CDK-dependent phosphorylation of Alp7-Alp14 (TACC-TOG) promotes its nuclear accumulation and spindle microtubule assembly.
As cells transition from interphase to mitosis, the microtubule cytoskeleton is reorganized to form the mitotic spindle. In the closed mitosis of fission yeast, a microtubule-associated protein complex, Alp7-Alp14 (transforming acidic coiled-coil-tumor overexpressed gene), enters the nucleus upon mitotic entry and promotes spindle formation. However, how the complex is controlled to accumulate in the nucleus only during mitosis remains elusive. Here we demonstrate that Alp7-Alp14 is excluded from the nucleus during interphase using the nuclear export signal in Alp14 but is accumulated in the nucleus during mitosis through phosphorylation of Alp7 by the cyclin-dependent kinase (CDK). Five phosphorylation sites reside around the nuclear localization signal of Alp7, and the phosphodeficient alp7-5A mutant fails to accumulate in the nucleus during mitosis and exhibits partial spindle defects. Thus our results reveal one way that CDK regulates spindle assembly at mitotic entry: CDK phosphorylates the Alp7-Alp14 complex to localize it to the nucleus.
Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan.
Naoyuki
N
Okada
Laboratory of Cell Regulation, Cancer Research UK London Research Institute, London WC2A 3LY, United Kingdom.
Takashi
T
Toda
Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Tokyo 113-0033, JapanLaboratory of Cell Response, National Institute for Basic Biology, Okazaki 444-8585, Japan.
Masayuki
M
Yamamoto
Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo, Tokyo 113-0033, JapanDepartment of Life Science and Medical Bioscience, Graduate School of Advanced Science and Engineering, Waseda University, Center for Advanced Biomedical Sciences (TWIns), Tokyo 162-8480, JapanPrecursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan masasato@waseda.jp.
Masamitsu
M
Sato
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000502:physiology*; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000378:metabolism*; D008870:Microtubules; D008969:Molecular Sequence Data; D049790:Nuclear Export Signals; D010766:Phosphorylation; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000378:metabolism*
C479626:Alp7 protein, S pombe; D008869:Microtubule-Associated Proteins; D049790:Nuclear Export Signals; D029702:Schizosaccharomyces pombe Proteins; C432090:alp14 protein, S pombe; D018844:Cyclin-Dependent Kinases