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Decreased methylation rates of DNA in SV40-transformed human fibroblasts
Abstract:
The rates of methylation of total cellular DNA and newly synthesized DNA were measured in four unrelated SV40-transformed human fibroblast lines and in four control parent fibroblast lines. Rates of methylation of total cellular DNA were decreased by a factor of 1.8-2.3 in the transformed cells relative to control cells. Methylation was largely (75%-87%) restricted to newly synthesized DNA in control and transformed fibroblasts, and methylation rates of newly synthesized DNA were diminished in transformed cells by 12- to 19-fold relative to control cells. Growth rates were similar in the normal and transformed cells. The cellular uptake of methionine and conversion to S-adenosylmethionine were similar in the normal and transformed cells, suggesting no major differences between the normal and transformed cells in the cellular transport of methionine, methionine S-adenosyltransferase activity, or the intracellular concentrations of methionine and S-adenosylmethionine. The diminished rates of DNA methylation that we have observed suggest a possible mechanism for altered gene expression and growth control in transformed cells.
Insights
DNA methylation rates are significantly lower in transformed human fibroblasts compared to normal cells. This reduced DNA methylation, particularly in newly synthesized DNA, may impact gene expression and growth control in cancer.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Cellular transformation involves alterations in DNA structure and function.
- DNA methylation plays a crucial role in regulating gene expression and maintaining genomic stability.
- Understanding methylation changes in transformed cells is key to deciphering cancer development.
Purpose of the Study:
- To quantify and compare DNA methylation rates in SV40-transformed human fibroblasts versus normal fibroblasts.
- To investigate the distribution of methylation between total and newly synthesized DNA.
- To explore potential mechanisms underlying altered methylation in transformed cells.
Main Methods:
- Measurement of DNA methylation rates in total and newly synthesized DNA.
- Comparison of methylation kinetics in four transformed and four control human fibroblast lines.
- Assessment of methionine uptake and S-adenosylmethionine conversion to evaluate methylation capacity.
Main Results:
- Total cellular DNA methylation decreased 1.8-2.3 fold in transformed cells.
- Methylation of newly synthesized DNA was significantly reduced (12-19 fold) in transformed cells.
- Methionine metabolism and S-adenosylmethionine levels were comparable between normal and transformed cells.
Conclusions:
- Transformed cells exhibit markedly diminished DNA methylation rates, especially on newly synthesized DNA.
- The observed decrease in DNA methylation suggests a potential mechanism for altered gene expression and aberrant growth control in cancer.
- Differences in methylation, not methionine availability, likely contribute to transformation-associated changes.