Exportin 4 mediates a novel nuclear import pathway for Sox family transcription factors

SRY and other Sox-type transcription factors are important developmental regulators with various implications in human disease. In this study, we identified Exp4 (exportin 4) as an interaction partner of Sox2 in mouse embryonic stem cells and neural progenitors. We show that, besides its established function in nuclear export, Exp4 acts as a bona fide nuclear import receptor for Sox2 and SRY. Thus, Exp4 is an example of a nuclear transport receptor carrying distinct cargoes into different directions. In contrast to a published study, we observed that the import activity of Imp-α (importin-a) isoforms toward Sox2 is negligible. Instead, we found that Imp9 and the Imp-β/7 heterodimer mediate nuclear import of Sox2 in parallel to Exp4. Import signals for the three pathways overlap and include conserved residues in the Sox2 high-mobility group (HMG) box domain that are also critical for DNA binding. This suggests that nuclear import of Sox proteins is facilitated by several parallel import pathways.

[1]  References , 1971 .

[2]  Robin Lovell-Badge,et al.  A gene from the human sex-determining region encodes a protein with homology to a conserved DNA-binding motif , 1990, Nature.

[3]  S. Adam,et al.  Nuclear protein import in permeabilized mammalian cells requires soluble cytoplasmic factors , 1990, The Journal of cell biology.

[4]  A. Gronenborn,et al.  Molecular basis of human 46X,Y sex reversal revealed from the three-dimensional solution structure of the human SRY-DNA complex , 1995, Cell.

[5]  N. Lamb,et al.  Nuclear localization of the testis determining gene product SRY , 1995, The Journal of cell biology.

[6]  G. Dreyfuss,et al.  A Novel Receptor-Mediated Nuclear Protein Import Pathway , 1996, Cell.

[7]  What is This? Downloaded from , 1995 .

[8]  G. Scherer,et al.  Two Independent Nuclear Localization Signals Are Present in the DNA-binding High-mobility Group Domains of SRY and SOX9* , 1997, The Journal of Biological Chemistry.

[9]  Dirk Görlich,et al.  RanBP1 is crucial for the release of RanGTP from importin β‐related nuclear transport factors , 1997, FEBS letters.

[10]  Stefan Jaekel,et al.  Importin β, transportin, RanBP5 and RanBP7 mediate nuclear import of ribosomal proteins in mammalian cells , 1998, The EMBO journal.

[11]  I. Mattaj,et al.  Nucleocytoplasmic transport: the soluble phase. , 1998, Annual review of biochemistry.

[12]  F. Bischoff,et al.  The importin β/importin 7 heterodimer is a functional nuclear import receptor for histone H1 , 1999, The EMBO journal.

[13]  U. Kutay,et al.  The translocation of transportin–cargo complexes through nuclear pores is independent of both Ran and energy , 1999, Current Biology.

[14]  F. Bischoff,et al.  Evidence for Distinct Substrate Specificities of Importin α Family Members in Nuclear Protein Import , 1999, Molecular and Cellular Biology.

[15]  U. Kutay,et al.  Transport between the cell nucleus and the cytoplasm. , 1999, Annual review of cell and developmental biology.

[16]  E. O’Shea,et al.  Regulation of nuclear localization: a key to a door. , 1999, Annual review of cell and developmental biology.

[17]  G. Lipowsky,et al.  Exportin 4: a mediator of a novel nuclear export pathway in higher eukaryotes , 2000, The EMBO journal.

[18]  D. Görlich,et al.  Signal recognition particle protein 19 is imported into the nucleus by importin 8 (RanBP8) and transportin. , 2001, Journal of cell science.

[19]  R. Kraft,et al.  Importin 13: a novel mediator of nuclear import and export , 2001, The EMBO journal.

[20]  G. Blobel,et al.  The Karyopherin Kap142p/Msn5p Mediates Nuclear Import and Nuclear Export of Different Cargo Proteins , 2001, The Journal of cell biology.

[21]  G M Clore,et al.  Structural basis for SRY-dependent 46-X,Y sex reversal: modulation of DNA bending by a naturally occurring point mutation. , 2001, Journal of molecular biology.

[22]  U. Kutay,et al.  Multiple pathways contribute to nuclear import of core histones , 2001, EMBO reports.

[23]  D. Görlich,et al.  The permeability barrier of nuclear pore complexes appears to operate via hydrophobic exclusion , 2002, The EMBO journal.

[24]  P. Schwarzmaier,et al.  Importins fulfil a dual function as nuclear import receptors and cytoplasmic chaperones for exposed basic domains , 2002, The EMBO journal.

[25]  J. Forwood,et al.  Defective importin β recognition and nuclear import of the sex-determining factor SRY are associated with XY sex-reversing mutations , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[26]  R. Lovell-Badge,et al.  Multipotent cell lineages in early mouse development depend on SOX2 function. , 2003, Genes & development.

[27]  L. Pevny,et al.  SOX2 Functions to Maintain Neural Progenitor Identity , 2003, Neuron.

[28]  Austin G Smith,et al.  Conversion of embryonic stem cells into neuroectodermal precursors in adherent monoculture , 2003, Nature Biotechnology.

[29]  Pier Paolo Pandolfi,et al.  Sox2 deficiency causes neurodegeneration and impaired neurogenesis in the adult mouse brain , 2004, Development.

[30]  Karen P. Steel,et al.  Sox2 is required for sensory organ development in the mammalian inner ear , 2005, Nature.

[31]  Austin G Smith,et al.  Niche-Independent Symmetrical Self-Renewal of a Mammalian Tissue Stem Cell , 2005, PLoS biology.

[32]  B. Paschal,et al.  Mechanisms of Receptor‐Mediated Nuclear Import and Nuclear Export , 2005, Traffic.

[33]  D. Fitzpatrick,et al.  Mutations in SOX2 cause anophthalmia-esophageal-genital (AEG) syndrome. , 2006, Human molecular genetics.

[34]  C. Heldin,et al.  The Mechanism of Nuclear Export of Smad3 Involves Exportin 4 and Ran , 2006, Molecular and Cellular Biology.

[35]  D. Görlich,et al.  A selective block of nuclear actin export stabilizes the giant nuclei of Xenopus oocytes , 2006, Nature Cell Biology.

[36]  S. Magness,et al.  SOX2 is a dose-dependent regulator of retinal neural progenitor competence. , 2006, Genes & development.

[37]  S. Yamanaka,et al.  Induction of Pluripotent Stem Cells from Mouse Embryonic and Adult Fibroblast Cultures by Defined Factors , 2006, Cell.

[38]  Normal brain development in importin-alpha5 deficient-mice. , 2007, Nature cell biology.

[39]  Hisato Kondoh,et al.  Triggering neural differentiation of ES cells by subtype switching of importin-α , 2007, Nature Cell Biology.

[40]  B. Hogan,et al.  Multiple dose-dependent roles for Sox2 in the patterning and differentiation of anterior foregut endoderm , 2007, Development.

[41]  V. Lefebvre,et al.  Control of cell fate and differentiation by Sry-related high-mobility-group box (Sox) transcription factors. , 2007, The international journal of biochemistry & cell biology.

[42]  C. Sánchez,et al.  Proteomics Analysis of Ring1B/Rnf2 Interactors Identifies a Novel Complex with the Fbxl10/Jhdm1B Histone Demethylase and the Bcl6 Interacting Corepressor*S , 2007, Molecular & Cellular Proteomics.

[43]  Alexei A. Sharov,et al.  Pluripotency governed by Sox2 via regulation of Oct3/4 expression in mouse embryonic stem cells , 2007, Nature Cell Biology.