Opposite Carcinogenic Effects of Circadian Clock Gene BMAL1

Abstract

The circadian clock confers daily rhythmicity on many biochemical and physiological functions and its disruption is associated with increased risks of developing obesity, diabetes, heart disease and cancer. Although, there are studies on the role of Bmal1 in carcinogenesis using germline, conditional or tissue-specific knockouts, it is still not well understood how BMAL1 gene affects cancer-related biological events at the molecular level. We, therefore, took an in vitro approach to understand the contribution of BMAL1 in this molecular mechanism using human breast epithelial cell lines by knocking out BMAL1 gene with CRISPR technology. We preferred epithelial cells over fibroblasts as the most of cancers originate from epithelial cells. After obtaining BMAL1 knockouts by targeting the gene at two different sites from non-tumorigenic MCF10A and invasive tumorigenic MDA-MB-231 cells, we analysed apoptosis and invasion properties of the cell lines as representative events in tumor development. BMAL1 disruption sensitized both cell lines to a bulky-DNA adduct forming agent (cisplatin) and a double-strand break-inducing agent (doxorubicin), while it enhanced the invasive properties of MDA-MB-231 cells. These results show that the disruption of clock genes may have opposing carcinogenic effects.

Extracellular Acidosis Promotes Metastatic Potency via Decrease of the BMAL1 Circadian Clock Gene in Breast Cancer

“…Since tumor hypoxia and acidosis are well-known to promote tumor metastasis in cancers including MDA-MB-231 cells, targeting the tumor hypoxia and acidosis is likely important in treating tumors [40][41][42][43]. Interestingly, the previous study reported that knocked-out BMAL1 promotes metastasis in MDA-MB-231 cells, and previously our results showed that BMAL1 was reduced by tumor hypoxia-induced acidosis and recovered by selectively targeting the acidic pH in breast cancer cells [19]. Based on these references and our results, we hypothesized that promoted metastasis under acidosis is caused by a decrease of BMAL1, and maintaining BMAL1 by buffering acidic pH is a therapeutic approach to prevent metastasis.…”

“…There has been extensive research to overcome breast cancer metastasis, but it has not been adequately solved. According to previous reports, circadian genes, which are significantly reduced in cancer, suppress tumor progression including metastasis [16][17][18][19]. For this reason, we wanted to find a way to recover the reduced circadian genes in cancer to increase the survival rate by preventing metastasis.…”

“…BMAL1, which is one of the most important circadian clock genes, regulates overall circadian oscillations in humans, and previous reports have suggested that reduced BMAL1 is closely associated with tumor progression in cancer cells [16][17][18]. In particular, knocked-out BMAL1 significantly promoted tumor metastasis in MDA-MB-231 breast cancer cells [19]. Although BMAL1 is known to inhibit tumor progression, the mechanism for decreasing BMAL1 in cancer is largely unknown.…”

The tumour suppressing role of the circadian clock

“…PER2 mutant cells harbour a functional circadian oscillator, whereas BMAL1 is the only gene whose deletion alone leads to complete loss of rhythmicity. In contrast to PER2 mutant cells, apoptosis is enhanced in BMAL1 mutant breast epithelial cells, in response to chemotherapeutic agents, Cisplatin and Doxorubicin . This suggests that interfering with BMAL1 expression and abolishing circadian rhythms might be protective against tumour initiation following DNA damage insults.…”

“…Studies have shown that inhibition of CRY1 , PER2 or BMAL1 results in enhanced cell migration or invasion via the Akt signalling pathway, in osteosarcoma ( CRY1 and PER2 ) and lung cancer and glioma cells ( BMAL1 ). In addition, BMAL1 knockout, resulting in loss of circadian rhythmicity, results in increased invasion of breast cancer cells . The EMT is a key step in cancer progression, and enables cancer cell invasion and metastasis.…”