In brown adipocytes, adrenergically induced β₁-/β₃-(Gs)-, α₂-(Gi)- and α₁-(Gq)-signalling to Erk1/2 activation is not mediated via EGF receptor transactivation.
Brown adipose tissue is unusual in that the neurotransmitter norepinephrine influences cell destiny in ways generally associated with effects of classical growth factors: regulation of cell proliferation, of apoptosis, and progression of differentiation. The norepinephrine effects are mediated through G-protein-coupled receptors; further mediation of such stimulation to e.g. Erk1/2 activation is in cell biology in general accepted to occur through transactivation of the EGF receptor (by external or internal pathways). We have examined here the significance of such transactivation in brown adipocytes. Stimulation of mature brown adipocytes with cirazoline (α1-adrenoceptor coupled via Gq), clonidine (α2 via Gi) or CL316243 (β3 via Gs) or via β1-receptors significantly activated Erk1/2. Pretreatment with the EGF receptor kinase inhibitor AG1478 had, remarkably, no significant effect on Erk1/2 activation induced by any of these adrenergic agonists (although it fully abolished EGF-induced Erk1/2 activation), demonstrating absence of EGF receptor-mediated transactivation. Results with brown preadipocytes (cells in more proliferative states) were not qualitatively different. Joint stimulation of all adrenoceptors with norepinephrine did not result in synergism on Erk1/2 activation. AG1478 action on EGF-stimulated Erk1/2 phosphorylation showed a sharp concentration-response relationship (IC50 0.3µM); a minor apparent effect of AG1478 on norepinephrine-stimulated Erk1/2 phosphorylation showed nonspecific kinetics, implying caution in interpretation of partial effects of AG1478 as reported in other systems. Transactivation of the EGF receptor is clearly not a universal prerequisite for coupling of G-protein coupled receptors to Erk1/2 signalling cascades.
Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm SE-106 91, Sweden.
Yanling
Y
Wang
Johanna M
JM
Fälting
Charlotte L
CL
Mattsson
Therése E
TE
Holmström
Jan
J
Nedergaard
D052437:Adipocytes, Brown / Q000187:drug effects / Q000378:metabolism*; D018674:Adrenergic Antagonists / Q000494:pharmacology; D058646:Adrenergic alpha-1 Receptor Agonists / Q000494:pharmacology; D058647:Adrenergic alpha-2 Receptor Agonists / Q000494:pharmacology; D058665:Adrenergic beta-1 Receptor Agonists / Q000494:pharmacology; D058667:Adrenergic beta-3 Receptor Agonists / Q000494:pharmacology; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004149:Dioxoles / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010766:Phosphorylation; D011799:Quinazolines / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000378:metabolism*; D020032:Tyrphostins / Q000494:pharmacology
D018674:Adrenergic Antagonists; D058646:Adrenergic alpha-1 Receptor Agonists; D058647:Adrenergic alpha-2 Receptor Agonists; D058665:Adrenergic beta-1 Receptor Agonists; D058667:Adrenergic beta-3 Receptor Agonists; D004149:Dioxoles; D007093:Imidazoles; D011799:Quinazolines; D011941:Receptors, Adrenergic; D020032:Tyrphostins; C076126:disodium (R,R)-5-(2-((2-(3-chlorophenyl)-2-hydroxyethyl)-amino)propyl)-1,3-benzodioxole-2,3-dicarboxylate; C101044:RTKI cpd; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D003000:Clonidine; C014282:cirazoline; D009638:Norepinephrine
Brown adipocytes; Erk1/2 activation; G-protein-coupled receptors; Norepinephrine; Transactivation