title: Thrombopoietin promotes adhesion of primitive human hemopoietic cells to fibronectin and vascular cell adhesion molecule-1: role of activation of very late antigen (VLA)-4 and VLA-5.
abstract: Thrombopoietin (Tpo), the ligand for c-mpl and a principal regulator of megakaryocytopoiesis and platelet production, has been demonstrated to stimulate the growth and differentiation of megakaryocyte as well as multipotent hemopoietic progenitor cells. In the present study we demonstrate that Tpo can stimulate the adhesion of the Mo7e progenitor cell line to fibronectin (Fn) as well as vascular cell adhesion molecule-1 through activation of very late antigen (VLA)-4 and VLA-5, adhesion molecules previously demonstrated to be involved in regulation of steady state hemopoiesis. Tpo-induced adhesion was concentration dependent, reached a maximum following 30 min, and appeared to be dependent on adenylate cyclase, and tyrosine kinase activity. Furthermore, second messenger inhibitors implicated essential and complimentary roles of phosphatidylinositol-3-kinase and protein kinase C in mediating Tpo-induced adhesion. The ability of Tpo to promote adhesion to fibronectin was comparable to that of IL-3, but less than that of stem cell factor. Unlike the ability of these cytokines to synergistically enhance growth of Mo7e as well as normal progenitor cells, no synergy was observed with regard to their ability to enhance adhesion. Finally, Tpo stimulated adhesion of primitive (CD34+ CD38-) human bone marrow cells to fibronectin, predominantly through activation of VLA-5, whereas no such effect could be observed on CD34+ CD38+ bone marrow cells. Thus, Tpo might play an important role in early hemopoiesis, at least in part through its ability to promote adhesion through activation of adhesion molecules on hemopoietic progenitor cells.
authors.affiliation: Department of Internal Medicine, Lund University Hospital, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Cui
authors.forename: V
authors.initials: V
authors.lastname: Ramsfjell
authors.forename: O J
authors.initials: OJ
authors.lastname: Borge
authors.forename: O P
authors.initials: OP
authors.lastname: Veiby
authors.forename: S
authors.initials: S
authors.lastname: Lok
authors.forename: S E
authors.initials: SE
authors.lastname: Jacobsen
mesh_terms: D036541:ADP-ribosyl Cyclase; D051997:ADP-ribosyl Cyclase 1; D000818:Animals; D015703:Antigens, CD; D018952:Antigens, CD34 / Q000032:analysis; D000943:Antigens, Differentiation / Q000032:analysis; D001854:Bone Marrow Cells; D002448:Cell Adhesion / Q000187:drug effects; D005353:Fibronectins / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000502:physiology*; D008562:Membrane Glycoproteins; D051379:Mice; D009699:N-Glycosyl Hydrolases / Q000032:analysis; D017469:Receptors, Fibronectin / Q000502:physiology*; D016201:Receptors, Lymphocyte Homing / Q000502:physiology*; D015290:Second Messenger Systems / Q000502:physiology; D013926:Thrombopoietin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D019010:Vascular Cell Adhesion Molecule-1 / Q000502:physiology*
chemical_list: D015703:Antigens, CD; D018952:Antigens, CD34; D000943:Antigens, Differentiation; D005353:Fibronectins; D039041:Integrin alpha4beta1; D016023:Integrins; D008562:Membrane Glycoproteins; D017469:Receptors, Fibronectin; D016201:Receptors, Lymphocyte Homing; D019010:Vascular Cell Adhesion Molecule-1; D013926:Thrombopoietin; D009699:N-Glycosyl Hydrolases; D036541:ADP-ribosyl Cyclase; C498154:CD38 protein, human; C498155:Cd38 protein, mouse; D051997:ADP-ribosyl Cyclase 1