Subcellular localization of the hypusine-containing eukaryotic initiation factor 5A by immunofluorescent staining and green fluorescent protein tagging

J Cell Biochem. 2002;86(3):590-600. doi: 10.1002/jcb.10235.

Abstract

Eukaryotic initiation factor 5A (eIF-5A) is the only protein in nature that contains hypusine, an unusual amino acid residue formed posttranslationally by deoxyhypusine synthase and deoxyhypusine hydroxylase. Although the eIF-5A gene is essential for cell survival and proliferation, the precise function and localization of eIF-5A remain unclear. In this study, we have determined the subcellular distribution of eIF-5A by indirect immunofluorescent staining and by direct visualization of green fluorescent protein tagged eIF-5A (GFP-eIF5A). Immunofluorescent staining of the formaldehyde-fixed cells showed that eIF-5A was present in both the nucleus and cytoplasm. Only the nuclear eIF-5A was resistant to Triton extraction. Direct visualization of GFP tagged eIF-5A in living cells revealed the same whole-cell distribution pattern. However, a fusion of an additional pyruvate kinase (PK) moiety into GFP-eIF-5A precluded the nuclear localization of GFP-PK-eIF-5A fusion protein. Fusion of the GFP-PK tag with three different domains of eIF-5A also failed to reveal any nuclear localization of the fusion proteins, suggesting the absence of receptor-mediated nuclear import. Using interspecies heterokaryon fusion assay, we could detect the nuclear export of GFP-Rev, but not of GFP-eIF-5A. The whole-cell distribution pattern of eIF-5A was recalcitrant to the treatments that included energy depletion, heat shock, and inhibition of transcription, translation, polyamine synthesis, or CRM1-dependent nuclear export. Collectively, our data indicate that eIF-5A gains nuclear entry via passive diffusion, but it does not undergo active nucleocytoplasmic shuttling.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3 Cells
  • Active Transport, Cell Nucleus
  • Animals
  • COS Cells
  • Calnexin / analysis
  • Cell Nucleus / chemistry
  • Cell Nucleus / metabolism
  • Cell Survival
  • Eukaryotic Initiation Factors / analysis*
  • Eukaryotic Initiation Factors / immunology
  • Eukaryotic Initiation Factors / metabolism
  • Eukaryotic Translation Initiation Factor 5A
  • Exportin 1 Protein
  • Fluorescent Antibody Technique, Indirect
  • Green Fluorescent Proteins
  • HeLa Cells
  • Humans
  • Karyopherins / analysis
  • Luminescent Proteins / analysis*
  • Lysine / analogs & derivatives*
  • Lysine / analysis*
  • Mice
  • Nuclear Localization Signals
  • Peptide Initiation Factors / analysis*
  • Peptide Initiation Factors / immunology
  • Peptide Initiation Factors / metabolism
  • Protein Transport
  • RNA-Binding Proteins*
  • Receptors, Cytoplasmic and Nuclear*

Substances

  • Eukaryotic Initiation Factors
  • Karyopherins
  • Luminescent Proteins
  • Nuclear Localization Signals
  • Peptide Initiation Factors
  • RNA-Binding Proteins
  • Receptors, Cytoplasmic and Nuclear
  • Calnexin
  • Green Fluorescent Proteins
  • hypusine
  • Lysine