Epithelin 1 and 2 are
cysteine-rich
proteins that act as growth modulators of epithelial cells. In this report, we have characterized the
epithelins receptors of MDA-MB-468 human
breast carcinoma cells using both binding and cross-linking techniques. Equilibrium binding studies of iodinated
epithelin 1 indicated that two classes of binding sites are expressed at the surface of
breast carcinoma cells. The high affinity sites had a dissociation constant of approximately 2 x 10(-10) M, with approximately 290 receptors/cell. The low affinity sites had a dissociation constant of approximately 10(-8) M, with approximately 32,000 receptors/cell. Binding of iodinated
epithelin 1 was specifically inhibited by unlabeled
epithelin 1, 2, or 3, but not by other
growth factors tested. We also performed competition binding studies of 125I-epithelin 1 to
cell surface receptors in the presence of unlabeled
epithelin 1, 2, or 3. Binding results analyzed by the method of Scatchard suggested that all three
epithelins interact with a same receptor. A 140-145-kDa
epithelin 1-binding
protein complex was identified by chemical cross-linking of 125I-epithelin 1 to
breast cancer cells. Formation of such a complex was prevented by coincubation of 125I-epithelin 1 with an excess of unlabeled
epithelin 1, 2, or 3.