Restoration of TET2 deficiency inhibits tumor growth in head neck squamous cell carcinoma

Landscape of TET2 Mutations: From Hematological Malignancies to Solid Tumors

BACKGROUND

The ten-eleven translocation (TET) enzyme family is a key regulator of DNA methylation, responsible for the conversion of 5-methylcytosine to 5-hydroxymethylcytosine to promote locus-specific demethylation. Thus, it is not surprising that loss or attenuation of TET enzymes is implicated in genomic hypermethylation and transcriptional reprogramming that drives cancer development. Somatic mutations in TET2 are observed in the bone marrow of 5%-10% of healthy adults over 65 years of age, imparting a hematopoietic stem cell advantage and subsequent clonal hematopoiesis of indeterminate potential (CHIP), a condition which is associated with increased risk of myeloid malignancy. Somatic TET2 mutations are frequently reported in myeloid disorders, including myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Evidence suggests that TET2 mutations also affect prognosis in myeloid leukemia and other hematopoietic malignancies. However, there is a paucity of collated data on the frequency of TET2 mutations in solid human cancers.

OBJECTIVES

We review the published literature on TET2 mutation in human solid cancers and explore their frequency and impact on patient outcomes.

RESULTS & CONCLUSIONS

Somatic TET2 mutations are reported in numerous solid human cancers, including those arising in the skin, lung and prostate. Many of the somatic TET2 mutations reported in solid cancers are recurrent, suggesting functionality. There is also evidence to suggest that somatic TET2 mutations affect prognosis in solid human cancers.

Targeting Epigenetic Dysregulations in Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is one of the deadliest human cancers, with the overall 5-year survival rate stagnating in recent decades due to the lack of innovative treatment approaches. Apart from the recently Food and Drug Administration-approved epidermal growth factor receptor inhibitor and immune checkpoint inhibitor, alternative therapeutic strategies that target epigenetic abnormalities, an emerging cancer hallmark, remain to be fully explored. A pathological epigenetic landscape, characterized by widespread reprogramming of chromatin modifications such as DNA methylation and histone modifications, which drives transcription deregulation and genome reorganization, has been extensively documented in numerous cancers, including HNSCC. Growing evidence indicates that these frequent epigenomic alterations play pivotal roles in regulating malignant transformation, promoting metastasis and invasion, and reshaping the tumor microenvironment. Furthermore, these epigenetic changes also present unique vulnerabilities that open new avenues for identifying novel prognostic biomarkers and developing targeted antitumor therapies. In this review, we summarize recent discoveries of epigenetic dysregulations in HNSCC, with a focus on deregulated chromatin modifications, which include aberrant DNA methylation, oncohistone H3 lysine 36 to methionine (H3K36M) mutation, as well as recurrent mutations or altered expression of chromatin-modifying enzymes such as NSD1, EZH2, and KMT2C/D. Importantly, we discuss the various molecular mechanisms underlying the contributions of these epigenetic alterations to HNSCC development, particularly their involvement in deregulated cell proliferation and cell death, metabolic reprogramming, tumor immune evasion, and phenotypic plasticity. Finally, we conclude by highlighting the translational and clinical implications of targeting the epigenetic machinery, which offers promising prospects for overcoming resistance to conventional radiotherapy/chemotherapy and enhancing the response to immunotherapy in HNSCC.

Bridging tissue repair and epithelial carcinogenesis: epigenetic memory and field cancerization

The epigenome coordinates spatial-temporal specific gene expression during development and in adulthood, for the maintenance of homeostasis and upon tissue repair. The upheaval of the epigenetic landscape is a key event in the onset of many pathologies including tumours, where epigenetic changes cooperate with genetic aberrations to establish the neoplastic phenotype and to drive cell plasticity during its evolution. DNA methylation, histone modifiers and readers or other chromatin components are indeed often altered in cancers, such as carcinomas that develop in epithelia. Lining the surfaces and the cavities of our body and acting as a barrier from the environment, epithelia are frequently subjected to acute or chronic tissue damages, such as mechanical injuries or inflammatory episodes. These events can activate plasticity mechanisms, with a deep impact on cells' epigenome. Despite being very effective, tissue repair mechanisms are closely associated with tumour onset. Here we review the similarities between tissue repair and carcinogenesis, with a special focus on the epigenetic mechanisms activated by cells during repair and opted by carcinoma cells in multiple epithelia. Moreover, we discuss the recent findings on inflammatory and wound memory in epithelia and describe the epigenetic modifications that characterise them. Finally, as wound memory in epithelial cells promotes carcinogenesis, we highlight how it represents an early step for the establishment of field cancerization.

TET3 downregulation and low 5-hydroxymethylcytosine are epigenetic signatures of head and neck carcinoma

BACKGROUND

Ten-eleven translocases (TETs) are enzymes responsible for demethylation processes, playing a crucial role in maintaining the body's methylation balance. Dysregulation of TET expression can lead to abnormal methylation levels. Isocitrate dehydrogenases (IDH) are upstream genes involved in Kreb cycle responsible for production of α-ketoglutarate (α-KG). α-KG and vitamin C are cofactors of TET3 enzyme. There is limited data on the relationship between TET3 and its cofactor Vitamin C in head and neck carcinoma (H&NC).

METHODS AND RESULTS

In this study, we have investigated the expression of the TET3 gene along with IDH1/2 genes involved in the Krebs cycle in the peripheral blood of 32 H&NC patients compared to 32 healthy controls. We estimated serum levels of TET3 protein and vitamin C and 5-hydroxymethylcytosine (5-hmC) percentage in DNA isolated from EDTA blood samples. Our findings revealed that TET3 and IDH1/2 were downregulated in H&NC patients compared to healthy controls. Serum levels of TET3 and Vitamin C were low in H&NC patients compared to healthy controls. Diminished levels of percentage 5-hmC were detected in EDTA blood samples of H&NC patients compared to controls. Spearman correlation analysis revealed a significant positive correlation between TET3 levels, vitamin C levels and 5-hmC percentage.

CONCLUSION

The low levels of Vitamin C are believed to contribute to decreased activity of the TET3 gene and less conversion of 5-methylcytosine (5-mC) to 5-hmC. Dietary supplementation of Vitamin C may increase TET3 activity.

Expression of ten-eleven translocation 2 and glutathione-S-transferase pi in colorectal cancer patients with and without type 2 diabetes mellitus

AIMS

To highlight possible correlations of type 2 diabetes mellitus (T2DM) with microscopic / macroscopic characteristics of colorectal cancer tissues, along with the expression of Ten-Eleven Translocation 2 (TET2) and glutathione-S-transferase pi (GST-pi) proteins.

TET2 deficiency promotes anxiety and depression-like behaviors by activating NLRP3/IL-1β pathway in microglia of allergic rhinitis mice

BACKGROUND

Anxiety and depression-like behaviors in allergic rhinitis (AR) are attracting attention, while the precise mechanism has not been clearly elucidated. Recent evidence shows that neuroinflammation in anterior cingulate cortex (ACC) may be the core of these neuropsychiatric symptoms in AR. Here, we investigated the molecular link between the anxiety and depression-like behaviors and neuroinflammation in ACC.

METHODS

Mice were sensitized and challenged with ovalbumin (OVA) to induce AR. Nasal inflammation levels were assessed by H&E staining and PAS staining. Anxiety and depression-like behaviors were evaluated by behavioral experiments including open field test, forced swimming test, and sucrose preference test. Neuronal impairment was characterized via Nissl staining and 18FDG-PET. The role of ten-eleven translocation 2 (TET2) in AR-related anxiety and depression was assessed by Tet2-/- mice. In addition, the murine BV2 microglial cell line was utilized to explore the molecular mechanisms by which TET2 mediates neuroinflammation. The levels of TET2, NLRP3 and their downstream molecules were detected by immunohistochemistry, Western blot, Dot blot and ELISA. The effects of metformin on depression-like behaviors in AR mice were also evaluated.

RESULTS

AR mice showed significant anxiety and depression-like behaviors, which associated with the activation of ACC. Loss of TET2 activated the NLRP3/IL-1β pathway of microglia in AR mice, further accelerating the anxiety and depression-like behaviors. In addition, knockdown of TET2 activated the NLRP3/IL-1β pathway in BV2 cells. Metformin improved the neuropsychiatric symptoms of AR mice by reducing the activation of NLRP3/IL-1β pathway after upregulating TET2.

CONCLUSION

TET2 deficiency activates the NLRP3/IL-1β pathway of microglia in the ACC, promoting the pathological process of anxiety and depression-like behavior in AR. Metformin could be effective in treating neuroinflammation by regulating microglia via TET2 up-regulation, indicating that metformin is a potential way to treat anxiety and depression-like behaviors in AR.

The CTBP2-PCIF1 complex regulates m6Am modification of mRNA in head and neck squamous cell carcinoma

PCIF1 can mediate the methylation of N6,2'-O-dimethyladenosine (m6Am) in mRNA. Yet, the detailed interplay between PCIF1 and the potential cofactors and its pathological significance remain elusive. Here, we demonstrated that PCIF1-mediated cap mRNA m6Am modification promoted head and neck squamous cell carcinoma progression both in vitro and in vivo. CTBP2 was identified as a cofactor of PCIF1 to catalyze m6Am deposition on mRNA. CLIP-Seq data demonstrated that CTBP2 bound to similar mRNAs as compared with PCIF1. We then used the m6Am-Seq method to profile the mRNA m6Am site at single-base resolution and found that mRNA of TET2, a well-known tumor suppressor, was a major target substrate of the PCIF1-CTBP2 complex. Mechanistically, knockout of CTBP2 reduced PCIF1 occupancy on TET2 mRNA, and the PCIF1-CTBP2 complex negatively regulated the translation of TET2 mRNA. Collectively, our study demonstrates the oncogenic function of the epitranscriptome regulator PCIF1-CTBP2 complex, highlighting the importance of the m6Am modification in tumor progression.

Organic Acids Derived from Saliva-amalgamated Betel Quid Filtrate Are Predicted as a Ten-eleven Translocation-2 Inhibitor

There is a lack of evidence regarding the use of betel quid (BQ) and its potential contribution to oral cancer. Limited attention has been directed towards investigating the involvement of BQ-derived organic acids in the modulation of metabolic-epigenomic pathways associated with oral cancer initiation and progression. We employed novel protocol for preparing saliva-amalgamated BQ filtrate (SABFI) that mimics the oral cavity environment. SABFI and saliva control were further purified by an in-house developed vertical tube gel electrophoresis tool. The purified SABFI was then subjected to liquid chromatography-high resolution mass spectrometry analysis to identify the presence of organic acids. Profiling of SABFI showed a pool of prominent organic acids such as citric acid. malic acid, fumaric acid, 2-methylcitric acid, 2-hydroxyglutarate, cis-aconitic acid, succinic acid, 2-hydroxyglutaric acid lactone, tartaric acid and β-ketoglutaric acid. SABFI showed anti-proliferative and early apoptosis effects in oral cancer cells. Molecular docking and molecular dynamics simulations predicted that SABFI-derived organic acids as potential inhibitors of the epigenetic demethylase enzyme, Ten-Eleven Translocation-2 (TET2). By binding to the active site of α-ketoglutarate, a known substrate of TET2, these organic acids are likely to act as competitive inhibitors. This study reports a novel approach to study SABFI-derived organic acids that could mimic the chemical composition of BQ in the oral cavity. These SABFI-derived organic acids projected as inhibitors of TET2 and could be explored for their role oral cancer.

Ascorbate content of clinical glioma tissues is related to tumour grade and to global levels of 5-hydroxymethyl cytosine

Gliomas are incurable brain cancers with poor prognosis, with epigenetic dysregulation being a distinctive feature. 5-hydroxymethylcytosine (5-hmC), an intermediate generated in the demethylation of 5-methylcytosine, is present at reduced levels in glioma tissue compared with normal brain, and that higher levels of 5-hmC are associated with improved patient survival. DNA demethylation is enzymatically driven by the ten–eleven translocation (TET) dioxygenases that require ascorbate as an essential cofactor. There is limited data on ascorbate in gliomas and the relationship between ascorbate and 5-hmC in gliomas has never been reported. Clinical glioma samples (11 low-grade, 26 high-grade) were analysed for ascorbate, global DNA methylation and hydroxymethylation, and methylation status of the O-6-methylguanine-DNA methyltransferase (MGMT) promoter. Low-grade gliomas contained significantly higher levels of ascorbate than high-grade gliomas (p = 0.026). Levels of 5-hmC were significantly higher in low-grade than high-grade glioma (p = 0.0013). There was a strong association between higher ascorbate and higher 5-hmC (p = 0.004). Gliomas with unmethylated and methylated MGMT promoters had similar ascorbate levels (p = 0.96). One mechanism by which epigenetic modifications could occur is through ascorbate-mediated optimisation of TET activity in gliomas. These findings open the door to clinical intervention trials in patients with glioma to provide both mechanistic information and potential avenues for adjuvant ascorbate therapy.

Regulation of 5-Hydroxymethylcytosine by TET2 Contributes to Squamous Cell Carcinoma Tumorigenesis

DNA methylation is a key regulatory event controlling a variety of physiological processes and can have dramatic effects on gene transcription. Methylated cytosine (5-methylcytosine) can be oxidized by the TET family of enzymes to 5-hydroxymethylcytosine (5-hmC), a key intermediate in the demethylation cycle, and 5-hmC levels are reduced in malignancies such as acute myeloid leukemia and melanoma. We constructed a tissue microarray of human cutaneous squamous cell carcinoma tumors and found a global reduction in 5-hmC levels compared with that in the adjacent skin. Using a murine K14-CreER system, we have found that loss of Tet2 promotes carcinogen-induced squamous cell carcinoma and cooperates with loss of Tp53 to drive spontaneous squamous cell carcinoma tumors in epithelial tissues. Analysis of changes in 5-hmC and gene expression after loss of Tet2 in the epidermis revealed focal alterations in 5-hmC levels and an increase in hair follicle transient amplifying cell genes along with a reduction in epidermal differentiation genes. These results show a role for TET2 in epidermal lineage specification, consistent with reported roles for TET enzymes in controlling lineage commitment in hematopoietic stem cells and embryonic stem cells and establishing TET2 as a bone fide tumor suppressor in squamous cell carcinoma.

Metformin combats obesity by targeting FTO in an m6A-YTHDF2-dependent manner

Obesity has become a health threat and hard enough to deal with. Evidences show that metformin could inhibit adipogenesis and combat obesity, while its mechanisms remain to be elucidated more comprehensively. In this study, we found that administration of metformin could combat obesity induced by high-fat diet (HFD), indicated by strikingly decreased body weight and weight of inguinal white adipose tissue (iWAT) and epidydimal white adipose tissue (eWAT) compared to the control group. Mechanically, we revealed that metformin could inhibit protein expression of FTO, leading to increased m⁶A methylation levels of cyclin D1 (Ccnd1) and cyclin dependent kinase 2 (Cdk2), two crucial regulators in cell cycle. Ccnd1 and Cdk2 with increased m⁶A levels were recognized by YTH m⁶A RNA binding protein 2 (YTHDF2), causing a YTHDF2-dependent decay and decreased protein expressions. In consequence, mitotic clonal expansion (MCE) process was blocked and adipogenesis was inhibited.

Enhancing Characteristic Gene Selection and Tumor Classification by the Robust Laplacian Supervised Discriminative Sparse PCA

Characteristic gene selection and tumor classification of gene expression data play major roles in genomic research. Due to the characteristics of a small sample size and high dimensionality of gene expression data, it is a common practice to perform dimensionality reduction prior to the use of machine learning-based methods to analyze the expression data. In this context, classical principal component analysis (PCA) and its improved versions have been widely used. Recently, methods based on supervised discriminative sparse PCA have been developed to improve the performance of data dimensionality reduction. However, such methods still have limitations: most of them have not taken into consideration the improvement of robustness to outliers and noise, label information, sparsity, as well as capturing intrinsic geometrical structures in one objective function. To address this drawback, in this study, we propose a novel PCA-based method, known as the robust Laplacian supervised discriminative sparse PCA, termed RLSDSPCA, which enforces the L2,1 norm on the error function and incorporates the graph Laplacian into supervised discriminative sparse PCA. To evaluate the efficacy of the proposed RLSDSPCA, we applied it to the problems of characteristic gene selection and tumor classification problems using gene expression data. The results demonstrate that the proposed RLSDSPCA method, when used in combination with other related methods, can effectively identify new pathogenic genes associated with diseases. In addition, RLSDSPCA has also achieved the best performance compared with the state-of-the-art methods on tumor classification in terms of major performance metrics. The codes and data sets used in the study are freely available at http://csbio.njust.edu.cn/bioinf/rlsdspca/.

Epigenetic and metabolic interplay in cutaneous squamous cell carcinoma

With the ageing of the population and increased levels of recreational sun exposure and immunosuppression, cutaneous squamous cell carcinoma (cSCC), is both an enormous and expanding clinical and economic issue. Despite advances in therapy, up to 5000-8000 people are estimated to die every year from cSCC in the U.S., highlighting the need for both better prevention and treatments. Two emerging areas of scientific discovery that may offer new therapeutic approaches for cSCC are epigenetics and metabolism. Importantly, these disciplines display extensive crosstalk, with metabolic inputs contributing to the chromatin landscape, while the dynamic epigenome shapes transcriptional and cellular responses that feedback into cellular metabolism. Recent evidence suggests that indeed, epigenetic and metabolic dysregulation may be critical contributors to cSCC pathogenesis. Here, we synthesize the latest findings from these fast-moving fields, including how they may drive cSCC, yet also be harnessed for therapy.

Roles and Regulations of TET Enzymes in Solid Tumors

The mechanisms governing the methylome profile of tumor suppressors and oncogenes have expanded with the discovery of oxidized states of 5-methylcytosine (5mC). Ten-eleven translocation (TET) enzymes are a family of dioxygenases that iteratively catalyze 5mC oxidation and promote cytosine demethylation, thereby creating a dynamic global and local methylation landscape. While the catalytic function of TET enzymes during stem cell differentiation and development have been well studied, less is known about the multifaceted roles of TET enzymes during carcinogenesis. This review outlines several tiers of TET regulation and overviews how TET deregulation promotes a cancer phenotype. Defining the tissue-specific and context-dependent roles of TET enzymes will deepen our understanding of the epigenetic perturbations that promote or inhibit carcinogenesis.

Ten-eleven translocase: key regulator of the methylation landscape in cancer

PURPOSE

Methylation of 5th residue of cytosine in CpG island forms 5-methylcytosine which is stable, heritable epigenetic mark. Methylation levels are broadly governed by methyltransferases and demethylases. An aberration in the demethylation process contributes to the silencing of gene expression. Ten eleven translocation (TET) dioxygenase (1-3) the de novo demethylase is responsible for conversion of 5-methylcytosine (5-mC) to 5-hydroxymethylcytosine (5-hmC), 5-formylcytosisne (5-fC) and 5-carboxycytosine (5-caC) during demethylation process. Mutations and abnormal expression of TET proteins contribute to carcinogenesis. Discovery of TET proteins has offered various pathways for the reversal of methylation levels thus, enhancing our knowledge as to how methylation effects cancer progression.

METHODS

We searched "PubMed" and "Google scholar" databases and selected studies with the following keywords "TET enzyme", "cancer", "5-hmC", and "DNA demethylation". In this review, we have discussed combinatorial use of vitamin C in inhibiting tumour growth by enhancing the catalytic activity of TET enzymes and consequently, increasing the 5-hmC levels. 5-Hydroxymethylcytosine holds promise as a prognostic biomarker in solid cancers. The contribution of induction and suppression of TET enzymes and 5-hmC carcinogenesis are discussed in haematological and solid cancers.

RESULTS

We found that TET enzymes play central role in maintaining the methylation balance. Any anomaly in their expression may dip the balance towards cancer progression. Low levels of TET enzymes and 5-hmC correlate with tumour invasion, progression and metastasis. Also, use of vitamin C enhances TET activity.

CONCLUSION

TET enzymes play vital role in shaping the methylation landscape in body. 5-hmC can be used as prognostic marker in solid cancers.

High-Dose Vitamin C: Preclinical Evidence for Tailoring Treatment in Cancer Patients

Simple Summary

Vitamin C is an indispensable micronutrient in the human diet due to the multiple functions it carries out in the body. Reports of clinical studies have indicated that, when administered at high dosage by the intravenous route, vitamin C may exert beneficial antitumor effects in patients with advanced stage cancers, including those refractory to previous treatment with chemotherapy. The aim of this article is to provide an overview of the current scientific evidence concerning the different mechanisms of action by which high-dose vitamin C may kill tumor cells. A special focus will be given to those mechanisms that provide the rationale basis for tailoring vitamin C treatment according to specific molecular alterations present in the tumor and for the selection of the most appropriate companion drugs.

Abstract

High-dose vitamin C has been proposed as a potential therapeutic approach for patients with advanced tumors who failed previous treatment with chemotherapy. Due to vitamin C complex pharmacokinetics, only intravenous administration allows reaching sufficiently high plasma concentrations required for most of the antitumor effects observed in preclinical studies (>0.250 mM). Moreover, vitamin C entry into cells is tightly regulated by SVCT and GLUT transporters, and is cell type-dependent. Importantly, besides its well-recognized pro-oxidant effects, vitamin C modulates TET enzymes promoting DNA demethylation and acts as cofactor of HIF hydroxylases, whose activity is required for HIF-1α proteasomal degradation. Furthermore, at pharmacological concentrations lower than those required for its pro-oxidant activity (<1 mM), vitamin C in specific genetic contexts may alter the DNA damage response by increasing 5-hydroxymethylcytosine levels. These more recently described vitamin C mechanisms offer new treatment opportunities for tumors with specific molecular defects (e.g., HIF-1α over-expression or TET2, IDH1/2, and WT1 alterations). Moreover, vitamin C action at DNA levels may provide the rationale basis for combination therapies with PARP inhibitors and hypomethylating agents. This review outlines the pharmacokinetic and pharmacodynamic properties of vitamin C to be taken into account in designing clinical studies that evaluate its potential use as anticancer agent.