Plasma membrane glycoprotein which mediates adhesion of fibroblasts to collagen

Abstract

DEFECTS in cell behaviour associated with malignancy may be causally related to alterations in the plasma membrane of the cell on transformation¹. Much interest has focused on a protein found on the surface of normal but not transformed cells ^2–7. This protein, designated SF (ref. 5), LETS (ref. 8), band 1 (ref. 9), L1 (ref. 3) or CSP (ref. 10), is a glycoprotein^7,9,11 with a molecular weight of 210,000–250,000 (refs 7, 8 and 12). It is present in the serum¹² and is sensitive to removal from the surface of normal fibroblasts by low levels of trypsin^2,3,9. Several biological properties of this protein have been described. Normal fibroblasts arrested in mitosis lack this protein^8,9. As normal cells approach confluency, there is a quantitative increase in the amount of this protein present on the cell surface^8,9, whereas confluent normal cells, stimulated by the addition of serum, have lowered levels⁸. In conflict with these results, implying a growth regulatory function, is the finding that stimulation of growth-arrested normal cells by thrombin leads to thymidine incorporation without a concomitant decrease in the levels of this protein¹³. We now present evidence which points to a functional role for the protein as a mediator of the adhesion of fibroblasts to collagen. The protein is probably identical to a serum factor previously reported to be necessary for the attachment of SV40-transformed 3T3 fibroblasts to collagen-coated dishes14. Based on this functional role, we propose the name cell adhesion factor (CAF) for this protein.