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Phosphorylation of Cdc6 at serine 74, but not at serine 106, drives translocation of Cdc6 to the cytoplasm

Authors

  • Hyungshin Yim,

    Corresponding author
    1. Division of Pharmaceutical Biosciences, Research Institute for Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul, Republic of Korea
    2. Department of Pharmacy, College of Pharmacy, Hanyang University, Ansan, Gyeonggi-do, Republic of Korea
    • College of Pharmacy, Hanyang University, Ansan, 426-791, Republic of Korea.
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  • Ji-Woong Park,

    1. Division of Pharmaceutical Biosciences, Research Institute for Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul, Republic of Korea
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  • Sang Uk Woo,

    1. Department of Pharmacy, College of Pharmacy, Hanyang University, Ansan, Gyeonggi-do, Republic of Korea
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  • Seong-Taek Kim,

    1. Division of Pharmaceutical Biosciences, Research Institute for Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul, Republic of Korea
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  • Linhua Liu,

    1. Division of Pharmaceutical Biosciences, Research Institute for Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul, Republic of Korea
    2. Department of Biochemistry, Institute of Glycobiology, Dalian Medical University, Dalian, Liaoning, China
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  • Chul-Hoon Lee,

    1. Department of Pharmacy, College of Pharmacy, Hanyang University, Ansan, Gyeonggi-do, Republic of Korea
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  • Seung Ki Lee

    Corresponding author
    1. Division of Pharmaceutical Biosciences, Research Institute for Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul, Republic of Korea
    • Division of Pharmaceutical Biosciences, Research Institute for Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul 151-742, Republic of Korea.
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  • The authors declare no conflict of interest.

Abstract

Phosphorylation-dependent cytoplasmic translocation of human Cdc6 during S phase is sufficient to control its activity after origin firing. Export from the nucleus also serves as a mechanism for preventing re-replication in mammalian cells. Phosphorylation of the CDK consensus serine residues 54, 74, and 106 has been suggested to be involved in the cytoplasmic translocation of Cdc6. To determine the relative importance of the three phosphorylation sites, we have generated Cdc6 variants by substituting one or more of the three serine residues with alanine or aspartic acid and have assessed their cytoplasmic translocation behavior. Phosphorylation of serine 74 mainly contributes to the cytoplasmic translocation of Cdc6, while serine 54 phosphorylation provides a minor contribution. In contrast, phosphorylation at serine 106 does not affect the nuclear export of Cdc6. Comparative results were found in cells coexpressing the phosphorylation defective mutants of Cdc6 and cyclin A as well as in non-transfected cells synchronized by their release from a double thymidine block. We conclude that Cdk-mediated phosphorylation of Cdc6 at serine 74 is required for the cytoplasmic translocalization of Cdc6 during the cell cycle. Phosphorylation of Cdc6 at serine 54 plays a minor role and phosphorylation of serine 106 plays no role in the cytoplasmic localization of Cdc6. The phosphorylation of S74 in Cdc6 could be important for binding to the nuclear export protein for translocalization. J. Cell. Physiol. 228: 1221–1228, 2013. © 2012 Wiley Periodicals, Inc.

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