Investigation of the functions of 53BP1 in DNA demethylation

DNA damage can be caused by various forms of genotoxic stress, including endogenous (reactive oxygen species, abnormal replication intermediates) and exogenous (UV, IR, and reactive chemicals) sources. DNA double-strand break (DSB) is believed to be one of the most serious lesions to cells becaus...

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Bibliographic Details
Main Author: Wang, Linfang
Contributors: Engenhart-Cabillic, R. (Prof. Dr.) (Thesis advisor)
Format: Dissertation
Language:English
Published: Philipps-Universität Marburg 2009
Klinik für Strahlentherapie
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Summary:DNA damage can be caused by various forms of genotoxic stress, including endogenous (reactive oxygen species, abnormal replication intermediates) and exogenous (UV, IR, and reactive chemicals) sources. DNA double-strand break (DSB) is believed to be one of the most serious lesions to cells because it can result in loss or rearrangement of genetic information, leading to cell death or carcinogenesis. The DNA damage response (DDR) involves multiple signal transduction pathways in that several different components act in concert to activate the cellular checkpoint. These components consist of sensors that sense DNA damage, signal transducers that generate and amplify the DNA damage signal, and effectors that induce cell cycle delay, programmed cell death, and DNA repair. Even though several candidate proteins have been implicated in DNA damage response, an official checkpoint-specific damage sensor is still unknown. 53BP1 seems to be one of the key-sensors of DNA DSBs, upstream of ATM. The function of 53BP1 is important for coupling ATM to its downstream targets, including p53 and Gadd45a. The activation of Gadd45a as a stress protein promotes epigenetic gene activation by repair-mediated DNA demethylation, thus linking both processes. DNA methylation is mediated by MBD2 as well as a class of DNMTs, which encompassing DNMT1, DNMT3a and DNMT3b. Recent studies have demonstrated that the DNA methylation mediated by DNMTs is associated with p53 signalling in maintaining genome stability. Since p53 is one of the downstream targets of 53BP1, it will be of interest to investigate the functions of 53BP1 in DNA demethylation and determine the possible link between 53BP1 and these related genes. The data presented here indicate that 53BP1 can induce DNA demethylation of single copy gene as well as repetitive elements in A549 cells. Meanwhile, the transient expression of 53BP1 can enhance DNA demethylation in combination with IR. Furthermore, the tumor suppressor gene RASSF1A was re-expressed following predominantly demethylation of CpG islands in the promoter analyzed by MSP and RT-PCR. Moreover, overexpression of 53BP1 caused a marked decrease in DNMT1 and DNMT3a mRNA expression as well as a significant increase in Gadd45a and MBD2 mRNA expression. To our best knowledge, the present study shows for the first time the involvement of 53BP1 in DNA demethylation process. Understanding the 53BP1-mediated network will certainly have an impact on numerous fields of medicine. However, how 53BP1 regulates different member of DNMTs need to be characterized. Further experiments of the precise mechanisms of 53BP1 in DNA demethylation may clarify this association and develop therapeutic alternatives designed to promote hypomethylation and re-activation of tumor suppressor genes.
DOI:https://doi.org/10.17192/z2009.0600