Abstract
Bacillus thuringiensis (Bt) Cry toxins are used to control Aedes aegypti, an important vector of dengue fever and yellow fever. Bt Cry toxin forms pores in the gut cells, provoking larvae death by osmotic shock. Little is known, however, about the endocytic and/or degradative cell processes that may counteract the toxin action at low doses. The purpose of this work is to describe the mechanisms of internalization and detoxification of Cry toxins, at low doses, into Mos20 cells from A. aegypti, following endocytotic and cytoskeletal markers or specific chemical inhibitors. Here, we show that both clathrin-dependent and clathrin-independent endocytosis are involved in the internalization into Mos20 cells of Cry11Aa, a toxin specific for Dipteran, and Cry1Ab, a toxin specific for Lepidoptera. Cry11Aa and Cry1Ab are not directed to secretory lysosomes. Instead, Mos20 cells use the Rab5 and Rab11 pathways as a common mechanism, most probably for the expulsion of Cry11Aa and Cry1Ab toxins. In conclusion, we propose that endocytosis is a mechanism induced by Cry toxins independently of specificity, probably as part of a basal immune response. We found, however, that actin is necessary for defense-specific response to Cry11Aa, because actin-silenced Mos20 cells become more sensitive to the toxic action of Cry11A toxin. Cry toxin internalization analysis in insect cell lines may contribute to a better understanding to Cry resistance in mosquitoes.
Highlights
Aedes aegypti is the most important vector for the transmission of dengue fever, yellow fever and other tropical diseases
Our results demonstrated that low doses of toxin trigger early and recycling endocytosis, similar to the response reported for higher doses of pore-forming toxin family (PFT)-dependent remodeling of the membrane [8,17]
Mos20 cells were exposed to Bacillus thuringiensis (Bt) toxins at low doses with the intention to maintain cellular integrity and function and to analyze the role of different endocytosis-related proteins during the intoxication process
Summary
Aedes aegypti is the most important vector for the transmission of dengue fever, yellow fever and other tropical diseases. Human health and other animal species and the emergence of insects that are resistant to chemical insecticides have led to a search for safer alternatives and compounds with higher specificity against mosquitoes. One of these control strategies involves the use of Bacillus thuringiensis Cry toxins. These toxins belong to the pore-forming toxin family (PFT), which constitute the most widespread group of toxins produced by bacteria. The defense cell mechanisms triggered by small doses of PFT are less known
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