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Transforming growth factor-beta 1 modulates adenylyl cyclase signaling elements and epidermal growth factor signaling
1Department of Pharmacology, University of Tennessee, Memphis 38163, USA.
Abstract:
Studies presented in this report were designed to investigate the effects of transforming growth factor-beta 1 (TGF-beta 1) on epidermal growth factor (EGF)-mediated stimulation of cAMP accumulation in cardiac myocytes and elucidate the mechanism(s) involved in this modulation. TGF-beta 1 (20 pM) treatment of cardiac myocytes, in a time-dependent manner, decreased the ability of EGF (100 nM) to increase cAMP accumulation. Significant attenuation of EGF-elicited cAMP accumulation was observed 2 h after exposure to TGF-beta 1 and 18 h after addition of TGF-beta 1, the ability of EGF to increase cAMP accumulation was completely obliterated. TGF-beta 1 neither decreased immunoprecipitable EGF receptors in membranes from cardiomyocytes nor altered the specific binding of [125I]EGF to cardiomyocyte membranes. However, TGF-beta 1 decreased the ability of EGF to phosphorylate membrane proteins on tyrosine residues. TGF-beta 1 treatment of cardiomyocytes also decreased the ability of forskolin to augment cAMP accumulation in intact cells and stimulate adenylyl cyclase activity. Similarly, in membranes of TGF-beta 1-treated cells, neither isoproterenol nor EGF stimulated adenylyl cyclase activity. Interestingly, as assessed by the ability of A1F4- to stimulate adenylyl cyclase, TGF-beta 1 did not alter the coupling between Gs and catalytic subunits. Likewise, TGF-beta 1 did not alter the functional activity of the inhibitory regulatory element of the system, Gi. Western analysis of cellular proteins revealed that TGF-beta 1 did not alter the amounts of Ga alpha, Gi alpha 2, and Gi alpha 3. We conclude that TGF-beta 1 attenuates EGF-elicited cAMP accumulation in cardiomyocytes, in part, by decreasing the EGF receptor kinase function and that TGF-beta 1-mediated alterations in the activity of adenylyl cyclase catalytic subunit also contribute toward the regulation of adenylyl cyclase by various agonists.
Insights
Transforming growth factor-beta 1 (TGF-beta 1) inhibits epidermal growth factor (EGF)-induced cAMP in cardiac cells. This occurs via reduced EGF receptor kinase activity and altered adenylyl cyclase function.
Area of Science:
- Cardiovascular Biology
- Cell Signaling
- Molecular Endocrinology
Background:
- Epidermal growth factor (EGF) stimulates cAMP accumulation in cardiac myocytes, a process crucial for cellular function.
- Transforming growth factor-beta 1 (TGF-beta 1) is known to modulate various cellular processes, but its specific effects on EGF signaling in cardiomyocytes require elucidation.
Purpose of the Study:
- To investigate the impact of TGF-beta 1 on EGF-mediated cAMP stimulation in cardiac myocytes.
- To elucidate the underlying molecular mechanisms by which TGF-beta 1 modulates this signaling pathway.
Main Methods:
- Cardiac myocytes were treated with TGF-beta 1 and EGF.
- Measurements included cAMP accumulation, EGF receptor binding and phosphorylation, adenylyl cyclase activity, and Western blot analysis of regulatory proteins.
Main Results:
- TGF-beta 1 significantly attenuated EGF-induced cAMP accumulation in a time-dependent manner.
- TGF-beta 1 reduced EGF receptor phosphorylation but did not affect EGF receptor expression or binding.
- TGF-beta 1 impaired adenylyl cyclase activity stimulated by various agonists, independent of Gs or Gi protein function.
Conclusions:
- TGF-beta 1 attenuates EGF-elicited cAMP accumulation in cardiomyocytes.
- This attenuation is mediated by decreased EGF receptor kinase function and alterations in adenylyl cyclase catalytic subunit activity.