Relevance of histone marks H3K9me3 and H4K20me3 in cancer.

Background: Circulating nucleosomes are valuable biomarkers for therapy monitoring and estimation of prognosis in cancer disease. While epigenetic and genetic modifications of DNA have been reported in blood of cancer patients, little is known about modifications of histones on circulating nucleosomes.

Patients And Methods: Sera of 45 cancer patients (21 colorectal, 4 pancreatic, 15 breast, 5 lung cancer), 12 patients with benign gastrointestinal and inflammatory diseases, and 28 healthy individuals were investigated. Histone modifications were detected by chromatin-immunoprecipitation (ChIP) using antibodies for triple histone methylations at sites H3K9me3 and H4K20me3 and subsequent real-time polymerase chain reaction using primers for the centromeric satellites SAT2. Additionally, the amount of circulating nucleosomes, as well as of carcino-embryonic antigen (CEA) and cancer antigen (CA) 19-9 were measured.

Results: Levels of SAT2 on H3K9me3 (median 0.507 ng/ml) and on H4K20me3 (0.292 ng/ml) were elevated in sera of patients with breast cancer when compared with healthy controls (0.049 and 0.035 ng/ml), but were lower in patients with colorectal cancer (0.039 and 0.027 ng/ml). Both histone marks were correlated with each other but did not correlate with CEA or CA 19-9 in cancer patients. When H3K9me3 and H4K20me3 were normalized to nucleosome content in sera, ratios were significantly higher in all types of cancer as well as in colorectal and breast subtypes when compared with healthy controls. Best discrimination was achieved by normalized H4K20me3 reaching areas under the curves (AUC) of 79.1%, 90.4% and 81.2% in receiver operating characteristic (ROC) curves of these three comparisons.

Conclusion: SAT2 levels on H3K9me3 and H4K20me3 are up-regulated in breast cancer and down-regulated in colorectal cancer. Normalization to total nucleosome content enables better discrimination between cancer and control groups.