Dioxygenase that catalyzes the conversion of the modified genomic base 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC) and plays a key role in active DNA demethylation. Has a preference for 5-hydroxymethylcytosine in CpG motifs. Also mediates subsequent conversion of 5hmC into 5-formylcytosine (5fC), and conversion of 5fC to 5-carboxylcytosine (5caC). Conversion of 5mC into 5hmC, 5fC and 5caC probably constitutes the first step in cytosine demethylation. Methylation at the C5 position of cytosine bases is an epigenetic modification of the mammalian genome which plays an important role in transcriptional regulation. In addition to its role in DNA demethylation, also involved in the recruitment of the O-GlcNAc transferase OGT to CpG-rich transcription start sites of active genes, thereby promoting histone H2B GlcNAcylation by OGT. 2-oxoglutarate + a 5-methyl-2'-deoxycytidine in DNA + O2 = a 5-hydroxymethyl-2'-deoxycytidine in DNA + CO2 + succinate Binds 1 Fe(2+) ion per subunit. Binds 3 zinc ions per subunit. The zinc ions have a structural role (PubMed:24315485). Interacts with HCFC1 and OGT. Broadly expressed. Highly expressed in hematopoietic cells; highest expression observed in granulocytes. Expression is reduced in granulocytes from peripheral blood of patients affected by myelodysplastic syndromes. May be glycosylated. It is unclear whether interaction with OGT leads to GlcNAcylation. According to a report, it is not GlcNAcylated by OGT (PubMed:23353889). In contrast, another group reports GlcNAcylation by OGT in mouse ortholog. TET2 is frequently mutated in myeloproliferative disorders (MPD). These constitute a heterogeneous group of disorders, also known as myeloproliferative diseases or myeloproliferative neoplasms (MPN), characterized by cellular proliferation of one or more hematologic cell lines in the peripheral blood, distinct from acute leukemia. Included diseases are: essential thrombocythemia, polycythemia vera, primary myelofibrosis (chronic idiopathic myelofibrosis). Bone marrow samples from patients display uniformly low levels of hmC in genomic DNA compared to bone marrow samples from healthy controls as well as hypomethylation relative to controls at the majority of differentially methylated CpG sites. The disease is caused by variants affecting the gene represented in this entry. TET2 is frequently mutated in systemic mastocytosis; also known as systemic mast cell disease. A condition with features in common with myeloproliferative diseases. It is a clonal disorder of the mast cell and its precursor cells. The clinical symptoms and signs of systemic mastocytosis are due to accumulation of clonally derived mast cells in different tissues, including bone marrow, skin, the gastrointestinal tract, the liver, and the spleen. The disease is caused by variants affecting the gene represented in this entry. Bone marrow samples from patients display uniformly low levels of hmC in genomic DNA compared to bone marrow samples from healthy controls as well as hypomethylation relative to controls at the majority of differentially methylated CpG sites. The disease is caused by variants affecting the gene represented in this entry. May be produced at very low levels due to a premature stop codon in the mRNA, leading to nonsense-mediated mRNA decay. Belongs to the TET family. Subsequent steps in cytosine demethylation are subject to discussion. According to a first model cytosine demethylation occurs through deamination of 5hmC into 5-hydroxymethyluracil (5hmU) and subsequent replacement by unmethylated cytosine by the base excision repair system. According to another model, cytosine demethylation is rather mediated via conversion of 5hmC into 5fC and 5caC, followed by excision by TDG (PubMed:21817016). Truncated C-terminus. Contaminating sequence. Potential poly-A sequence. Truncated N-terminus.