Identification and characterization of eukaryotic initiation factor 5A-2.

  • Clement P
  • Henderson C
  • Jenkins Z
 et al. 
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Abstract

The phylogenetically conserved eukaryotic translation initiation factor 5A (eIF5A) is the only known cellular protein to contain the post-translationally derived amino acid hypusine Nepsilon-(4-amino-2-hydroxybutyl)lysine. Both eIF5A and its hypusine modification are essential for sustained cell proliferation. Normally only one eIF5A protein is expressed in human cells. Recently, we identified a second human EIF5A gene that would encode an isoform (eIF5A-2) of 84% sequence identity. Overexpression of eIF5A-2 mRNA in certain human cancer cells, in contrast to weak normal expression limited to human testis and brain, suggests EIF5A2 as a potential oncogene. However, eIF5A-2 protein has not been described in human or mammalian cells heretofore. Here, we describe the identification of eIF5A-2 protein in human colorectal and ovarian cancer lines, SW-480 and UACC-1598, that overexpress eIF5A-2 mRNAs. Functional characterization of the human isoforms revealed that either human EIF5A gene can complement growth of a yeast strain in which the yeast EIF5A genes were disrupted. This indicates functional similarity of the human isoforms in yeast and suggests that eIF5A-2 has an important role in eukaryotic cell survival similar to that of the ubiquitous eIF5A-1. Detectable structural differences were also noted, including lack of immunological cross-reactivity, formation of different complexes with deoxyhypusine synthase, and Km values (1.5 0.2 vs. 8.3 1.4 microm for eIF5A-1 and -2, respectively) as substrates for deoxyhypusine synthase in vitro. These physical characteristics and distinct amino acid sequences in the C-terminal domain together with differences in gene expression patterns imply differentiated, tissue-specific functions of the eIF5A-2 isoform in the mammalian organism and in cancer.

Author-supplied keywords

  • 1
  • 18 kda
  • a small
  • deoxyhypusine
  • eif5a
  • eif5a 2
  • essential
  • eukaryotic initiation factor 5a
  • fig
  • hypusine
  • polyamines
  • post translational modification
  • universally conserved protein

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  • PMID: 14622290

Authors

  • Paul M J Clement

  • C Allen Henderson

  • Zandra A Jenkins

  • Zeljka Smit-McBride

  • Edith C Wolff

  • John W B Hershey

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