CELL-ADHESION AND ACQUISITION OF DETERGENT RESISTANCE BY THE CYTOSKELETON OF CULTURED CHICK FIBROBLASTS

About 30% of the proteins of adherent cultured chick embryo fibroblasts were not solubilized by the non-ionic detergent Triton X-100 and remained firmly attached to the substratum. The insoluble residue contains most of the cell''s cytoskeleton and consists of large external transformation-sensitive (LETS) protein, H chain of myosin, a 52,000 MW protein and actin. Kinetic studies reveal that cytoskeleton insolubility in Triton is acquired concurrently with, or close to, cell adhesion. Cell adhesion or binding of the Triton cytoskeleton to the substratum did not require de novo synthesis of protein. The role of LETS protein in cytoskeleton attachment, is shown when trypsin-detached cells rapidly acquire Triton-insoluble cytoskeleton although their LETS protein content is about 15-20% of its level in long-term cultures. Removal of most of LETS molecules of adherent cultures by urea or trypsin treatment does not affect the relative amount or composition of the anchored cytoskeletal proteins. LETS protein of cultures exposed to cycloheximide for extended periods of time is reduced to 10% of its maximum amount without much affecting the attachment and composition of the cytoskeleton. Most of LETS protein is apparently not required for the attachment of the Triton cytoskeleton to the substratum.