| Summary: | Peroxiredoxins are a family of antioxidant proteins that protect cells from oxidative damage caused by reactive oxygen species (ROS). Herein, the peroxiredoxin 3 gene from grass carp (<i>Ctenopharyngodon idellus</i>), named <i>CiPrx3</i>, was cloned and analyzed. The full-length cDNA of <i>CiPrx3</i> is 1068 bp long, with a 753 bp open reading frame (ORF) that contains a thioredoxin-2 domain, two peroxiredoxin signature motifs, and two highly conserved cysteine residues. <i>CiPrx3</i> was ubiquitously expressed in all the tested tissues, while its expression level was altered significantly after exposure to grass carp reovirus (GCRV) and pathogen-associated molecular patterns (PAMPs). <i>CiPrx3</i> was localized in the mitochondria of transfected cells and concentrated in the nucleus after poly (I:C) treatment. Transformation of <i>CiPrx3</i> into <i>Escherichia coli</i> enhanced host resistance to H<sub>2</sub>O<sub>2</sub> and heavy metals. Purified recombinant <i>CiPrx3</i> proteins could protect DNA against oxidative damage. Overexpression of <i>CiPrx3</i> in fish cells reduced intracellular ROS, increased cell viability, and decreased cell apoptosis caused by H<sub>2</sub>O<sub>2</sub> stimulation and GCRV infection. Further study indicated that <i>CiPrx3</i> induced autophagy to inhibit GCRV replication in fish cells. Collectively, these results imply that grass carp Prx3 elevates host antioxidant activity and induces autophagy to inhibit GCRV replication.
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