Regulation of apoptosis by the circadian clock through NF-kappaB signaling

In mice and humans the circadian rhythm of many biochemical reactions, physiology, and behavior is generated by a transcriptional-translation feedback loop (TTFL) made up of the so-called core clock genes/proteins. The circadian system interfaces with most signaling pathways including those involved in cell proliferation and inflammation. Cryptochrome (CRY) is a core clock protein that plays an essential role in the repressive arm of the TTFL. It was recently reported that mutation of CRY in p53-null mice delayed the onset of cancer. It was therefore suggested that CRY mutation may activate p53-independent apoptosis pathways, which eliminate premalignant and malignant cells and thus delay overt tumor formation. Here we show that CRY mutation sensitizes p53 mutant and oncogenically transformed cells to tumor necrosis factor α (TNFα)-initiated apoptosis by interfacing with the NF-κB signaling pathway through the GSK3β kinase and alleviating prosurvival NF-κB signaling. These findings provide a mechanistic foundation for the delayed onset of tumorigenesis in clock-disrupted p53 mutant mice and suggest unique therapeutic strategies for treating cancers associated with p53 mutation.