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-alpha (TGF-alpha) in cultured smooth muscle (GCM) and epithelial (GPC) cells derived from guinea pig intestine. The relative order of binding affinities in the GCM cells was TGF-alpha > EGF-URO, in keeping with the relative order of biological potencies of these polypeptides in a guinea pig gastric circular muscle contractile bioassay. These data established by ligand binding criteria the presence of a TGF-alpha-preferring receptor in the guinea pig. In contrast, there was a reversed order of binding affinities (EGF-URO > TGF-alpha) for the polypeptides in GPC cells, in accord with an identical order of bioassay potencies previously observed in a guinea pig gastric longitudinal muscle contractile bioassay. Using a reverse transcription-polymerase chain reaction approach, we also cloned and sequenced putative EGF-URO receptor ligand binding domain III from each cell type. Although the binding specificity 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 biological potencies of EGF-URO and TGF-alpha in the contractile bioassay preparations are due to the distinct receptor binding affinities of EGF-URO and TGF-alpha that can be detected in different tissues. However, our data document that the distinct relative binding affinities for EGF-URO and TGF-alpha that can be observed in different cell types from the same species cannot be accounted for solely by the sequence of putative receptor ligand binding domain III.