Inhibition of transcriptional activity of c-JUN by SIRT1

Area of Science:

• Molecular Biology
• Epigenetics
• Gene Regulation

Background:

• c-JUN is a key transcription factor (Activator Protein-1, AP-1) regulating cell proliferation, inflammation, and stress responses.
• Sirtuin 1 (SIRT1), a histone deacetylase, influences gene transcription via chromatin modification, but its role in c-JUN regulation was unclear.

Purpose of the Study:

• To investigate whether SIRT1 regulates c-JUN activity in controlling gene transcription.
• To elucidate the mechanism by which SIRT1 affects AP-1 transcriptional activity.

Main Methods:

• Co-immunoprecipitation to detect SIRT1-c-JUN association.
• Mammalian two-hybrid system to assess transcriptional activity.
• Chromatin immunoprecipitation (ChIP) assay to analyze SIRT1 binding and histone acetylation at the MMP9 promoter.
• Gene expression analysis (mRNA and protein levels) of MMP9.
• Experiments using SIRT1-deficient mouse embryonic fibroblasts (MEFs).

Main Results:

• SIRT1 directly associates with c-JUN and inhibits its transcriptional activity.
• SIRT1 binds to the AP-1 response element in the MMP9 promoter, reducing histone 3 acetylation.
• SIRT1 activation (Resveratrol) induced its binding and inhibited MMP9 expression, while AP-1 activation (PMA) reduced SIRT1 binding.
• MMP9 expression was elevated in SIRT1-deficient MEFs, and Resveratrol's inhibitory effect was diminished.
• SIRT1 inhibits glucose-induced MMP9 expression, particularly in response to Resveratrol.

Conclusions:

• SIRT1 directly inhibits the transcriptional activity of AP-1 by targeting c-JUN.
• This mechanism involves SIRT1 binding to the MMP9 promoter, reducing histone acetylation and subsequent gene expression.
• SIRT1 plays a critical role in regulating MMP9 expression, with implications for cellular responses to stress and inflammation.