Transcriptional regulation of antioxidant enzymes by FoxO1 under dehydration stress.

Antioxidant defenses are an important part of adaptation to environmental stress for many organisms. This study analyzed responses to dehydration stress by manganese-dependent superoxide dismutase (MnSOD) and catalase, and the role of forkhead box class O type 1 (FoxO1) transcription factor in regulating their up-regulation, in selected tissues of the African clawed frogs, Xenopus laevis. Protein and mRNA levels of MnSOD and catalase were analyzed by immunoblotting and PCR. Analysis of FoxO1 included protein and phosphoprotein (FoxO1(ser245)) levels, nuclear versus cytoplasmic distribution, and FoxO1 binding to DNA. MnSOD protein increased significantly in the liver during dehydration whereas catalase rose in the liver and skeletal muscle. This was supported in liver by 1.5-2.2 fold increases in MnSOD and catalase mRNA levels. FoxO1 transcriptional activity was enhanced in liver of dehydrated versus control frogs as evidenced by: (a) 1.8-fold increase in FoxO1 protein in the nucleus, (b) strong decreases in inactive phosphorylated FoxO1(ser245) in total and nuclear extracts, and (c) a 57% increase in FoxO1 binding to DNA in nuclear extracts. The study documents up-regulation of MnSOD and catalase in frog organs during dehydration and indicates a role for FoxO1 in controlling expression of these genes in liver. Dehydration-rehydration has components of an ischemia-reperfusion event and the oxidative stress that this generates appears to be effectively addressed, at least in X. laevis liver, by enhanced production of antioxidant enzymes under FoxO1 regulation.