The methylation landscape of tumour metastasis.

The metastatic cascade which leads to the death of cancer patients results from a multi-step process of tumour progression caused by genetic and epigenetic alterations in key regulatory molecules. It is, therefore, crucial to improve our understanding of the regulation of genes controlling the metastatic process to identify predictive biomarkers and to develop more effective therapies to treat advanced disease. The study of epigenetic mechanisms of gene regulation offers a novel approach for innovative diagnosis and treatment of cancer patients. Recent discoveries provide compelling evidence that the methylation landscape (changes in both DNA methylation and histone post-translational modifications) is profoundly altered in cancer cells and contributes to the altered expression of genes regulating tumour phenotypes. However, the impact of methylation events specifically on the advanced metastatic process is poorly understood compared with the initial oncogenic events. Moreover, the characterisation of a large number of histone-modifying enzymes has revealed their active roles in cancer progression, via the regulation of specific target genes controlling different metastatic phenotypes. Here, we discuss two main methylating events (DNA methylation and histone-tail methylation) involved in oncogenesis and metastasis formation. The potential reversibility of these molecular events makes them promising biomarkers of metastatic potential and potential therapeutic targets.