Single-CpG resolution mapping of 5-hydroxymethylcytosine by chemical labeling and exonuclease digestion identifies evolutionarily unconserved CpGs as TET targets

TET2-mediated epigenetic reprogramming of breast cancer cells impairs lysosome biogenesis

TET2-mediated oxidation of 5-methylcytosine establishes an antiviral state and contributes to MYC-dependent down-regulation of genes involved in lysosome biogenesis and function in breast cancer cells.

Methylation and demethylation of cytosines in DNA are believed to act as keystones of cell-specific gene expression by controlling the chromatin structure and accessibility to transcription factors. Cancer cells have their own transcriptional programs, and we sought to alter such a cancer-specific program by enforcing expression of the catalytic domain (CD) of the methylcytosine dioxygenase TET2 in breast cancer cells. The TET2 CD decreased the tumorigenic potential of cancer cells through both activation and repression of a repertoire of genes that, interestingly, differed in part from the one observed upon treatment with the hypomethylating agent decitabine. In addition to promoting the establishment of an antiviral state, TET2 activated 5mC turnover at thousands of MYC-binding motifs and down-regulated a panel of known MYC-repressed genes involved in lysosome biogenesis and function. Thus, an extensive cross-talk between TET2 and the oncogenic transcription factor MYC establishes a lysosomal storage disease–like state that contributes to an exacerbated sensitivity to autophagy inducers.

The hydroxymethylome of multiple myeloma identifies FAM72D as a 1q21 marker linked to proliferation

Cell identity relies on the cross-talk between genetics and epigenetics and their impact on gene expression. Oxidation of 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC) is the first step of an active DNA demethylation process occurring mainly at enhancers and gene bodies and, as such, participates in processes governing cell identity in normal and pathological conditions. Although genetic alterations are well documented in multiple myeloma (MM), epigenetic alterations associated with this disease have not yet been thoroughly analyzed. To gain insight into the biology of MM, genome-wide 5hmC profiles were obtained and showed that regions enriched in this modified base overlap with MM enhancers and super enhancers and are close to highly expressed genes. Through the definition of a MM-specific 5hmC signature, we identified FAM72D as a poor prognostic gene located on 1q21, a region amplified in high risk myeloma. We further uncovered that FAM72D functions as part of the FOXM1 transcription factor network controlling cell proliferation and survival and we evidenced an increased sensitivity of cells expressing high levels of FOXM1 and FAM72 to epigenetic drugs targeting histone deacetylases and DNA methyltransferases.

Compilation of Modern Technologies To Map Genome-Wide Cytosine Modifications in DNA

Over the past few decades, various DNA modification detection methods have been developed; many of the high-resolution methods are based on bisulfite treatment, which leads to DNA degradation, to a degree. Thus, novel bisulfite-free approaches have been developed in recent years and shown to be useful for epigenome analysis in otherwise difficult-to-handle, but important, DNA samples, such as hmC-seal and hmC-CATCH. Herein, an overview of advances in the development of epigenome sequencing methods for these important DNA modifications is provided.

Epigenetic modification of nucleic acids: from basic studies to medical applications

The epigenetic modification of nucleic acids represents one of the most significant areas of study in the field of nucleic acids because it makes gene regulation more complex and heredity more complicated, thus indicating its profound impact on aspects of heredity, growth, and diseases. The recent characterization of epigenetic modifications of DNA and RNA using chemical labelling strategies has promoted the discovery of these modifications, and the newly developed single-base or single-cell resolution mapping strategies have enabled large-scale epigenetic studies in eukaryotes. Due to these technological breakthroughs, several new epigenetic marks have been discovered that have greatly extended the scope and impact of epigenetic modifications in nucleic acids over the past few years. Because epigenetics is reversible and susceptible to environmental factors, it could potentially be a promising direction for clinical medicine research. In this review, we have comprehensively discussed how these epigenetic marks are involved in disease, including the pathogenesis, prevention, diagnosis and treatment of disease. These findings have revealed that the epigenetic modification of nucleic acids has considerable significance in various areas from methodology to clinical medicine and even in biomedical applications.

Target specificity of mammalian DNA methylation and demethylation machinery

We review here the molecular mechanisms employed by DNMTs and TET enzymes that are responsible for shaping the DNA methylation pattern of a mammalian cell.

TET-mediated active DNA demethylation: mechanism, function and beyond

In mammals, DNA methylation in the form of 5-methylcytosine (5mC) can be actively reversed to unmodified cytosine (C) through TET dioxygenase-mediated oxidation of 5mC to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC), followed by replication-dependent dilution or thymine DNA glycosylase (TDG)-dependent base excision repair. In the past few years, biochemical and structural studies have revealed mechanistic insights into how TET and TDG mediate active DNA demethylation. Additionally, many regulatory mechanisms of this process have been identified. Technological advances in mapping and tracing the oxidized forms of 5mC allow further dissection of their functions. Furthermore, the biological functions of active DNA demethylation in various biological contexts have also been revealed. In this Review, we summarize the recent advances and highlight key unanswered questions.

Cytosine modifications modulate the chromatin architecture of transcriptional enhancers

Epigenetic mechanisms are believed to play key roles in the establishment of cell-specific transcription programs. Accordingly, the modified bases 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) have been observed in DNA of genomic regulatory regions such as enhancers, and oxidation of 5mC into 5hmC by Ten-eleven translocation (TET) proteins correlates with enhancer activation. However, the functional relationship between cytosine modifications and the chromatin architecture of enhancers remains elusive. To gain insights into their function, 5mC and 5hmC levels were perturbed by inhibiting DNA methyltransferases and TETs during differentiation of mouse embryonal carcinoma cells into neural progenitors, and chromatin characteristics of enhancers bound by the pioneer transcription factors FOXA1, MEIS1, and PBX1 were interrogated. In a large fraction of the tested enhancers, inhibition of DNA methylation was associated with a significant increase in monomethylation of H3K4, a characteristic mark of enhancer priming. In addition, at some specific enhancers, 5mC oxidation by TETs facilitated chromatin opening, a process that may stabilize MEIS1 binding to these genomic regions.