EPIDERMAL GROWTH FACTOR BINDING BY MEMBRANES OF HUMAN RENAL CELL CARCINOMAS: ESTABLISHMENT OF AN EPIDERMAL GROWTH FACTOR RECEPTOR ASSAY FOR CLINICAL USE

In order to quantitate epidermal growth factor receptors (EGFR) in human renal cell carcinoma (RCC) tissues, the binding of isotope-labeled epidermal growth factor (¹²⁵I-EGF) to pooled membrane samples from human RCC was studied. Specific EGF binding to membranes at 4C reached a plateau after 2 h of incubation and remained constant up to 8 h; specific binding at 25C reached a plateau after 30 min of incubation, then decreased gradually. ¹²⁵I-EGF binding to the membrane was displaced by both EGF and transforming growth factor-aL, but not by insulin and basic fibroblast growth factor. Scatchard analysis of the specific EGF binding generated a straight line, indicating a single class of binding sites for EGF, with a dissociation constant (Kd) of 21.1 times10¹⁰M and a maximum number of binding sites of 57.2fmol/mg membrane protein. When the protein concentration in the incubation medium was adjusted from 0.71mg/ml to 2.84 mg/ml, Scatchard analysis revealed identical Kd values, and the maximum number of binding sites was proportional to the protein concentration. These results demonstrate the presence of EGFR on RCC membranes and indicate that these receptors can be studied quantitatively.