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Cyclic AMP and cyclic GMP concentrations in serum- and density-restricted fibroblast cultures
Abstract:
Mouse fibroblasts transformed by simian virus 40 (SV3T3 cells) are characterized by cyclic AMP and cyclic GMP levels, respectively, about half and twice those found in growing untransformed 3T3 cells. Density-dependent inhibition of growth is correlated with reduced cyclic GMP concentrations in 3T3 and four different density-restricted revertant lines derived from SV3T3. The levels of cyclic AMP are not increased at confluence. Upon serum restriction, serum-dependent cell lines show a greater increase in intracellular cAMP than serum-insensitive lines. Cyclic GMP levels are greatly reduced, even in serum-insensitive density revertants, but not in SV3T3. Serum readdition to all serum-dependent lines is followed by a rapid decrease in cyclic AMP and increase in cyclic GMP concentrations. The magnitude of these responses is decreased in SV3T3 and density revertants.
Insights
Simian virus 40 (SV40) transformation alters cellular cyclic nucleotide levels. Transformed cells show reduced cyclic GMP, impacting growth regulation and serum response, unlike normal fibroblasts.
Area of Science:
- Cell Biology
- Virology
- Biochemistry
Background:
- Simian virus 40 (SV40) transformation of mouse fibroblasts (SV3T3 cells) significantly alters cellular physiology.
- Cyclic nucleotides, including cyclic AMP (cAMP) and cyclic GMP (cGMP), are critical second messengers involved in regulating cell growth and behavior.
Purpose of the Study:
- To investigate the specific changes in intracellular cAMP and cGMP levels in SV40-transformed mouse fibroblasts compared to untransformed cells.
- To determine the correlation between cyclic nucleotide concentrations and density-dependent growth inhibition.
- To analyze the impact of serum availability on cyclic nucleotide levels in both normal and transformed cells.
Main Methods:
- Measurement of intracellular cyclic AMP and cyclic GMP levels in 3T3 cells and SV3T3 cells under various conditions.
- Comparison of cyclic nucleotide levels in growing cells versus confluent cells.
- Assessment of cyclic nucleotide responses to serum restriction and readdition in different cell lines.
Main Results:
- SV3T3 cells exhibited approximately half the cAMP and twice the cGMP levels of normal 3T3 cells.
- Reduced cGMP concentrations were correlated with density-dependent growth inhibition in 3T3 cells and revertant lines.
- Serum restriction led to greater cAMP increases in serum-dependent cell lines, with altered cAMP and cGMP responses upon serum readdition in SV3T3 and revertant cells.
Conclusions:
- SV40 transformation profoundly affects cellular cyclic nucleotide homeostasis.
- Changes in cGMP levels are linked to the loss of density-dependent growth control in transformed cells.
- Altered cyclic nucleotide dynamics in SV3T3 cells contribute to their altered responses to serum growth factors.