Clonally derived cell lines with altered DNA methylation as models for error correction and mutation in tumours
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1Molecular Science Group, Peter MacCallum Cancer Institute, Melbourne, Victoria, Australia.
Abstract:
We have investigated the relative importance of DNA methylation-directed repair of replication errors to the production of mutation/gene rearrangements in mammalian cells with hypomethylated genomes. Using a series of sibling (Chinese hamster derived) cell clones with stably altered DNA methylation levels, we found that genomic hypomethylation was frequently associated with an elevated spontaneous mutation rate in the hypoxanthine phosphoribosyl transferase (HPRT) gene and with increased sensitivity to 2-aminopurine, a known inducer of DNA base mismatches. However, while there are some alterations in sites of DNA methylation around the HPRT gene, there was no systematic direction of change to differentiate between cells with normal or with elevated mutation rates. Further, the nature of gene alterations giving rise to the HPRT mutations suggested that methylation-directed mismatch repair is of little if any significance in influencing error avoidance in mammalian cells with hypomethylated genomes and that increased mutation associated with DNA hypomethylation is more likely to be due to increased genomic instability through activation of such factors as transposable elements.
Insights
Genomic hypomethylation increases mutation rates in mammalian cells, but DNA methylation-directed repair is not the primary cause. Increased genomic instability, possibly from transposable elements, is more likely responsible for DNA hypomethylation-induced mutations.
Area of Science:
- Molecular Biology
- Genetics
- Epigenetics
Background:
- DNA methylation plays a crucial role in maintaining genome stability and regulating gene expression in mammalian cells.
- Hypomethylation, a reduction in DNA methylation, is linked to genomic instability and increased mutation rates.
- The role of DNA methylation-directed mismatch repair in error avoidance in hypomethylated genomes remains unclear.
Purpose of the Study:
- To investigate the significance of DNA methylation-directed repair in producing mutations and gene rearrangements in mammalian cells with hypomethylated genomes.
- To determine if genomic hypomethylation directly influences mutation rates and sensitivity to mutagens.
- To explore the mechanisms underlying increased mutation rates in hypomethylated cells.
Main Methods:
- Utilized sibling cell clones (Chinese hamster derived) with stably altered DNA methylation levels.
- Assessed spontaneous mutation rates in the hypoxanthine phosphoribosyl transferase (HPRT) gene.
- Evaluated sensitivity to 2-aminopurine, a DNA base mismatch inducer.
- Analyzed DNA methylation patterns around the HPRT gene and characterized gene alterations.
Main Results:
- Genomic hypomethylation correlated with elevated spontaneous mutation rates at the HPRT gene.
- Hypomethylated cells showed increased sensitivity to 2-aminopurine.
- Alterations in DNA methylation sites around the HPRT gene did not systematically differentiate mutation rates.
- The nature of HPRT gene alterations suggested limited significance of methylation-directed mismatch repair.
Conclusions:
- Methylation-directed mismatch repair appears to have minimal impact on error avoidance in mammalian cells with hypomethylated genomes.
- Increased mutation rates associated with DNA hypomethylation are more likely attributed to heightened genomic instability.
- Activation of factors such as transposable elements may contribute to increased mutation in hypomethylated genomes.