Integrin-associated protein immunoglobulin domain is necessary for efficient vitronectin bead binding.
Integrin-associated protein (IAP/CD47) is physically associated with the alpha v beta 3 vitronectin (Vn) receptor and a functionally and immunologically related integrin on neutrophils (PMN) and monocytes. Anti-IAP antibodies inhibit multiple phagocyte functions, including Arg-Gly-Asp (RGD)-initiated activation of phagocytosis, chemotaxis, and respiratory burst; PMN adhesion to entactin; and PMN transendothelial and transepithelial migration at a step subsequent to tight intercellular adhesion. Anti-IAP antibodies also inhibit binding of Vn-coated particles to many cells expressing alpha v beta 3. However, prior studies with anti-IAP did not directly address IAP function because they could not distinguish between IAP blockade and antibody-induced signaling effects on cells. To better determine the function of IAP, we have characterized and used an IAP-deficient human cell line. Despite expressing alpha v integrins, these cells do not bind Vn-coated particles unless transfected with IAP expression constructs. Increasing the level of alpha v beta 3 expression or increasing Vn density on the particle does not overcome the requirement for IAP. All known splice variants of IAP restore Vn particle binding equivalently. Indeed, the membrane-anchored IAP Ig variable domain suffices to mediate Vn particle binding in this system, while the multiply membrane-spanning and cytoplasmic domains are dispensable. In all cases, adhesion to a Vn-coated surface and fibronectin particle binding through alpha 5 beta 1 fibronectin receptors are independent of IAP expression. These data demonstrate that some alpha v integrin ligand-binding functions are IAP independent, whereas others require IAP, presumably through direct physical interaction between its Ig domain and the integrin.
Lindberg
F P
FP
Department of Infectious Diseases, Washington University School of Medicine, St. Louis, Missouri 63110, USA. lindberg@id.wustl.edu
Gresham
H D
HD
Reinhold
M I
MI
Brown
E J
EJ
D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D051928:CD47 Antigen; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002448:Cell Adhesion; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm; D017931:DNA Primers; D015870:Gene Expression; D006801:Humans; D007135:Immunoglobulin Variable Region; D039564:Integrin alphaV; D039661:Integrin beta3; D008024:Ligands; D008863:Microspheres; D008969:Molecular Sequence Data; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D011233:Precipitin Tests; D019030:Receptors, Vitronectin / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D019096:Vitronectin / Q000378:metabolism*
D015703:Antigens, CD; D051928:CD47 Antigen; C497894:CD47 protein, human; D002352:Carrier Proteins; D017931:DNA Primers; D007135:Immunoglobulin Variable Region; D039564:Integrin alphaV; D039661:Integrin beta3; D008024:Ligands; D010980:Platelet Membrane Glycoproteins; D019030:Receptors, Vitronectin; D019096:Vitronectin