Baseline susceptibility of three cell lines to activated Cry1Ac and Cry2Ab

While Cry1Ac has been known to bind with larval midgut proteins cadherin, APN (amino peptidase N), ALP (alkaline phosphatase) and ABCC2 (ATP-binding cassette transporter subfamily C2), little is known about the receptors of Cry2Ab. To provide a clue to the receptors of Cry2Ab, we tested the baseline cytotoxicity of activated Cry1Ac and Cry2Ab against the midgut and fatbody cell lines of Helicoverpa zea and the ovary cell line of Spodoptera frugiperda (SF9). As expected, the descending order of cytotoxicity of Cry1Ac against the three cell lines in terms of LC₅₀ was midgut (31 μg/ml) >fatbody (59 μg/ml) and SF9 cell (100 μg/ml). By contrast, the fatbody cell line (LC₅₀ =7.7 μg/ml) was 2 times more susceptible to Cry2Ab than the midgut cell line (16 μg/ml), whose susceptibility was not significantly greater than that of SF9 cell (18 μg/ml). These results indicate that the receptors of Cry2Ab were enriched in fatbody cells and thus largely different from the receptors of Cry1Ac, which were enriched in midgut cells.