Human 3-Methyladenine-DNA Glycosylase: Effect of Sequence Context on Excision, Association with PCNA, and Stimulation by AP Endonuclease

Xia, Liqun; Zheng, Lirong; Lee, Hyun‐Wook; Bates, Steven; Federico, Laura; Shen, Binghui; O’Connor, Timothy

doi:10.1016/j.jmb.2005.01.014

Cited by 82 publications

(80 citation statements)

References 108 publications

(113 reference statements)

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“…It should be emphasized that the kinetic values obtained here may not necessarily be applicable to all sequences, as recently shown for the N-methylpurine-DNA glycosylase (50). However, similar results were obtained with longer (63-mer) substrates (data not shown).…”

Section: Discussionsupporting

confidence: 77%

The DNAN-Glycosylase MED1 Exhibits Preference for Halogenated Pyrimidines and Is Involved in the Cytotoxicity of 5-Iododeoxyuridine

et al. 2006

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The base excision repair protein MED1 (also known as MBD4), an interactor with the mismatch repair protein MLH1, has a central role in the maintenance of genomic stability with dual functions in DNA damage response and repair. MED1 acts as a thymine and uracil DNA N-glycosylase on T:G and U:G mismatches that occur at cytosine-phosphate-guanine (CpG) methylation sites due to spontaneous deamination of 5-methylcytosine and cytosine, respectively. To elucidate the mechanisms that underlie sequence discrimination by MED1, we did single-turnover kinetics with the isolated, recombinant glycosylase domain of MED1. Quantification of MED1 substrate hierarchy confirmed MED1 preference for mismatches within a CpG context and showed preference for hemimethylated base mismatches. Furthermore, the k st values obtained with the uracil analogues 5-fluorouracil and 5-iodouracil were over 20-to 30-fold higher than those obtained with uracil, indicating substantially higher affinity for halogenated bases. A 5-iodouracil precursor is the halogenated nucleotide 5-iododeoxyuridine (5IdU), a cytotoxic and radiosensitizing agent. Cultures of mouse embryo fibroblasts (MEF) with different Med1 genotype derived from mice with targeted inactivation of the gene were evaluated for sensitivity to 5IdU. The results revealed that Med1-null MEFs are more sensitive to 5IdU than wild-type MEFs in both 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and colony formation assays. Furthermore, high-performance liquid chromatography analyses revealed that Med1-null cells exhibit increased levels of 5IdU in their DNA due to increased incorporation or reduced removal. These findings establish MED1 as a bona fide repair activity for the removal of halogenated bases and indicate that MED1 may play a significant role in 5IdU cytotoxicity. (Cancer Res 2006; 66(15): 7686-93)

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Section: Discussionsupporting

confidence: 77%

The DNAN-Glycosylase MED1 Exhibits Preference for Halogenated Pyrimidines and Is Involved in the Cytotoxicity of 5-Iododeoxyuridine

et al. 2006

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“…In this study, we suggest an alternative pathway that gadd45a as one of p53 downstream genes might also play a role in the enhancement of BER by modulation of localization of APE1/Ref1, which is known to involve BER as well as to activate p53. Gadd45a has been implicated in the enhancement of BER by the interaction with proliferating cell nuclear antigen (PCNA) (Smith et al, 2000), which is recently reported to interact with APE1/Ref1 (Xia et al, 2005). Future studies will ascertain if Gadd45a can function independent of p53.…”

Section: Detection Of Ap Sitesmentioning

confidence: 99%

“…A very recent study has suggested that PCNA interacts with a key component of the BER pathway, APE1/Ref1 in the nucleus (Xia et al, 2005), implying that Gadd45a could potentially affect BER via PCNA and APE1/Ref1 interaction.…”

Section: Introductionmentioning

confidence: 99%

Base excision DNA repair defect in Gadd45a-deficient cells

et al. 2007

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“…Finally, PCNA functions as a scaffold for factors functioning in base excision repair (BER). More specifically, PCNA has been shown to interact with the UNG2, MPG, and NTH1 DNA glycosylases, as well as the APE2 AP endonuclease, stimulating their ability to generate abasic sites and cleave them in order for repair to take place (Ko and Bennett, 2005;Oyama et al, 2004;Tsuchimoto et al, 2001;Xia et al, 2005). An interaction between PCNA and the structure-specific repair endonuclease xeroderma pigmentosum (XP) G was also found, suggesting a function in nucleotide excision repair (NER) (Gary et al, 1997), but in this case PCNA is recruited by XPG upon nucleotide excision by ERCC1, resulting in the gap filling by polymerase (Mocquet et al, 2008).…”

Section: Proliferating Cell Nuclear Antigen (Pcna)mentioning

confidence: 99%