Impaired hydroxylation of 5-methylcytosine in myeloid cancers with mutant TET2

Abstract

TET2 is a close relative of TET1, an enzyme that converts 5-methylcytosine (5-mC) to 5-hydroxymethylcytosine (5-hmC) in DNA1,2. The gene encoding TET2 resides at chromosome 4q24, in a region showing recurrent microdeletions and copy-neutral loss of heterozygosity (CN-LOH) in patients with diverse myeloid malignancies3. Somatic TET2 mutations are frequently observed in myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), MDS/MPN overlap syndromes including chronic myelomonocytic leukemia (CMML), acute myeloid leukemias (AML) and secondary AML (sAML)4–12. We show here that TET2 mutations associated with myeloid malignancies compromise TET2 catalytic activity. Bone marrow samples from patients with TET2 mutations displayed uniformly low levels of 5-hmC in genomic DNA compared to bone marrow samples from healthy controls. Moreover, small hairpin RNA (shRNA)-mediated depletion of Tet2 in mouse haematopoietic precursors skewed their differentiation towards monocyte/macrophage lineages in culture. There was no significant difference in DNA methylation between bone marrow samples from patients with high 5-hmC versus healthy controls, but samples from patients with low 5-hmC showed hypomethylation relative to controls at the majority of differentially-methylated CpG sites. Our results demonstrate that TET2 is important for normal myelopoiesis, and suggest that disruption of TET2 enzymatic activity favours myeloid tumorigenesis. Measurement of 5-hmC levels in myeloid malignancies may prove valuable as a diagnostic and prognostic tool, to tailor therapies and assess responses to anti-cancer drugs.

TET2 repression by androgen hormone regulates global hydroxymethylation status and prostate cancer progression

“…5-Hydroxymethylation of cytosine bases (5-hmC) is a newly identified epigenetic marker; this nontraditional DNA modification involves methylation of cytosine bases (5-mC) in CpG dinucleotide sequences 2,3 and their oxidation by the ten-eleven translocation (TET) family of proteins. While 5-hmC is a potentially useful indicator of disease states such as cancer [4][5][6][7][8] , the mechanisms controlling its abundance in tumours and its impact on gene expression and cancer cell fate are unclear.…”

Succinate dehydrogenase deficiency is associated with decreased 5-hydroxymethylcytosine production in gastrointestinal stromal tumors: implications for mechanisms of tumorigenesis

“…In support of this idea, studies have predominantly demonstrated hypermethylation signatures in both TET2-and IDH-mutant acute myeloid leukemias, 28 as well as in IDHmutant gliomas 29 and enchondromas, 32 although other authors have reported conflicting results. 41 However, although inhibition of TET function appears to be associated with DNA hypermethylation, it remains unclear how these epigenetic changes regulate gene expression, as studies have, as of yet, failed to demonstrate direct links between changes in the promoter methylation status of specific genes and alterations in the expression levels of those genes. This may reflect the fact that although epigenetic changes can alter the accessibility of loci to transcriptional machinery, additional factors, including the availability of transcription factors, coactivators, and corepressors, also have a role in dictating changes in gene expression.…”

Uses and Abuses of JAK2 and MPL Mutation Tests in Myeloproliferative Neoplasms

“…TET2 mutations occur across several of the gene's 12 exons. 4 TET proteins catalyze conversion of 5-methylcytosine to 5-hydroxymethylcytosine, 28,29 and, accordingly, TET2 mutations are thought to contribute to epigenetic dysregulation of transcription. TET2 mutational frequencies are estimated at 16% in PV, 5% in ET, 17% in PMF, and 17% in blast-phase MPN.…”

“…19,[37][38][39] TET2, ASXL1, and EZH2 mutations might contribute to epigenetic dysregulation of transcription. 28,29,31 …”