HIPK2 restricts SIRT1 activity upon severe DNA damage by a phosphorylation-controlled mechanism

Area of Science:

• Cellular biology
• Molecular mechanisms of DNA damage response
• Tumor suppressor pathways

Background:

• Severe DNA damage activates tumor suppressor p53 and initiates cell death.
• Sirtuin 1 (SIRT1) deacetylase activity suppresses DNA damage-induced cell death by inhibiting p53 acetylation.
• Regulation of SIRT1 activity during DNA damage is crucial but not fully understood.

Purpose of the Study:

• To investigate the regulation of SIRT1 activity following severe DNA damage.
• To elucidate the role of HIPK2 in controlling SIRT1 function in response to DNA damage.

Main Methods:

• Co-immunoprecipitation to detect protein interactions.
• Western blotting to assess protein phosphorylation.
• Immunofluorescence microscopy to determine protein localization.
• PML depletion studies using siRNA.
• Analysis of p53 acetylation and target gene expression.

Main Results:

• DNA damage induces interaction between SIRT1 and HIPK2.
• HIPK2 phosphorylates SIRT1 at Serine 682 upon lethal DNA damage.
• SIRT1 and HIPK2 colocalize at PML nuclear bodies; PML depletion inhibits SIRT1 phosphorylation.
• Serine 682 phosphorylation inhibits SIRT1 deacetylase activity, affecting p53 acetylation and apoptosis.
• Phosphorylation disrupts the SIRT1-AROS activator complex.

Conclusions:

• HIPK2-mediated phosphorylation of SIRT1 at Serine 682 restricts SIRT1 activity upon severe DNA damage.
• This regulation is critical for modulating the p53-mediated apoptotic response.
• HIPK2 acts as a key regulator of SIRT1 in the DNA damage response pathway.