title: Regulation of megakaryocytopoiesis by thrombopoietin and stromal cells.
abstract: Thrombopoietin (Tpo) is a cytokine which stimulates megakaryocyte maturation. We found that Tpo is constitutively and ubiquitously expressed in all tissues examined, including bone marrow stromal cells, even in thrombocytopenia, thrombosis and steady-state condition in mice. Thus, platelet level in circulation is not regulated by Tpo gene expression. Furthermore, when the purified megakaryocytes were cocultured with the stromal cells, most of the megakaryocytes adhered to the stromal cells and remained unchanged, while free megakaryocytes induced proplatelet formation. Thus the stromal cells in bone marrow secrete Tpo and stimulate megakaryocytopoiesis, but the interaction of megakaryocytes with the stromal cells may suppress platelet formation. Study on signal transduction through Mp1 revealed that Tpo induces activation of JAK2 and Tyk2, which in turn activate STAT1, STAT3 and STAT5. Further, Tpo stimulates transcription factors GATA-1 and NF-E2, which induce differentiation markers, GPIIb/IIIa and Pm-1. In addition, Shc, Vav, Ras, Raf-1, MAPKK, MAPK and Pim-1 are also activated. Thus, Tpo activates a lineage-specific cascade as well as a specific JAK-STAT cascade and a common signaling cascade.
authors.forename: Y
authors.initials: Y
authors.lastname: Nagata
authors.forename: H
authors.initials: H
authors.lastname: Nagahisa
authors.forename: T
authors.initials: T
authors.lastname: Nagasawa
authors.forename: K
authors.initials: K
authors.lastname: Todokoro
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells; D002454:Cell Differentiation; D004268:DNA-Binding Proteins / Q000378:metabolism; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000502:physiology; D053614:Janus Kinase 2; D008533:Megakaryocytes / Q000166:cytology* / Q000502:physiology; D051379:Mice; D008894:Milk Proteins; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; D015398:Signal Transduction; D017154:Stromal Cells / Q000166:cytology; D053634:TYK2 Kinase; D013926:Thrombopoietin / Q000096:biosynthesis / Q000502:physiology*; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D008894:Milk Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D050799:STAT5 Transcription Factor; C494080:Stat1 protein, mouse; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D013926:Thrombopoietin; D011505:Protein-Tyrosine Kinases; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2; D053634:TYK2 Kinase; C499356:Tyk2 protein, mouse