Nonantioxidant functions of alpha-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 recogn ized uniquely; therefore, it may exert an exclusive function. alpha -Tocoph erol possesses distinct properties that are independent of its prooxidant, antioxidant or radical-scavenging ability. alpha -Tocopherol specifically i nhibits 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 -to copherol nor probucol possessed the same specialty functions as alpha -toco pherol. Recently, we isolated a new ubiquitous cytosolic alpha -tocopherol binding protein (TAP). Its motifs suggest that it is a member of the hydrop hobic ligand-binding protein family (CRAL-TRIO). TAP may also be involved i n the regulation of cellular alpha -tocopherol concentration and alpha -toc opherol-mediated signaling.