Characterization, in some human breast cancer cell lines, of gastrin‐releasing peptide‐like receptors which are absent in normal breast epithelial cells

The binding of 125 I‐Tyr 4 bombesin was investigated on plasma membranes of 8 human breast cancer cell lines and 2 long‐term cultures of normal human breast epithelial cells. Scatchard plots were compatible with high‐affinity, single‐site class of receptors in 3 cell lines (K D of 0.75 ± 10 −9 and 10 −9 M, B max of 0.75 ± 10 −13 and 9.7 ± 10 −13 M/mg protein in MDAMB231 and in T47D cells, respectively) while no binding was observed in 5 other cell lines and normal epithelial cells. The neuropeptide and its structural analogues (natural or synthetic) inhibited the binding of 125 I‐Tyr 4 bombesin in the following order of potency: gastrin‐releasing peptide (GRP, EC 50 = 1.7 ± −10 M) > BIM 26159 > bombesin, Tyr 4 bombesin > BIM 26147 > litorin > neuromedin C. In contrast, 125 I‐Tyr 4 bombesin binding was not displaced by neuromedin B, somatostatin, bradykinin and insulin. In agreement with our binding data, SDS‐PAGE of the complex 125 I‐Tyr 4 bombesin‐receptor covalently linked by ethylene glycol‐bis succinimidyl succinate (EGS) identified after autoradiography a single band with a molecular weight of 75,000, which disappeared in the presence of bombesin in excess. No transcription of either GRP or neuromedin B mRNA could be shown in tumor or normal cells. Exogenous gastrin‐releasing peptide had no effect on growth of the cell lines when a serum‐free medium was used, implicating that in breast cancer cell lines this receptor does not mediate growth but has a functional role.