Characterization and localization of receptors for epidermal growth factor in ovine skin.
Specific receptor sites for murine epidermal growth factor (EGF) have been characterized and their distribution determined in ovine skin. Binding of 125I-labelled EGF to skin membrane particles was temperature- and time-dependent, with equilibrium being reached within 1 h at 23 degrees C. Analysis of skin biopsies collected from ten castrated Merino sheep demonstrated the presence of a single class of saturable, high-affinity binding sites with a dissociation constant of 64 +/- 4 (S.E.M.) pmol/l and a binding capacity of 33.8 +/- 4.5 fmol/mg protein. Skin particle binding of 125I-labelled EGF was inhibited equipotently by mouse salivary gland EGF, EGF produced by recombinant DNA procedures and urogastrone. The EGF peptides 1-48, 6-53 and 7-53, derived from the native molecule by enzymatic cleavage, were much less potent. The relative binding potency of these molecules was correlated with their ability to induce precocious eyelid opening in mice and to inhibit wool follicle activity. Synthetic fragments representing the major structural domains of the EGF molecule (EGF(29-44), EGF(33-42) and EGF(3-31] were inactive in both the receptor and bioassays. Autoradiography of skin sections incubated with 125I-labelled EGF in vitro or of sections from skin which was perfused with 125I-labelled EGF in vivo demonstrated that EGF receptors were localized in undifferentiated cells of the epidermis and sebaceous glands, the inner and outer root sheath and bulb of wool follicles and in dermal arterioles. Differences in receptor concentration were observed between follicles following in-vivo perfusion of 125I-labelled EGF but not when the in-vitro labelling technique was used. The presence of receptors in these regions is consistent with the morphological changes in sheep skin in response to EGF administration which have been reported previously.