Project description:The MYC oncogene encodes for the MYC protein and is frequently dysregulated across multiple cancer cell types, making it an attractive target for cancer therapy. MYC overexpression leads to MYC binding at active enhancers, resulting in a global transcriptional amplification of active genes. Since superenhancers are frequently dysregulated in cancer, we hypothesized that MYC preferentially invades into superenhancers and alters the cancer genome organization. To that end, we performed ChIP-seq, RNA-seq, 4C-seq and SIQHiC (Spike-in Quantitative Hi-C) on the U2OS osteosarcoma cell line with tetracycline-inducible MYC. MYC overexpression in U2OS cells modulated histone acetylation and increased MYC binding at superenhancers. SIQHiC analysis revealed increased global chromatin contact frequency, particularly at chromatin interactions connecting MYC binding sites at promoters and enhancers. Immunofluorescence staining showed that MYC molecules formed punctate foci at these transcriptionally active domains after MYC overexpression. These results demonstrate the accumulation of overexpressed MYC at promoter-enhancer hubs and suggest that MYC invades into enhancers through spatial proximity. At the same time, the increased protein-protein interactions may strengthen these chromatin interactions to increase chromatin contact frequency. CTCF siRNA knockdown in MYC overexpressed U2OS cells demonstrated that removal of architectural proteins can disperse MYC and abrogate the increase in chromatin contacts. By elucidating the chromatin landscape of MYC driven cancers, we can potentially target MYC associated chromatin interactions for cancer therapy.
Project description:Systemic metabolic alterations associated with increased consumption of saturated fat and obesity are linked with increased risk of prostate cancer progression and mortality, but the molecular underpinnings of this association are poorly understood. Here, we demonstrate in a murine prostate cancer model, that high-fat diet (HFD) enhances the MYC transcriptional program through metabolic alterations that favour histone H4K20 hypomethylation at the promoter regions of MYC regulated genes, leading to increased cellular proliferation and tumour burden. Saturated fat intake (SFI) is also associated with an enhanced MYC transcriptional signature in prostate cancer patients. The SFI-induced MYC signature independently predicts prostate cancer progression and death. Finally, switching from a high-fat to a low-fat diet, attenuates the MYC transcriptional program in mice. Our findings suggest that in primary prostate cancer, dietary SFI contributes to tumour progression by mimicking MYC over expression, setting the stage for therapeutic approaches involving changes to the diet.
Project description:Prostate cancer is the commonest male cancer in Europe and the USA. The androgen receptor is a key transcription factor contributing to the development of all stages of the disease. In addition, other transcription factors have been associated with poor prognosis in prostate cancer, amongst which c-Myc is a well-established oncogene in many other cancers. We have previously reported that a role for the androgen receptor in prostate cancer is to promote glycolysis and anabolic metabolism. Many of these metabolic pathways are also c-Myc-regulated in other cancers. In this study we report that de novo purine biosynthesis is a c-Myc-dependent pathway in prostate cancer cells as determined by commensurate changes in the levels of enzymes in the pathway in response to siRNA knockdown of c-Myc and inducible overexpression of c-Myc. In addition c-Myc is recruited to the promoters of genes in the pathway as determined by chromatin immunoprecipitation. Using immunohistochemistry and real-time transcript detection we show that two enzymes (PAICS and IMPDH2) within the pathway are overexpressed in prostate cancers. An inhibitor of IMPDH2 reduces cell proliferation and significantly reduces the levels of guanosine triphosphate within treated cells. This imposes nucleolar stress on cells as determined by significant reductions in the levels of guanine nucleotide binding protein-like 3 (GNL3). In addition the levels of c-Myc, p53 and the androgen receptor are affected and the expression of tumour suppressive microRNA-34b is increased. Combining the IMPDH2 inhibitor with anti-androgens results in a combinatorial inhibition of cell proliferation. In conclusion we propose using enzymes within the de novo purine biosynthesis as cancer biomarkers and applying drugs to alter the flux through this pathway may represent an effective means of stratifying patients for therapy and sensitising some to AR-targeted therapies. Total RNA of three biological replicates for each condition was extracted using the RNeasy kit (Qiagen), conditions are: 5 h vehicle, 5 h Doxycycline, 12 h vehicle, 12 h Doxycyline