Loss of 5-hydroxymethylcytosine is an epigenetic hallmark of melanoma

DNA methylation at the 5-position of cytosine (5-mC) is a key epigenetic mark critical for varius biological and pathological processes. 5-mC can be converted to 5-hydroxymethylcytosine (5-hmC) by the Ten-Eleven Translocation (TET) family of DNA hydroxylases. Here we report that "loss of 5-hmC" is an epigenetic hallmark of melanoma with diagonostic and prognostic implications. Genome-wide mapping of 5-hmC in nevi and melanomas for the first time revealed loss of 5-hmC landscape in the melanoma epigenome. Downregulation of Isocitrate Dehydrogenase 2 (IDH2) and TET family enzymes proved to be one of the mechanisms underlying the loss of 5-hmC during melanoma development, and rebuilding the 5-hmC landscape in the melanoma epigenome by reintroducing active TET2 or IDH2 suppressed melanoma growth and increased tumor-free survival. Thus, our study establishes that "loss of 5-hmC" is a new epigenetic hallmark of melanoma and links IDH and TET family enzymes-mediated 5-hmC putative tumor suppressor pathway to the suppression of melanoma progression. Determine the genome-wide distribution of 5mC and 5hmC in benign nevus tissue, melanoma tissue, A2058 MOCK cells (overexpressing empty vector), A2058 TET2 cells (overexpressing wild type human TET), and A2058 TET2M cells (overexpressing mutant human TET).