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Increasing cAMP antagonizes hypertrophic response to angiotensin II without affecting Ras and MAP kinase activation
T Takahashi1, Y Kawahara, M Okuda
1Department of Internal Medicine (1st Division), Kobe University School of Medicine, Japan.
Abstract:
Angiotensin II (Ang II), a potent hypertrophic factor for vascular smooth muscle cells (VSMC), induces activation of the ras proto-oncogene product (Ras) and mitogen-activated protein (MAP) kinases, and tyrosine phosphorylation of a focal adhesion-associated protein, paxillin. Forskolin, a direct activator of adenylate cyclase, and dibutyryl cAMP (Bt2 cAMP), a membrane permeable cAMP analogue, potently inhibited Ang II-stimulated protein synthesis. However, they did not inhibit Ang II-induced activation of Ras and MAP kinases. Although both forskolin and Bt2 cAMP potently reduced background tyrosine phosphorylation of paxillin, they allowed Ang II to induce the same reaction. These results indicate that increasing cAMP antagonizes the hypertrophic response to Ang II without affecting Ras and MAP kinase activation in VSMC and suggest that it does not interrupt signaling from the Ang II receptor to focal adhesions.
Insights
Increasing cyclic AMP (cAMP) inhibits Angiotensin II (Ang II)-induced vascular smooth muscle cell (VSMC) hypertrophy. This effect occurs without altering Ras and MAP kinase activation, suggesting a downstream inhibitory mechanism.
Area of Science:
- Molecular Biology
- Cell Signaling
- Cardiovascular Research
Background:
- Angiotensin II (Ang II) is a key hypertrophic factor for vascular smooth muscle cells (VSMC).
- Ang II signaling involves activation of Ras, MAP kinases, and paxillin tyrosine phosphorylation.
- Understanding VSMC hypertrophy regulation is crucial for cardiovascular disease management.
Purpose of the Study:
- To investigate the effect of increased cyclic AMP (cAMP) on Ang II-induced VSMC hypertrophy.
- To determine if cAMP modulates Ang II-stimulated Ras and MAP kinase activation.
- To examine the impact of cAMP on Ang II-induced paxillin tyrosine phosphorylation.
Main Methods:
- VSMC cultures were treated with Ang II alone or in combination with forskolin or dibutyryl cAMP (Bt2 cAMP).
- Protein synthesis was measured to assess hypertrophy.
- Activation of Ras, MAP kinases, and tyrosine phosphorylation of paxillin were analyzed.
Main Results:
- Forskolin and Bt2 cAMP potently inhibited Ang II-stimulated protein synthesis in VSMC.
- These cAMP-elevating agents did not inhibit Ang II-induced activation of Ras and MAP kinases.
- While reducing basal paxillin phosphorylation, forskolin and Bt2 cAMP did not block Ang II-induced paxillin tyrosine phosphorylation.
Conclusions:
- Elevated cAMP antagonizes Ang II-induced VSMC hypertrophy.
- The inhibitory effect of cAMP is independent of Ras and MAP kinase activation.
- cAMP likely interferes with Ang II signaling downstream of the receptor and upstream of focal adhesions.