JAK2V617F leads to increased 5-hmC and genome-wide loss of cytosine methylation in primary patient samples. JAK2V617F leads to increased 5-hmC and genome-wide loss of cytosine methylation in primary patient samples. A and B, Constitutively active form of JAK2 (JAK2V617F) in patients with the myeloproliferative disorder polycythemia vera exhibit elevated levels of TET activity and 5-hmC content without affecting 5-mC levels. Primary CD34+ cells purified from patient samples or healthy donors were cultured for 6 days and basophilic erythroblasts generated from these patient samples were used to determine TET2 activity and 5-hmC contents. C, FDCP cells were transfected with JAK2V617F and wild-type (WT) JAK2, and genome-wide cytosine methylation was determined by the HELP assay. Unsupervised clustering revealed that samples with JAK2V617F mutation were epigenetically distinct and were characterized by more hypomethylated loci. D, Differentially demethylated loci were significantly more than hypermethylated loci in JAK2V617F FDCP cells. E and F, Integration with gene-expression profiling done in the same samples revealed that hypomethylation affecting gene promoters was associated with increased gene expression, as shown for Meis1 and Hoxa9 genes. The blue bars above baseline represent hypomethylation, whereas the red bars below baseline represent hypermethylation. G, Unsupervised clustering of methylation profiles generated by the HELP assay from 4 patients with myelofibrosis with JAK2V617F mutation (without TET2 mutation) and 3 healthy controls shows that the controls are distinct from the JAK2+ cases. H, Volcano plot shows 911 significantly hypomethylated loci in JAK2-mutant samples as opposed to 188 hypermethylated loci. I, Unsupervised clustering of gene-expression profiles from 8 patients with myelofibrosis with JAK2V617F mutation and 11 healthy controls shows distinct clustering. J, Volcano plot shows 1,986 overexpressed genes in JAK2-mutant samples as opposed to 564 underexpressed genes. Jong Jin Jeong et al. Cancer Discov 2019;9:778-795 ©2019 by American Association for Cancer Research