The Mr 140,000 fibronectin receptor complex in normal and virus-transformed human fibroblasts and in fibrosarcoma cells: identical localization and function.

We studied the function and localization of the fibronectin receptor complex in cultured normal and SV40-transformed human fibroblasts and in human fibrosarcoma cells by using monoclonal antibodies (MAbs) against the beta sub-unit of the receptor. Immunoprecipitation, fibronectin fragment affinity chromatography and immunoblotting results suggested that all the cells studied had similar amounts of the receptor. In normal fibroblasts MAbs additionally immunoprecipitated a smaller polypeptide, revealed as the precursor for the beta sub-unit and another polypeptide shown to be the alpha sub-unit of the VLA-I complex. The emergence of vinculin-positive focal adhesion sites and actin stress fibers was slower in the malignant cells than in normal fibroblasts when the cells were plated on non-coated glass-substrate in serum-free conditions and the fibronectin receptor complex did not become located to focal adhesions in any of the cells studied. Added substratum-bound but not soluble fibronectin mediated assembly of the fibronectin receptor complex to the focal adhesions in both normal and malignant cells. On fibronectin-coated growth substrate stress fibers also emerged as rapidly in the malignant cells as in normal fibroblasts. In all the cells the receptor complex, however, became largely dissociated from the focal adhesions within 48 hr. In cell adhesion conditions MAb against the alpha sub-unit of VLA-I complex revealed an even cell-surface labelling in normal fibroblasts and lack of labelling in malignant cells.