Molecular cloning and oxidative stress response of a sigma-class glutathione S-transferase of the bumblebee Bombus ignitus

Glutathione S-transferases (EC 2.5.1.18; GSTs) are multifunctional enzymes that are mainly involved in xenobiotic metabolism and protection against oxidative damage. Most studies of GSTs in insects have been focused on their role in detoxifying exogenous compounds in particular insecticides. Here, we show the expression profiles of GSTs of the bumblebee Bombus ignitus in response to oxidative stress. We identified a sigma-class GST from B. ignitus (BiGSTS). The BiGSTS gene consists of 4 exons that encode 201 amino acids. Comparative analysis indicates that the predicted amino acid sequence of BiGSTS shares a high identity with the sigma-class GSTs of hymenopteran insects such as Apis mellifera (70% protein sequence identity) and Solenopsis invicta (59% protein sequence identity). Tissue distribution analyses showed the presence of BiGSTS in all tissues examined, including the fat body, midgut, muscle and epidermis. The oxidative stress responses analyzed by quantitative real-time PCR showed that under H2O2 overload, BiGSTS and BiGSTD (identified in our previous study) were upregulated in all tissues examined, including the fat body and midgut of B. ignitus worker bees. Under uniform conditions of H2O2 overload, the expression profile of GSTs and other antioxidant enzyme genes, such as phospholipid-hydroperoxide glutathione peroxidase (Bi-PHGPx) and peroxiredoxins (BiPrx1 and BiTPx1), showed that other antioxidant enzyme genes are acutely induced at 3 h after H2O2 exposure, whereas BiGSTS and BiGSTD are highly induced at 9 h after H2O2 exposure in the fat body of B. ignitus worker bees. These findings indicate that GSTs and other antioxidant enzyme genes in B. ignitus are differentially expressed in response to oxidative stress. Taken together, our findings indicate that BiGSTS and BiGSTD are oxidative stress-inducible antioxidant enzymes that may play a role in oxidative stress response.