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alpha-Tocopherol specifically inactivates cellular protein kinase C alpha by changing its phosphorylation state
R Ricciarelli1, A Tasinato, S Clément
1Department of Experimental Medicine, University of Genoa, Via LB Alberti 2, Genoa, Italy.
The Biochemical Journal
|August 7, 1998
Summary
Alpha-tocopherol inhibits protein kinase C (PKC) in smooth muscle cells by dephosphorylating the PKCalpha isoform. This inhibition is mediated by activating protein phosphatase type 2A, not direct enzyme interaction.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Protein kinase C (PKC) plays a crucial role in cellular signaling pathways.
- Alpha-tocopherol, a form of Vitamin E, is known for its antioxidant properties.
- Understanding the regulatory mechanisms of PKC is vital for various physiological processes.
Purpose of the Study:
- To investigate the mechanism by which alpha-tocopherol regulates protein kinase C (PKC) in smooth muscle cells.
- To identify the specific PKC isoforms affected by alpha-tocopherol treatment.
- To elucidate the molecular pathways involved in alpha-tocopherol-induced PKC inhibition.
Main Methods:
- Treatment of rat aortic A7r5 smooth muscle cells with varying concentrations and durations of alpha-tocopherol.
- Western blot analysis to detect PKC isoform expression.
- Assays for autophosphorylation and kinase activity of different PKC isoforms.
- In vitro studies to assess the effect of alpha-tocopherol on protein phosphatase type 2A (PP2A) activity.
Main Results:
- Alpha-tocopherol caused a time- and dose-dependent inhibition of total PKC activity.
- Only the PKCalpha isoform was found to be inhibited by alpha-tocopherol; other isoforms (beta, delta, epsilon, zeta, micro) were unaffected.
- The inhibition of PKCalpha was associated with its dephosphorylation.
- Alpha-tocopherol activated protein phosphatase type 2A (PP2A) in vitro.
- Beta-tocopherol, an antioxidant analogue, did not mimic the inhibitory effects of alpha-tocopherol on PKCalpha.
Conclusions:
- Alpha-tocopherol inhibits PKCalpha activity in smooth muscle cells through a mechanism involving dephosphorylation.
- The activation of protein phosphatase type 2A (PP2A) by alpha-tocopherol is likely responsible for the dephosphorylation and subsequent inhibition of PKCalpha.
- This study reveals a novel regulatory pathway for PKCalpha by alpha-tocopherol, independent of direct enzyme interaction or expression changes.