A mechanism of nucleocytoplasmic trafficking for the homeodomain protein PRH

  • Jonathan E. Ploski
  • Ivan Topisirovic
  • Kevin W. Park
  • Katherine L. B. Borden
  • Aurelian Radu


Proline-rich homeodomain (PRH)/hematopoietically expressed homeodomain (Hex) is a homeodomain protein that plays an important role in early embryonic patterning and hematopoiesis. PRH can act as either a tumor suppressor or an oncogene and its expression is dysregulated in certain types of lymphoid and myeloid leukemias. Aberrant exclusion of PRH from the nuclei has been associated with thyroid and breast cancers and a subset of myeloid leukemias. Accordingly, nuclear localization of PRH was found to be necessary for the inhibition of eIF4E-dependent transformation. Since PRH’s nuclear–cytoplasmic localization has been associated with neoplastic transformation we sought to better understand how PRH is transported to the nuclear compartment. Here, we report an essential element that controls the mechanism of PRH nucleocytoplasmic trafficking, namely that it is imported into the nuclei by Karyopherin/Importin 7. Kap7 was identified as a binding partner for PRH in a GST-pull down from a HeLa cell protein lysate, followed by mass-spectrometry. The Kap7–PRH complex is dissociated in the presence of RanGTP, as expected for a nuclear import complex. Kap7 can bind directly to PRH in a GST-pull down assay with purified proteins, as well as mediates the transport of PRH to the nuclear compartment in a digitonin permeabilized cells assay. Finally, in vivo depletion of Kap7 dramatically reduces accumulation of PRH in the nucleus. Our data open the way for investigations of the mechanism of perturbed PRH localization in tumors and possible therapeutic interventions.


PRH Hex Importin Karyopherin Nucleocytoplasmic Trafficking 



We thank Dr. Elias Coutavas for valuable suggestions and Drs. Dirk Görlich and Tarick Soliman for DNA constructs. This study was supported by grants from the National Institutes of Health (R01 GM057569 to AR and RO1 80728 to KLBB). KLBB holds a Canada Research Chair in Molecular Biology of the Cell Nucleus. IT is a Special Fellow of the Leukemia and Lymphoma Society, USA.


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Copyright information

© Springer Science+Business Media, LLC. 2009

Authors and Affiliations

  • Jonathan E. Ploski
    • 1
  • Ivan Topisirovic
    • 2
    • 4
  • Kevin W. Park
    • 1
  • Katherine L. B. Borden
    • 2
  • Aurelian Radu
    • 3
  1. 1.Department of PsychologyYale UniversityNew HavenUSA
  2. 2.Department of Pathology and Cell Biology, Institute for Research in Immunovirology and CancerUniversité de MontréalMontrealCanada
  3. 3.Developmental and Regenerative BiologyMount Sinai School of MedicineNew YorkUSA
  4. 4.Department of Biochemistry and Goodman Cancer CentreMcGill UniversityMontrealCanada

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