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

Abstract

In mice and humans the circadian rhythm of many biochemical reactions, physiology, and behavior is generated by a transcriptionaltranslation 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. hepatocellular carcinoma | inflammatory cytokine | extrinsic apoptotic pathway T he circadian rhythm in mammalian organisms is generated by a molecular clock comprising four gene/protein groups (1-5): The CLOCK (NPAS2) and BMAL1 transactivators and the cryptochrome 1 and 2 (CRY1/2) and the period 1 and 2 (PER1/ 2) repressors. CLOCK (or NPAS2) and BMAL1 make heterodimers, which act on the promoters of CRY1/2 and PER1/2 and activate their transcription. The CRY and PER proteins in turn, after a time delay of ill-defined mechanism, inhibit the CLOCK-BMAL1 transactivator and hence their own transcription to close the TTFL. This core TTFL directly or indirectly affects most cellular functions, and as a result, clock disruption by core clock gene mutation is expected to have serious repercussions at the cellular and organismal levels.We recently reported that mice of the p53 −/− Cry1 −/− Cry −/− (hereafter p53 KO Cry DKO ) genotype exhibited delayed onset of spontaneous cancer relative to p53 −/− (p53 KO ) mice (6). When analyzed for their response to genotoxic stress, it was found that p53 KO Cry DKO cells were more sensitive to UV-induced apoptosis than p53 KO cells even though they are identical in terms of DNA repair and DNA damage checkpoint functions (6). Therefore, we ascribed the reduced clonogenic survival of p53 KO Cry DKO cells upon UV irradiation, relative to p53 KO cells, to enhanced p53-independent apoptosis as a consequence of CRY mutation. We also suggested that the delayed onset of cancer and prolonged lifespan of mice of p53 KO Cry DKO genotype may have been caused by enhanced apoptosis of oncogenically transformed cells before giving rise to macroscopic tumors (6). In line with these findings we recently determined that p53 KO Cry DKO tumors are more responsive to oxaliplatin than p53 KO tumors (7). However, UV and oxaliplatin...

Core circadian protein CLOCK is a positive regulator of NF-κB–mediated transcription

“…Although this hypothesis has yet to be tested, it is supported by the timing of the effect of CLOCK on the NF-κB response, by BMAL1-dependent repression of CLOCK modulation of the NF-κB response, and by several reports showing less nuclear CLOCK at times of higher CLOCK/BMAL1-dependent transcriptional activation of circadian promoters (17,32,33). Although at this time it cannot be concluded that the previously observed impairment of NF-κB activation in the absence of CRYs occurs through the mechanism that we have described, the reversal of this phenotype by the down-regulation of BMAL1 (27) and the demonstration of the formation of a ternary complex involving CLOCK, BMAL1, and CRY1 (34) are consistent with our hypothetical model.…”

“…CRY1 represses CLOCK/BMAL1-dependent transactivation on the Per1 promoter but has no effect on CLOCK-dependent up-regulation of the κB promoter in response to TNF-α. clock, increases susceptibility of cells to TNF-α-induced apoptosis resulting from impaired activation of NF-κB (27). However, the exact molecular mechanisms underlying cross-talk between circadian and NF-κB pathways have not been understood.…”

Circadian clock regulates the host response to Salmonella

“…Conversely, the circadian system dictates the right timing for the host response to infection by regulating components of the immune system both at the level of individual cells and at the systemic level, through autonomic and endocrine outputs (18). The circadian system modulates the activity of several transcription factors that are important regulators of immune functions, including HIF1-α, STAT1, STAT3, and NF-κB (38)(39)(40). We were able to confirm that these factors, together with many more, create the main transcriptional regulatory networks during infection in our genomic profiling analysis.…”

A Circadian Clock Transcription Model for the Personalization of Cancer Chronotherapy

“…Indeed the delivery of medications according to circadian timing could shift the current cancer treatment paradigm from "the worse the toxicity, the better the efficacy" toward "the better the tolerability, the better the efficacy" (1,6,8). Chronotherapy effects resulted from the rhythmic control of drug absorption, transport, metabolism, detoxification, drug targets, cell cycle, and apoptosis by circadian clocks (1,(9)(10)(11)(12)(13)(14)(15)(16). Indeed, a molecular clock ticks within most body cells through 3 main interwoven transcriptional/posttranslational feedback loops.…”