LIGAND-BINDING CHARACTERIZATION AND MOLECULAR ANALYSIS OF DISTINCT EPIDERMAL GROWTH FACTOR-UROGASTRONE RECEPTORS IN CULTURED SMOOTH-MUSCLE AND EPITHELIAL-CELLS FROM GUINEA-PIG INTESTINE

In parallel, we measured the receptor binding affinities for epidermal growth factor-urogastrone (EGF-URO) and transforming growth factor-al pha (TGF-alpha) in cultured smooth muscle (GCM) and epithelial (GPC) c ells derived from guinea pig intestine. The relative order of binding affinities in the GCM cells was TGF-alpha > EGF-URO, in keeping with t he relative order of biological potencies of these polypeptides in a g uinea pig gastric circular muscle contractile bioassay. These data est ablished by ligand binding criteria the presence of a TGF-alpha-prefer ring receptor in the guinea pig. In contrast, there was a reversed ord er of binding affinities (EGF-URO > TGF-alpha) for the polypeptides in GPC cells, in accord with an identical order of bioassay potencies pr eviously observed in a guinea pig gastric longitudinal muscle contract ile bioassay. Using a reverse transcription-polymerase chain reaction approach, we also cloned and sequenced putative EGF-URO receptor ligan d binding domain III from each cell type. Although the binding specifi city for TGF-alpha and EGF-URO differed in the GCM and GPC cells, the amino acid sequences of receptor domain III were identical in the two cell types. We conclude that the previously measured differences in bi ological potencies of EGF-URO and TGF-alpha in the contractile bioassa y preparations are due to the distinct receptor binding affinities of EGF-URO and TGF-alpha that can be detected in different tissues. Howev er, our data document that the distinct relative binding affinites for EGF-URO and TGF-alpha that can be observed in different cell types fr om the same species cannot be accounted for solely by the sequence of putative receptor ligand binding domain III.