Overexpression of the ADP (E3-11.6K) Protein Increases Cell Lysis and Spread of Adenovirus

Abstract

Adenoviruses replicate in the nucleus and induce lytic cell death. We have shown previously that efficient cell lysis and release of adenovirus from infected cells requires an 11.6-kDa protein named Adenovirus Death Protein (ADP). The adp gene is located in the early E3 transcription unit, but the gene is expressed primarily at very late stages of infection. The putative function of ADP was discerned previously from the use of virus mutants that lack functional ADP. Here we describe two adenovirus mutants, named VRX-006 and VRX-007, that overexpress ADP. VRX-006 lacks all other genes in the E3 region, and VRX-007 lacks all other E3 genes except 12.5K. VRX-006 and VRX-007 display the phenotype predicted by the proposed function for ADP: they produce early cytopathic effect, early cell lysis, large plaques, and increased cell-to-cell spread. They grow as well in cultured cells as does adenovirus type 5. These results are consistent with the conclusion that ADP functions in adenovirus infections to promote virus release from cells at the culmination of infection.

Inefficient killing of quiescent human epithelial cells by replicating adenoviruses: potential implications for their use as oncolytic agents

“…ADP is expressed at low levels at early times in the lytic cycle, but synthesized in large amounts from mRNAs derived from the major late promoter. 17,18 Therefore, a reduction in MLP activity as indicated by a reduction in hexon mRNA and protein expression could also affect killing of infected cells, thus leading to greater attenuation in quiescent cells. Additional studies are needed to understand the mechanism that leads to reduced late gene expression in quiescent cells.…”

Anticancer activity of oncolytic adenovirus vector armed with IFN-α and ADP is enhanced by pharmacologically controlled expression of TRAIL

“…Figure 1a) is an oncolytic Ad vector that replicates selectively in cancer cells due to the dl1101/1107 mutation in the e1a gene which abolishes binding of E1A proteins to cellular p300/CBP and pRb, and it has improved virus release and spread due to overexpression of ADP. 6,31 The KD3-IFN vector ( Figure 1a) is a derivative of KD3, which expresses human IFN-a late in infection, and it has superior anticancer activity in vivo relative to KD3. 5 In addition, the combination of the dl1101/1107 mutation and IFN-a expression resulted in reduced hepatotoxicity of KD3-IFN in mice as compared to KD3.…”

“…RC Ad vectors support replication of coinfected RD Ad leading to amplification of transgene expression from the RD vector. 6,20,22,23,31,42 rtTA, used in the TetON system, is known to have some affinity for TetO sequences within the TRE in the absence of Dox, leading to low basal expression of the transgene in the absence of inducer. 19,43 Together, the presence of the helper virus plus Dox mediated up to 231-fold activation of SEAP expression from the TetON-SEAP vector.…”

“…6,31 We studied the effect of TRAIL-induced apoptosis on the release of KD3 from Hep3B cells infected with KD3 and TetON-TRAIL. The extracellular titers of KD3 from TetON-TRAIL coinfected cells were increased as compared to those from TetON-EGFP coinfected cells at early time points but not at a late time point.…”

“…It has been reported previously that oncolytic Ad supports the replication of RD Ad when two viruses coinfect the cell. 6,20,31,34,35 We have previously demonstrated that each coinfected A549 cell produced 300 infectious units of RD Ad-bgal vector upon coinfection with RC KD3 vector. 6 Trans-complementation allows for amplification of transgene expression from a non-replicative virus.…”