VRK1 Phosphorylates Tip60/KAT5 and Is Required for H4K16 Acetylation in Response to DNA Damage

Area of Science:

• Epigenetics and Chromatin Biology
• DNA Damage Response
• Cellular Signaling

Background:

• Dynamic chromatin remodeling relies on histone acetylation and methylation, involving coordinated enzyme activity.
• DNA damage triggers histone H4K16 acetylation (H4K16ac), a marker of chromatin relaxation, in G0/G1 phase cells.
• The role of VRK1 (Vaccinia-related kinase 1), a DNA damage-activated chromatin kinase, in this process was unclear.

Purpose of the Study:

• To investigate the role of VRK1 in the early steps of DNA damage response, specifically focusing on histone acetylation.
• To elucidate the mechanism by which VRK1 influences H4K16ac and ATM activation following DNA damage.

Main Methods:

• VRK1 depletion and inhibition of Tip60/KAT5 (using MG149) to assess H4K16ac levels.
• Analysis of Tip60 phosphorylation in chromatin fractions after doxorubicin-induced DNA damage.
• Investigating VRK1-Tip60 interaction and VRK1's effect on Tip60 phosphorylation in ATM-proficient and deficient cells.
• Assessing the impact of kinase-active vs. kinase-dead VRK1 on Tip60 phosphorylation and ATM activation.

Main Results:

• VRK1 depletion or Tip60/KAT5 inhibition led to a loss of H4K16ac.
• DNA damage induced Tip60 phosphorylation by VRK1 within the chromatin fraction; VRK1 directly interacts with and phosphorylates Tip60.
• VRK1-mediated Tip60 phosphorylation was necessary for ATM activation and subsequent autophosphorylation, independent of ATM status.
• Kinase-active VRK1, but not kinase-dead VRK1, rescued DNA damage-induced Tip60 phosphorylation.

Conclusions:

• VRK1 acts as an upstream regulator of histone acetylation in response to DNA damage.
• VRK1-mediated Tip60 phosphorylation is a critical early event in the DNA damage response pathway.
• This pathway involving VRK1 and Tip60 is essential for initiating ATM signaling following DNA damage.