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Adenovirus late-phase infection is controlled by a novel L4 promoter.

ABSTRACT: During human adenovirus 5 infection, a temporal cascade of gene expression leads ultimately to the production of large amounts of the proteins needed to construct progeny virions. However, the mechanism for the activation of the major late gene that encodes these viral structural proteins has not been well understood. We show here that two key positive regulators of the major late gene, L4-22K and L4-33K, previously thought to be expressed under the control of the major late promoter itself, initially are expressed from a novel promoter that is embedded within the major late gene and dedicated to their expression. This L4 promoter is required for late gene expression and is activated by a combination of viral protein activators produced during the infection, including E1A, E4 Orf3, and the intermediate-phase protein IVa2, and also by viral genome replication. This new understanding redraws the long-established view of how adenoviral gene expression patterns are controlled and offers new ways to manipulate that gene expression cascade for adenovirus vector applications.

SUBMITTER: Morris SJ

PROVIDER: S-EPMC2898241 | biostudies-literature | 2010 Jul

REPOSITORIES: biostudies-literature

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Adenovirus late-phase infection is controlled by a novel L4 promoter.

Morris Susan J SJ Scott Gillian E GE Leppard Keith N KN

Journal of virology 20100505 14

During human adenovirus 5 infection, a temporal cascade of gene expression leads ultimately to the production of large amounts of the proteins needed to construct progeny virions. However, the mechanism for the activation of the major late gene that encodes these viral structural proteins has not been well understood. We show here that two key positive regulators of the major late gene, L4-22K and L4-33K, previously thought to be expressed under the control of the major late promoter itself, ini ...[more]

PMID: 20444889

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Project description:Assembly of the adenovirus capsid protein hexon depends on the assistance of the molecular chaperone L4-100K. However, the chaperone mechanisms remain unclear. In this study, we found that L4-100K was involved in the hexon translation process and could prevent hexon degradation by the proteasome in cotransfected human cells. Two nonadjacent domains, 84-133 and 656-697, at the N-terminal and C-terminal regions of human adenovirus type 5 L4-100K, respectively, were found to be crucial and cooperatively responsible for hexon trimer expression and assembly. These two chaperone-related domains were conserved in the sequence of L4-100K and in the function of hexon assembly across different adenovirus serotypes. Different degrees of cross-activity of hexon trimerization with different serotypes were detected in subgroups B, C, and D, which were proven to be controlled by the interaction between the C-terminal chaperone-related domain of L4-100K and hypervariable regions (HVR) of hexon. Additionally, HVR-chimeric hexon mutants were successfully assembled with the assistance of the 1-697 mutant. Structural analysis of 656-697 by nuclear magnetic resonance and structural prediction of L4-100K using Robetta showed that the two conserved domains are mainly composed of α-helices and are located on the surface of the highly folded core region. Our research provides a more complete understanding of hexon assembly and guidance for the development of hexon-chimeric adenovirus vectors that will be safer, smarter, and more efficient. IMPORTANCE Adenovirus vectors have been widely used in clinical trials of vaccines and gene therapy, although some deficiencies remain. Chimeric modification of the hexon was expected to improve the potency of preexisting immune evasion and targeting, but in many cases, viral packaging is prevented by the inability of the chimeric hexon to assemble correctly. So far, few studies have examined the mechanisms of hexon trimer assembly. Here, we show how the chaperone protein L4-100K contributes to the assembly of the adenovirus capsid protein hexon, and these data will provide a guide for novel adenovirus vector design and development, as we desired.

Project description:Replicating viruses have broad applications in biomedicine, notably in cancer virotherapy and in the design of attenuated vaccines, however uncontrolled virus replication in vulnerable tissues can give pathology and often restricts the use of potent strains. Increased knowledge of tissue-selective microRNA expression now affords the possibility of engineering replicating viruses that are attenuated at the RNA level in sites of potential pathology, but retain wild type replication activity at sites not expressing the relevant microRNA. To assess the usefulness of this approach for the DNA virus, adenovirus, we have engineered a hepatocyte-safe wild type adenovirus 5 (Ad5), which normally mediates significant toxicity and is potentially lethal in mice. To do this we have included binding sites for hepatocyte-selective microRNA122a within the 3' UTR of the E1A transcription cassette. Imaging versions of these viruses, produced by fusing E1A with luciferase, showed that inclusion of microRNA122a binding sites caused up to 80 fold decreased hepatic expression of E1A following intravenous delivery to mice. Animals administered a ten-times lethal dose of wild type Ad5 (5 x 1010 viral particles/mouse) showed substantial hepatic genome replication and extensive liver pathology, while inclusion of 4 microRNA binding sites decreased replication 50-fold and virtually abrogated liver toxicity. This modified wild type virus retained full activity within cancer cells and provides a potent, liver-safe oncolytic virus. In addition to providing many potent new viruses for cancer virotherapy, microRNA-control of virus replication should provide a new strategy for designing safe attenuated vaccines applied across a broad range of viral diseases. four groups which we had were: WT: RNA extracted from livers of mice treated with wild type Ad5, 3 Replicates miR: RNA extracted from livers of mice treated with wild type Ad5 bearing mir122-binding sites in the 3'UTR of E1A (3 Replicates) Luc: RNA extracted from livers of mice treated with non-replicating Ad5 (3 Replicates) PBS: RNA extracted from livers of mice treated with PBS only (3 Replicates)

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Adenovirus late-phase infection is controlled by a novel L4 promoter.

Publications

Adenovirus late-phase infection is controlled by a novel L4 promoter.

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