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cAMP abrogates the p21ras-mitogen-activated protein kinase pathway in fibroblasts
P L Hordijk1, I Verlaan, K Jalink
1Division of Cellular Biochemistry, Netherlands Cancer Institute, Amsterdam.
Abstract:
The mechanism by which cAMP inhibits growth factor-induced DNA synthesis in fibroblasts is not understood. Here we show that in Rat-1 fibroblasts, cAMP-raising agents inhibit p21ras-mediated mitogen-activated protein (MAP) kinase activation induced by either epidermal growth factor or lysophosphatidic acid. Under the same conditions, however, epidermal growth factor- or lysophosphatidic acid-induced protein tyrosine phosphorylation, Ca2+ mobilization, and activation of Na+/H+ exchange are not attenuated. In ras-transformed Rat-1 cells, 8-bromo-cAMP rapidly deactivates constitutively active MAP kinase without reducing p21ras.GTP levels; long term 8-bromo-cAMP treatment of these cells leads to growth arrest and reversion of the transformed phenotype. These results show that elevation of intracellular cAMP levels abrogates the p21ras MAP kinase pathway at a step downstream of p21ras activation. This finding provides a molecular basis for the growth-inhibitory action of cAMP in normal and transformed fibroblasts.
Insights
Cyclic adenosine monophosphate (cAMP) inhibits fibroblast growth by blocking the p21ras-mediated mitogen-activated protein (MAP) kinase pathway. This occurs downstream of p21ras activation, offering a molecular explanation for cAMP
Area of Science:
- Cellular Biology
- Molecular Biology
- Cancer Research
Background:
- The precise mechanism by which cyclic adenosine monophosphate (cAMP) inhibits growth factor-induced DNA synthesis in fibroblasts remains unclear.
- Understanding this pathway is crucial for developing targeted therapies for fibroblast-related conditions, including cancer.
Purpose of the Study:
- To elucidate the molecular mechanism through which cAMP inhibits growth factor-induced DNA synthesis in fibroblasts.
- To investigate the effect of cAMP on the p21ras-mediated mitogen-activated protein (MAP) kinase pathway.
Main Methods:
- Utilized Rat-1 fibroblasts and ras-transformed Rat-1 cells.
- Administered cAMP-raising agents (e.g., 8-bromo-cAMP) and growth factors (epidermal growth factor, lysophosphatidic acid).
- Assessed protein tyrosine phosphorylation, Ca2+ mobilization, Na+/H+ exchange activation, p21ras-GTP levels, and MAP kinase activity.
Main Results:
- cAMP-raising agents inhibited p21ras-mediated MAP kinase activation induced by growth factors in Rat-1 fibroblasts.
- Growth factor-induced protein tyrosine phosphorylation, Ca2+ mobilization, and Na+/H+ exchange were not affected by cAMP.
- In ras-transformed cells, 8-bromo-cAMP deactivated MAP kinase without altering p21ras-GTP levels, leading to growth arrest and phenotype reversion.
Conclusions:
- Elevated intracellular cAMP abrogates the p21ras MAP kinase pathway downstream of p21ras activation.
- This study provides a molecular basis for the observed growth-inhibitory effects of cAMP in both normal and transformed fibroblasts.
- Findings suggest cAMP as a potential therapeutic target for modulating fibroblast proliferation.