Arylphorin is a mitogen in the Heliothis virescens midgut cell secretome upon Cry1Ac intoxication

Insecticidal crystal (Cry) proteins produced by the bacterium Bacillus thuringiensis (Bt) target cells in the midgut epithelium of susceptible larvae. While the mode of action of Cry toxins has been extensively investigated, the midgut response to Cry intoxication and its regulation are not well characterized. In this work, we report the secreted proteome (secretome) of primary mature midgut cell cultures from Heliothis virescens larvae after exposure to Cry1Ac toxin compared to control buffer treatment. Biological activity of the Cry1Ac-induced secretome was monitored as higher proliferation and differentiation and an overall reduction in total cell mortality over time in primary H. virescens midgut stem cell cultures when compared to treatment with control buffer secretome. Differential proteomics identified 4 proteins with significant differences in abundance comparing Cry1Ac-treated and control secretomes. The most significant difference detected in the Cry1Ac secretome was an arylphorin protein not detected in the control secretome. Feeding of purified arylphorin to H. virescens larvae resulted in midgut hyperplasia and significantly reduced susceptibility to Cry1Ac toxin compared to controls. These data identify arylphorin as a protein with a putative relevant role in the midgut regeneration process in response to Cry1Ac intoxication.