mRNAs containing extensive secondary structure in their 5′ non-coding region translate efficiently in cells overexpressing initiation factor eIF-4E.

Abstract

Cellular eukaryotic mRNAs (except organellar) contain at the 5′ terminus the structure m7(5′)Gppp(5′)N (where N is any nucleotide), termed cap. Cap recognition by eukaryotic initiation factor eIF‐4F plays an important role in regulating the overall rate of translation. eIF‐4F is believed to mediate the melting of mRNA 5′ end secondary structure and facilitate 43S ribosome binding to capped mRNAs. eIF‐4E, the cap‐binding subunit of eIF‐4F, plays an important role in cell growth; its overexpression results in malignant transformation of rodent cells, and its phosphorylation is implicated in signal transduction pathways of mitogens and growth factors. The molecular mechanism by which eIF‐4E transforms cells is not known. Here, we report that overexpression of eIF‐4E facilitates the translation of mRNAs containing excessive secondary structure in their 5′ non‐coding region. This effect may represent one mechanism by which eIF‐4E regulates cell growth and transforms cells in culture.

The p20 and Ded1 proteins have antagonistic roles in eIF4E-dependent translation in Saccharomyces cerevisiae

“…In the mammalian system, unwinding of secondary structures in the 5Ј untranslated region of mRNAs is attributed to the helicase activity of eIF4A (4,5). Moreover, overexpression of eIF4E facilitates translation of highly structured mRNAs, presumably by recruiting RNA helicase activity to the mRNA (44). These data indicate the necessity of RNA helicases in translation initiation.…”

Differential expression of Myc1 and Myc2 isoforms in cells transformed by eIF4E: evidence for internal ribosome repositioning in the human c-myc 5′UTR

“…Translation of the upstream mRNA will then be inhibited due to arrest of the scanning machinery, but not that of the downstream IRES-driven mRNA. The stem ± loop structure must be stable enough to block translation by scanning: a DG near 780 kcal/mol to completely knock out initiation (Koromilas et al, 1992). A hairpin structure was used to probe for IRES activity in the cmyc 5'UTR in the context of a bicistronic construct (Nanbru et al, 1997), but the hairpin had a DG of only 760 kcal/mol.…”

Elevated expression of eIF4E and FGF-2 isoforms during vascularization of breast carcinomas

“…No tissue culture property of 435AS cells was grossly altered, but their capacity to translate FGF-2 was impaired, and presumably that of a few other mRNAs with complex 5'-leaders. These mRNAs, perhaps 1% of all cellular mRNAs, require excess eIF4E/F for e cient translation and are subject to tight translational control (Koromilas et al, 1992;Kevil et al, 1995;Sonenberg, 1996). Cancer cells, which constitutively overexpress eIF4E, may exploit a normal pathway of auto/ paracrine stimulation that originally evolved in vascular endothelium in response to pathologic 2 in 14 animals 49 ± 80 days 10 days 1 Logarithmically growing cells were plated at a density of 2610 3 cells per cm 2 in 6-well plates (in duplicates).…”

“…Furthermore, eIF4E is elevated 3 ± 30-fold in breast carcinomas, but not in ®broadenomas, indicating that its overexpression may mark a critical transition in the genesis of breast cancer (Kerakatte et al, 1995). We have proposed that eIF4E causes some of its e ects by speci®cally increasing the translation of certain growth factors, since conditioned medium from cells transformed with eIF4E is strongly mitogenic (Kevil et al, 1995;Koromilas et al, 1992). This was con®rmed with the identi®cation of a large translational increase of two powerful cytokines and angiogenic inducers: FGF-2 and Vascular Permeability Factor (Kevil et al, 1995(Kevil et al, , 1996.…”