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Originally published In Press as doi:10.1074/jbc.M103634200 on June 4, 2001
J. Biol. Chem., Vol. 276, Issue 33, 31238-31246, August 17, 2001
Hormonal Control of Insulin-like Growth Factor I Gene
Transcription in Human Osteoblasts
DUAL ACTIONS OF cAMP-DEPENDENT PROTEIN KINASE ON
CCAAT/ENHANCER-BINDING PROTEIN *
Julia
Billiard ,
Savraj S.
Grewal§,
Lisa
Lukaesko§,
Philip
J. S.
Stork§, and
Peter
Rotwein ¶
From Oregon Health Sciences University, Molecular
Medicine Division, Department of Medicine, Portland, Oregon 97201-3098 and the § Vollum Institute and Oregon Health Sciences
University, Portland, Oregon 97201
Insulin-like growth factor-I (IGF-I) is essential
for somatic growth and promotes bone cell replication and
differentiation. IGF-I production by rat osteoblasts is stimulated by
activation of cAMP-dependent protein kinase (PKA). In this
report, we define two interacting PKA-regulated pathways that control
IGF-I gene transcription in cultured human osteoblasts. Stimulation of
cAMP led to a 12-fold increase in IGF-I mRNA and enhanced IGF-I
promoter activity through a DNA response element termed HS3D and the
transcription factor CCAAT/enhancer-binding protein (C/EBP ).
Under basal conditions, C/EBP was found in osteoblast nuclei but was
transcriptionally silent. Treatment with the PKA inhibitor H-89 caused
redistribution of C/EBP to the cytoplasm. After hormone treatment,
the catalytic subunit of PKA accumulated in osteoblast nuclei.
Inhibition of active PKA with targeted nuclear expression of PKA
inhibitor had no effect on the subcellular location of C/EBP
but prevented hormone-induced IGF-I gene activation, while cytoplasmic
PKA inhibitor additionally caused the removal of C/EBP from the
nucleus. These results show that IGF-I gene expression is controlled in
human osteoblasts by two PKA-dependent pathways.
Cytoplasmic PKA mediates nuclear localization of C/EBP under basal
conditions, and nuclear PKA stimulates its transcriptional activity
upon hormone treatment. Both mechanisms are indirect, since PKA failed
to phosphorylate human C/EBP in vitro.
*
These studies were supported by National Institutes of
Health Grants 5-RO1-DK37449 (to P. R.) and 5F32-DK09802 (to J. B.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
¶
To whom correspondence should be addressed: Oregon Health
Sciences University, Molecular Medicine Division, 3181 S.W. Sam Jackson
Park Rd., Mail code: NRC3, Portland, OR 97201-3098. Tel.: 503-494-0536;
Fax: 503-494-7368; E-mail: rotweinp@ohsu.edu.
Copyright © 2001 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 2001 by the American Society for Biochemistry and Molecular Biology.
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