Direct linkage of EGF to its receptor: Characterization and biological relevance

Abstract

A small portion of the ¹²⁵I‐EGF that binds specifically to intact cells or isolated membranes from a variety of sources becomes directly and irreversibly linked to EGF receptors. This provides a simple technique for affinity labeling the EGF receptor. Membranes isolated from the human epidermoid carcinoma cell line A431, which posesses extraordinarily high numbers of EGF receptors, gave rise to three major direct linkage complexes of MW = 160,000, 145,000, and 115,000. The time course for formation of each is similar, showing that ¹²⁵I‐EGF can form direct linkage complexes with several preexisting forms of the EGF receptor. The direct linkage of EGF to receptor is slow in comparison to ¹²⁵I‐EGF binding, but both processes have similar susceptibilities to competition by unlabeled EGF. EGF was modified chemically with the amino site‐specific reagent, N‐hydroxysuccinimidyl biotin. The biotinyl‐EGF had a reduced capacity to engage in direct linkage complex formation with no concomitant reduction in its ability to bind to EGF receptors. Since native and biotinyl EGF have identical abilities to stimulate the uptake of ³H‐thymidine into DNA when incubated with cultured murine 3T3 cells, the direct linkage of EGF to its receptor does not appear to play an important role in EGF‐stimulated mitogenesis.