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Stability of epigenetic control in normal and transformed human cells

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Author(s):
Érica Sara Souza de Araújo
Total Authors: 1
Document type: Master's Dissertation
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
Defense date:
Examining board members:
Lygia da Veiga Pereira Carramaschi; Miriam Galvonas Jasiulionis; Luciana dos Reis Vasques
Advisor: Lygia da Veiga Pereira Carramaschi
Abstract

Epigenetics refers to mechanisms related to gene activity through conformational modifications in DNA without changes in the nucleotide sequence. Key players in the epigenetic control are DNA methylation and histone acetylation, which are related to gene activation and repression, respectively. Two striking epigenetic phenomena in mammalians are X chromosome inactivation (XCI) and genomic imprinting. XCI triggers the transcriptional silencing of all but one X chromosome in each female cell, while genomic imprinting is a process that leads to mono-allelic gene expression based on parental origin. In the present study, we intended to verify the maintenance of epigenetic control in normal and transformed human cells under the same conditions of epigenetic disturbance. For this purpose, 5-aza-2\'-deoxycytidine (5-aza-dC) and valproic acid (VPA) were used to cause DNA hypomethylation and histone hyperacetylation, respectively. By monitoring allelic-specific expression using single nucleotide polymorphisms present in coding regions, we were able to check the effects of the modifications in the expression pattern of imprinted or subjected to XCI genes. While in female normal cells XCI and genomic imprinting were not affected by VPA or 5-aza-dC treatments, transformed male cells showed XIST activation and loss of imprinting of PEG10, IGF2 and H19 genes in the hypomethylation scenario. In addition, both drugs can decrease the expression of DNMT1, and 5-aza-dC alters the balance between acetylation and deacethylation of histone H4. Furthermore, we could see different degrees of histone H4 acetylation levels and of XIST and PEG10 expression, depending on which of the drugs was added first. Our data suggest that the epigenetic control in normal human cells is more stable when compared to transformed human cells. In addition, both XCI and genomic imprinting are epigenetic features equally hard to disturb. Finally, depending on the initial epigenetic modification (global demethylation or acethylation), it will induce different epigenetic control networks, with consequence to the final status of gene expression. (AU)