Article: article from journal or magazin.
alpha-Tocopherol specifically inactivates cellular protein kinase C alpha by changing its phosphorylation state
Journal Article Research Support, Non-U.S. Gov't --- Old month value: Aug 15
The mechanism of protein kinase C (PKC) regulation by alpha-tocopherol has been investigated in smooth-muscle cells. Treatment of rat aortic A7r5 smooth-muscle cells with alpha-tocopherol resulted in a time- and dose-dependent inhibition of PKC. The inhibition was not related to a direct interaction of alpha-tocopherol with the enzyme nor with a diminution of its expression. Western analysis demonstrated the presence of PKCalpha, beta, delta, epsilon, zeta and micro isoforms in these cells. Autophosphorylation and kinase activities of the different isoforms have shown that only PKCalpha was inhibited by alpha-tocopherol. The inhibitory effects were not mimicked by beta-tocopherol, an analogue of alpha-tocopherol with similar antioxidant properties. The inhibition of PKCalpha by alpha-tocopherol has been found to be associated with its dephosphorylation. Moreover the finding of an activation of protein phosphatase type 2A in vitro by alpha-tocopherol suggests that this enzyme might be responsible for the observed dephosphorylation and subsequent deactivation of PKCalpha. It is therefore proposed that PKCalpha inhibition by alpha-tocopherol is linked to the activation of a protein phosphatase, which in turn dephosphorylates PKCalpha and inhibits its activity.
Animals Aorta Cell Line Isoenzymes/*antagonists & inhibitors/metabolism Kinetics Muscle, Smooth, Vascular/*enzymology Phosphoprotein Phosphatase/metabolism Phosphorylation Protein Kinase C/*antagonists & inhibitors/*metabolism Protein Kinase C-alpha Protein Kinase C-delta Protein Kinase C-epsilon Rats Vitamin E/*pharmacology
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