title: Delta-opioid receptors activate ERK/MAP kinase via integrin-stimulated receptor tyrosine kinases.
abstract: Integrin-mediated cell adherence to extracellular matrix proteins results in stimulation of ERK1/2 activity, a mechanism involving focal adhesion tyrosine kinases (pp125FAK, Pyk-2) and epidermal growth factor receptors (EGFRs). G protein-coupled receptors (GPCRs) may also mediate ERK1/2 activation in an integrin-dependent manner, the underlying signaling mechanism of which still remains unclear. Here we demonstrate that the delta-opioid receptor (DOR), a typical GPCR, stimulates ERK1/2 activity in HEK293 cells via integrin-mediated transactivation of EGFR function. Inhibition of integrin signaling by RGDT peptides, cytochalasin, and by keeping the cells in suspension culture both blocked [D-Ala(2), D-Leu(5)]enkephalin (DADLE)- and etorphine-stimulated ERK1/2 activity. Integrin-dependent ERK1/2 activation does not involve FAK/Pyk-2, because over-expression of the FAK/Pyk-2 inhibitor SOCS-3 failed to attenuate DOR signaling. Exposure of the cells to the EGFR inhibitors AG1478 and BPIQ-I blocked DOR-mediated ERK1/2 activation. Because RGDT peptides also prevented DOR-mediated EGFR activation, the present findings indicate that in HEK293 cells DOR-stimulated ERK1/2 activity is mediated by integrin-stimulated EGFRs. Further studies with the phospholipase C (PLC) inhibitors U73122 and ET-18-OCH(3) revealed that opioid-stimulated integrin activation is sensitive to PLC. In contrast, integrin-mediated transactivation of EGFR function appears to be dependent on PKC-delta, as indicated by studies with rottlerin and siRNA knock-down. A similar ERK1/2 signaling pathway was observed for NG108-15 cells, a neuronal cell line endogenously expressing the DOR. In these cells, the nerve growth factor TrkA receptor replaces the EGFR in connecting DOR-activated integrins to the Ras/Raf/ERK1/2 pathway. Together, these data describe an alternative ERK1/2 signaling pathway in which the DOR transactivates the growth factor receptor associated mitogen-activated protein kinase cascade in an integrin-dependent manner.
authors.affiliation: Institute of Pharmacology, Toxicology and Pharmacy, University of Munich, Königinstrasse 16, D-80539 München, Germany. Eisinger@lrz.uni-muenchen.de
authors.forename: Daniela A
authors.initials: DA
authors.lastname: Eisinger
authors.forename: Hermann
authors.initials: H
authors.lastname: Ammer
mesh_terms: D002478:Cells, Cultured; D016308:Enkephalin, Leucine-2-Alanine / Q000494:pharmacology; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004963:Estrenes / Q000494:pharmacology; D005048:Etorphine / Q000494:pharmacology; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology; D010766:Phosphorylation; D051745:Protein Kinase C-delta / Q000037:antagonists & inhibitors / Q000378:metabolism; D011760:Pyrrolidinones / Q000494:pharmacology; D011799:Quinazolines; D017465:Receptors, Opioid, delta / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism; D020032:Tyrphostins / Q000494:pharmacology
chemical_list: D004963:Estrenes; D016023:Integrins; D009842:Oligopeptides; D011760:Pyrrolidinones; D011799:Quinazolines; D017465:Receptors, Opioid, delta; D020032:Tyrphostins; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C101044:RTKI cpd; D005048:Etorphine; D016308:Enkephalin, Leucine-2-Alanine; C047981:arginyl-glycyl-aspartic acid; D066246:ErbB Receptors; D051416:Focal Adhesion Protein-Tyrosine Kinases; D051745:Protein Kinase C-delta; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D010738:Type C Phospholipases