The Role of XPG in Processing (CAG) n/(CTG) n DNA Hairpins

Caixia Hou, Tianyi Zhang, Lei Tian, Jian Huang, Liya Gu, Guo Min Li

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Background: During DNA replication or repair, disease-associated (CAG) n/(CTG) n expansion can result from formation of hairpin structures in the repeat tract of the newly synthesized or nicked DNA strand. Recent studies identified a nick-directed (CAG) n/(CTG) n hairpin repair (HPR) system that removes (CAG) n/(CTG) n hairpins from human cells via endonucleolytic incisions. Because the process is highly similar to the mechanism by which XPG and XPF endonucleases remove bulky DNA lesions during nucleotide excision repair, we assessed the potential role of XPG in conducting (CAG) n/(CTG) n HPR.Results: To determine if the XPG endonuclease is involved in (CAG) n/(CTG) n hairpin removal, two XPG-deficient cell lines (GM16024 and AG08802) were examined for their ability to process (CAG) n/(CTG) n hairpins in vitro. We demonstrated that the GM16024 cell line processes all hairpin substrates as efficiently as HeLa cells, and that the AG08802 cell line is partially defective in HPR. Analysis of repair intermediates revealed that nuclear extracts from both XPG-deficient lines remove CAG/CTG hairpins via incisions, but the incision products are distinct from those generated in HeLa extracts. We also show that purified recombinant XPG protein greatly stimulates HPR in XPG-deficient extracts by promoting an incision 5' to the hairpin.Conclusions: Our results strongly suggest that 1) human cells possess multiple pathways to remove (CAG) n/(CTG) n hairpins located in newly synthesized (or nicked) DNA strand; and 2) XPG, although not essential for (CAG) n/(CTG) n hairpin removal, stimulates HPR by facilitating a 5' incision to the hairpin. This study reveals a novel role for XPG in genome-maintenance and implicates XPG in diseases caused by trinucleotide repeat expansion.

Original languageEnglish (US)
Article number11
JournalCell and Bioscience
Volume1
Issue number1
DOIs
StatePublished - Mar 9 2011

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Repair
Endonucleases
Cell Line
DNA Repair
DNA
Processing
Trinucleotide Repeat Expansion
Cells
DNA Replication
HeLa Cells
Recombinant Proteins
Maintenance
Genome
Trinucleotide Repeats
Recombinant proteins
Nucleotides
Genes
Substrates
In Vitro Techniques

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)

Cite this

The Role of XPG in Processing (CAG) n/(CTG) n DNA Hairpins. / Hou, Caixia; Zhang, Tianyi; Tian, Lei; Huang, Jian; Gu, Liya; Li, Guo Min.

In: Cell and Bioscience, Vol. 1, No. 1, 11, 09.03.2011.

Research output: Contribution to journalArticle

Hou, Caixia ; Zhang, Tianyi ; Tian, Lei ; Huang, Jian ; Gu, Liya ; Li, Guo Min. / The Role of XPG in Processing (CAG) n/(CTG) n DNA Hairpins. In: Cell and Bioscience. 2011 ; Vol. 1, No. 1.
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AB - Background: During DNA replication or repair, disease-associated (CAG) n/(CTG) n expansion can result from formation of hairpin structures in the repeat tract of the newly synthesized or nicked DNA strand. Recent studies identified a nick-directed (CAG) n/(CTG) n hairpin repair (HPR) system that removes (CAG) n/(CTG) n hairpins from human cells via endonucleolytic incisions. Because the process is highly similar to the mechanism by which XPG and XPF endonucleases remove bulky DNA lesions during nucleotide excision repair, we assessed the potential role of XPG in conducting (CAG) n/(CTG) n HPR.Results: To determine if the XPG endonuclease is involved in (CAG) n/(CTG) n hairpin removal, two XPG-deficient cell lines (GM16024 and AG08802) were examined for their ability to process (CAG) n/(CTG) n hairpins in vitro. We demonstrated that the GM16024 cell line processes all hairpin substrates as efficiently as HeLa cells, and that the AG08802 cell line is partially defective in HPR. Analysis of repair intermediates revealed that nuclear extracts from both XPG-deficient lines remove CAG/CTG hairpins via incisions, but the incision products are distinct from those generated in HeLa extracts. We also show that purified recombinant XPG protein greatly stimulates HPR in XPG-deficient extracts by promoting an incision 5' to the hairpin.Conclusions: Our results strongly suggest that 1) human cells possess multiple pathways to remove (CAG) n/(CTG) n hairpins located in newly synthesized (or nicked) DNA strand; and 2) XPG, although not essential for (CAG) n/(CTG) n hairpin removal, stimulates HPR by facilitating a 5' incision to the hairpin. This study reveals a novel role for XPG in genome-maintenance and implicates XPG in diseases caused by trinucleotide repeat expansion.

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