Paradoxical association of TET loss of function with genome-wide hypomethylation

Cancer genomes are characterized by focal increases in DNA methylation, co-occurring with widespread hypomethylation. Here we show that TET loss-of-function results in a similar genomic footprint. Both 5hmC in wildtype genomes, and DNA hypermethylation in TET-deficient genomes, are largely confined to the active euchromatic compartment, consistent with the known functions of TET proteins in DNA demethylation and the known distribution of 5hmC at transcribed genes and active enhancers. In contrast, an unexpected DNA hypomethylation noted in multiple TET-deficient genomes is primarily observed in the heterochromatin compartment. In a mouse model of T cell lymphoma driven by TET deficiency (Tet2/3 DKO T cells), genomic analysis of malignant T cells revealed DNA hypomethylation in the heterochromatic genomic compartment, as well as reactivation of repeat elements and enrichment for single nucleotide alterations, primarily in heterochromatic regions of the genome. Overall design: WGBS (MethylC-seq), Hi-C, and total (ribodepleted) RNA-seq, in WT and Tet2/3 DKO iNKT cells