Secretion of cell-adhesion-promoting factors, fibronectin, fibronectin fragments and a 53-kDa protein, by human rectal adenocarcinoma cells.

Production of cell-adhesion proteins was examined in 10 cell lines and 5 cultured human cancer cells at an early passage. Two-thirds of the tested cells produced and secreted into their culture medium variable amounts of material active in promoting cell attachment. One of the rectal carcinoma cell lines, CaR-I, grew well in serum-free medium and secreted a large amount of the active principle. The active principles produced by CaR-I cells were characterized after partial purification, and were found to be fibronectin and its fragments. The presence of fibronectin and its fragments was proved by the following facts: (1) reactivity to the monoclonal antibodies which recognize different epitopes of fibronectin, and (2) reactivity to RGD peptide which is the attachment sequence of fibronectin. In addition to fibronectin and its fragments, CaR-I cells were also shown to produce a 53-kDa attachment factor. Unexpectedly, the protein was proved to be most probably the p53 suppressor gene product.