Exploring the Molecular Mechanism of Deregulated Circadian Clock in Tumorigenesis (II)

In mammals, various physiological processes (such as gene expression, metabolism, and behavior) are controlled by an internal circadian clock to entrain to the 24-hour day. All known circadian oscillators use transcription-translation feedback loops that rely on positive and negative elements in oscillators. Therefore, the strong daily cycling of circadian clock genes mRNA, clock protein, and clock-controlled gene RNA and protein is characteristic of circadian systems. Disruption of circadian rhythm and deregulation of peripheral circadian clock genes has been associated with various cancers. Our previous studies showed the expression of PER3 is significantly downregulated in leukocytes from chronic myeloid leukemia (CML), acute leukemias and head and neck squamous cell carcinoma. Furthermore, we also found oscillations of PER3 in healthy individuals and the oscillations of the PER3 were abolished in CML patients. Accumulated evidence suggests a minor role of genetic mutations but possibly a major role of epigenetic modifications in circadian rhythm regulation. Recently, emerging evidence has connected cell metabolism to circadian rhythms. The expression of genes that are crucial in metabolic processes exhibits a circadian pattern. Clock/Clock-mutant mice become hyperphagic and obese and develop classic signs of metabolic syndrome (hyperglycemia, dyslipidemia, hepatic steatosis). As clock function and integration of inputs rely on transcriptional regulation, it is possible that chromatin remodeling is a key control mechanism during circadian cycles and in response to signals that regulate the clock. CLOCK possesses histone acetyltransferases (HAT) activity and mediates acetylation of BMAL1, which is essential for circadian clock-controlled gene expression. SIRT1 (sirtuin 1) is a NAD+-dependent histone deacetylases that counteracts the HAT activity of CLOCK and thus regulates circadian rhythms. Since NAD+ directly control the deacetylase activity of SIRT1, circadian regulation of NAD+ levels seems to be a crucial regulatory mechanism in controlling circadian rhythms, cell metabolism, and cell growth. Base on our previous studies in human cancers, the relationship between dysfunction of circadian clock and tumorigensis is definite but the underlying mechanism, particularly direct association with dysfunction in chromatin remodeling, remain unclear. Therefore, we aim to elucidate these unsolved questions. We have successfully established PER3- and CRY2- overexpressed stable cell lines using K562 and FaDu in our granted MOST project of year 103 but the stable cell lines of overexpression of other circadian clock genes and knockdowns are still on the way. In this project we hope to continue our proposed experiments as following: 1st year: Continue to establish circadian clock gene-knockdown and overexpression stable cell lines for functional study of circadian clock gene. 2nd year: Functional analysis of the established circadian clock gene-knockdown or overexpression stable cell lines and to investigate the regulatory pathways. 3rd year: Clarify the NAMPT-mediated NAD+ biosynthesis pathway and the regulation of CLOCK:BMAL1 by the NAD+-dependent SIRT1 through chromatin remodeling using cell lines.

Project ID:PC10408-1720
External Project ID:MOST104-2320-B182-018