Nonantioxidant functions of α-tocopherol in smooth muscle cells

Most tocopherols and tocotrienols, with the exception of alpha -tocopherol, are not retained by humans. This suggests that alpha -tocopherol is recognized uniquely; therefore, it may exert an exclusive function. alpha -Tocopherol possesses distinct properties that are independent of its prooxidant, antioxidant or radical-scavenging ability. alpha -Tocopherol specifically inhibits protein kinase C, the growth of certain cells and the transcription of the CD36 acid collagenase genes. Activation events have also been seen on the protein phosphatase 2A (PP(2)A) and on the expression of other genes (alpha -tropomyosin and connective tissue growth factor). Neither beta -tocopherol nor probucol possessed the same specialty functions as alpha -tocopherol. Recently, we isolated a new ubiquitous cytosolic alpha -tocopherol binding protein (TAP). Its motifs suggest that it is a member of the hydrophobic ligand-binding protein family (CRAL-TRIO). TAP may also be involved in the regulation of cellular alpha -tocopherol concentration and alpha -tocopherol-mediated signaling.