Thromboxane a2-stimulated phospholipase d in osteoblast-like cells:
possible involvement of protein kinase c activation.
Shinoda, Junji, Atsushi Suzuki, Yutaka Oiso, and Osamu Kozawa.
First Department of Internal Medicine, Nagoya University School of
Medicine, Nagoya 466, Japan; and Department of Biochemistry,
Institute for Developmental Research, Aichi Prefectural Colony,
Kasugai, Aichi 480-03, Japan
APStracts 2:0071E, 1995.
We examined the effect of thromboxane A2 (TXA2) on
phosphatidylcholine-hydrolyzing phospholipase D activity in
osteoblast-like MC3T3-E1 cells. 9,11-Epithio-11,12-methano
-thromboxane A2 (STA2), a stable analogue of TXA2, stimulated the
formations of both choline and inositol phosphates in a dose
-dependent manner in the range between 10 nM and 10 [mu]M. The
formation of choline stimulated by a combination of STA2 and 12-O
-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C- activating
phorbol ester, was not additive. H-7, an inhibitor of protein
kinases, suppressed the formation of choline induced by STA2 as well
as that by TPA, but 20 [mu]M HA1004, a control for H-7 as a protein
kinase C-inhibitor, had little effect. Calphostin C, a potent and
specific inhibitor of protein kinase C, also suppressed the formation
of choline induced by STA2. The STA2-induced formation of choline was
significantly reduced by chelating extracellular Ca2+ with EGTA. STA2
dose dependently stimulated 45Ca2+ influx from extracellular space.
STA2 stimulated DNA synthesis of MC3T3-E1 cells and increased the
number of these cells. These results suggest that TXA2 stimulates
phospholipase D in osteoblast-like cells, resulting in the direction
of their proliferation, and that the activation of protein kinase C
is involved in the stimulation of phospholipase D.
Received 30 December 1994; accepted in final form 11 April 1995.
APS Manuscript Number E536-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 April 1995.