Biphasic Functional Interaction between the Adenovirus E4orf4 Protein and DNA-PK.

Area of Science:

• Molecular Virology
• DNA Damage Response (DDR)
• Cancer Biology

Background:

• DNA viruses inhibit the cellular DNA damage response (DDR) as an antiviral strategy.
• Adenovirus (Ad) E4orf4 protein inhibits ATM and ATR signaling, impairing DNA repair and sensitizing cancer cells to DNA-damaging drugs.
• The precise mechanism of E4orf4-mediated DDR inhibition and its role in viral replication and cancer cell selectivity remain incompletely understood.

Purpose of the Study:

• To investigate the direct interaction between Ad E4orf4 protein and the DDR.
• To elucidate the functional relationship between E4orf4 and DNA-dependent protein kinase (DNA-PK).
• To determine the role of the E4orf4-DNA-PK interaction in Ad replication and E4orf4-induced cancer cell death.

Main Methods:

• Co-immunoprecipitation assays to demonstrate physical association between E4orf4 and DNA-PK.
• Functional assays measuring DNA-PK autophosphorylation and DDR signaling inhibition.
• Confocal microscopy to assess colocalization of DNA-PK with Ad replication centers.
• Treatment with DNA-PK inhibitors at different stages of infection.

Main Results:

• E4orf4 physically associates with DNA-PK, exhibiting a biphasic interaction pattern.
• Early in infection, E4orf4 requires DNA-PK activity to inhibit ATM/ATR; later, E4orf4 inhibits DNA-PK itself.
• DNA-PK colocalizes with early Ad replication centers and dissociates from late centers, with delayed DNA-PK inhibition enhancing viral replication.
• E4orf4 recruitment to DNA damage sites is DNA-PK dependent, and DNA-PK inhibition reduces E4orf4-induced cancer cell death.

Conclusions:

• The E4orf4-DNA-PK interaction is a novel mechanism for Ad-mediated DDR inhibition.
• This biphasic interaction regulates viral replication efficiency and contributes to the cancer-selective cytotoxicity of E4orf4.
• Targeting the E4orf4-DNA-PK interaction could be a strategy for antiviral therapy or cancer treatment.