Quantitative comparison of PTH1R in breast cancer MCF7 and osteosarcoma SaOS‐2 cell lines

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Abstract
The aim of the present study was to compare the classical parathyroid hormone/parathyroid hormone‐related peptide (PTH/PTHrP) receptors in MCF7 breast cancer cells with SaOS‐2 osteosarcoma cell line. Quantitative binding showed that 125I‐PTHrP‐1‐34Tyr binds with a single binding site in both cells. However 125I‐PTHrP‐1‐34Tyr has higher affinity binding in MCF7 (KD = 1.88 ± 0.08 nM) than in SaOS‐2 cells (KD = 4.4 ± 0.185 nM). The competitive binding using 3.3 nM 125I‐PTHrP‐1‐34Tyr with increasing amounts (0.33–33 nM) of unlabelled human PTHrP‐1‐34, PTHrP‐7‐34, PTHrP‐1‐86 His5‐PTHrP‐1‐36, His5‐Phe23‐PTHrP‐1‐36 or PTH‐1‐34 revealed different displacements. In SaOS‐2 the PTHrP‐7‐34 and PTHrP‐1‐86 caused similar displacement compared with 73% by PTH‐1‐34 and 70% by PTHrP‐1‐34. However, in MCF7, PTHrP‐7‐34, PTHrP‐1‐86 and PTH‐1‐34 displaced by 54%, 72% and 67%, respectively, compared to 87% by PTHrP‐1‐34. The His5‐Phe23‐PTHrP‐1‐36 caused an increase in the KD from 2.0 ± 0.03 nM to 2.75 ± 0.045 nM in MCF7 cells, but had no significant effect in SaOS‐2 cells. The PTH/PTHrP receptor in both cell lines revealed a single 85 KDa band with different intensity. Our results suggest that the PTH/PTHrP receptor in MCF7 cells has higher binding affinity for PTHrP than PTH compared to the receptor in SaOS‐2 cells. Copyright © 2008 John Wiley & Sons, Ltd.

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