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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| Format: | Doctoral Thesis |
| Language: | English |
| Published: |
Philipps-Universität Marburg
2009
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| Online Access: | PDF Full Text |
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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. |
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| Physical Description: | 78 Pages |
| DOI: | 10.17192/z2009.0600 |