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J. Biol. Chem., Vol. 280, Issue 24, 22606-22615, June 17, 2005

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Characterization of a Novel Positive Transcription Regulatory Element That Differentially Regulates the Insulin-like Growth Factor Binding Protein-3 (IGFBP-3) Gene in Senescent Cells^*

Xiao Feng Lu, Xiao Gang Jiang, Yun Biao Lu, Jun Hai Bai, and Ze Bin Mao¶

From the Department of Biochemistry and Molecular Biology, Health Science Center, Peking University, 38 Xueyuan Road, Beijing 100083, China, and Department of Biochemistry and Molecular Biology, School of Medicine, Xi'an Jiaotong University, Xi'an 710061, China

Insulin-like growth factor binding protein-3 (IGFBP-3) is a well documented growth inhibitor and pro-apoptotic factor. IGFBP-3 mRNA and its protein are overexpressed by senescent human diploid fibroblasts. However, the mechanism responsible for the up-regulation of its expression is still unclear. This report describes a novel transcriptional regulatory element, IGFBP-3 enhancer element (IEE), identified in the 5' untranslated region of the IGFBP-3 gene. This element differentially activates IGFBP-3 expression in senescent versus young fibroblasts. Electrophoretic mobility shift assays revealed abundant complexes in senescent cell nuclear extracts compared with young cell nuclear extracts. Similar to young proliferative cells, young quiescent cells showed reduced binding activity; enhancement of this activity was specific to senescent cells and not an effect of cell cycle arrest. The DNase I footprint revealed the protein-binding core sequence within the IEE through which the protein binds the IEE. Site-directed mutagenesis within IEE abolished binding activity and selectively decreased IGFBP-3 promoter activity in senescent (but not young) cells. Furthermore, introduction of an IEE decoy suppressed the endogenous IGFBP-3 gene expression specifically in senescent cells. These results point to the IEE as being a positive transcription regulatory element that contributes to the up-regulation of IGFBP-3 during cellular senescence.

Received for publication, October 25, 2004 , and in revised form, March 2, 2005.

^* This work was supported by Grants 30171027 and 30471914 from the National Science Foundation of China. The costs of publication of this article were defrayed in part by the payment of page charges. This 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: Dept. of Biochemistry and Molecular Biology, Health Science Center, Peking University, 38 Xueyuan Road, Beijing 100083, China. Tel.: 8610-82802527; E-mail: zbmao{at}bjmu.edu.cn.

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