Transcriptional integration of TLR2 and TLR4 signaling at the NCoR derepression checkpoint

Area of Science:

• Immunology
• Molecular Biology
• Cell Signaling

Background:

• Toll-like receptors (TLRs) are crucial for innate and acquired immunity, initiating inflammatory responses.
• Activation of inflammatory genes requires the removal of the nuclear receptor corepressor NCoR from target promoters.
• The precise mechanisms governing NCoR turnover remain incompletely understood.

Purpose of the Study:

• To elucidate the distinct molecular mechanisms by which TLR4 and TLR2 signaling pathways mediate NCoR clearance.
• To investigate the integration of TLR, calcium, and nuclear receptor signaling in regulating inflammatory gene expression.

Main Methods:

• Investigated TLR4 signaling using NFkappaB to recruit IKKepsilon to promoters with integrated kappaB and AP-1 sites.
• Examined TLR2 signaling involving CaMKII activation and phosphorylation of the NCoR complex component TBLR1.
• Assessed the sensitivity of these NCoR clearance pathways to transrepression by liver X receptors.

Main Results:

• TLR4 signaling induces c-Jun phosphorylation via IKKepsilon, facilitating NCoR clearance at promoters with integrated kappaB elements.
• TLR2 signaling activates CaMKII, leading to TBLR1 phosphorylation and NCoR clearance, independent of c-Jun phosphorylation.
• The IKKepsilon-dependent pathway is sensitive to liver X receptor transrepression, while the CaMKII-dependent pathway is not.

Conclusions:

• Reveals distinct, signal-dependent mechanisms for NCoR clearance utilized by TLR4 and TLR2.
• Highlights the integration of TLR, calcium, and nuclear receptor signaling in pathogen-specific inflammatory responses.
• Provides insights into disease-specific inflammatory programs regulated by these signaling networks.