Studies On The Programmed Cell Death In Spodoptera Litura Cells Induced By Amino Acid Starvation

Programmed cell death (PCD) is one of important defensive strategies for host during the interaction between the microbe and the host. It is benefit to understand the types and molecular mechanisms of PCD in host cells for the management of pests using microbe. The studies about autophagic cell death also became popular besides the classic way of PCD--apoptosis in recent years. Furthermore, some new types of PCD, such as paraptosis and mitotic catastrophe, started to attract people’s attention.In the previous experiments, we simulated two kinds of Lepidoptera insect cell lines with the rapamycin. The rates of cell death in that experiment presented totally different. In the Bmn-e cell line (a kind of cell line from silkworm), we observed apoptosis and autophagy after 12 h of treatment, however, these changes firstly appeared at least after 48 h of treatment in the Spodoptera litura cell line(SL), which meant that SL cells may be stronger resistant to amino acid starvation and the PCD in starvated SL cells may be different from Bmn-e cells’.In order to explore the influence of amino acid starvation on SL cells further, we deprived amino acids from SL cells instead of rapamycin to avoid the potential toxicity. Using cell chemistry, enzyme analysis, flow cytometry assay and DNA gel electrophoresis et al., we tried to investigate the types of PCD and the anti-starvation mechanisms in the treated cells. The results showed that in the early time of starvation, the number and the volume of lysosomes increased while the number of mitochondria decreased which showed that the level of autophagy rised significantly. Electron microscopic analysis revealed that large clusters of ribosomal granules and autophagic lysosomes appeared in part of SL cells after starvation. After 72 to 96 h of starvation, the rates of cell death increased gradually, but the rates of cell death were only 45-55 percent after 96 h of starvation. But only a small number of cells appeared fractured chromatin and the quantity of apoptotic bodies were few, even thugh the activity of caspase-3 rised, it is far below the apoptotic cells induced by actinomycin D, which indicated that other types of PCD occurred in starvated cells and apoptosis was just one of them. In the late stage of starvation, the membrane phosphatidyl serine evaginated cells achieved 38 percent using the flow cytometry assay, while the caspase activity was lower than the apoptotic cells induced by actinomycin D, suggested that the dead cells had some characteristics of paraptosis in late times. Therefore, all of apoptosis, autophagy and paraptosis occurred in the starvated SL cells.Cytochrome c (cyto c) plays an important role in the process of apoptosis in mammalian cells but this is disputable in insect cells. Early studies have shown that the release of cyto c can be detected in apoptotic SL cells induced by virus or UV and the inducing apoptosis can be inhibited by cyclosporin A which block the permeably transition pores located on the mitochondrial outer membrane. In this experiment, we compared apoptosis induced by cyto c from horse cardiac muscle cell in kinds of cell-free systems, the results indicated that the cyto c induced activations in mammalian cell-free systems and insect cell-free systems need different conditions.