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

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 125 I‐PTHrP‐1‐34 Tyr binds with a single binding site in both cells. However 125 I‐PTHrP‐1‐34 Tyr has higher affinity binding in MCF7 ( K D  = 1.88 ± 0.08 nM) than in SaOS‐2 cells ( K D  = 4.4 ± 0.185 nM). The competitive binding using 3.3 nM 125 I‐PTHrP‐1‐34 Tyr with increasing amounts (0.33–33 nM) of unlabelled human PTHrP‐1‐34, PTHrP‐7‐34, PTHrP‐1‐86 His 5 ‐PTHrP‐1‐36, His 5 ‐Phe 23 ‐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 His 5 ‐Phe 23 ‐PTHrP‐1‐36 caused an increase in the K D 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.