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

A small portion of the 125I-EGF that binds specifically to intact cells or isolated membrane 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 possesses 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 information 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.