The parathyroid hormone-like peptide associated with humoral hypercalcemia of malignancy and parathyroid hormone bind to the same receptor on the plasma membrane of ROS 17/2.8 cells

Abstract

[Tyr36]human adenylate cyclase stimulating peptide (1-36)-NH2, an amino-terminal analog of a tumor peptide which is associated with hypercalcemia of malignancy, and [Nle8, Nle18, Tyr34]bovine parathyroid hormone (PTH)-(1-34)-NH2 both bind with similar affinities to receptors on rat osteosarcoma cells, ROS 17/2.8, when either of the peptides is used as the radioligand. Pretreatment of the cells with either peptide down-regulates available binding sites for either radioligand and desensitizes the cAMP accumulation stimulated by either peptide. Prior exposure of the cells to dexamethasone increases these responses to both peptides. Photoderivatized radioiodinated [Tyr36]human adenylate cyclase-stimulating peptide (1-36)-NH2 and [Nle8, Nle18, Tyr34]bovine PTH-(1-34)-NH2 both specifically label a Mr = 80,000 membrane protein on ROS 17/2.8 cells. The intensity of labeling this receptor band by either photoprobe is reduced by co-incubation with either peptide over the same dose range. Equivalent dose-dependent down-regulation of receptors which bind both photoprobes is also found when ROS 17/2.8 cells are preincubated with either peptide. Dexamethasone increases the intensity of receptor labeling. Our findings strongly indicate that both peptides recognize the same plasma membrane receptor on ROS 17/2.8 cells. Although the physiological function(s) of human adenylate cyclase-stimulating peptide is unknown, these results could explain why its biological actions on mineral ion metabolism so closely simulate those of PTH and raise interesting questions about the general biological and evolutionary significance of the use of the same receptor by chemically distinct peptides.