Control of adenovirus major late gene expression at multiple levels

Larsson, Stefan; Svensson, Christina; Akusjärvi, Göran

doi:10.1016/0022-2836(92)90922-7

Cited by 37 publications

(34 citation statements)

References 46 publications

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“…The E1a 12s and L5 mRNA of Ad.TK RC could be readily detected suggesting viral DNA replication and late protein synthesis. 15,16 As expected, wild-type Ad5-infected cells expressed all three viral RNAs and in the Ad.TK-transduced cells none of the viral RNAs were detectable by RNA dot blot.…”

Section: Resultssupporting

confidence: 78%

Adenoviral vectors capable of replication improve the efficacy of HSVtk/GCV suicide gene therapy of cancer

et al. 1999

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A major obstacle to the success of gene therapy strategies with ME180 tumors. Treatment of tumors with Ad.TK RC that directly target cancer cells is the poor vector distriwithout GCV resulted in a similar antitumor effect, conbution within solid tumors. To address this problem, we firming that the replicating vector has an oncolytic effect. developed an E1b 55 kDa attenuated, replicationWhen GCV was initiated 3 days after Ad.TK RC injection, competent adenovirus (Ad.TK RC ) which expresses the hersurvival of mice with each tumor type was greatly propes simplex-1 thymidine kinase (HSVtk) gene to sensitize longed, with 60% of animals with ME180 tumors surviving tumors to ganciclovir (GCV). Efficacy of this combined for over 160 days. These results confirm that both the strategy was tested in nude mice with subcutaneous oncolysis caused by a replicating virus and suicide/prodrug human A375 melanoma and ME180 cervical carcinomas.gene therapy with HSVtk/GCV have potent antitumor Intratumoral injection of a replication-defective adenoviral effects. When combined, these two approaches are compvector expressing HSVtk (Ad.TK) followed by GCV treatlementary resulting in a significantly improved treatment ment resulted in doubling of the survival time of mice bearoutcome. ing A375 tumors and 20% long-term survival of mice

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Section: Resultssupporting

confidence: 78%

Adenoviral vectors capable of replication improve the efficacy of HSVtk/GCV suicide gene therapy of cancer

et al. 1999

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“…We propose that small amounts of L4 expression precipitate this switch in a feed-forward activation process. The timing of L4 expression during infection, early in the onset of full MLTU activity, supports this idea (24). Further work is now required to determine the detailed molecular mechanism involved.…”

Section: Discussionmentioning

confidence: 79%

“…Immediately following the onset of replication, L4 poly(A) site usage becomes as prominent as that of L1, significantly before L2, L3, and L5 poly(A) sites are used (24). This timing of L4 expression would fit with one or more of its products having a role in enhancing expression from the other MLTU subregions.…”

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confidence: 99%

Activation of the Early-Late Switch in Adenovirus Type 5 Major Late Transcription Unit Expression by L4 Gene Products

Farley

Brown

Leppard

2004

J Virol

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The adenovirus major late transcription unit (MLTU) encodes multiple proteins from five regions, L1 to L5, through differential splicing and polyadenylation. MLTU expression is temporally regulated; only a single product from L1 (52/55K) is expressed prior to replication, but a subsequent switch, the mechanism of which has not been defined, leads to full expression that encompasses L1 IIIa and all L2 to L5 products. Transfection of a plasmid containing the complete MLTU gave a full array of proteins in proportions similar to those in a late infection, and in a time course, the temporal pattern of expression in a natural infection was reproduced. However, a plasmid truncated after the L3 poly(A) site exclusively expressed the L1 52/55K protein and was defective in the switch to full gene expression from L1 to L3. The L4 33K protein, supplied in trans, was sufficient to upregulate cytoplasmic mRNA for MLTU products characteristic of the late pattern of expression to levels comparable to those produced by the full-length MLTU. There was a corresponding increase in expression of the L1 IIIa, L2, and L3 proteins, except hexon. Hexon protein expression additionally required both the L4 100K protein in trans and sequences downstream of the L3 poly(A) site in cis. These results indicate that induction of L4 protein expression is a key event in the early-late switch in MLTU expression, which we propose is precipitated by small amounts of L4 expression in a feed-forward activation mechanism.Human adenoviruses, especially group C viruses such as serotype 5 (Ad5), have been studied extensively; their tropism, gene expression, host cell interactions, and transforming capabilities are well characterized. Despite this knowledge, however, there remain important aspects of adenovirus biology that are not understood. One of these is the control of protein expression from the major late transcription unit (MLTU) during the infectious cycle.Upon Ad5 infection, a temporally phased program of gene expression occurs. The E1A gene products are produced immediately and upregulate transcription from all of the early regions: E1A, E1B, E2, E3, and E4. The MLTU, which encodes the majority of the virus structural proteins within five subregions, L1 to L5, is also active at a low level during this early phase, but transcription proceeds only as far as the L3 region and mRNA production is focused on the L1 52/55K reading frame (33). After replication, the major late promoter (MLP) becomes fully activated and transcription is allowed to proceed through the full length of the MLTU to supply the proteins for the packaging of newly replicated genomes into virions. The MLP is activated by the E1A 289R protein (32) and also by the intermediate-late protein IVa2 (28). However, unreplicated genomes from virus allowed to superinfect cells already in the late phase of infection, and hence containing these activators, continue to display the early pattern of MLTU expression until they themselves have begun to replicate (44). This indicates a role for a ...

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“…Thus, although nuclear transcription proceeds across at least the L1, L2 and L3 poly(A) sites at early times of infection, only mRNAs from the L1 region accumulate in the cytoplasm. We have further shown that at a transient stage following initiation of DNA replication mRNAs from both the L1 and L4 regions are expressed (7). The significance of this initial burst of L4 mRNA expression has previously not been understood.…”

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confidence: 71%

L4-33K, an Adenovirus-encoded Alternative RNA Splicing Factor

Törmänen¹,

Backström²,

Carlsson

et al. 2006

Journal of Biological Chemistry

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Splicing of the adenovirus IIIa mRNA is subjected to a strict temporal regulation during virus infection such that efficient IIIa 3 splice site usage is confined to the late phase of the infectious cycle. Here we show that the adenovirus L4-33K protein functions as a virus-encoded RNA splicing factor that preferentially activates splicing of transcripts with a weak 3 splice site sequence context, a sequence configuration that is shared by many of the late adenovirus 3 splice sites. Furthermore, we show that L4-33K activates IIIa splicing through the IIIa virus infection-dependent splicing enhancer element (3VDE). This element was previously shown to be the minimal element, both necessary and sufficient, for activation of IIIa splicing in the context of an adenovirus-infected cell. L4-33K stimulates an early step in spliceosome assembly and appears to be the only viral protein necessary to convert a nuclear extract prepared from uninfected HeLa cells to an extract with splicing properties very similar to a nuclear extract prepared from adenovirus lateinfected cells. Collectively, our results suggest that L4-33K is the key viral protein required to activate the early to late switch in adenovirus major late L1 alternative splicing.Most late adenovirus proteins are translated from mRNAs originating from the major late transcription unit (MLTU), 3 which extends from the major late promoter (MLP) at coordinate 16.8 to a termination signal close to the right-hand end of the genome (reviewed in Ref. 1). The ϳ28,000-nucleotide pre-mRNA expressed from the MLTU becomes polyadenylated at one of five possible sites, generating five families of mRNAs with co-terminal 3Ј-ends (L1-L5; Fig. 1A). Following selection of a poly(A) site, the primary transcript is spliced in such a way that each mature mRNA receives a common set of three short 5Ј-leader segments, the tripartite leader (Fig. 1A). This leader is then spliced to one of several alternative 3Ј splice sites, generating a total of more than 20 cytoplasmic mRNAs.The accumulation of mRNA from the MLTU is subjected to a temporal regulation at the levels of transcription elongation, poly(A) site choice and alternative 3Ј splice site selection (reviewed in Ref. 1). Thus, during the early phase of infection the MLP is active at a level comparable with the other early transcription units, whereas the same promoter accounts for most of the transcriptional activity at late times of infection (2, 3). However, at early times transcription initiated at the MLP decreases gradually over a large region beginning after the L1 unit, with few RNA polymerases extending beyond the L3 polyadenylation sequence (4). At late times, this block in elongation is alleviated and transcripts initiated at the MLP continue to the right hand end of the genome. The control of MLTU transcription is further regulated by events taking place at the level of poly(A) and alternative 3Ј splice site selection (2, 5, 6). Thus, although nuclear transcription proceeds across at least the L1, L2 and L3 poly(A) sites a...

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Control of adenovirus major late gene expression at multiple levels

Cited by 37 publications

References 46 publications

Adenoviral vectors capable of replication improve the efficacy of HSVtk/GCV suicide gene therapy of cancer

Adenoviral vectors capable of replication improve the efficacy of HSVtk/GCV suicide gene therapy of cancer

Activation of the Early-Late Switch in Adenovirus Type 5 Major Late Transcription Unit Expression by L4 Gene Products

L4-33K, an Adenovirus-encoded Alternative RNA Splicing Factor

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