Down-regulation of the receptor for parathyroid hormone (PTH) and PTH-related peptide by PTH in primary fetal rat osteoblasts.

We studied the effects of parathyroid hormone (PTH) on PTH parathyroid hormone related peptide (PTHrP) receptor mRNA level, PTHrP binding and PTH-stimulated cyclic adenosine monophosphate (cAMP) accumulation in osteoblasts, derived from fetal rat calvariae (ROB). Cells isolated during 10-70 minutes of collagenase treatment were seeded at a density of 25,000 cells/cm2 and cultured for 4 days. These cells show a fast increase in cAMP production after stimulation for 5 minutes with 20 nM bovine parathyroid hormone(1-34) (bPTH(1-34)).

Expression of the parathyroid hormone receptor and correlation with other osteoblastic parameters in fetal rat osteoblasts.

Primary fetal rat calvarial cell cultures were examined for the expression of different osteoblastic parameters at the single cell level and in the whole population. The presence of the parathyroid hormone (PTH) receptor was studied by employing receptor autoradiography. After 3 days of culture, 10% of the cells expressed the PTH receptor.

Down-regulation and differential restoration of cAMP responses upon transient phorbol ester treatment of primary osteoblastic cells.

We studied cAMP responses induced by parathyroid hormone (PTH), prostaglandin E2 (PGE2) and forskolin in foetal rat calvariae-derived osteoblastic cells after 24 h treatment with a protein kinase C (PKC) activating phorbol ester. After this treatment, meant to down-regulate PKC activity, all tested cAMP responses were attenuated and were indeed accompanied by a decline in PKC activity. PTH receptor affinity was not altered and PTH receptor number was only slightly lowered after 24 h phorbol ester treatment.

Down-regulation of the receptor for parathyroid hormone (PTH) and PTH-related peptide by transforming growth factor-beta in primary fetal rat osteoblasts.

We studied the effects of transforming growth factor-beta 2 (TGF beta 2) on the level of PTH/PTH-related peptide-(PTHrP) receptor messenger RNA (mRNA), PTHrP binding, and PTH-stimulated cAMP accumulation in cultured osteoblasts derived from fetal rat calvariae (ROB). When ROB were pretreated with TGF beta 2 at concentrations ranging from 1-100 pM for 24 h, dose-dependent decreases in the level of PTH/PTHrP receptor mRNA, PTHrP binding, and PTH-stimulated cAMP accumulation were observed. For the PTH/PTHrP receptor mRNA level and PTH-stimulated cAMP accumulation, the half-maximal effective concentration was approximately 4 pM.

Regulation of protein kinase C activity by phorbol ester, thrombin, parathyroid hormone and transforming growth factor-beta 2 in different types of osteoblastic cells.

We investigated the role of protein kinase C (PKC) in osteoblast function using a set of putative PKC modulating factors and an in situ peptide substrate-based kinase assay in different types of osteoblastic cells. Primary calvarial rat osteoblastic cells (ROB) and ROS 17/2.8 osteosarcoma cells showed an equally high PKC activity when a maximal dose of PKC-activating phorbol ester was applied.