Role of nitric oxide synthase in insect cell radioresistance: an in-silico analysis

Comparative Proteomics Analysis Between the Short-Term Stress and Long-Term Adaptation of the Blattella germanica (Blattodea: Blattellidae) in Response to Beta-Cypermethrin

A proteomic method combining two-dimensional polyacrylamide gel electrophoresis and tandem mass spectrometry was used to compare the hemolymph expression profiles of a beta-cypermethrin-resistant Blattella germanica L. strain (R) and a susceptible strain (S) after 24 h of beta-cypermethrin induction. The results showed that there were 42 differentially expressed proteins after induction of the R strain: 4 proteins were upregulated and 38 proteins were downregulated. One hundred one hemolymph proteins were differentially expressed after induction of the S strain: 53 proteins were upregulated and 48 proteins were downregulated. The identified proteins were mainly classified into the following categories: energy metabolism proteins such as arginine kinase and triose phosphate isomerase, detoxification-related proteins such as glutathione S-transferases (GSTs), signal molecule-regulated proteins such as nitric oxide synthase (NOS), and other proteins such as kinetic-related proteins and gene expression-related proteins. Several proteins show significant differences in response to short-term stress and long-term adaptation, and differential expression of these proteins reflects an overall change in cellular structure and metabolism associated with resistance to pyrethroid insecticides. In summary, our research has improved the understanding of the molecular mechanisms of beta-cypermethrin resistance in German cockroaches, which will facilitate the development of rational methods to improve the management of this pest.

Radioresistant Sf9 insect cells display efficient antioxidant defence against high dose γ-radiation

PURPOSE

To investigate the effect of gamma radiation-induced alterations in antioxidant defence of radioresistant Sf9 insect cells.

MATERIALS AND METHODS

Sf9 cells were irradiated at doses ranging from 0.5-200 Gy. Lipid peroxidation and protein carbonylation levels were observed at 4 h post-exposure along with reduced glutathione/oxidized glutathione (GSH/GSSG) profile as well as specific activities of redox active enzymes superoxide dismutase (SOD), catalase, ascorbate peroxidase (APOx), and glutathione reductase (GR). Human brain malignant glioma (BMG-1) cells were used for comparing radiation response of mammalian cells.

RESULTS

Sf9 cells displayed significantly less radiation-induced reactive oxygen/nitrogen species (ROS/RNS) generation, protein carbonylation and growth inhibition as compared to mammalian cells. Sf9 cells have higher basal APOx (∼4-fold), catalase (∼1.7-fold), SOD (∼1.3-fold) activity and GSH level (∼2.2-fold) compared to mammalian cells. A radiation dose-dependent increase in SOD, Catalase and APOx activity was found in Sf9 cells at least up to 100 Gy dose, while maximum activity in mammalian cells was achieved by 10 Gy.

CONCLUSION

The present study suggests that Lepidopteran insect cells carry a stronger antioxidant system that protects against radiation-induced macromolecular damage, growth inhibition and cell death.

Differential expression of hemolymph proteins between susceptible and insecticide-resistant Blattella germanica (Blattodea: Blattellidae)

A proteomic approach combining two-dimensional polyacrylamide gel electrophoresis and tandem mass spectrometry was used to compare hemolymph expression profiles of a beta-cypermethrin-resistant Blattella germanica L. strain and a beta-cypermethrin-susceptible strain. Twenty-eight hemolymph proteins were differentially expressed in the resistant cockroach strain; 19 proteins were upregulated and 9 proteins were downregulated compared with the susceptible strain. Protein identification indicated that expression of putative cuticular protein, nitric oxide synthase, triosephosphate isomerase, alpha-amylase, ABC transporter, and Per a 3 allergen was elevated, and expression of arginine kinase and glycosidase was reduced. The differential expression of these proteins reflects the overall change in cellular structure and metabolism related to the resistance of pyrethroid insecticides.

Radioresistant Sf9 insect cells undergo an atypical form of Bax-dependent apoptosis at very high doses of γ-radiation

PURPOSE

To investigate the underlying mechanisms of cell-death at extremely high doses of radiation in radioresistant Spodoptera frugiperda-9 (Sf9) insect cells.

MATERIALS AND METHODS

Morphology, cell proliferation and DNA-fragmentation analysis was performed at 500-2000 Gy. Changes in intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), cardiolipin oxidation and Annexin-V externalization were studied using flow-cytometry. Cytochrome-c release was measured using immunofluorescence microscopy. Inhibitors of apoptosis, i.e., Bongkrekic acid (BKA), Caspase-9 inhibitor (C9i), 5-(4-fluorosulfonylbenzoyl) adenosine hydrochloride (FSBA) and Cyclosporin-A (CsA) were used to dissect apoptotic mechanism at many classical steps. Caspase-3 activity was measured using a caspase-activity assay kit.

RESULTS

A dose-dependent induction of typical apoptosis was observed at extremely high doses, marked by extensive apoptotic body formation. However, certain atypical responses such as cellular hypertrophy and the lack of phosphatidylserine-externalization were observed during the initial hours after radiation. Loss of mitochondrial membrane potential observed at 48 h following a 2000 Gy dose was accompanied by an increase in ROS that caused significant cardiolipin oxidation leading to cytochrome-c release, caspase activation and internucleosomal DNA fragmentation. Inhibitors of B-cell lymphoma-2 (Bcl-2)-associated X protein (Bax)-mediated cytochrome-c release, apoptosome formation and caspase-9 effectively prevented radiation-induced apoptosis, strongly suggesting the role of Bax-dependent cell death mechanism.

CONCLUSIONS

Our study demonstrates that the Sf9 insect cells display good homology with human cells in the mitochondria-dependent events during radiation-induced apoptosis, although doses eliciting similar responses were 50-200 times higher than human cells. Factors upstream to mitochondrial damage remain pertinent for a thorough understanding of this extreme radioresistance displayed by lepidopteran cells.

Evidence for involvement of cytosolic thioredoxin peroxidase in the excessive resistance of Sf9 Lepidopteran insect cells against radiation-induced apoptosis

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.

What goes up must come down: transcription factors have their say in making ecdysone pulses

Insect metamorphosis is one of the most fascinating biological processes in the animal kingdom. The dramatic transition from an immature juvenile to a reproductive adult is under the control of the steroid hormone ecdysone, also known as the insect molting hormone. During Drosophila development, periodic pulses of ecdysone are released from the prothoracic glands, upon which the hormone is rapidly converted in peripheral tissues to its biologically active form, 20-hydroxyecdysone. Each hormone pulse has a unique profile and causes different developmental events, but we only have a rudimentary understanding of how the timing, amplitude, and duration of a given pulse are controlled. A key component involved in the timing of ecdysone pulses is PTTH, a brain-derived neuropeptide. PTTH stimulates ecdysone production through a Ras/Raf/ERK signaling cascade; however, comparatively little is known about the downstream targets of this pathway. In recent years, it has become apparent that transcriptional regulation plays a critical role in regulating the synthesis of ecdysone, but only one transcription factor has a well-defined link to PTTH. Interestingly, many of the ecdysteroidogenic transcription factors were originally characterized as primary response genes in the ecdysone signaling cascade that elicits the biological responses to the hormone in target tissues. To review these developments, we will first provide an overview of the transcription factors that act in the Drosophila ecdysone regulatory hierarchy. We will then discuss the roles of these transcriptional regulators in controlling ecdysone synthesis. In the last section, we will briefly outline transcription factors that likely have roles in regulating ecdysone synthesis but have not been formally identified as downstream effectors of ecdysone.

Radioresistant Sf9 insect cells display moderate resistance against cumene hydroperoxide

Lepidopteran insect cells serve as excellent model to study stress responses and are known to display resistance against DNA damaging agents including ionizing radiation; however, limited information is available on the effects of membrane damaging agents in these cells. In this study, we investigated the response of Sf9 cells (derived from ovaries of Spodoptera frugiperda; order Lepidoptera) to cumene hydroperoxide (CHPx), compared to human BMG-1 cells. CHPx treatment at doses lethal for human cells also caused typical necrosis in Sf9. Severe necrosis in human BMG-1 cells was observed at 125 μM, whereas similar effect in Sf9 cells was observed at 250 μM. In Sf9 cells, CHPx (250 μM) induced negligible changes in mitochondrial membrane potential and intracellular reactive oxygen species, while moderate effect was observed on intracellular calcium distribution. Reduced DNA damage and lipid (including cardiolipin) oxidation was observed in Sf9 cells that could be due to moderate total antioxidant status and constitutive/induced glutathione S-transferase activity. This study importantly demonstrates that Lepidopteran insect cells having extensive resistance towards DNA damaging agents show only moderately higher resistance to membrane damaging agents. A stronger reducing environment involving efficient antioxidant system seems to contribute significantly in this response.

A calcium-insensitive attenuated nitrosative stress response contributes significantly in the radioresistance of Sf9 insect cells

Lepidopteran insects/insect cells display 50-100 times higher radioresistance than humans, and are evolutionarily closest to mammals amongst all radioresistant organisms known. Compared to mammalian cells, Lepidopteran cells (TN-368, Sf9) display more efficient antioxidant system and DNA repair and suffer considerably less radiation-induced DNA/cytogenetic damage and apoptosis. Recent studies indicate that a considerably lower radiation-induced oxidative stress may significantly reduce macromolecular damage in Lepidopteran cells. Since nitrosative stress contributes in radiation-induced cellular damage, we investigated its nature in the γ-irradiated Sf9 cells (derived from Spodoptera frugiperda; order Lepidoptera; family Noctuidae) and compared with BMG-1 human cell line having significant NOS expression. Radiation induced considerably less ROS/RNS in Sf9 cells, which remained unchanged on treatment with NOS inhibitor l-NMMA. Surprisingly, growth of Sf9 cultures or irradiation could not induce NO or its metabolites, indicating negligible basal/radiation-induced NOS activity that remained unchanged even after supplementation with arginine. Cytosolic calcium release following high-dose (1000-2000Gy at 61.1cGys(-1)) γ-irradiation or H(2)O(2) (250μM) treatment also failed to generate NO in Sf9 cells having high constitutive levels of calmodulin, whereas BMG-1 cells displayed considerable calcium-dependent NO generation even following 10Gy dose. These results strongly imply the lack of calcium-mediated NOS activity in Sf9 cells. Addition of exogenous NO from GSH-NO caused considerable increase in radiation-induced apoptosis, indicating significant contribution of constitutively attenuated nitrosative stress response into the radioresistance of Lepidopteran cells. Our study demonstrates for the first time that a calcium-insensitive, attenuated nitrosative stress response may contribute significantly in the unusual radioresistance displayed by Lepidopteran insect cells.

Mitochondrial antioxidant defence in radio-resistant Lepidopteran insect cells

Cells isolated from Lepidopteran insects (butterfly and moths) display very high radioresistance as compared to mammals and other insect species. Since free radical induced mitochondrial damage under stress conditions is very crucial for cellular fate determination, antioxidant system is the major protective modality required to minimize stress-induced damage and to modulate cellular sensitivity. In this study, we predict the mitochondrial localization potential and co-existence of important antioxidant enzymes in insect cells and compare with other radiosensitive (mammals, Dipteran insects) and radioresistant (nematodes) species. Our study clearly demonstrates the inter-species variation in then localization potential of various antioxidant enzymes. A higher mitochondrial localization potential as a function of mitoprot score was evident for all important antioxidant enzymes in the lepidopteran insect Bombyx mori (Mn-SOD, 0.694; GPx, 0.862; TRPx, 0.997; TR, 0.9), besides an unusual mitochondrial localization prediction for catalase (0.453). We further found coexistence of glutathione and thioredoxin system in the mitochondria of lepidopteran insects as also reported in various plant species. On the basis of above observations, we hypothesize that a strong mitochondrial antioxidant enzyme system including the unusual coexistence of catalase, glutathione and thioredoxin system may help minimize the free radical mediated damage to mitochondria and can contribute to the intrinsic radioresistance of lepidopteran insects.