Temporal regulation of the Mre11-Rad50-Nbs1 complex during adenovirus infection

Area of Science:

• Molecular Virology
• DNA Damage Response
• Cellular Biology

Background:

• Adenovirus infection elicits a cellular DNA damage response (DDR).
• This DDR can inhibit viral DNA replication and lead to viral genome concatenation.
• Adenovirus employs E4-ORF3 and E4-ORF6/E1B-55K proteins to counteract the DDR by targeting the Mre11-Rad50-Nbs1 (MRN) complex.

Purpose of the Study:

• To determine if input adenovirus DNA alone is sufficient to trigger the DDR.
• To investigate the timing and mechanisms of MRN complex inactivation by adenovirus E4 proteins.
• To elucidate the impact of DDR activation on viral DNA processing and genome integrity.

Main Methods:

• Analysis of MRN complex localization and degradation during adenovirus infection.
• Assessment of viral DNA replication and processing in the presence of functional or mutated E4 proteins.
• Sequencing of viral DNA concatemeric junctions to identify ligation mechanisms and genomic alterations.

Main Results:

• Input adenovirus DNA is sufficient to induce the DDR.
• The MRN complex is inactivated by E4-ORF3 (relocalization) or E4-ORF6/E1B-55K (degradation) before significant viral DNA replication occurs.
• DDR activation in E4 mutant infections prevents terminal protein cleavage and degradation of replication origins.
• Nonhomologous end joining mediates viral DNA ligation, resulting in concatemers with large deletions, indicating late-stage processing.

Conclusions:

• Adenovirus actively suppresses the host DDR early in infection using E4 proteins to target the MRN complex.
• Viral DNA concatenation and deletion are late events, occurring after the DDR is suppressed and viral DNA replication has initiated.
• The findings clarify the interplay between adenovirus and the host DDR machinery, highlighting viral strategies for replication and genome maintenance.