Phosphorylation regulates SIRT1 function.

Area of Science:

• Cellular Biology
• Biochemistry
• Aging Research

Background:

• Sirtuin 1 (SIRT1) is a key NAD(+)-dependent deacetylase involved in regulating lifespan across various species.
• SIRT1 levels correlate with mitotic activity, suggesting post-transcriptional regulation, but its post-translational modifications remain largely uncharacterized.

Purpose of the Study:

• To investigate the post-translational modifications of SIRT1, focusing on phosphorylation.
• To elucidate the role of SIRT1 phosphorylation in its enzymatic activity and cellular function.

Main Methods:

• Mass spectrometry was used to identify phosphorylated residues on SIRT1 in vivo.
• In vitro dephosphorylation assays were performed using phosphatases.
• CyclinB/Cdk1 kinase activity was assessed in relation to SIRT1 phosphorylation and complex formation.
• Mutagenesis of key phosphorylation sites (Thr530, Ser540) was performed.

Main Results:

• Thirteen residues in SIRT1 were identified as phosphorylated in vivo.
• Dephosphorylation reduced SIRT1's NAD(+)-dependent deacetylase activity.
• CyclinB/Cdk1 was identified as a kinase that phosphorylates SIRT1, forming a complex with it.
• Mutations at Thr530 and Ser540 impaired cell cycle progression and SIRT1 function in deficient cells.

Conclusions:

• Phosphorylation by cell cycle-dependent kinases is a major regulatory mechanism for SIRT1 activity and levels.
• Understanding SIRT1 regulation is vital for human health, particularly concerning aging, type 2 diabetes, and metabolic syndrome.
• These findings complement known protein-protein interactions that modulate SIRT1 activity.