title: Arrestin serves as a molecular switch, linking endogenous alpha2-adrenergic receptor to SRC-dependent, but not SRC-independent, ERK activation.
abstract: Our previous studies have demonstrated that neither receptor endocytosis nor arrestin is required for ERK activation by the alpha2-adrenergic receptor (Wang, Q., Zhao, J., Brady, A. E., Feng, J., Allen, P. B., Lefkowitz, R. J., Greengard, P., and Limbird, L. E. (2004) Science 304, 1940-1944). The present studies address whether arrestin plays a role in determining the route of alpha2AR-evoked ERK signaling activation, taking advantage of endogenous expression of the alpha(2A)AR subtype in mouse embryonic fibroblasts (MEFs) and the availability of MEFs without arrestin expression (derived from Arr2,3-/- mice). Our data demonstrate that the endogenous alpha(2A)AR evokes ERK phosphorylation through both a Src-dependent and a Src-independent pathway, both of which are G protein dependent and converge on the Ras-Raf-MEK pathway. Arrestin is essential to recruit Src to this process, as alpha(2A)AR-mediated ERK signaling in Arr2,3-/- MEFs does not involve Src. Stimulation of alpha(2A)AR enhances arrestin-Src interaction and promotes activation of Src. alpha2 agonists have similar potencies in stimulating Src-dependent and Src-independent ERK phosphorylation in wild-type and Arr2,3-/- cells, respectively. However, Src-independent alpha(2A)AR-mediated ERK stimulation has both a longer duration of activation and a more rapid translocation of pERK into the nucleus when compared with Src-dependent activation. These data not only affirm the role of arrestin as an escort for signaling molecules such as Src family kinases but also demonstrate the impact of arrestin-dependent modulation on both the temporal and spatial properties of ERK activation.
authors.affiliation: Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA. qwang@uab.edu
authors.forename: Qin
authors.initials: Q
authors.lastname: Wang
authors.forename: Roujian
authors.initials: R
authors.lastname: Lu
authors.forename: Jiali
authors.initials: J
authors.lastname: Zhao
authors.forename: Lee E
authors.initials: LE
authors.lastname: Limbird
mesh_terms: D000818:Animals; D019390:Arrestins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D006801:Humans; D051379:Mice; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D048490:raf Kinases / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: C547768:ADRA2A protein, human; C547769:Adra2a protein, mouse; D019390:Arrestins; D004791:Enzyme Inhibitors; D020033:Protein Isoforms; D018341:Receptors, Adrenergic, alpha-2; D011993:Recombinant Fusion Proteins; D019061:src-Family Kinases; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D018631:ras Proteins