The circadian clock is an internal timing system that allows the entrainment of physiological and behavioural processes to the geophysical time with a periodicity of about 24 hours. It consists of a central pacemaker in the suprachiasmatic nucleus (SCN) and peripheral clocks in every cell. In mammals, a distinct set of genes is interconnected in regulatory feedback loops, thereby generating oscillations in gene expression in the core-clock itself as well as in numerous target genes. Known clock target genes are, among others, involved in cellular processes connected to tumour development and progression, including metabolic pathways, drug response pathways and the cell cycle. Malfunctions of the circadian clock are associated with different pathologies including cancer and studies link the disruption of the clock to an enhanced susceptibility to develop cancer, bad treatment response and poor prognosis. Attempts have already been made to apply chronotherapy in cancer treatment. However, to date studies fail to give clear messages due to tumour heterogeneity, genetic complexity and the missing knowledge about the involvement of the circadian clock in stage-specific tumour signatures.
The aim of this project was to study the role of the circadian clock in tumour development and progression with a focus on cancer metabolism and treatment response. The role of a deregulated clock was investigated in an in vitro model of colorectal cancer progression, namely, SW480 cells derived from a primary tumour and SW620 cells derived from a lymph node metastasis of the same patient. The investigated cell lines showed clear differences with respect to their clock phenotypes. A time course analysis of both cell lines on the transcriptome level revealed a global shift of 24 h oscillating genes as well as distinct alterations in metabolic pathways such as glycolysis and oxidative phosphorylation. Within these pathways a set of candidate genes, including the glycolytic gene Hkdc1, was identified that might mediate clock-driven metabolic alterations in tumourigenesis. A knockdown (KD) of the core-clock gene Bmal1 was introduced to study the effects of a disrupted clock on gene expression and cell metabolism. Bmal1-KD in SW480 cells induced a metastatic phenotype similar to SW620 wild type (WT) cells, as indicated by faster proliferation, lower apoptosis rate and a highly energetic metabolic phenotype. Furthermore, Bmal1-KD induced metabolic phenotype rewiring as seen by altered glycolytic activity and mitochondrial respiration, a change in time-dependent metabolic profile, gene expression changes in the tested candidate genes and modified treatment response to metabolism-targeting anticancer treatment. A reciprocal interplay between Bmal1 and the glycolytic gene Hkdc1 seems to be a possible mechanism of clock-driven metabolic reprogramming in tumorigenesis. Findings from the model system could partly be confirmed in two primary cell systems, primary fibroblasts isolated from normal colon (NF) and colon adenocarcinoma (CAF) of the same patient and human fallopian tube organoids. Furthermore, co-culture experiments with NFs and CAFs and cancer cell lines showed that cell-to-cell communication influences both the clock phenotype and cell metabolism. The results obtained in this project reinforce the postulated role of Bmal1 as a tumour suppressor and elucidate a reciprocal interplay between the circadian clock and cancer metabolism with implications in metabolic phenotype rewiring during tumour progression. Novel connections between both systems identified in this project may play a pivotal role in colorectal cancer progression and in response to anticancer therapy.
|Advisor:||Relógio , Angela , Meyer , Thomas F., Baldus , Claudia|
|School:||Humboldt Universitaet zu Berlin (Germany)|
|Source:||DAI-C 81/7(E), Dissertation Abstracts International|
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