Abstract
Lepidopteran insect cells display 50–100 times higher radioresistance compared to human cells, and reportedly have more efficient antioxidant system that can significantly reduce radiation-induced oxidative stress and cell death. However, the antioxidant mechanisms that contribute substantially to this excessive resistance still need to be understood thoroughly. In this study, we investigated the role of thioredoxin peroxidase (TPx) in high-dose γ-radiation response of Sf9 cell line derived from Spodoptera frugiperda, the Fall armyworm. We identified a TPx orthologue (Sf-TPx) in Spodoptera system, with primarily cytosolic localization. Gamma-irradiation at 500 Gy dose significantly up-regulated Sf-TPx, while higher doses (1000 Gy–2000 Gy) had no such effect. G2/M checkpoint induced following 500 Gy was associated with transition of Sf-TPx decamer into enzymatically active dimer. Same effect was observed during G2/M block induced by 5 nM okadaic acid or 10 µM CDK1 (cycline dependent kinase-1) inhibitor roscovitine, thus indicating that radiation-induced Sf-TPx activity is mediated by CDKs. Accumulation of TPx dimer form during G2/M checkpoint might favour higher peroxidase activity facilitating efficient survival at this dose. Confirming this, higher lethal doses (1000 Gy–2000 Gy) caused significantly less accumulation of dimer form and induced dose-dependent apoptosis. A ∼50% knock-down of Sf-TPx by siRNA caused remarkable increase in radiation-induced ROS as well as caspase-3 dependent radiation-induced apoptosis, clearly implying TPx role in the radioresistance of Sf9 cells. Quite importantly, our study demonstrates for the first time that thioredoxin peroxidase contributes significantly in the radioresistance of Lepidopteran Sf9 insect cells, especially in their exemplary resistance against radiation-induced apoptosis. This is an important insight into the antioxidant mechanisms existing in this highly stress-resistant model cell system.
Highlights
Lepidopteran insects/insect cells, especially the moths and cell lines derived from moths, are considered an excellent higher eukaryotic model system for their excessive radioresistance amounting up to 100 times higher than human/mammalian cells [1]
The antioxidant role of peroxidases such as thioredoxin peroxidase (TPx) or peroxiredoxin (Prx) has been known to be quite important since these enzymes offer the first line of defence in the event of oxidative insult by the reactive oxygen species
Since TPx-mediated oxidative stress response has potentially important role in cellular radioresistance, the present study was conducted to study the nature of TPx and its role in the radioresistance of Sf9 insect cells derived from Spodoptera frugiperda, the Fall armyworm
Summary
Lepidopteran insects/insect cells, especially the moths and cell lines derived from moths, are considered an excellent higher eukaryotic model system for their excessive radioresistance amounting up to 100 times higher than human/mammalian cells [1]. Such an exemplary level of radioresistance has been attributed to a variety of factors (summarized in [2]) including lower level of radiation-induced DNA damage, efficient DNA repair, as well as an unusually reduced level of radiation-induced apoptosis [1,3]. Since TPx-mediated oxidative stress response has potentially important role in cellular radioresistance, the present study was conducted to study the nature of TPx and its role in the radioresistance of Sf9 insect cells derived from Spodoptera frugiperda, the Fall armyworm (class Insecta; order Lepidoptera)
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