002.36000] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
BACKGROUND & AIMS The neuropeptide neurotensin (NT) exerts its intracellular effect by interacting with 3 different receptors. Two of these receptors (NTR1 and NTR2) belong to the G protein-coupled receptor family, whereas the third one (NTR3) is a type I receptor with a single transmembrane domain. We recently showed that the 2 structurally different receptors NTR1 and NTR3 were coexpressed in several human cancer cells on which NT exerts proliferative effects. METHODS Here, by an immunoprecipitation approach, we provide biochemical evidence for an endogenous heterodimerization of the G protein-coupled receptor NTR1 with the NTR3 in the human adenocarcinoma cell line HT29. RESULTS We show that both receptors are expressed and colocalized within the cell surface of HT29 cells where they already interact to form a heterodimer. The NTR1-NTR3 complex is then internalized on NT stimulation. CONCLUSIONS The complex formed between these 2 structurally unrelated NT receptors modulates both the NT-induced phosphorylation of mitogen-activated protein kinases and the phosphoinositide (PI) turnover mediated by the NTR1.
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Affiliation(s)
- Stéphane Martin
- Institut de Pharmacologie Moléculaire et Cellulaire, Sophia Antipolis, Valbonne, France
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258
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Nevzorova J, Bengtsson T, Evans BA, Summers RJ. Characterization of the beta-adrenoceptor subtype involved in mediation of glucose transport in L6 cells. Br J Pharmacol 2002; 137:9-18. [PMID: 12183326 PMCID: PMC1573471 DOI: 10.1038/sj.bjp.0704845] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. The receptor that mediates the increase in glucose transport (GT) in response to beta-adrenoceptor (beta-AR) agonists was characterized in the rat skeletal muscle cell line L6, using the 2-deoxy-[(3)H]-D-glucose assay. 2. The beta(3)-AR agonist BRL37344 (pEC(50) = 6.89 +/- 0.21), the beta-AR agonist isoprenaline (pEC(50) = 8.99 +/ -0.24) and the beta(2)-AR agonist zinterol (pEC(50) = 9.74 +/- 0.15) increased GT as did insulin (pEC(50) = 6.93 +/- 0.15). The highly selective beta(3)-AR agonist CL316243 only weakly stimulated GT. 3. The pK(B) values calculated from the shift of the pEC(50) values of the agonists in the presence of the beta(1)-AR selective antagonist CGP 20712A or the beta(3)-AR selective antagonist SR 59230A were not indicative of activation of beta(1)- or beta(3)-ARs. Only (-)-propranolol and the beta(2)-AR selective antagonist ICI 118551 caused marked rightward shifts of CR curves to isoprenaline (pK(B) = 10.2 +/- 0.2 and 9.6 +/- 0.3), zinterol (pK(B) = 9.0 +/- 0.1 and 9.4 +/- 0.3) and BRL 37344 (pK(B) = 9.4 +/- 0.3 and 8.4 +/- .2), indicating participation of beta(2)-ARs. 4. The pharmacological analysis was supported by reverse transcription and polymerase chain reaction analysis of L6 mRNA, which showed high levels of expression of beta(2)-AR but not beta(1)- or beta(3)-AR in these cells. 5. Forskolin and dibutyryl cyclic AMP produced negligible increases in GT while the phosphatidylinositol-3 kinase inhibitor, wortmannin, significantly decreased both insulin- and zinterol-stimulated GT, suggesting a possible interaction between the insulin and beta(2)-AR pathways. 6. This study demonstrates that beta(2)-ARs mediate the increase in GT in L6 cells to beta-AR agonists, including the beta(3)-AR selective agonist BRL 37344. This effect does not appear to be directly related to increases in cyclic AMP but requires P13K.
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MESH Headings
- Adrenergic beta-Agonists/pharmacology
- Adrenergic beta-Antagonists/pharmacology
- Androstadienes/pharmacology
- Animals
- Biological Transport
- Bucladesine/pharmacology
- Cells, Cultured
- Colforsin/pharmacology
- Dose-Response Relationship, Drug
- Glucose/metabolism
- Insulin/pharmacology
- Insulin/physiology
- Muscle, Skeletal/cytology
- Muscle, Skeletal/metabolism
- RNA, Messenger/metabolism
- Rats
- Receptors, Adrenergic, beta/drug effects
- Receptors, Adrenergic, beta/genetics
- Receptors, Adrenergic, beta/physiology
- Reverse Transcriptase Polymerase Chain Reaction
- Wortmannin
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Affiliation(s)
- Julia Nevzorova
- Department of Pharmacology, PO Box 13E, Monash University, Victoria 3800, Australia
| | - Tore Bengtsson
- The Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Bronwyn A Evans
- Department of Pharmacology, PO Box 13E, Monash University, Victoria 3800, Australia
| | - Roger J Summers
- Department of Pharmacology, PO Box 13E, Monash University, Victoria 3800, Australia
- Author for correspondence:
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259
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Dalle S, Imamura T, Rose DW, Worrall DS, Ugi S, Hupfeld CJ, Olefsky JM. Insulin induces heterologous desensitization of G-protein-coupled receptor and insulin-like growth factor I signaling by downregulating beta-arrestin-1. Mol Cell Biol 2002; 22:6272-85. [PMID: 12167719 PMCID: PMC134007 DOI: 10.1128/mcb.22.17.6272-6285.2002] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
beta-Arrestin-1 mediates agonist-dependent desensitization and internalization of G protein-coupled receptors (GPCRs) and is also essential for GPCR mitogenic signaling. In addition, insulin-like growth factor I receptor (IGF-IR) endocytosis is facilitated by beta-arrestin-1, and internalization is necessary for IGF-I-stimulated mitogen-activated protein (MAP) kinase activation. Here, we report that treatment of cells for 12 h with insulin (100 ng/ml) induces an approximately 50% decrease in cellular beta-arrestin-1 content due to ubiquitination of beta-arrestin-1 and proteosome-mediated degradation. This insulin-induced decrease in beta-arrestin-1 content was blocked by inhibition of phosphatidylinositol-3 kinase (PI-3 kinase) and MEK with wortmannin and PD98059, respectively. We also found a marked decrease in the association of beta-arrestin-1 with the IGF-IR and a 55% inhibition of IGF-I-stimulated MAP kinase phosphorylation. In insulin-treated, beta-arrestin-1-downregulated cells, there was complete inhibition of lysophosphatidic acid (LPA) or isoproterenol (ISO)-stimulated MAP kinase phosphorylation. This was associated with a decrease in beta-arrestin-1 association with the beta2-AR as well as a decrease in beta-arrestin-1-Src and Src-beta2-AR association. Ectopic expression of wild-type beta-arrestin-1 in insulin-treated cells in which endogenous beta-arrestin-1 had been downregulated rescued IGF-I- and LPA-stimulated MAP kinase phosphorylation. In conclusion, we found the following. (i) Chronic insulin treatment leads to enhanced beta-arrestin-1 degradation. (ii) This downregulation of endogenous beta-arrestin-1 is associated with decreased IGF-I-, LPA-, and ISO-mediated MAP kinase signaling, which can be rescued by ectopic expression of wild-type beta-arrestin-1. (iii) Finally, these results describe a novel mechanism for heterologous desensitization, whereby insulin treatment can impair GPCR signaling, and highlight the importance of beta-arrestin-1 as a target molecule for this desensitization mechanism.
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Affiliation(s)
- Stéphane Dalle
- Department of Medicine, Division of Endocrinology and Metabolism, University of California, San Diego, La Jolla, California 92093-0673, USA
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260
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Zamah AM, Delahunty M, Luttrell LM, Lefkowitz RJ. Protein kinase A-mediated phosphorylation of the beta 2-adrenergic receptor regulates its coupling to Gs and Gi. Demonstration in a reconstituted system. J Biol Chem 2002; 277:31249-56. [PMID: 12063255 DOI: 10.1074/jbc.m202753200] [Citation(s) in RCA: 141] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
While classically viewed as a prototypic G(s) and adenylyl cyclase-coupled G protein-coupled receptor, recent studies have indicated that some aspects of beta(2)-adrenergic receptor (beta(2)-AR) signaling are inhibited by pertussis toxin, indicating that they are mediated by G(i)/G(o) proteins. These signals include activation of ERK MAPKs and Akt activation, as well as hypertrophic and anti-apoptotic pathways in cardiac myocytes. Studies in cultured cells have suggested the hypothesis that protein kinase A (PKA)-mediated phosphorylation of the beta(2)-AR regulates its coupling specificity with respect to G(s) and G(i). Using a Chinese hamster ovary cell system, we show that mutant beta(2)-ARs with Ala substituted for Ser at consensus PKA sites stimulate robust cyclic AMP accumulation (G(s)) but are unable to activate ERK (G(i)). In contrast, Ser --> Asp mutants are dramatically impaired in their ability to activate adenylyl cyclase but are significantly more active than wild type receptor in activating ERK. Activation of adenylyl cyclase by wild type and Ser --> Ala mutant receptors is not altered by pertussis toxin, whereas adenylyl cyclase stimulated through the Ser --> Asp mutant is enhanced. Activation of ERK by wild type and Ser --> Asp receptors is inhibited by pertussis toxin. To further rigorously test the hypothesis, we utilized a completely reconstituted system of purified recombinant wild type and PKA phosphorylation site mutant beta(2)-ARs and heterotrimeric G(s) and G(i). G protein coupling was measured by receptor-mediated stimulation of GTPgammaS binding to the G protein. PKA-mediated phosphorylation of the beta(2)-AR significantly decreased its ability to couple to G(s), while simultaneously dramatically increasing its ability to couple to G(i). These results are reproduced when a purified recombinant Ser --> Asp mutant beta(2)-AR is tested, whereas the Ser --> Ala receptor resembles the unphosphorylated wild type. These results provide strong experimental support for the idea that PKA-mediated phosphorylation of the beta(2)-adrenergic receptor switches its predominant coupling from G(s) to G(i).
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Affiliation(s)
- A Musa Zamah
- Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA
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261
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Gilmore AP, Valentijn AJ, Wang P, Ranger AM, Bundred N, O'Hare MJ, Wakeling A, Korsmeyer SJ, Streuli CH. Activation of BAD by therapeutic inhibition of epidermal growth factor receptor and transactivation by insulin-like growth factor receptor. J Biol Chem 2002; 277:27643-50. [PMID: 12011069 DOI: 10.1074/jbc.m108863200] [Citation(s) in RCA: 152] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Novel cancer chemotherapeutics are required to induce apoptosis by activating pro-apoptotic proteins. Both epidermal growth factor (EGF) and insulin-like growth factor (IGF) provide potent survival stimuli in many epithelia, and activation of their receptors is commonly observed in solid human tumors. Here we demonstrate that blockade of the EGF receptor by a new drug in phase III clinical trails for cancer, ZD1839, potently induces apoptosis in mammary epithelial cell lines and primary cultures, as well as in a primary pleural effusion from a breast cancer patient. We identified the mechanism of apoptosis induction by ZD1839. We showed that it prevents cell survival by activating the pro-apoptotic protein BAD. Moreover, we demonstrate that IGF transactivates the EGF receptor and that ZD1839 blocks IGF-mediated phosphorylation of MAPK and BAD. Many cancer therapies kill tumor cells by inducing apoptosis as a consequence of targeting DNA; however, the threshold at which apoptosis can be triggered through DNA damage is often different from that in normal cells. Our results indicate that by targeting a growth factor-mediated survival signaling pathway, BAD phosphorylation can be manipulated therapeutically to induce apoptosis.
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Affiliation(s)
- Andrew P Gilmore
- School of Biological Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, United Kingdom.
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262
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Cheng H, Kartenbeck J, Kabsch K, Mao X, Marqués M, Alonso A. Stress kinase p38 mediates EGFR transactivation by hyperosmolar concentrations of sorbitol. J Cell Physiol 2002; 192:234-43. [PMID: 12115730 DOI: 10.1002/jcp.10134] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Activation of the epidermal growth factor receptor (EGFR) has been shown to occur by ligand-dependent and ligand-independent mechanisms. Different molecular mechanisms have been found to be responsible for ligand-independent receptor transactivation. Here, we show that hyperosmolar concentrations of sorbitol activate the EGFR in human keratinocytes. Experiments using specific inhibitors of EGFR phosphorylation show that the increased amount of activated receptors is the result of a decreased rate of dephosphorylation. Furthermore, sorbitol treatment results in a strong activation of stress kinase p38. Treatment of the cells with SB203580, a known inhibitor of p38 alpha and beta kinases, results in impairment of receptor activation, indicating that the stress kinase is involved in receptor activation modulation. This is further reinforced by experiments showing that addition of Toxin B, known to be an inhibitor of the small Rho GTPases rac1, cdc42, and Rho A/B, to the cells results in a strong induction of EGFR activation. Our results point, therefore, to a mechanism by which osmotic shock activates EGFR through the small Rho GTPases-p38 stress kinase pathway.
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Affiliation(s)
- Hao Cheng
- Deutsches Krebsforschungszentrum, Heidelberg, Germany
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263
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Zhu X, Ma B, Babu S, Murage J, Knox BE, Craft CM. Mouse cone arrestin gene characterization: promoter targets expression to cone photoreceptors. FEBS Lett 2002; 524:116-22. [PMID: 12135752 DOI: 10.1016/s0014-5793(02)03014-4] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Cone arrestin (CAR) is a novel member of the arrestin superfamily expressed in retinal cone photoreceptors and the pineal gland. To understand the regulatory mechanisms controlling its cone- and pineal-specific expression, and to facilitate further functional studies using gene knockout approaches, we characterized the genomic organization and the 5'-flanking region of the mouse CAR (mCAR) gene. The mCAR gene is comprised of 17 exons and 16 introns, encoding five alternatively spliced transcripts. A 215-bp proximal promoter fragment containing a TATA box, an Sp1 site and four cone-rod homeobox-binding sites is sufficient to direct expression in cultured retinoblastoma cells and in cone photoreceptors and the pineal gland in transgenic Xenopus laevis.
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Affiliation(s)
- Xuemei Zhu
- The Mary D. Allen Laboratory for Vision Research, Doheny Eye Institute, Department of Cell and Neurobiology, The Keck School of Medicine of the University of Southern California, Los Angeles, CA 90089-9112, USA
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264
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Srinivasan D, Fujino H, Regan JW. Differential internalization of the prostaglandin f(2alpha) receptor isoforms: role of protein kinase C and clathrin. J Pharmacol Exp Ther 2002; 302:219-24. [PMID: 12065720 DOI: 10.1124/jpet.302.1.219] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
FP prostanoid receptors are G-protein-coupled receptors that mediate the actions of prostaglandin F(2alpha) (PGF(2alpha)). Alternative mRNA splicing gives rise to two isoforms, FP(A) and FP(B), which are identical except for their intracellular carboxyl termini. In this study, we examined the internalization of recombinant FLAG-epitope-tagged FP(A) and FP(B) receptors that were stably expressed in human embryonic kidney-293 cells. Cell surface receptors on live cells were labeled with anti-FLAG antibodies either in the presence or absence of PGF(2alpha) and were examined by immunofluorescence microscopy. In the absence of PGF(2alpha), FP(A)-expressing cells were labeled predominantly on the cell surface; however, FP(B)-expressing cells were labeled on both the cell surface and intracellularly, indicating constitutive internalization of the FP(B) isoform. After treatment with PGF(2alpha), FP(A)-expressing cells were labeled intracellularly, reflecting receptor internalization, which could be mimicked with phorbol 12-myristyl 13-acetate (PMA), an activator of protein kinase C (PKC). Pretreatment of FP(A)-expressing cells with Gö 6976 [12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo[2,3-a]pyrrolo[3,4-c]carbozole], an inhibitor of PKC, blocked both PGF(2alpha)- and PMA-induced receptor internalization. However, Gö 6976 did not block constitutive internalization of the FP(B) isoform, suggesting that the mechanisms of receptor internalization differ between the FP(A) and FP(B) isoforms. Furthermore, pretreatment with sucrose, an inhibitor of clathrin-dependent internalization, blocked PGF(2alpha)-induced internalization of the FP(A) isoform but did not block constitutive internalization of the FP(B) isoform. In conclusion, the FP(A) receptor isoform shows an agonist-induced internalization involving PKC and clathrin, whereas the FP(B) isoform undergoes agonist-independent internalization that does not involve PKC or clathrin.
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Affiliation(s)
- Dinesh Srinivasan
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson, AZ 85721-0207, USA
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265
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Affiliation(s)
- Hildegard M Schuller
- Department of Pathology, College of Veterinary Medicine, University of Tennessee, 2407 River Drive, Knoxville, Tennessee 37996, USA.
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266
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Correa-Meyer E, Pesce L, Guerrero C, Sznajder JI. Cyclic stretch activates ERK1/2 via G proteins and EGFR in alveolar epithelial cells. Am J Physiol Lung Cell Mol Physiol 2002; 282:L883-91. [PMID: 11943650 DOI: 10.1152/ajplung.00203.2001] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mechanical stimuli are transduced into intracellular signals in lung alveolar epithelial cells (AEC). We studied whether mitogen-activated protein kinase (MAPK) pathways are activated during cyclic stretch of AEC. Cyclic stretch induced a rapid (within 5 min) increase in extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation in AEC. The inhibition of Na(+), L-type Ca(2+) and stretch-activated ion channels with amiloride, nifedipine, and gadolinium did not prevent the stretch-induced ERK1/2 activation. The inhibition of Grb2-SOS interaction with an SH3 binding sequence peptide, Ras with a farnesyl transferase inhibitor, and Raf-1 with forskolin did not affect the stretch-induced ERK1/2 phosphorylation. Moreover, cyclic stretch did not increase Ras activity, suggesting that stretch-induced ERK1/2 activation is independent of the classical receptor tyrosine kinase-MAPK pathway. Pertussis toxin and two specific epidermal growth factor receptor (EGFR) inhibitors (AG-1478 and PD-153035) prevented the stretch-induced ERK1/2 activation. Accordingly, in primary AEC, cyclic stretch activates ERK1/2 via G proteins and EGFR, in Na(+) and Ca(2+) influxes and Grb2-SOS-, Ras-, and Raf-1-independent pathways.
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Affiliation(s)
- Eduardo Correa-Meyer
- Division of Pulmonary and Critical Care Medicine, Northwestern University, Chicago, Illinois 60611, USA
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267
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Feldman RD. Deactivation of vasodilator responses by GRK2 overexpression: a mechanism or the mechanism for hypertension? Mol Pharmacol 2002; 61:707-9. [PMID: 11901207 DOI: 10.1124/mol.61.4.707] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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268
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Abstract
A hallmark of many signaling pathways is the spatial separation of activation and deactivation of signaling proteins. Quantitative analysis demonstrates that the spatial separation of a membrane-bound kinase and a cytosolic phosphatase potentially results in precipitous gradients of target phosphoproteins. Hypothetically, such gradients in the mitogen-activated protein kinase (MAPK) cascade would result in a strong attenuation of the phosphorylation signal towards the nucleus. When effective signal transduction is hampered by slow protein diffusion and rapid dephosphorylation, phosphoprotein trafficking within endocytic vesicles might be an efficient way to propagate the signals. Additional mechanisms facilitating information transfer could involve the assembly of MAP kinases on a scaffolding protein and active transport of signaling complexes by molecular motors. The proposed mechanism explains recent observations that MAPK activation can be strongly suppressed by various inhibitors of endocytosis.
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Affiliation(s)
- Boris N Kholodenko
- Dept of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, 1020 Locust Street, Philadelphia, PA 19107, USA.
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269
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Hutchinson DS, Bengtsson T, Evans BA, Summers RJ. Mouse beta 3a- and beta 3b-adrenoceptors expressed in Chinese hamster ovary cells display identical pharmacology but utilize distinct signalling pathways. Br J Pharmacol 2002; 135:1903-14. [PMID: 11959793 PMCID: PMC1573318 DOI: 10.1038/sj.bjp.0704654] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. This study characterizes the mouse beta(3a)-adrenoceptor (AR) and the splice variant of the beta(3)-AR (beta(3b)-AR) expressed in Chinese hamster ovary cells (CHO-K1). 2. Stable clones with high (approximately 1200), medium (approximately 500) or low receptor expression (approximately 100 fmol mg protein(-1)) were determined by saturation binding with [(125)I]-(-)-cyanopindolol. Competition binding studies showed no significant differences in affinity of beta-AR ligands for either receptor. 3. Several functional responses of each receptor were measured, namely extracellular acidification rate (EAR; cytosensor microphysiometer), cyclic AMP accumulation, and Erk1/2 phosphorylation. The beta(3)-AR agonists BRL37344, CL316243, GR265162X, L755507, SB251023, the non-conventional partial beta-AR agonist CGP12177 and the beta-AR agonist (-)-isoprenaline caused concentration-dependent increases in EAR in cells expressing either splice variant. CL316243 caused concentration-dependent increases in cyclic AMP accumulation and Erk1/2 phosphorylation in cells expressing either receptor. 4. PTX treatment increased maximum EAR and cyclic AMP responses to CL316243 in cells expressing the beta(3b)-AR but not in cells expressing the beta(3a)-AR at all levels of receptor expression. 5. CL316243 increased Erk1/2 phosphorylation with pEC(50) values and maximum responses that were not significantly different in cells expressing either splice variant. Erk1/2 phosphorylation was insensitive to PTX or H89 (PKA inhibitor) but was inhibited by LY294002 (PI3K gamma inhibitor), PP2 (c-Src inhibitor), genistein (tyrosine kinase inhibitor) and PD98059 (MEK inhibitor). 6. The adenylate cyclase activators forskolin or cholera toxin failed to increase Erk1/2 levels although both treatments markedly increased cyclic AMP accumulation in both beta(3a)- or beta(3b)-AR transfected cells. 7. These results suggest that in CHO-K1 cells, the beta(3b)-AR, can couple to both G(s) and G(i) to stimulate and inhibit cyclic AMP production respectively, while the beta(3a)-AR, couples solely to G(s) to increase cyclic AMP levels. However, the increase in Erk1/2 phosphorylation following receptor activation is not dependent upon coupling of the receptors to G(i) or the generation of cyclic AMP.
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Affiliation(s)
- Dana S Hutchinson
- Department of Pharmacology, P.O. Box 13E, Monash University, Victoria 3800, Australia
- The Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Tore Bengtsson
- The Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, SE-106 91 Stockholm, Sweden
| | - Bronwyn A Evans
- Department of Pharmacology, P.O. Box 13E, Monash University, Victoria 3800, Australia
| | - Roger J Summers
- Department of Pharmacology, P.O. Box 13E, Monash University, Victoria 3800, Australia
- Author for correspondence:
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270
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Seta K, Nanamori M, Modrall JG, Neubig RR, Sadoshima J. AT1 receptor mutant lacking heterotrimeric G protein coupling activates the Src-Ras-ERK pathway without nuclear translocation of ERKs. J Biol Chem 2002; 277:9268-77. [PMID: 11777928 DOI: 10.1074/jbc.m109221200] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Angiotensin II (Ang II) type 1 receptors (AT1Rs) activate tyrosine kinases, including Src. Whether or not tyrosine kinase activation by AT1R occurs independently of heterotrimeric G protein coupling and, if so, the cellular function of such a mechanism are unknown. To address these questions, we used an AT1aR intracellular second loop mutant, which lacks heterotrimeric G protein coupling (AT1a-i2m). Surprisingly, Ang II-induced Src activation was preserved in AT1a-i2m, which was not attenuated by inhibiting protein kinase C and Ca(2+) or by inhibiting Galpha(i) or Galpha(q) in CHO-K1 cells. By contrast, Ang II-induced Src activation was abolished in a C-terminally truncated AT1a-(1--309), where Ang II-induced inositol phosphate response was preserved. Ang II activates ERKs via a Src-Ras-dependent mechanism in AT1a-i2m. ERKs activated by AT1a-i2m phosphorylate their cytoplasmic targets, including p90(RSK), but fail to translocate into the nucleus or to cause cell proliferation. Ang II-induced nuclear translocation of ERKs by wild type AT1aR was inhibited by overexpression of nuclear exportin Crm-1, while that by AT1a-i2m was restored by leptomycin B, an inhibitor of Crm-1. In summary, while Src and ERKs are activated by Ang II even without heterotrimeric G protein coupling, the carboxyl terminus of the AT1 receptor is required for activation of Src. Interestingly, ERKs activated by heterotrimeric G protein-independent mechanisms fail to phosphorylate nuclear targets due to lack of inhibition of Crm-1-induced nuclear export of ERKs. These results suggest that heterotrimeric G protein-dependent and -independent signaling mechanisms play distinct roles in Ang II-mediated cellular responses.
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Affiliation(s)
- Koichi Seta
- Cardiovascular Research Institute, Department of Cell Biology and Molecular Medicine, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07103, USA
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271
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Tohgo A, Pierce KL, Choy EW, Lefkowitz RJ, Luttrell LM. beta-Arrestin scaffolding of the ERK cascade enhances cytosolic ERK activity but inhibits ERK-mediated transcription following angiotensin AT1a receptor stimulation. J Biol Chem 2002; 277:9429-36. [PMID: 11777902 DOI: 10.1074/jbc.m106457200] [Citation(s) in RCA: 300] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
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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Affiliation(s)
- Akira Tohgo
- Howard Hughes Medical Institute and the Departments of Medicine and Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA
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272
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Lee FS, Rajagopal R, Kim AH, Chang PC, Chao MV. Activation of Trk neurotrophin receptor signaling by pituitary adenylate cyclase-activating polypeptides. J Biol Chem 2002; 277:9096-102. [PMID: 11784714 DOI: 10.1074/jbc.m107421200] [Citation(s) in RCA: 152] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide that acts through G protein-coupled receptors, exerts neuroprotective effects upon many neuronal populations. However, the intracellular signaling mechanisms that account for PACAP's trophic effects are not well characterized. Here we have tested the possibility that PACAP uses neurotrophin signaling pathways. We have found that PACAP treatment resulted in an increase in TrkA tyrosine kinase activity in PC12 cells and TrkB activity in hippocampal neurons. The activation of TrkA receptors by PACAP required at least 1 h of treatment and did not involve binding to nerve growth factor. Moreover, PACAP induced an increase in activated Akt through a Trk-dependent mechanism that resulted in increased cell survival after trophic factor withdrawal. The increases in Trk and Akt were blocked by K252a, an inhibitor of Trk receptor activity. In addition, transactivation of TrkA receptors by PACAP could be inhibited with PP1, an inhibitor of Src family kinases or BAPTA/AM, (1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid acetoxymethyl ester), an intracellular calcium chelator. Therefore, PACAP can exert trophic effects through a mechanism involving Trk receptors and utilization of tyrosine kinase signaling. This ability may explain several neuroprotective actions of PACAP upon neuronal populations after injury, nerve lesion, or neurotrophin deprivation.
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Affiliation(s)
- Francis S Lee
- Department of Psychiatry, Weill Medical College, Cornell University, New York, New York 10021, USA.
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273
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Shah BH, Alberto Olivares-Reyes J, Yesilkaya A, Catt KJ. Independence of angiotensin II-induced MAP kinase activation from angiotensin type 1 receptor internalization in clone 9 hepatocytes. Mol Endocrinol 2002; 16:610-20. [PMID: 11875120 DOI: 10.1210/mend.16.3.0781] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The agonist-induced internalization of several G protein-coupled receptors is an obligatory requirement for their activation of MAPKs. Studies on the relationship between endocytosis of the angiotensin II (Ang II) type 1 receptor (AT1-R) and Ang II-induced ERK1/2 activation were performed in clone 9 (C9) rat hepatic cells treated with inhibitors of endocytosis [sucrose, phenylarsine oxide (PAO), and concanavalin A]. Although Ang II-induced endocytosis of the AT1-R was prevented by sucrose and PAO, and was partially inhibited by concanavalin A, there was no impairment of Ang II-induced ERK activation. However, the specific epidermal growth factor receptor (EGF-R) kinase inhibitor, AG1478, abolished Ang II-induced activation of ERK1/2. Sucrose and PAO also inhibited EGFinduced internalization of the EGF-R in C9 cells, and the inability of these agents to impair EGF-induced ERK activation suggested that the latter is also independent of receptor endocytosis. In COS-7 cells transiently expressing the rat AT1A-R, Ang II also caused ERK activation through EGF-R transactivation. Furthermore, a mutant AT1A-R with truncated carboxyl terminus and impaired internalization retained full ability to activate ERK1/2 in response to Ang II stimulation. These findings demonstrate that Ang II-induced ERK1/2 activation in C9 hepatocytes is independent of both AT1-R and EGF-R endocytosis and is mediated by transactivation of the EGF-R.
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Affiliation(s)
- Bukhtiar H Shah
- Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510, USA
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274
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Abstract
It is well established that the function of most heptahelical receptors (seven-transmembrane-span receptors; 7TMRs) is tightly regulated by the desensitizing actions of arrestins. Desensitization is the waning of 7TMR-mediated signals after prolonged exposure to agonist and occurs when arrestins bind to agonist-occupied and phosphorylated receptors, uncoupling the receptors from G proteins and preventing further signaling. Recently, there has been a marked shift in the focus of research into arrestin function because it has become clear that they not only prevent signaling from 7TMRs but also initiate and direct new signals from the very 7TMRs that they desensitize.
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Affiliation(s)
- Stephen J Perry
- Howard Hughes Medical Institute, Depts of Medicine and Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
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275
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Yusoff P, Lao DH, Ong SH, Wong ESM, Lim J, Lo TL, Leong HF, Fong CW, Guy GR. Sprouty2 inhibits the Ras/MAP kinase pathway by inhibiting the activation of Raf. J Biol Chem 2002; 277:3195-201. [PMID: 11698404 DOI: 10.1074/jbc.m108368200] [Citation(s) in RCA: 184] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Several genetic studies in Drosophila have shown that the dSprouty (dSpry) protein inhibits the Ras/mitogen-activated protein (MAP) kinase pathway induced by various activated receptor tyrosine kinase receptors, most notably those of the epidermal growth factor receptor (EGFR) and fibroblast growth factor receptor (FGFR). Currently, the mode of action of dSpry is unknown, and the point of inhibition remains controversial. There are at least four mammalian Spry isoforms that have been shown to co-express preferentially with FGFRs as compared with EGFRs. In this study, we investigated the effects of the various mammalian Spry isoforms on the Ras/MAP kinase pathway in cells overexpressing constitutively active FGFR1. hSpry2 was significantly more potent than mSpry1 or mSpry4 in inhibiting the Ras/MAP kinase pathway. Additional experiments indicated that full-length hSpry2 was required for its full potency. hSpry2 had no inhibitory effect on either the JNK or the p38 pathway and displayed no inhibition of FRS2 phosphorylation, Akt activation, and Ras activation. Constitutively active mutants of Ras, Raf, and Mek were employed to locate the prospective point of inhibition of hSpry2 downstream of activated Ras. Results from this study indicated that hSpry2 exerted its inhibitory effect at the level of Raf, which was verified in a Raf activation assay in an FGF signaling context.
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Affiliation(s)
- Permeen Yusoff
- Signal Transduction Laboratory, Institute of Molecular and Cell Biology, National University of Singapore, Singapore 117609, Singapore
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276
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Lee FS, Rajagopal R, Chao MV. Distinctive features of Trk neurotrophin receptor transactivation by G protein-coupled receptors. Cytokine Growth Factor Rev 2002; 13:11-7. [PMID: 11750876 DOI: 10.1016/s1359-6101(01)00024-7] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Ligands for G protein-coupled receptors (GPCR) are capable of activating mitogenic receptor tyrosine kinases, in addition to the mitogen-activated protein (MAP) kinase signaling pathway and classic G protein-dependent signaling pathways involving adenylyl cyclase and phospholipase. For example, receptors for epidermal growth factor (EGF), insulin-like growth-1 and platelet-derived growth factor and can be transactivated through G protein-coupled receptors. Neurotrophins, such as NGF, BDNF and NT-3 also utilize receptor tyrosine kinases, namely TrkA, TrkB and TrkC. Recently, it has been shown that activation of Trk receptor tyrosine kinases can also occur via a G protein-coupled receptor mechanism, without involvement of neurotrophins. Adenosine and adenosine agonists can activate Trk receptor phosphorylation specifically through the seven transmembrane spanning adenosine 2A (A2A) receptor. Several features of Trk receptor transactivation are noteworthy and differ significantly from other transactivation events. Trk receptor transactivation is slower and results in a selective increase in activated Akt. Unlike the biological actions of other tyrosine kinase receptors, increased Trk receptor activity by adenosine resulted in increased cell survival. This article will discuss potential mechanisms by which adenosine can activate trophic responses through Trk tyrosine kinase receptors.
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Affiliation(s)
- Francis S Lee
- Department of Psychiatry, Weill Medical College of Cornell University, New York, NY 10021, USA
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277
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Dubuisson L, Desmoulière A, Decourt B, Evadé L, Bedin C, Boussarie L, Barrier L, Vidaud M, Rosenbaum J. Inhibition of rat liver fibrogenesis through noradrenergic antagonism. Hepatology 2002; 35:325-31. [PMID: 11826405 DOI: 10.1053/jhep.2002.31166] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The effect of adrenergic innervation and/or circulating catecholamines on the function of liver fibrogenic cells is poorly understood. Our aim was to investigate the effects of noradrenergic antagonism on carbon tetrachloride (CCl4)-induced liver fibrosis in rats. Two weeks of CCl4 induced an approximately 5-fold increase in the area of fibrosis as compared with controls. The addition of 6-hydroxydopamine (OHDA), a toxin that destroys noradrenergic fibers, decreased fibrosis by 60%. After 6 weeks of CCl4, the area of fibrosis increased about 30-fold in CCl4-treated animals and was decreased by 36% with OHDA. At 2 weeks, OHDA abrogated the CCl4-induced increase in mRNA level of tissue inhibitor of matrix metalloproteinases-1 (TIMP-1), an inhibitor of extracellular matrix degradation, and it greatly reduced it at 6 weeks. Finally, when rats treated with CCl4 for 2 weeks also received prazosin, an antagonist of alpha1-adrenergic receptors, fibrosis was decreased by 83%. In conclusion, destruction of noradrenergic fibers or antagonism of noradrenergic signaling through alpha1 receptors inhibited the development of liver fibrosis. Because adrenoreceptor antagonists have a very sound safety profile, they appear as attractive drugs to reduce liver fibrogenesis.
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Affiliation(s)
- Liliane Dubuisson
- Groupe de Recherches pour l'Etude du Foie, INSERM E9917, Université Victor Segalen Bordeaux 2, Bordeaux, France
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278
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Metabotropic glutamate receptor 5-induced phosphorylation of extracellular signal-regulated kinase in astrocytes depends on transactivation of the epidermal growth factor receptor. J Neurosci 2002. [PMID: 11739572 DOI: 10.1523/jneurosci.21-24-09619.2001] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
G-protein-coupled receptors (GPCRs) induce the phosphorylation of mitogen-activated protein (MAP) kinase by actions on any of a number of signal transduction systems. Previous studies have revealed that activation of the G(q)-coupled metabotropic glutamate receptor 5 (mGluR5) induces phosphorylation of the MAP kinase extracellular signal-regulated kinase 2 (ERK2) in cultured rat cortical astrocytes. We performed a series of studies to determine the mechanisms underlying mGluR5-induced phosphorylation of MAP kinase in these cells. Interestingly, our studies suggest that mGluR5-mediated ERK2 phosphorylation is dependent on the activation of G(alphaq) but is not mediated by the activation of phospholipase Cbeta1, activation of protein kinase C, or increases in intracellular calcium. Studies with peptide inhibitors suggest that this response is not dependent on G(betagamma) subunits. However, the activation of ERK2 was dependent on activation of the epidermal growth factor (EGF) receptor and activation of a Src family tyrosine kinase. Furthermore, activation of mGluR5 induced an association of this receptor and the EGF receptor, suggesting the formation of a signaling complex involved in the activation of ERK2. These data suggest that mGluR5 increases ERK2 phosphorylation in astrocytes by a novel mechanism involving the activation of G(alphaq) and both receptor and nonreceptor tyrosine kinases but that is independent of the activation of phospholipase Cbeta1.
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279
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Abstract
An enigmatic yet fundamental principle of signal transduction is that parallel signaling pathways assembled from a common repertoire of enzymes are able to propagate diverse physiological responses. A key feature of such a mechanism is that separate signaling pathways are organized into localized transduction units, each tailored to respond optimally to a particular signal. Protein-protein interactions maintained by anchoring, adapter and scaffolding proteins provide the molecular glue that holds these signal transduction units together. A major objective of the signaling community is to ascertain how signals flow through compartmentalized transduction units that contain transmembrane receptors, protein kinases, phosphatases and their substrates.
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Affiliation(s)
- F Donelson Smith
- Howard Hughes Medical Institute, Vollum Institute, Oregon Health and Sciences University, 3181 S.W. Sam Jackson Park Road, Portland, Oregon 97201-3098, USA
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280
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Lemjabbar H, Basbaum C. Platelet-activating factor receptor and ADAM10 mediate responses to Staphylococcus aureus in epithelial cells. Nat Med 2002; 8:41-6. [PMID: 11786905 DOI: 10.1038/nm0102-41] [Citation(s) in RCA: 269] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In the lungs of cystic fibrosis patients, overproduction of mucus leads to morbidity and mortality by obstructing airflow and shielding bacteria from antibiotics. Here we demonstrate that overproduction of mucus is a direct result of the activation of mucin gene expression by Gram-positive bacteria. Bacterial lipoteichoic acid activates the platelet-activating factor receptor, which is G protein-coupled. This results in activation of a disintegrin and metalloproteinase (ADAM10), kuzbanian, cleavage of pro heparin-binding epidermal growth factor and activation of the epidermal growth factor receptor. Unlike responses in macrophages, the epithelial-cell response to lipoteichoic acid does not require Toll-like receptor 2 or 4.
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Affiliation(s)
- Hassan Lemjabbar
- Biomedical Sciences Program, Cardiovascular Research Institute and Department of Anatomy, University of California, San Francisco, California, USA
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281
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Affiliation(s)
- Jennifer R Wood
- Center for Research on Reproduction and Women's Health, University of Pennsylvania Medical Center, Philadelphia, PA 19104, USA
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282
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Belcheva MM, Coscia CJ. Diversity of G protein-coupled receptor signaling pathways to ERK/MAP kinase. Neurosignals 2002; 11:34-44. [PMID: 11943881 PMCID: PMC2581518 DOI: 10.1159/000057320] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
One of the most intriguing examples of cross talk between signaling systems is the interrelationship between G protein-coupled receptor and growth factor receptor pathways leading to activation of the ERK/MAP kinase phosphorylation cascade. This review focuses on the mechanism of this cross talk, denoting primarily signaling components known to occur in the G protein-coupled receptor branch of the MAP kinase pathways in neural cells. Recent evidence is presented on the existence of a plethora of pathways, due to the multiplicity of G protein-coupled receptors, their differential interaction with heterotrimeric G protein isoforms, various effectors and second messengers. In light of this rich diversity, the review will discuss different points of convergence of G protein-coupled receptor and growth factor receptor pathways that may feature a requirement for growth factor receptor transactivation, receptor internalization and scaffolds to assemble receptor, adaptor and anchoring proteins into multiprotein complexes.
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Affiliation(s)
- Mariana M Belcheva
- E.A. Doisy Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, St. Louis, Mo. 63104, USA
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283
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Hanke S, Nürnberg B, Groll DH, Liebmann C. Cross talk between beta-adrenergic and bradykinin B(2) receptors results in cooperative regulation of cyclic AMP accumulation and mitogen-activated protein kinase activity. Mol Cell Biol 2001; 21:8452-60. [PMID: 11713280 PMCID: PMC100008 DOI: 10.1128/mcb.21.24.8452-8460.2001] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2000] [Accepted: 09/21/2001] [Indexed: 11/20/2022] Open
Abstract
Costimulation of G protein-coupled receptors (GPCRs) may result in cross talk interactions between their downstream signaling pathways. Stimulation of GPCRs may also lead to cross talk regulation of receptor tyrosine kinase signaling and thereby to activation of mitogen-activated protein kinase (MAPK). In COS-7 cells, we investigated the interactions between two particular mitogenic receptor pathways, the endogenously expressed beta-adrenergic receptor (beta-AR) and the transiently transfected human bradykinin (BK) B(2) receptor (B(2)R). When beta-AR and B(2)R are costimulated, we found two different cross talk mechanisms. First, the predominantly G(q) protein-coupled B(2)R is enabled to activate a G(i) protein and, subsequently, type II adenylate cyclase. This results in augmentation of beta-AR-mediated cyclic AMP (cAMP) accumulation by BK, which alone is unable to increase the cAMP level. Second, independently of BK-induced superactivation of the cAMP system, costimulation of beta-AR leads to protein kinase A-mediated blockade of phospholipase C activation by BK. Thereby, the pathway from B(2)R to MAPK, which essentially involves protein kinase C activation, is selectively switched off. The MAPK activation in response to isoproterenol was not affected due to costimulation. Furthermore, in the presence of isoproterenol, BK lost its ability to stimulate DNA synthesis in COS-7 cells. Thus, our findings might establish a novel paradigm: cooperation between simultaneously activated mitogenic pathways may prevent multiple stimulation of MAPK activity and increased cell growth.
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Affiliation(s)
- S Hanke
- Institut für Biochemie und Biophysik, Biologisch-Pharmazeutische Fakultät, Friedrich-Schiller-Universität, Philosophenweg 12, D-07743 Jena, Germany
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284
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Liebmann C. Regulation of MAP kinase activity by peptide receptor signalling pathway: paradigms of multiplicity. Cell Signal 2001; 13:777-85. [PMID: 11583913 DOI: 10.1016/s0898-6568(01)00192-9] [Citation(s) in RCA: 216] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
G protein-coupled receptors (GPCRs) can stimulate the mitogen-activated protein kinase (MAPK) cascade and thereby induce cellular proliferation like receptor tyrosine kinases (RTKs). Work over the past 5 years has established several models which reduce the links of G(i)-, G(q)-, and G(s)-coupled receptors to MAPK on few principle pathways. They include (i) Ras-dependent activation of MAPK via transactivation of RTKs such as the epidermal growth factor receptor (EGFR), (ii) Ras-independent MAPK activation via protein kinase C (PKC) that converges with the RTK signalling at the level of Raf, and (iii) activation as well as inactivation of MAPK via the cAMP/protein kinase A (PKA) pathway in dependency on the type of Raf. Most of these generalizing hypotheses are founded on experimental data obtained from expression studies and using a limited set of individual receptors. This review will compare these models with pathways to MAPK found for a great variety of peptide hormone and neuropeptide receptor subtypes in various cells. It becomes evident that under endogenous conditions, the transactivation pathway is less dominant as postulated, whereas pathways involving isoforms of PKC and, especially, phosphoinositide 3-kinase (PI-3K) appear to play a more important role as assumed so far. Highly cell-specific and unusual connections of signalling proteins towards MAPK, in particular tumour cells, might provide points of attacks for new therapeutic concepts.
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Affiliation(s)
- C Liebmann
- Institute of Biochemistry and Biophysics, Biological and Pharmaceutical Faculty, Friedrich-Schiller University, Philosophenweg 12, D-07743, Jena, Germany.
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285
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Hislop JN, Everest HM, Flynn A, Harding T, Uney JB, Troskie BE, Millar RP, McArdle CA. Differential internalization of mammalian and non-mammalian gonadotropin-releasing hormone receptors. Uncoupling of dynamin-dependent internalization from mitogen-activated protein kinase signaling. J Biol Chem 2001; 276:39685-94. [PMID: 11495905 DOI: 10.1074/jbc.m104542200] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Desensitization and internalization of G-protein-coupled receptors can reflect receptor phosphorylation-dependent binding of beta-arrestin, which prevents G-protein activation and targets receptors for internalization via clathrin-coated vesicles. These can be pinched off by a dynamin collar, and proteins controlling receptor internalization can also mediate mitogen-activated protein kinase signaling. Gonadotropin-releasing hormone (GnRH) stimulates internalization of its receptors via clathrin-coated vesicles. Mammalian GnRH receptors (GnRH-Rs) are unique in that they lack C-terminal tails and do not rapidly desensitize, whereas non-mammalian GnRH-R have C-terminal tails and, where investigated, do rapidly desensitize and internalize. Using recombinant adenovirus expressing human and Xenopus GnRH-Rs we have explored the relationship between receptor internalization and mitogen-activated protein kinase signaling in HeLa cells with regulated tetracycline-controlled expression of wild-type or a dominant negative mutant (K44A) of dynamin. These receptors were phospholipase C-coupled and had appropriate ligand affinity and specificity. K44A dynamin expression did not alter human GnRH-R internalization but dramatically reduced internalization of Xenopus GnRH-R (and epidermal growth factor (EGF) receptor). Blockade of clathrin-mediated internalization (sucrose) abolished internalization of all three receptors. Both GnRH-Rs also mediated phosphorylation of ERK 2 and for both receptors, this was inhibited by K44A dynamin. The same was true for EGF- and protein kinase C-mediated ERK 2 phosphorylation. ERK 2 phosphorylation was also inhibited by a protein kinase C inhibitor but not affected by an EGF receptor tyrosine kinase inhibitor. We conclude that a) desensitizing and non-desensitizing GnRH-Rs are targeted for clathrin-coated vesicle-mediated internalization by functionally distinct mechanisms, b) GnRH-R signaling to ERK 2 is dynamin-dependent and c) this does not reflect a dependence on dynamin-dependent GnRH-R internalization.
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Affiliation(s)
- J N Hislop
- University Research Centre for Neuroendocrinology, University of Bristol, Bristol, BS2 8HW, United Kingdom
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286
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Cramer H, Schmenger K, Heinrich K, Horstmeyer A, Böning H, Breit A, Piiper A, Lundstrom K, Müller-Esterl W, Schroeder C. Coupling of endothelin receptors to the ERK/MAP kinase pathway. Roles of palmitoylation and G(alpha)q. EUROPEAN JOURNAL OF BIOCHEMISTRY 2001; 268:5449-59. [PMID: 11606208 DOI: 10.1046/j.0014-2956.2001.02486.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Endothelins are potent mitogens that stimulate extracellular signal-regulated kinases (ERK/MAP kinases) through their cognate G-protein-coupled receptors, ET(A) and ET(B). To address the role of post-translational ET receptor modifications such as acylation on ERK activation and to identify relevant downstream effectors coupling the ET receptor to the ERK signaling cascades we have constructed a panel of palmitoylation-deficient ET receptor mutants with differential G(alpha) protein binding capacity. Endothelin-1 stimulation of wild-type ET(A) or ET(B) induced a fivefold to sixfold increase in ERK in COS-7 and CHO cells whereas full-length nonpalmitoylated ET(A) and ET(B) mutants failed to stimulate ERK. A truncated ET(B) lacking the C-terminal tail domain including putative phosphorylation and arrestin binding site(s) but retaining the critical palmitoylation site(s) was still able to fully stimulate ERK activation. Using mutated ET receptors with selective G-protein-coupling we found that endothelin-induced stimulation of G(alpha)q, but not of G(alpha)i or G(alpha)s, is essential for endothelin-mediated ERK activation. Inhibition of protein kinases A and C or epidermal growth factor receptor kinase failed to prevent ET(A)- and ET(B)-mediated ERK activation whereas blockage of phospholipase C-beta completely abrogated endothelin-promoted ERK activation through ET(A) and ET(B) in recombinant COS-7 and native C6 cells. Complex formation of Ca2+ or inhibition of Src family tyrosine kinases prevented ET-1-induced ERK-2 activation in C6-cells. Our results indicate that endothelin-promoted ERK/MAPK activation criticially depends on palmitoylation but not on phosphorylation of ET receptors, and that the G(alpha)q/phospholipase C-beta/Ca2+/Src signaling cascade is necessary for efficient coupling of ET receptors to the ERK/MAPK pathway.
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Affiliation(s)
- H Cramer
- Institute for Biochemistry II, Johann Wolfgang Goethe University Frankfurt, Theodor-Stern-Kai7, Germany
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287
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Abstract
The last few years have seen a marked expansion in appreciation of the diversity of roles played by the betaArrestins in regulating GPCR functions. Originally discovered as molecules that desensitize such receptors, the roles of betaArrestins have expanded to include acting as signalling adapters or intermediates that recruit other key molecules to the GPCRs in an agonist-regulated fashion. For example, interactions with components of the endocytic machinery, such as clathrin, the adapter protein AP-2 and the N-ethylmaleimide sensitive fusion protein (NSF), demonstrate the ability of betaArrestins to act as adapters to facilitate the clathrin-mediated endocytosis of certain members of the GPCR family. BetaArrestins have also been shown to serve as signalling molecules. The Ras-dependent activation of ERK1/2 may involve the betaArrestin-dependent recruitment of c-Src to the beta2-adrenergic receptor (beta2-AR). More recently, betaArrestins have been shown to act as molecular scaffolds that coordinate the assembly of certain MAP kinase complexes that lead to the stimulation of either ERK1/2 or JNK3. Finally, long-term accumulation of arrestin-rhodopsin complexes, in photoreceptor cells has been shown to trigger apoptosis.
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Affiliation(s)
- P H McDonald
- Department of Medicine, Howard Hughes Medical Institute, Duke University Medical Center, Box 3821, Durham, NC 27710, USA
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288
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Abstract
The basic module of signal transduction that involves G-protein-coupled receptors is usually portrayed as comprising a receptor, a heterotrimeric G protein and an effector. It is now well established that regulated interactions between receptors and arrestins, and between G proteins and regulators of G-protein signalling alter the effectiveness and kinetics of information transfer. However, more recent studies have begun to identify a host of other proteins that interact selectively with individual receptors at both the intracellular and extracellular face of the membrane. Although the functional relevance of many of these interactions is only beginning to be understood, current information indicates that these interactions might determine receptor properties, such as cellular compartmentalization or signal selection, and can promote protein scaffolding into complexes that integrate function.
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Affiliation(s)
- G Milligan
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, G12 8QQ, Glasgow, UK.
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289
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Abstract
Inflammatory pain, characterized by a decrease in mechanical nociceptive threshold (hyperalgesia), arises through actions of inflammatory mediators, many of which sensitize primary afferent nociceptors via G-protein-coupled receptors. Two signaling pathways, one involving protein kinase A (PKA) and one involving the epsilon isozyme of protein kinase C (PKCepsilon), have been implicated in primary afferent nociceptor sensitization. Here we describe a third, independent pathway that involves activation of extracellular signal-regulated kinases (ERKs) 1 and 2. Epinephrine, which induces hyperalgesia by direct action at beta(2)-adrenergic receptors on primary afferent nociceptors, stimulated phosphorylation of ERK1/2 in cultured rat dorsal root ganglion cells. This was inhibited by a beta(2)-adrenergic receptor blocker and by an inhibitor of mitogen and extracellular signal-regulated kinase kinase (MEK), which phosphorylates and activates ERK1/2. Inhibitors of G(i/o)-proteins, Ras farnesyltransferases, and MEK decreased epinephrine-induced hyper-algesia. In a similar manner, phosphorylation of ERK1/2 was also decreased by these inhibitors. Local injection of dominant active MEK produced hyperalgesia that was unaffected by PKA or PKCepsilon inhibitors. Conversely, hyperalgesia produced by agents that activate PKA or PKCepsilon was unaffected by MEK inhibitors. We conclude that a Ras-MEK-ERK1/2 cascade acts independent of PKA or PKCepsilon as a novel signaling pathway for the production of inflammatory pain. This pathway may present a target for a new class of analgesic agents.
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290
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Belcheva MM, Szùcs M, Wang D, Sadee W, Coscia CJ. mu-Opioid receptor-mediated ERK activation involves calmodulin-dependent epidermal growth factor receptor transactivation. J Biol Chem 2001; 276:33847-53. [PMID: 11457825 DOI: 10.1074/jbc.m101535200] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphorylation of the MAPK isoform ERK by G protein-coupled receptors involves multiple signaling pathways. One of these pathways entails growth factor receptor transactivation followed by ERK activation. This study demonstrates that a similar signaling pathway is used by the mu-opioid receptor (MOR) expressed in HEK293 cells and involves calmodulin (CaM). Stimulation of MOR resulted in both epidermal growth factor receptor (EGFR) and ERK phosphorylation. Data obtained with inhibitors of EGFR Tyr kinase and membrane metalloproteases support an intermediate role of EGFR activation, involving release of endogenous membrane-bound epidermal growth factor. Previous studies had demonstrated a role for CaM in opioid signaling based on direct CaM binding to MOR. To test whether CaM contributes to EGFR transactivation and ERK phosphorylation by MOR, we compared wild-type MOR with mutant K273A MOR, which binds CaM poorly, but couples normally to G proteins. Stimulation of K273A MOR with [D-Ala(2),MePhe(4),Gly-ol(5)]enkephalin (10-100 nm) resulted in significantly reduced ERK phosphorylation. Furthermore, wild-type MOR stimulated EGFR Tyr phosphorylation 3-fold more than K273A MOR, indicating that direct CaM-MOR interaction plays a key role in the transactivation process. Inhibitors of CaM and protein kinase C also attenuated [D-Ala(2),MePhe(4),Gly-ol(5)]enkephalin-induced EGFR transactivation in wild-type (but not mutant) MOR-expressing cells. This novel pathway of EGFR transactivation may be shared by other G protein-coupled receptors shown to interact with CaM.
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Affiliation(s)
- M M Belcheva
- Department Biochemistry and Molecular Biology, St. Louis University School of Medicine, St. Louis, Missouri 63104, USA
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291
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McNamara N, Basbaum C. Signaling networks controlling mucin production in response to Gram-positive and Gram-negative bacteria. Glycoconj J 2001; 18:715-22. [PMID: 12386457 DOI: 10.1023/a:1020875423678] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Human lung cells exposed to pathogenic bacteria upregulate the production of mucin, the major macromolecular component of mucus. Generally this upregulation is beneficial for the host, however, in the lungs of cystic fibrosis patients, overproduction of mucin can lead to the plugging of pulmonary airways. Mucus plugging impedes airflow and creates an environment that is highly compartmentalized: those bacteria within the mucus layer are shielded from high doses of antibiotics whereas those outside the mucus are exposed. These conditions augment mutation rate and the development of drug resistance in bacteria that colonize the lungs of cystic fibrosis patients. While therapeutic inhibition of mucin induction would improve airflow and reduce antibiotic resistance in these patients, the challenge is to develop drugs that block excessive mucin production while leaving beneficial aspects of the response intact. To do this, we must understand the molecular mechanisms underlying mucin production. Here we review the signal transduction pathways that control mucin production in response to Gram-positive and Gram-negative bacteria.
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Affiliation(s)
- N McNamara
- Biomedical Sciences Program, Cardiovascular Research Institute and Department of Anatomy, University of California, San Francisco, CA 94143, USA
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292
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Weisman G, Griffin K, Santiago-Pérez L, Liu J, Krugh B, Flores R, Chorna N, Santos-Berríos C, Vivas-Mejía P, Garrad R, González F, Erb L. P2Y2receptors regulate multiple signal transduction pathways in monocytic cells. Drug Dev Res 2001. [DOI: 10.1002/ddr.1187] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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293
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Millar R, Lowe S, Conklin D, Pawson A, Maudsley S, Troskie B, Ott T, Millar M, Lincoln G, Sellar R, Faurholm B, Scobie G, Kuestner R, Terasawa E, Katz A. A novel mammalian receptor for the evolutionarily conserved type II GnRH. Proc Natl Acad Sci U S A 2001; 98:9636-41. [PMID: 11493674 PMCID: PMC55504 DOI: 10.1073/pnas.141048498] [Citation(s) in RCA: 183] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2001] [Indexed: 11/18/2022] Open
Abstract
Mammalian gonadotropin-releasing hormone (GnRH I: pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) stimulates pituitary gonadotropin secretion, which in turn stimulates the gonads. Whereas a hypothalamic form of GnRH of variable structure (designated type I) had been shown to regulate reproduction through a cognate type I receptor, it has recently become evident that most vertebrates have one or two other forms of GnRH. One of these, designated type II GnRH (GnRH II: pGlu-His-Ser-His-Gly-Trp-Tyr-Pro-Gly-NH2), is conserved from fish to man and is widely distributed in the brain, suggesting important neuromodulatory functions such as regulating K+ channels and stimulating sexual arousal. We now report the cloning of a type II GnRH receptor from marmoset cDNA. The receptor has only 41% identity with the type I receptor and, unlike the type I receptor, has a carboxyl-terminal tail. The receptor is highly selective for GnRH II. As with the type I receptor, it couples to G(alpha)q/11 and also activates extracellular signal-regulated kinase (ERK1/2) but differs in activating p38 mitogen activated protein (MAP) kinase. The type II receptor is more widely distributed than the type I receptor and is expressed throughout the brain, including areas associated with sexual arousal, and in diverse non-neural and reproductive tissues, suggesting a variety of functions. Surprisingly, the type II receptor is expressed in the majority of gonadotropes. The presence of two GnRH receptors in gonadotropes, together with the differences in their signaling, suggests different roles in gonadotrope functioning.
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MESH Headings
- Amino Acid Sequence
- Animals
- COS Cells
- Callithrix
- Chlorocebus aethiops
- Cloning, Molecular
- Evolution, Molecular
- Expressed Sequence Tags
- Female
- Follicle Stimulating Hormone/metabolism
- Gonadotropin-Releasing Hormone/analogs & derivatives
- Gonadotropin-Releasing Hormone/physiology
- Haplorhini
- Humans
- Inositol Phosphates/metabolism
- Luteinizing Hormone/metabolism
- Male
- Mice
- Molecular Sequence Data
- Nerve Tissue Proteins/drug effects
- Nerve Tissue Proteins/genetics
- Nerve Tissue Proteins/isolation & purification
- Nerve Tissue Proteins/physiology
- Nervous System/embryology
- Polymerase Chain Reaction
- Protein Structure, Tertiary
- Receptors, LHRH/drug effects
- Receptors, LHRH/genetics
- Receptors, LHRH/isolation & purification
- Receptors, LHRH/physiology
- Recombinant Fusion Proteins/metabolism
- Reproduction/physiology
- Sequence Alignment
- Sequence Homology, Amino Acid
- Sequence Homology, Nucleic Acid
- Sexual Behavior, Animal/physiology
- Sheep
- Signal Transduction
- Species Specificity
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Affiliation(s)
- R Millar
- Medical Research Council Human Reproductive Sciences Unit, Edinburgh EH3 9ET, Scotland.
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294
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Mellado M, Rodríguez-Frade JM, Mañes S, Martínez-A C. Chemokine signaling and functional responses: the role of receptor dimerization and TK pathway activation. Annu Rev Immunol 2001; 19:397-421. [PMID: 11244042 DOI: 10.1146/annurev.immunol.19.1.397] [Citation(s) in RCA: 288] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A broad array of biological responses, including cell polarization, movement, immune and inflammatory responses, and prevention of HIV-1 infection, are triggered by the chemokines, a family of structurally related chemoattractant proteins that bind to specific seven-transmembrane receptors linked to G proteins. Here we discuss one of the early signaling pathways activated by chemokines, the JAK/STAT pathway. Through this pathway, and possibly in conjunction with other signaling pathways, the chemokines promote changes in cellular morphology, collectively known as polarization, required for chemotactic responses. The polarized cell expresses the chemokine receptors at the leading cell edge, to which they are conveyed by rafts, a cholesterol-enriched membrane fraction fundamental to the lateral organization of the plasma membrane. Finally, the mechanisms through which the chemokines promote their effect are discussed in the context of the prevention of HIV-1 infection.
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Affiliation(s)
- M Mellado
- Department of Immunology and Oncology, Centro Nacional de Biotecnología/CSIC, UAM Campus de Cantoblanco, Madrid, E-28049 Spain
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295
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Oak JN, Lavine N, Van Tol HH. Dopamine D(4) and D(2L) Receptor Stimulation of the Mitogen-Activated Protein Kinase Pathway Is Dependent on trans-Activation of the Platelet-Derived Growth Factor Receptor. Mol Pharmacol 2001; 60:92-103. [PMID: 11408604 DOI: 10.1124/mol.60.1.92] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The ability of dopamine D(4) and D(2) receptors to activate extracellular signal-regulated kinases (ERKs) 1 and 2 was compared using Chinese hamster ovary (CHO-K1) cells transfected with D(4.2), D(4.4), D(4.7), and D(2L) receptors. Dopamine stimulation of D(4) or D(2L) receptors produced a transient, dose-dependent increase in ERK1/2 activity. Receptor-specific activation of the ERK mitogen-activated protein kinase (MAPK) pathway was confirmed using the D(2)-like receptor-selective agonist quinpirole, whereas the specific antagonist haloperidol blocked activation. MAPK stimulation was dependent on a pertussis-toxin-sensitive G protein (G(i/o)). trans-Activation of the platelet-derived growth factor (PDGF) receptor was an essential step in D(4) and D(2L) receptor-induced MAPK activation. PDGF receptor-selective tyrosine kinase inhibitors tyrphostin A9 and AG1295 abolished or significantly inhibited ERK1/2 activation by D(4) and D(2L) receptors. Dopamine stimulation of the D(4) receptor also produced a rapid increase in tyrosine phosphorylation of the PDGF receptor-beta. The Src-family tyrosine kinase inhibitor PP2 blocked MAPK activation by dopamine; however, this drug was also found to inhibit PDGF-BB-stimulated ERK activity and autophosphorylation of the PDGF receptor-beta. Downstream signaling pathways support the involvement of a receptor tyrosine kinase. The phosphoinositide 3-kinase inhibitors wortmannin and LY294002, protein kinase C inhibitors GF109203X and Calphostin C, dominant-negative RasN17, and the MEK inhibitor PD98059 significantly attenuated or abolished activation of MAPK by dopamine D(4) and D(2L) receptors. Our results indicate that D(4) and D(2L) receptors activate the ERK kinase cascade by first mobilizing signaling by the PDGF receptor, followed by the subsequent activation of ERK1/2 by pathways associated with this receptor tyrosine kinase.
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Affiliation(s)
- J N Oak
- Laboratory of Molecular Neurobiology, Centre for Addiction and Mental Health, Toronto, Ontario, Canada
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296
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Marinissen MJ, Gutkind JS. G-protein-coupled receptors and signaling networks: emerging paradigms. Trends Pharmacol Sci 2001; 22:368-76. [PMID: 11431032 DOI: 10.1016/s0165-6147(00)01678-3] [Citation(s) in RCA: 719] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
G-protein-coupled receptors (GPCRs) constitute the largest family of cell-surface molecules involved in signal transmission. These receptors play key physiological roles and their dysfunction results in several diseases. Recently, it has been shown that many of the cellular responses mediated by GPCRs do not involve the sole stimulation of conventional second-messenger-generating systems, but instead result from the functional integration of an intricate network of intracellular signaling pathways. Effectors for GPCRs that are independent of G proteins have now also been identified, thus changing the conventional view of the GPCR-heterotrimeric-G-protein-associated effector. The emerging information is expected to help elucidate the most basic mechanism by which these receptors exert their numerous physiological roles, in addition to determining why the perturbation of their function results in many pathological conditions.
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Affiliation(s)
- M J Marinissen
- Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research/NIH, 30 Convent Drive, Building 30, Room 211, Bethesda, MD 20892-4340, USA.
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297
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Grewal JS, Luttrell LM, Raymond JR. G Protein-coupled Receptors Desensitize and Down-regulate Epidermal Growth Factor Receptors in Renal Mesangial Cells. J Biol Chem 2001; 276:27335-44. [PMID: 11371570 DOI: 10.1074/jbc.m103578200] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Different types of plasma membrane receptors engage in various forms of cross-talk. We used cultures of rat renal mesangial cells to study the regulation of EGF receptors (EGFRs) by various endogenous G protein-coupled receptors (GPCRs). GPCRs (5-hydroxytryptamine(2A), lysophosphatidic acid, angiotensin AT(1), bradykinin B(2)) were shown to transactivate EGFRs through a protein kinase C-dependent pathway. This transactivation resulted in the initiation of multiple cellular signals (phosphorylation of the EGFRs and ERK and activation of cAMP-responsive element-binding protein (CREB), NF-kappaB, and E2F), as well as subsequent rapid down-regulation of cell-surface EGFRs and internalization and desensitization of the EGFRs without change in the total cellular complement of EGFRs. Internalization of the EGFRs and the down-regulation of cell-surface receptors in mesangial cells were blocked by pharmacological inhibitors of clathrin-mediated endocytosis and in HEK293 cells by transfection of cDNA constructs that encode dominant negative beta-arrestin-1 or dynamin. Whereas all of the effects of GPCRs on EGFRs were dependent to a great extent on protein kinase C, those initiated by EGF were not. These studies demonstrate that GPCRs can induce multiple signals through protein kinase C-dependent transactivation of EGFRs. Moreover, GPCRs induce profound desensitization of EGFRs by a process associated with the loss of cell-surface EGFRs through clathrin-mediated endocytosis.
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Affiliation(s)
- J S Grewal
- Nephrology Division, Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425, USA
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298
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Jourdan KB, Mason NA, Long L, Philips PG, Wilkins MR, Morrell NW. Characterization of adenylyl cyclase isoforms in rat peripheral pulmonary arteries. Am J Physiol Lung Cell Mol Physiol 2001; 280:L1359-69. [PMID: 11350817 DOI: 10.1152/ajplung.2001.280.6.l1359] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Activation of adenylyl cyclase (AC), of which there are 10 diversely regulated isoforms, is important in regulating pulmonary vascular tone and remodeling. Immunohistochemistry in rat lungs demonstrated that AC2, AC3, and AC5/6 predominated in vascular and bronchial smooth muscle. Isoforms 1, 4, 7, and 8 localized to the bronchial epithelium. Exposure of animals to hypoxia did not change the pattern of isoform expression. RT-PCR confirmed mRNA expression of AC2, AC3, AC5, and AC6 and demonstrated AC7 and AC8 transcripts in smooth muscle. Western blotting confirmed the presence of AC2, AC3, and AC5/6 proteins. Functional studies provided evidence of cAMP regulation by Ca(2+) and protein kinase C-activated but not G(i)-inhibited pathways, supporting a role for AC2 and a Ca(2+)-stimulated isoform, AC8. However, NKH-477, an AC5-selective activator, was more potent than forskolin in elevating cAMP and inhibiting serum-stimulated [(3)H]thymidine incorporation, supporting the presence of AC5. These studies demonstrate differential expression of AC isoforms in rat lungs and provide evidence that AC2, AC5, and AC8 are functionally important in cAMP regulation and growth pathways in pulmonary artery myocytes.
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MESH Headings
- Adenylyl Cyclases/chemistry
- Adenylyl Cyclases/genetics
- Adenylyl Cyclases/metabolism
- Animals
- Blotting, Western
- Cell Division/drug effects
- Cells, Cultured
- Colforsin/analogs & derivatives
- Colforsin/pharmacology
- Cyclic AMP/metabolism
- Dose-Response Relationship, Drug
- Enzyme Activation/drug effects
- Enzyme Activators/pharmacology
- Enzyme Inhibitors/pharmacology
- Hypertension, Pulmonary/metabolism
- Hypoxia/enzymology
- Immunohistochemistry
- Isoenzymes/chemistry
- Isoenzymes/metabolism
- Male
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/enzymology
- Organ Specificity
- Protein Kinase C/antagonists & inhibitors
- Protein Kinase C/metabolism
- Pulmonary Artery/cytology
- Pulmonary Artery/enzymology
- RNA, Messenger/biosynthesis
- Rats
- Rats, Inbred WKY
- Reverse Transcriptase Polymerase Chain Reaction
- Vasodilator Agents/pharmacology
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Affiliation(s)
- K B Jourdan
- Department of Medicine, Addenbrooke's Hospital, University of Cambridge, Hills Road, Cambridge CB2 2QQ, United Kingdom
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299
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Reusch HP, Schaefer M, Plum C, Schultz G, Paul M. Gbeta gamma mediate differentiation of vascular smooth muscle cells. J Biol Chem 2001; 276:19540-7. [PMID: 11279222 DOI: 10.1074/jbc.m101963200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Proliferation and subsequent dedifferentiation of vascular smooth muscle (VSM) cells contribute to the pathogenesis of atherosclerosis and postangioplastic restenosis. The dedifferentiation of VSM cells in vivo or in cell culture is characterized by a loss of contractile proteins such as smooth muscle-specific alpha-actin and myosin heavy chain (SM-MHC). Serum increased the expression of contractile proteins in neonatal rat VSM cells, indicating a redifferentiation process. RNase protection assays defined thrombin as a serum component that increases the abundance of SM-MHC transcripts. Additionally, serum and thrombin transiently elevated cytosolic Ca(2+) concentrations, led to a biphasic extracellular signal-regulated kinase (ERK) phosphorylation, up-regulated a transfected SM-MHC promoter construct, and induced expression of the contractile proteins SM-MHC and alpha-actin. Pertussis toxin, N17-Ras/Raf, and PD98059 prevented both the serum- and thrombin-induced second phase ERK phosphorylation and SM-MHC promoter activation. Constitutively active Galpha(q), Galpha(i), Galpha(12), and Galpha(13) failed to up-regulate SM-MHC transcription, whereas Gbetagamma concentration-dependently increased the SM-MHC promoter activity. Furthermore, the Gbetagamma scavenger beta-adrenergic receptor kinase 1 C-terminal peptide abolished the serum-mediated differentiation. We conclude that receptor-mediated differentiation of VSM cells requires Gbetagamma and an intact Ras/Raf/MEK/ERK signaling.
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MESH Headings
- Actins/biosynthesis
- Animals
- Animals, Newborn
- Calcium/metabolism
- Cell Differentiation
- Cell Division
- Cells, Cultured
- Cytosol/metabolism
- Dose-Response Relationship, Drug
- Enzyme Inhibitors/pharmacology
- Flavonoids/pharmacology
- GTP-Binding Protein beta Subunits
- GTP-Binding Protein gamma Subunits
- Heterotrimeric GTP-Binding Proteins/metabolism
- Heterotrimeric GTP-Binding Proteins/physiology
- Immunoblotting
- Microscopy, Fluorescence
- Mitogen-Activated Protein Kinases/metabolism
- Muscle, Smooth, Vascular/cytology
- Myosin Heavy Chains/biosynthesis
- Pertussis Toxin
- Phosphorylation
- Promoter Regions, Genetic
- RNA, Messenger/metabolism
- Rats
- Ribonucleases/metabolism
- Signal Transduction
- Thrombin/metabolism
- Time Factors
- Transcription, Genetic
- Transfection
- Up-Regulation
- Virulence Factors, Bordetella/pharmacology
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Affiliation(s)
- H P Reusch
- Institute of Clinical Pharmacology and Toxicology and the Institute of Pharmacology, Benjamin Franklin Medical Center, Freie Universität Berlin, Berlin 14195, Germany
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300
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Stantchev TS, Broder CC. Human immunodeficiency virus type-1 and chemokines: beyond competition for common cellular receptors. Cytokine Growth Factor Rev 2001; 12:219-43. [PMID: 11325604 DOI: 10.1016/s1359-6101(00)00033-2] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The chemokines and their receptors have been receiving exceptional attention in recent years following the discoveries that some chemokines could specifically block human immunodeficiency virus type 1 (HIV-1) infection and that certain chemokine receptors were the long-sought coreceptors which, along with CD4, are required for the productive entry of HIV-1 and HIV-2 isolates. Several chemokine receptors or orphan chemokine receptor-like molecules can support the entry of various viral strains, but the clinical significance of the CXCR4 and CCR5 coreceptors appear to overshadow a critical role for any of the other coreceptors and all HIV-1 and HIV-2 strains best employ one or both of these coreceptors. Binding of the HIV-1 envelope glycoprotein gp120 subunit to CD4 and/or an appropriate chemokine receptor triggers conformational changes in the envelope glycoprotein oligomer that allow it to facilitate the fusion of the viral and host cell membranes. During these interactions, gp120 appears to be capable of inducing a variety of signaling events, all of which are still not defined in detail. In addition, the more recently observed dichotomous effects, of both inhibition and enhancement, that chemokines and their receptor signaling events elicit on the HIV-1 entry and replication processes has once again highlighted the intricate and complex balance of factors that govern the pathogenic process. Here, we will review and discuss these new observations summarizing the potential significance these processes may have in HIV-1 infection. Understanding the complexities and significance of the signaling processes that the chemokines and viral products induce may substantially enhance our understanding of HIV-1 pathogenesis, and perhaps facilitate the discovery of new ways for the prevention and treatment of HIV-1 disease.
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Affiliation(s)
- T S Stantchev
- Department of Microbiology and Immunology, F. Edward Hébert School of Medicine, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Bethesda, MD 20814-4799, USA.
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