Showing papers on "Regulation of gene expression published in 2015"

Integrative analysis of 111 reference human epigenomes

Abstract: The reference human genome sequence set the stage for studies of genetic variation and its association with human disease, but epigenomic studies lack a similar reference. To address this need, the NIH Roadmap Epigenomics Consortium generated the largest collection so far of human epigenomes for primary cells and tissues. Here we describe the integrative analysis of 111 reference human epigenomes generated as part of the programme, profiled for histone modification patterns, DNA accessibility, DNA methylation and RNA expression. We establish global maps of regulatory elements, define regulatory modules of coordinated activity, and their likely activators and repressors. We show that disease- and trait-associated genetic variants are enriched in tissue-specific epigenomic marks, revealing biologically relevant cell types for diverse human traits, and providing a resource for interpreting the molecular basis of human disease. Our results demonstrate the central role of epigenomic information for understanding gene regulation, cellular differentiation and human disease.

The Genotype-Tissue Expression (GTEx) pilot analysis: Multitissue gene regulation in humans

Abstract: Understanding the functional consequences of genetic variation, and how it affects complex human disease and quantitative traits, remains a critical challenge for biomedicine. We present an analysi...

Spatial reconstruction of single-cell gene expression data

Abstract: Spatial localization is a key determinant of cellular fate and behavior, but methods for spatially resolved, transcriptome-wide gene expression profiling across complex tissues are lacking. RNA staining methods assay only a small number of transcripts, whereas single-cell RNA-seq, which measures global gene expression, separates cells from their native spatial context. Here we present Seurat, a computational strategy to infer cellular localization by integrating single-cell RNA-seq data with in situ RNA patterns. We applied Seurat to spatially map 851 single cells from dissociated zebrafish (Danio rerio) embryos and generated a transcriptome-wide map of spatial patterning. We confirmed Seurat's accuracy using several experimental approaches, then used the strategy to identify a set of archetypal expression patterns and spatial markers. Seurat correctly localizes rare subpopulations, accurately mapping both spatially restricted and scattered groups. Seurat will be applicable to mapping cellular localization within complex patterned tissues in diverse systems.

Genome-scale transcriptional activation by an engineered CRISPR-Cas9 complex

Abstract: Systematic interrogation of gene function requires the ability to perturb gene expression in a robust and generalizable manner. Here we describe structure-guided engineering of a CRISPR-Cas9 complex to mediate efficient transcriptional activation at endogenous genomic loci. We used these engineered Cas9 activation complexes to investigate single-guide RNA (sgRNA) targeting rules for effective transcriptional activation, to demonstrate multiplexed activation of ten genes simultaneously, and to upregulate long intergenic non-coding RNA (lincRNA) transcripts. We also synthesized a library consisting of 70,290 guides targeting all human RefSeq coding isoforms to screen for genes that, upon activation, confer resistance to a BRAF inhibitor. The top hits included genes previously shown to be able to confer resistance, and novel candidates were validated using individual sgRNA and complementary DNA overexpression. A gene expression signature based on the top screening hits correlated with markers of BRAF inhibitor resistance in cell lines and patient-derived samples. These results collectively demonstrate the potential of Cas9-based activators as a powerful genetic perturbation technology.

Exon-intron circular RNAs regulate transcription in the nucleus

Abstract: Noncoding RNAs (ncRNAs) have numerous roles in development and disease, and one of the prominent roles is to regulate gene expression A vast number of circular RNAs (circRNAs) have been identified, and some have been shown to function as microRNA sponges in animal cells Here, we report a class of circRNAs associated with RNA polymerase II in human cells In these circRNAs, exons are circularized with introns 'retained' between exons; we term them exon-intron circRNAs or EIciRNAs EIciRNAs predominantly localize in the nucleus, interact with U1 snRNP and promote transcription of their parental genes Our findings reveal a new role for circRNAs in regulating gene expression in the nucleus, in which EIciRNAs enhance the expression of their parental genes in cis, and highlight a regulatory strategy for transcriptional control via specific RNA-RNA interaction between U1 snRNA and EIciRNAs

MicroRNA biogenesis pathways in cancer

Abstract: MicroRNAs (miRNAs) are critical regulators of gene expression. Amplification and overexpression of individual 'oncomiRs' or genetic loss of tumour suppressor miRNAs are associated with human cancer and are sufficient to drive tumorigenesis in mouse models. Furthermore, global miRNA depletion caused by genetic and epigenetic alterations in components of the miRNA biogenesis machinery is oncogenic. This, together with the recent identification of novel miRNA regulatory factors and pathways, highlights the importance of miRNA dysregulation in cancer.

Genetic and Epigenetic Fine-Mapping of Causal Autoimmune Disease Variants

Abstract: Genome-wide association studies have identified loci underlying human diseases, but the causal nucleotide changes and mechanisms remain largely unknown. Here we developed a fine-mapping algorithm to identify candidate causal variants for 21 autoimmune diseases from genotyping data. We integrated these predictions with transcription and cis-regulatory element annotations, derived by mapping RNA and chromatin in primary immune cells, including resting and stimulated CD4(+) T-cell subsets, regulatory T cells, CD8(+) T cells, B cells, and monocytes. We find that ∼90% of causal variants are non-coding, with ∼60% mapping to immune-cell enhancers, many of which gain histone acetylation and transcribe enhancer-associated RNA upon immune stimulation. Causal variants tend to occur near binding sites for master regulators of immune differentiation and stimulus-dependent gene activation, but only 10-20% directly alter recognizable transcription factor binding motifs. Rather, most non-coding risk variants, including those that alter gene expression, affect non-canonical sequence determinants not well-explained by current gene regulatory models.

Function and information content of DNA methylation

Abstract: Cytosine methylation is a DNA modification generally associated with transcriptional silencing. Factors that regulate methylation have been linked to human disease, yet how they contribute to malignances remains largely unknown. Genomic maps of DNA methylation have revealed unexpected dynamics at gene regulatory regions, including active demethylation by TET proteins at binding sites for transcription factors. These observations indicate that the underlying DNA sequence largely accounts for local patterns of methylation. As a result, this mark is highly informative when studying gene regulation in normal and diseased cells, and it can potentially function as a biomarker. Although these findings challenge the view that methylation is generally instructive for gene silencing, several open questions remain, including how methylation is targeted and recognized and in what context it affects genome readout.

Epigenome editing by a CRISPR-Cas9-based acetyltransferase activates genes from promoters and enhancers

Abstract: Technologies that enable targeted manipulation of epigenetic marks could be used to precisely control cell phenotype or interrogate the relationship between the epigenome and transcriptional control. Here we describe a programmable, CRISPR-Cas9-based acetyltransferase consisting of the nuclease-null dCas9 protein fused to the catalytic core of the human acetyltransferase p300. The fusion protein catalyzes acetylation of histone H3 lysine 27 at its target sites, leading to robust transcriptional activation of target genes from promoters and both proximal and distal enhancers. Gene activation by the targeted acetyltransferase was highly specific across the genome. In contrast to previous dCas9-based activators, the acetyltransferase activates genes from enhancer regions and with an individual guide RNA. We also show that the core p300 domain can be fused to other programmable DNA-binding proteins. These results support targeted acetylation as a causal mechanism of transactivation and provide a robust tool for manipulating gene regulation.

Control of adaptive immunity by the innate immune system

Abstract: Microbial infections are recognized by the innate immune system both to elicit immediate defense and to generate long-lasting adaptive immunity. To detect and respond to vastly different groups of pathogens, the innate immune system uses several recognition systems that rely on sensing common structural and functional features associated with different classes of microorganisms. These recognition systems determine microbial location, viability, replication and pathogenicity. Detection of these features by recognition pathways of the innate immune system is translated into different classes of effector responses though specialized populations of dendritic cells. Multiple mechanisms for the induction of immune responses are variations on a common design principle wherein the cells that sense infections produce one set of cytokines to induce lymphocytes to produce another set of cytokines, which in turn activate effector responses. Here we discuss these emerging principles of innate control of adaptive immunity.

Highly efficient Cas9-mediated transcriptional programming

Abstract: The RNA-guided nuclease Cas9 can be reengineered as a programmable transcription factor. However, modest levels of gene activation have limited potential applications. We describe an improved transcriptional regulator obtained through the rational design of a tripartite activator, VP64-p65-Rta (VPR), fused to nuclease-null Cas9. We demonstrate its utility in activating endogenous coding and noncoding genes, targeting several genes simultaneously and stimulating neuronal differentiation of human induced pluripotent stem cells (iPSCs).

The JAK-STAT Pathway: Impact on Human Disease and Therapeutic Intervention*

Abstract: The Janus kinase (JAK)–signal transducer of activators of transcription (STAT) pathway is now recognized as an evolutionarily conserved signaling pathway employed by diverse cytokines, interferons, growth factors, and related molecules. This pathway provides an elegant and remarkably straightforward mechanism whereby extracellular factors control gene expression. It thus serves as a fundamental paradigm for how cells sense environmental cues and interpret these signals to regulate cell growth and differentiation. Genetic mutations and polymorphisms are functionally relevant to a variety of human diseases, especially cancer and immune-related conditions. The clinical relevance of the pathway has been confirmed by the emergence of a new class of therapeutics that targets JAKs.

N6-methyladenosine marks primary microRNAs for processing

Abstract: The first step in the biogenesis of microRNAs is the processing of primary microRNAs (pri-miRNAs) by the microprocessor complex, composed of the RNA-binding protein DGCR8 and the type III RNase DROSHA. This initial event requires recognition of the junction between the stem and the flanking single-stranded RNA of the pri-miRNA hairpin by DGCR8 followed by recruitment of DROSHA, which cleaves the RNA duplex to yield the pre-miRNA product. While the mechanisms underlying pri-miRNA processing have been determined, the mechanism by which DGCR8 recognizes and binds pri-miRNAs, as opposed to other secondary structures present in transcripts, is not understood. Here we find in mammalian cells that methyltransferase-like 3 (METTL3) methylates pri-miRNAs, marking them for recognition and processing by DGCR8. Consistent with this, METTL3 depletion reduced the binding of DGCR8 to pri-miRNAs and resulted in the global reduction of mature miRNAs and concomitant accumulation of unprocessed pri-miRNAs. In vitro processing reactions confirmed the sufficiency of the N(6)-methyladenosine (m(6)A) mark in promoting pri-miRNA processing. Finally, gain-of-function experiments revealed that METTL3 is sufficient to enhance miRNA maturation in a global and non-cell-type-specific manner. Our findings reveal that the m(6)A mark acts as a key post-transcriptional modification that promotes the initiation of miRNA biogenesis.

The Xist lncRNA interacts directly with SHARP to silence transcription through HDAC3

Abstract: Many long non-coding RNAs (lncRNAs) affect gene expression, but the mechanisms by which they act are still largely unknown. One of the best-studied lncRNAs is Xist, which is required for transcriptional silencing of one X chromosome during development in female mammals. Despite extensive efforts to define the mechanism of Xist-mediated transcriptional silencing, we still do not know any proteins required for this role. The main challenge is that there are currently no methods to comprehensively define the proteins that directly interact with a lncRNA in the cell. Here we develop a method to purify a lncRNA from cells and identify proteins interacting with it directly using quantitative mass spectrometry. We identify ten proteins that specifically associate with Xist, three of these proteins--SHARP, SAF-A and LBR--are required for Xist-mediated transcriptional silencing. We show that SHARP, which interacts with the SMRT co-repressor that activates HDAC3, is not only essential for silencing, but is also required for the exclusion of RNA polymerase II (Pol II) from the inactive X. Both SMRT and HDAC3 are also required for silencing and Pol II exclusion. In addition to silencing transcription, SHARP and HDAC3 are required for Xist-mediated recruitment of the polycomb repressive complex 2 (PRC2) across the X chromosome. Our results suggest that Xist silences transcription by directly interacting with SHARP, recruiting SMRT, activating HDAC3, and deacetylating histones to exclude Pol II across the X chromosome.

Stromal gene expression defines poor-prognosis subtypes in colorectal cancer

Abstract: Recent molecular classifications of colorectal cancer (CRC) based on global gene expression profiles have defined subtypes displaying resistance to therapy and poor prognosis. Upon evaluation of these classification systems, we discovered that their predictive power arises from genes expressed by stromal cells rather than epithelial tumor cells. Bioinformatic and immunohistochemical analyses identify stromal markers that associate robustly with disease relapse across the various classifications. Functional studies indicate that cancer-associated fibroblasts (CAFs) increase the frequency of tumor-initiating cells, an effect that is dramatically enhanced by transforming growth factor (TGF)-β signaling. Likewise, we find that all poor-prognosis CRC subtypes share a gene program induced by TGF-β in tumor stromal cells. Using patient-derived tumor organoids and xenografts, we show that the use of TGF-β signaling inhibitors to block the cross-talk between cancer cells and the microenvironment halts disease progression.

MYC, Metabolism, and Cancer

Abstract: The MYC oncogene encodes a transcription factor, MYC, whose broad effects make its precise oncogenic role enigmatically elusive. The evidence to date suggests that MYC triggers selective gene expression amplification to promote cell growth and proliferation. Through its targets, MYC coordinates nutrient acquisition to produce ATP and key cellular building blocks that increase cell mass and trigger DNA replication and cell division. In cancer, genetic and epigenetic derangements silence checkpoints and unleash MYC9s cell growth– and proliferation-promoting metabolic activities. Unbridled growth in response to deregulated MYC expression creates dependence on MYC-driven metabolic pathways, such that reliance on specific metabolic enzymes provides novel targets for cancer therapy. Significance: MYC9s expression and activity are tightly regulated in normal cells by multiple mechanisms, including a dependence upon growth factor stimulation and replete nutrient status. In cancer, genetic deregulation of MYC expression and loss of checkpoint components, such as TP53, permit MYC to drive malignant transformation. However, because of the reliance of MYC-driven cancers on specific metabolic pathways, synthetic lethal interactions between MYC overexpression and specific enzyme inhibitors provide novel cancer therapeutic opportunities. Cancer Discov; 5(10); 1024–39. ©2015 AACR.

Highly specific epigenome editing by CRISPR-Cas9 repressors for silencing of distal regulatory elements

Abstract: Epigenome editing with the CRISPR (clustered, regularly interspaced, short palindromic repeats)-Cas9 platform is a promising technology for modulating gene expression to direct cell phenotype and to dissect the causal epigenetic mechanisms of gene regulation. Fusions of nuclease-inactive dCas9 to the Kruppel-associated box (KRAB) repressor (dCas9-KRAB) can silence target gene expression, but the genome-wide specificity and the extent of heterochromatin formation catalyzed by dCas9-KRAB are not known. We targeted dCas9-KRAB to the HS2 enhancer, a distal regulatory element that orchestrates the expression of multiple globin genes, and observed highly specific induction of H3K9 trimethylation (H3K9me3) at the enhancer and decreased chromatin accessibility of both the enhancer and its promoter targets. Targeted epigenetic modification of HS2 silenced the expression of multiple globin genes, with minimal off-target changes in global gene expression. These results demonstrate that repression mediated by dCas9-KRAB is sufficiently specific to disrupt the activity of individual enhancers via local modification of the epigenome.

Dissecting molecular cross-talk between Nrf2 and NF-κB response pathways.

Abstract: In most tissues, cells are exposed to frequent changes in levels of oxidative stress and inflammation. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and nuclear factor-κB (NF-κB) are the two key transcription factors that regulate cellular responses to oxidative stress and inflammation respectively. Pharmacological and genetic studies suggest that there is functional cross-talk between these two important pathways. The absence of Nrf2 can exacerbate NF-κB activity leading to increased cytokine production, whereas NF-κB can modulate Nrf2 transcription and activity, having both positive and negative effects on the target gene expression. This review focuses on the potentially complex molecular mechanisms that link the Nrf2 and NF-κB pathways and the importance of designing more effective therapeutic strategies to prevent or treat a broad range of neurological disorders.

Selective Small Molecule Induced Degradation of the BET Bromodomain Protein BRD4

Abstract: The Bromo- and Extra-Terminal (BET) proteins BRD2, BRD3, and BRD4 play important roles in transcriptional regulation, epigenetics, and cancer and are the targets of pan-BET selective bromodomain inhibitor JQ1. However, the lack of intra-BET selectivity limits the scope of current inhibitors as probes for target validation and could lead to unwanted side effects or toxicity in a therapeutic setting. We designed Proteolysis Targeted Chimeras (PROTACs) that tether JQ1 to a ligand for the E3 ubiquitin ligase VHL, aimed at triggering the intracellular destruction of BET proteins. Compound MZ1 potently and rapidly induces reversible, long-lasting, and unexpectedly selective removal of BRD4 over BRD2 and BRD3. The activity of MZ1 is dependent on binding to VHL but is achieved at a sufficiently low concentration not to induce stabilization of HIF-1α. Gene expression profiles of selected cancer-related genes responsive to JQ1 reveal distinct and more limited transcriptional responses induced by MZ1, consistent wit...

siRNA Versus miRNA as Therapeutics for Gene Silencing

Abstract: Discovered a little over two decades ago, small interfering RNAs (siRNAs) and microRNAs (miRNAs) are noncoding RNAs with important roles in gene regulation. They have recently been investigated as novel classes of therapeutic agents for the treatment of a wide range of disorders including cancers and infections. Clinical trials of siRNA- and miRNA-based drugs have already been initiated. siRNAs and miRNAs share many similarities, both are short duplex RNA molecules that exert gene silencing effects at the post-transcriptional level by targeting messenger RNA (mRNA), yet their mechanisms of action and clinical applications are distinct. The major difference between siRNAs and miRNAs is that the former are highly specific with only one mRNA target, whereas the latter have multiple targets. The therapeutic approaches of siRNAs and miRNAs are therefore very different. Hence, this review provides a comparison between therapeutic siRNAs and miRNAs in terms of their mechanisms of action, physicochemical properties, delivery, and clinical applications. Moreover, the challenges in developing both classes of RNA as therapeutics are also discussed.

RNA N6-methyladenosine methylation in post-transcriptional gene expression regulation

Abstract: Both DNA and histone proteins undergo dynamic and reversible chemical modifications to control gene expression (Strahl and Allis 2000; Bird 2001; Suzuki and Bird 2008; Bhutani et al. 2011; Jones 2012; Kohli and Zhang 2013). Although post-transcriptional modifications are known to occur to RNAs, the impact of these modifications on gene expression regulation has only recently begun to be explored (He 2010). To date, more than a hundred structurally distinct chemical modifications have been found in eukaryotic RNAs (Cantara et al. 2011; Machnicka et al. 2013); however, the enzymes responsible for each modification and the biological consequences of these modified RNAs are largely unknown. RNA modifications were once considered to be static, but a flurry of recent discoveries has demonstrated that some chemical modifications can be dynamic and participate in the regulation of diverse physiological processes (Motorin and Helm 2011; Yi and Pan 2011; Chan et al. 2012; Fu et al. 2014; Meyer and Jaffrey 2014; Kirchner and Ignatova 2015). The presence of N6-methyladenosine (m6A) in polyadenylated mRNA was first discovered in the 1970s (Desrosiers et al. 1974; Perry and Kelley 1974; Lavi and Shatkin 1975; Wei et al. 1975; Schibler et al. 1977; Wei and Moss 1977) by researchers who were characterizing the 5′ cap structure of messenger RNA (mRNA) in mammalian cells. Since then, m6A has been identified as the most prevalent internal modification in mRNA and long noncoding RNA (lncRNA) in higher eukaryotes. It is widely conserved among eukaryotic species that range from yeast, plants, and flies to mammals as well as among viral mRNAs that replicate inside host nuclei (Krug et al. 1976; Beemon and Keith 1977; Horowitz et al. 1984; Bokar 2005). In addition to its occurrence in mRNA, m6A also exists in various classes of RNA in eukaryotes, bacteria, and archaea, including ribosomal RNAs, small nuclear RNAs, and transfer RNAs (Bjork et al. 1987; Maden 1990; Shimba et al. 1995; Gu et al. 1996; Agris et al. 2007; Piekna-Przybylska et al. 2008). Despite its widespread distribution in the mammalian transcriptome (on average, approximately three m6A sites per mRNA), functional insight has been lacking, possibly due to the low abundance of m6A mRNA and technical difficulties in global detection. Interest in the biological relevance of m6A in mRNA resurfaced after the discovery of two mammalian RNA demethylases, FTO (fat mass and obesity-associated protein) (Jia et al. 2011) and its homolog, ALKBH5 (Zheng et al. 2013), which selectively reverse m6A to adenosine in nuclear RNA. FTO is associated with human obesity (Dina et al. 2007; Frayling et al. 2007; Loos and Yeo 2014) and mental development (Hess et al. 2013), while ALKBH5 is shown to affect mouse spermatogenesis in a demethylation-dependent manner (Zheng et al. 2013), suggesting broad roles of m6A in various physiological processes. Shortly after these findings, YTHDF2 (YTH domain-containing family protein 2) was identified as the first m6A reader protein that preferentially recognizes m6A-containing mRNA (Dominissini et al. 2012; Wang et al. 2014a) and mediates mRNA decay (Wang et al. 2014a), thereby suggesting a role for m6A RNA as a negative regulator of gene expression. On the other hand, a transcriptome-wide m6A profiling method was developed to decipher the m6A RNA landscape (Dominissini et al. 2012; Meyer et al. 2012). Intriguingly, m6A sites in mammalian polyadenylated RNA are dominated by the conserved Pu[G > A]m6AC[A/C/U] motif that localizes near stop codons, in 3′ untranslated regions (UTRs), within long internal exons, and at 5′ UTRs (Dominissini et al. 2012; Meyer et al. 2012; Schwartz et al. 2013; Li et al. 2014; Luo et al. 2014), immediately raising the question of how this specificity is achieved. The m6A RNA landscape is initially sculptured by a methyltransferase complex, but for a long time, METTL3 (methyltransferase-like 3) was the only known SAM (S-adenosyl methionine)-binding subunit associated with mRNA methylation (Bokar et al. 1997). In 2014, a new mammalian methyltransferase, METTL14, was discovered to catalyze m6A methylation. Together with METTL3, these two proteins form a stable heterodimer complex that mediates cellular m6A deposition on mammalian mRNAs (Liu et al. 2014; Wang et al. 2014b). Recently, the mammalian splicing factor WTAP (Wilms’ tumor 1-associating protein) was identified as the third auxiliary factor of the core methyltransferase complex that affects cellular m6A methylation (Liu et al. 2014; Ping et al. 2014). The identification and characterization of the complete mammalian m6A methylation machinery are the first steps toward deciphering the selectivity and biological functions of m6A deposition in eukaryotic mRNAs. In this review, we mainly summarize recent progress in the study of m6A methylation in mRNA across different eukaryotes and discuss their newly discovered roles in post-transcriptional gene expression regulation. We first describe the features of m6A on a global scale and briefly introduce the mammalian m6A writers, erasers, and readers that specifically install, remove, or bind to m6A at defined sequence motifs (Fig. 1). We then discuss the evolutional conservation of the m6A methylation machinery across eukaryotic species that range from yeast, plants, and flies to mammals, highlighting the broad roles of methyltransferases and m6A in regulating cell status and embryonic development. Finally, we discuss the emerging functions of m6A in several mechanisms of post-transcriptional gene expression regulation with a special focus on the effects of m6A on differentiation and reprograming of stem cells. Figure 1. Illustration of the cellular pathways of m6A in nuclear RNAs. The m6A methyltransferases and demethylases dynamically control the m6A methylation landscape within the nucleus. The m6A reader proteins preferentially bind to the methylated RNA and mediate ...

50 years of protein acetylation: from gene regulation to epigenetics, metabolism and beyond

Abstract: In 1964, Vincent Allfrey and colleagues reported the identification of histone acetylation and with deep insight proposed a regulatory role for this protein modification in transcription regulation. Subsequently, histone acetyltransferases (HATs), histone deacetylases (HDACs) and acetyl-Lys-binding proteins were identified as transcription regulators, thereby providing compelling evidence for his daring hypothesis. During the past 15 years, reversible protein acetylation and its modifying enzymes have been implicated in many cellular functions beyond transcription regulation. Here, we review the progress accomplished during the past 50 years and discuss the future of protein acetylation.

Human body epigenome maps reveal noncanonical DNA methylation variation

Abstract: Understanding the diversity of human tissues is fundamental to disease and requires linking genetic information, which is identical in most of an individual's cells, with epigenetic mechanisms that could have tissue-specific roles. Surveys of DNA methylation in human tissues have established a complex landscape including both tissue-specific and invariant methylation patterns. Here we report high coverage methylomes that catalogue cytosine methylation in all contexts for the major human organ systems, integrated with matched transcriptomes and genomic sequence. By combining these diverse data types with each individuals' phased genome, we identified widespread tissue-specific differential CG methylation (mCG), partially methylated domains, allele-specific methylation and transcription, and the unexpected presence of non-CG methylation (mCH) in almost all human tissues. mCH correlated with tissue-specific functions, and using this mark, we made novel predictions of genes that escape X-chromosome inactivation in specific tissues. Overall, DNA methylation in several genomic contexts varies substantially among human tissues.

A comprehensive transcriptional portrait of human cancer cell lines

Abstract: Tumor-derived cell lines have served as vital models to advance our understanding of oncogene function and therapeutic responses. Although substantial effort has been made to define the genomic constitution of cancer cell line panels, the transcriptome remains understudied. Here we describe RNA sequencing and single-nucleotide polymorphism (SNP) array analysis of 675 human cancer cell lines. We report comprehensive analyses of transcriptome features including gene expression, mutations, gene fusions and expression of non-human sequences. Of the 2,200 gene fusions catalogued, 1,435 consist of genes not previously found in fusions, providing many leads for further investigation. We combine multiple genome and transcriptome features in a pathway-based approach to enhance prediction of response to targeted therapeutics. Our results provide a valuable resource for studies that use cancer cell lines.

Distinct emt programs control normal mammary stem cells and tumour-initiating cells

Abstract: Tumour-initiating cells (TICs) are responsible for metastatic dissemination and clinical relapse in a variety of cancers. Analogies between TICs and normal tissue stem cells have led to the proposal that activation of the normal stem-cell program within a tissue serves as the major mechanism for generating TICs. Supporting this notion, we and others previously established that the Slug epithelial-to-mesenchymal transition-inducing transcription factor (EMT-TF), a member of the Snail family, serves as a master regulator of the gland-reconstituting activity of normal mammary stem cells, and that forced expression of Slug in collaboration with Sox9 in breast cancer cells can efficiently induce entrance into the TIC state. However, these earlier studies focused on xenograft models with cultured cell lines and involved ectopic expression of EMT-TFs, often at non-physiological levels. Using genetically engineered knock-in reporter mouse lines, here we show that normal gland-reconstituting mammary stem cells residing in the basal layer of the mammary epithelium and breast TICs originating in the luminal layer exploit the paralogous EMT-TFs Slug and Snail, respectively, which induce distinct EMT programs. Broadly, our findings suggest that the seemingly similar stem-cell programs operating in TICs and normal stem cells of the corresponding normal tissue are likely to differ significantly in their details.

NRF2 regulates serine biosynthesis in non-small cell lung cancer

Abstract: Tumors have high energetic and anabolic needs for rapid cell growth and proliferation, and the serine biosynthetic pathway was recently identified as an important source of metabolic intermediates for these processes. We integrated metabolic tracing and transcriptional profiling of a large panel of non-small cell lung cancer (NSCLC) cell lines to characterize the activity and regulation of the serine/glycine biosynthetic pathway in NSCLC. Here we show that the activity of this pathway is highly heterogeneous and is regulated by NRF2, a transcription factor frequently deregulated in NSCLC. We found that NRF2 controls the expression of the key serine/glycine biosynthesis enzyme genes PHGDH, PSAT1 and SHMT2 via ATF4 to support glutathione and nucleotide production. Moreover, we show that expression of these genes confers poor prognosis in human NSCLC. Thus, a substantial fraction of human NSCLCs activates an NRF2-dependent transcriptional program that regulates serine and glycine metabolism and is linked to clinical aggressiveness.