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

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Abstract
The binding of 125I‐Tyr4 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 (KD of 0.75 ± 10−9 and 10−9 M, Bmax 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 125I‐Tyr4 bombesin in the following order of potency: gastrin‐releasing peptide (GRP, EC50 = 1.7 ± −10 M) > BIM 26159 > bombesin, Tyr4 bombesin > BIM 26147 > litorin > neuromedin C. In contrast, 125I‐Tyr4 bombesin binding was not displaced by neuromedin B, somatostatin, bradykinin and insulin. In agreement with our binding data, SDS‐PAGE of the complex 125I‐Tyr4 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.