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Originally published In Press as doi:10.1074/jbc.M002354200 on July 10, 2000
J. Biol. Chem., Vol. 275, Issue 41, 31609-31615, October 13, 2000
Thyrotropin-releasing Hormone and Epidermal Growth Factor
Regulate Iron-regulatory Protein Binding in Pituitary Cells via Protein
Kinase C-dependent and -independent Signaling Pathways*
Andrew M.
Thomson ,
Jack T.
Rogers§, and
Peter J.
Leedman ¶
From the Laboratory for Cancer Medicine and
University Department of Medicine, University of Western Australia,
Western Australian Institute for Medical Research, Royal Perth
Hospital, Perth, Western Australia 6000, Australia and the
§ Genetics and Aging Unit, Massachusetts General Hospital
(East), Harvard Medical School,
Charlestown, Massachusetts 02129
Intracellular iron homeostasis is regulated, in
part, by interactions between iron-regulatory proteins (IRP1 and IRP2)
and iron-responsive elements (IREs) in ferritin and transferrin
receptor mRNAs. In addition to iron, cellular oxidative stress
induced by H2O2, nitric oxide, and
hypoxia, and hormonal activation by thyroid hormone and erythropoeitin
have each been shown to regulate IRP binding to IREs. Hormonal signals,
in particular mediated through protein kinase C (PKC), play a central
role in the modulation of IRP/IRE interactions since phorbol esters
were shown to activate IRP binding (Eisenstein, R. S., Tuazon,
P. T., Schalinske, K. L., Anderson, S. A., and Traugh,
J. A. (1993) J. Biol. Chem. 268, 27363-27370).
In pituitary thyrotrophs (TtT97), we found that thyrotropin releasing
hormone (TRH) and epidermal growth factor (EGF) increased IRP binding
to a ferritin IRE, dependent on PKC and mitogen-activated protein
kinase (MAPK) activity. In contrast, TRH and EGF decreased IRP binding
in pituitary lactotrophs (GH3), despite activation of PKC and MAPK.
IRP1 and IRP2 levels remained constant and IRP2 binding was predominant
throughout. TRH and EGF markedly decreased IRP binding in MAPK kinase
inhibitor-treated GH3 cells, whereas, they increased IRP binding in
phosphatase inhibitor-treated GH3 cells. IRE-dependent CAT
reporter translational expression closely reflected IRP binding to the
ferritin IRE in both GH3 and TtT97 cells. Interestingly, ferritin
protein levels were regulated similarly by TRH in both cell lines.
These data link two different cell receptor systems to common signaling
pathways that regulate IRP binding and ferritin expression. Remarkably, for TRH and EGF, these effects may be PKC-dependent or
-independent determined by the cell type.
*
This work was supported in part by grants from the Medical
Research Fund of Western Australia, the Raine Medical Research Foundation of Western Australia, and the Royal Perth Hospital Medical
Research Foundation (to P. J. L.). The work was also
supported by grants from the American Federation for Aging Research,
the Institute for the Study of Aging (ISOA), and an RO3 pilot grant from the NIA, National Institutes of Health (to J. T. R.).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: University Dept.
of Medicine, Royal Perth Hospital, Box X2213 GPO, Perth, Western Australia 6001, Australia. Tel.: 61-89-2240323; Fax:
61-89-2240246; E-mail: peterl@cyllene.uwa.edu.au.
Copyright © 2000 by The American Society for Biochemistry and Molecular Biology, Inc.

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Copyright © 2000 by the American Society for Biochemistry and Molecular Biology.
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