title: Phosphatidylinositol 3-kinase is necessary but not sufficient for thrombopoietin-induced proliferation in engineered Mpl-bearing cell lines as well as in primary megakaryocytic progenitors.
abstract: Thrombopoietin and its receptor (Mpl) support survival and proliferation in megakaryocyte progenitors and in BaF3 cells engineered to stably express Mpl (BaF3/Mpl). The binding of thrombopoietin to Mpl activates multiple kinase pathways, including the Jak/STAT, Ras/Raf/MAPK, and phosphatidylinositol 3-kinase pathways, but it is not clear how these kinases promote cell cycling. Here, we show that thrombopoietin induces phosphatidylinositol 3-kinase and that phosphatidylinositol 3-kinase is required for thrombopoietin-induced cell cycling in BaF3/Mpl cells and in primary megakaryocyte progenitors. Treatment of BaF3/Mpl cells and megakaryocytes with the phosphatidylinositol 3-kinase inhibitor LY294002 inhibited mitotic and endomitotic cell cycl-ing. BaF3/Mpl cells treated with thrombopoietin and LY294002 were blocked in G(1), whereas megakaryocyte progenitors treated with thrombopoietin and LY294002 showed both a G(1) and a G(2) cell cycle block. Expression of constitutively active Akt in BaF3/Mpl cells restored the ability of thrombopoietin to promote cell cycling in the presence of LY294002. Constitutively active Akt was not sufficient to drive proliferation of BaF3/Mpl cells in the absence of thrombopoietin. We conclude that in BaF3/Mpl cells and megakaryocyte progenitors, thrombopoietin-induced phosphatidylinositol 3-kinase activity is necessary but not sufficient for thrombopoietin-induced cell cycle progression. Phosphatidylinositol 3-kinase activity is likely to be involved in regulating the G(1)/S transition.
authors: Division of Hematology, Department of Medicine, University of Washington, Seattle, Washington 98195-7710, USA.
authors: A E
authors: AE
authors: Geddis
authors: N E
authors: NE
authors: Fox
authors: K
authors: K
authors: Kaushansky
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D005260:Female; D008533:Megakaryocytes / Q000502:physiology*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D009363:Neoplasm Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; D013926:Thrombopoietin / Q000494:pharmacology*
chemical_list: D002867:Chromones; D020928:Mitogen-Activated Protein Kinases; D009025:Morpholines; D009363:Neoplasm Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; D013926:Thrombopoietin; C082218:MPL protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one