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J. Biol. Chem., Vol. 281, Issue 6, 3145-3156, February 10, 2006

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Reduced Stability of Mitogen-activated Protein Kinase Kinase-2 mRNA and Phosphorylation of Poly(A)-binding Protein (PABP) in Cells Overexpressing PABP^*

From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada

The poly(A)-binding protein (PABP) is an important regulator of mRNA translation and stability. The cellular level of PABP is controlled by regulating its mRNA translation by a feedback mechanism. The important aspect of this mechanism is that PABP binds to an adenosine-rich cis-element at the 5'-untranslated region of its own mRNA and inhibits its translation. To assess the importance of controlling the PABP level, we studied the effect of PABP overexpression on the transcription profile using the microarray technique. In PABP-overexpressing cells, 19 mRNAs showed a reduction in cellular levels due to reduced mRNA stability, and one showed an increase due to increased mRNA stability. Among these mRNAs, the MKK-2 mRNA encodes the protein kinase activator of ERK1/2 kinase, which is involved in the phosphorylation of eukaryotic initiation factor (eIF) 4E. As a result, mRNA translation may be regulated by the cellular level of MKK-2. In this study, we show that the abundance of the MKK-2 polypeptide is reduced in PABP-overexpressing cells. In these cells, the levels of phosphorylated PABP, eIF4E, and ERK2 are also reduced. Treatment of HeLa cells with the MKK-2 inhibitor U0126 reduced PABP phosphorylation, suggesting that the phosphorylation of PABP is mediated by the MKK-2/ERK signaling pathway. Thus, a novel signaling pathway involving MKK-2 and ERK1/2 may down-regulate the activity of PABP and eIF4E by controlling their phosphorylation and compensates for the effect of excess cellular PABP.

Received for publication, August 12, 2005 , and in revised form, December 6, 2005.

^* This work was supported by a grant from the Canadian Institutes of Health Research. 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.

¹ To whom correspondence should be addressed: Dept. of Molecular and Cellular Biology, University of Guelph, 50 Stone Rd., Guelph, Ontario N1G 2W1, Canada. Tel.: 519-824-4120 (ext. 53390); Fax: 519-837-2075; E-mail: jbag{at}uoguelph.ca.

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