Adhesion of phospholipid vesicles to Chinese hamster fibroblasts: Role of cell surface proteins

Abstract

The adhesion of artificially generated lipid membrane vesicles to Chinese hamster V79 fibroblasts in suspension was used as a model system for studying membrane interactions. Below their gel-liquid crystalline phase transition temperature, vesicles comprised of dipalmitoyl lecithin (DPL) or dimyristoyl lecithin (DML) adsorbed to the surfaces of EDTA-dissociated cells. These adherent vesicles could not be removed by repeated washings of the treated cells but could be released into the medium by treatment with trypsin. EM autoradiographic studies of cells treated with [3H]DML or [3H]DPL vesicles showed that most of the radioactive lipids were confined to the cell periphery. Scanning electron microscopy and fluorescence microscopy further confirmed the presence of adherent vesicles at the cell surface. Adhesion of DML or DPL vesicles to EDTA-dissociated cells modified the lactoperoxidase-catalyzed iodination pattern of the cell surface proteins; the inhibition of labeling of 2 proteins with an .apprx. 60,000-dalton MW was particularly evident. Incubation of cells with 3H-lipid vesicles followed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis showed that some of the 3H-lipid migrated preferentially with these 60,000 MW proteins. Studies of the temperature dependence of vesicle uptake and subsequent release by trypsin showed that DML or DPL vesicle adhesion to EDTA-dissociated cells increased with decreasing temperatures. Cells trypsinized before incubation with vesicles showed practically no temperature dependence of vesicle uptake. The 2 pathways suggested for adhesion of lipid vesicles to the cell surface were a temperature-sensitive one involving cell surface proteins and a temperature-independent one. These findings were discussed in terms of current models for cell-cell interactions.