title: Beta 3- and alpha1-adrenergic Erk1/2 activation is Src- but not Gi-mediated in Brown adipocytes.
abstract: A novel signaling pathway for mediation of beta(3)-adrenergic activation of the mitogen-activated protein kinases Erk1/2 (associated with proliferation, differentiation, and apoptosis) has recently been proposed, which implies mediation via constitutively coupled G(i)-proteins and Gbetagamma-subunits, distinct from the classical cAMP pathway of beta-adrenergic stimulation. To verify the significance of this pathway in cells in primary cultures that entopically express beta(3)-adrenoreceptors, we examined the functionality of this pathway in cultured brown adipocytes. Norepinephrine activated Erk1/2 via both beta(3) receptors and alpha(1) receptors but not via alpha(2) receptors. Forskolin induced Erk1/2 activation similarly to beta(3) activation, indicating cAMP-mediation; this induction could be inhibited with H89, implying protein kinase A mediation. The G(i)-pathway was functional in these cells, as pertussis toxin increased agonist-induced cAMP accumulation. However, pertussis toxin was unable to affect adrenergically induced Erk1/2 activation. Also, wortmannin was without effect, implying that Gbetagamma activation of the phosphatidylinositol 3-kinase pathway was not involved. PP1/2, which inhibits Src, abolished both beta(3)- and alpha(1)-induced Erk1/2 activation. Thus, the proposed novel G(i) pathway for beta(3) mediation is not universal, because it is not functional in the untransformed primary cell culture system with entopically expressed beta(3) receptors examined here. Here, the beta(3) signal is mediated classically via cAMP/protein kinase A. beta(3) and alpha(1) signals converge at Src, which thus mediates Erk1/2 activation in both pathways.
authors.affiliation: Wenner-Gren Institute, The Arrhenius Laboratories F3, Stockholm University, SE-106 91 Stockholm, Sweden. johanna@zoofys.su.se
authors.forename: J M
authors.initials: JM
authors.lastname: Lindquist
authors.forename: J M
authors.initials: JM
authors.lastname: Fredriksson
authors.forename: S
authors.initials: S
authors.lastname: Rehnmark
authors.forename: B
authors.initials: B
authors.lastname: Cannon
authors.forename: J
authors.initials: J
authors.lastname: Nedergaard
mesh_terms: D017667:Adipocytes / Q000201:enzymology; D002001:Adipose Tissue, Brown / Q000166:cytology / Q000201:enzymology*; D000818:Animals; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology*; D006801:Humans; D008297:Male; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D015688:Oncogene Protein pp60(v-src) / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D022702:Receptors, Adrenergic, beta-3
chemical_list: D018340:Receptors, Adrenergic, alpha-1; D011943:Receptors, Adrenergic, beta; D022702:Receptors, Adrenergic, beta-3; D019869:Phosphatidylinositol 3-Kinases; D015688:Oncogene Protein pp60(v-src); D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins; D009638:Norepinephrine