Alterations of symbiosis between microbiota and intestinal epithelial cells (IEC) are associated with intestinal and systemic pathologies. Interactions between bacterial products (MAMPs) and Toll-like receptors (TLRs) are known to be mandatory for IEC homeostasis, but how TLRs may time homeostatic functions with circadian changes is unknown. Our functional and molecular dissections of the IEC circadian clock demonstrate that its integrity is required for microbiota-IEC dialog. In IEC, the antiphasic expression of the RORα activator and RevErbα repressor clock output regulators generates a circadian rhythmic TLR expression that converts the temporally arrhythmic microbiota signaling into circadian rhythmic JNK and IKKβ activities, which prevents RevErbα activation by PPARα that would disrupt the circadian clock. Moreover, through activation of AP1 and NF-κB, these activities, together with RORα and RevErbα, enable timing homeostatic functions of numerous genes with IEC circadian events. Interestingly, microbiota signaling deficiencies induce a prediabetic syndrome due to ileal corticosterone overproduction consequent to clock disruption.

The glucocorticoid (GC) receptor (GR), when liganded to GC, activates transcription through direct binding to simple (+)GRE DNA binding sequences (DBS). GC-induced direct repression via GR binding to complex "negative" GREs (nGREs) has been reported. However, GR-mediated transrepression was generally ascribed to indirect "tethered" interaction with other DNA-bound factors. We report that GC-induces direct transrepression via the binding of GR to simple DBS (IR nGREs) unrelated to (+)GRE. These DBS act on agonist-liganded GR, promoting the assembly of cis-acting GR-SMRT/NCoR repressing complexes. IR nGREs are present in over 1000 mouse/human ortholog genes, which are repressed by GC in vivo. Thus variations in the levels of a single ligand can coordinately turn genes on or off depending in their response element DBS, allowing an additional level of regulation in GR signaling. This mechanism suits GR signaling remarkably well, given that adrenal secretion of GC fluctuates in a circadian and stress-related fashion.