Integrin-associated protein immunoglobulin domain is necessary for efficient vitronectin bead binding

J Cell Biol. 1996 Sep;134(5):1313-22. doi: 10.1083/jcb.134.5.1313.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Antigens, CD / genetics
  • Antigens, CD / metabolism*
  • Base Sequence
  • Binding Sites
  • CD47 Antigen
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cell Adhesion
  • Cell Membrane / metabolism
  • Cytoplasm
  • DNA Primers
  • Gene Expression
  • Humans
  • Immunoglobulin Variable Region
  • Integrin alphaV
  • Integrin beta3
  • Ligands
  • Microspheres
  • Molecular Sequence Data
  • Platelet Membrane Glycoproteins / metabolism
  • Precipitin Tests
  • Receptors, Vitronectin / metabolism
  • Transfection
  • Tumor Cells, Cultured
  • Vitronectin / metabolism*

Substances

  • Antigens, CD
  • CD47 Antigen
  • CD47 protein, human
  • Carrier Proteins
  • DNA Primers
  • Immunoglobulin Variable Region
  • Integrin alphaV
  • Integrin beta3
  • Ligands
  • Platelet Membrane Glycoproteins
  • Receptors, Vitronectin
  • Vitronectin