α-Tocopherol induces calnexin in renal tubular cells: Another protective mechanism against free radical-induced cellular damage

Pre-administration of α-tocopherol is protective against oxidative renal tubular damage and subsequent carcinogenesis by ferric nitrilotriacetate (Fe-NTA) in rats. We searched for mechanisms other than the scavenging effect of α-tocopherol with microarray analyses, which implicated calnexin, a chaperone for glycoproteins. Renal mRNA levels of calnexin significantly increased 3 h after an injection of Fe-NTA in rats fed a standard diet whereas those fed an α-tocopherol-supplemented diet showed an increase prior to injection, but after injection showed a decrease in renal calnexin mRNA levels, with unaltered protein levels. In experiments using LLC-PK1 cells, addition of α-tocopherol was protective against oxidative stress by H2O2, concomitant with calnexin induction. Knockdown of calnexin by siRNA significantly reduced this protection. Furthermore, COS-7 cells transfected with the calnexin gene were more resistant to H2O2. Together with the fact that α-tocopherol induced N-acetylglucosaminyltransferase 3, our data suggest that α-tocopherol modifies glycoprotein metabolism partially by conferring mild ER stress. This adds another molecular mechanism of α-tocopherol toward cancer prevention.