RESUMEN
The self-renewing cancer stem cells (CSCs) represent one of the distinct cell populations occurring in a tumour that can differentiate into multiple lineages. This group of sparsely abundant cells play a vital role in tumour survival and resistance to different treatments during cancer. The lack of exclusive markers associated with CSCs makes diagnosis and prognosis in cancer patients extremely difficult. This calls for the identification of unique regulators and markers for CSCs. Various signalling pathways like the Wnt/ß-catenin pathway, Hedgehog pathway, Notch pathway, and TGFß/BMP play a major role in the regulation and maintenance of CSCs. Epigenetic regulatory mechanisms add another layer of complexity to control these signalling pathways. In this chapter, we discuss about the role of epigenetic mechanisms in regulating the cellular signalling pathways in CSCs. The epigenetic regulatory mechanisms such as DNA methylation, histone modification and microRNAs can modulate the diverse effectors of signalling pathways and consequently the growth, differentiation and tumorigenicity of CSCs. In the end, we briefly discuss the therapeutic potential of targeting these epigenetic regulators and their target genes in CSCs.
Asunto(s)
Proteínas Hedgehog , Neoplasias , Humanos , Proteínas Hedgehog/genética , Proteínas Hedgehog/metabolismo , Proteínas Hedgehog/uso terapéutico , Neoplasias/patología , Células Madre Neoplásicas/metabolismo , Células Madre Neoplásicas/patología , Vía de Señalización Wnt/genética , Epigénesis GenéticaRESUMEN
Poly-ADP-ribosylation (PARylation) is regarded as a protein-specific modification. However, some PARPs were recently shown to modify DNA termini in vitro. Here, we use ultrasensitive mass spectrometry (LC-MS/MS), anti-PAR antibodies, and anti-PAR reagents to show that mammalian DNA is physiologically PARylated and to different levels in primary tissues. Inhibition of PAR glycohydrolase (PARG) increases DNA PARylation, supporting that the modification is reversible. DNA PARylation requires PARP1 and in vitro PARP1 PARylates single-stranded DNA, while PARG reverts the modification. DNA PARylation occurs at the N1-position of adenosine residues to form N1-Poly(ADP-ribosyl)-deoxyadenosine. Through partial hydrolysis of mammalian gDNA we identify PAR-DNA via the diagnostic deamination product N1-ribosyl-deoxyinosine to occur in vivo. The discovery of N1-adenosine PARylation as a DNA modification establishes the conceptual and methodological framework to elucidate its biological relevance and extends the role of PARP enzymes.
Asunto(s)
Poli ADP Ribosilación , Inhibidores de Poli(ADP-Ribosa) Polimerasas , Adenosina , Adenosina Difosfato , Animales , Cromatografía Liquida , ADN/metabolismo , ADN de Cadena Simple , Desoxiadenosinas , Glicósido Hidrolasas/metabolismo , Mamíferos/genética , Poli(ADP-Ribosa) Polimerasa-1/metabolismo , Poli Adenosina Difosfato Ribosa/metabolismo , Espectrometría de Masas en TándemRESUMEN
DNMT3L is an important epigenetic regulator in mammals, integrating DNA methylation and histone modification based epigenetic circuits. Here we show DNMT3L to be a part of the machinery that enables inheritance of epigenetic modifications from one generation to the next. Ectopic expression of DNMT3L in Drosophila, which lacks DNMT3L and its normal interacting partners DNMT3A and DNMT3B, lead to nuclear reprogramming that was gradual and progressive, resulting in melanotic tumors that were observed only when these flies were maintained for five generations. This global gene expression misregulation was accompanied by aberrations in the levels of H3K4me3 and H3K36me3, globally as well as at specific gene promoters. The levels of these epigenetic aberrations (epimutations) also increased progressively across successive generations. The accumulation and inheritance of epimutations across multiple generations recapitulates the important role of DNMT3L in intergenerational epigenetic inheritance in mammals.
Asunto(s)
ADN (Citosina-5-)-Metiltransferasas/genética , Drosophila melanogaster/genética , Epigénesis Genética , Patrón de Herencia/genética , Animales , Animales Modificados Genéticamente , Inmunoprecipitación de Cromatina , ADN (Citosina-5-)-Metiltransferasas/metabolismo , Ojo/patología , Genes de Insecto , Histonas/metabolismo , Larva/genética , Melanoma/genética , Melanoma/patología , Metilación , Familia de Multigenes , Análisis de Secuencia por Matrices de Oligonucleótidos , Especificidad de Órganos , Fenotipo , Regiones Promotoras Genéticas , Transcripción Genética , Alas de Animales/anatomía & histologíaRESUMEN
DNMT3L, a member of DNA methyltransferases family, is present only in mammals. As it provides specificity to the action of de novo methyltransferases, DNMT3A and DNMT3B and interacts with histone H3, DNMT3L has been invoked as the molecule that can read the histone code and translate it into DNA methylation. It plays an important role in the initiation of genomic imprints during gametogenesis and in nuclear reprogramming. With important functions attributed to it, it is imperative that the DNMT3L expression is tightly controlled. Previously, we had identified a CpG island within the human DNMT3L promoter and first exon that showed loss of DNA methylation in cancer samples. Here we show that this Differentially Methylated CpG island within DNMT3L (DNMT3L DMC) acts to repress transcription, is a Polycomb/Trithorax Response Element (PRE) and interacts with both PRC1 and PRC2 Polycomb repressive complexes. In addition, it adopts inactive chromatin conformation and is associated with other inactive chromatin-specific proteins like SUV39H1 and HP1. The presence of DNMT3L DMC also influences the adjacent promoter to adopt repressive histone post-translational modifications. Due to its association with multiple layers of repressive epigenetic modifications, we believe that PRE within the DNMT3L DMC is responsible for the tight regulation of DNMT3L expression and the aberrant epigenetic modifications of this region leading to DNMT3L overexpression could be the reason of nuclear programming during carcinogenesis.