PMID:19129452

Citation	Thomas, MA, Broughton, RS, Goodrum, FD and Ornelles, DA (2009) E4orf1 limits the oncolytic potential of the E1B-55K deletion mutant adenovirus. J. Virol. 83:2406-16
Abstract	Clinical trials have shown oncolytic adenoviruses to be tumor selective with minimal toxicity toward normal tissue. The virus ONYX-015, in which the gene encoding the early region 1B 55-kDa (E1B-55K) protein is deleted, has been most effective when used in combination with either chemotherapy or radiation therapy. Therefore, improving the oncolytic nature of tumor-selective adenoviruses remains an important objective for improving this form of cancer therapy. Cells infected during the G(1) phase of the cell cycle with the E1B-55K deletion mutant virus exhibit a reduced rate of viral late protein synthesis, produce fewer viral progeny, and are less efficiently killed than cells infected during the S phase. Here we demonstrate that the G(1) restriction imposed on the E1B-55K deletion mutant virus is due to the viral oncogene encoded by open reading frame 1 of early region 4 (E4orf1). E4orf1 has been reported to signal through the phosphatidylinositol 3'-kinase pathway leading to the activation of Akt, mTOR, and p70 S6K. Evidence presented here shows that E4orf1 may also induce the phosphorylation of Akt and p70 S6K in a manner that depends on Rac1 and its guanine nucleotide exchange factor Tiam1. Accordingly, agents that have been reported to disrupt the Tiam1-Rac1 interaction or to prevent phosphorylation of the ribosomal S6 kinase partially alleviated the E4orf1 restriction to late viral protein synthesis and enhanced tumor cell killing by the E1B-55K mutant virus. These results demonstrate that E4orf1 limits the oncolytic nature of a conditionally replicating adenovirus such as ONYX-015. The therapeutic value of similar oncolytic adenoviruses may be improved by abrogating E4orf1 function.
Links	PubMed PMC2648266 Online version:10.1128/JVI.01972-08
Keywords	Adenoviridae/genetics; Adenoviridae/growth & development; Gene Deletion; Guanine Nucleotide Exchange Factors/metabolism; HeLa Cells; Host-Pathogen Interactions; Humans; Oncogene Protein v-akt/metabolism; Oncogene Proteins, Viral/genetics; Oncogene Proteins, Viral/metabolism; Oncolytic Viruses/genetics; Oncolytic Viruses/growth & development; Phosphorylation; Ribosomal Protein S6 Kinases, 70-kDa/metabolism; rac1 GTP-Binding Protein/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
HUMAN:RAC1		GO:0060154: cellular process regulating host cell cycle in response to virus	ECO:0000315:		P		Figure 5C. Figure 5 shows that in cells infected with dl1520 and under cell conditions in which Rac1 can work normally(lane1) that Akt and p70 S6K are phosphorylated which areknow to be involved in the control of the cell cycle. When invected but Rac1 in knocked down (lane 2 and 3)by using a mutant Rac1 that is negative dominant, those proteins are not phosphorylated.Figure 6B. middle graph-Cells that were infected with dl1520 and treated with NSC23766 which stops Rac1 from functioning in its normal manner resulted in a major drop of viable cells suggesting its important in response to a virus affecting cell prolifeation. It is IMP because of their use of a dominant negative Rac1 mutant phenotype.	complete
HUMAN:RAC1		GO:0006468: protein phosphorylation	ECO:0000315:		P		Figure 5C. lane one shows dl1520 infection with normally working Rac1 in the cell and the phosphorylation of p70S6K and Akt. Lanes 2 and 3 show that when infected but dominant negative Rac1 is added that phosphorylation is not seen showing that in viral response Rac1 is involved in phosphorylation. It is IMP because the use dnRac1 phenotypically does not have normal function and in dominant not allowing the normal cellular Rac1 to function well.	complete
ADE05:Q2KRY6		GO:0048525: negative regulation of viral reproduction	ECO:0000315:		P		Figure 1. A-In the G1 phase, cells that were deleted for E1B and had E4orf1 had a large decrease in the amount of viral progeny within the cells compared to those that had E1B or were deleted for both E1B and E4orf1. Because more viral progeny were able to be made without both of than that if viruses only had E4orf1 it suggest that E4orf1 is restricting the ability to reproduce. The decreased PFU (figure1B) in the cells that had E4orf1 without E1B and E4orf2 suggest that is it E4orf1 that is negatively effecting the ability for viral replication (lanes 2 and 3). It is not seen in the presence of E1B which may stop the negative regulation ability of E4orf1, and when E4orf1 is gone, some viral reproduction ability recovers also suggests it is a negative regulator. It is IMP because of the use of mutated Adenovirus 5 that resulted in ultered phenotypes allowing comparison to determine the effects of specific proteins.	complete

References

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