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Human MutSalpha specifically binds to DNA containing aminofluorene and acetylaminofluorene adducts
1Department of Pathology and Laboratory of Medicine, Markey Cancer Center, University of Kentucky Medical Center, Lexington, Kentucky 40536, USA.
Abstract:
Defects in mismatch repair are associated with several types of cancer. It is also generally believed that environmental carcinogens are responsible for the initiation of cancers by the induction of mutations in critical genes. Prior genetic studies have suggested that the mismatch repair system can also recognize certain forms of DNA damage such as O6-methylguanine and UV photoproducts, and, therefore, mismatch repair may play a role in environmental agent-induced carcinogenesis. To examine this hypothesis, hMutSalpha, a heterodimer which consists of hMSH2 and GTBP and participates in strand-specific mismatch repair, was tested for its ability to recognize DNA containing a site-specific C8-guanine adduct of aminofluorene (AF) or N-acetyl-2-aminofluorene (AAF). We show here that hMutSalpha specifically binds to both AF and AAF adducts. This binding requires both hMSH2 and GTBP. Results from competition and titration experiments indicate that the binding efficiency of hMutSalpha to AF and AAF is about 60% of that to a G-T mismatch, but is at least 10-fold that to an otherwise identical homoduplex DNA without the chemical modification. The specific binding of AF and AAF adducts by hMutSalpha suggests that strand-specific mismatch repair is involved in processing DNA damage induced by environmental carcinogens.
Insights
The mismatch repair system, involving hMutSalpha (hMSH2 and GTBP), specifically binds to DNA adducts from environmental carcinogens like aminofluorene (AF) and N-acetyl-2-aminofluorene (AAF). This suggests a role for mismatch repair in processing carcinogen-induced DNA damage.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- Defects in DNA mismatch repair are linked to various cancers.
- Environmental carcinogens initiate cancer by causing DNA mutations.
- The mismatch repair system may process DNA damage from environmental agents.
Purpose of the Study:
- To investigate if the hMutSalpha complex recognizes DNA adducts formed by environmental carcinogens aminofluorene (AF) and N-acetyl-2-aminofluorene (AAF).
Main Methods:
- Tested the binding of hMutSalpha (hMSH2/GTBP heterodimer) to DNA containing site-specific C8-guanine adducts of AF and AAF.
- Utilized competition and titration experiments to quantify binding efficiency relative to G-T mismatches and unmodified DNA.
Main Results:
- h hMutSalpha specifically binds to both AF and AAF DNA adducts, requiring both hMSH2 and GTBP.
- Binding efficiency to AF/AAF adducts was approximately 60% of that to a G-T mismatch.
- Binding was at least 10-fold higher to adducts than to unmodified DNA.
Conclusions:
- The specific binding of AF and AAF adducts by hMutSalpha indicates its involvement in the repair of DNA damage induced by environmental carcinogens.
- This finding supports the hypothesis that mismatch repair pathways play a role in environmental carcinogenesis.