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The human MLH1 cDNA complements DNA mismatch repair defects in Mlh1-deficient mouse embryonic fibroblasts
A B Buermeyer1, C Wilson-Van Patten, S M Baker
1Department of Molecular and Medical Genetics, Oregon Health Sciences University, Portland 97201-3098, USA.
Abstract:
The DNA mismatch repair gene hMLH1 is reported to function in mutation avoidance, cell cycle checkpoint control, the cytotoxicity of various DNA-damaging agents, and transcription-coupled nucleotide excision repair. Formal proof of the involvement of hMLH1 in these processes requires single gene complementation. We have stably expressed hMLH1 from a transfected cDNA in Mlh1-deficient mouse embryonic fibroblasts. Expression of hMLH1 restored normal levels of mPMS2 protein, reduced spontaneous base substitution and microsatellite mutations, increased sensitivity to the toxic effects of 6-thioguanine (6-TG), and restored 6-TG-induced cell cycle arrest. Our studies confirm that hMLH1 has an essential role in the maintenance of genomic stability and the potentiation of 6-TG cytotoxicity and provide a system for detailed structure/function analysis of the hMLH1 protein.
Insights
The human MutL homolog 1 (hMLH1) gene is crucial for genomic stability and DNA repair. Restoring hMLH1 in deficient cells reduced mutations and enhanced sensitivity to 6-thioguanine (6-TG).
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- The DNA mismatch repair gene hMLH1 plays roles in mutation avoidance, cell cycle control, and DNA repair.
- Formal validation of hMLH1's functions necessitates single gene complementation studies.
Purpose of the Study:
- To investigate the role of hMLH1 in maintaining genomic stability.
- To confirm hMLH1's involvement in potentiating the cytotoxicity of 6-thioguanine (6-TG).
- To establish a system for structure/function analysis of hMLH1.
Main Methods:
- Stable expression of hMLH1 via transfected cDNA in Mlh1-deficient mouse embryonic fibroblasts.
- Assessment of mPMS2 protein levels.
- Quantification of spontaneous base substitution and microsatellite mutations.
- Evaluation of sensitivity to 6-thioguanine (6-TG) and 6-TG-induced cell cycle arrest.
Main Results:
- hMLH1 expression restored normal mPMS2 protein levels.
- Spontaneous mutations (base substitution and microsatellite) were reduced.
- Sensitivity to 6-thioguanine (6-TG) cytotoxicity was increased.
- 6-TG-induced cell cycle arrest was restored.
Conclusions:
- hMLH1 is essential for maintaining genomic stability.
- hMLH1 potentiates the cytotoxic effects of 6-thioguanine.
- The study provides a model for detailed hMLH1 structure/function analysis.