Alpha-fetoprotein receptors in a human breast cancer cell line.

Abstract Evidence is presented for the existence of specific receptors for alpha-fetoprotein on the surface of MCF-7 human breast cancer cells. At 4°C, the binding of alpha-fetoprotein to these cells displayed a biphasic saturation curve. Scatchard analysis revealed the presence of at least two binding sites with dissociation constants of 4.5 × 10 −9 M (2,000 sites/cell) and 1.3 × 10 −8 M (135,000 sites/cell), respectively. Binding was inhibited by 85% in the presence of a 5,000-fold excess of unlabeled alpha-fetoprotein and by 50% with the same excess of serum albumin. Competition by other serum proteins was not significant. At 37°C, alpha-fetoprotein was endocytosed and the uptake curve reached a plateau after 3–4 hours of incubation.