Identification and characterization of eukaryotic initiation factor 5A-2


  • Enzymes: deoxyhypusine hydroxylase (EC; deoxyhypusine synthase (EC

    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:


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.