Journal
RNA
Volume 11, Issue 9, Pages 1385-1399Publisher
COLD SPRING HARBOR LAB PRESS, PUBLICATIONS DEPT
DOI: 10.1261/rna.7226105
Keywords
LEF-1; IRES; WNT signaling; cancer; 5 '-UTR; translation
Categories
Funding
- NCI NIH HHS [CA83982, CA096878, R01 CA096878, R01 CA083982] Funding Source: Medline
- NIAID NIH HHS [R01 AI026765, R56 AI026765, AI26765] Funding Source: Medline
- NIGMS NIH HHS [T32 GM007311, GM067285-02, F31 GM067285] Funding Source: Medline
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The lymphoid enhancer factor-1 LEF1 locus produces multiple mRNAs via alternative promoters. Full-length LEF-1 protein is produced via translation of an mRNA with a 1.2-kb, GC-rich 5'-untranslated region (UTR), whereas a truncated LEF-1 isoform is produced by an mRNA with a short, 60-nucleotide (nt) 5'-UTR. Full-length LEF-1 promotes cell growth via its interaction with the WNT signaling mediator beta-catenin. Truncated LEF-1 lacks the beta-catenin binding domain and opposes WNT signaling as a competitive inhibitor for WNT response elements. In this study we tested the hypothesis that the long, GC-rich 5'-UTR within the full-length LEF1 mRNA contains an internal ribosome entry site (IRES). Using a dicistronic vector in transient DNA transfections, we show that the LEF1 5'-UTR mediates cap-independent translation. Additional experiments involving a promoter-less dicistronic vector, Northern blot analysis, and transient transfections of dicistronic mRNAs into cultured mammalian cells compromised for cap-dependent translation demonstrate that the 5'-UTR of full-length LEF1 mRNA contains a bona fide IRES. Deletion analysis of the 5'-UTR shows that maximal IRES activity requires the majority of the 5'-UTR, consistent with the notion that cellular IRESs require multiple modules for efficient activity. This study demonstrates that full-length LEF1 mRNA has evolved to utilize a cap-independent mechanism for translation of full-length LEF-1, whereas the truncated isoform is produced via the canonical cap-dependent ribosome scanning mechanism.
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