Differential expression of eIF5A-1 and eIF5A-2 in human cancer cells.
Eukaryotic translation initiation factor 5A (eIF5A) is the only cellular protein that contains the unusual amino acid hypusine [N(epsilon)-(4-amino-2-hydroxybutyl)lysine]. Vertebrates carry two genes that encode two eIF5A isoforms, eIF5A-1 and eIF5A-2, which, in humans, are 84% identical. eIF5A-1 mRNA (1.3 kb) and protein (18 kDa) are constitutively expressed in human cells. In contrast, expression of eIF5A-2 mRNA (0.7-5.6 kb) and eIF5A-2 protein (20 kDa) varies widely. Whereas eIF5A-2 mRNA was demonstrable in most cells, eIF5A-2 protein was detectable only in the colorectal and ovarian cancer-derived cell lines SW-480 and UACC-1598, which showed high overexpression of eIF5A-2 mRNA. Multiple forms of eIF5A-2 mRNA (5.6, 3.8, 1.6 and 0.7 kb) were identified as the products of one gene with various lengths of 3'-UTR, resulting from the use of different polyadenylation (AAUAAA) signals. The eIF5A-1 and eIF5A-2 precursor proteins were modified comparably in UACC-1598 cells and both were similarly stable. When eIF5A-1 and eIF5A-2 coding sequences were expressed from mammalian vectors in 293T cells, eIF5A-2 precursor was synthesized at a level comparable to that of eIF5A-1 precursor, indicating that the elements causing inefficient translation of eIF5A-2 mRNA reside outside of the open reading frame. On sucrose gradient separation of cytoplasmic RNA, only a small portion of total eIF5A-2 mRNA was associated with the polysomal fraction, compared with a much larger portion of eIF5A-1 mRNA in the polysomes. These findings suggest that the failure to detect eIF5A-2 protein even in eIF5A-2 mRNA positive cells is, at least in part, due to inefficient translation.
Clement
Paul M J
PM
Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892-4340, USA.
Johansson
Hans E
HE
Wolff
Edith C
EC
Park
Myung H
MH
D001483:Base Sequence; D002460:Cell Line; D045744:Cell Line, Tumor; D006801:Humans; D008239:Lysine / Q000031:analogs & derivatives / Q000096:biosynthesis; D008969:Molecular Sequence Data; D009369:Neoplasms / Q000378:metabolism*; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000378:metabolism; D010448:Peptide Initiation Factors / Q000235:genetics / Q000378:metabolism*; D026723:Polyadenylation; D011132:Polyribosomes; D014176:Protein Biosynthesis; D020033:Protein Isoforms; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D000097574:Eukaryotic Translation Initiation Factor 5A
D008239:Lysine; D000587:Oxidoreductases Acting on CH-NH Group Donors; D010448:Peptide Initiation Factors; D020033:Protein Isoforms; D011498:Protein Precursors; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D000097574:Eukaryotic Translation Initiation Factor 5A; C425967:eIF-5A2; C100028:hypusine; C063507:deoxyhypusine synthase