ONCOGENIC MYC DISRUPTS THE MOLECULAR CLOCK AND METABOLISM IN CANCER CELLS AND DROSOPHILA

MYC;Circadain rhythm;Cancer;Drosophila;Cell Biology

Hsieh, Annie LeeIsaacs, John T. ;

Johns Hopkins University

关键词: MYC;    Circadain rhythm;    Cancer;    Drosophila;    Cell Biology;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/40720/HSIEH-DISSERTATION-2016.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Circadian rhythm is a biological rhythm with a period about 24 hours, which coordinates the organismal biological processes with environmental day and night cycle. This 24-hour rhythm is exhibited in every cell in the organism and is generated by the molecular clock circuitry that comprises transcriptional and translational feedback loops. While loss of circadian rhythm or alteration of clock gene expression is broadly observed in human cancers, the molecular basis underlying these perturbations and their functional implications are poorly understood. MYC oncogene is amplified in more than half of the human cancers. Its encoded protein, MYC, is a transcription factor that binds to the E-box sequence (5’-CACGTG-3’), which is the identical binding site of the master circadian transcription factor CLOCK::BMAL1.Thereby we hypothesized that deregulated circadian rhythm in cancer cells is a consequence of perturbation of E-box-containing clock genes by ectopically overexpressed MYC. In this thesis, we provide evidence that MYC or N-MYC activation alters expression of E-box-containing clock genes including PER1, PER2, REV-ERB, REV-ERB and CRY1 in cell lines derived from human Burkitts lymphoma, human osteosarcoma, mouse hepatocellular carcinoma and human neuroblastoma. MYC activation also significantly suppress the expression and oscillation of the circadian transcription factor BMAL1. Although public available MYC ChIP-seq data suggest that MYC directly binds to the promoter of PER1, PER2, REV-ERB, REV-ERB and CRY1 in U2OS cells, only silencing of REV-ERB and REV-ERB is able to rescue BMAL1 suppression by MYC. Strikingly, in two independent patient cohorts, high REV-ERB and low BMAL1 expression are associated with more aggressive tumor and poorer clinical outcome of patients with neuroblastoma. Moreover, overexpressing BMAL1 suppresses colony formation of neuroblastoma cells. Finally, activation of MYC also greatly perturbs glucose metabolism and phospho-AMPK oscillation in U2OS cells. To further analyze MYC effects on circadian clock in vivo, we manipulated Drosophila Myc (dMyc) level using genetic models and assess their circadian locomotor behavior. Here, we have demonstrated that overexpressed dMyc in specific clock cell type resulted in reduction of rhythmicity. dMyc activation is able to induce several clock-controlled genes, including per, tim, cry and cwo. However, no suppression of clk, Drosophila homolog of mammalian BMAL1 is observed. Reduction of the clock synchronizing peptide PDF in the fly brain observed by immunohistochemistry and reduction of valine and leucine in the fly heads measured by GC-MS suggested that dMyc-associated arrhythmicity can be resulted from perturbation of PDF level or branch-chain amino acid metabolism. To explore how endogenous dMyc affect circadian behavior of flies, we also examine the circadian behavior in dMyc hypomorph mutant flies. Surprisingly, loss of dMyc leads to bimodal distribution of rhythmicity, which can be rescued by mutation of dMnt, a known suppressor of dMyc activity. Immunohistochemistry revealed Per staining is dramatically diminished in arrhythmic dMyc mutant flies but not in rhythmic dMyc mutant flies and can be rescued by dMnt mutation, suggesting endogenous dMyc is essential for Per expression. Our results demonstrate a novel role of dMyc in maintaining the integrity of Drosophila circadian locomotor behavior. Together, our data showed that a novel role of MYC and dMyc in modulating the molecular clock in cancer cells and in Drosophila. While MYC induces E-box gene REV-ERB to suppress BMAL1 and clock-regulated metabolism in cancer cells, dMyc is required to maintain E-box gene Per expression to ensure adequate circadian behavior. Our findings not only provide therapeutic opportunities between non-oscillatory cancer cells and circadian-regulated normal cells but also create a new avenue for the role of physiological dMyc in Drosophila circadian clock regulation.