Identification and characterization of eukaryotic initiation factor 5A-2.
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.
Clement
Paul M J
PM
Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD, USA.
Henderson
C Allen
CA
Jenkins
Zandra A
ZA
Smit-McBride
Zeljka
Z
Wolff
Edith C
EC
Hershey
John W B
JW
Park
Myung Hee
MH
Johansson
Hans E
HE
D000595:Amino Acid Sequence; D001483:Base Sequence; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D017931:DNA Primers; D018076:DNA, Complementary; D024202:Electrophoretic Mobility Shift Assay; D005260:Female; D006801:Humans; D008969:Molecular Sequence Data; D010448:Peptide Initiation Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000235:genetics; D017386:Sequence Homology, Amino Acid
D017931:DNA Primers; D018076:DNA, Complementary; D010448:Peptide Initiation Factors; C425967:eIF-5A2