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The mammalian bombesin-like peptides gastrin-releasing peptide (GRP) and neuromedin B regulate numerous and varied cell physiologic processes in various cell types and have also been implicated as autocrine growth factors influencing the pathogenesis and progression of human small cell lung carcinomas. We report here the molecular characterization of the bombesin/GRP receptor. Structural analysis of cDNA clones isolated from Swiss 3T3 murine embryonal fibroblasts shows that the GRP receptor is a member of the guanine nucleotide binding protein-coupled receptor superfamily with seven predicted hydrophobic transmembrane domains. In vitro transcripts from cloned cDNA templates encompassing the predicted protein coding domain, when injected into Xenopus oocytes, resulted in expression of functional GRP receptors. The predicted amino acid sequence of the open reading frame in cDNA clones matches the aminoterminal sequence as well as the sequence of four tryptic fragments isolated from the purified protein. Expression of the GRP receptor cDNA in model systems potentially provides a powerful assay for the development of subtype-specific receptor antagonists that may prove to be of therapeutic importance in human small cell lung carcinoma.The mammalian bombesin-like peptides gastrin-releasing peptide (GRP) and neuromedin B (NMB) are regulatory peptides of importance in a wide variety of cell physiologic processes including secretion, smooth muscle contraction, and modulation of neuron firing rate (for review, see refs. 1 and 2). In addition, bombesin-like peptides can function as growth factors in Swiss 3T3 murine embryonal fibroblasts (3) and have been implicated as autocrine growth factors in the pathogenesis of some human small cell lung carcinomas (4). The bioactivities associated with the mammalian bombesinlike peptides are mediated by high-afflinity binding to cell surface receptors present on many target cells (for review, see ref. 1). The properties of high-affinity bombesin/GRP receptors found in relatively high numbers (=100,000 receptors per cell) on Swiss 3T3 fibroblasts have been extensively studied (5), with subsequent purification of the protein to near homogeneity (6). Molecular cloning ofthe gene encoding the Swiss 3T3 bombesin/GRP receptor is the next step to understanding the diversity and function of mammalian bombesin-like peptides and their receptors in physiologic and pathologic processes. In this paper, we report the isolation and characterization of cDNA clones § encoding the Swiss 3T3 bombesin/GRP receptor, defining the structure of the receptor polypeptide. The clones obtained should provide a basis for further molecular analysis ofthe structure, function, and expression of receptors in Swiss 3T3 cells. In addition, these clones provide a means for a similar analysis of this receptor and other related bombesin peptide receptors expressed in the various cell types known to respond to this family of peptides. MATERIALS AND METHODSReceptor Protein Purification and Peptide Sequencing. The ...

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