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Molecular and Cellular Biology, May 2001, p. 3057-3070, Vol. 21, No. 9
Departments of Developmental and Molecular
Biology and Medicine, The Albert Einstein Cancer
Center,1 and Department of Pharmacology,
Albert Einstein College of Medicine,2 Bronx, New
York 10461; Department of Medicine, University of Cambridge,
Addenbrooke's Hospital, Cambridge CB2 2QQ, United
Kingdom3; and Division of Endocrinology,
Diabetes, and Metabolism, University of Pennsylvania School of
Medicine, Philadelphia, Pennsylvania 191044
Received 6 September 2000/Returned for modification 9 October
2000/Accepted 13 February 2001
The nuclear receptor peroxisome proliferator-activated receptor
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.9.3057-3070.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Inhibition of Cellular Proliferation through
I
B Kinase-Independent and Peroxisome Proliferator-Activated
Receptor
-Dependent Repression of Cyclin D1
(PPAR
) is a ligand-regulated nuclear receptor superfamily member.
Liganded PPAR
exerts diverse biological effects, promoting adipocyte
differentiation, inhibiting tumor cellular proliferation, and
regulating monocyte/macrophage and anti-inflammatory activities in
vitro. In vivo studies with PPAR
ligands showed enhancement of tumor
growth, raising the possibility that reduced immune function and tumor
surveillance may outweigh the direct inhibitory effects of PPAR
ligands on cellular proliferation. Recent findings that PPAR
ligands
convey PPAR
-independent activities through I
B kinase (IKK) raises
important questions about the specific mechanisms through which PPAR
ligands inhibit cellular proliferation. We investigated the mechanisms
regulating the antiproliferative effect of PPAR
. Herein PPAR
,
liganded by either natural (15d-PGJ2 and PGD2)
or synthetic ligands (BRL49653 and troglitazone), selectively inhibited
expression of the cyclin D1 gene. The inhibition of S-phase
entry and activity of the cyclin D1-dependent serine-threonine kinase
(Cdk) by 15d-PGJ2 was not observed in PPAR
-deficient
cells. Cyclin D1 overexpression reversed the S-phase inhibition by
15d-PGJ2. Cyclin D1 repression was independent of IKK, as
prostaglandins (PGs) which bound PPAR
but lacked the IKK interactive
cyclopentone ring carbonyl group repressed cyclin D1. Cyclin D1
repression by PPAR
involved competition for limiting abundance of
p300, directed through a c-Fos binding site of the cyclin D1 promoter. 15d-PGJ2 enhanced recruitment of p300 to PPAR
but
reduced binding to c-Fos. The identification of distinct pathways
through which eicosanoids regulate anti-inflammatory and
antiproliferative effects may improve the utility of COX2 inhibitors.
*
Corresponding author. Mailing address: The Albert
Einstein Cancer Center, Department of Developmental and Molecular
Biology, Albert Einstein College of Medicine, Chanin 302, 1300 Morris
Park Ave., Bronx, NY 10461. Phone: (718) 430-8662. Fax: (718) 430-8674. E-mail: pestell{at}aecom.yu.edu.
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