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The mammalian heme oxygenase (HO) plays an important role in cytoprotection against oxidative-stress-induced cell damage; however, functional characterization of insect HO is still limited. In this study, cDNA encoding a HO, named Sf HO, was cloned from Spodoptera frugiperda. Analysis of the transcription level and enzymatic activity showed that exposure of the LC 30 concentration of chlorantraniliprole to the third instar larvae significantly upregulated both the mRNA level and enzymatic activity of Sf HO at 24 h after treatment. Further injection of the HO activator, hemin, into the third instar larvae led to the upregulation of Sf HO as well as decreased susceptibility of S. frugiperda to chlorantraniliprole. Consistently, overexpression of Sf HO increased the Sf9 cell viability under chlorantraniliprole treatment. Strikingly, both RNAi and the dual-luciferase reporter assay in Sf9 cells revealed that, unlike mammalian HO that is regulated by the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), Sf HO was not subject to the regulation by cap 'n' collar isoform C (CncC), the Nrf2 homologue in insects. These data provide insights into the function and regulatory mechanism of insect HOs and had applied implications for the control of S. frugiperda.

The AMP-activated protein kinase (AMPK) has important roles in the regulation of energy metabolism, and AMPK activity and its regulation have been the focus of relevant investigations. However, functional characterization of AMPK is still limited in insects. In this study, the full-length cDNA coding AMPKα (TcAMPKα) was isolated from the red flour beetle, Tribolium castaneum. The TcAMPKα gene contains an ORF of 1581 bp encoding a protein of 526 amino acid residues, which shared conserved domain structure with Drosophila melanogaster and mammalian orthologs. Exposure of female adults to oxidative, heat, and cold stresses caused an increase in TcAMPKα mRNA expression levels and phosphorylation of Thr-173 in the activation loop. The RNAi-mediated knockdown of TcAMPKα resulted in the increased sensitivity of T. castaneum to oxidative, heat, and cold stresses. These results suggest that stress signals regulate TcAMPKα activity, and TcAMPKα plays an important role in enabling protective mechanisms and processes that confer resistance to environmental stress.

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