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Identification of mismatch repair protein complexes in HeLa nuclear extracts and their interaction with heteroduplex
N Matton1, J Simonetti, K Williams
1Department of Biological Sciences/Biomedical Program, University of Alaska, Anchorage, Alaska 99508, USA.
Abstract:
Deficiencies in DNA mismatch repair (MMR) have been found in hereditary colon cancers (hereditary non-polyposis colon cancer, HNPCC) as well as in sporadic cancers, illustrating the importance of MMR in maintaining genomic integrity. We have examined the interactions of specific mismatch repair proteins in human nuclear extracts. Western blot and co-immunoprecipitation studies indicate two complexes as follows: one consisting of hMSH2, hMSH6, hMLH1, and hPMS2 and the other consisting of hMSH2, hMSH6, hMLH1, and hPMS1. These interactions occur without the addition of ATP. Furthermore, the protein complexes specifically bind to mismatched DNA and not to a similar homoduplex oligonucleotide. The protein complex-DNA interactions occur primarily through hMSH6, although hMSH2 can also become cross-linked to the mismatched substrate when not participating in the MMR protein complex. In the presence of ATP the binding of hMSH6 to mismatched DNA is decreased. In addition, hMLH1, hPMS2, and hPMS1 no longer interact with each other or with the hMutSalpha complex (hMSH2 and hMSH6). However, the ability of hMLH1 to co-immunoprecipitate mismatched DNA increases in the presence of ATP. This interaction is dependent on the presence of the mismatch and does not appear to involve a direct binding of hMLH1 to the DNA.
Insights
DNA mismatch repair (MMR) protein complexes are crucial for genomic integrity. This study identifies two key MMR complexes and reveals their ATP-dependent DNA binding dynamics, offering insights into cancer prevention.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- Deficiencies in DNA mismatch repair (MMR) are implicated in hereditary non-polyposis colon cancer (HNPCC) and sporadic cancers.
- MMR is essential for maintaining genomic integrity.
- Understanding MMR protein interactions is key to comprehending its role in cancer.
Purpose of the Study:
- To investigate the interactions of specific DNA mismatch repair proteins in human nuclear extracts.
- To characterize the composition and DNA-binding properties of MMR protein complexes.
- To elucidate the role of ATP in MMR protein complex formation and function.
Main Methods:
- Western blot analysis to identify protein components.
- Co-immunoprecipitation studies to determine protein interactions.
- DNA binding assays using mismatched and homoduplex oligonucleotides.
Main Results:
- Two distinct MMR protein complexes were identified: [hMSH2, hMSH6, hMLH1, hPMS2] and [hMSH2, hMSH6, hMLH1, hPMS1].
- These complexes bind specifically to mismatched DNA, primarily via hMSH6.
- ATP affects complex dynamics: decreasing hMSH6 binding but increasing hMLH1's interaction with mismatched DNA.
Conclusions:
- The study elucidates the composition of key human MMR protein complexes.
- ATP plays a critical regulatory role in the DNA binding and interaction dynamics of MMR proteins.
- These findings contribute to understanding MMR's role in preventing genomic instability and cancer.
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