Mutants of Balb/c 3T3 fibroblasts defective in adhesiveness to substratum: evidence for alteration in cell surface proteins.

Two mutants of Balb/c 3T3 cells defective in adhesiveness to substratum have been isolated. After exposure to a mutagen a cell population was treated with prostaglandin E1 and methylisobutylxanthine to elevate the cells 3':5'-cyclic AMP levels and adhesion to the substratum; then, loosley adherent cells were harvested by gentle detachment. After four cycles of selection two clones were isolated. Both are characterized by a round morphology and a decreased adhesion to substratum. The defect in adhesion appears to be responsible for the change in cell shape, since the mutant cells become flattened and look similar to wild-type cells when treated with dibutyryl cyclic AMP even though their adhesiveness remains decreased. Further, the surface of both mutants is chemically altered. Lactoperoxidase-catalyzed iodination of the cell surface shows that two iodinated polypeptides (molecular weight, Mr, 90,000 and 135-140,000) present in wild-type cells are not detected on the surface of the mutants, and another iodinated band (110-120,000 Mr) is markedly decreased. In addition, one mutant is also missing the high-molecular-weight (230,000) cell surface protein that is sensitive to transformation. No changes have been found in the content of cyclic AMP or free or polymerized tubulin. The exponential growth rate and saturation density are not altered in these adhesion--eficient cells. This last result suggests that modulation of adhesion to substratum per se does not play an important role in the growth control of Balb/c 3T3 cells in vitro.