Disruption of the circadian clock in lung cancer

Project Summary Disruption of the molecular circadian clock is indicative of poor prognosis in non-small cell lung cancers (NSCLCs), but direct evidence for a causal link between circadian clock deregulation and malignancy in human cancer is missing. We found that BMAL1 is downregulated in human NSCLCs, indicative of circadian disruption, low BMAL1 is an indicator of aggressive disease and poor prognosis. In addition, deletion of BMAL1 in a mouse model of NSCLC accelerates cancer progression. These data suggest that BMAL1, and by extension, circadian rhythms, exert a tumor-suppressive role in lung cancer. However, how BMAL1 restrains tumorigenesis and the mechanisms involved in suppression of BMAL1 remain unclear. A potential cause for BMAL1 suppression is the upregulation of MYC-family oncoproteins, which are amplified 50% of NSCLCs. We were the first to show that the molecular clock is disrupted by amplified MYC. In addition, our preliminary data suggest that, even in the presence of glucocorticoids, MYC suppresses BMAL1 expression in both NSCLC and normal lung epithelium, and thus disrupts circadian clock oscillation. To date, MYC amplification is the only identifiable cause of this circadian disruption in NSCLC. While CLOCK-BMAL1, and thus, oscillation of the molecular circadian clock, are necessary to maintain normal lung architecture and identity, we found that MYC activation led to loss of normal lung alveolar epithelial identity and induction of inappropriate proliferation. Notably, glucocorticoids have been shown to slow or halt the growth of some NSCLCs in preclinical and clinical studies, and our preliminary data suggest that glucocorticoids fail to suppress proliferation of lung cells when MYC is overexpressed. Taken together, we hypothesize that BMAL1 suppression and circadian disruption by MYC in NSCLC is critical for loss of alveolar cell identity, the emergence of malignancy, and resistance to glucocorticoids. To test this hypothesis, we propose two Aims. In our first Aim, we will interrogate the degree to which MYC suppression of BMAL1 and disruption of the clock drive loss of lung alveolar cell identity and malignant cell transformation. To test this, we will restore BMAL1 expression in MYC-amplified lung organoids, mouse models. As part of this Aim, we will test the hypothesis that MYC prevents BMAL1 from binding its typical DNA targets. We will also test the association between MYC, BMAL1, and malignancy in human tumor samples. This will for the first time demonstrate that MYC disruption of the clock is critical in driving the earliest stages of NSCLC development. In the second Aim, we will test the degree to which MYC and circadian disruption suppress NSCLC response to glucocorticoids. We will determine, using in vitro and in vivo models of NSCLC from mice and human patients, whether MYC overrides glucocorticoid-mediated growth suppression via suppression of BMAL1. We will also determine the mechanism by which MYC controls the glucocorticoid receptor and molecular clock response to glucocorticoids. Overall, these experiments will demonstrate that BMAL1 is a tumor suppressive protein in NSCLC that is disabled by MYC to drive malignancy.