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

Yang Shen,Andrew R Morris,Mehari Endale,Carrie L Partch,John B Hogenesch,David W Hammers,Andrew C Liu,Wei Wang,Zhao-Hui Wu,Lauren J Francey,Rachel L Harold,Zhiguang Huo,Achim Kramer

doi:10.1371/journal.pgen.1009933

Abstract

In mammals, the circadian clock coordinates cell physiological processes including inflammation. Recent studies suggested a crosstalk between these two pathways. However, the mechanism of how inflammation affects the clock is not well understood. Here, we investigated the role of the proinflammatory transcription factor NF-κB in regulating clock function. Using a combination of genetic and pharmacological approaches, we show that perturbation of the canonical NF-κB subunit RELA in the human U2OS cellular model altered core clock gene expression. While RELA activation shortened period length and dampened amplitude, its inhibition lengthened period length and caused amplitude phenotypes. NF-κB perturbation also altered circadian rhythms in the master suprachiasmatic nucleus (SCN) clock and locomotor activity behavior under different light/dark conditions. We show that RELA, like the clock repressor CRY1, repressed the transcriptional activity of BMAL1/CLOCK at the circadian E-box cis-element. Biochemical and biophysical analysis showed that RELA binds to the transactivation domain of BMAL1. These data support a model in which NF-kB competes with CRY1 and coactivator CBP/p300 for BMAL1 binding to affect circadian transcription. This is further supported by chromatin immunoprecipitation analysis showing that binding of RELA, BMAL1 and CLOCK converges on the E-boxes of clock genes. Taken together, these data support a significant role for NF-κB in directly regulating the circadian clock and highlight mutual regulation between the circadian and inflammatory pathways.

Highlights

Endogenous circadian clocks allow organisms to coordinate behavior, physiology and metabolism to align with the external light-dark cycle [1]
We investigated the role of NF-κB in regulating the central and peripheral circadian clocks
Using biochemical and biophysical methods, we show that NF-kB directly binds to the transactivation domain of BMAL1 where clock coregulators CBP/p300 and CRY bind; and as a result, like CRY, NF-kB represses E-box transcription

Summary

Introduction

Endogenous circadian clocks allow organisms to coordinate behavior, physiology and metabolism to align with the external light-dark cycle [1]. The SCN receives photic inputs and relays the light/dark information to peripheral tissues via neural and endocrine signals. In this manner, the SCN coordinates the peripheral oscillators into a coherent timing system [3]. The circadian clock regulates physiological functions in various tissues in mammals, including the immune and inflammatory responses [4,5,6]. Given the physiological importance of circadian timing, it is not surprising that its disruption is associated with a variety of pathological conditions and disease states, including neurodegenerative disorders, metabolic disorders, cardiovascular diseases, cancer, and aging [7,8,9]

Results

Discussion

Conclusion