XB-ART-39625Gene August 1, 2009; 442 (1-2): 99-107.
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Activation of antioxidant defense during dehydration stress in the African clawed frog.
The glutathione S-transferase (GST) and aldo-keto reductase (AKR) families of proteins are major groups of detoxifying enzymes that are known to be regulated by the NF-E2 related factor 2 (Nrf2) transcription factor via the antioxidant response element that is present in the promoter regions of GST and AKR genes. Expression of Nrf2, GST and AKR proteins was analyzed in the African clawed frog, Xenopus laevis, focusing on their responses to dehydration stress. Dehydration/rehydration cycles can generate oxidative stress and this could be ameliorated by enhancing antioxidant defenses. Dehydration to 28% of total body water lost triggered organ-specific changes in nrf2 mRNA expression (a 2-fold increase in liver), total Nrf2 protein (2-4-fold elevation in lung, heart, skin and liver), and a 4.3-fold increase in the content of Nrf2 in the nucleus in muscle. Protein levels of six GST and three AKR family members were assessed and showed organ-specific patterns of expression during dehydration. In particular, GSTP1 was strongly induced in liver, heart and skin, levels rising by 9-, 2.6- and 1.7-fold, respectively, whereas GSTM1 and M3 rose in skeletal muscle, kidney and skin. Selective expression of GSTK1, A3 and T1 also occurred. Dehydration also stimulated organ-specific increases in the levels of AKR family members (AKR1B4, AKR1A3, AFAR1) by 1.5-2-fold. The results show that metabolic responses to dehydration include activation of the Nrf2 transcription factor and selective up-regulation of genes under Nrf2 control.
PubMed ID: 19379800
Article link: Gene
Species referenced: Xenopus laevis
Genes referenced: akr1a1 akr1b1 gabpa gstk1 gstm1 gstp1
Article Images: [+] show captions
|Fig. 1. Effect of dehydration on X. laevis Nrf2. (A) Representative western blots show Nrf2 protein expression under control (C) and dehydrated (D) conditions in four tissues with two independent samples shown per tissue. Histogram shows normalized protein levels in six tissues. (B) Representative bands on agarose gels show PCR product levels of amplified nrf2 and α-tubulin for two preparations from liver. Histogram shows normalized nrf2 mRNA levels in the muscle and liver. (C) Representative western blots show levels of Nrf2 protein in nuclear extracts. Histogram shows relative protein distribution of Nrf2 in nuclear extracts of muscle and liver from control versus dehydrated frogs. Data in histograms are means ± S.E.M., n = 3–5 independent trials on tissue from different animals. ★Significantly different from the corresponding control, P < 0.05.|
|Fig. 2. Effect of dehydration on the expression of GST pi and mu family members in six tissues of X. laevis: (A) GSTP1, (B) GSTM1, (C) GSTM3. In all panels, representative bands show western blots of protein levels in tissues from control (C) and dehydrated (D) conditions; bands for two independent samples are shown per tissue. Histograms show normalized protein levels for control versus dehydrated conditions; data are means ± S.E.M., n = 3–5 independent trials on tissue from different animals. ★Significantly different from the corresponding control, P < 0.05.|
|Fig. 3. Effect of dehydration on the expression of GST kappa, alpha and theta family members in tissues of X. laevis: (A) GSK1, (B) GSTA3, (C) GSTT1. Other information as in Fig. 2.|
|Fig. 4. Effect of dehydration on the expression of AKR family members in X. laevis: (A) AFAR1, (B) AKR1B4, (C) AKR1A3. Other information as in Fig. 2.|