title: Activation of the mitogen-activated protein kinases Erk1/2 by erythropoietin receptor via a G(i )protein beta gamma-subunit-initiated pathway.
abstract: We have recently shown that a heterotrimeric G(i) protein is coupled to the erythropoietin (Epo) receptor. The G(i) protein constitutively associates in its heterotrimeric form with the intracellular domain of Epo receptor (EpoR). After Epo stimulation G(i) is released from the receptor and activated. In the present study we have investigated the functional role of the heterotrimeric G(i) protein bound to EpoR. In Chinese hamster ovary cells expressing EpoR, the G(i) inhibitor pertussis toxin blocked mitogen-activated protein kinase (MAPK) Erk1/2 activation induced by Epo. Epo-dependent MAPK activation was also sensitive to the G beta gamma competitive inhibitor beta ARK1-ct (C-terminal fragment of the beta-adrenergic receptor kinase), to the Ras dominant negative mutant RasN17, and to the phosphoinositide 3-kinase (PI3K) inhibitor LY 294002. A region of 7 amino acids (469-475) in the C-terminal end of EpoR was shown to be required for G(i) binding to EpoR in vivo. Deletion of this region in EpoR abolished both MAPK and PI3K activation in response to Epo. We conclude that in Chinese hamster ovary cells, Epo activates MAPK via a novel pathway dependent on G(i) association to EpoR, G beta gamma subunit, Ras, and PI3K. The tyrosine kinase Jak2 also contributes to this new pathway, more likely downstream of beta gamma and upstream of Ras and PI3K. This pathway is similar to the best characterized pathway used by seven transmembrane receptors coupled to G(i) to activate MAPK and may cooperate with other described Epo-dependent MAPK activation pathways in hematopoietic cells.
authors.affiliation: Department of Hematology, Institut Cochin, INSERM U567, CNRS UMR 8104, Université René Descartes, 27 rue du Faubourg Saint-Jacques, 75014 Paris, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Guillard
authors.forename: Stany
authors.initials: S
authors.lastname: Chrétien
authors.forename: Anne-Sophie
authors.initials: AS
authors.lastname: Pelus
authors.forename: Françoise
authors.initials: F
authors.lastname: Porteu
authors.forename: Odile
authors.initials: O
authors.lastname: Muller
authors.forename: Patrick
authors.initials: P
authors.lastname: Mayeux
authors.forename: Véronique
authors.initials: V
authors.lastname: Duprez
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D017467:Receptors, Erythropoietin / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D017467:Receptors, Erythropoietin; D011994:Recombinant Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins