Osteopontin adhesion receptors on gingival fibroblasts

Osteopontin (OPN) promotes attachment and spreading of cells in an RGD dependent fashion, suggesting that OPN interacts with integrins on cell surfaces. Here in, we show that LM-609, a monoclonal antibody to the α_vβ₃ integrin (a vitronectin receptor), inhibited OPN-mediated attachment of gingival fibroblasts. To characterize the cell surface receptors responsible for this interaction, we performed OPN-sepharose affinity chromatography using detergent extracts of ³⁵S-methionine or ^l25I-surface labeled gingival fibroblasts. Proteins bound to the OPN-matrix were eluted with EDTA and subjected to SDS-PAGE under reducing conditions. EDTA eluates from both ¹²⁵I-surface labeled and ³⁵Smethionine labeled extracts demonstrated prominent bands in the 90kDa and 50kDa regions, by both autoradiography and fluorography, respectively. These studies suggest that OPN is associated with other cell surface molecules in addition to α_vβ₃. Furthermore, these as yet to be characterized proteins, may prove to have a stronger affinity for OPN than α_vβ₃.