Insulin stimulates ecdysteroid production through a conserved signaling cascade in the mosquito Aedes aegypti

Selective activators and inhibitors of insulin signaling cascades in mammalian cells were tested for their effects on insulin stimulated steroidogenesis by ovaries of Aedes aegypti. Bovine insulin in the concentration range of 1.7 μM to 85 μM stimulated ecdysteroidogenesis in vitro. Pervanadate, an inhibitor of tyrosine kinase phosphatase, stimulated ecdysteroid production at concentrations of 250 μM to 1 mM. Okidaic acid, a serine/threonine phosphatase inhibitor, stimulated steroidogenesis with an ED₅₀ of 77.39 nM. A selective inhibitor of tyrosine kinase activity, HNMPA- (AM₃), inhibited ecdysteroid production with an IC₅₀ of 14.2 μM. Two selective inhibitors of phosphatidylinositol 3-kinase, wortmannin and LY294002, inhibited ecdysteroid production at low concentrations (IC₅₀ = 1.6 nM and 30 nM, respectively). These concentrations are similar to those inhibiting insulin action in mammalian cells. A selective inhibitor of mitogen, activated protein kinase, PD098059, had no effect on ecdysteroid production even up to 100 μM. Thus, insulin stimulation of ecdysteroid production by ovaries in vitro appears to be controlled by the tyrosine kinase activity of the mosquito insulin receptor and the signaling cascade involving phosphatidylinositol 3-kinase and protein kinase B.