A new cell surface, detergent-insoluble glycoprotein matrix of human and hamster fibroblasts. The role of disulfide bonds in stabilization of the matrix.

Extraction of cell surface labeled human fibroblasts with a zwitterionic detergent, Empigen BB, solubilizes most of the cytoplasmic and membrane components.The remaining insoluble cell matrix, with numerous fibrillar meshwork structures, is composed of prominent nuclei, cytoskeletal components, and four major cell surface glycoprotein: fibronectin (FN), GP250, GP170, and GP140.F'ibronectin and GP170 are rapidly released from the cell surface and the Empigen BBinsoluble cell matrix by mild trypsin digestion.In contrast, both GP250 and GP140 are resistant to trypsin digestion.None of the glycoproteins are sensitive to digestion with collagenase.Neither GP260, GP170, nor GP140 cross-reacts with antisera prepared against fibronectin and are therefore not derived from fibronectin by proteolytic processing.Extraction of the Empigen BB-insoluble matrix with sodium dodecyl sulfate solubilized all of the GP250, GP170, GP140, and approximately half of the fibronectin.Chromatography of the sodium dodecyl sulfate extract on Sepharose ZB under nonreducing conditions resolved a high molecular weight protein matrix that was subsequently resolved into the subunits: GP140, GP260, and fibronectin under reducing conditions.This new type of disulfide-dependent glycoprotein matrix at the cell surface is composed of fibronectin multimers, GP250 multimers, and GP140 multimers.The GP140 and GP2SO are not disulfide bonded to fibronectin since immune precipitation of the sodium dodecyl sulfate extract with anti-fibronectin antibodies specifically precipitates only fibronectin.(However, evidence is presented suggesting that GP250 and GP140 may form disulfide-dependent heteromultirners.)Since extraction with hot sodium dodecyl sulfate would destroy all noncovalent interactions, the possibility that GP140 and GP250 may form noncovalent interactions with fibronectin in the intact cell is discussed.In studies of the mechanisms and components involved in cell attachment and spreading (for reviews see Refs. 1-3),as well as cell-cell interactions (4-6), FN,' a major transforma-