Cell surface morphology and adhesive properties of normal and virally transformed cells treated with tunicamycin, an inhibitor of protein glycosylation

Normal and virally transformed mouse (3T3) fibroblasts were treated with tunicamycin, a fungal antibiotic that specifically inhibits the synthesis of peptidyl asparaginyl-linked oligosaccharides. All cell lines exhibited changes in cell surface morphology, surface-associated proteins and adhesion to the culture plate in the presence of tunicamycin. Scanning electron microscopy (SEM) revealed that treated fibroblasts assumed a spherical shape and were partially detached from the substratum. In addition, the 3T3 cells showed numerous cell surface ruffles. Tunicamycin-treated cells exhibited no marked ultrastructural changes when compared with control cells. There were indications, however, that the rough endoplasmic reticulum was dilated and that there were fewer membrane-bound ribosomes in treated 3T3 cells. Surface iodination of pretrypsinized tunicamycin-treated cells, followed by analysis of the labeled proteins on sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis, showed a marked reduction in a cell surface protein, identical or similar to fibronectin. Both tunicamycin-treated 3T3 and transformed 3T3 cells demonstrated a reduction in plating efficiency as shown by attachment assays of viable cells. In addition, treated cells showed a reduction in adhesiveness and a delay in spreading. The latter changes were more pronounced in the virally transformed cell lines. These findings suggest that cell surface glycoproteins, including fibronectin, play a role in determining the surface morphology and adhesive properties of cells.