Expression - Level Dependent Activation of Recombinant Human Parathyroid Hormone/Parathyroid Hormone-Related Peptide Receptor: Effect of Human Parathyroid Hormone (1-34), (1-31), and (28-48)

Abstract

A stable recombinant Chinese hamster ovary (CHO) cell model system expressing the human type-1 receptor for parathyroid hormone and parathyroid hormone-related peptide (hPTH-R) was established for the analysis of human PTH (hPTH) variants. The cell lines showed receptor expression in the range from 10⁵ to 1.9xl0⁶ receptors per cell. The affinity of the receptors for hPTH-(l-34) was independent of the receptor number per cell (K<j = 8 nmol/1). The induction of cAMP by hPTH-(l-34) is maximal in clones expressing >2xl0⁵ receptors per cell and Ca⁺⁺ signals were maximal in cell lines expressing >1.4xl0⁶ receptors per cell. Second messenger specific inhibitors demonstrated that PTH-induced increases in intracellular cAMP and Ca⁺⁺ are independent and Ca⁺⁺ ions are derived from intracellular stores. The cAMP-specific receptor activator hPTH-(l-31) showed also an increase in intracellular Ca⁺⁺. Even in cell lines expressing more than 10 receptors per cell the Ca⁺⁺/PKC specific activator hPTH-(28-48) did not activate hPTH-Rs. Based on these results, synthesis of further derivatives of PTH is required to identify pathway-specific ligands for the type-1 hPTH-R.