Regulation of PTH/PTH-Related Protein Receptor Expression by Endogenous PTH-Related Protein in the Rat Osteosarcoma Cell Line ROS 17/2.8

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Abstract
We have utilized clonal lines of the rat osteoblastic cell line ROS 17/2.8 stably transfected with full-length parathyroid hormone-related protein (PTHrP) cDNA in a sense or an antisense orientation to examine the effects of alteration in the production of endogenous PTHrP on expression of the PTH/PTHrP receptor. In the stably transfected clonal cell lines, changes in PTH/PTHrP receptor expression were evaluated by Northern blot analysis, whole-cell ligand binding of 125I-[Tyr36] PTHrP (1–36), and exogenous PTHrP (1–34)-stimulated cyclic adenosine monophosphate (cAMP) accumulation. Compared to control (vector-transfected) cells, PTHP-overproducing (sense-transfected) cells exhibited a marked decrease in the expression of PTH/PTHrP receptor mRNA and PTHrP ligand binding, as well as a corresponding decrease in the PTHrP (1–34)-stimulated cAMP response. By contrast, the antisense-transfected cells showed a marked increase in expression of PTH/PTHrP receptor mRNA and PTHrP (1–34) ligand binding, but a significant increase in the PTHrP (1–34)-stimulated cAMP response was not detected. Using antisense-transfected ROS cells, PTH/PTHrP receptor mRNA expression and 125I-[Tyr36] PTHrP (1–36) binding were downregulated by treatment for 24 h with exogenous PTHrP (1–36), forskolin, or dibutyryl cAMP. The findings extend those of earlier studies showing receptor downregulation by exogenous PTH by indicating that endogenous PTHrP, as well as circulating PTH, may help regulate receptor production; and suggesting that even very low concentrations of the peptide may influence receptor production.