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Functional Interaction of the Ras Effector RASSF5 with the Tyrosine Kinase Lck: Critical Role in Nucleocytoplasmic Transport and Cell Cycle Regulation
Sundarasamy Mahalingam
Published in
2010
PMID: 20064523
Volume: 397
   
Issue: 1
Pages: 89 - 109
Abstract
RASSF5 is a member of the Ras association domain family, which is known to be involved in cell growth regulation. Expression of RASSF5 is extinguished selectively by epigenetic mechanism(s) in different cancers and cell lines, and reexpression usually suppresses cell proliferation and tumorigenicity. To date, the mechanism regulating RASSF5 nuclear transport and its role in cell growth regulation remains unclear. Using heterokaryon assay, we have demonstrated that RASSF5 shuttles between the nucleus and the cytoplasm, and its export from the nucleus is sensitive to leptomycin B, suggesting that RASSF5 is exported from the nucleus by a CRM-1-dependent export pathway. We further demonstrate that RASSF5 contains a hydrophobic-rich nuclear export signal (NES) towards the C-terminus and two nuclear localization signals-one each at the N-terminus and the C-terminus. Combination of mutational and immunofluorescence analyses suggests that the functional NES residing between amino acids 260 and 300 in the C-terminus is necessary for the efficient export of RASSF5 from the nucleus. In addition, substitution of conserved hydrophobic residues within the minimal NES impaired RASSF5 export from the nucleus. Furthermore, exchange of proline residues within the putative Src homology 3 binding motifs altered the export of RASSF5 from the nucleus despite the presence of functional NES, suggesting that multiple domains independently modulate the nucleocytoplasmic transport of RASSF5. Interestingly, the present investigation provided evidence that RASSF5 interacts with the tyrosine kinase Lck through its C-terminal Src homology 2 binding motif and showed that Lck-mediated phosphorylation is critical for the efficient translocation of RASSF5 into the nuclear compartment. Interestingly, our data demonstrate that wild type and nuclear export defective (ΔNES) mutant of RASSF5 but not the import defective mutant of accumulate the cells at G1/S phase and induce apoptosis. Furthermore, the Lck-interaction-defective mutant of RASSF5 induces apoptosis without altering cell cycle progression, suggesting that RASSF5 induces apoptosis independent of cell cycle arrest. Together, our data demonstrate that interaction with Lck is critical for RASSF5 phosphorylation, which in turn regulates the cell growth control activity of RASSF5. Finally, we have shown that RASSF5 encodes four splice variants and is translocated to the nucleus by the classical nuclear import pathway. One of the splice variants, RASSF5C, was found to be localized in the cytoplasm and translocated into the nucleus upon leptomycin B treatment despite the absence of N-terminal nuclear localization signal, suggesting that distribution of RASSF5 variants in different cellular compartments may be critical for Ras-dependent cell growth regulation. Collectively, the present investigation provided evidence that Lck-mediated phosphorylation regulates the nucleocytoplasmic shuttling and cell growth control activities of RASSF5. © 2010 Elsevier Ltd. All rights reserved.
About the journal
JournalJournal of Molecular Biology
ISSN00222836
Open AccessNo
Concepts (60)
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    Binding protein
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    Karyopherin alpha
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    Karyopherin beta
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    LEPTOMYCIN B
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    PROTEIN KINASE LCK
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    PROTEIN SH2
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    PROTEIN SH3
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    RAS ASSOCIATION DOMAIN FAMILY PROTEIN 5
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    Unclassified drug
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    Amino terminal sequence
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    Animal cell
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    Apoptosis
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    Article
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    Carboxy terminal sequence
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    Cell cycle arrest
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    Cell cycle progression
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    CELL CYCLE REGULATION
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    Cell growth
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    Cell proliferation
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    Cellular distribution
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    Controlled study
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    Gene mutation
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    Gene translocation
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    Genetic variability
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    GROWTH REGULATION
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    Human
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    Human cell
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    Hydrophobicity
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    Immunofluorescence
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    Mutational analysis
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    Nonhuman
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    Nucleocytoplasmic transport
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    Priority journal
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    Protein binding
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    Protein motif
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    Protein phosphorylation
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    Protein protein interaction
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    Sequence homology
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    Signal transduction
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    ACTIVE TRANSPORT, CELL NUCLEUS
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    ALPHA KARYOPHERINS
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    ALTERNATIVE SPLICING
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    Amino acid motifs
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    Amino acid sequence
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    Animals
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    Beta karyopherins
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    Cell cycle
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    Cell line
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    Cell nucleus
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    Humans
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    LYMPHOCYTE SPECIFIC PROTEIN TYROSINE KINASE P56(LCK)
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    Molecular sequence data
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    MONOMERIC GTP-BINDING PROTEINS
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    Nuclear localization signals
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    Peptides
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    PHOSPHOTYROSINE
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    Protein structure, tertiary
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    Structure-activity relationship
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    SUBCELLULAR FRACTIONS
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    Substrate specificity