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Features in the N and C termini of the MAPK-interacting kinase Mnk1 mediate its nucleocytoplasmic shuttling

Josep-Lluis Parra-Palau1, Gert C Scheper, Mary L Wilson

  • 1Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, Dow St., Dundee DD1 5EH, United Kingdom.

The Journal of Biological Chemistry
|September 2, 2003
PubMed

Insights

Mitogen-activated protein kinase-interacting kinase 1 (Mnk1) is exported from the nucleus via a CRM1-dependent pathway. Its nuclear import requires specific residues that also mediate binding to importin alpha and scaffold protein eIF4G.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Eukaryotic initiation factor 4E (eIF4E) is crucial for cap-dependent translation initiation.
  • Mitogen-activated protein kinase-interacting kinases (Mnk1 and Mnk2) phosphorylate eIF4E, regulating its activity.
  • Mnk1, while primarily cytoplasmic, interacts with both importin alpha for nuclear transport and the scaffold protein eIF4G.

Purpose of the Study:

  • To identify and characterize the nuclear export mechanism of Mnk1.
  • To investigate the specific regions and interactions of Mnk1 involved in its nuclear import.
  • To elucidate the functional relationship between Mnk1's interactions and eIF4E phosphorylation.

Main Methods:

  • Identification of a CRM1-type nuclear export motif in Mnk1.
  • Site-directed mutagenesis to alter hydrophobic residues within the export motif, inducing nuclear localization.
  • Analysis of Mnk1's polybasic region for roles in nuclear transport and eIF4G binding.
  • In vivo and in vitro assays to assess Mnk1-eIF4G interaction and eIF4E phosphorylation.

Main Results:

  • A CRM1-dependent nuclear export signal was identified in the C-terminus of Mnk1.
  • Mutations in this motif resulted in Mnk1 accumulating in the nucleus.
  • Nuclear import was dependent on specific residues within a polybasic region, which also mediates eIF4G binding.
  • Mnk1 interaction with eIF4G is essential for promoting eIF4E phosphorylation.

Conclusions:

  • Mnk1 nuclear import is regulated by specific residues that facilitate binding to importin alpha.
  • The polybasic region of Mnk1 plays a dual role in nuclear import and eIF4G interaction.
  • The Mnk1-eIF4G interaction is critical for Mnk1's function in enhancing eIF4E phosphorylation.

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