Leaky Scanning Is the Predominant Mechanism for Translation of Human Papillomavirus Type 16 E7 Oncoprotein from E6/E7 Bicistronic mRNA

Stacey, Simon; Jordan, Deborah; Williamson, Andrew J.K.; Brown, Michael D.; Coote, J.; Arrand, John R.

doi:10.1128/jvi.74.16.7284-7297.2000

Cited by 88 publications

(75 citation statements)

References 72 publications

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“…Different mechanisms that allow escape from an upstream initiator codon and direct initiation from internal codons have been described; these include context-dependent leaky-scanning (13,17,18,19,20,21), ribosome shunting (17,22,23,24,25,26,27), and IRES-mediated initiation (28). The internal initiation of ARFP/F/coreϩ1 translation in vivo might include features of one of these mechanisms.…”

Section: Discussionmentioning

confidence: 99%

Two Alternative Translation Mechanisms Are Responsible for the Expression of the HCV ARFP/F/Core+1 Coding Open Reading Frame

Vassilaki

Mavromara

2003

Journal of Biological Chemistry

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HCV-1 produces a novel protein, known as ARFP, F, or core؉1. This protein is encoded by an open reading frame (ORF) that overlaps the core gene in the ؉1 frame (core؉1 ORF). In vitro this protein is produced by a ribosomal frameshift mechanism. However, similar studies failed to detect the ARFP/F/core؉1 protein in the HCV-1a (H) isolate. To clarify this issue and to elucidate the functions of this protein, we examined the expression of the core؉1 ORF by the HCV-1 and HCV-1a (H) isolates in vivo, in transfected cells. For this purpose, we carried out luciferase (LUC) tagging experiments combined with site-directed mutagenesis studies. Our results showed that the core؉1-LUC chimeric protein was efficiently produced in vivo by both isolates. More importantly, neither changes in the specific 10-A residue region of HCV-1 (codons 8 -11), the proposed frameshift site for the production of the ARFP/F/core؉1 protein in vitro, nor the alteration of the ATG start site of the HCV polyprotein to a stop codon significantly affected the in vivo expression of the core؉1 ORF. Furthermore, we showed that efficient translation initiation of the core؉1 ORF is mediated by internal initiation codon(s) within the core/core؉1-coding sequence, located between nucleotides 583 and 606. Collectively, our data suggest the existence of an alternative translation initiation mechanism that may result in the synthesis of a shorter form of the core؉1 protein in transfected cells.

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Section: Discussionmentioning

confidence: 99%

Two Alternative Translation Mechanisms Are Responsible for the Expression of the HCV ARFP/F/Core+1 Coding Open Reading Frame

Vassilaki

Mavromara

2003

Journal of Biological Chemistry

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“…Controversial publications exist on the function of splicing and its effect on the efficiency of E7 translation. In vitro experiments favor the assumption that E7 can be only translated on E6* mRNA in a distance-dependent manner by reinitiation of translation (13,14). Moreover, modulation of splicing could so far only be linked to the autoregulatory functions of viral E6 and E2 themselves under in vitro conditions (15).…”

mentioning

confidence: 99%

Alternative splicing of human papillomavirus type-16 E6/E6* early mRNA is coupled to EGF signaling via Erk1/2 activation

Rosenberger

Arce

Langbein

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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Certain types of human papillomaviruses (HPVs) are etiologically linked to cervical cancer. Their transforming capacity is encoded by a polycistronic premRNA, where alternative splicing leads to the translation of functional distinct proteins such as E6, E6*, and E7. Here we show that splicing of HPV16 E6/E7 ORF cassette is regulated by the epidermal growth factor (EGF) pathway. The presence of EGF was coupled to preferential E6 expression, whereas depletion of EGF, or treatment with EGF receptor (EGFR) neutralizing antibodies or the EGFR inhibitor tyrphostin AG1478, resulted in E6 exon exclusion in favor of E6*. As a consequence, increased p53 levels and enhanced translation of E7 with a subsequent reduction of the retinoblastoma protein pRb could be discerned. E6 exon exclusion upon EGF depletion was independent from promoter usage, mRNA stability, or selective mRNA transport. Time-course experiments and incubation with cycloheximide demonstrated that E6 alternative splicing is a direct and reversible effect of EGF signal transduction, not depending on de novo protein synthesis. Within this process, Erk1/2-kinase activation was the critical event for E6 exon inclusion, mediated by the upstream MAP kinase MEK1/2. Moreover, siRNA knockdown experiments revealed an involvement of splicing factors hnRNPA1 and hnRNPA2 in E6 exon exclusion, whereas the splicing factors Brm and Sam68 were found to promote E6 exon inclusion. Because there is a natural gradient of EGF and EGF receptor expression in the stratified epithelium, it is reasonable to assume that EGF modulates E6/E7 splicing during the viral life cycle and transformation.P articular types of human papillomaviruses (HPVs) such as HPV16, 18, 31, and 33, respectively, are the etiological agents for the development of anogenital tumors. Their transforming potential is encoded by the viral oncoproteins E6 and E7, where among other functions, E6 labilizes p53 and prevents apoptosis, and E7 promotes cell cycle progression by degrading the retinoblastoma protein pRb (1). HPV gene transcription is regulated by two main promoters, the early p97 and the late p670 promoter (2). Activation of either promoter is regulated by differentiation, resulting in the synthesis of polycistronic mRNAs, which are further regulated by differential splicing (3, 4). For polycistronic mRNAs, it is known that only the first ORF is translated efficiently when intercistronic distances are short (5).Alternative splicing can be regulated dependent on the developmental stage or by extracellular stimuli, where an increasing number of pathways and splicing factors have been identified (6). For splicing reaction, the spliceosome recognizes exon-intron boundaries of the 5′-donor and 3′-acceptor splice site. Furthermore, specific sequence motifs within exons can positively or negatively influence the recognition of nearby splice sites (7). The activity of so-called exonic splicing enhancers or exonic splicing silencers can be modulated by splicing factors like SR proteins or hnRNPs, which in turn all...

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“…Because the small ribosomal subunit starts scanning at the 5Ј-terminal cap structure of the RNA and then migrates linearly in a 3Ј direction, translation usually starts at the AUG codon closest to the 5Ј end. In higher eukaryotes the AUG has to reside in a favorable sequence context; otherwise, at least some of the ribosomal subunits can pass by and initiate at an AUG further downstream (5,6), which can result in expression of different proteins from one mRNA (7,8).…”

mentioning

confidence: 99%

Translation of the Minor Capsid Protein of a Calicivirus Is Initiated by a Novel Termination-dependent Reinitiation Mechanism

Meyers¹

2003

Journal of Biological Chemistry

181

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Caliciviruses represent a family of positive strand RNA viruses responsible for a variety of syndromes in man and animals. VP10, a minor structural protein of the calicivirus rabbit hemorrhagic disease virus, is encoded in the small 3-terminal open reading frame (ORF) 2 and is translated with an efficiency of ϳ20% of the preceding ORF1. The presence of the ORF1 termination codon is crucial for VP10 expression. Translation of VP10 starts at an AUG codon located at positions ؊5 to ؊3 of the ORF1 termination codon. However, VP10 was also expressed in the absence of an AUG initiation codon. The majority of ORF1 could be deleted or replaced by different sequences without significant influence on VP10 expression as long as translation terminated at the given position. The RNA sequence of the 3-terminal 84 nucleotides of ORF1 but not the encoded peptide was found to be crucial for VP10 expression. In contrast, nearly the entire ORF2 could be replaced by a foreign sequence without abrogation of its translation. Accordingly, VP10 is expressed in a translation termination/reinitiation process that is particular because it is independent of an AUG translational start codon and requires the presence of a sequence element upstream of the initiation site.

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Leaky Scanning Is the Predominant Mechanism for Translation of Human Papillomavirus Type 16 E7 Oncoprotein from E6/E7 Bicistronic mRNA

Cited by 88 publications

References 72 publications

Two Alternative Translation Mechanisms Are Responsible for the Expression of the HCV ARFP/F/Core+1 Coding Open Reading Frame

Two Alternative Translation Mechanisms Are Responsible for the Expression of the HCV ARFP/F/Core+1 Coding Open Reading Frame

Alternative splicing of human papillomavirus type-16 E6/E6* early mRNA is coupled to EGF signaling via Erk1/2 activation

Translation of the Minor Capsid Protein of a Calicivirus Is Initiated by a Novel Termination-dependent Reinitiation Mechanism

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