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Cyclic AMP: a mitogenic signal for Swiss 3T3 cells
Summary
Cholera toxin stimulates DNA synthesis in Swiss 3T3 cells by increasing cyclic AMP (cAMP) levels. This finding suggests cAMP acts as a mitogenic signal, challenging the view that it inhibits fibroblast proliferation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Fibroblast proliferation is crucial for tissue repair and development.
- The role of cyclic AMP (cAMP) in fibroblast proliferation has been debated, with some evidence suggesting inhibition.
Purpose of the Study:
- To investigate the effect of cholera toxin on DNA synthesis in Swiss 3T3 cells.
- To determine the role of cyclic AMP (cAMP) as a potential mitogenic signal in fibroblast proliferation.
Main Methods:
- Quiescent Swiss 3T3 cells were treated with cholera toxin and various growth factors.
- Levels of DNA synthesis were measured by [3H]thymidine incorporation.
- Intracellular cyclic AMP (cAMP) levels were quantified.
- Inhibitors of cyclic nucleotide phosphodiesterase were used to modulate cAMP levels.
Main Results:
- Cholera toxin synergistically stimulated DNA synthesis with serum, insulin, and growth factors.
- Cholera toxin and phosphodiesterase inhibitors increased intracellular cAMP levels.
- A strong correlation was observed between increased cAMP levels and stimulated DNA synthesis.
- DNA synthesis was initiated after a lag period following treatment with cholera toxin and insulin, or cholera toxin, insulin, and a phosphodiesterase inhibitor.
Conclusions:
- Cyclic AMP (cAMP) acts as a mitogenic signal for Swiss 3T3 cells.
- This finding contradicts the established notion that cAMP inhibits fibroblast proliferation.
- Cholera toxin's ability to induce DNA synthesis highlights a novel signaling pathway involving cAMP.