title: Akt-mediated phosphorylation increases the binding affinity of hTERT for importin α to promote nuclear translocation.
abstract: Telomeres are essential for chromosome integrity and protection, and their maintenance requires the ribonucleoprotein enzyme telomerase. Previously, we have shown that human telomerase reverse transcriptase (hTERT) contains a bipartite nuclear localization signal (NLS; residues 222-240) that is responsible for nuclear import, and that Akt-mediated phosphorylation of residue S227 is important for efficient nuclear import of hTERT. Here, we show that hTERT binds to importin-α proteins through the bipartite NLS and that this heterodimer then forms a complex with importin-β proteins to interact with the nuclear pore complex. Depletion of individual importin-α proteins results in a failure of hTERT nuclear import, and the resulting cytoplasmic hTERT is degraded by ubiquitin-dependent proteolysis. Crystallographic analysis reveals that the bipartite NLS interacts with both the major and minor sites of importin-α proteins. We also show that Akt-mediated phosphorylation of S227 increases the binding affinity for importin-α proteins and promotes nuclear import of hTERT, thereby resulting in increased telomerase activity. These data provide details of a binding mechanism that enables hTERT to interact with the nuclear import receptors and of the control of the dynamic nuclear transport of hTERT through phosphorylation.
authors.affiliation: Department of Integrated Omics for Biomedical Science, Yonsei University, Seoul 120-749, Korea.
authors.forename: Sun Ah
authors.initials: SA
authors.lastname: Jeong
authors.affiliation: Department of Systems Biology, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea.
authors.forename: Kuglae
authors.initials: K
authors.lastname: Kim
authors.affiliation: Department of Integrated Omics for Biomedical Science, Yonsei University, Seoul 120-749, Korea.
authors.forename: Ji Hoon
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Systems Biology, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea.
authors.forename: Jeong Seok
authors.initials: JS
authors.lastname: Cha
authors.affiliation: Department of Integrated Omics for Biomedical Science, Yonsei University, Seoul 120-749, Korea.
authors.forename: Prabhat
authors.initials: P
authors.lastname: Khadka
authors.affiliation: Department of Systems Biology, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea hscho8@yonsei.ac.kr topoviro@yonsei.ac.kr.
authors.forename: Hyun-Soo
authors.initials: HS
authors.lastname: Cho
authors.affiliation: Department of Integrated Omics for Biomedical Science, Yonsei University, Seoul 120-749, Korea Department of Systems Biology, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea hscho8@yonsei.ac.kr topoviro@yonsei.ac.kr.
authors.forename: In Kwon
authors.initials: IK
authors.lastname: Chung
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D015153:Blotting, Western; D002467:Cell Nucleus / Q000235:genetics*; D005455:Fluorescent Antibody Technique; D006801:Humans; D061986:MCF-7 Cells; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019913:Nuclear Localization Signals; D010766:Phosphorylation; D010768:Phosphoserine / Q000737:chemistry; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D019098:Telomerase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D028901:alpha Karyopherins / Q000235:genetics / Q000378:metabolism*
chemical_list: D050505:Mutant Proteins; D019913:Nuclear Localization Signals; D012333:RNA, Messenger; D028901:alpha Karyopherins; C087978:karyopherin alpha 2; D010768:Phosphoserine; D051057:Proto-Oncogene Proteins c-akt; C509186:TERT protein, human; D019098:Telomerase
keywords: Akt; Importin receptor; Nuclear localization signal; Phosphorylation; Telomerase reverse transcriptase