title: Functional down-regulation of alpha 5 beta 1 integrin in keratinocytes is reversible but commitment to terminal differentiation is not.
abstract: Extracellular matrix receptors of the integrin family have a dual role in the epidermis, regulating both adhesion and differentiation. Loss of contact with the extracellular matrix causes keratinocytes to become committed to terminal differentiation, and results in a decrease in the ability of the alpha 5 beta 1 integrin to bind fibronectin. We have investigated whether the decrease in ligand-binding ability is reversible and, if so, whether commitment to terminal differentiation can also be reversed. Keratinocytes that had been placed in suspension for 5 hours to induce commitment were compared with the starting population (0 hour cells) in the presence or absence of 8A2, an activating anti-beta 1 antibody. 8A2 IgG or FAb fragments increased the amount of alpha 5 beta 1 in cell extracts that bound to fibronectin-Sepharose and in the presence of 8A2 the amount of bound alpha 5 beta 1 in 0 hour and 5 hour extracts was equal. 8A2 also restored alpha 5 beta 1 function in adhesion assays of intact 5 hour cells. Ca2+, Mg2+ and Mn2+ alone, at concentrations of up to 1 mM, did not increase the adhesiveness of 5 hour cells relative to 0 hour cells; however, the effect of 8A2 on keratinocytes was dependent on Ca2+. Although 8A2 restored alpha 5 beta 1 ligand-binding ability it did not prevent committed cells from withdrawing from the cell cycle and expressing involucrin, a differentiation marker.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Keratinocyte Laboratory, Imperial Cancer Research Fund, Lincoln's Inn Fields, London, UK.
authors.forename: N A
authors.initials: NA
authors.lastname: Hotchin
authors.forename: N L
authors.initials: NL
authors.lastname: Kovach
authors.forename: F M
authors.initials: FM
authors.lastname: Watt
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D015536:Down-Regulation; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D016023:Integrins / Q000276:immunology / Q000378:metabolism*; D015603:Keratinocytes / Q000378:metabolism*; D008024:Ligands; D017469:Receptors, Fibronectin
chemical_list: D000911:Antibodies, Monoclonal; D002413:Cations, Divalent; D016326:Extracellular Matrix Proteins; D005353:Fibronectins; D016023:Integrins; D008024:Ligands; D017469:Receptors, Fibronectin