High-density functional gastrin releasing peptide receptors on primate cells

Gastrin releasing peptide (GRP) is a 27 amino acid hormone that elicits a variety of biological effects. Receptor-binding antagonists of GRP may have therapeutic use in several pathologic conditions including cancer. The identification and characterization of GRP receptor antagonists have been aided by the use of murine 3T3 cells that possess functional GRP receptors. However, no human or primate cell lines that possess high-density GRP receptors and exhibit a biochemical or biological response to GRP have been described. To address this problem, we examined a series of cell lines and found that GRP specifically binds to Cos-7 monkey cells and stimulates elevation of intracellular calcium in these cells. Cos-7 cells exhibit a single class of high-affinity (dissociation constant = 0.13 nM) GRP binding sites (35,000/cell). Cross-linking experiments that use radiolabeled GRP identified two species of putative GRP receptor proteins (relative molecular mass, 90,000 and 22,000). Competitive binding inhibition studies indicate that Cos-7 cells tightly bind GRP-specific receptor antagonists. These antagonists block the binding of radiolabeled GRP to Cos-7 cells and inhibit GRP-stimulated elevation of intracellular calcium. These properties make Cos-7 cells a useful reagent for the study of GRP receptor antagonists.