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Molecular and Cellular Biology, September 2005, p. 7605-7615, Vol. 25, No. 17
0270-7306/05/$08.00+0     doi:10.1128/MCB.25.17.7605-7615.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Differential Phosphorylation Controls Maskin Association with Eukaryotic Translation Initiation Factor 4E and Localization on the Mitotic Apparatus

Daron C. Barnard, Quiping Cao, and Joel D. Richter*

Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605

Received 13 April 2005/ Returned for modification 18 May 2005/ Accepted 17 June 2005

Several cytoplasmic polyadenylation element (CPE)-containing mRNAs that are repressed in Xenopus oocytes become active during meiotic maturation. A group of factors that are anchored to the CPE are responsible for this repression and activation. Two of the most important are CPEB, which binds directly to the CPE, and Maskin, which associates with CPEB. In oocytes, Maskin also binds eukaryotic translation initiation factor 4E (eIF4E), an interaction that excludes eIF4G and prevents formation of the eIF4F initiation complex. When the oocytes are stimulated to reenter the meiotic divisions (maturation), CPEB promotes cytoplasmic polyadenylation. The newly elongated poly(A) tail becomes bound by poly(A) binding protein (PABP), which in turn binds eIF4G and helps it displace Maskin from eIF4E, thereby inducing translation. Here we show that Maskin undergoes several phosphorylation events during oocyte maturation, some of which are important for its dissociation from eIF4E and translational activation of CPE-containing mRNA. These sites are T58, S152, S311, S343, S453, and S638 and are phosphorylated by cdk1. Mutation of these sites to alanine alleviates the cdk1-induced dissociation of Maskin from eIF4E. Prior to maturation, Maskin is phosphorylated on S626 by protein kinase A. While this modification has no detectable effect on translation during oocyte maturation, it is critical for this protein to localize on the mitotic apparatus in somatic cells. These results show that Maskin activity and localization is controlled by differential phosphorylation.

* Corresponding author. Mailing address: Biotech 2, Suite 204, Program in Molecular Medicine, University of Massachusetts Medical School, 373 Plantation Street, Worcester, MA 01605. Phone: (508) 856-8615. Fax: (508) 856-4289. E-mail: joel.richter{at}umassmed.edu.

Molecular and Cellular Biology, September 2005, p. 7605-7615, Vol. 25, No. 17
0022-538X/05/$08.00+0     doi:10.1128/MCB.25.17.7605-7615.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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