Distinct effects of thrombopoietin depending on a threshold level of activated Mpl in BaF-3 cells.
Thrombopoietin (TPO) plays a critical role in megakaryopoiesis through binding to its receptor Mpl. This involves activation of various intracellular signaling pathways, including phosphoinositide 3-kinase (PI3K) and the mitogen-activated protein kinase (MAPK) pathways. Their precise role in TPO-mediated proliferation, survival and differentiation is not fully understood. In the present study, we show that TPO induces different biological responses in Mpl-transduced BaF-3 cells, depending on the cell surface density of Mpl and the resulting activation level of signaling pathways. TPO mediates cell proliferation in cells expressing high levels of Mpl but only mediates survival without proliferation in cells expressing low levels of the receptor. By using the kinase inhibitors PD98059 and LY294002, we further showed that the activation level of the PI3K and MAPK p42/44 pathways is a determining factor for the proliferative effect. In cells expressing low levels of Mpl, the survival effect was strongly dependent on the activation level of the PI3K/AKT, but not the MAPK p42/44 pathway. Moreover, this effect was correlated with the phosphorylation level of BAD but not with the expression level of Bcl-X(L). However, PI3K pathway inhibition did not increase apoptosis when BaF-3 cells proliferated in response to TPO, indicating a compensating mechanism from other Mpl signaling pathways in this case.
Millot
Gaël A
GA
INSERM U362, Laboratoire Hématopoïèse et Cellules Souches, Institut Gustave Roussy, 39 rue Camille Desmoulins, Villejuif, France. millot@ijm.jussieu.fr
Vainchenker
William
W
Duménil
Dominique
D
Svinarchuk
Fédor
F
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002999:Clone Cells / Q000187:drug effects / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005057:Eukaryotic Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008894:Milk Proteins; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism; D009363:Neoplasm Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D018121:Receptors, Cytokine / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D053628:Receptors, Thrombopoietin; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013926:Thrombopoietin / Q000378:metabolism* / Q000494:pharmacology; D015534:Trans-Activators / Q000187:drug effects / Q000378:metabolism; D051025:bcl-Associated Death Protein
C494820:Bad protein, mouse; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D008894:Milk Proteins; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D018121:Receptors, Cytokine; D053628:Receptors, Thrombopoietin; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D051025:bcl-Associated Death Protein; C082218:MPL protein, human; D013926:Thrombopoietin; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases