Identification and characterization of eukaryotic initiation factor 5A-2

Authors

  • Paul M. J. Clement,

    1. Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
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      Present address: Laboratory of Oncology, Catholic University of Leuven, Belgium.
  • C. Allen Henderson,

    1. Department of Biological Chemistry, School of Medicine, University of California at Davis, CA, USA
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  • Zandra A. Jenkins,

    1. CHORI (Children's Hospital Oakland Research Institute), Oakland, CA, USA
    2. Department of Cell and Molecular Biology; Uppsala University, Sweden
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      † Present address: Department Paediatrics and Child Health, Dunedin School of Medicine, The University of Otago, New Zealand.
  • Zeljka Smit-McBride,

    1. Department of Biological Chemistry, School of Medicine, University of California at Davis, CA, USA
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  • Edith C Wolff,

    1. Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
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  • John W. B. Hershey,

    1. Department of Biological Chemistry, School of Medicine, University of California at Davis, CA, USA
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  • Myung Hee Park,

    1. Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA
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  • Hans E Johansson

    1. CHORI (Children's Hospital Oakland Research Institute), Oakland, CA, USA
    2. Department of Cell and Molecular Biology; Uppsala University, Sweden
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  • Enzymes: deoxyhypusine hydroxylase (EC 1.14.99.29); deoxyhypusine synthase (EC 2.5.1.46).

    Present address: Laboratory of Oncology, Catholic University of Leuven, Belgium.

    Present address: Department Paediatrics and Child Health, Dunedin School of Medicine, The University of Otago, New Zealand.

H. E. Johansson, CHORI (Children's Hospital Oakland Research Institute); 5700 Martin Luther King Jr. Way; Oakland, CA 94609-1673, USA. Fax: +1 510 450 7910, Tel.: +1 510 450 7649, E-mail: hjohansson@chori.org

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 [Nε-(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 µm 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.

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