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Alternative splicing (AS) enables differential inclusion of exons from a given transcript, thereby contributing to the transcriptome and proteome diversity. Aberrant AS patterns play major roles in the development of different pathologies, including breast cancer. N6-methyladenosine (m6A), the most abundant internal modification of eukaryotic mRNA, influences tumor progression and metastasis of breast cancer, and it has been recently linked to AS regulation. Here, we identify a specific AS signature associated with breast tumorigenesis in vitro. We characterize for the first time the role of METTL3 in modulating breast cancer-associated AS programs, expanding the role of the m6A-methyltransferase in tumorigenesis. Specifically, we find that both m6A deposition in splice site boundaries and in splicing and transcription factor transcripts, such as PHF5A and MYC, direct AS switches of specific breast cancer-associated transcripts. Finally, we show that five of the AS events validated in vitro are associated with a poor overall survival rate for patients with breast cancer, suggesting the use of these AS events as a novel potential prognostic biomarker.

The pluripotent state is not solely governed by the action of the core transcription factors OCT4, SOX2, and NANOG, but also by a series of co-transcriptional and post-transcriptional events, including alternative splicing (AS) and the interaction of RNA-binding proteins (RBPs) with defined subpopulations of RNAs. Zinc Finger Protein 207 (ZFP207) is an essential transcription factor for mammalian embryonic development. Here, we employ multiple functional analyses to characterize its role in mouse embryonic stem cells (ESCs). We find that ZFP207 plays a pivotal role in ESC maintenance, and silencing of Zfp207 leads to severe neuroectodermal differentiation defects. In striking contrast to human ESCs, mouse ZFP207 does not transcriptionally regulate neuronal and stem cell-related genes but exerts its effects by controlling AS networks and by acting as an RBP. Our study expands the role of ZFP207 in maintaining ESC identity, and underscores the functional versatility of ZFP207 in regulating neural fate commitment.

The MODOMICS database has been, since 2006, a manually curated and centralized resource, storing and distributing comprehensive information about modified ribonucleosides. Originally, it only contained data on the chemical structures of modified ribonucleosides, their biosynthetic pathways, the location of modified residues in RNA sequences, and RNA-modifying enzymes. Over the years, prompted by the accumulation of new knowledge and new types of data, it has been updated with new information and functionalities. In this new release, we have created a catalog of RNA modifications linked to human diseases, e.g., due to mutations in genes encoding modification enzymes. MODOMICS has been linked extensively to RCSB Protein Data Bank, and sequences of experimentally determined RNA structures with modified residues have been added. This expansion was accompanied by including nucleotide 5′-monophosphate residues. We redesigned the web interface and upgraded the database backend. In addition, a search engine for chemically similar modified residues has been included that can be queried by SMILES codes or by drawing chemical molecules. Finally, previously available datasets of modified residues, biosynthetic pathways, and RNA-modifying enzymes have been updated. Overall, we provide users with a new, enhanced, and restyled tool for research on RNA modification. MODOMICS is available at https://iimcb.genesilico.pl/modomics/.

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSC) provide a powerful model system to uncover fundamental mechanisms that control cellular identity during mammalian development. Histone methylation governs gene expression programs that play a key role in the regulation of the balance between self-renewal and differentiation of ESCs. Lysine-specific demethylase 1 (LSD1, also known as KDM1A), the first identified histone lysine demethylase, demethylates H3K4me1/2 and H3K9me1/2 at target loci in a context-dependent manner. Moreover, it has also been shown to demethylate non-histone substrates playing a central role in the regulation of numerous cellular processes. In this review, we summarize current knowledge about LSD1 and the molecular mechanism by which LSD1 influences the stem cells state, including the regulatory circuitry underlying self-renewal and pluripotency.

N6-methyladenosine (m6A) is the most abundant internal modification on messenger RNAs (mRNAs) and long noncoding RNAs (lncRNAs) in eukaryotes. It influences gene expression by regulating RNA processing, nuclear export, mRNA decay, and translation. Hence, m6A controls fundamental cellular processes, and dysregulated deposition of m6A has been acknowledged to play a role in a broad range of human diseases, including cancer. m6A RNA immunoprecipitation followed by high-throughput sequencing (MeRIP-seq or m6A-seq) is a powerful technique to map m6A in a transcriptome-wide level. After immunoprecipitation of fragmented polyadenylated (poly(A)+) rich RNA by using specific anti-m6A antibodies, both the immunoprecipitated RNA fragments together with the input control are subjected to massively parallel sequencing. The generation of such comprehensive methylation profiles of signal enrichment relative to input control is necessary in order to better comprehend the pathogenesis behind aberrant m6A deposition.

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Collectively referred to as the epitranscriptome, RNA modifications play important roles in gene expression control regulating relevant cellular processes. In the last few decades, growing numbers of RNA modifications have been identified not only in abundant ribosomal (rRNA) and transfer RNA (tRNA) but also in messenger RNA (mRNA). In addition, many writers, erasers and readers that dynamically regulate the chemical marks have also been characterized. Correct deposition of RNA modifications is prerequisite for cellular homeostasis, and its alteration results in aberrant transcriptional programs that dictate human disease, including breast cancer, the most frequent female malignancy, and the leading cause of cancer-related death in women. In this review, we emphasize the major RNA modifications that are present in tRNA, rRNA and mRNA. We have categorized breast cancer-associated chemical marks and summarize their contribution to breast tumorigenesis. In addition, we describe less abundant tRNA modifications with related pathways implicated in breast cancer. Finally, we discuss current limitations and perspectives on epitranscriptomics for use in therapeutic strategies against breast and other cancers., Graphical Abstract Graphical AbstractModifications of RNA known in breast cancer.

Cancer stem cells (CSCs) are a small but critical cell population for cancer biology since they display inherent resistance to standard therapies and give rise to metastases. Despite accruing evidence establishing a link between deregulation of epitranscriptome-related players and tumorigenic process, the role of messenger RNA (mRNA) modifications in the regulation of CSC properties remains poorly understood. Here, we show that the cytoplasmic pool of fat mass and obesity-associated protein (FTO) impedes CSC abilities in colorectal cancer through its N6,2’-O-dimethyladenosine (m6Am) demethylase activity. While m6Am is strategically located next to the m7G-mRNA cap, its biological function is not well understood and has not been addressed in cancer. Low FTO expression in patient-derived cell lines elevates m6Am level in mRNA which results in enhanced in vivo tumorigenicity and chemoresistance. Inhibition of the nuclear m6Am methyltransferase, PCIF1/CAPAM, fully reverses this phenotype, stressing the role of m6Am modification in stem-like properties acquisition. FTO-mediated regulation of m6Am marking constitutes a reversible pathway controlling CSC abilities. Altogether, our findings bring to light the first biological function of the m6Am modification and its potential adverse consequences for colorectal cancer management., The demethylase FTO was shown to remove on N6-methyladenosine (m6A) and N6, 2’-O-dimethyladenosine (m6Am) modifications on RNAs. Here the authors show that FTO impedes cancer stem cell-like abilities in colorectal cancer cells through its m6Am demethylase activity, not through internal m6A demethylase activity.

The pluripotent state is not solely governed by the action of the core transcription factors Oct4, Sox2, and Nanog, but also by a series of co-transcriptional and post-transcriptional events, including alternative splicing (AS) and the interaction of RNA-binding proteins (RBPs) with defined subpopulations of RNAs. Zinc Finger Protein 207 (ZFP207) is an essential transcription factor for mammalian embryonic development. Here, we employ multiple functional analyses to characterize the role of ZFP207 in mouse embryonic stem cells (ESCs). We find that ZFP207 plays a pivotal role in ESC maintenance, and silencing of Zfp207 leads to severe neuroectodermal differentiation defects. In striking contrast to human ESCs, ZFP207 does not transcriptionally regulate stem cell and neuronal-related genes but exerts its effects by control AS networks and acting as an RBP. Our study expands the role of ZFP207 to maintain ESC identity, and underscores ZFP207 functional versatility with key roles in neural fate commitment.

RNA modifications have recently emerged as a widespread and complex facet of gene expression regulation. Counting more than 170 distinct chemical modifications with far-reaching implications for RNA fate, they are collectively referred to as the epitranscriptome. These modifications can occur in all RNA species, including messenger RNAs (mRNAs) and noncoding RNAs (ncRNAs). In mRNAs the deposition, removal, and recognition of chemical marks by writers, erasers and readers influence their structure, localization, stability, and translation. In turn, this modulates key molecular and cellular processes such as RNA metabolism, cell cycle, apoptosis, and others. Unsurprisingly, given their relevance for cellular and organismal functions, alterations of epitranscriptomic marks have been observed in a broad range of human diseases, including cancer, neurological and metabolic disorders. Here, we will review the major types of mRNA modifications and editing processes in conjunction with the enzymes involved in their metabolism and describe their impact on human diseases. We present the current knowledge in an updated catalog. We will also discuss the emerging evidence on the crosstalk of epitranscriptomic marks and what this interplay could imply for the dynamics of mRNA modifications. Understanding how this complex regulatory layer can affect the course of human pathologies will ultimately lead to its exploitation toward novel epitranscriptomic therapeutic strategies.

Comprehensive analysis of the mammalian genome uncovered the discovery of pervasive transcription of large RNA transcripts that do not code for proteins, namely, long noncoding RNAs (lncRNAs). LncRNAs play important roles in the regulation of gene expression from integration of chromatin remodeling complexes to transcriptional and posttranscriptional regulation of protein-coding genes. Application of next-generation sequencing technologies to cancer transcriptomes has revealed that aberrant expression of lncRNAs is associated with tumor progression and metastasis. Although thousands of lncRNAs have been shown to be dysregulated in different cancer types, just few of them have been fully characterized. In this book chapter, we aim to highlight recent findings of the mechanistic function of lncRNAs in breast cancer and summarize key examples of lncRNAs that are misregulated during breast tumorigenesis. We have categorized breast cancer–associated lncRNA according to their contribution to tumor suppression or tumor progression based on recent studies. Because some of them are expressed in a specific molecular breast cancer subtype, we have outlined lncRNAs that can potentially serve as diagnostic and prognostic markers, in which expression is linked to chemotherapy resistance. Finally, we have discussed current limitations and perspectives on potential lncRNA targets for use in therapies against breast cancer.

High-throughput analyses have revealed that the vast majority of the transcriptome does not code for proteins. These non-translated transcripts, when larger than 200 nucleotides, are termed long non-coding RNAs (lncRNAs), and play fundamental roles in diverse cellular processes. LncRNAs are subject to dynamic chemical modification, adding another layer of complexity to our understanding of the potential roles that lncRNAs play in health and disease. Many lncRNAs regulate transcriptional programs by influencing the epigenetic state through direct interactions with chromatin-modifying proteins. Among these proteins, Polycomb repressive complexes 1 and 2 (PRC1 and PRC2) have been shown to be recruited by lncRNAs to silence target genes. Aberrant expression, deficiency or mutation of both lncRNA and Polycomb have been associated with numerous human diseases, including cancer. In this review, we have highlighted recent findings regarding the concerted mechanism of action of Polycomb group proteins (PcG), acting together with some classically defined lncRNAs including X-inactive specific transcript (XIST), antisense non-coding RNA in the INK4 locus (ANRIL), metastasis associated lung adenocarcinoma transcript 1 (MALAT1), and HOX transcript antisense RNA (HOTAIR).

Chemical modifications of RNA provide a direct and rapid way to manipulate the existing transcriptome, allowing rapid responses to the changing environment further enriching the regulatory capacity of RNA. N6-Methyladenosine (m6A) has been identified as the most abundant internal modification of messenger RNA in eukaryotes, linking external stimuli to an intricate network of transcriptional, post-transcriptional and translational processes. M6A modification affects a broad spectrum of cellular functions, including maintenance of the pluripotency of embryonic stem cells (ESCs) and the reprogramming of somatic cells into induced pluripotent stem cells (iPSCs). In this review, we summarize the most recent findings on m6A modification with special focus on the different studies describing how m6A is implicated in ESC self-renewal, cell fate specification and iPSC generation.

We observed overexpression and increased intra-nuclear accumulation of the PRMT5/WDR77 in breast cancer cell lines relative to immortalized breast epithelial cells. Utilizing mass spectrometry and biochemistry approaches we identified the Zn-finger protein ZNF326, as a novel interaction partner and substrate of the nuclear PRMT5/WDR77 complex. ZNF326 is symmetrically dimethylated at arginine 175 (R175) and this modification is lost in a PRMT5 and WDR77-dependent manner. Loss of PRMT5 or WDR77 in MDA-MB-231 cells leads to defects in alternative splicing, including inclusion of A-T rich exons in target genes, a phenomenon that has previously been observed upon loss of ZNF326. We observed that the alternatively spliced transcripts of a subset of these genes, involved in proliferation and tumor cell migration like REPIN1/AP4, ST3GAL6, TRNAU1AP and PFKM are degraded upon loss of PRMT5. In summary, we have identified a novel mechanism through which the PRMT5/WDR77 complex maintains the balance between splicing and mRNA stability through methylation of ZNF326.

Summary THAP1 (THAP [Thanatos-associated protein] domain-containing, apoptosis-associated protein 1) is a ubiquitously expressed member of a family of transcription factors with highly conserved DNA-binding and protein-interacting regions. Mutations in THAP1 cause dystonia, DYT6, a neurologic movement disorder. THAP1 downstream targets and the mechanism via which it causes dystonia are largely unknown. Here, we show that wild-type THAP1 regulates embryonic stem cell (ESC) potential, survival, and proliferation. Our findings identify THAP1 as an essential factor underlying mouse ESC survival and to some extent, differentiation, particularly neuroectodermal. Loss of THAP1 or replacement with a disease-causing mutation results in an enhanced rate of cell death, prolongs Nanog, Prdm14, and/or Rex1 expression upon differentiation, and results in failure to upregulate ectodermal genes. ChIP-Seq reveals that these activities are likely due in part to indirect regulation of gene expression., Highlights • Wild-type THAP1 regulates ESC potential, survival, and proliferation • THAP1 is essential for ESC differentiation, particularly neuroectodermal • Thap1C54Y or ΔExon2 ESCs prolong expression of pluripotent genes upon differentiation • Thap1C54Y or ΔExon2 EBs show increased cell death and abnormal differentiation, Ehrlich and colleagues identified THAP1, mutations of which cause dystonia (DYT6), as an essential regulator of ESC survival, proliferation, and differentiation. As THAP1 mutations result in a neurologic disease, this work examined the effects of a causative mutation, C54Y, and an essentially null allele, ΔExon2, on neuronal differentiation.

Cancer-initiating cells (CIC) undergo asymmetric growth patterns that increase phenotypic diversity and drive selection for chemotherapeutic resistance and tumor relapse. WNT signaling is a hallmark of colon CIC, often caused by APC mutations, which enable activation of β-catenin and MYC. Accumulating evidence indicates that long noncoding RNAs (lncRNA) contribute to the stem-like character of colon cancer cells. In this study, we report enrichment of the lncRNA RBM5-AS1/LUST during sphere formation of colon CIC. Its silencing impaired WNT signaling, whereas its overexpression enforced WNT signaling, cell growth, and survival in serum-free media. RBM5-AS1 has been little characterized previously, and we determined it to be a nuclear-retained transcript that selectively interacted with β-catenin. Mechanistic investigations showed that silencing or overexpression of RBM5-AS1 caused a respective loss or retention of β-catenin from TCF4 complexes bound to the WNT target genes SGK1, YAP1, and MYC. Our work suggests that RBM5-AS1 activity is critical for the functional enablement of colon cancer stem-like cells. Furthermore, it defines the mechanism of action of RBM5-AS1 in the WNT pathway via physical interactions with β-catenin, helping organize transcriptional complexes that sustain colon CIC function. Cancer Res; 76(19); 5615–27. ©2016 AACR.

Epigenetic and epitranscriptomic networks have important functions in maintaining the pluripotency of embryonic stem cells (ESCs) and somatic cell reprogramming. However, the mechanisms integrating the actions of these distinct networks are only partially understood. Here we show that the chromatin-associated zinc finger protein 217 (ZFP217) coordinates epigenetic and epitranscriptomic regulation. ZFP217 interacts with several epigenetic regulators, activates the transcription of key pluripotency genes, and modulates N6-methyladenosine (m(6)A) deposition on their transcripts by sequestering the enzyme m(6)A methyltransferase-like 3 (METTL3). Consistently, Zfp217 depletion compromises ESC self-renewal and somatic cell reprogramming, globally increases m(6)A RNA levels, and enhances m(6)A modification of the Nanog, Sox2, Klf4, and c-Myc mRNAs, promoting their degradation. ZFP217 binds its own target gene mRNAs, which are also METTL3 associated, and is enriched at promoters of m(6)A-modified transcripts. Collectively, these findings shed light on how a transcription factor can tightly couple gene transcription to m(6)A RNA modification to ensure ESC identity.

The Kruppel-like transcription factor zinc finger protein 217 (ZNF217) (mouse homolog ZFP217) contributes to tumorigenesis by dysregulating gene expression programs. The newly discovered molecular function of ZFP217 in controlling N6-methyladenosine (m6A) deposition in embryonic stem cells (ESCs) sheds new light on the role of this transcription factor in tumor development.

Chemical modifications of RNA provide a direct and rapid way to modulate the existing transcriptome, allowing the cells to adapt rapidly to the changing environment. Among these modifications, N

Chemical modifications of RNA provide a direct and rapid way to manipulate the existing transcriptome, allowing rapid responses to the changing environment further enriching the regulatory capacity of RNA. N6-methyladenosine (m6A) has been identified as the most abundant internal modification of messenger RNA in eukaryotes, linking external stimuli to an intricate network of transcriptional, post-transcriptional and translational processes. M6A modification affects a broad spectrum of cellular functions, including maintenance of the pluripotency of embryonic stem cells (ESCs) and the reprogramming of somatic cells into induced pluripotent stem cells (iPSCs). In this review, we summarize the most recent findings on m6A modification with special focus on the different studies describing how m6A is implicated in ESC self-renewal, cell fate specification and iPSC generation.

The INK4/ARF locus regulates senescence and is frequently altered in cancer. In normal cells, the INK4/ARF locus is found silenced by Polycomb repressive complexes (PRCs). Which are the mechanisms responsible for the recruitment of PRCs to INK4/ARF and their other target genes remains unclear. In a genetic screen for transcription factors regulating senescence, we identified the homeodomain-containing protein HLX1 (H2.0-like homeobox 1). Expression of HLX1 extends cellular lifespan and blunts oncogene-induced senescence. Using quantitative proteomics, we identified p16INK4a as the key target mediating the effects of HLX1 in senescence. HLX1 represses p16INK4a transcription by recruiting PRCs and HDAC1. This mechanism has broader implications, as HLX1 also regulates a subset of PRC targets besides p16INK4a. Finally, sampling members of the Homeobox family, we identified multiple genes with ability to repress p16INK4a. Among them, we found HOXA9 (Homeobox A9), a putative oncogene in leukaemia, which also recruits PRCs and HDAC1 to regulate p16INK4a. Our results reveal an unexpected and conserved interplay between homeodomain-containing proteins and PRCs with implications in senescence, development and cancer.

The long non-coding RNA CDKN2B-AS1, commonly referred to as the A ntisense N on-coding R NA in the I NK4 L ocus (ANRIL), is a 3.8-kb-long RNA transcribed from the short arm of human chromosome 9 on p21.3 that overlaps a critical region encompassing three major tumor suppressor loci juxtaposed to the INK4b-ARF-INK4a gene cluster and the methyl-thioadenosine phosphorylase (MTAP) gene. Genome-wide association studies have identified this region with a remarkable and growing number of disease-associated DNA alterations and single nucleotide polymorphisms, which corresponds to increased susceptibility to human disease. Recent attention has been devoted on whether these alterations in the ANRIL sequence affect its expression levels and/or its splicing transcript variation, and in consequence, global cellular homeostasis. Moreover, recent evidence postulates that ANRIL not only can regulate their immediate genomic neighbors in cis, but also has the capacity to regulate additional loci in trans. This action would further increase the complexity for mechanisms imposed through ANRIL and furthering the scope of this lncRNA in disease pathogenesis. In this chapter, we summarize the most recent findings on the investigation of ANRIL and provide a perspective on the biological and clinical significance of ANRIL as a putative biomarker, specifically, its potential role in directing cellular fates leading to cancer and cardiovascular disease.

Acetoacetyl-CoA synthetase (AACS) is a cytoplasmic enzyme that activates the ketone body acetoacetate for lipogenesis. Aacs is expressed in liver, thus this tissue produces and consumes ketone bodies. To understand this apparent paradox we studied the expression of Aacs in liver during the transition from fasting to feeding, and characterized the kinetic parameters of the human enzyme. We show that Aacs liver expression is down-regulated by fasting and only up-regulated after 5 h of refeeding, while the levels of circulating ketone bodies returned to basal levels within 20 min of food availability. Since the human enzyme has a high affinity for the ketone body acetoacetate (KM = 37.6 μM), these results indicates that AACS utilizes ketones during periods of feeding. Human AACS was also characterized as an acetylated enzyme in vivo, where lysine 633 (from a P4XGK domain) plays a critical role in the catalytic activity but not in the acetylation state of the protein.

The control of transcription is regulated through the well-coordinated spatial and temporal interactions between distal genomic regulatory elements required for specialized cell-type and developmental gene expression programs. With recent findings CFTR has served as a model to understand the principles that govern genome-wide and topological organization of distal intra-chromosomal contacts as it relates to transcriptional control. This is due to the extensive characterization of the DNase hypersensitivity sites, modification of chromatin, transcription factor binding sites and the arrangement of these sites in CFTR consistent with the restrictive expression in epithelial cell types. Here, we identified CHD6 from a screen among several chromatin-remodeling proteins as a putative epigenetic modulator of CFTR expression. Moreover, our findings of CTCF interactions with CHD6 are consistent with the role described previously for CTCF in CFTR regulation. Our results now reveal that the CHD6 protein lies within the infrastructure of multiple transcriptional complexes, such as the FACT, PBAF, PAF1C, Mediator, SMC/Cohesion and MLL complexes. This model underlies the fundamental role CHD6 facilitates by tethering cis-acting regulatory elements of CFTR in proximity to these multi-subunit transcriptional protein complexes. Finally, we indicate that CHD6 structurally coordinates a three-dimensional stricture between intragenic elements of CFTR bound by several cell-type specific transcription factors, such as CDX2, SOX18, HNF4α and HNF1α. Therefore, our results reveal new insights into the epigenetic regulation of CFTR expression, whereas the manipulation of CFTR gene topology could be considered for treating specific indications of cystic fibrosis and/or pancreatitis.

Many long non-coding RNAs (lncRNAs) that regulate the capacity of cells to undergo oncogenic transformation still remain unknown. However, their involvement in chromatin organization has been an emerging principle in cancer epigenomics. This recent concept has been documented through recent studies of the gene -poor chromosomal region 8q24 surrounding the C-MYC locus to understand the mechanisms enforcing or suppressing tumor cell growth from C-MYC transcription levels. In light of such examples informing us of the DNA elements and the epigenomic composition that become integrated into molecular programs that regulate C-MYC, some lncRNAs in non-genic regions are considered landmarks that enforce chromatin state changes to accommodate C-MYC expression. Here, we use an integrative genomic and proteomic approach to gain insight of how an endogenously tagged lncRNA PCAT-1 utilizes the chromatin and biochemical context to shape C-MYC locus topology to promote tumor cell growth, survival and fitness. Our results now find that WDR74 forms an integrative hub involving recognition of the m7G cap of lncRNA transcripts along with, RNMT, RAM, BRD4, β catenin, EZH2 that assist in a program that enforce C-MYC transcription and stabilize transcripts through utilizing a comprehensive mixture of cis-acting DNA elements, lncRNAs and trans functioning transcriptional and RNA capping complexes for prostate tumor cell growth. Our results now place the lncRNA PCAT-1 and the novel interacting WD40 repeat protein WDR74 at the axis along with β catenin, BRD4 and EZH2, and additional RBPs as a non -canonical chromatin complex to shape the chromosomal topology that benefit prostate cancer cell growth. Citation Format: Fan Zhang, Won-min Song, SiDe Li, Vashisht Ajay, Francesca Aguilo, Anindya Bagchi, James A. Wohlschlegel, Bin Zhang, Martin Walsh. The enhancer landscape involves a core noncoding RNA protein interaction network for C-MYC expression. [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer: Mechanisms to Medicines ; 2015 Dec 4-7; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2016;76(6 Suppl):Abstract nr PR06.

The INK4/ARF locus regulates senescence and is frequently altered in cancer. In normal cells, the INK4/ARF locus is found silenced by Polycomb repressive complexes (PRCs). Which are the mechanisms responsible for the recruitment of PRCs to INK4/ARF and their other target genes remains unclear. In a genetic screen for transcription factors regulating senescence, we identified the homeodomain-containing protein HLX1 (H2.0-like homeobox 1). Expression of HLX1 extends cellular lifespan and blunts oncogene-induced senescence. Using quantitative proteomics, we identified p16(INK4a) as the key target mediating the effects of HLX1 in senescence. HLX1 represses p16(INK4a) transcription by recruiting PRCs and HDAC1. This mechanism has broader implications, as HLX1 also regulates a subset of PRC targets besides p16(INK4a). Finally, sampling members of the Homeobox family, we identified multiple genes with ability to repress p16(INK4a). Among them, we found HOXA9 (Homeobox A9), a putative oncogene in leukaemia, which also recruits PRCs and HDAC1 to regulate p16(INK4a). Our results reveal an unexpected and conserved interplay between homeodomain-containing proteins and PRCs with implications in senescence, development and cancer.

Fetal liver and adult bone marrow hematopoietic stem cells (HSCs) renew or differentiate into committed progenitors to generate all blood cells. PRDM16 is involved in human leukemic translocations and is expressed highly in some karyotypically normal acute myeloblastic leukemias. As many genes involved in leukemogenic fusions play a role in normal hematopoiesis, we analyzed the role of Prdm16 in the biology of HSCs using Prdm16-deficient mice. We show here that, within the hematopoietic system, Prdm16 is expressed very selectively in the earliest stem and progenitor compartments, and, consistent with this expression pattern, is critical for the establishment and maintenance of the HSC pool during development and after transplantation. Prdm16 deletion enhances apoptosis and cycling of HSCs. Expression analysis revealed that Prdm16 regulates a remarkable number of genes that, based on knockout models, both enhance and suppress HSC function, and affect quiescence, cell cycling, renewal, differentiation, and apoptosis to various extents. These data suggest that Prdm16 may be a critical node in a network that contains negative and positive feedback loops and integrates HSC renewal, quiescence, apoptosis, and differentiation.

In the cytosol of lipogenic tissue, ketone bodies are activated by AACS (acetoacetyl-CoA synthetase) and incorporated into cholesterol and fatty acids. AACS gene expression is particularly abundant in white adipose tissue, as it is induced during adipocyte differentiation. In order to elucidate the mechanism controlling the gene expression of human AACS and to clarify its physiological role, we isolated the human promoter, characterized the elements required to initiate transcription and analysed the expression of the gene in response to PPARγ (peroxisome-proliferator-activated receptor γ), an inducer of adipogenesis. We show that the human AACS promoter is a PPARγ target gene and that this nuclear receptor is recruited to the AACS promoter by direct interaction with Sp1 (stimulating protein-1).

The INK/ARF (CDKN2A) locus expresses p15Ink4B, p16Ink4A, p14Arf and is under control of Polycomb Repressive Complexes PRC1 and PRC2 to impose transcriptional silencing to bypass cellular senescence upon oncogenic stress. Previously, we had identified a constituent member of human PRC1, known as the chromobox protein 7 (CBX7), is endowed the capacity to bind specifically to elements of the long non-coding RNA identified as the non-coding anti-sense RNA of the INK locus (ANRIL) RNA transcript as a mature processed polyadenylated RNA transcript. ANRIL represent a large heterogeneous population of individual transcripts and their isoforms arising from the localized genomic region overlapping INK/ARF. These transcripts reveal independent patterns of expression dependent on the state of cell growth and differentiation. Moreover, specific transcripts overlapping the ANRIL region of chromosome 9p21.3 provide strict correlation to human embryonic stem cell pluripotency and self-renewal versus differentiation. We recently identify specific ANRIL transcripts and isoforms that are correlative with human prostate tumor stages and states of malignancy. We had previously shown that certain transcripts correlate with PRC1 is organized on the INK/ARF locus through the interaction between CBX7 and the nascent ANRIL transcript to help establish and maintain repressive histone H3K27 methylation and H2AK119 monoubiquitination. Both PRC1 and PRC2 can interact with different ANRIL transcript regions and it remains unclear whether this activity is cooperative. This activity is abrogated in the absence of RNA polymerase II activity thereby requiring nascent transcription of anti-sense transcripts of INK/ARF by RNA polymerase II (RNA POLII). Interestingly, TAF15/TAFII68 can be tethered to CBX7 in prostate carcinoma cells where the ANRIL ncRNA transcripts are elevated. Our recent finding is that specific ANRIL transcripts directed by RNAPOLII are influenced by RNA polymerase III (RNA POLIII) as measured through the depletion of the core RNA POLIII factor BRF1. This evidence suggests that RNA POLIII may populate RNA synthesis of shorter transcripts to influence PRC1 and PRC2 binding thereby instructing the behavior of RNA POLII synthesis. This provides a rational mechanism whereby RNA POLIII with RNAPOLIII provide the genomic RNA context to instruct PRC1 and PRC2 to exert antisense transcription at the expense of transcriptional activity of INK/ARF. Citation Format: Martin J. Walsh, Francesca Aguilo, SiDe Li, Kyoko Yap, Jesus Gil, Ming-Ming Zhou. Navigating the balance of INK4/ARF expression in cancer: ncRNAs as sensors and regulators of transcription [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer; 2012 Jan 8-11; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(2 Suppl):Abstract nr IA2.

SummaryThe Peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) is a transcriptional co-activator that plays a central role in adapted metabolic responses. PGC-1α is dynamically methylated and unmethylated at the residue K779 by the methyltransferase SET7/9 and the Lysine Specific Demethylase 1A (LSD1), respectively. Interactions of methylated PGC-1α[K779me] with the Spt-Ada-Gcn5-acetyltransferase (SAGA) complex, the Mediator members MED1 and MED17, and the NOP2/Sun RNA methytransferase 7 (NSUN7) reinforce transcription, and are concomitant with the m5C mark on enhancer RNAs (eRNAs). Consistently, loss of Set7/9 and NSun7 in liver cell model systems resulted in depletion of the PGC-1α target genes Pfkl, Sirt5, Idh3b, and Hmox2, which was accompanied by a decrease in the eRNAs levels associated with these loci. Enrichment of m5C within eRNA species coincides with metabolic stress of fasting in vivo. Collectively, these findings illustrate the complex epigenetic circuitry imposed by PGC-1α at the eRNA level to fine-tune energy metabolism.

SummaryMany signals must be integrated to maintain self-renewal and pluripotency in embryonic stem cells (ESCs) and to enable induced pluripotent stem cell (iPSC) reprogramming. However, the exact molecular regulatory mechanisms remain elusive. To unravel the essential internal and external signals required for sustaining the ESC state, we conducted a short hairpin (sh) RNA screen of 104 ESC-associated phosphoregulators. Depletion of one such molecule, aurora kinase A (Aurka), resulted in compromised self-renewal and consequent differentiation. By integrating global gene expression and computational analyses, we discovered that loss of Aurka leads to upregulated p53 activity that triggers ESC differentiation. Specifically, Aurka regulates pluripotency through phosphorylation-mediated inhibition of p53-directed ectodermal and mesodermal gene expression. Phosphorylation of p53 not only impairs p53-induced ESC differentiation but also p53-mediated suppression of iPSC reprogramming. Our studies demonstrate an essential role for Aurka-p53 signaling in the regulation of self-renewal, differentiation, and somatic cell reprogramming.