Mineralocorticoid action in rat osteoblastic cells.
Agarwal, M. K., F. Mirshahi, *m. Mirshahi, S. Bracq, J. Chentoufi, M.
Hott, A. Jullienne, P. J. Marie.
HORMONE LABORATORY, INSERM U-86, CENTRE UNIVERSITAIRE DES
CORDELIERS, INSERM U-349, HOPITAL LARIBOISIERE, PARIS, FRANCE
APStracts 2:0425C, 1995.
We studied the presence of the mineralocorticoid receptor (MCR) and
the biological action of mineralotropic steroids in osteoblastic
cells isolated from rat calvaria. The proliferation of osteoblastic
cells was significantly enhanced by low concentrations of the natural
hormone aldosterone, an effect that was inhibited by two MCR-specific
antagonists, RU 26752 and ZK 91587. In addition, the activity of
alkaline phosphatase, a marker of the osteoblast phenotype, was
inhibited by aldosterone in a dose dependent manner. This effect was
reversed by RU 26752, suggesting the presence of a functional MCR.
Cytoplasmic staining for MCR was observed in rat calvaria osteoblasts
incubated with a specific polyclonal antiserum raised against rat
kidney MCR. This anti-MCR IgG immunoprecipitated and macroaggregated
the MCR-3H-RU 26752 complex in osteoblast cytosol. A single 98 kDa
band was observed when osteoblast cytosol was analyzed by Western
blotting with the anti-MCR serum. The 98 kDa band was also obtained
following autoradiography of osteoblast cytosol irradiated in the
presence of 3H-R 5020. This fluorographic pattern was abolished when
RU 26752, an antagonist specific to the MCR, was allowed to compete
with radiolabelled promegestone. A p26MR probe, specific to the
carboxy-terminal end of MCR, hybridized with the predicted PCR
product, following amplification of total cell RNA by polymerase
chain reaction technique. Hybridization of poly A mRNA from rat
calvaria osteoblastic cells with the MCR-specific p26MR probe
revealed a major band of about 4.2 kb, further confirming that these
cells express the MCR. Collectively, the evidence presented here
demonstrates the existence of a functional mineralocorticoid receptor
in rat calvaria osteoblasts. Therefore, bone represents an
interesting new target to delineate the mechanism of action of
mineralotropic hormones.
Received 2 May 1995; accepted in final form 18 October 1995.
APS Manuscript Number C240-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95