title: Dual control by divalent cations and mitogenic cytokines of alpha 4 beta 1 and alpha 5 beta 1 integrin avidity expressed by human hemopoietic cells.
abstract: Beta-1 integrins have essential functions in hemopoietic and immune systems by controlling phenomenons such as cell homing and cell activation. The function alpha 4 beta 1 and alpha 5 beta 1 integrins is regulated by divalent cations and, as demonstrated more recently, by mitogenic cytokines which activate them by "inside-out" mechanisms. Using the adhesive interaction of a cytokine-dependent human hemopoietic cell line to immobilized fibronectin, we have analyzed the requirements in divalent cations Mn2+, Mg2+ and Ca2+ for alpha 4 beta 1 and alpha 5 beta 1 activation by "inside-out" mechanisms triggered by cytokines such as granulocyte-macrophage colony stimulating factor or KIT ligand, or by external conformational constraints with the function-activating anti-beta 1 integrin monoclonal antibody 8A2. The intrinsic difference between these two modes of beta 1 integrin activation was revealed by their different requirements in divalent cations. We found that in the absence of any divalent cations, alpha 4 beta 1 and alpha 5 beta 1 were non-functional even after further stimulation by cytokines or 8A2. However, whilst either Ca2+, Mg2+ or Mn2+ were able to restore adhesive functions of alpha 4 beta 1 and alpha 5 beta 1 when activated by 8A2, only Mg2+ and Mn2+ were able to support activation of alpha 4 beta 1 and alpha 5 beta 1 by cytokines. Furthermore, high concentrations of Ca2+ exceeding 20 mM dramatically inhibited cell adhesion to fibronectin induced by Mn2+ and cytokines but not by 8A2. On the contrary, in the presence of both Ca2+ and Mg2+, Mn2+ had an additive effect on the activation of alpha 4 beta 1 and alpha 5 beta 1 by mitogenic cytokines. The presence of the absence of these divalent cations did not inhibit early tyrosine phosphorylation induced by the binding of KIT ligand to its tyrosine-kinase receptor KIT. Therefore, we propose that in hemopoietic cells, Ca2+, Mg2+ and Mn2+ may modulate in vivo alpha 4 beta 1 and alpha 5 beta 1 regulation by mitogenic cytokines, a phenomenon involved in the regulation of hemopoietic progenitor cell homing within the bone marrow.
authors.affiliation: Matthew Roberts Foundation Laboratory, Leukaemia Research Unit, Hanson Centre for Cancer Research, Adelaide, Australia.
authors.forename: Y
authors.initials: Y
authors.lastname: Takamatsu
authors.forename: P J
authors.initials: PJ
authors.lastname: Simmons
authors.forename: J P
authors.initials: JP
authors.lastname: Lévesque
mesh_terms: D018926:Anti-Allergic Agents / Q000276:immunology / Q000378:metabolism; D000911:Antibodies, Monoclonal / Q000276:immunology; D002122:Calcium Chloride / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology; D002448:Cell Adhesion / Q000187:drug effects / Q000276:immunology; D016207:Cytokines / Q000276:immunology / Q000378:metabolism; D000939:Epitopes / Q000276:immunology; D005353:Fibronectins / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology; D005434:Flow Cytometry; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D006801:Humans; D039041:Integrin alpha4beta1; D016023:Integrins / Q000276:immunology* / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D010766:Phosphorylation; D017469:Receptors, Fibronectin / Q000276:immunology* / Q000378:metabolism; D016201:Receptors, Lymphocyte Homing / Q000276:immunology* / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
chemical_list: D018926:Anti-Allergic Agents; D000911:Antibodies, Monoclonal; D002413:Cations, Divalent; D016207:Cytokines; D000939:Epitopes; D005353:Fibronectins; D039041:Integrin alpha4beta1; D016023:Integrins; D017469:Receptors, Fibronectin; D016201:Receptors, Lymphocyte Homing; D014443:Tyrosine; D008345:Manganese; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D008274:Magnesium; D002122:Calcium Chloride