TET Enzymes in the Immune System: From DNA Demethylation to Immunotherapy, Inflammation, and Cancer.

Ten-eleven translocation (TET) proteins are iron-dependent and α-ketoglutarate-dependent dioxygenases that sequentially oxidize the methyl group of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC). All three epigenetic modifications are intermediates in DNA demethylation. TET proteins are recruited by transcription factors and by RNA polymerase II to modify 5mC at enhancers and gene bodies, thereby regulating gene expression during development, cell lineage specification, and cell activation. It is not yet clear, however, how the established biochemical activities of TET enzymes in oxidizing 5mC and mediating DNA demethylation relate to the known association of TET deficiency with inflammation, clonal hematopoiesis, and cancer. There are hints that the ability of TET deficiency to promote cell proliferation in a signal-dependent manner may be harnessed for cancer immunotherapy. In this review, we draw upon recent findings in cells of the immune system to illustrate established as well as emerging ideas of how TET proteins influence cellular function.

Inducible disruption of Tet genes results in myeloid malignancy, readthrough transcription, and a heterochromatin-to-euchromatin switch.

The three mammalian TET dioxygenases oxidize the methyl group of 5-methylcytosine in DNA, and the oxidized methylcytosines are essential intermediates in all known pathways of DNA demethylation. To define the in vivo consequences of complete TET deficiency, we inducibly deleted all three Tet genes in the mouse genome. Tet1/2/3-inducible TKO (iTKO) mice succumbed to acute myeloid leukemia (AML) by 4 to 5 wk. Single-cell RNA sequencing of Tet iTKO bone marrow cells revealed the appearance of new myeloid cell populations characterized by a striking increase in expression of all members of the stefin/cystatin gene cluster on mouse chromosome 16. In patients with AML, high stefin/cystatin gene expression correlates with poor clinical outcomes. Increased expression of the clustered stefin/cystatin genes was associated with a heterochromatin-to-euchromatin compartment switch with readthrough transcription downstream of the clustered stefin/cystatin genes as well as other highly expressed genes, but only minor changes in DNA methylation. Our data highlight roles for TET enzymes that are distinct from their established function in DNA demethylation and instead involve increased transcriptional readthrough and changes in three-dimensional genome organization.

Loss of adipose TET proteins enhances ß-adrenergic responses and protects against obesity by epigenetic regulation of ß3-AR expression.

ß-adrenergic receptor (ß-AR) signaling plays predominant roles in modulating energy expenditure by triggering lipolysis and thermogenesis in adipose tissue, thereby conferring obesity resistance. Obesity is associated with diminished ß3-adrenergic receptor (ß3-AR) expression and decreased ß-adrenergic responses, but the molecular mechanism coupling nutrient overload to catecholamine resistance remains poorly defined. Ten-eleven translocation (TET) proteins are dioxygenases that alter the methylation status of DNA by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine and further oxidized derivatives. Here, we show that TET proteins are pivotal epigenetic suppressors of ß3-AR expression in adipocytes, thereby attenuating the responsiveness to ß-adrenergic stimulation. Deletion of all three Tet genes in adipocytes led to increased ß3-AR expression and thereby enhanced the downstream ß-adrenergic responses, including lipolysis, thermogenic gene induction, oxidative metabolism, and fat browning in vitro and in vivo. In mouse adipose tissues, Tet expression was elevated after mice ate a high-fat diet. Mice with adipose-specific ablation of all TET proteins maintained higher levels of ß3-AR in both white and brown adipose tissues and remained sensitive to ß-AR stimuli under high-fat diet challenge, leading to augmented energy expenditure and decreased fat accumulation. Consequently, they exhibited improved cold tolerance and were substantially protected from diet-induced obesity, inflammation, and metabolic complications, including insulin resistance and hyperlipidemia. Mechanistically, TET proteins directly repressed ß3-AR transcription, mainly in an enzymatic activity-independent manner, and involved the recruitment of histone deacetylases to increase deacetylation of its promoter. Thus, the TET-histone deacetylase-ß3-AR axis could be targeted to treat obesity and related metabolic diseases.

Epigenetic Modification of Cytosines in Hematopoietic Differentiation and Malignant Transformation.

The mammalian DNA methylation landscape is established and maintained by the combined activities of the two key epigenetic modifiers, DNA methyltransferases (DNMT) and Ten-eleven-translocation (TET) enzymes. Once DNMTs produce 5-methylcytosine (5mC), TET proteins fine-tune the DNA methylation status by consecutively oxidizing 5mC to 5-hydroxymethylcytosine (5hmC) and further oxidized derivatives. The 5mC and oxidized methylcytosines are essential for the maintenance of cellular identity and function during differentiation. Cytosine modifications with DNMT and TET enzymes exert pleiotropic effects on various aspects of hematopoiesis, including self-renewal of hematopoietic stem/progenitor cells (HSPCs), lineage determination, differentiation, and function. Under pathological conditions, these enzymes are frequently dysregulated, leading to loss of function. In particular, the loss of DNMT3A and TET2 function is conspicuous in diverse hematological disorders, including myeloid and lymphoid malignancies, and causally related to clonal hematopoiesis and malignant transformation. Here, we update recent advances in understanding how the maintenance of DNA methylation homeostasis by DNMT and TET proteins influences normal hematopoiesis and malignant transformation, highlighting the potential impact of DNMT3A and TET2 dysregulation on clonal dominance and evolution of pre-leukemic stem cells to full-blown malignancies. Clarification of the normal and pathological functions of DNA-modifying epigenetic regulators will be crucial to future innovations in epigenetic therapies for treating hematological disorders.

Editorial for the Special Issue "Molecular Mechanism of Leukemia".

Hematopoiesis is the intricate process responsible for all blood cell formation and maintenance, and is tightly regulated by a myriad of intrinsic and extrinsic factors [...].

Development of Novel Epigenetic Anti-Cancer Therapy Targeting TET Proteins.

Epigenetic dysregulation, particularly alterations in DNA methylation and hydroxymethylation, plays a pivotal role in cancer initiation and progression. Ten-eleven translocation (TET) proteins catalyze the successive oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) and further oxidized methylcytosines in DNA, thereby serving as central modulators of DNA methylation-demethylation dynamics. TET loss of function is causally related to neoplastic transformation across various cell types while its genetic or pharmacological activation exhibits anti-cancer effects, making TET proteins promising targets for epigenetic cancer therapy. Here, we developed a robust cell-based screening system to identify novel TET activators and evaluated their potential as anti-cancer agents. Using a carefully curated library of 4533 compounds provided by the National Cancer Institute, Bethesda, MD, USA, we identified mitoxantrone as a potent TET agonist. Through rigorous validation employing various assays, including immunohistochemistry and dot blot studies, we demonstrated that mitoxantrone significantly elevated 5hmC levels. Notably, this elevation manifested only in wild-type (WT) but not TET-deficient mouse embryonic fibroblasts, primary bone marrow-derived macrophages, and leukemia cell lines. Furthermore, mitoxantrone-induced cell death in leukemia cell lines occurred in a TET-dependent manner, indicating the critical role of TET proteins in mediating its anti-cancer effects. Our findings highlight mitoxantrone's potential to induce tumor cell death via a novel mechanism involving the restoration of TET activity, paving the way for targeted epigenetic therapies in cancer treatment.

Decreased vitamin C uptake mediated by SLC2A3 promotes leukaemia progression and impedes TET2 restoration.

BACKGROUND: Vitamin C suppresses leukaemogenesis by modulating Tet methylcytosine dioxygenase (TET) activity. However, its beneficial effect in the treatment of patients with acute myeloid leukaemia (AML) remains controversial. In this study, we aimed to identify a potential predictive biomarker for vitamin C treatment in AML. METHODS: Gene expression patterns and their relevance to the survival of AML patients were analysed with The Cancer Genome Atlas (TCGA) and Therapeutically Applicable Research to Generate Effective Treatments (TARGET) database cases. In vitro experiments were performed on AML cell lines, a SLC2A3-knockdown cell line and patient-derived primary AML cells. RESULTS: SLC2A3 expression was significantly decreased in leukaemic blast cells. Below-median SLC2A3 expression was associated with poor overall survival. Low SLC2A3 expression was associated with less effective demethylation, and a diminished vitamin C effect in the AML and lymphoma cell lines. SLC2A3 knockdown in the KG-1 cell line decreased the response of vitamin C. In patient-derived primary AML cells, vitamin C only restored TET2 activity when SLC2A3 was expressed. CONCLUSION: SLC2A3 could be used as a potential biomarker to predict the effect of vitamin C treatment in AML.

D-2-hydroxyglutarate produced by mutant IDH1 perturbs collagen maturation and basement membrane function.

Isocitrate dehydrogenase-1 (IDH1) R132 mutations occur in glioma, but their physiological significance is unknown. Here we describe the generation and characterization of brain-specific Idh1 R132H conditional knock-in (KI) mice. Idh1 mutation results in hemorrhage and perinatal lethality. Surprisingly, intracellular reactive oxygen species (ROS) are attenuated in Idh1-KI brain cells despite an apparent increase in the NADP(+)/NADPH ratio. Idh1-KI cells also show high levels of D-2-hydroxyglutarate (D2HG) that are associated with inhibited prolyl-hydroxylation of hypoxia-inducible transcription factor-1α (Hif1α) and up-regulated Hif1α target gene transcription. Intriguingly, D2HG also blocks prolyl-hydroxylation of collagen, causing a defect in collagen protein maturation. An endoplasmic reticulum (ER) stress response induced by the accumulation of immature collagens may account for the embryonic lethality of these mutants. Importantly, D2HG-mediated impairment of collagen maturation also led to basement membrane (BM) aberrations that could play a part in glioma progression. Our study presents strong in vivo evidence that the D2HG produced by the mutant Idh1 enzyme is responsible for the above effects.

Modulation of TET2 expression and 5-methylcytosine oxidation by the CXXC domain protein IDAX.

TET (ten-eleven-translocation) proteins are Fe(ii)- and α-ketoglutarate-dependent dioxygenases that modify the methylation status of DNA by successively oxidizing 5-methylcytosine to 5-hydroxymethylcytosine, 5-formylcytosine and 5-carboxycytosine, potential intermediates in the active erasure of DNA-methylation marks. Here we show that IDAX (also known as CXXC4), a reported inhibitor of Wnt signalling that has been implicated in malignant renal cell carcinoma and colonic villous adenoma, regulates TET2 protein expression. IDAX was originally encoded within an ancestral TET2 gene that underwent a chromosomal gene inversion during evolution, thus separating the TET2 CXXC domain from the catalytic domain. The IDAX CXXC domain binds DNA sequences containing unmethylated CpG dinucleotides, localizes to promoters and CpG islands in genomic DNA and interacts directly with the catalytic domain of TET2. Unexpectedly, IDAX expression results in caspase activation and TET2 protein downregulation, in a manner that depends on DNA binding through the IDAX CXXC domain, suggesting that IDAX recruits TET2 to DNA before degradation. IDAX depletion prevents TET2 downregulation in differentiating mouse embryonic stem cells, and short hairpin RNA against IDAX increases TET2 protein expression in the human monocytic cell line U937. Notably, we find that the expression and activity of TET3 is also regulated through its CXXC domain. Taken together, these results establish the separate and linked CXXC domains of TET2 and TET3, respectively, as previously unknown regulators of caspase activation and TET enzymatic activity.

TET proteins and 5-methylcytosine oxidation in hematological cancers.

DNA methylation has pivotal regulatory roles in mammalian development, retrotransposon silencing, genomic imprinting, and X-chromosome inactivation. Cancer cells display highly dysregulated DNA methylation profiles characterized by global hypomethylation in conjunction with hypermethylation of promoter CpG islands that presumably lead to genome instability and aberrant expression of tumor suppressor genes or oncogenes. The recent discovery of ten-eleven-translocation (TET) family dioxygenases that oxidize 5mC to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC) in DNA has led to profound progress in understanding the mechanism underlying DNA demethylation. Among the three TET genes, TET2 recurrently undergoes inactivating mutations in a wide range of myeloid and lymphoid malignancies. TET2 functions as a bona fide tumor suppressor particularly in the pathogenesis of myeloid malignancies resembling chronic myelomonocytic leukemia (CMML) and myelodysplastic syndromes (MDS) in human. Here we review diverse functions of TET proteins and the novel epigenetic marks that they generate in DNA methylation/demethylation dynamics and normal and malignant hematopoietic differentiation. The impact of TET2 inactivation in hematopoiesis and various mechanisms modulating the expression or activity of TET proteins are also discussed. Furthermore, we also present evidence that TET2 and TET3 collaborate to suppress aberrant hematopoiesis and hematopoietic transformation. A detailed understanding of the normal and pathological functions of TET proteins may provide new avenues to develop novel epigenetic therapies for treating hematological malignancies.

Genome-wide mapping of 5-hydroxymethylcytosine in embryonic stem cells.

5-hydroxymethylcytosine (5hmC) is a modified base present at low levels in diverse cell types in mammals. 5hmC is generated by the TET family of Fe(II) and 2-oxoglutarate-dependent enzymes through oxidation of 5-methylcytosine (5mC). 5hmC and TET proteins have been implicated in stem cell biology and cancer, but information on the genome-wide distribution of 5hmC is limited. Here we describe two novel and specific approaches to profile the genomic localization of 5hmC. The first approach, termed GLIB (glucosylation, periodate oxidation, biotinylation) uses a combination of enzymatic and chemical steps to isolate DNA fragments containing as few as a single 5hmC. The second approach involves conversion of 5hmC to cytosine 5-methylenesulphonate (CMS) by treatment of genomic DNA with sodium bisulphite, followed by immunoprecipitation of CMS-containing DNA with a specific antiserum to CMS. High-throughput sequencing of 5hmC-containing DNA from mouse embryonic stem (ES) cells showed strong enrichment within exons and near transcriptional start sites. 5hmC was especially enriched at the start sites of genes whose promoters bear dual histone 3 lysine 27 trimethylation (H3K27me3) and histone 3 lysine 4 trimethylation (H3K4me3) marks. Our results indicate that 5hmC has a probable role in transcriptional regulation, and suggest a model in which 5hmC contributes to the 'poised' chromatin signature found at developmentally-regulated genes in ES cells.

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

TET2 is a close relative of TET1, an enzyme that converts 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in DNA. 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 malignancies. Somatic TET2 mutations are frequently observed in myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPN), MDS/MPN overlap syndromes including chronic myelomonocytic leukaemia (CMML), acute myeloid leukaemias (AML) and secondary AML (sAML). We show here that TET2 mutations associated with myeloid malignancies compromise catalytic activity. Bone marrow samples from patients with TET2 mutations displayed uniformly low levels of 5hmC 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 5hmC versus healthy controls, but samples from patients with low 5hmC 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 5hmC levels in myeloid malignancies may prove valuable as a diagnostic and prognostic tool, to tailor therapies and assess responses to anticancer drugs.

The SWI/SNF-like BAF complex is essential for early B cell development.

During the process of B cell development, transcription factors, such as E2A and Ebf1, have been known to play key roles. Although transcription factors and chromatin regulators work in concert to direct the expression of B lineage-specific genes, little is known about the involvement of regulators for chromatin structure during B lymphopoiesis. In this article, we show that deletion of Srg3/mBaf155, a scaffold subunit of the SWI/SNF-like BAF complex, in the hematopoietic lineage caused defects at both the common lymphoid progenitor stage and the transition from pre-pro-B to early pro-B cells due to failures in the expression of B lineage-specific genes, such as Ebf1 and Il7ra, and their downstream target genes. Moreover, mice that were deficient in the expression of Brg1, a subunit of the complex with ATPase activity, also showed defects in early B cell development. We also found that the expression of Ebf1 and Il7ra is directly regulated by the SWI/SNF-like BAF complex. Thus, our results suggest that the SWI/SNF-like BAF complex facilitates early B cell development by regulating the expression of B lineage-specific genes.

Ten-Eleven-Translocation 2 (TET2) negatively regulates homeostasis and differentiation of hematopoietic stem cells in mice.

The Ten-Eleven-Translocation 2 (TET2) gene encodes a member of TET family enzymes that alters the epigenetic status of DNA by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). Somatic loss-of-function mutations of TET2 are frequently observed in patients with diverse myeloid malignancies, including myelodysplastic syndromes, myeloproliferative neoplasms, and chronic myelomonocytic leukemia. By analyzing mice with targeted disruption of the Tet2 catalytic domain, we show here that Tet2 is a critical regulator of self-renewal and differentiation of hematopoietic stem cells (HSCs). Tet2 deficiency led to decreased genomic levels of 5hmC and augmented the size of the hematopoietic stem/progenitor cell pool in a cell-autonomous manner. In competitive transplantation assays, Tet2-deficient HSCs were capable of multilineage reconstitution and possessed a competitive advantage over wild-type HSCs, resulting in enhanced hematopoiesis into both lymphoid and myeloid lineages. In vitro, Tet2 deficiency delayed HSC differentiation and skewed development toward the monocyte/macrophage lineage. Our data indicate that Tet2 has a critical role in regulating the expansion and function of HSCs, presumably by controlling 5hmC levels at genes important for the self-renewal, proliferation, and differentiation of HSCs.

Epigenetic Regulators of DNA Cytosine Modification: Promising Targets for Cancer Therapy.

Epigenetic modifications are crucial regulators of gene expression that critically impact cell lineage differentiation, survival, and proliferation, and dysregulations are commonly observed in various cancers. The aberrantly modified epigenome confers unique features on tumor cells, including sustained proliferative potential, resistance to growth-suppressive or cell death signals, augmented replicative immortality, invasion, and metastasis. As a result, epigenetic abnormalities exhibit significant impacts on all stages of oncogenesis from its onset to progression to metastasis. Among various epigenetic mechanisms in mammals, DNA cytosine methylation-demethylation is recurrently disrupted in cancers. Due to its inherent reversibility, targeting DNA methylation dynamics has gained tremendous attention as a promising therapeutic option that can ameliorate the effects of cancer-specific epigenetic abnormalities by restoring normal conditions. Various small molecules targeting DNA (de)methylation regulators have been developed as potential cancer therapeutics, some of which are approved for usage in clinics. Clinical trials of many other molecules are underway for both hematological malignancies and solid tumors. In this review, we discuss the DNA methylation/demethylation pathway as a promising target for therapeutic intervention in cancer and highlight the development of various epigenetic drugs targeting DNA-modifying enzymes such as DNA methyltransferases (DNMTs) and ten-eleven translocation (TET) enzymes.

Pharmacological GLUT3 salvage augments the efficacy of vitamin C-induced TET2 restoration in acute myeloid leukemia.

Vitamin C has been demonstrated to regulate hematopoietic stem cell frequencies and leukemogenesis by augmenting and restoring Ten-Eleven Translocation-2 (TET2) function, potentially acting as a promising adjunctive therapeutic agent for leukemia. However, glucose transporter 3 (GLUT3) deficiency in acute myeloid leukemia (AML) impedes vitamin C uptake and abolishes the clinical benefit of vitamin C. In this study, we aimed to investigate the therapeutic value of GLUT3 restoration in AML. In vitro GLUT3 restoration was conducted with the transduction of GLUT3-overexpressing lentivirus or the pharmacological salvage with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) treatment to OCI-AML3, a naturally GLUT3-deficient AML cell line. The effects of GLUT3 salvage were further confirmed in patient-derived primary AML cells. Upregulation of GLUT3 expression made AML cells successfully augment TET2 activity and enhanced the vitamin C-induced anti-leukemic effect. Pharmacological GLUT3 salvage has the potential to overcome GLUT3 deficiency in AML and improves the antileukemic effect of vitamin C treatments.

A fast and label-free detection of hydroxymethylated DNA using a nozzle-jet printed AuNPs@Ti3C2 MXene-based electrochemical sensor.

5-hydroxymethylcytosine (5hmC) is a key epigenetic mark in the mammalian genome that has been proposed as a promising cancer biomarker with diagnostic and prognostic potentials. A new type of two-dimensional (2D) material called MXene includes transition metal carbides and nitrides and possesses unique physico-chemical properties suitable for diverse applications, including electrochemical sensors. Here, we report a new nozzle-jet printed electrochemical sensor using gold nanoparticles (AuNPs)@Ti3C2 MXene nanocomposite for the real-time and label-free detection of 5hmC in the genome. We utilized Ti3C2 MXene as a platform to immobilize AuNPs, which have been shown to exhibit different affinity interactions toward 5-methylcytosine (5 mC) and 5hmC, and thus produce distinct electrochemical responses. To fabricate the electrode, a highly conductive and adhesive silver ink was prepared to generate a silver line onto polyethylene terephthalate (PET) substrate using nozzle-jet printing, followed by deposition of AuNPs@Ti3C2 MXene ink at one end via dropcasting. Analyses of morphology and chemical composition showed that all steps of the sensor fabrication were successful. The fabricated sensor coupled with cyclic voltammetry showed excellent performance in distinguishing 5 mC- or 5hmC-enriched cellular genomic DNAs. As a proof-of-concept investigation, we confirmed that our sensor readily and consistently detected 5hmC diminution in multiple tumors, compared to the paired normal tissues. Thus, our simple and cost-effective sensing strategy using printable AuNPs@Ti3C2 MXene ink holds promise for a wide range of practical applications in epigenetic studies as well as clinical settings.

BAP1 shapes the bone marrow niche for lymphopoiesis by fine-tuning epigenetic profiles in endosteal mesenchymal stromal cells.

Hematopoiesis occurs within a unique bone marrow (BM) microenvironment, which consists of various niche cells, cytokines, growth factors, and extracellular matrix components. These multiple components directly or indirectly regulate the maintenance and differentiation of hematopoietic stem cells (HSCs). Here we report that BAP1 in BM mesenchymal stromal cells (MSCs) is critical for the maintenance of HSCs and B lymphopoiesis. Mice lacking BAP1 in MSCs show aberrant differentiation of hematopoietic stem and progenitor cells, impaired B lymphoid differentiation, and expansion of myeloid lineages. Mechanistically, BAP1 loss in distinct endosteal MSCs, expressing PRX1 but not LEPR, leads to aberrant expression of genes affiliated with BM niche functions. BAP1 deficiency leads to a reduced expression of pro-hematopoietic factors such as Scf caused by increased H2AK119-ub1 and H3K27-me3 levels on the promoter region of these genes. On the other hand, the expression of myelopoiesis stimulating factors including Csf3 was increased by enriched H3K4-me3 and H3K27-ac levels on their promoter, causing myeloid skewing. Notably, loss of BAP1 substantially blocks B lymphopoiesis and skews the differentiation of hematopoietic precursors toward myeloid lineages in vitro, which is reversed by G-CSF neutralization. Thus, our study uncovers a key role for BAP1 expressed in endosteal MSCs in controlling normal hematopoiesis in mice by modulating expression of various niche factors governing lymphopoiesis and myelopoiesis via histone modifications.

Rapid and Label-Free Detection of 5-Hydroxymethylcytosine in Genomic DNA Using an Au/ZnO Nanorods Hybrid Nanostructure-Based Electrochemical Sensor.

Ten-eleven-translocation (TET) proteins modify DNA methylation by oxidizing 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). Loss of 5hmC, a widely accepted epigenetic hallmark of cancers, is proposed as a biomarker for early cancer diagnosis and prognosis. Thus, precise quantification of 5hmC holds great potential for diverse clinical applications. DNAs containing 5mC or 5hmC display different adsorption affinity toward the gold surface, thus producing different electrochemical responses. Here a novel, label-free electrochemical sensor based on gold nanoparticles (Au NPs)/zinc oxide nanorods (ZnO NRs) nanostructure for the facile and real-time detection of 5hmC-enriched DNAs is reported. The hybrid structure is fabricated by the vertical hydrothermal growth of ZnO NRs onto indium tin oxide glass substrate, followed by the decoration of ZnO NRs with Au NPs via sputtering. Successful fabrication is confirmed by analyzing the morphology and chemical composition of the sensor. By coupling the fabricated sensor with cyclic voltammetry, its functionality in distinguishing genomic DNAs containing different levels of 5hmC is validated. Notably, the sensor device successfully and consistently detects 5hmC loss in primary hepatocellular carcinoma, compared to the normal tissues. Thus, the novel sensing strategy to assess DNA hydroxymethylation will likely find broad applications in early cancer diagnosis and prognosis evaluation.