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.