[125I]EGF binding ability is stable throughout the replicative life-span of WI-38 cells

Abstract

Using a serum-free medium supplemented with hormones and growth factors, which included epidermal growth factor (EGF), we investigated the binding and processing-degradation of [¹²⁵I]EGF in WI-38 cells of various in vitro ages. The binding and processing-degradation systems of these cells remained esentially unchanged throughout their lifespan. The number of specific [¹²⁵I]EGF binding sites per cell increased as the cultures senesced, thought the number of specific binding sites per μm²(surface area) remained constant. The kinetics of ligand degradation as well as the qualitative and quantitative nature of the degradation products also remained essentially unchanged throughout the life-span. The only consistent alteration in any of the binding parameters measured was the slight decrease in the apparent k_d of the ligand-receptor complex, independent of temperature. Quantitation of EGF-stimulated DNA synthesis revealed a decrease in the percentage of cells incorporating [³H]thymidine ([³H]TdR) during a 30-h exposure from 45% in young cells to 0.25% in senescent cells, although [¹²⁵I]EGF binding or processing-degradation did not differ significantly in yong and old cells. Thus, EGF binding does not decrease in senescence.