SIGNALING FUNCTIONS OF ALPHA-TOCOPHEROL IN SMOOTH-MUSCLE CELLS

alpha-Tocopherol but not beta-tocopherol, activates protein phosphatas e 2A, decreases protein kinase C activity and attenuates smooth muscle cell proliferation at physiological concentrations. beta-Tocopherol p revents the effects of alpha-tocopherol. Inhibition of protein kinase C alpha but not of the other isoforms, by the inhibitor Go6976 prevent s the effect of alpha-tocopherol. Protein kinase C alpha, immunoprecip itated from alpha-tocopherol treated cells, is less phosphorylated and inactive. It is proposed that the specific activation of protein phos phatase 2A by alpha-tocopherol results in dephosphorylation and inacti vation of protein kinase C alpha. Finally, this cascade of events lead s to smooth muscle cell proliferation inhibition.