Biological significance of 5-hydroxymethylcytosine in oral epithelial dysplasia and oral 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.

Unidirectional alteration of methylation and hydroxymethylation at the promoters and differential gene expression in oral squamous cell carcinoma

Background: Oral squamous cell carcinoma (OSCC) is one of the most common types of cancer worldwide. Although overall losses of 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) have been previously observed, a genome-wide, single-base-resolution, and simultaneous mapping of 5mC and 5hmC in OSCC is still unaccomplished. Similarly, the mechanism of how 5mC and 5hmC collectively lead to abnormal gene expression in OSCC is largely unexplored. Using parallel whole-genome bisulfite sequencing (WGBS) and whole-genome oxidative bisulfite sequencing (oxWGBS), we characterized 5mC- and 5hmC-profiles at single-nucleotide resolution in paired primary OSCC samples and their normal adjacent tissues (NATs). We also analyzed the effect of 5mC- and 5hmC-modifications on differential gene expression in OSCC using multi-omics analysis. Results: An overall reduction of both 5mC and 5hmC in various genomic regions have been observed in OSCC samples. At promoter regions, a total of 6,921 differentially methylated regions and 1,024 differentially hydroxymethylated regions were identified in OSCC. Interestingly, compared to bidirectional modification with 5mC and 5hmC, unidirectional modification with 5mC and 5hmC at the promoters is associated with bigger change in the gene expression. Additionally, genes bearing unidirectional modification with 5mC and 5hmC at the promoters are enriched in signaling pathways like cell proliferation, cell differentiation, and receptor tyrosine kinase pathway that are essential for the tumorigenesis. Finally, the grouped expression signature of top 20 genes bearing promoter-unidirectional-modification with 5mC and 5hmC tends to correlate with the clinical outcome of certain subtypes of head and neck squamous cell carcinoma. Conclusion: Using parallel WGBS and oxWGBS analyses, we observed an overall reduction of 5mC- and 5hmC-modifications at various genomic regions in OSCC. Unidirectional modification with 5mC and 5hmC at the promoters is associated with enhanced changes in gene expression in OSCC tissues. Furthermore, such differentially expressed genes bearing unidirectional modifications with 5mC and 5hmC at the promoters might have clinical relevance to the outcome of OSCC.

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.

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.

Expression of transmembrane protein aquaporin-3 in oral epithelial dysplasia and oral squamous cell carcinoma

OBJECTIVES

The objective of this study was to evaluate aquaporin-3 (AQP3) expression in patient samples of oral epithelial dysplasia (OED) and oral squamous cell carcinoma (OSCC), thereby assessing the potential of AQP3 as a molecular marker for tumor progression.

STUDY DESIGN

An in vitro comparative study was done to determine the AQP3 expression on 20 surgical biopsy specimens each of OED and OSCC using immunohistochemistry. Twenty specimens of normal oral mucosa were kept as controls. The results were statistically analyzed using one-way analysis of variance and post hoc analysis.

RESULTS

The expression of AQP3 was analyzed and further semiquantified using H-scores. The mean H-score showed a statistically significant difference between OSCC, OED, and normal oral mucosa (P < .05). There was a significant increase in the expression of AQP3 in OSCC and OED compared to normal oral mucosa. The highest expression was observed in OSCC (P < .01).

CONCLUSION

The observations of the study indicate that staining intensity of AQP3 increased from dysplastic noninvasive lesion to invasive OSCC, suggesting a possible role of AQP3 as a biomarker for tumor progression.

Comprehensive analysis of 5-hydroxymethylcytosine in zw10 kinetochore protein as a promising biomarker for screening and diagnosis of early colorectal cancer

BACKGROUND

As a new epigenetic biomarker, 5-hydroxymethylcytosine (5hmC) is broadly involved in various diseases including cancers. However, the function and diagnostic performance of 5hmC in colorectal cancer (CRC) remain unclear.

RESULTS

High-throughput sequencing was used to profile 5hmC levels in adjacent normal colon, advanced adenomas, and CRC. The expression and 5hmC levels in zw10 kinetochore protein (ZW10) were significantly increased in the tissues and blood samples for patients with advanced adenoma and CRC, and were much higher in the early stages of CRC (I and II). The receiver operating characteristic analysis had potential diagnostic value for CRC. The area under the curve (AUC) of ZW10 5hmC levels in tissue samples of CRC was 0.901. In blood samples, the AUC was 0.748 for CRC. In addition, the ZW10 5hmC level had much higher diagnostic performance in early stages of CRC (AUC = 0.857) than it did in advanced stages (AUC = 0.594). Compared with FHC cell, ZW10 expression in HT29 cell was significantly increased. The ZW10 knockdown could inhibit cell proliferation and the ZW10 overexpression could promote cell proliferation in HT-29 cell. Furthermore, ZW10 knockdown inhibited AKT and mTOR phosphorylation, and ZW10 overexpression promoted AKT and mTOR phosphorylation.

CONCLUSIONS

The ZW10 5hmC level may serve as an effective epigenetic biomarker for minimally invasive screening and diagnosis of CRC, and it has higher diagnostic performance in early stages of CRC than it does in advanced stages. In addition, ZW10 could regulate CRC progression through the AKT-mTOR signaling.

A Literature Review of the Potential Diagnostic Biomarkers of Head and Neck Neoplasms

Head and neck neoplasms have a poor prognosis because of their late diagnosis. Finding a biomarker to detect these tumors in an early phase could improve the prognosis and survival rate. This literature review provides an overview of biomarkers, covering the different -omics fields to diagnose head and neck neoplasms in the early phase. To date, not a single biomarker, nor a panel of biomarkers for the detection of head and neck tumors has been detected with clinical applicability. Limitations for the clinical implementation of the investigated biomarkers are mainly the heterogeneity of the study groups (e.g., small population in which the biomarker was tested, and/or only including high-risk populations) and a low sensitivity and/or specificity of the biomarkers under study. Further research on biomarkers to diagnose head and neck neoplasms in an early stage, is therefore needed.

Fisetin Modulates Human Oral Squamous Cell Carcinoma Proliferation by Blocking PAK4 Signaling Pathways

Objective

Human oral squamous cell carcinoma (OSCC) is a major cause of mortality and morbidity worldwide. There is an urgent need to identify bioactive molecules and potential target genes that could inhibit carcinogenesis for OSCC therapy. Fisetin (3,7,3′,4′-tetrahydroxyflavone), a naturally occurring flavonoid, has been previously shown to have anti-proliferative activities in OSCC; however, its molecular mechanism is unknown.

Methods

Colony formation, cell viability, Boyden chamber, wound healing, and tumor xenograft assays were used to detect the impact of fisetin on OSCC cells in vitro and in vivo. Western blot analysis was used to examine the corresponding protein expression.

Results

Fisetin treatment significantly inhibited proliferation and promoted apoptosis by repressing PAK4 expression. Moreover, fisetin treatment attenuated cell migration by blocking PAK4 signaling pathways. In addition, the tumor xenograft showed anti-tumor growth effects of fisetin exposure in vivo.

Conclusion

Fisetin may represent a potential therapeutic strategy for human OSCC by targeting PAK4 signaling pathways.

Metabolic changes during malignant transformation in primary cells of oral lichen planus: Succinate accumulation and tumour suppression

Oral squamous cell carcinoma (OSCC) is usually diagnosed at late stages, which leads to high morbidity. There are evidence that chronic inflammation (eg oral lichen planus [OLP]) was a risk factor of OSCC, but often misdiagnosed or ignored until invasion and metastasis. By applying precision medicine, the molecular microenvironment variations and relevant biomarkers for the malignant transformation from OLP to OSCC can be fully investigated. Several studies pointed out that the metabolic pathway were suppressed in OSCC. However, it remains unclear how the systemic profile of the metabolites change during the malignant transformation. In this study, we examined and compared the mucosa samples from 11 healthy individuals, 10 OLP patients and 21 OSCC patients. Based on the results, succinate, a key metabolite of the tricarboxylic acid cycle pathway, was accumulated in the primary cultured precancerous OLP keratinocytes and OSCC cells. Then, we found that succinate activated the hypoxia‐inducible factor‐1 alpha (HIF‐1α) pathway and induced apoptosis, which could also be up‐regulated by the tumour suppressor lncRNA MEG3. These results suggested the critical roles of succinate and MEG3 in the metabolic changes during malignant transformation from OLP to OSCC, which indicated that succinate, HIF1α and downstream proteins might serve as new biomarkers of precancerous OLP for early diagnosis and therapeutic monitoring. In addition, succinate or its prodrugs might become a potential therapy for the prevention or treatment of OSCC.

Diagnostic utility of dual 5-hydroxymethylcytosine/Melan-A immunohistochemistry in differentiating nodal nevus from metastatic melanoma: An effective first-line test for the workup of sentinel lymph node specimen

BACKGROUND

Distinguishing benign nodal nevus from metastatic melanoma can be diagnostically challenging, with important clinical consequences. Recently, the loss of epigenetic marker, 5-hydroxymethylcytosine (5-hmC) expression by immunohistochemistry has been found in melanomas and atypical melanocytic neoplasms.

METHODS

About 41 metastatic melanomas and 20 nodal nevi were retrieved. Nuclear 5-hmC (brown) and cytoplasmic Melan-A Red (red) double immunohistochemical staining was performed.

RESULTS

Total or partial loss of nuclear expression of 5-hmC was noted in 40/41 metastatic melanomas; these tumor cells were strongly positive for Melan-A Red, except in one case of desmoplastic melanoma. All cases of nodal nevus showed uniformly retained nuclear expression of 5-hmC accompanied by strong Melan-A Red cytoplasmic staining. In two cases containing both nodal nevus and metastatic melanoma, all tumor cells were positive for Melan-A Red, but a nuclear expression of 5-hmC was selectively absent only in the melanoma tumor cells.

CONCLUSION

Dual 5-hmC/Melan-A Red immunohistochemistry is highly specific in distinguishing nodal nevus from metastatic melanoma. Our protocol for brown and red chromogens used in this study provides excellent color contrast and is easy to interpret. Furthermore, this dual staining method allows the preservation of limited tumor tissue, which could be used for potential molecular studies.