The leukemia-associated Mllt10/Af10-Dot1l are Tcf4/β-catenin coactivators essential for intestinal homeostasis

Rare de novo gain-of-function missense variants in DOT1L are associated with developmental delay and congenital anomalies

Misregulation of histone lysine methylation is associated with several human cancers and with human developmental disorders. DOT1L is an evolutionarily conserved gene encoding a lysine methyltransferase (KMT) that methylates histone 3 lysine-79 (H3K79) and was not previously associated with a Mendelian disease in OMIM. We have identified nine unrelated individuals with seven different de novo heterozygous missense variants in DOT1L through the Undiagnosed Disease Network (UDN), the SickKids Complex Care genomics project, and GeneMatcher. All probands had some degree of global developmental delay/intellectual disability, and most had one or more major congenital anomalies. To assess the pathogenicity of the DOT1L variants, functional studies were performed in Drosophila and human cells. The fruit fly DOT1L ortholog, grappa, is expressed in most cells including neurons in the central nervous system. The identified DOT1L variants behave as gain-of-function alleles in flies and lead to increased H3K79 methylation levels in flies and human cells. Our results show that human DOT1L and fly grappa are required for proper development and that de novo heterozygous variants in DOT1L are associated with a Mendelian disease.

The effect of ITLN1, XCL2 and DOT1L variants on knee osteoarthritis risk in the Han population

BACKGROUND

Knee osteoarthritis (KOA) is a complex multifactorial disease, in which genetic factors account for 50% of the risk of osteoarthritis. This study investigated the association between ITLN1, XCL2 and DOT1L variants and KOA risk in the Han population.

METHODS

We applied Agena MassARRAY technology platform to genotype five single-nucleotide polymorphisms (SNPs) in 710 KOA patients and 709 controls. The correlation between ITLN1, XCL2 and DOT1L SNPs (rs2274908, rs4282797, rs4301615 and rs3815308) and KOA risk was calculated by logistic regression analysis, with odds ratio (OR) and 95% confidence intervals (CIs). Also, the relationship between genotypes at these different loci and clinical parameters (White blood cell, Eosinophil ratio, Neutrophil count, Eosinophil count, Monocyte ratio and Monocyte count) among patients and controls was analyzed.

RESULTS

In the overall results, rs2274908, rs4301615 and rs3815308 were correlated with KOA susceptibility. After gender stratification analysis, ITLN1 rs2274908 and XCL2 rs4301615 were related to an increased risk of KOA in males, and ITLN1 rs2274908 and DOT1L rs3815308 were related to an increased risk of KOA in females. After age stratification analysis, ITLN1 rs2274908 and XCL2 rs4301615 were correlated with an increased risk of KOA in people aged > 65 year old. After smoking stratification analysis and drinking stratification analysis, ITLN1 rs2274908, XCL2 rs4301615 and DOT1L rs3815308 were still associated with the risk of KOA.

CONCLUSION

In short, ITLN1 rs2274908, XCL2 rs4301615 and DOT1L rs3815308 were related to KOA risk in the Han population, which was helpful to clarify the pathogenesis of these sites in KOA.

Neuronal Dot1l Activity Acts as a Mitochondrial Gene-Repressor Associated with Human Brain Aging via H3K79 Hypermethylation

Methylation of histone 3 at lysine 79 (H3K79) and its catalyst, a disrupter of telomeric silencing (DOT1l), have been coupled to multiple forms of stress, such as bioenergetic and ER challenges. However, studies on H3K79 methylation and Dot1l in the (aging) brain and neurons are limited. This, together with the increasing evidence of a dynamic neuroepigenome, made us wonder if H3K79 methylation and its activator Dot1l could play important roles in brain aging and associated disorders. In aged humans, we found strong and consistent global hypermethylation of H3K79 in neurons. Specific in dopaminergic neurons, we found a strong increase in H3K79 methylation in lipofucsin positive neurons, which are linked to pathology. In animals, where we conditionally removed Dot1l, we found a rapid loss of H3K79 methylation. As a consequence, we found some decrease in specific dopaminergic genes, and surprisingly, a clear up-regulation of almost all genes belonging to the family of the respiratory chain. These data, in relation to the observed increase in global H3K79 methylation, suggest that there is an inverse relationship between H3K79 methylation and the capacity of energy metabolism in neuronal systems.

DOT1L Is a Novel Cancer Stem Cell Target for Triple-Negative Breast Cancer

PURPOSE

Although chemotherapies kill most cancer cells, stem cell-enriched survivors seed metastasis, particularly in triple-negative breast cancers (TNBC). TNBCs arise from and are enriched for tumor stem cells. Here, we tested if inhibition of DOT1L, an epigenetic regulator of normal tissue stem/progenitor populations, would target TNBC stem cells.

EXPERIMENTAL DESIGN

Effects of DOT1L inhibition by EPZ-5676 on stem cell properties were tested in three TNBC lines and four patient-derived xenograft (PDX) models and in isolated cancer stem cell (CSC)-enriched ALDH1+ and ALDH1- populations. RNA sequencing compared DOT1L regulated pathways in ALDH1+ and ALDH1- cells. To test if EPZ-5676 decreases CSC in vivo, limiting dilution assays of EPZ-5676/vehicle pretreated ALDH1+ and ALDH1- cells were performed. Tumor latency, growth, and metastasis were evaluated. Antitumor activity was also tested in TNBC PDX and PDX-derived organoids.

RESULTS

ALDH1+ TNBC cells exhibit higher DOT1L and H3K79me2 than ALDH1-. DOT1L maintains MYC expression and self-renewal in ALDH1+ cells. Global profiling revealed that DOT1L governs oxidative phosphorylation, cMyc targets, DNA damage response, and WNT activation in ALDH1+ but not in ALDH1- cells. EPZ-5676 reduced tumorspheres and ALDH1+ cells in vitro and decreased tumor-initiating stem cells and metastasis in xenografts generated from ALDH1+ but not ALDH1- populations in vivo. EPZ-5676 significantly reduced growth in vivo of one of two TNBC PDX tested and decreased clonogenic 3D growth of two other PDX-derived organoid cultures.

CONCLUSIONS

DOT1L emerges as a key CSC regulator in TNBC. Present data support further clinical investigation of DOT1L inhibitors to target stem cell-enriched TNBC.

Histone Methyltransferase DOT1L as a Promising Epigenetic Target for Treatment of Solid Tumors

The histone lysine methyltransferase DOT1L (DOT1-like histone lysine methyltransferase) is responsible for the epigenetic regulation of gene expression through specific methylation of lysine79 residue of histone H3 (H3K79) in actively transcribed genes. Its normal activity is crucial for embryonic development and adult tissues functions, whereas its aberrant functioning is known to contribute to leukemogenesis. DOT1L is the only lysine methyltransferase that does not contain a SET domain, which is a feature that allowed the development of selective DOT1L inhibitors that are currently investigated in Phase I clinical trials for cancer treatment. Recently, abnormal expression of this enzyme has been associated with poor survival and increased aggressiveness of several solid tumors. In this review evidences of aberrant DOT1L expression and activity in breast, ovarian, prostate, colon, and other solid tumors, and its relationships with biological and clinical behavior of the disease and response to therapies, are summarized. Current knowledge of the structural basis of DOT1L ability to regulate cell proliferation, invasion, plasticity and stemness, cell cycle progression, cell-to-cell signaling, epithelial-to-mesenchymal transition, and chemoresistance, through cooperation with several molecular partners including noncoding RNAs, is also reviewed. Finally, available options for the treatment of therapeutically challenging solid tumors by targeting DOT1L are discussed.

DOT1L affects colorectal carcinogenesis via altering T cell subsets and oncogenic pathway

Chronic inflammation and oncogenic pathway activation are key-contributing factors in colorectal cancer pathogenesis. However, colorectal intrinsic mechanisms linking these two factors in cancer development are poorly defined. Here, we show that intestinal epithelial cell (IEC)-specific deletion of Dot1l histone methyltransferase (Dot1l^ΔIEC) reduced H3K79 dimethylation (H3K79me2) in IECs and inhibited intestinal tumor formation in Apc^Min- and AOM-DSS-induced colorectal cancer models. IEC-Dot1l abrogation was accompanied by alleviative colorectal inflammation and reduced Wnt/β-catenin signaling activation. Mechanistically, Dot1l deficiency resulted in an increase in Foxp3⁺RORϒ⁺ regulatory T (Treg) cells and a decrease in inflammatory Th17 and Th22 cells, thereby reducing local inflammation in the intestinal tumor microenvironment. Furthermore, Dot1l deficiency caused a reduction of H3K79me2 occupancies in the promoters of the Wnt/β-catenin signaling genes, thereby diminishing Wnt/β-catenin oncogenic signaling pathway activation in colorectal cancer cells. Clinically, high levels of tumor H3K79me2 were detected in patients with colorectal carcinomas as compared to adenomas, and negatively correlated with RORϒ⁺FOXP3⁺ Treg cells. Altogether, we conclude that DOT1L is an intrinsic molecular node connecting chronic immune activation and oncogenic signaling pathways in colorectal cancer. Our work suggests that targeting the DOT1L pathway may control colorectal carcinogenesis. Significance: IEC-intrinsic DOT1L controls T cell subset balance and key oncogenic pathway activation, impacting colorectal carcinogenesis.

Thyroid Hormone Nuclear Receptor TRα1 and Canonical WNT Pathway Cross-Regulation in Normal Intestine and Cancer

A pivotal role of thyroid hormones and their nuclear receptors in intestinal development and homeostasis have been described, whereas their involvement in intestinal carcinogenesis is still controversial. In this perspective article we briefly summarize the recent advances in this field and present new data regarding their functional interaction with one of the most important signaling pathway, such as WNT, regulating intestinal development and carcinogenesis. These complex interactions unveil new concepts and will surely be of importance for translational research.

Targeting of histone methyltransferase DOT1L plays a dual role in chemosensitization of retinoblastoma cells and enhances the efficacy of chemotherapy

Aberrant and exclusive expression of chromatin regulators in retinoblastoma (RB) in contrast to terminally differentiated normal retina presents a unique opportunity of selective targeting for RB. However, precise roles of these chromatin regulators in RB development and their potential as therapeutic targets have not been defined thoroughly. Here, we report that targeting of disruptor of telomeric silencing 1-like (DOT1L), a histone H3K79 methyltransferase, sensitizes RB cells to chemotherapeutic drugs by impairing the DNA damage response and thereby potentiating apoptosis while it is largely inefficacious as a single-agent therapy. Moreover, we identified high mobility group AT-hook 2 (HMGA2) as a novel DOT1L target gene in RB cells and found that its aberrant expression is dependent on DOT1L. As HMGA2 depletion reduced CHK1 phosphorylation during DNA damage response and augmented the drug sensitivity in RB cells, our results suggested that DOT1L targeting has a dual role in chemosensitization of RB cells by directly interfering with the immediate involvement of DOT1L in early DNA damage response upon genotoxic insults and also by downregulating the expression of HMGA2 as a rather late effect of DOT1L inhibition. Furthermore, we provide the first preclinical evidence demonstrating that combined therapy with a DOT1L inhibitor significantly improves the therapeutic efficacy of etoposide in murine orthotopic xenografts of RB by rendering the response to etoposide more potent and stable. Taken together, these results support the therapeutic benefits of DOT1L targeting in combination with other chemotherapeutic agents in RB, with mechanistic insights into how DOT1L targeting can improve the current chemotherapy in an RB cell-selective manner.

Wnt/β-catenin signaling in cancers and targeted therapies

Wnt/β-catenin signaling has been broadly implicated in human cancers and experimental cancer models of animals. Aberrant activation of Wnt/β-catenin signaling is tightly linked with the increment of prevalence, advancement of malignant progression, development of poor prognostics, and even ascendence of the cancer-associated mortality. Early experimental investigations have proposed the theoretical potential that efficient repression of this signaling might provide promising therapeutic choices in managing various types of cancers. Up to date, many therapies targeting Wnt/β-catenin signaling in cancers have been developed, which is assumed to endow clinicians with new opportunities of developing more satisfactory and precise remedies for cancer patients with aberrant Wnt/β-catenin signaling. However, current facts indicate that the clinical translations of Wnt/β-catenin signaling-dependent targeted therapies have faced un-neglectable crises and challenges. Therefore, in this study, we systematically reviewed the most updated knowledge of Wnt/β-catenin signaling in cancers and relatively targeted therapies to generate a clearer and more accurate awareness of both the developmental stage and underlying limitations of Wnt/β-catenin-targeted therapies in cancers. Insights of this study will help readers better understand the roles of Wnt/β-catenin signaling in cancers and provide insights to acknowledge the current opportunities and challenges of targeting this signaling in cancers.

DOT1L complex regulates transcriptional initiation in human erythroleukemic cells

DOT1L, the only H3K79 methyltransferase in human cells and a homolog of the yeast Dot1, normally forms a complex with AF10, AF17, and ENL or AF9, is dysregulated in most cases of mixed-lineage leukemia (MLLr), and has been believed to regulate transcriptional elongation on the basis of its colocalization with RNA polymerase II (Pol II), the sharing of subunits (AF9 and ENL) between the DOT1L and super elongation complexes, and the distribution of H3K79 methylation on both promoters and transcribed regions of active genes. Here we show that DOT1L depletion in erythroleukemic cells reduces its global occupancy without affecting the traveling ratio or the elongation rate (assessed by 4sUDRB-seq) of Pol II, suggesting that DOT1L does not play a major role in elongation in these cells. In contrast, analyses of transcription initiation factor binding reveal that DOT1L and ENL depletions each result in reduced TATA binding protein (TBP) occupancies on thousands of genes. More importantly, DOT1L and ENL depletions concomitantly reduce TBP and Pol II occupancies on a significant fraction of direct (DOT1L-bound) target genes, indicating a role for the DOT1L complex in transcription initiation. Mechanistically, proteomic and biochemical studies suggest that the DOT1L complex may regulate transcriptional initiation by facilitating the recruitment or stabilization of transcription factor IID, likely in a monoubiquitinated H2B (H2Bub1)-enhanced manner. Additional studies show that DOT1L enhances H2Bub1 levels by limiting recruitment of the Spt-Ada-Gcn5-acetyltransferase (SAGA) complex. These results advance our understanding of roles of the DOT1L complex in transcriptional regulation and have important implications for MLLr leukemias.

Epigenetic Regulation of Wnt Signaling by Carboxamide-Substituted Benzhydryl Amines that Function as Histone Demethylase Inhibitors

Aberrant activation of Wnt signaling triggered by mutations in either Adenomatous Polyposis Coli (APC) or CTNNB1 (β-catenin) is a hallmark of colorectal cancers (CRC). As part of a program to develop epigenetic regulators for cancer therapy, we developed carboxamide-substituted benzhydryl amines (CBAs) bearing either aryl or heteroaryl groups that selectively targeted histone lysine demethylases (KDMs) and functioned as inhibitors of the Wnt pathway. A biotinylated variant of N-((5-chloro-8-hydroxyquinolin-7-yl) (4-(diethylamino)phenyl)-methyl)butyramide (CBA-1) identified KDM3A as a binding partner. KDM3A is a Jumonji (JmjC) domain-containing demethylase that is significantly upregulated in CRC. KDM3A regulates the demethylation of histone H3's lysine 9 (H3K9Me₂), a repressive marker for transcription. Inhibiting KDM3 increased H3K9Me₂ levels, repressed Wnt target genes, and curtailed in vitro CRC cell proliferation. CBA-1 also exhibited in vivo inhibition of Wnt signaling in a zebrafish model without displaying in vivo toxicity.

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A class of carboxamide-substituted benzhydryl amine (CBA) Wnt inhibitors

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A biological active, biotinylated CBA to identify KDM3A as a direct target

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CBA-1 interacted with the Mn²⁺ ion in the JmjC domains of KDM3A/3B

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CBA-1 inhibited Wnt signaling in colon cancer cells and in zebrafish models

Transcriptional Regulation of Wnt/β-Catenin Pathway in Colorectal Cancer

The Wnt/β-catenin signaling pathway exerts integral roles in embryogenesis and adult homeostasis. Aberrant activation of the pathway is implicated in growth-associated diseases and cancers, especially as a key driver in the initiation and progression of colorectal cancer (CRC). Loss or inactivation of Adenomatous polyposis coli (APC) results in constitutive activation of Wnt/β-catenin signaling, which is considered as an initiating event in the development of CRC. Increased Wnt/β-catenin signaling is observed in virtually all CRC patients, underscoring the importance of this pathway for therapeutic intervention. Prior studies have deciphered the regulatory networks required for the cytoplasmic stabilisation or degradation of the Wnt pathway effector, β-catenin. However, the mechanism whereby nuclear β-catenin drives or inhibits expression of Wnt target genes is more diverse and less well characterised. Here, we describe a brief synopsis of the core canonical Wnt pathway components, set the spotlight on nuclear mediators and highlight the emerging role of chromatin regulators as modulators of β-catenin-dependent transcription activity and oncogenic output.

The miR-216a-Dot1l Regulatory Axis Is Necessary and Sufficient for Müller Glia Reprogramming during Retina Regeneration

Unlike the adult mammalian retina, Müller glia (MG) in the adult zebrafish retina are able to dedifferentiate into a ‘‘stem cell’’-like state and give rise to multipotent progenitor cells upon retinal damage. We show that miR-216a is downregulated in MG after constant intense light lesioning and that miR-216a suppression is necessary and sufficient for MG dedifferentiation and proliferation during retina regeneration. miR-216a targets the H3K79 methyltransferase Dot1l, which is upregulated in proliferating MG after retinal damage. Loss-of-function experiments show that Dot1l is necessary for MG reprogramming and mediates MG proliferation downstream of miR-216a. We further demonstrate that miR-216a and Dot1l regulate MG-mediated retina regeneration through canonical Wnt signaling. This article reports a regulatory mechanism upstream of Wnt signaling during retina regeneration and provides potential targets for enhancing regeneration in the adult mammalian retina.

Unlike the adult mammalian retina, Müller glia in the adult zebrafish retina are able to reprogram into a stem cell-like state and give rise to multipotent progenitor cells upon retinal damage. Kara et al. show that miR-216a suppression stimulates Müller glia reprogramming through upregulation of the H3K79 methyltransferase Dot1l and activation of Wnt/β-catenin signaling.

MLLT10 in benign and malignant hematopoiesis

Non-random chromosomal translocations involving the putative transcription factor Mixed Lineage Leukemia Translocated to 10 (MLLT10, also known as AF10) are commonly observed in both acute myeloid and lymphoid leukemias and are indicative of a poor prognosis. Despite the well-described actions of oncogenic MLLT10 fusion proteins, the role of wild-type MLLT10 in hematopoiesis is not well characterized. The protein structure and several interacting partners have been described and provide indications as to the potential functions of MLLT10. This review examines these aspects of MLLT10, contextualizing its function in benign and malignant hematopoiesis.

Keeping RNA polymerase II on the run: Functions of MLL fusion partners in transcriptional regulation

Since the identification of key MLL fusion partners as transcription elongation factors regulating expression of HOX cluster genes during hematopoiesis, extensive work from the last decade has resulted in significant progress in our overall mechanistic understanding of role of MLL fusion partner proteins in transcriptional regulation of diverse set of genes beyond just the HOX cluster. In this review, we are going to detail overall understanding of role of MLL fusion partner proteins in transcriptional regulation and thus provide mechanistic insights into possible MLL fusion protein-mediated transcriptional misregulation leading to aberrant hematopoiesis and leukemogenesis.

Androgen receptor with short polyglutamine tract preferably enhances Wnt/β-catenin-mediated prostatic tumorigenesis

Polyglutamine (polyQ) tract polymorphism within the human androgen receptor (AR) shows population heterogeneity. African American men possess short polyQ tracts significantly more frequently than Caucasian American men. The length of polyQ tracts is inversely correlated with the risk of prostate cancer, age of onset, and aggressiveness at diagnosis. Aberrant activation of Wnt signaling also reveals frequently in advanced prostate cancer, and an enrichment of androgen and Wnt signaling activation has been observed in African American patients. Here, we assessed aberrant expression of AR bearing different polyQ tracts and stabilized β-catenin in prostate tumorigenesis using newly generated mouse models. We observed an early onset oncogenic transformation, accelerated tumor cell growth, and aggressive tumor phenotypes in the compound mice bearing short polyQ tract AR and stabilized β-catenin. RNA sequencing analysis showed a robust enrichment of Myc-regulated downstream genes in tumor samples bearing short polyQ AR versus those with longer polyQ tract AR. Upstream regulator analysis further identified Myc as the top candidate of transcriptional regulators in tumor cells from the above mouse samples with short polyQ tract AR and β-catenin. Chromatin immunoprecipitation analyses revealed increased recruitment of β-catenin and AR on the c-Myc gene regulatory locus in the tumor tissues expressing stabilized β-catenin and shorter polyQ tract AR. These data demonstrate a promotional role of aberrant activation of Wnt/β-catenin in combination with short polyQ AR expression in prostate tumorigenesis and suggest a potential mechanism underlying aggressive prostatic tumor development, which has been frequently observed in African American patients.

Aberrant activation of hepatocyte growth factor/MET signaling promotes β-catenin-mediated prostatic tumorigenesis

Co-occurrence of aberrant hepatocyte growth factor (HGF)/MET proto-oncogene receptor tyrosine kinase (MET) and Wnt/β-catenin signaling pathways has been observed in advanced and metastatic prostate cancers. This co-occurrence positively correlates with prostate cancer progression and castration-resistant prostate cancer development. However, the biological consequences of these abnormalities in these disease processes remain largely unknown. Here, we investigated the aberrant activation of HGF/MET and Wnt/β-catenin cascades in prostate tumorigenesis by using a newly generated mouse model in which both murine Met transgene and stabilized β-catenin are conditionally co-expressed in prostatic epithelial cells. These compound mice displayed accelerated prostate tumor formation and invasion compared with their littermates that expressed only stabilized β-catenin. RNA-Seq and quantitative RT-PCR analyses revealed increased expression of genes associated with tumor cell proliferation, progression, and metastasis. Moreover, Wnt signaling pathways were robustly enriched in prostate tumor samples from the compound mice. ChIP-qPCR experiments revealed increased β-catenin recruitment within the regulatory regions of the Myc gene in tumor cells of the compound mice. Interestingly, the occupancy of MET on the Myc promoter also appeared in the compound mouse tumor samples, implicating a novel role of MET in β-catenin-mediated transcription. Results from implanting prostate graft tissues derived from the compound mice and controls into HGF-transgenic mice further uncovered that HGF induces prostatic oncogenic transformation and cell growth. These results indicate a role of HGF/MET in β-catenin-mediated prostate cancer cell growth and progression and implicate a molecular mechanism whereby nuclear MET promotes aberrant Wnt/β-catenin signaling-mediated prostate tumorigenesis.

Characterization of Copy Number Variations in Oral Cavity Squamous Cell Carcinoma Reveals a Novel Role for MLLT3 in Cell Invasiveness

BACKGROUND

DNA copy number variations (CNVs) are a hallmark of cancer, and the current study aimed to demonstrate the profile of the CNVs for oral cavity squamous cell carcinoma (OSCC) and elucidate the clinicopathological associations and molecular mechanisms of a potential marker derived from CNVs, mixed-lineage leukemia translocated to chromosome 3 protein (MLLT3), in OSCC carcinogenesis.

MATERIALS AND METHODS

CNVs in 37 OSCC tissue specimens were analyzed using a high-resolution microarray, the OncoScan array. Gene expression was analyzed by real-time polymerase chain reaction in 127 OSCC and normal tissue samples. Cell function assays included cell cycle, migration, invasion and chromatin immunoprecipitation assays.

RESULTS

We found a novel copy number amplified region, chromosome 9p, encompassing MLLT3 via the comparison of our data set with six other OSCC genome-wide CNV data sets. MLLT3 overexpression was associated with poorer overall survival in patients with OSCC (p = .048). MLLT3 knockdown reduced cell migration and invasion. The reduced invasion ability in MLLT3-knockdown cells was rescued with double knockdown of MLLT3 and CBP/p300-interacting transactivator with ED rich carboxy-terminal domain 4 (CITED4; 21.0% vs. 61.5%). Knockdown of MLLT3 impaired disruptor of telomeric silencing-1-like (Dot1L)-associated hypermethylation in the promoter of the tumor suppressor, CITED4 (p < .001), and hence dysregulated HIF-1α-mediated genes (TWIST, MMP1, MMP2, VIM, and CDH1) in OSCC cells.

CONCLUSION

We identified unique CNVs in tumors of Taiwanese patients with OSCC. Notably, MLLT3 overexpression is related to the poorer prognosis of patients with OSCC and is required for Dot1L-mediated transcriptional repression of CITED4, leading to dysregulation of HIF-1α-mediated genes.

IMPLICATIONS FOR PRACTICE

This article reports unique copy number variations in oral cavity squamous cell carcinoma (OSCC) tumors of Taiwanese patients. Notably, MLLT3 overexpression is related to the poorer prognosis of patients with OSCC and is required for Dot1L-mediated transcriptional repression of CITED4, leading to dysregulation of HIF-1α-mediated genes.

DNA methylation and chromatin modifiers in colorectal cancer

Colorectal carcinogenesis is a multistep process involving the accumulation of genetic alterations over time that ultimately leads to disease progression and metastasis. Binding of transcription factors to gene promoter regions alone cannot explain the complex regulation pattern of gene expression during this process. It is the chromatin structure that allows for a high grade of regulatory flexibility for gene expression. Posttranslational modifications on histone proteins such as acetylation, methylation, or phosphorylation determine the accessibility of transcription factors to DNA. DNA methylation, a chemical modification of DNA that modulates chromatin structure and gene transcription acts in concert with these chromatin conformation alterations. Another epigenetic mechanism regulating gene expression is represented by small non-coding RNAs. Only very recently epigenetic alterations have been included in molecular subtype classification of colorectal cancer (CRC). In this chapter, we will provide examples of the different epigenetic players, focus on their role for epithelial-mesenchymal transition and metastatic processes and discuss their prognostic value in CRC.

MLLT10 promotes tumor migration, invasion, and metastasis in human colorectal cancer

OBJECTIVES

Colorectal cancer (CRC), one of the most aggressive gastrointestinal malignancies, is a frequently diagnosed life-threatening cancer worldwide. Most CRC patients have poor prognosis mainly because of frequent metastasis and recurrence. Thus, it is crucial to find out some new biomarkers and to show deeper insights into the mechanisms of CRC. MLLT10, Myeloid/lymphoid or mixed-lineage leukemia translocated to 10, also known as AF10, a recurrent MLL partner. In this study, we found that MLLT10 promotes CRC tumor invasion and metastasis both in vitro and in vivo.

METHODS

Here, the expression of MLLT10 was evaluated by immunohistochemistry. Then, the plasmid and lentivirus particles for MLLT10 overexpression or knockdown were designed and constructed into SW620 and HT29 cells. Finally, cell proliferation assay, cell adhesion assay, transwell migration, and invasion assay were used to detect the migration and invasion ability of MLLT10 in CRC cells. A tail vein injection assay was employed to evaluate the role of MLLT10 in tumor metastases.

RESULTS

MLLT10 expression was significantly higher in CRC tissues than in noncancerous tissues and was associated with some clinicopathological factors. In vitro, the overexpression of MLLT10 promoted CRC cell migration and invasion, while after MLLT10 was knocked down, the opposite results were observed. Furthermore, we used animal metastasis models to detect the function of MLLT10 in vivo, the results are same with the outcomes in vitro. In lung metastasis sites, the knockdown of MLLT10 in SW620 cells significantly inhibited Vimentin expression, whereas the E-Cadherin was increased.

CONCLUSIONS

These results indicate that MLLT10 regulates the metastasis of CRC cells via EMT.

Signaling and epigenetic mechanisms of intestinal stem cells and progenitors: insight into crypt homeostasis, plasticity, and niches

The rapid turnover of intestinal epithelial cells is maintained by a small number of stem cells located in pocket-like gland structures called crypts. While our understanding of the identity and function of intestinal stem cells (ISCs) has rapidly progressed, epigenetic and transcriptional regulation in crypt stem cell and progenitor pools remains an active field of investigation. Surrounded by various types of cells in the stroma, crypt progenitors display high levels of plasticity, harboring the ability to interconvert in the face of epithelial damage. Recent studies analyzing epigenetic patterns of intestinal epithelial cells have provided evidence that plasticity is maintained by a broadly permissive epigenomic state, wherein cell-lineage specification is directed through activation of signaling pathways and transcription factor (TF) expression. New studies also have shown that the ISC niche, which is comprised of surrounding epithelial and mesenchymal tissues, plays a crucial role in supporting the maintenance and differentiation of stem cells by providing contextual information in the form of signaling cascades, such as Wnt, Notch, and Hippo. These cascades ultimately govern TF expression to promote early cell-lineage decisions in both crypt stem cells and progenitors. Highlighting recent studies investigating signaling, transcriptional, and epigenetic mechanisms of intestinal epithelial cells, we will discuss the mechanisms underlying crypt homeostasis, plasticity, and niches. WIREs Dev Biol 2017, 6:e281. doi: 10.1002/wdev.281 For further resources related to this article, please visit the WIREs website.

DOT1L safeguards cartilage homeostasis and protects against osteoarthritis

Osteoarthritis is the most prevalent and crippling joint disease, and lacks curative treatment, as the underlying molecular basis is unclear. Here, we show that DOT1L, an enzyme involved in histone methylation, is a master protector of cartilage health. Loss of DOT1L disrupts the molecular signature of healthy chondrocytes in vitro and causes osteoarthritis in mice. Mechanistically, the protective function of DOT1L is attributable to inhibition of Wnt signalling, a pathway that when hyper-activated can lead to joint disease. Unexpectedly, DOT1L suppresses Wnt signalling by inhibiting the activity of sirtuin-1 (SIRT1), an important regulator of gene transcription. Inhibition of SIRT1 protects against osteoarthritis triggered by loss of DOT1L activity. Modulating the DOT1L network might therefore be a therapeutic approach to protect the cartilage against osteoarthritis.

The regulation of β-catenin activity and function in cancer: therapeutic opportunities

Wnt/β-catenin signaling is an evolutionarily conserved and versatile pathway that is known to be involved in embryonic development, tissue homeostasis and a wide variety of human diseases. Aberrant activation of this pathway gives rise to the accumulation of β-catenin in the nucleus and promotes the transcription of many oncogenes such as c-Myc and CyclinD-1. As a result, it contributes to carcinogenesis and tumor progression of several cancers, including colon cancer, hepatocellular carcinoma, pancreatic cancer, lung cancer and ovarian cancer. β-Catenin is a pivotal component of the Wnt signaling pathway and it is tightly regulated at three hierarchical levels: protein stability, subcellular localization and transcriptional activity. Uncovering the regulatory mechanisms of β-catenin will provide new insights into the pathogenesis of cancer and other diseases, as well as new therapeutic strategies against these diseases. In this review we dissect the concrete regulatory mechanisms of β-catenin from three aspects mentioned above. Then we focus on the role of β-catenin in cancer initiation, progression, dormancy, immunity and cancer stem cell maintenance. At last, we summarize the recent progress in the development of agents for the pharmacological modulation of β-catenin activity in cancer therapy.

Mutations of Chromatin Structure Regulating Genes in Human Malignancies

Chromatin structure regulating processes mediated by the adenosine triphosphate (ATP) –dependent chromatin remodeling complex and the covalent histone-modifying complexes are critical to gene transcriptional control and normal cellular processes, including cell stemness, differentiation, and proliferation. Gene mutations, structural abnormalities, and epigenetic modifications that lead to aberrant expression of chromatin structure regulating members have been observed in most of human malignancies. Advances in next-generation sequencing (NGS) technologies in recent years have allowed in-depth study of somatic mutations in human cancer samples. The Cancer Genome Atlas (TCGA) is the largest effort to date to characterize cancer genome using NGS technology. In this review, we summarize somatic mutations of chromatin-structure regulating genes from TCGA publications and other cancer genome studies, providing an overview of genomic alterations of chromatin regulating genes in human malignancies.

Wnt Protein Signaling Reduces Nuclear Acetyl-CoA Levels to Suppress Gene Expression during Osteoblast Differentiation

Developmental signals in metazoans play critical roles in inducing cell differentiation from multipotent progenitors. The existing paradigm posits that the signals operate directly through their downstream transcription factors to activate expression of cell type-specific genes, which are the hallmark of cell identity. We have investigated the mechanism through which Wnt signaling induces osteoblast differentiation in an osteoblast-adipocyte bipotent progenitor cell line. Unexpectedly, Wnt3a acutely suppresses the expression of a large number of genes while inducing osteoblast differentiation. The suppressed genes include Pparg and Cebpa, which encode adipocyte-specifying transcription factors and suppression of which is sufficient to induce osteoblast differentiation. The large scale gene suppression induced by Wnt3a corresponds to a global decrease in histone acetylation, an epigenetic modification that is associated with gene activation. Mechanistically, Wnt3a does not alter histone acetyltransferase or deacetylase activities but, rather, decreases the level of acetyl-CoA in the nucleus. The Wnt-induced decrease in histone acetylation is independent of β-catenin signaling but, rather, correlates with suppression of glucose metabolism in the tricarboxylic acid cycle. Functionally, preventing histone deacetylation by increasing nucleocytoplasmic acetyl-CoA levels impairs Wnt3a-induced osteoblast differentiation. Thus, Wnt signaling induces osteoblast differentiation in part through histone deacetylation and epigenetic suppression of an alternative cell fate.

Wnt signaling in cartilage development and diseases: lessons from animal studies

Cartilage not only plays essential roles in skeletal development and growth during pre- and postnatal stages but also serves to provide smooth movement of skeletons throughout life. Thus, dysfunction of cartilage causes a variety of skeletal disorders. Results from animal studies reveal that β-catenin-dependent canonical and independent non-canonical Wnt signaling pathways have multiple roles in regulation of cartilage development, growth, and maintenance. β-Catenin-dependent signaling is required for progression of endochondral ossification and growth of axial and appendicular skeletons, while excessive activation of this signaling can cause severe inhibition of initial cartilage formation and growth plate organization and function in mice. In contrast, non-canonical Wnt signaling is important in columnar organization of growth plate chondrocytes. Manipulation of Wnt signaling causes or ameliorates articular cartilage degeneration in rodent osteoarthritis models. Human genetic studies indicate that Wnt/β-catenin signaling is a risk factor for osteoarthritis. Accumulative findings from analysis of expression of Wnt signaling molecules and in vivo and in vitro functional experiments suggest that Wnt signaling is a therapeutic target for osteoarthritis. The target tissues of Wnt signaling may be not only articular cartilage but also synovium and subchondral bone.

Patterns of Wnt signaling in the life cycle of Podocoryna carnea and its implications for medusae evolution in Hydrozoa (Cnidaria)

Hydrozoans are known for their complex life cycles, alternating between benthic, asexually reproducing polyps and pelagic, sexually reproducing medusae. Although patterning in hydrozoan polyps has been well studied, little is known about the signaling mechanisms governing medusa development. In order to investigate the role of Wnt signaling in medusa development, we use RNA-Seq data collected from three discrete life cycle stages of Podocoryna carnea to assemble, annotate, and assess enrichment and differential expression (DE) of Wnt pathway elements in P. carnea's transcriptome. Enrichment analyses revealed a statistically significant enrichment of DE Wnt signaling transcripts in the transcriptome of P. carnea, of which, the vast majority of these were significantly up-regulated in developing and adult medusae stages. Whole mount in situ hybridization (ISH) reveals co-expression of the Wnt ligand, Wnt3, and a membrane bound Wnt receptor, frizzled3, at the distal and oral ends of the developmental axes of medusae and polyps in P. carnea. DE and ISH results presented here reveal expression of Wnt signaling components consistent with it playing a role in medusa development. Specifically, Wnt ligand expression in the oral region suggests that the Wnt pathway may play a role in medusa patterning, similar to that of polyps. Previous Wnt expression studies in hydrozoan taxa with reduced medusa have failed to detect co-expression of Wnt3 and a frizzled receptor at their truncated developmental axes, suggesting that down regulation of Wnt pathway elements may play a key role in the loss of the medusa life cycle stage in hydrozoan evolution.

Generation of an Enhancer-Trapping Vector for Insertional Mutagenesis in Zebrafish

Enhancer trapping (ET) is a powerful approach to establish tissue- or cell-specific reporters and identify expression patterns of uncharacterized genes. Although a number of enhancer-trapping vectors have been developed and a large library of fish lines with distinct tissue- or cell-specific expression of reporter genes have been generated, the specificity and efficiency of trapping vectors need to be improved because of the bias interaction of minimal promoters with genomic enhancers. Accordingly, we generated an enhancer-trapping vector pTME that contains a minimal mouse metallothionein gene (mMTI) promoter upstream of EGFP reporter. In the first round of screening, twelve zebrafish lines that carry a single copy of ET cassettes were characterized to have tissue- or cell-specific EGFP expression. One of the highly conserved noncoding elements near an insertion site of trapping cassettes was characterized as an enhancer that can specifically regulate the expression of EGFP in cells of the central nervous system. In addition, the pTME vector contains a mutation-cassette that is able to effectively block the transcription of an endogenous gene in an ET line with ubiquitous EGFP expression. Thus, the pTME vector can be used as an alternative tool for both enhancer trapping and mutagenesis across a target genome.

Targeting the WNT Signaling Pathway in Cancer Therapeutics

The WNT signaling cascade is integral in numerous biological processes including embryonic development, cell cycle regulation, inflammation, and cancer. Hyperactivation of WNT signaling secondary to alterations to varying nodes of the pathway have been identified in multiple tumor types. These alterations converge into increased tumorigenicity, sustained proliferation, and enhanced metastatic potential. This review seeks to evaluate the evidence supporting the WNT pathway in cancer, the therapeutic strategies in modulating this pathway, and potential challenges in drug development.

Targets, models and challenges in osteoarthritis research

Osteoarthritis is a chronic degenerative disorder of the joint and represents one of the most common diseases worldwide. Its prevalence and severity are increasing owing to aging of the population, but treatment options remain largely limited to painkillers and anti-inflammatory drugs, which only provide symptomatic relief. In the late stages of the disease, surgical interventions are often necessary to partially restore joint function. Although the focus of osteoarthritis research has been originally on the articular cartilage, novel findings are now pointing to osteoarthritis as a disease of the whole joint, in which failure of different joint components can occur. In this Review, we summarize recent progress in the field, including data from novel ‘omics’ technologies and from a number of preclinical and clinical trials. We describe different in vitro and in vivo systems that can be used to study molecules, pathways and cells that are involved in osteoarthritis. We illustrate that a comprehensive and multisystem approach is necessary to understand the complexity and heterogeneity of the disease and to better guide the development of novel therapeutic strategies for osteoarthritis.

Epigenetic regulation of the intestinal epithelium

The intestinal epithelium is an ideal model system for the study of normal and pathological differentiation processes. The mammalian intestinal epithelium is a single cell layer comprising proliferative crypts and differentiated villi. The crypts contain both proliferating and quiescent stem cell populations that self-renew and produce all the differentiated cell types, which are replaced every 3-5 days. The genetics of intestinal development, homeostasis, and disease are well defined, but less is known about the contribution of epigenetics in modulating these processes. Epigenetics refers to heritable phenotypic traits, including gene expression, which are independent of mutations in the DNA sequence. We have known for several decades that human colorectal cancers contain hypomethylated DNA, but the causes and consequences of this phenomenon are not fully understood. In contrast, tumor suppressor gene promoters are often hypermethylated in colorectal cancer, resulting in decreased expression of the associated gene. In this review, we describe the role that epigenetics plays in intestinal homeostasis and disease, with an emphasis on results from mouse models. We highlight the importance of producing and analyzing next-generation sequencing data detailing the epigenome from intestinal stem cell to differentiated intestinal villus cell.

Association between single nucleotide polymorphisms of DOT1L gene and risk of knee osteoarthritis in a Chinese Han population

To investigate associations between single nucleotide polymorphisms rs12982744 and rs12459350 in the DOT1L gene and knee osteoarthritis (OA) susceptibility in a Chinese Han population. DOT1L rs12982744 and rs12459350 polymorphisms were genotyped in patients with knee OA and age- and sex-matched OA-free controls from a Chinese Han population. A total of 605 patients with knee OA and 615 controls were enrolled in the study. GC and CC genotypes of rs12982744, and variant C, were associated with a significantly increased risk of knee OA. On stratification analysis, the association between the risk of OA and rs12982744 GC heterozygotes compared with GG homozygotes was stronger in females and those aged >65 years. In contrast, the GA and AA genotypes of rs12459350 were not significantly associated with the risk of knee OA, even after further stratification analysis according to age or sex. Our results showed that DOT1L rs12982744 G to C change and variant C genotype may contribute to knee OA risk in a Chinese Han population.

Identification of a DNA methylation signature to predict disease-free survival in locally advanced rectal cancer

In locally advanced rectal cancer a preoperative predictive biomarker is necessary to adjust treatment specifically for those patients expected to suffer relapse. We applied whole genome methylation CpG island array analyses to an initial set of patients (n=11) to identify differentially methylated regions (DMRs) that separate a good from a bad prognosis group. Using a quantitative high-resolution approach, candidate DMRs were first validated in a set of 61 patients (test set) and then confirmed DMRs were further validated in additional independent patient cohorts (n=71, n=42). We identified twenty highly discriminative DMRs and validated them in the test set using the MassARRAY technique. Ten DMRs could be confirmed which allowed separation into prognosis groups (p=0.0207, HR=4.09). The classifier was validated in two additional cohorts (n=71, p=0.0345, HR=3.57 and n=42, p=0.0113, HR=3.78). Interestingly, six of the ten DMRs represented regions close to the transcriptional start sites of genes which are also marked by the Polycomb Repressor Complex component EZH2. In conclusion we present a classifier comprising 10 DMRs which predicts patient prognosis with a high degree of accuracy. These data may now help to discriminate between patients that may respond better to standard treatments from those that may require alternative modalities.

Dot1 histone methyltransferases share a distributive mechanism but have highly diverged catalytic properties

The conserved histone methyltransferase Dot1 establishes an H3K79 methylation pattern consisting of mono-, di- and trimethylation states on histone H3 via a distributive mechanism. This mechanism has been shown to be important for the regulation of the different H3K79 methylation states in yeast. Dot1 enzymes in yeast, Trypanosoma brucei (TbDot1A and TbDot1B, which methylate H3K76) and human (hDot1L) generate very divergent methylation patterns. To understand how these species-specific methylation patterns are generated, the methylation output of the Dot1 enzymes was compared by expressing them in yeast at various expression levels. Computational simulations based on these data showed that the Dot1 enzymes have highly distinct catalytic properties, but share a distributive mechanism. The mechanism of methylation and the distinct rate constants have implications for the regulation of H3K79/K76 methylation. A mathematical model of H3K76 methylation during the trypanosome cell cycle suggests that temporally-regulated consecutive action of TbDot1A and TbDot1B is required for the observed regulation of H3K76 methylation states.

Androgen signaling is a confounding factor for β-catenin-mediated prostate tumorigenesis

Emerging evidence has demonstrated the critical roles for both androgen and Wnt pathways in prostate tumorigenesis. A recent integrative genomic analysis of human prostate cancers has revealed a unique enrichment of androgen and Wnt signaling in early onset prostate cancers, implying their clinical significance in the disease. Additionally, interaction between the androgen receptor (AR) and β-catenin has long been detected in prostate cancer cells. However, the consequence of this interaction in prostate tumorigenesis is still unknown. Because mutations in adenomatous polyposis coli (APC), β-catenin, and other components of the destruction-complex are generally rare in prostate cancers, other mechanisms of aberrant Wnt signaling activation have been speculated. To address these critical questions, we developed Ctnnb1^L(ex3)/+/R26hAR^L/+:PB-Cre4 mice, in which transgenic AR and stabilized β-catenin are co-expressed in prostatic epithelial cells. We observed accelerated tumor development, aggressive tumor invasion, and a decreased survival rate in Ctnnb1^L(ex3)/+/R26hAR^L/+:PB-Cre4 compound mice compared to age-matched Ctnnb1^L(ex3)/+:PB-Cre4 littermate controls, which only have stabilized β-catenin expression in the prostate. Castration of the above transgenic mice resulted in significant tumor regression, implying an essential role of androgen signaling in tumor growth and maintenance. Implantation of the prostatic epithelial cells isolated from the transgenic mice regenerated PIN and prostatic adenocarcinoma lesions. Microarray analyses of transcriptional profiles showed more robust enrichment of known tumor and metastasis promoting genes: Spp1, Egr1, c-Myc, Sp5, and Sp6 genes in samples isolated from Ctnnb1^L(ex3)/+/R26hAR^L/+:PB-Cre4 compound mice than those from Ctnnb1^L(ex3)/+:PB-Cre4 and R26hAR^L/+:PB-Cre4 littermate controls. Together, these data demonstrate a confounding role of androgen signaling in β-catenin initiated oncogenic transformation in prostate tumorigenesis.

Regulation of Wnt signaling target gene expression by the histone methyltransferase DOT1L

The histone methyltransferase DOT1L, solely responsible for histone H3 lysine 79 (H3K79) methylation, is associated with gene activation. Human leukemias carrying MLL gene rearrangements aberrantly recruit DOT1L to leukemogenic genes leading to increased H3K79 methylation and their transcriptional activation. Recent studies suggest that Wnt-targeted genes also depend on H3K79 methylation. Employing a chemical biology approach, the requirement for H3K79 methylation was investigated in Wnt pathway-inducible HEK293 cells and human colon adenocarcinoma-derived cell lines by inhibiting DOT1L with EPZ004777, a selective and potent S-adenosylmethionine competitive inhibitor. Our findings indicate that H3K79 methylation is not essential for the canonical Wnt signaling pathway, in particular for maintenance or activation of Wnt pathway target gene expression. Furthermore, H3K79 methylation is not elevated in human colon carcinoma samples in comparison with normal colon tissue. Therefore, our findings indicate that inhibition of DOT1L histone methyltransferase activity is likely not a viable therapeutic strategy in colon cancer.

Targeting histone lysine methylation in cancer

Within the vast landscape of histone modifications lysine methylation has gained increasing attention because of its profound regulatory potential. The methylation of lysine residues on histone proteins modulates chromatin structure and thereby contributes to the regulation of DNA-based nuclear processes such as transcription, replication and repair. Protein families with opposing catalytic activities, lysine methyltransferases (KMTs) and demethylases (KDMs), dynamically control levels of histone lysine methylation and individual enzymes within these families have become candidate oncology targets in recent years. A number of high quality small molecule inhibitors of these enzymes have been identified. Several of these compounds elicit selective cancer cell killing in vitro and robust efficacy in vivo, suggesting that targeting 'histone lysine methylation pathways' may be a relevant, emerging cancer therapeutic strategy. Here, we discuss individual histone lysine methylation pathway targets, the properties of currently available small molecule inhibitors and their application in the context of cancer.

Wnt some lose some: transcriptional governance of stem cells by Wnt/β-catenin signaling

In mammals, Wnt/β-catenin signaling features prominently in stem cells and cancers, but how and for what purposes have been matters of much debate. In this review, we summarize our current knowledge of Wnt/β-catenin signaling and its downstream transcriptional regulators in normal and malignant stem cells. We centered this review largely on three types of stem cells--embryonic stem cells, hair follicle stem cells, and intestinal epithelial stem cells--in which the roles of Wnt/β-catenin have been extensively studied. Using these models, we unravel how many controversial issues surrounding Wnt signaling have been resolved by dissecting the diversity of its downstream circuitry and effectors, often leading to opposite outcomes of Wnt/β-catenin-mediated regulation and differences rooted in stage- and context-dependent effects.

Brg1 loss attenuates aberrant wnt-signalling and prevents wnt-dependent tumourigenesis in the murine small intestine

Tumourigenesis within the intestine is potently driven by deregulation of the Wnt pathway, a process epigenetically regulated by the chromatin remodelling factor Brg1. We aimed to investigate this interdependency in an in vivo setting and assess the viability of Brg1 as a potential therapeutic target. Using a range of transgenic approaches, we deleted Brg1 in the context of Wnt-activated murine small intestinal epithelium. Pan-epithelial loss of Brg1 using VillinCreERT2 and AhCreERT transgenes attenuated expression of Wnt target genes, including a subset of stem cell-specific genes and suppressed Wnt-driven tumourigenesis improving animal survival. A similar increase in survival was observed when Wnt activation and Brg1 loss were restricted to the Lgr5 expressing intestinal stem cell population. We propose a mechanism whereby Brg1 function is required for aberrant Wnt signalling and ultimately for the maintenance of the tumour initiating cell compartment, such that loss of Brg1 in an Apc-deficient context suppresses adenoma formation. Our results highlight potential therapeutic value of targeting Brg1 and serve as a proof of concept that targeting the cells of origin of cancer may be of therapeutic relevance.

Neuronal migration is regulated by endogenous RNAi and chromatin-binding factor ZFP-1/AF10 in Caenorhabditis elegans

Endogenous short RNAs and the conserved plant homeodomain (PHD) zinc-finger protein ZFP-1/AF10 regulate overlapping sets of genes in Caenorhabditis elegans, which suggests that they control common biological pathways. We have shown recently that the RNAi factor RDE-4 and ZFP-1 negatively modulate transcription of the insulin/PI3 signaling-dependent kinase PDK-1 to promote C. elegans fitness. Moreover, we have demonstrated that the insulin/IGF-1-PI3K-signaling pathway regulates the activity of the DAF-16/FOXO transcription factor in the hypodermis to nonautonomously promote the anterior migrations of the hermaphrodite-specific neurons (HSNs) during embryogenesis of C. elegans. In this study, we implicate the PHD-containing isoform of ZFP-1 and endogenous RNAi in the regulation of HSN migration. ZFP-1 affects HSN migration in part through its negative effect on pdk-1 transcription and modulation of downstream DAF-16 activity. We also identify a novel role for ZFP-1 and RNAi pathway components, including RDE-4, in the regulation of HSN migration in parallel with DAF-16. Therefore, the coordinated activities of DAF-16, ZFP-1, and endogenous RNAi contribute to gene regulation during development to ensure proper neuronal positioning.

Epigenetic plasticity: a central regulator of epithelial-to-mesenchymal transition in cancer

Tumor metastasis is the major cause of mortality and morbidity in most solid cancers. A growing body of evidence suggests that the epithelial-to-mesenchymal transition (EMT) plays a central role during tumor metastasis and frequently imparts a stem cell-like phenotype and therapeutic resistance to tumor cells. The induction of EMT is accompanied by a dynamic reprogramming of the epigenome involving changes in DNA methylation and several post-translational histone modifications. These changes in turn promote the expression of mesenchymal genes or repress those associated with an epithelial phenotype. Importantly, in order for metastatic colonization and the formation of macrometastases to occur, tumor cells frequently undergo a reversal of EMT referred to as the mesenchymal-to-epithelial transition (MET). Thus, a high degree of epigenetic plasticity is required in order to induce and reverse EMT during tumor progression. In this review, we describe various epigenetic regulatory mechanisms employed by tumor cells during EMT and elaborate on the importance of the histone code in controlling both the expression and activity of EMT-associated transcription factors. We propose that a more thorough understanding of the epigenetic mechanisms controlling EMT may provide new opportunities which may be harnessed for improved and individualized cancer therapy based on defined molecular mechanisms.

The histone methyltransferase Dot1/DOT1L as a critical regulator of the cell cycle

Dot1/DOT1L catalyzes the methylation of histone H3 lysine 79 (H3K79), which regulates diverse cellular processes, such as development, reprogramming, differentiation, and proliferation. In regards to these processes, studies of Dot1/DOT1L-dependent H3K79 methylation have mainly focused on the transcriptional regulation of specific genes. Although the gene transcription mediated by Dot1/DOT1L during the cell cycle is not fully understood, H3K79 methylation plays a critical role in the progression of G 1 phase, S phase, mitosis, and meiosis. This modification may contribute to the chromatin structure that controls gene expression, replication initiation, DNA damage response, microtubule reorganization, chromosome segregation, and heterochromatin formation. Overall, Dot1/DOT1L is required to maintain genomic and chromosomal stability. This review summarizes the several functions of Dot1/DOT1L and highlights its role in cell cycle regulation.

An investigation of the effects of the core protein telomerase reverse transcriptase on Wnt signaling in breast cancer cells

Telomerase canonically maintains telomeres, but recent reports have suggested that the core protein mammalian telomerase reverse transcriptase (TERT) component, together with the chromatin remodeling factor BRG1 and β-catenin, may also bind to and promote expression of Wnt target genes. However, this proposed noncanonical role of TERT in Wnt signaling has been controversial. Here, we investigated the effects of human TERT (hTERT) on Wnt signaling in human breast cancer lines and HeLa cells. We failed to find evidence for physical association of hTERT with BRG1 or β-catenin; instead, we present evidence that anti-FLAG antibody cross-reactivity properties may explain the previously reported interaction of hTERT with β-catenin. Furthermore, altering hTERT levels in four different breast cancer cell lines caused minimal and discordant effects on Wnt target and Wnt pathway gene expression. Although hTERT's role in Wnt signaling was addressed only indirectly, no significant representation of Wnt target genes was detected in chromatin immunoprecipitation-sequencing (ChIP-seq) and chromatin isolation by RNA purification and sequencing (ChIRP-seq) loci cooccupied in HeLa S3 cells by both BRG1 and hTR. In summary, our evidence fails to support the idea of a biologically consistent hTERT interaction with the Wnt pathway in human breast cancer cells, and any detectable influence of hTERT depended on cell type and experimental system.

Advances in osteoarthritis genetics

Osteoarthritis (OA), the most common form of arthritis, is a highly debilitating disease of the joints and can lead to severe pain and disability. There is no cure for OA. Current treatments often fail to alleviate its symptoms leading to an increased demand for joint replacement surgery. Previous epidemiological and genetic research has established that OA is a multifactorial disease with both environmental and genetic components. Over the past 6 years, a candidate gene study and several genome-wide association scans (GWAS) in populations of Asian and European descent have collectively established 15 loci associated with knee or hip OA that have been replicated with genome-wide significance, shedding some light on the aetiogenesis of the disease. All OA associated variants to date are common in frequency and appear to confer moderate to small effect sizes. Some of the associated variants are found within or near genes with clear roles in OA pathogenesis, whereas others point to unsuspected, less characterised pathways. These studies have also provided further evidence in support of the existence of ethnic, sex, and joint specific effects in OA and have highlighted the importance of expanded and more homogeneous phenotype definitions in genetic studies of OA.

Epigenetics and colorectal cancer pathogenesis

Colorectal cancer (CRC) develops through a multistage process that results from the progressive accumulation of genetic mutations, and frequently as a result of mutations in the Wnt signaling pathway. However, it has become evident over the past two decades that epigenetic alterations of the chromatin, particularly the chromatin components in the promoter regions of tumor suppressors and oncogenes, play key roles in CRC pathogenesis. Epigenetic regulation is organized at multiple levels, involving primarily DNA methylation and selective histone modifications in cancer cells. Assessment of the CRC epigenome has revealed that virtually all CRCs have aberrantly methylated genes and that the average CRC methylome has thousands of abnormally methylated genes. Although relatively less is known about the patterns of specific histone modifications in CRC, selective histone modifications and resultant chromatin conformation have been shown to act, in concert with DNA methylation, to regulate gene expression to mediate CRC pathogenesis. Moreover, it is now clear that not only DNA methylation but also histone modifications are reversible processes. The increased understanding of epigenetic regulation of gene expression in the context of CRC pathogenesis has led to development of epigenetic biomarkers for CRC diagnosis and epigenetic drugs for CRC therapy.

Association between genetic determinants of peak height velocity during puberty and predisposition to adolescent idiopathic scoliosis

STUDY DESIGN

An association study to comprehensively clarify variations of genetic determinants of peak height velocity (PHV) during puberty in adolescent idiopathic scoliosis (AIS).

OBJECTIVE

To investigate whether the genetic determinants of timing and magnitude of PHV during puberty are associated with the susceptibility or curve progression of the female patients with AIS.

SUMMARY OF BACKGROUND DATA

An involvement of abnormal pubertal growth pattern in the etiopathogenesis of AIS has been implicated in previous studies. However, there is no clear consensus on the anthropometric variations of stature or growth rate. The recent advance in the longitudinally identified genetic determinants of PHV offers new opportunities to facilitate analysis of the association of pubertal growth with the susceptibility or curve severity of AIS.

METHODS

A gene-based association study was conducted using 9 single nucleotide polymorphisms (SNPs) in or near SOCS2, SF3B4/SV2A, C17orf67, CABLES1, DOT1L, CDK6, C6orf106, and LIN28B with confirmed association with PHV, peak growth age, or adult height. A total of 500 patients with AIS and 494 age-matched healthy controls were genotyped using the PCR-based Invader assay. Case-control study and case-only study were performed to define the contribution of the 9 SNPs to predisposition and curve severity of AIS.

RESULTS

Strong associations between rs12459350 in DOT1L, rs4794665 in C17orf67, and susceptibility of AIS were found, with the PHV increasing allele G of rs12459350 and PHV/adult height increasing allele A of rs4794665 both being significant predisposition alleles of AIS (P = 0.001 for rs12459350, odds ratio = 1.16, 95% confidence interval = 1.06-1.27; P = 0.006 for rs4794665, odd ratio = 1.33, 95% confidence interval = 1.09-1.62). None of the genotyped SNPs was associated with curve severity in patients with AIS.

CONCLUSION

Polymorphisms of the rs4794665 in C17orf67 and rs12459350 in DOT1L were associated with combined predisposition to AIS susceptibility and higher pubertal PHV, which strongly mirrored the anthropometric findings of taller pubertal stature and accelerated growth rate described in AIS.

Fibroblast growth factor receptor 2c signaling is required for intestinal cell differentiation in zebrafish

Background

There are four cell lineages derived from intestinal stem cells that are located at the crypt and villus in the mammalian intestine the non-secretory absorptive enterocytes, and the secretory cells, which include mucous-secreting goblet cells, regulatory peptide-secreting enteroendocrine cells and antimicrobial peptide-secreting Paneth cells. Although fibroblast growth factor (Fgf) signaling is important for cell proliferation and differentiation in various tissues, its role in intestinal differentiation is less well understood.

Methodology/Principal Findings

We used a loss of function approach to investigate the importance of Fgf signaling in intestinal cell differentiation in zebrafish; abnormal differentiation of goblet cells was observed when Fgf signaling was inhibited using SU5402 or in the Tg(hsp70ldnfgfr1-EGFP) transgenic line. We identified Fgfr2c as an important receptor for cell differentiation. The number of goblet cells and enteroendocrine cells was reduced in fgfr2c morphants. In addition to secretory cells, enterocyte differentiation was also disrupted in fgfr2c morphants. Furthermore, proliferating cells were increased in the morphants. Interestingly, the loss of fgfr2c expression repressed secretory cell differentiation and increased cell proliferation in the mib^ta52b mutant that had defective Notch signaling.

Conclusions/Significance

In conclusion, we found that Fgfr2c signaling derived from mesenchymal cells is important for regulating the differentiation of zebrafish intestine epithelial cells by promoting cell cycle exit. The results of Fgfr2c knockdown in mib^ta52b mutants indicated that Fgfr2c signaling is required for intestinal cell differentiation. These findings provide new evidences that Fgf signaling is required for the differentiation of intestinal cells in the zebrafish developing gut.

To Wnt or not to Wnt: the bone and joint health dilemma

The Wnt signalling cascades have essential roles in development, growth and homeostasis of joints and the skeleton. Progress in basic research, particularly relating to our understanding of intracellular signalling cascades and fine regulation of receptor activation in the extracellular space, has provided novel insights into the roles of Wnt signalling in chronic arthritis. Cartilage and bone homeostasis require finely tuned Wnt signalling; both activation and suppression of the Wnt-β-catenin cascade can lead to osteoarthritis in rodent models. Genetic associations with the Wnt antagonist encoded by FRZB and the transcriptional regulator encoded by Dot1l with osteoarthritis further corroborate the essential part played by Wnts in the joint. In rheumatoid arthritis, inhibition of Wnt signalling has a role in the persistence of bone erosions, whereas Wnts have been associated with the ankylosing phenotype in spondyloarthritis. Together, these observations identify the Wnt pathway as an attractive target for therapeutic intervention; however, the complexity of the Wnt signalling cascades and the potential secondary effects of drug interventions targeting them highlight the need for further research and suggest that our understanding of this exciting pathway is still in its infancy.