Abstract
Three-dimensional cellular structures formed by MCF-7human mammary carcinoma cells within collagen gels were isolated with collagenase and cultivated on plastic substratum to examine whether the cytoskeleton specific for cells forming cellular structures (S-type) changes to that specific for cells grown as monolayers (M-type). The cytoskeleton isolated as 0.05% Triton-insoluble fraction from the cellular structures after culture for 1 day on plastic was exclusively S-type. However, both types of cytoskeletons were observed in the cellular structures cultivated for 7 days on plastic as well as in the cells grown as monolayers for 2 days after dissociation of the cellular structures with trypsin. By use of an antibody raised against a 65-kD polypeptide that was specific for the M-type cytoskeleton, the presence of the polypeptide was found to be restricted to the cells grown out as monolayers from the edge of the cellular structures. In the cells grown for 2 days as monolayers, a mixture of cells both having and lacking the polypeptide was observed. After a 7-day culture of the dissociated cells as monolayers on plastic, however, most of the cells had M-type cytoskeletons. The present results show that the apparent change in the cytoskeleton of MCF-7cells from S-type to M-type does not occur in cells in volved in the three-dimensional cellular structures even in the absence of collagen gels, but that it occurs in cells which are grown as monolayers for at least 7 days on plastic substratum.
