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Molecular and Cellular Biology, February 2008, p. 1081-1091, Vol. 28, No. 3
0270-7306/08/$08.00+0 doi:10.1128/MCB.00967-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Alternative Mechanisms by Which Mediator Subunit MED1/TRAP220 Regulates Peroxisome Proliferator-Activated Receptor 
-Stimulated Adipogenesis and Target Gene Expression
Kai Ge,1,2*
Young-Wook Cho,1,
Hong Guo,1,
Teresa B. Hong,3,
Mohamed Guermah,2
Mitsuhiro Ito,2,
Hong Yu,1
Markus Kalkum,3 and
Robert G. Roeder2*
Nuclear Receptor Biology Section, Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892,1 Laboratory of Biochemistry and Molecular Biology, Rockefeller University, 1230 York Avenue, New York, New York 10021,2 Beckman Research Institute of the City of Hope, Immunology Division, Duarte, California 910103
Received 31 May 2007/ Returned for modification 29 June 2007/ Accepted 5 November 2007
Mediator is a general coactivator complex connecting transcription activators and RNA polymerase II. Recent work has shown that the nuclear receptor-interacting MED1/TRAP220 subunit of Mediator is required for peroxisome proliferator-activated receptor 
(PPAR)-stimulated adipogenesis of mouse embryonic fibroblasts (MEFs). However, the molecular mechanisms remain undefined. Here, we show an intracellular PPAR-Mediator interaction that requires the two LXXLL nuclear receptor recognition motifs on MED1/TRAP220 and, furthermore, we show that the intact LXXLL motifs are essential for optimal PPAR function in a reconstituted cell-free transcription system. Surprisingly, a conserved N-terminal region of MED1/TRAP220 that lacks the LXXLL motifs but gets incorporated into Mediator fully supports PPAR-stimulated adipogenesis. Moreover, in undifferentiated MEFs, MED1/TRAP220 is dispensable both for PPAR-mediated target gene activation and for recruitment of Mediator to a PPAR response element on the aP2 target gene promoter. However, PPAR shows significantly reduced transcriptional activity in cells deficient for a subunit (MED24/TRAP100) important for the integrity of the Mediator complex, indicating a general Mediator requirement for PPAR function. These results indicate that there is a conditional requirement for MED1/TRAP220 and that a direct interaction between PPAR and Mediator through MED1/TRAP220 is not essential either for PPAR-stimulated adipogenesis or for PPAR target gene expression in cultured fibroblasts. As Mediator is apparently essential for PPAR transcriptional activity, our data indicate the presence of alternative mechanisms for Mediator recruitment, possibly through intermediate cofactors or other cofactors that are functionally redundant with MED1/TRAP220.
* Corresponding author. Mailing address for Kai Ge: Building 10, Room 8N307C, NIH, Bethesda, MD 20892. Phone: (301) 451-1998. Fax: (301) 480-1021. E-mail: kaig{at}niddk.nih.gov. Mailing address for Robert G. Roeder: Laboratory of Biochemistry and Molecular Biology, Rockefeller University, 1230 York Avenue, New York, NY 10021. Phone: (212) 327-7600. Fax: (212) 327-7949. E-mail: roeder{at}mail.rockefeller.edu
Published ahead of print on 26 November 2007.
These authors contributed equally to this work.
Present address: Department of Medical Technology and Laboratory of Hematology, Kobe University School of Medicine, Kobe 654-0142, Japan.
Molecular and Cellular Biology, February 2008, p. 1081-1091, Vol. 28, No. 3
0270-7306/08/$08.00+0 doi:10.1128/MCB.00967-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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