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Molecular and Cellular Biology, November 2005, p. 9687-9699, Vol. 25, No. 21
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.21.9687-9699.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Peptidyl-Prolyl Isomerase 1 (Pin1) Serves as a Coactivator of Steroid Receptor by Regulating the Activity of Phosphorylated Steroid Receptor Coactivator 3 (SRC-3/AIB1)

Ping Yi,1 Ray-Chang Wu,1 Joshua Sandquist,2 Jiemin Wong,1 Sophia Y. Tsai,1 Ming-Jer Tsai,1 Anthony R. Means,2 and Bert W. O'Malley1*

Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030,1 Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 277102

Received 15 March 2005/ Returned for modification 4 May 2005/ Accepted 4 August 2005

Steroid receptor coactivator 3 (SRC-3/AIB1) interacts with steroid receptors in a ligand-dependent manner to activate receptor-mediated transcription. A number of intracellular signaling pathways initiated by growth factors and hormones induce phosphorylation of SRC-3, regulating its function and contributing to its oncogenic potential. However, the range of mechanisms by which phosphorylation affects coactivator function remains largely undefined. We demonstrate here that peptidyl-prolyl isomerase 1 (Pin1), which catalyzes the isomerization of phosphorylated Ser/Thr-Pro peptide bonds to induce conformational changes of its target proteins, interacts selectively with phosphorylated SRC-3. In addition, Pin1 and SRC-3 activate nuclear-receptor-regulated transcription synergistically. Depletion of Pin1 by small interfering RNA (siRNA) reduces hormone-dependent transcription from both transfected reporters and an endogenous steroid receptor target gene. We present evidence that Pin1 modulates interactions between SRC-3 and CBP/p300. The interaction is enhanced in vitro and in vivo by Pin1 and diminished when cellular Pin1 is reduced by siRNA or in stable Pin1-depleted cell lines. Depletion of Pin1 in MCF-7 human breast cancer cells reduces the endogenous estrogen-dependent recruitment of p300 to the promoters of estrogen receptor-dependent genes. Pin1 overexpression enhanced SRC-3 cellular turnover, and depletion of Pin1 stabilized SRC-3. Our results suggest that Pin1 functions as a transcriptional coactivator of nuclear receptors by modulating SRC-3 coactivator protein-protein complex formation and ultimately by also promoting the turnover of the activated SRC-3 oncoprotein.


* Corresponding author. Mailing address: Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Phone: (713) 798-6205. Fax: (713) 798-5599. E-mail: berto{at}bcm.tmc.edu.


Molecular and Cellular Biology, November 2005, p. 9687-9699, Vol. 25, No. 21
0022-538X/05/$08.00+0     doi:10.1128/MCB.25.21.9687-9699.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.




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