Decrease in tumor‐cell attachment and in a 140‐kDa fibronectin receptor correlate with greater expression of multiple 34‐kDa surface proteins and cytoplasmic 54‐kDa components

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Abstract
B 16 melanoma cells attach to matrix‐bound fibronectin but fail to adhere to albumin‐coated surfaces supplemented with soluble fibronectin. Attachment to substratum h also decreased in the presence of an adhesion‐disrupting antibody, or when cells are seeded on substrates poorly adhesive for these cells, such as collagen gels. We have now investigated some of the more general adhesion‐related alterations that occur between flattened and poorly attached cells. Immune blots of octylglucoside extracts with the adhesion‐disrupting IgG revealed a 140‐kDa component in flattened cells, in contrast to the increased detection of a 54‐kDa species in a comparable assay with rounded cells. Surface iodination also showed a decreased external exposure of a 140‐kDa fibronectin binding species and an increased labelling in multiple 34‐kDa protein species, in cells with decreased attachment to substratum. Analysis of 35S‐methionine‐labelled cell aggregates cultured on collagen gels also revealed a decrease in the 140‐kDa region and a greater labelling of multiple 54‐kDa components, compared to the same cells flattened on fibronectin. A change in 54‐ and 34‐kDa species was also teen in matrix‐associated components of rounded cells that failed to attach with soluble fibronectin. Since the 34‐kDa species increase in poorly adherent cells is mainly detected by inclination, and the 54‐kDa species increase in the same celts is partly associated with the corresponding detergent‐insoluble matrices, we propose that these I novel proteins may relate to cell rounding, through a trans membrane modulation involving both surface membrane and cytoskeletal structures.