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

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. The circadian clock coordinates daily cell physiology. There has been considerable interest in identifying mechanisms that link cell physiology to circadian time-keeping. NF-κB is a major network hub controlling innate immunity and inflammation. Chronic constitutive activation of NF-κB is one of the primary causes of a number of human diseases and conditions such as immune diseases, metabolic disorders, neurodegenerative diseases, cancer and aging. Here we investigated the role of NF-κB in regulating the central and peripheral circadian clocks. Using a combination of genetic and pharmacological approaches we show that NF-κB perturbation alters clock oscillations in cells and tissues, as well as in mice. Further, 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. Together, these results support a significant role for NF-kB in linking inflammation to circadian timekeeping.