Repair of alkylated DNA: Recent advances
Department of Biomedical Sciences , Florida State University, Tallahassee, Florida, United StatesDNA Repair (Impact Factor: 3.11). 05/2007; 6(4):429-42. DOI: 10.1016/j.dnarep.2006.10.005
Cytotoxic and mutagenic methylated bases in DNA can be generated by endogenous and environmental alkylating agents. Such damaged bases are removed by three distinct strategies. The abundant toxic lesion 3-methyladenine (3-alkyladenine) is excised by a specific DNA glycosylase that initiates a base excision-repair process. The toxic lesions 1-methyladenine and 3-methylcytosine are corrected by oxidative DNA demethylation catalyzed by DNA dioxygenases. These enzymes release the methyl moiety as formaldehyde, directly reversing the base damage. The third strategy involves the mutagenic and cytotoxic lesion O(6)-methylguanine which is also repaired by direct reversal but uses a different mechanism. Here, the methyl group is transferred from the lesion to a specific cysteine residue within the methyltransferase itself. In this review, we briefly describe endogenous alkylating agents and the extensively investigated DNA repair enzymes, mammalian 3-methyladenine-DNA glycosylase and O(6)-methylguanine-DNA methyltransferase. We provide a more detailed description of the structures and biochemical properties of the recently discovered DNA dioxygenases.
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- "Alkylation is a major mechanism by which nucleic acids are modified, and repair of these adducts is critical since they are mutagenic and may cause DNA breaks (Sedgwick et al, 2007; Fu et al, 2012). Alkylation damage is repaired by at least three different pathways, including base-excision repair (BER), suicidal methyltransferases such as methyl-guanine methyltransferase (MGMT), and direct methylation/ alkylation reversal by the AlkB family of demethylases (Drablos et al, 2004; Sedgwick et al, 2007; Fu et al, 2012). Originally discovered in Escherichia coli, the AlkB protein catalyzes oxidative demethylation of cytotoxic adducts of DNA bases alkylated at the N1 position of purines and N3 position of pyrimidines (Falnes et al, 2002; Trewick et al, 2002). "
ABSTRACT: Repair of DNA alkylation damage is critical for genomic stability and involves multiple conserved enzymatic pathways. Alkylation damage resistance, which is critical in cancer chemotherapy, depends on the overexpression of alkylation repair proteins. However, the mechanisms responsible for this upregulation are unknown. Here, we show that an OTU domain deubiquitinase, OTUD4, is a positive regulator of ALKBH2 and ALKBH3, two DNA demethylases critical for alkylation repair. Remarkably, we find that OTUD4 catalytic activity is completely dispensable for this function. Rather, OTUD4 is a scaffold for USP7 and USP9X, two deubiquitinases that act directly on the AlkB proteins. Moreover, we show that loss of OTUD4, USP7, or USP9X in tumor cells makes them significantly more sensitive to alkylating agents. Taken together, this work reveals a novel, noncanonical mechanism by which an OTU family deubiquitinase regulates its substrates, and provides multiple new targets for alkylation chemotherapy sensitization of tumors. © 2015 The Authors.The EMBO Journal 05/2015; 34(12):1687-1703. DOI:10.15252/embj.201490497 · 10.43 Impact Factor
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- "Wild-type as well as silenced cells displayed similar GAPDH activity levels to the corresponding non-treated controls (Fig. 2C), which indicated that neither genotoxic agent oxidizes the catalytic C149 residue. This observation is compatible with the action mechanism of these compounds (Sedgwick et al., 2007; Povirk, 1996). Overall, these results suggested that the role of GAPDH in DNA repair may depend on the reduced state of C149. "
ABSTRACT: Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional protein with diverse biological functions in human cells. In bacteria, moonlighting GAPDH functions have only been described for the secreted protein in pathogens or probiotics. At the intracellular level, we previously reported the interaction of Escherichia coli GAPDH with phosphoglycolate phosphatase, a protein involved in the metabolism of the DNA repair product 2-phosphoglycolate, thus suggesting a putative role of GAPDH in DNA repair processes. Here, we provide evidence that GAPDH is required for the efficient repair of DNA lesions in E. coli. We show that GAPDH-deficient cells are more sensitive to bleomycin or methyl methanesulfonate. In cells challenged with these genotoxic agents GAPDH deficiency results in reduced cell viability and filamentous growth. In addition, the gapA knockout mutant accumulates a higher number of spontaneous abasic sites and displays higher spontaneous mutation frequencies than the parental strain. Pull-down experiments in different genetic backgrounds show interaction between GAPDH and enzymes of the base excision repair pathway, namely the AP-endonuclease Endo IV and uracil DNA glycosylase. This finding suggests that GAPDH is a component of a protein complex dedicated to the maintenance of genomic DNA integrity. Our results also show interaction of GAPDH with the single-stranded DNA binding protein. This interaction may recruit GAPDH to the repair sites and implicates GAPDH in DNA repair pathways activated by profuse DNA damage, such as homologous recombination or the SOS response.The International Journal of Biochemistry & Cell Biology 01/2015; 12. DOI:10.1016/j.biocel.2015.01.008 · 4.05 Impact Factor
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- "MGMT silencing is associated with increased progression-free survival and OS in patients treated with TMZ, and can therefore predict a favourable outcome    . However, this is oversimplistic as hypermethylation of the mgmt promoter also results in the so-called ''mutator phenotype'' that is observed in up to 30% of primary GBM and is considered to be an early malignant event due to its destabilising effect on the genome      . "
ABSTRACT: Glioblastoma multiforme (GBM) is a malignant and incurable glial brain tumour. The current best treatment for GBM includes maximal safe surgical resection followed by concomitant radiotherapy and adjuvant temozolomide. Despite this, median survival is still only 14–16 months. Mechanisms that lead to chemo- and radio-resistance underpin treatment failure. Insights into the DNA repair mechanisms that permit resistance to chemoradiotherapy in GBM may help improve patient responses to currently available therapies.Journal of Clinical Neuroscience 11/2014; 22(1). DOI:10.1016/j.jocn.2014.09.003 · 1.38 Impact Factor
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