Harnessing targeted DNA methylation and demethylation using dCas9

Hypermethylation of the ADIRF promoter regulates its expression level and is involved in NNK-induced malignant transformation of lung bronchial epithelial cells

The carcinogenic mechanism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a well-known tobacco carcinogen, has not been fully elucidated in epigenetic studies. 5-Methylcytosine (5mC) modification plays a major role in epigenetic regulation. In this study, the 5mC level increased in both BEAS-2B human bronchial epithelium cells treated with 100 mg/L NNK for 24 h and NNK-induced malignant-transformed BEAS-2B cells (2B-NNK cells), suggesting that 5mC modification is associated with the malignant transformation mechanism of NNK. Using a combination of Methylated DNA Immunoprecipitation Sequencing (MeDIP-seq), RNA sequencing (RNA-seq), and bioinformatics analysis of data from the Genomic Data Commons database, we found that the Adipogenesis regulatory factor (ADIRF) promoter region was abnormally hypermethylated, yielding low ADIRF mRNA expression, and that ADIRF overexpression could inhibit the proliferation, migration, and invasion of 2B-NNK cells. This finding suggests that ADIRF plays a tumor suppressor role in the NNK-induced malignant transformation of cells. Subsequently, using 5-Aza-2'-deoxycytidine (5-Aza-2'-dC) and the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Catalytically Dead Cas9 (dCas9 system), we verified that the demethylation of the ADIRF promoter region in 2B-NNK cells inhibited the proliferation, migration, and invasion ability of the cells and increased their apoptosis ability. These results suggest that abnormal 5mC modification of the ADIRF promoter plays a positive regulatory role in the pathogenesis of NNK-induced lung cancer. This study offers a new experimental basis for the epigenetic mechanism of NNK-induced lung cancer.

Large-scale manipulation of promoter DNA methylation reveals context-specific transcriptional responses and stability

Background

Cytosine DNA methylation is widely described as a transcriptional repressive mark with the capacity to silence promoters. Epigenome engineering techniques enable direct testing of the effect of induced DNA methylation on endogenous promoters; however, the downstream effects have not yet been comprehensively assessed.

Results

Here, we simultaneously induce methylation at thousands of promoters in human cells using an engineered zinc finger-DNMT3A fusion protein, enabling us to test the effect of forced DNA methylation upon transcription, chromatin accessibility, histone modifications, and DNA methylation persistence after the removal of the fusion protein. We find that transcriptional responses to DNA methylation are highly context-specific, including lack of repression, as well as cases of increased gene expression, which appears to be driven by the eviction of methyl-sensitive transcriptional repressors. Furthermore, we find that some regulatory networks can override DNA methylation and that promoter methylation can cause alternative promoter usage. DNA methylation deposited at promoter and distal regulatory regions is rapidly erased after removal of the zinc finger-DNMT3A fusion protein, in a process combining passive and TET-mediated demethylation. Finally, we demonstrate that induced DNA methylation can exist simultaneously on promoter nucleosomes that possess the active histone modification H3K4me3, or DNA bound by the initiated form of RNA polymerase II.

Conclusions

These findings have important implications for epigenome engineering and demonstrate that the response of promoters to DNA methylation is more complex than previously appreciated.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13059-022-02728-5.

On demand expression control of endogenous genes with DExCon, DExogron and LUXon reveals differential dynamics of Rab11 family members

CRISPR technology has made generation of gene knock-outs widely achievable in cells. However, once inactivated, their re-activation remains difficult, especially in diploid cells. Here, we present DExCon (Doxycycline-mediated endogenous gene Expression Control), DExogron (DExCon combined with auxin-mediated targeted protein degradation), and LUXon (light responsive DExCon) approaches which combine one-step CRISPR-Cas9-mediated targeted knockin of fluorescent proteins with an advanced Tet-inducible TRE3GS promoter. These approaches combine blockade of active gene expression with the ability to re-activate expression on demand, including activation of silenced genes. Systematic control can be exerted using doxycycline or spatiotemporally by light, and we demonstrate functional knock-out/rescue in the closely related Rab11 family of vesicle trafficking regulators. Fluorescent protein knock-in results in bright signals compatible with low-light live microscopy from monoallelic modification, the potential to simultaneously image different alleles of the same gene, and bypasses the need to work with clones. Protein levels are easily tunable to correspond with endogenous expression through cell sorting (DExCon), timing of light illumination (LUXon), or by exposing cells to different levels of auxin (DExogron). Furthermore, our approach allowed us to quantify previously unforeseen differences in vesicle dynamics, transferrin receptor recycling, expression kinetics, and protein stability among highly similar endogenous Rab11 family members and their colocalization in triple knock-in ovarian cancer cell lines.

Epigenetic Editing in Prostate Cancer: Challenges and Opportunities

Epigenome editing consists of fusing a predesigned DNA recognition unit to the catalytic domain of a chromatin modifying enzyme leading to the introduction or removal of an epigenetic mark at a specific locus. These platforms enabled the study of the mechanisms and roles of epigenetic changes in several research domains such as those addressing pathogenesis and progression of cancer. Despite the continued efforts required to overcome some limitations, which include specificity, off-target effects, efficacy, and longevity, these tools have been rapidly progressing and improving.Since prostate cancer is characterized by multiple genetic and epigenetic alterations that affect different signalling pathways, epigenetic editing constitutes a promising strategy to hamper cancer progression. Therefore, by modulating chromatin structure through epigenome editing, its conformation might be better understood and events that drive prostate carcinogenesis might be further unveiled.This review describes the different epigenome engineering tools, their mechanisms concerning gene's expression and regulation, highlighting the challenges and opportunities concerning prostate cancer research.

Hypermethylation of Mitochondrial Cytochrome b and Cytochrome c Oxidase II Genes with Decreased Mitochondrial DNA Copy Numbers in the APP/PS1 Transgenic Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia. Increasing evidence shows that mitochondrial DNA (mtDNA) methylation plays an essential role in many diseases related to mitochondrial dysfunction. Since mitochondrial impairment is a key feature of AD, mtDNA methylation may also contribute to AD, but few studies have addressed this issue. Methylation changes of the mitochondrial cytochrome b (CYTB) and cytochrome c oxidase II (COX II) genes in AD have not been reported. We analyzed mtDNA methylation changes of the CYTB and COX II genes in an APP/PS1 transgenic mouse model of AD using pyrosequencing. We examined mtDNA copy numbers and the levels of expression by quantitative real-time PCR. Average methylation levels of different CpG sites were ≤ 4.0%. Methylated mtDNA accounted for only a small part of the total mtDNA. We also observed hypermethylation of mitochondrial CYTB and COX II genes with decreased mtDNA copy numbers and expression in the hippocampi of APP/PS1 transgenic mice. mtDNA methylation may play an important role in AD pathology, which may open a new window for AD therapy.

Deciphering the multifaceted roles of TET proteins in T-cell lineage specification and malignant transformation

TET proteins are DNA demethylases that can oxidize 5-methylcytosine (5mC) to generate 5-hydroxymethylcytosine (5hmC) and other oxidized mC bases (oxi-mCs). Importantly, TET proteins govern cell fate decisions during development of various cell types by activating a cell-specific gene expression program. In this review, we focus on the role of TET proteins in T-cell lineage specification. We explore the multifaceted roles of TET proteins in regulating gene expression in the contexts of T-cell development, lineage specification, function, and disease. Finally, we discuss the future directions and experimental strategies required to decipher the precise mechanisms employed by TET proteins to fine-tune gene expression and safeguard cell identity.

Genomic Targeting of TET Activity for Targeted Demethylation Using CRISPR/Cas9

Methylation of DNA at cytosine bases is an important DNA modification underlying normal development and disease states. Despite decades of research into the biological function of DNA methylation, most of the observations so far have relied primarily on associative data between observed changes in DNA methylation states and local changes in transcriptional activity or chromatin state processes. This is primarily due to the lack of molecular tools to precisely modify DNA methylation in the genome. Recent advances in genome editing technologies have allowed repurposing the CRISPR-Cas9 system for epigenome editing by fusing the catalytically dead Cas9 (dCas9) to epigenome modifying enzymes. Moreover, methods of recruiting multiple protein domains, including the SunTag system, have increased the efficacy of epigenome editing at target sites. Here, we describe an end-to-end protocol for efficient targeted removal of DNA methylation by recruiting multiple catalytic domain of TET1 enzymes to the target sites with the dCas9-SunTag system, including sgRNA design, molecular cloning, delivery of plasmid into mammalian cells, and targeted DNA methylation analysis.

Site-Specific DNA Demethylation as a Potential Target for Cancer Epigenetic Therapy

Aberrant promoter DNA hypermethylation is a typical characteristic of cancer and it is often seen in malignancies. Recent studies showed that regulatory cis-elements found up-stream of many tumor suppressor gene promoter CpG island (CGI) attract DNA methyltransferases (DNMT) that hypermethylates and silence the genes. As epigenetic alterations are potentially reversible, they make attractive targets for therapeutic intervention. The currently used decitabine (DAC) and azacitidine (AZA) are DNMT inhibitors that follow the passive demethylation pathway. However, they lead to genome-wide demethylation of CpGs in cells, which makes difficult to use it for causal effect analysis and treatment of specific epimutations. Demethylation through specific demethylase enzymes is thus critical for epigenetic resetting of silenced genes and modified chromatins. Yet DNA-binding factors likely play a major role to guide the candidate demethylase enzymes upon its fusion. Before the advent of clustered regulatory interspaced short palindromic repeats (CRISPR), both zinc finger proteins (ZNFs) and transcription activator-like effector protein (TALEs) were used as binding platforms for ten-eleven translocation (TET) enzymes and both systems were able to induce transcription at targeted loci in an in vitro as well as in vivo model. Consequently, the development of site-specific and active demethylation molecular trackers becomes more than hypothetical to makes a big difference in the treatment of cancer in the future. This review is thus to recap the novel albeit distinct studies on the potential use of site-specific demethylation for the development of epigenetic based cancer therapy.