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Significance Genomic imprinting is essential for human development and occurs in germ cells before fertilization. The noncoding RNA, nc886, is the only known example of more than 100 such human genes which shows variable frequencies of maternal imprinting. Here, we show that the DNA methylation imprint is present in oocytes and that the probability of imprinting increases as a function of maternal age. Importantly, we demonstrate that alcohol consumption but not cigarette smoking is associated with a lower frequency of imprinting. While most studies focus on the postconceptional developmental time, our work indicates that maternal age and exposures the year prior to pregnancy may alter the epigenome and therefore the developing child., Genomic imprinting occurs before fertilization, impacts every cell of the developing child, and may be sensitive to environmental perturbations. The noncoding RNA, nc886 (also called VTRNA2-1) is the only known example of the ∼100 human genes imprinted by DNA methylation, that shows polymorphic imprinting in the population. The nc886 gene is part of an ∼1.6-kb differentially methylated region (DMR) that is methylated in the oocyte and silenced on the maternal allele in about 75% of humans worldwide. Here, we show that the presence or absence of imprinting at the nc886 DMR in an individual is consistent across different tissues, confirming that the imprint is established before cellular differentiation and is maintained into adulthood. We investigated the relationships between the frequency of imprinting in newborns and maternal age, alcohol consumption and cigarette smoking before conception in more than 1,100 mother/child pairs from South Africa. The probability of imprinting in newborns was increased in older mothers and decreased in mothers who drank alcohol before conception. On the other hand, cigarette smoking had no apparent relationship with the frequency of imprinting. These data show an epigenetic change during oocyte maturation which is potentially subject to environmental influence. Much focus has been placed on avoiding alcohol consumption during pregnancy, but our data suggest that drinking before conception may affect the epigenome of the newborn.

The anaphase-promoting complex/cyclosome (APC/C) is an E3 ubiquitin ligase and critical regulator of cell cycle progression. Despite its vital role, it has remained challenging to globally map APC/C substrates. By combining orthogonal features of known substrates, we predicted APC/C substrates in silico. This analysis identified many known substrates and suggested numerous candidates. Unexpectedly, chromatin regulatory proteins are enriched among putative substrates, and we show experimentally that several chromatin proteins bind APC/C, oscillate during the cell cycle, and are degraded following APC/C activation, consistent with being direct APC/C substrates. Additional analysis revealed detailed mechanisms of ubiquitylation for UHRF1, a key chromatin regulator involved in histone ubiquitylation and DNA methylation maintenance. Disrupting UHRF1 degradation at mitotic exit accelerates G1-phase cell cycle progression and perturbs global DNA methylation patterning in the genome. We conclude that APC/C coordinates crosstalk between cell cycle and chromatin regulatory proteins. This has potential consequences in normal cell physiology, where the chromatin environment changes depending on proliferative state, as well as in disease., This study shows that the cell cycle E3 ubiquitin ligase APC/C is a regulator of several chromatin regulatory proteins, including the multivalent epigenetic reader and writer UHRF1. Perturbing UHRF1 ubiquitylation and degradation alters cell cycle and DNA methylation patterning, pointing to a key role for cell cycle degradation in shaping chromatin environments.

The chromatin-binding E3 ubiquitin ligase ubiquitin-like with PHD and RING finger domains 1 (UHRF1) contributes to the maintenance of aberrant DNA methylation patterning in cancer cells through multivalent histone and DNA recognition. The tandem Tudor domain (TTD) of UHRF1 is well-characterized as a reader of lysine 9 di- and tri-methylation on histone H3 (H3K9me2/me3) and, more recently, lysine 126 di- and tri-methylation on DNA ligase 1 (LIG1K126me2/me3). However, the functional significance and selectivity of these interactions remain unclear. In this study, we used protein domain microarrays to search for additional readers of LIG1K126me2, the preferred methyl state bound by the UHRF1 TTD. We show that the UHRF1 TTD binds LIG1K126me2 with high affinity and selectivity compared to other known methyllysine readers. Notably, and unlike H3K9me2/me3, the UHRF1 plant homeodomain (PHD) and its N-terminal linker (L2) do not contribute to multivalent LIG1K126me2 recognition along with the TTD. To test the functional significance of this interaction, we designed a LIG1K126me2 cell-penetrating peptide (CPP). Consistent with LIG1 knockdown, uptake of the CPP had no significant effect on the propagation of DNA methylation patterning across the genomes of bulk populations from high-resolution analysis of several cancer cell lines. Further, we did not detect significant changes in DNA methylation patterning from bulk cell populations after chemical or genetic disruption of lysine methyltransferase activity associated with LIG1K126me2 and H3K9me2. Collectively, these studies identify UHRF1 as a selective reader of LIG1K126me2 in vitro and further implicate the histone and non-histone methyllysine reader activity of the UHRF1 TTD as a dispensable domain function for cancer cell DNA methylation maintenance.

The Anaphase-Promoting Complex/Cyclosome (APC/C) is an E3 ubiquitin ligase and critical regulator of cell cycle progression. Despite its vital role, it has remained challenging to globally map APC/C substrates. By combining orthogonal features of known substrates, we predicted APC/C substratesin silico. This analysis identified many known substrates and suggested numerous candidates. Unexpectedly, chromatin regulatory proteins are enriched among putative substrates and we show that several chromatin proteins bind APC/C, oscillate during the cell cycle and are degraded following APC/C activation, consistent with being direct APC/C substrates. Additional analysis revealed detailed mechanisms of ubiquitylation for UHRF1, a key chromatin regulator involved in histone ubiquitylation and DNA methylation maintenance. Disrupting UHRF1 degradation at mitotic exit accelerates G1-phase cell cycle progression and perturbs global DNA methylation patterning in the genome. We conclude that APC/C coordinates crosstalk between cell cycle and chromatin regulatory proteins. This has potential consequences in normal cell physiology, where the chromatin environment changes depending on proliferative state, as well as in disease.

Chromatin immunoprecipitation followed by next-generation sequencing (ChIP-seq) is a key technique for mapping the distribution and relative abundance of histone posttranslational modifications (PTMs) and chromatin-associated factors across genomes. There is a perceived challenge regarding the ability to quantitatively plot ChIP-seq data, and as such, approaches making use of exogenous additives, or “spike-ins” have recently been developed. Relying on the fact that the IP step of ChIP-seq is a competitive binding reaction, we present a quantitative framework for ChIP-seq analysis that circumvents the need to modify standard sample preparation pipelines with spike-in reagents. We also introduce a visualization technique that, when paired with our formal developments, produces a much more rich characterization of sequencing data.

Summary UHRF1 facilitates the establishment and maintenance of DNA methylation patterns in mammalian cells. The establishment domains are defined, including E3 ligase function, but the maintenance domains are poorly characterized. Here, we demonstrate that UHRF1 histone- and hemimethylated DNA binding functions, but not E3 ligase activity, maintain cancer-specific DNA methylation in human colorectal cancer (CRC) cells. Disrupting either chromatin reader activity reverses DNA hypermethylation, reactivates epigenetically silenced tumor suppressor genes (TSGs), and reduces CRC oncogenic properties. Moreover, an inverse correlation between high UHRF1 and low TSG expression tracks with CRC progression and reduced patient survival. Defining critical UHRF1 domain functions and its relationship with CRC prognosis suggests directions for, and value of, targeting this protein to develop therapeutic DNA demethylating agents.

SUMMARY A role for cancer cell epithelial-to-mesenchymal transition (EMT) in cancer is well established. Here, we show that, in addition to cancer cell EMT, ovarian cancer cell metastasis relies on an epigenomic mesenchymal-to-epithelial transition (MET) in host mesenchymal stem cells (MSCs). These reprogrammed MSCs, termed carcinoma-associated MSCs (CA-MSCs), acquire pro-tumorigenic functions and directly bind cancer cells to serve as a metastatic driver/chaperone. Cancer cells induce this epigenomic MET characterized by enhancer-enriched DNA hypermethylation, altered chromatin accessibility, and differential histone modifications. This phenomenon appears clinically relevant, as CA-MSC MET is highly correlated with patient survival. Mechanistically, mirroring MET observed in development, MET in CA-MSCs is mediated by WT1 and EZH2. Importantly, EZH2 inhibitors, which are clinically available, significantly inhibited CA-MSC-mediated metastasis in mouse models of ovarian cancer., Graphical Abstract, In Brief Fan et al. demonstrate that ovarian cancer reprograms the epigenome of stromal cells, inducing a mesenchymal-to-epithelial transition (MET) to form carcinoma-associated mesenchymal stem cells (CA-MSCs). This MET, mediated by WT1 and EZH2, enables CA-MSC:cancer cell co-metastasis. EZH2 inhibition decreases CA-MSC-mediated metastasis, presenting a potential therapeutic opportunity in ovarian cancer.

Histone post-translational modifications (PTMs) are important genomic regulators often studied by chromatin immunoprecipitation (ChIP), whereby their locations and relative abundance are inferred by antibody capture of nucleosomes and associated DNA. However, the specificity of antibodies within these experiments have not been systematically studied. Here, we use histone peptide arrays and internally calibrated ChIP (ICeChIP) to characterize 52 commercial antibodies purported to distinguish the H3K4 methylforms (me1, me2, and me3, with each ascribed distinct biological functions). We find that many widely-used antibodies poorly distinguish the methylforms and that high- and low-specificity reagents can yield dramatically different biological interpretations, resulting in substantial divergence from the literature for numerous H3K4 methylform paradigms. Using ICeChIP, we also discern quantitative relationships between enhancer H3K4 methylation and promoter transcriptional output and can measure global PTM abundance changes. Our results illustrate how poor antibody specificity contributes to the “reproducibility crisis,” demonstrating the need for rigorous, platform-appropriate validation.

// Emily L. Putiri 1 , Rochelle L. Tiedemann 1,2 , Chunsheng Liu 1 , Jeong-Hyeon Choi 2 and Keith D. Robertson 1 1 Department of Molecular Pharmacology and Experimental Therapeutics and Center for Individualized Medicine, Mayo Clinic, Rochester, MN 2 Cancer Center, Georgia Regents University, Augusta, GA Correspondence: Keith D. Robertson, email: // Keywords : DNA methylation, epigenetics, cancer, histone modification, histone methylation Received : May 05, 2014 Accepted : July 13, 2014 Published : July 14, 2014 Abstract The correlation between DNA methylation and a subset of histone post-translational modifications (positive and negative) has hinted at an underlying regulatory crosstalk between histone marks and DNA methylation in patterning the human DNA methylome, an idea further supported by corresponding alterations to both histone marks and DNA methylation during malignant transformation. This study investigated the framework by which histone marks influence DNA methylation at a genome-wide level. Using RNAi in a pluripotent human embryonic carcinoma cell line we depleted essential components of the MLL/COMPASS, polycomb repressive complex 2 (PRC2), and PRC1 histone modifying complexes that establish, respectively, the post-translational modifications H3K4me3, H3K27me3, and H2AK119ub, and assayed the impact of the subsequent depletion of these marks on the DNA methylome. Absence of H2AK119ub resulted predominantly in hypomethylation across the genome. Depletion of H3K4me3 and, surprisingly, H3K27me3 caused CpG island hypermethylation at a subset of loci. Intriguingly, many promoters were co-regulated by all three histone marks, becoming hypermethylated with loss of H3K4me3 or H3K27me3 and hypomethylated with depletion of H2AK119ub, and many of these co-regulated loci were among those commonly targeted for aberrant hypermethylation in cancer. Taken together, our results elucidate novel roles for polycomb and MLL/COMPASS in regulating DNA methylation and define targets of this regulation.

Pancreatic cancer has a disproportionate death-to-incidence rate largely resultant from late stage diagnoses, leading to advanced cancers which have metastasized and have increased resistance to common chemotherapeutics. This malignant progression is characterized by the increase of many molecular markers, and developing novel therapeutics targeting these late stage markers is essential for improving patient prognoses. We have identified several proteins within the non-canonical Wnt pathway that are upregulated in advanced pancreatic ductal adenocarcinomas (PDAC), and we are exploring the mechanisms driving upregulation and the resulting alterations to cell signaling. Analysis of microarray data from human derived organoids (from 6 normal pancreas samples and 38 tumor samples) revealed that two receptors in the Wnt pathway, Frizzled 2 (FZD2) and Frizzled 6 (FZD6), have increased expression levels in late-stage PDAC. The temporal increase of these non-canonical, planar cell polarity altering receptors suggests a previously underappreciated role for Wnt signaling in the progression of pancreatic cancer. The increase of these two receptors in tumor tissue was confirmed through analysis of RNA-sequencing of patient samples, including 179 tumor and 171 normal samples. Interestingly, after analyzing patient overall survival and progression free survival we found that, out of the ten members of the Frizzled receptor family, higher levels of FZD2 and FZD6 result in the worst patient prognoses. Additionally, retrospective analysis of gene expression data from Moffitt et al. suggests that FZD2 and FZD6 are higher in the aggressive “basal-like” sub-category of pancreatic cancer. To begin to understand the mechanism for these changes we have used a panel of PDAC cell lines, grown in both traditional and 3-dimensional culture. We have found that decreasing levels of FZD2 and FZD6, through stable sh-RNA knockdown, results in cells which are less motile (observed via Transwell and scratch assays) and are also less capable of anchorage independent growth. Also, cell lines with increased levels of FZD2 result in cells migrating through 3D-matrix as small cell clusters rather than as single cells, which has also been observed in partial-epithelial to mesenchymal transition cell lines. Taken together, non-canonical Wnt signaling in PDAC, mediated by FZD2 and/or FZD6 receptors, results in phenotypic alterations which are consistent with those often observed during cancer progression. These changes may help explain why patients with increased expression of FZD2 and FZD6 have worse prognoses and may also warrant more exploration into specific Frizzled inhibitors. Citation Format: Payton D. Stevens, Adam Racette, Rochelle L. Tiedemann, Bart O. Williams. Non-canonical Wnt signaling in late-stage PDAC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2628.

Nucleosomes are the basic unit of chromatin. Nucleosome positioning (NP) plays a key role in transcriptional regulation and other biological processes. To better understand NP we used MNase-seq to investigate changes that occur as human embryonic stem cells (hESCs) transition to nascent mesoderm and then to smooth muscle cells (SMCs). Compared to differentiated cell derivatives, nucleosome occupancy at promoters and other notable genic sites, such as exon/intron junctions and adjacent regions, in hESCs shows a stronger correlation with transcript abundance and is less influenced by sequence content. Upon hESC differentiation, genes being silenced, but not genes being activated, display a substantial change in nucleosome occupancy at their promoters. Genome-wide, we detected a shift of NP to regions of higher G+C content as hESCs differentiate to SMCs. Notably, genomic regions with higher nucleosome occupancy harbor twice as many G↔C changes but fewer than half A↔T changes, compared to regions with lower nucleosome occupancy. Finally, our analysis indicates that the hESC genome is not rearranged and has a sequence mutation rate resembling normal human genomes. Our study reveals another unique feature of hESC chromatin, and sheds light on the relationship between nucleosome occupancy and sequence G+C content.

DNA methylation, mediated by the combined action of three DNA methyltransferases (DNMT1, DNMT3A, and DNMT3B), is essential for mammalian development and is a major contributor to cellular transformation. To elucidate how DNA methylation is targeted, we mapped the genome-wide localization of all DNMTs and methylation, and examined the relationships among these markers, histone modifications, and nucleosome structure in a pluripotent human tumor cell line in its undifferentiated and differentiated states. Our findings reveal a strong link between DNMTs and transcribed loci, and that DNA methylation is not a simple sum of DNMT localization patterns. A comparison of the epigenomes of normal and cancerous stem cells, and pluripotent and differentiated states shows that the presence of at least two DNMTs is strongly associated with loci targeted for DNA hypermethylation. Taken together, these results shed important light on the determinants of DNA methylation and how it may become disrupted in cancer cells., National Institutes of Health (U.S.) (Grant RC1HG005334), National Science Foundation (U.S.) (Postdoctoral Fellowship 0905968)

DNA methyltransferases (DNMTs) are responsible for establishing (DNMT3A, 3B, 3L) and maintaining (DNMT1) DNA methylation genome-wide. Aberrant DNA methylation is frequently observed in cancer; however, little is known about how regulation of this modification goes awry. In this study, we aim to understand how DNA methylation is regulated by the DNMTs throughout the genome by identifying specific and broad changes in methylation patterning upon depletion of the DNMTs. We utilize siRNA technology to acutely deplete NCCIT embryonal carcinoma cells of DNMT mRNA (individually and in combination), and then assay the impact on genome-wide DNA methylation patterns using the HumanMethylation450 Bead Chip (450K array). Depletion of DNMT1 (individual/combination) resulted in widespread hypomethylation, most notably in gene bodies, 3′UTRs, and intergenic sequences. DNMT3 knockdown resulted in more specific changes in DNA methylation, but surprisingly, more hypermethylation (predominately in gene bodies) than hypomethylation events occurred. These specific hypermethylation events, particularly in samples with DNMT3B KD, significantly overlapped with sites hypomethylated in DNMT1 KD conditions, indicating a potential cross-regulatory role for DNMT1 and DNMT3B in regulating DNA methylation across gene bodies. To gain a more comprehensive genome-wide view of DNA methylation in the absence of DNMT3B, we performed Methyl-CpG-Binding-Domain(MBD)-seq on DNMT3B KD cells. MBD-seq revealed dynamic changes in methylation with minor hypermethylation in promoters and subtle hypomethylation across gene bodies; however, analysis of only the most significant methylation changes (> 4-fold) revealed that more hypermethylation events occur in intronic sequences, consistent with results obtained using the 450K array. To further investigate the overlap between DNMT1 hypomethylated and DNMT3B hypermethylated sites, we examined DNA methylation in HCT116 colorectal carcinoma cells lacking (KO) or over-expressing (KI) DNMT1/DNMT3B. Interestingly, a marked number of CpG sites that gained methylation in the DNMT3B KO overlapped significantly with sites that became hypermethylated in DNMT1 and DNMT3B KI, and hypomethylated in DNMT1 KO. Additionally, these HCT116 hypermethylated CpG sites gained methylation in NCCIT DNMT3B KD (individual/combination) and lost methylation in DNMT1 KD. Taken together, these results suggest that DNMT1 and DNMT3B co-regulate DNA methylation at conserved loci across cell types in an opposing fashion, providing novel insight into a potential regulatory mechanism for DNA methylation patterning. Further elucidation of this DNMT1 and DNMT3B co-regulation holds the potential to yield novel therapeutic strategies for correcting aberrant methylation events in cancer. Citation Format: Rochelle Tiedemann, Jeong-Hyeon Choi, Keith Robertson. Acute depletion reveals novel co-regulation of DNA methylation at conserved loci by DNMT1 and DNMT3B. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2305. doi:10.1158/1538-7445.AM2014-2305

The Ten-eleven translocation (TET) family of dioxygenases hydroxylate 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) in DNA. 5mC provides important epigenetic instructions during development, and its aberrant control is a major contributor to cellular transformation; however TET functions in regulating the epigenome, particularly in cancer, remain largely unknown. We targeted TET1, TET2, and TET3 for siRNA-mediated depletion in pluripotent human embryonic carcinoma cells and examined the impact on 5mC and 5hmC genome-wide localization. TET1, TET2, and TET3 co-regulate 5hmC at many sites, and depletion of only one of the TETs is sufficient to reduce 5hmC at these co-regulated sites, suggesting a functional co-dependence for TETs. Depletion of TET1 and TET2 had the greatest impact on 5hmC levels at high and low CpG density promoters, respectively, indicating that TETs exhibit DNA sequence-based functional specificity. All TETs prevent hypermethylation throughout the genome, especially in CpG island shores, where TET depletion resulted in prolific hypermethylation. Promoter hypermethylation resulting from TET depletion was associated with histone H2AK119 monoubiquitination, DNMT1, and DNMT3B occupancy. Surprisingly, TETs also promote cytosine methylation, as many loci became hypomethylated following TET depletion. Induction of differentiation generally caused 5hmC reduction, except at transcriptionally activated genes, which become enriched for 5hmC. Importantly, genes prone to promoter hypermethylation in cancer become depleted of intragenic 5hmC and 5mC with TET deficiency. This study highlights the multi-dimensional functions of TETs in mediating DNA methylation, hydroxymethylation, and gene expression patterns, and the results reveal that chromatin landscape and DNA sequence composition are regulators of TET function. Citation Format: Emily L. Putiri, Rochelle L. Tiedemann, Jeong-Hyeon Choi, Keith D. Robertson. Dynamics of TET methylcytosine dioxygenases in 5-methylcytosine and 5-hydroxymethylcytosine patterning in human cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2319. doi:10.1158/1538-7445.AM2014-2319

Dysregulation of the intrinsic DNA methylation landscape is a ubiquitous feature of human carcinogenesis, manifested by global hypomethylation and promoter-specific hypermethylation, ultimately resulting in genome instability and tumor suppressor gene silencing, respectively. Alterations in DNA methylation are particularly apparent in hepatocellular carcinoma (HCC) which afflicts roughly 750,000 new patients each year [1]. Indeed, it has been demonstrated that a variety of tumor suppressor genes (e.g. p53, E-cadherin) are hypermethylated and silenced in HCC [2-4]. Importantly, HCC is accompanied by the premalignant stage of cirrhosis in 80% of cases. One major roadblock to understanding the methylome in HCC is the presence of multiple etiologies such as Hepatitis C virus (HCV), Hepatitis B virus (HBV), and chronic alcoholism. Therefore, we performed genome-wide methylation profiling to dissect the methylation patterns of more than 170 primary liver samples to stratify etiologic and stage-specific changes in the DNA methylation landscape. Our results profile the DNA methylation landscape across normal, cirrhotic, and HCC livers in the largest study of its kind to date. We unveil distinct locus-specific and large-scale effects of HCV, HBV, and chronic alcoholism in hepatocarcinogenesis. Furthermore, analysis indicates a specific methylation profile for individual etiologies as well as conserved patterns throughout cirrhosis and hepatocellular carcinoma. Our study demonstrates that each etiology contains potential biomarkers and targets for downstream clinical therapeutics. This study is our first step toward defining the epigenome in cirrhosis and hepatocellular carcinoma and will be combined with future genomic and epimutational data (e.g. transcription, histone modifications, miRNA) to determine the true extent and interplay between epigenetic marks across different stages of liver cancer. Overall, this research has the potential to improve our understanding of epigenetics and result in diagnostic, prognostic, and therapeutic epigenetic signatures in cirrhosis and hepatocellular carcinoma, which are expected to allow for more timely and efficient detection of disease. 1. Jemal, A., et al., Global cancer statistics. CA: a cancer journal for clinicians, 2011. 61(2): p. 69-90. 2. Tischoff, I. and A. Tannapfe, DNA methylation in hepatocellular carcinoma. World journal of gastroenterology : WJG, 2008. 14(11): p. 1741-8. 3. Calvisi, D.F., et al., Mechanistic and prognostic significance of aberrant methylation in the molecular pathogenesis of human hepatocellular carcinoma. The Journal of clinical investigation, 2007. 117(9): p. 2713-22. 4. Lambert, M.P., et al., Aberrant DNA methylation distinguishes hepatocellular carcinoma associated with HBV and HCV infection and alcohol intake. Journal of hepatology, 2011. 54(4): p. 705-15. Citation Format: Ryan A. Hlady, Rochelle Tiedemann, William Puszyk, Chen Liu, Jeong-Hyeon Choi, Keith D. Robertson. Identification of common and unique epigenetic signatures of chronic hepatitis infection and alcohol abuse in human liver disease. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2309. doi:10.1158/1538-7445.AM2014-2309

Background: The TET family of dioxygenases catalyze conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), but their involvement in establishing normal 5mC patterns during mammalian development and their contributions to aberrant control of 5mC during cellular transformation remain largely unknown. We depleted TET1, TET2, and TET3 in a pluripotent embryonic carcinoma cell model and examined the impact on genome-wide 5mC, 5hmC, and transcriptional patterns. Results: TET1 depletion yields widespread reduction of 5hmC, while depletion of TET2 and TET3 reduces 5hmC at a subset of TET1 targets suggesting functional co-dependence. TET2 or TET3 depletion also causes increased 5hmC, suggesting these proteins play a major role in 5hmC removal. All TETs prevent hypermethylation throughout the genome, a finding dramatically illustrated in CpG island shores, where TET depletion results in prolific hypermethylation. Surprisingly, TETs also promote methylation, as hypomethylation was associated with 5hmC reduction. TET function is highly specific to chromatin environment: 5hmC maintenance by all TETs occurs at polycomb-marked chromatin and genes expressed at moderate levels; 5hmC removal by TET2 is associated with highly transcribed genes enriched for H3K4me3 and H3K36me3. Importantly, genes prone to hypermethylation in cancer become depleted of 5hmC with TET deficiency, suggesting that TETs normally promote 5hmC at these loci. Finally, all three TETs, but especially TET2, are required for 5hmC enrichment at enhancers, a condition necessary for expression of adjacent genes. Conclusions: These results provide novel insight into the division of labor among TET proteins and reveal important connections between TET activity, the chromatin landscape, and gene expression. Background Vertebrate cellular identity arises through intricate differentiation events orchestrated by epigenetic regulation of gene expression. One key epigenetic mechanism is methylation of DNA. DNA is covalently modified by methylation of the carbon-5 position within cytosine nucleotides (5mC), an epigenetic mark that, when occurring in gene promoters, is associated with transcriptional repression. DNA methylation primarily occurs in the context of cytosine followed by guanine (CpG), and normal CpG methylation patterns have been extensively characterized

DNA methyltransferases (DNMTs) are responsible for establishing (DNMT3A, DNMT3B, DNMT3L) and maintaining (DNMT1) DNA methylation genome-wide. Hypomethylation of repetitive sequences and transposable elements coupled with gene-specific promoter hypermethylation events contribute to the genomic instability and loss of tumor suppressor gene transcription observed in cancer. Regulation of aberrant methylation in cancer remains poorly understood. The aim of our study was to identify unique and overlapping target sites for each of the DNMTs to better understand regulation of normal and aberrant DNA methylation. We hypothesized that acute depletion of the DNMTs (individual and combination) mediated by siRNA technology in NCCIT human embryonic carcinoma cells would result in both distinct and broad changes in DNA methylation patterning. Genome-wide methylation was assayed using the HumanMethylation450 Bead Chip (450K array) allowing for specific CpG site methylation status determination. Select target sites were verified by bisulfite genomic sequencing. DNMT1 knockdown samples (individual/combination) revealed genome-wide hypomethylation, with the strongest demethylation occurring in gene bodies, 3′UTR, and intergenic sequences. Interestingly, only the DNMT1 individual knockdown showed significant hypermethylation in gene promoters. DNMT3 knockdowns showed more specific changes in DNA methylation, but surprisingly, more hypermethylation events occurred than hypomethylation at CpG dinucleotides. Hypermethylation observed in DNMT3 knockdown occurred primarily in gene bodies and 3′UTR, and overlapped significantly with those genes that become hypomethylated in DNMT1 knockdown, indicating a potential cross-regulatory role for the DNMTs to maintain proper regulation of DNA methylation at specific gene termini. Conversely, gene promoters were targeted for hypomethylation in DNMT3 knockdown, and did not significantly overlap with genes that become hypermethylated in DNMT1 knockdown. Of particular interest was that DNMT3B knockdown resulted in widespread non-CpG hypomethylation. In contrast, DNMT3L knockdown showed non-CpG hypermethylation, indicating a potential mechanism for regulation of non-CpG methylation where DNMT3B is responsible for non-CpG methylation, and DNMT3L acts to restrict DNMT3B's activity at non-CpG dinucleotides. Our results reveal a complex view of DNA methylation regulation, in which DNMTs not only target specific sites for methylation, but also cooperate to establish and maintain proper levels of DNA methylation at CpG and non-CpG dinucleotides. Moving forward, we believe our results will provide the framework needed to define the regulatory mechanisms by which DNA methylation is conferred and ultimately develop therapeutic strategies to correct aberrant methylation events that occur in cancer. Citation Format: Rochelle L. Tiedemann, Jeong-Hyeon Choi, Keith D. Robertson. Acute depletion reveals novel divisions of labor among human DNA methyltransferases in cancer. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr B34.

DNA methyltransferases (DNMTs) are responsible for establishing (DNMT3A, DNMT3B, DNMT3L) and maintaining (DNMT1) DNA methylation to regulate gene transcription and promote overall genome stability. Global changes in DNA methylation, such as hypomethylation of repetitive sequences and hypermethylation of tumor supressor gene promoters, are commonly observed in various types of cancer; however, the DNMTs’ contribution to this aberrant methylation remains largely unknown. In this study, we aim to identify unique and overlapping target sites for each of the DNMTs in order to better understand aberrant DNA methylation in cancer that will ultimately permit development of new therapeutic strategies. We utilize siRNA-mediated knockdown technology to acutely deplete the mRNA for each of the DNMTs in both individual and combinatorial fashion in NCCIT embryonal carcinoma cells. Subsequently, DNA methylation is observed genome-wide in each DNA sample using two different methodologies: (1) Methyl-CpG Binding Domain (MBD)-seq, which identifies regions of the genome that are enriched for DNA methylation, and (2) Illumina Infinium HumanMethylation450 BeadChip (450K array) allowing for specific CpG site methylation status determination. Aligned MBD-seq sequences for individual DNMT knockdowns are analyzed by read coverage nomalization within 100Kbp windows and using various peak-calling algorithms (e.g. MACS, BALM). For the 450K array, DNA samples for both individual and combination knockdowns undergo bisulfite conversion and array processing; β-values for each CpG site are derived from the array signal intensities using GenomeStudio and R/Bioconductor (minfi). Genome-wide DNA methylation analysis reveals that DNMT1 depletion, both individual and in combination with knockdown of other DNMTs, results in global demethylation among all genomic features. Interestingly, a small population of genes exhibit hypermethylation in gene-promoter CpG islands for DNMT1 (individual only) depletion. In contrast, de novo methyltransferase depletion (individual and combination) shows more specific demethylation effects. In particular, hypomethylation events resulting from DNMT3B depletion (individual and combination (not 3B+3L)) occur within gene bodies and largely outside of CpG islands and flanking regions (shores, shelves). Additionally, a number of hypermethylation events occurring within the 3’UTR region of genes are observed in de novo methyltransferase depleted samples. We anticipate further analysis will reveal unique and overlapping target sites for each of the DNMTs that will lay the ground-work necessary to characterize and understand DNMT recruitment both in normal and cancerous tissues. Citation Format: Rochelle L. Tiedemann, Jeong-Hyeon Choi, Keith D. Robertson. Acute depletion of DNA methyltransferases reveals unique and overlapping target sites in cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2970. doi:10.1158/1538-7445.AM2013-2970

Aberrant DNA methylation is commonly observed in cancer and is characterized by genome-wide hypomethylation and gene-specific hypermethylation, which is thought to contribute to genomic instability and tumor suppressor gene silencing, respectively. The DNA methyltransferases (DNMTs) are responsible for the establishment (DNMT3A, DNMT3B, DNMT3L) and maintenance (DNMT1) of DNA methylation patterns genome-wide. The mechanism by which DNA methylation patterns are altered in cancer is not well understood. Genome-wide unique and overlapping target sites for each of the DNMTs are also unknown both in normal and cancer states. Identification of DNMT target loci is essential in order to better understand how aberrant DNA methylation occurs in cancer. To study this process, DNMT mRNA levels were depleted both individually and in a combinatorial fashion via RNAi-based techniques in embryonic carcinoma cells. Following reduction in DNMT expression, the resulting DNA and RNA was analyzed for genome-wide DNA methylation and gene expression patterns, respectively. An affinity purification method, Methyl-Binding Domain (MBD)-seq, was used to capture and enrich methylated regions of the genome by utilizing the methyl-binding domain of MBD2b. The enriched methylated DNA was then used to construct an Illumina sequencing library. Global gene expression patterns were analyzed by microarray for each RNA sample. Next generation sequencing and microarray data were analyzed using several available algorithms (e.g. MACS) and high-throughput data software packages (e.g. Partek Genomics Suite) in order to construct and evaluate the DNA methylation profiles and subsequent gene expression changes that result from DNMT depletion. Our data show that distinct changes in DNA methylation profiles occur among the various DNMT knockdown samples that permit us to identify unique and cooperative target loci for each DNMT. Further elucidation of DNMT target sites holds great promise for enhancing our understanding of mechanisms that control aberrant DNA methylation that is observed in cancer as well as provide insight and rationale for targeting specific DNMTs in cancer therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5009. doi:1538-7445.AM2012-5009

Global patterns of DNA methylation, mediated by the DNA methyltransferases (DNMTs), are disrupted in all cancers by mechanisms that remain largely unknown, hampering their development as therapeutic targets. Combinatorial acute depletion of all DNMTs in a pluripotent human tumor cell line, followed by epigenome and transcriptome analysis, revealed DNMT functions in unprecedented detail. DNMT3B occupancy regulates methylation during differentiation, while an unexpected interplay was discovered in which DNMT1 and DNMT3B antithetically regulate methylation and hydroxymethylation in gene bodies, a finding confirmed in other cell types. DNMT3B mediated nonCpG methylation, while DNMT3L influenced the activity of DNMT3B toward nonCpG versus CpG site methylation. Taken together, these data reveal new functional targets of each DNMT suggesting that isoform selective inhibition would be therapeutically advantageous.