Cap-dependent and cap-independent translation in eukaryotic systems

Merrick, William C.

doi:10.1016/j.gene.2004.02.051

Cited by 220 publications

(139 citation statements)

References 82 publications

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“…[12,16,15,17,18] The first step in translation initiation involves 4E-BP1 releasing eIF4E to complex with two other factors, eIF4G and eIF4A to form the eIF4F complex resulting in the recruitment of the 40S ribosome and the beginning of translation. [19,17] We analyzed the expression and phosphorylation of a number of translation initiation proteins anticipating their relevance to be observed as a decrease in phosphorylation in the combination treatment (Figure 4). Interestingly, eIF4B phosphorylation was completely abrogated as shown through immunoblotting with the combination gefitinib and temsirolimus treatment.…”

Section: Resultsmentioning

confidence: 99%

“…The latter is also known as internal ribosome entry site (IRES) translation. [19] Eukaryotic cells are able to use cap-independent translation but mainly rely on the eIF proteins to mediate cap-dependent translation, comprising 95-97% of all translation. [14,21,19] It is believed that eIF4B is involved in cap-dependent translation and plays little to no role in cap-independent translation.…”

Section: Resultsmentioning

confidence: 99%

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Abrogating phosphorylation of eIF4B is required for EGFR and mTOR inhibitor synergy in triple-negative breast cancer

Madden

Mueller

Bollig‐Fischer

et al. 2014

Breast Cancer Res Treat

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Purpose Triple negative breast cancer (TNBC) patients suffer from a highly malignant and aggressive disease. They have a high rate of relapse and often develop resistance to standard chemotherapy. Many TNBCs have elevated epidermal growth factor receptor (EGFR) but are resistant to EGFR inhibitors as monotherapy. In this study we sought to find a combination therapy that could sensitize TNBC to EGFR inhibitors. Methods Phospho-mass spectrometry was performed on the TNBC cell line, BT20, treated with 0.5 μM gefitinib. Immunoblotting measured protein levels and phosphorylation. Colony formation and growth assays analyzed the treatment on cell proliferation while MTT assays determined the synergistic effect of inhibitor combination. A dual luciferase reporter gene plasmid measured translation. All statistical analysis was done on CalucuSyn and GraphPad Prism using ANOVAs. Results Phospho-proteomics identified the mTOR pathway to be of interest in EGFR inhibitor resistance. In our studies, combining gefitinib and temsirolimus decreased cell growth and survival in a synergistic manner. Our data identified eIF4B, as a potentially key fragile point in EGFR and mTOR inhibitor synergy. Decreased eIF4B phosphorylation correlated with drops in growth, viability, clonogenic survival, and cap-dependent translation. Conclusions Taken together these data suggest EGFR and mTOR inhibitors abrogate growth, viability, and survival via disruption of eIF4B phosphorylation leading to decreased translation in TNBC cell lines. Further, including an mTOR inhibitor along with an EGFR inhibitor in TNBC with increased EGFR expression should be further explored. Additionally, translational regulation may play in important role in regulating EGFR and mTOR inhibitor synergy and warrants further investigation.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Abrogating phosphorylation of eIF4B is required for EGFR and mTOR inhibitor synergy in triple-negative breast cancer

Madden

Mueller

Bollig‐Fischer

et al. 2014

Breast Cancer Res Treat

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“…The scanning mechanism requires recognition of the cap structure at the 5′ end of the mRNA by the cap-binding protein eIF4E, followed by recruitment of the activated 40S ribosomal subunit and subsequent downstream scanning along the 5′-untranslated region (UTR) to a suitable start codon (1). Nucleotide composition, length and secondary structures of the 5′-UTR determine the efficiency of translation initiation.…”

Section: Introductionmentioning

confidence: 99%

The leader region of Laminin B1 mRNA confers cap-independent translation

Petz

Kozina

Huber

et al. 2007

Nucleic Acids Research

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Translation initiation of eukaryotic mRNAs generally occurs by cap-dependent ribosome scanning. However, certain mRNAs contain internal ribosome entry sites (IRES) allowing cap-independent translation. Several of these IRES-competent transcripts and their corresponding proteins are involved in tumourigenesis. This study focused on IRES-driven translation control during the epithelial to mesenchymal transition (EMT) of hepatocytes that reflects crucial aspects of carcinoma progression. Expression profiling of EMT revealed Laminin B1 (LamB1) to be translationally upregulated. The 5′-untranslated region (UTR) of LamB1 was potent to direct IRES-dependent mRNA utilization of a bicistronic reporter construct. Stringent assays for cryptic promoter and splice sites showed no aberrantly expressed transcripts, suggesting that the reporter activity provided by the leader region of LamB1 mRNA exclusively depends on IRES. In accordance, LamB1 expression increased upon negative interference with cap-dependent translation by expression of human rhinovirus 2A protease or heat shock of cells. Finally, the enhanced expression of LamB1 during EMT correlated with an elevated IRES activity. Together, these data provide first evidence that the 5′-UTR of LamB1 contains a bona fide IRES that directs translational upregulation of LamB1 during stress conditions and neoplastic progression of hepatocytes.

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“…T ranslation initiation of most eukaryotic mRNAs occurs by a scanning mechanism, where the 43S ribosomal subunit enters the mRNA from an accessible 5= end, is dependent on the 7-methyl guanosine cap structure (m7GpppG), and scans in a 5=-to-3= direction in search of the initiation codon (1). The ribosomal subunit is recruited to the 5= end by the cap-binding protein factor eIF4E, which is bound to the 5= cap.…”

mentioning

confidence: 99%

A Unique 5′ Translation Element Discovered in Triticum Mosaic Virus

Roberts

Zhang

Mayberry

et al. 2015

J Virol

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Several plant viruses encode elements at the 5= end of their RNAs, which, unlike most cellular mRNAs, can initiate translation in the absence of a 5= m7GpppG cap. Here, we describe an exceptionally long (739-nucleotide [nt]) leader sequence in triticum mosaic virus (TriMV), a recently emerged wheat pathogen that belongs to the Potyviridae family of positive-strand RNA viruses. We demonstrate that the TriMV 5= leader drives strong cap-independent translation in both wheat germ extract and oat protoplasts through a novel, noncanonical translation mechanism. Translation preferentially initiates at the 13th start codon within the leader sequence independently of eIF4E but involves eIF4G. We truncated the 5= leader to a 300-nucleotide sequence that drives cap-independent translation from the 5= end. We show that within this sequence, translation activity relies on a stem-loop structure identified at nucleotide positions 469 to 490. The disruption of the stem significantly impairs the function of the 5= untranslated region (UTR) in driving translation and competing against a capped RNA. Additionally, the TriMV 5= UTR can direct translation from an internal position of a bicistronic mRNA, and unlike cap-driven translation, it is unimpaired when the 5= end is blocked by a strong hairpin in a monocistronic reporter. However, the disruption of the identified stem structure eliminates such a translational advantage. Our results reveal a potent and uniquely controlled translation enhancer that may provide new insights into mechanisms of plant virus translational regulation. IMPORTANCEMany members of the Potyviridae family rely on their 5= end for translation. Here, we show that the 739-nucleotide-long triticum mosaic virus 5= leader bears a powerful translation element with features distinct from those described for other plant viruses. Despite the presence of 12 AUG start codons within the TriMV 5= UTR, translation initiates primarily at the 13th AUG codon. The TriMV 5= UTR is capable of driving cap-independent translation in vitro and in vivo, is independent of eIF4E, and can drive internal translation initiation. A hairpin structure at nucleotide positions 469 to 490 is required for the cap-independent translation and internal translation initiation abilities of the element and plays a role in the ability of the TriMV UTR to compete against a capped RNA in vitro. Our results reveal a novel translation enhancer that may provide new insights into the large diversity of plant virus translation mechanisms. T ranslation initiation of most eukaryotic mRNAs occurs by a scanning mechanism, where the 43S ribosomal subunit enters the mRNA from an accessible 5= end, is dependent on the 7-methyl guanosine cap structure (m7GpppG), and scans in a 5=-to-3= direction in search of the initiation codon (1). The ribosomal subunit is recruited to the 5= end by the cap-binding protein factor eIF4E, which is bound to the 5= cap. eIF4E is the small subunit and cap-binding protein in the eIF4F complex. eIF4F is also comprised of the RNA...

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Cap-dependent and cap-independent translation in eukaryotic systems

Cited by 220 publications

References 82 publications

Abrogating phosphorylation of eIF4B is required for EGFR and mTOR inhibitor synergy in triple-negative breast cancer

Abrogating phosphorylation of eIF4B is required for EGFR and mTOR inhibitor synergy in triple-negative breast cancer

The leader region of Laminin B1 mRNA confers cap-independent translation

A Unique 5′ Translation Element Discovered in Triticum Mosaic Virus

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