Relocalization of the Mre11-Rad50-Nbs1 Complex by the Adenovirus E4 ORF3 Protein Is Required for Viral Replication

Abstract

Adenovirus replication is controlled by the relocalization or modification of nuclear protein complexes, including promyelocytic leukemia protein (PML) nuclear domains and the Mre11-Rad50-Nbs1 (MRN) DNA damage machinery. In this study, we demonstrated that the E4 ORF3 protein effects the relocalization of both PML and MRN proteins to similar structures within the nucleus at early times after infection. These proteins colocalize with E4 ORF3. Through the analysis of specific viral mutants, we found a direct correlation between MRN reorganization at early times after infection and the establishment of viral DNA replication domains. Further, the reorganization of MRN components may be uncoupled from the ability of E4 ORF3 to rearrange PML. At later stages of infection, components of the MRN complex disperse within the nucleus, Nbs1 is found within viral replication centers, Rad50 remains localized with E4 ORF3, and Mre11 is degraded. The importance of viral regulation of the MRN complex is underscored by the complementation of E4 mutant viruses in cells that lack Mre11 or Nbs1 activity. These results illustrate the importance of nuclear organization in virus growth and suggest that E4 ORF3 regulates activities in both PML nuclear bodies and the MRN complex to stimulate the viral replication program.

Adenovirus 12 E4orf6 inhibits ATR activation by promoting TOPBP1 degradation

“…It has previously been reported that p53 and MRN are relocalized to cytoplasmic aggresomes and nuclear track-like structures during Ad5 infection by E1B-55K and E4orf3, before degradation by E1B-55K and E4orf6 (23,24). However, we did not observe either type of staining for TOPBP1 in Ad5-or Ad12-infected cells (Fig.…”

SUMOylation of HMGA2: selective destabilization of promyelocytic leukemia protein via proteasome

“…To prove the principle that HMGA2-promoted PML degradation is biologically relevant, we showed that this process can be stimulated by ATO treatment and that HMGA2 counteracts PMLmediated enhancement of GR transactivation. Besides stimulating GR function (13,42), PML nuclear bodies are reportedly involved in the cellular response to DNA damage (43). For example, components of the DNA damage sensor MRN complex are also reported to be colocalized with PML or PML nuclear bodies (43 -47).…”

Recent lessons in gene expression, cell cycle control, and cell biology from adenovirus

“…For E1B-55K mutants, viral DNA replication is normal in p53-minus cells (Harada and Berk, 1999) even though MRN subunits are not degraded. This is because E4orf3 and E4orf6 proteins also inhibit MRN function (Boyer J et al, 1999;Shepard and Ornelles, 2004;Evans and Hearing, 2005). In HeLa and KB cells, the defect in E1B-55K mutant late viral protein synthesis results from a defect in export of late viral mRNAs from the nucleus to the cytoplasm (Babiss et al, 1985;Pilder et al, 1986;Leppard and Shenk, 1989;O'Shea et al, 2004).…”

“…The results with E1B-55K in adenovirus-infected cells indicate that aggresome formation is a protective response that increases the rate of degradation of polyubiquitinated proteins. In infected cells, MRN first interacts with E4orf3 in PML nuclear domains of altered morphology (Carvalho et al, 1995;Doucas et al, 1996;Evans and Hearing, 2005). E1B-55K then interacts with MRN in these modified PML nuclear bodies.…”