DNA damage response signaling triggers nuclear localization of the chicken anemia virus protein Apoptin

Area of Science:

• Virology
• Molecular Biology
• Cell Biology

Background:

• Chicken anemia virus (CAV) protein Apoptin induces apoptosis and cell cycle arrest specifically in cancer cells, independent of p53.
• Apoptin's pro-apoptotic activity is regulated by its cellular localization, being nuclear in cancer cells and cytoplasmic in normal cells.

Purpose of the Study:

• To elucidate the role of DNA damage response (DDR) signaling in Apoptin's localization and pro-apoptotic activity.
• To investigate the mechanism by which Apoptin interacts with DDR components and affects DNA damage signaling.

Main Methods:

• Utilized primary and transformed cells expressing Apoptin.
• Manipulated DNA damage response signaling using chemical inhibitors (ATM, DNA-PK) and RNA interference (RNAi).
• Assessed Apoptin localization via microscopy and its effect on DNA damage foci (53BP1, MDC1) and apoptosis.

Main Results:

• DNA damage response (DDR) signaling is essential for Apoptin's nuclear localization in primary cells, enabling apoptosis induction.
• Inhibition of DDR signaling (ATM, DNA-PK) caused Apoptin to remain cytoplasmic in transformed cells.
• Apoptin's nucleocytoplasmic shuttling is critical for DDR-induced localization changes.
• Nuclear Apoptin inhibited DNA damage foci formation by targeting MDC1 for degradation, suggesting APC/C involvement.

Conclusions:

• DNA damage response signaling dictates Apoptin's cellular localization and its ability to induce apoptosis.
• Apoptin interferes with DNA damage response pathways, potentially through targeting MDC1 and affecting the APC/C.
• These findings suggest a novel viral mechanism for inhibiting host DNA damage response.