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Department of Internal Medicine (H.T.) and Department of Orthopedics (A.H.), Chubu National Hospital, National Institute for Longevity Sciences, Obu, Aichi 474; Department of Pharmacology, Gifu University School of Medicine (O.K., T.U.), Gifu 500; and Department of Basic Gerontology, National Institute for Longevity Sciences (K.I.), Obu, Aichi 474, Japan
Address all correspondence and requests for reprints to: Haruhiko Tokuda, Department of Internal Medicine, Chubu National Hospital, National Institute for Longevity Sciences, Obu, Aichi 474, Japan.
In osteoblast-like MC3T3-E1 cells, we recently reported that
PGE1 and PGF2
induce interleukin (IL)-6
synthesis via activation of protein kinase A and protein kinase C,
respectively. Moreover, in the case of IL-1-induced IL-6 synthesis in
these cells, we showed that protein kinase C activation by IL-1 limits
the IL-6 synthesis. In the present study, we investigated the effect of
T3 on IL-6 synthesis induced by these agonists in MC3T3-E1
cells. T3, which by itself had little effect on IL-6
synthesis, significantly reduced the IL-6 synthesis induced by
PGE1 in a dose-dependent manner in the range between 10
pM and 10 nM. T3 also reduced
PGE1-induced activation of protein kinase A. T3
inhibited the IL-6 synthesis induced by cholera toxin, an activator of
Gs, or forskolin, which directly activates adenylate
cyclase. However, T3 did not affect
(Bu)2cAMP-induced IL-6 synthesis. In addition,
T3 reduced PGF2
-induced IL-6 synthesis dose
dependently in the range between 10 pM and 10
nM. T3 also inhibited IL-6 synthesis induced by
12-O-tetradecanoylphorbol-13-acetate, an activator of
protein kinase C. On the other hand, T3 markedly enhanced
IL-1-induced IL-6 synthesis. This enhancement by T3 was
potentiated in protein kinase C down-regulated cells. T3
hardly affected the protein kinase C activation induced by
PGF2
or IL-1. These results strongly suggest that
T3 modulates IL-6 synthesis at two points in osteoblasts as
follows; one is exerted at the point between adenylate cyclase and
protein kinase A, and the other is at a point downstream from protein
kinase C activation.
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