NF-κB modifies the mammalian circadian clock through interaction with the core clock protein BMAL1

Area of Science:

• Chronobiology
• Molecular Biology
• Immunology

Background:

• Mammalian circadian clocks regulate physiological processes, including inflammation.
• The precise mechanisms by which inflammation influences the circadian clock remain largely unknown.
• Investigating the role of the proinflammatory transcription factor NF-κB in clock regulation is crucial.

Purpose of the Study:

• To elucidate the role of the NF-κB pathway, specifically the RELA subunit, in modulating circadian clock function.
• To understand how NF-κB interacts with core clock components at a molecular level.
• To explore the impact of NF-κB perturbation on circadian rhythms in cellular and in vivo models.

Main Methods:

• Utilized genetic and pharmacological approaches to perturb NF-κB (RELA) in human U2OS cells.
• Assessed alterations in core clock gene expression, period length, and amplitude.
• Investigated circadian rhythms in the suprachiasmatic nucleus (SCN) and locomotor activity in vivo.
• Performed biochemical and biophysical analyses to determine protein-protein interactions.
• Conducted chromatin immunoprecipitation (ChIP) assays to analyze protein binding to cis-elements.

Main Results:

• Perturbation of RELA in U2OS cells altered core clock gene expression, affecting period and amplitude.
• NF-κB activation shortened circadian period length and dampened amplitude, while inhibition lengthened it.
• Circadian rhythms in the SCN and locomotor activity were disrupted by NF-κB perturbation.
• RELA was found to repress BMAL1/CLOCK transcriptional activity by binding to the E-box element.
• RELA competes with CRY1 and CBP/p300 for binding to BMAL1, influencing circadian transcription.

Conclusions:

• NF-κB plays a significant role in directly regulating the mammalian circadian clock.
• RELA directly impacts circadian transcription by interacting with BMAL1/CLOCK at the E-box.
• These findings highlight a mutual regulatory relationship between the circadian and inflammatory pathways.
• The study provides a molecular mechanism for how inflammation can affect circadian timing.