title: Role of Gab proteins in phosphatidylinositol 3-kinase activation by thrombopoietin (Tpo).
abstract: In this study, we show that upon thrombopoietin (Tpo) stimulation the two adapter proteins Gab1 and Gab2 are strongly tyrosine phosphorylated and associated with Shc, SHP2, PI 3-kinase and Grb2 in mpl-expressing UT7 cells. Although Gab1 and Gab2 seem to mediate overlapping biological signals in many cells, only Gab1 is expressed and phosphorylated in response to Tpo in primary human megakaryocytic progenitors; furthermore, it associates with the same proteins. Although a low level of tyrosine phosphorylated IRS-2 protein is also detected in PI 3-kinase immunoprecipitates, Gab proteins are the essential proteins associated with PI 3-kinase after Tpo stimulation. We demonstrate that, albeit no association is detected between the Tpo receptor mpl and Gab proteins, Y112 located in the C-terminal cytoplasmic domain of mpl is required for Gab1/2 tyrosine phosphorylation. Gab proteins are not tyrosine phosphorylated after Tpo stimulation of UT-7 and Ba/F3 cells expressing a mpl mutant lacking Y112. Moreover, no activation of the PI 3-kinase/Akt pathway is observed in cells expressing this mpl mutant. Finally, we show that this mutant does not allow cell proliferation, thereby confirming that PI 3-kinase activation is required for Tpo-induced cell proliferation.
authors.affiliation: Institut Cochin de Génétique Moléculaire (ICGM), Institut National de la Santé et de la Recherche Médicale (INSERM U363), Université René Descartes, France.
authors.forename: D
authors.initials: D
authors.lastname: Bouscary
authors.forename: C
authors.initials: C
authors.lastname: Lecoq-Lafon
authors.forename: S
authors.initials: S
authors.lastname: Chrétien
authors.forename: S
authors.initials: S
authors.lastname: Zompi
authors.forename: S
authors.initials: S
authors.lastname: Fichelson
authors.forename: O
authors.initials: O
authors.lastname: Muller
authors.forename: F
authors.initials: F
authors.lastname: Porteu
authors.forename: I
authors.initials: I
authors.lastname: Dusanter-Fourt
authors.forename: S
authors.initials: S
authors.lastname: Gisselbrecht
authors.forename: P
authors.initials: P
authors.lastname: Mayeux
authors.forename: C
authors.initials: C
authors.lastname: Lacombe
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects; D005312:Fetal Blood / Q000166:cytology; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008533:Megakaryocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011817:Rabbits; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013926:Thrombopoietin / Q000235:genetics / Q000494:pharmacology*; D014443:Tyrosine / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins; D013926:Thrombopoietin; D014443:Tyrosine; C098587:GAB1 protein, human; C490895:GAB2 protein, human; C490897:Gab1 protein, mouse; C490894:Gab2 protein, mouse; C494918:AKT1 protein, human