Adenovirus E1B55K Region Is Required To Enhance Cyclin E Expression for Efficient Viral DNA Replication

Abstract

Adenoviruses (Ads) with E1B55K mutations can selectively replicate in and destroy cancer cells. However, the mechanism of Ad-selective replication in tumor cells is not well characterized. We have shown previously that expression of several cell cycle-regulating genes is markedly affected by the Ad E1b gene in WI-38 human lung fibroblast cells (X. Rao, et al., Virology 350:418-428, 2006). In the current study, we show that the Ad E1B55K region is required to enhance cyclin E expression and that the failure to induce cyclin E overexpression due to E1B55K mutations prevents viral DNA from undergoing efficient replication in WI-38 cells, especially when the cells are arrested in the G 0 phase of the cell cycle by serum starvation. In contrast, cyclin E induction is less dependent on the function encoded in the E1B55K region in A549 and other cancer cells that are permissive for replication of E1B55K-mutated viruses, whether the cells are in the S phase or G 0 phase. The small interfering RNA that specifically inhibits cyclin E expression partially decreased viral replication. Our study provides evidence suggesting that E1B55K may be involved in cell cycle regulation that is important for efficient viral DNA replication and that cyclin E overexpression in cancer cells may be associated with the oncolytic replication of E1B55K-mutated viruses.

Indole-3-carbinol (I3C) increases apoptosis, represses growth of cancer cells, and enhances adenovirus-mediated oncolysis

“…We previously have reported that Ad E1B55K protein is involved in the induction of cell cycle-related genes, including cyclin E. 24 E1B55K-deleted Ads fail to induce cyclin E expression in normal cells and therefore their replication is restricted. 25 However, E1b55K-deleted oncolytic Ads can still efficiently induce cyclin E in cancer cells with dysregulated cyclin E and carry out sufficient oncolytic replication. 25,26 In this study, we observed that expression of cyclin E was downregulated in response to the treatment with I3C.…”

“…25 However, E1b55K-deleted oncolytic Ads can still efficiently induce cyclin E in cancer cells with dysregulated cyclin E and carry out sufficient oncolytic replication. 25,26 In this study, we observed that expression of cyclin E was downregulated in response to the treatment with I3C. As a consequence of repression of cyclin E induction, pretreatment with I3C repressed replication of Ads up to 10-fold (Fig.…”

“…Our previous studies have shown that Ad infection induces cyclin E expression 24,25 that activates CDK2 for efficient viral replication. 26 As cyclin E and CDK2 play an important role in Ad replication, inhibition of cyclin E and CDK2 by I3C treatment may affect Ad oncolytic replication.…”

Adenovirus with DNA Packaging Gene Mutations Increased Virus Release

“…Using these conditions, 213 µW/cm 2 UV type-C was produced, generating a total UV dose of 639 J/m 2 after 5 min exposure. Irradiated viruses were then used to infect Saos-2 cancer cells, in which Ads cannot replicate as well as in HEK293 and A549 cells [20]. Four hours (h) after infection, virus particles in the medium were removed by washing the cells with fresh media.…”

Homologous recombination-based adenovirus vector system for tumor cell-specific gene delivery

“…7 Other efforts that introduce mutation into E1A and/or E1B genes can improve the specificity of viral propagation in tumor cells, but often lead to decreased efficiency of viral replication. [8][9][10] An alternative strategy for tumor-selective adenoviral replication is to delete the Ad E1A and/or E1B, which are dispensable in tumor cells. 11,12 E1A and E1B are the immediate-early viral genes, and the expression of E1A and E1B can act as the main transactivator of other viral promoters, force quiescent cells into Cancer gene therapy requires tumor-specific delivery and expression of a transgene to maximize antitumor efficacy and minimize side effects.…”