Downregulation of the pth/pthrp receptor protein and transcript by
1,25(oh)2 vitamin d3 in the osteoblast-like ros 17/2.8 cells.
Xie, Lin Y, Albert Leung, Gino V. Segre, Itsuo Yamamoto, and Abdul B.
Abou-Samra.
Endocrine Unit, Massachusetts General Hospital & Harvard Medical
School, Boston MA 02114
APStracts 2:0235E, 1995.
Parathyroid hormone (PTH) and 1,25(OH)2D3 are the two major
calcitropic hormones that regulate extracellular calcium
concentrations; PTH stimulates the synthesis of 1,25(OH)2D3, whereas,
1,25(OH)2D3 suppresses PTH secretion. In this paper, we demonstrate
that 1,25(OH)2D3 also suppresses the expression of the PTH/PTHrP
receptor protein and mRNA levels in the osteoblastic cell line, ROS
17/2.8, thereby providing an additional mechanism to regulate the
function of the PTH system. Treatment of ROS 17/2.8 cells with
1,25(OH)2D3 caused time-dependent and dose-dependent suppression of
PTH/PTHrP receptor numbers, measured by a radioreceptor assay and a
double-antibody binding assay using a specific anti-rat PTH/PTHrP
receptor antibody. The effects required long incubation periods with
1,25(OH)2D3 (more than 24 h) and were maximal by 72 h with
1,25(OH)2D3 concentrations of 0.1 nM. Treatment of ROS 17/2.8 cells
with 1,25(OH)2D3 (10 nM) for only 24 h, followed by treatment with
control medium, caused downregulation of the PTH/PTHrP receptor at 48
and 72 h to the same levels obtained by daily treatment with
1,25(OH)2D3 for 48 and 72 h; the cells did not recover their
PTH/PTHrP receptors even after two additional days of treatment with
control medium. Treatment with low concentrations of 1,25(OH)2D3, as
low as 0.1 nM, dramatically decreased the PTH/PTHrP receptor mRNA
levels, which were maximal after 24 h of incubation. The half life of
the PTH/PTHrP receptor transcript, 6-8 h, was similar in control and
1,25(OH)2D3-treated cells, suggesting that 1,25(OH)2D3 acts in
controlling transcription of the PTH/PTHrP receptor gene, but does
not change the degradation rate of the PTH/PTHrP receptor
transcripts. These data indicate that 1,25(OH)2D3 has a potent
inhibitory effect on the expression of the PTH/PTHrP receptor protein
and mRNA in ROS 17/2.8 cells. Inhibition of expression of the
PTH/PTHrP receptor gene in osteoblastic cells provides a mechanism
for integrating the responses to PTH and vitamin D3.
Received 3 August 1995; accepted in final form 3 November 1995.
APS Manuscript Number E364-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95