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DNA amplification is rare in normal human cells
J A Wright1, H S Smith, F M Watt
1Imperial Cancer Research Fund Laboratories, London, United Kingdom.
Abstract:
Three types of normal human cells were selected in tissue culture with three drugs without observing a single amplification event from a total of 5 x 10(8) cells. No drug-resistant colonies were observed when normal foreskin keratinocytes were selected with N-(phosphonacetyl)-L-aspartate or with hydroxyurea or when normal mammary epithelial cells were selected with methotrexate. Some slightly resistant colonies with limited potential for growth were obtained when normal diploid fibroblast cells derived from fetal lung were selected with methotrexate or hydroxyurea but careful copy-number analysis of the dihydrofolate reductase and ribonucleotide reductase genes revealed no evidence of amplification. The rarity of DNA amplification in normal human cells contrasts strongly with the situation in tumors and in established cell lines, where amplification of oncogenes and of genes mediating drug resistance is frequent. The results suggest that tumors and cell lines have acquired the abnormal ability to amplify DNA with high frequency.
Insights
DNA amplification is rare in normal human cells, unlike in tumors and cell lines. This study found no amplification events in over 500 million normal cells treated with drugs, suggesting acquired amplification ability in cancer cells.
Area of Science:
- Cell Biology
- Genetics
- Cancer Research
Background:
- DNA amplification is a common genetic alteration in cancer cells, often conferring drug resistance or promoting oncogene activation.
- Understanding the frequency of DNA amplification in normal cells is crucial for distinguishing between normal cellular processes and cancer-related genetic instability.
Purpose of the Study:
- To investigate the frequency of DNA amplification in normal human cells under drug selection pressure.
- To compare the propensity for DNA amplification in normal cells versus established tumor cell lines and tumors.
Main Methods:
- Normal human cells (keratinocytes, mammary epithelial cells, fibroblasts) were cultured and exposed to specific drugs (N-(phosphonacetyl)-L-aspartate, hydroxyurea, methotrexate).
- Drug-resistant colonies were screened for DNA amplification events.
- Copy-number analysis was performed on key genes (dihydrofolate reductase, ribonucleotide reductase) in any observed resistant colonies.
Main Results:
- No DNA amplification events were observed in 5 x 10^8 normal human cells across three cell types and three drug treatments.
- Slightly resistant colonies in fibroblasts showed no evidence of gene amplification upon detailed analysis.
- A stark contrast exists between the rarity of amplification in normal cells and its frequency in tumors and cell lines.
Conclusions:
- Normal human cells exhibit a very low frequency of DNA amplification, even under selective drug pressure.
- Tumors and established cell lines appear to have acquired an enhanced capacity for DNA amplification.
- This acquired ability for high-frequency DNA amplification may be a critical step in tumorigenesis and cancer progression.