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Molecular and Cellular Biology, November 2007, p. 7791-7801, Vol. 27, No. 22
0270-7306/07/$08.00+0     doi:10.1128/MCB.01254-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Human TOB, an Antiproliferative Transcription Factor, Is a Poly(A)-Binding Protein-Dependent Positive Regulator of Cytoplasmic mRNA Deadenylation{triangledown} ,{dagger}

Nader Ezzeddine, Tsung-Cheng Chang,{ddagger} Wenmiao Zhu, Akio Yamashita,§ Chyi-Ying A. Chen, Zhenping Zhong, Yukiko Yamashita,§ Dinghai Zheng, and Ann-Bin Shyu*

Department of Biochemistry and Molecular Biology, The University of Texas Medical School, Houston, Texas 77030

Received 12 July 2007/ Returned for modification 10 August 2007/ Accepted 23 August 2007

In mammalian cells, mRNA decay begins with deadenylation, which involves two consecutive phases mediated by the PAN2-PAN3 and the CCR4-CAF1 complexes, respectively. The regulation of the critical deadenylation step and its relationship with RNA-processing bodies (P-bodies), which are thought to be a site where poly(A)-shortened mRNAs get degraded, are poorly understood. Using the Tet-Off transcriptional pulsing approach to investigate mRNA decay in mouse NIH 3T3 fibroblasts, we found that TOB, an antiproliferative transcription factor, enhances mRNA deadenylation in vivo. Results from glutathione S-transferase pull-down and coimmunoprecipitation experiments indicate that TOB can simultaneously interact with the poly(A) nuclease complex CCR4-CAF1 and the cytoplasmic poly(A)-binding protein, PABPC1. Combining these findings with those from mutagenesis studies, we further identified the protein motifs on TOB and PABPC1 that are necessary for their interaction and found that interaction with PABPC1 is necessary for TOB's deadenylation-enhancing effect. Moreover, our immunofluorescence microscopy results revealed that TOB colocalizes with P-bodies, suggesting a role of TOB in linking deadenylation to the P-bodies. Our findings reveal a new mechanism by which the fate of mammalian mRNA is modulated at the deadenylation step by a protein that recruits poly(A) nuclease(s) to the 3' poly(A) tail-PABP complex.

* Corresponding author. Mailing address: Department of Biochemistry and Molecular Biology, The University of Texas Medical School, Houston, TX 77030. Phone: (713) 500-6068. Fax: (713) 500-0652. E-mail: Ann-Bin.Shyu{at}uth.tmc.edu

{triangledown} Published ahead of print on 4 September 2007.

{dagger} Supplemental material for this article may be found at http://mcb.asm.org/.

{ddagger} Present address: The McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205.

§ Present address: Yokohama City University School of Medicine, 3-9 Fuku-ura, Kanazawa, Yokohama 236-0004, Japan.

Molecular and Cellular Biology, November 2007, p. 7791-7801, Vol. 27, No. 22
0270-7306/07/$08.00+0     doi:10.1128/MCB.01254-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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