Mutation rate at the hprt locus in human cancer cell lines with specific mismatch repair-gene defects.
Spontaneous mutation rates at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus were measured in human cancer cell lines defective in the mismatch repair (MMR) genes hMLH1, hPMS2, or GTBP, as well as in a cell line carrying mutations in both hMLH1 and hPMS2. The mutation rate was determined by quantitating mutant frequency increases within a single culture as a function of cell division. These MMR-deficient cell lines exhibited a 50- to 750-fold increase in mutation rate relative to a MMR-proficient cancer cell line. From lowest to highest, the spontaneous mutation rates relative to the MMR-gene defects studied here are as follows: hMLH1- < GTBP- < hPMS2- < hMLH1- / hPMS2-. In addition, a cell line in which MMR was restored by chromosome transfer exhibited a mutation rate 12-fold below the MMR-deficient parental cell line. These data support the notion that MMR plays an important role in controlling the rate of spontaneous mutation and suggest that different MMR-gene defects may vary in their ability to repair different types of DNA mismatches, thus leading to measurable quantitative differences in spontaneous mutagenesis. Furthermore, a difference in mutation rates was observed between a hPMS2-defective cell line (3.1 x 10(-5) mutations/cell/generation) and two hMLH1-defective cell lines (4.0 x 10(-6) and 7.3 x 10(-6) mutations/cell/generation). Assuming the hPMS2- and hMLH1-gene products only function in the proposed hMutL alpha heterodimer, then defects in either gene should yield comparable mutation rates. These data suggest that hPMS2 plays a critical role in MMR, while additional hMLH1 homologues or hPMS2 alone may function to partially complement defects in hMLH1.
Glaab
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Curriculum in Toxicology, University of North Carolina, Chapel Hill 27599, USA.
Tindall
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KR
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics*; D008040:Genetic Linkage; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics*; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009154:Mutation / Q000235:genetics*; D009363:Neoplasm Proteins / Q000235:genetics*; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D014407:Tumor Cells, Cultured; D014960:X Chromosome / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D007041:Hypoxanthine Phosphoribosyltransferase; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein