title: Characterization of the integrin alpha v beta 6 as a fibronectin-binding protein.
abstract: Integrins are a complex family of divalent cation-dependent cell adhesion receptors composed of one alpha and one beta subunit noncovalently bound to one another. A subset of integrins contains the alpha v subunit in association with one of several beta subunits (e.g. beta 3, beta 5, beta 1). We have recently identified a novel integrin beta subunit, beta 6, that is present in a number of epithelial cell lines. Using a polyclonal antibody raised against the carboxyl-terminal peptide of beta 6, we have now identified the integrin heterodimer, alpha v beta 6, on the surface of two human carcinoma cell lines. Using affinity chromatography of lysates from the pancreatic carcinoma cell line, FG-2, we demonstrate that alpha v beta 6 binds to fibronectin, but not to vitronectin or collagen I. In contrast, the alpha v beta 5 integrin, which is also expressed on FG-2 cells, binds exclusively to vitronectin. Immobilized collagen I does not interact with alpha v integrins, but binds beta 1-containing integrins. Both alpha v beta 6 and alpha v beta 5 are eluted from their respective immobilized ligands by a hexa-peptide containing the sequence Arg-Gly-Asp (RGD). RGD is highly effective in the presence of Ca2+, somewhat less effective in Mg2+, and virtually inactive in Mn2+. These results suggest that alpha v beta 6 functions as an RGD-dependent fibronectin receptor in FG-2 carcinoma cells. In agreement with this notion, cell adhesion assays show that FG-2 cell attachment to fibronectin is only partially inhibited by anti-beta 1 integrin antibodies, implying that other fibronectin receptors may be involved. Taken together with recent reports on the vitronectin receptor function of alpha v beta 5, our results suggest that the previously described carcinoma cell integrin, alpha v beta x (Cheresh, D. A., Smith, J. W., Cooper, H. M., and Quaranta, V. (1989) Cell 57, 59-69), is a mixture of at least two different receptors: alpha v beta 5, mediating adhesion to vitronectin, and alpha v beta 6, mediating adhesion to fibronectin.
authors.affiliation: Lung Biology Center, University of California, San Francisco 94143.
authors.forename: M
authors.initials: M
authors.lastname: Busk
authors.forename: R
authors.initials: R
authors.lastname: Pytela
authors.forename: D
authors.initials: D
authors.lastname: Sheppard
mesh_terms: D000595:Amino Acid Sequence; D000951:Antigens, Neoplasm; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D016023:Integrins / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008175:Lung Neoplasms; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010190:Pancreatic Neoplasms; D017469:Receptors, Fibronectin; D011971:Receptors, Immunologic / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000951:Antigens, Neoplasm; D005353:Fibronectins; D016023:Integrins; D046911:Macromolecular Substances; D017469:Receptors, Fibronectin; D011971:Receptors, Immunologic; C073878:integrin alphavbeta6