The steroid hormone 20-hydroxyecdysone binds to dopamine receptor to repress lepidopteran insect feeding and promote pupation

Holometabolous insects stop feeding at the final larval instar stage and then undergo metamorphosis; however, the mechanism is unclear. In the present study, using the serious lepidopteran agricultural pest Helicoverpa armigera as a model, we revealed that 20-hydroxyecdysone (20E) binds to the dopamine receptor (DopEcR), a G protein-coupled receptor, to stop larval feeding and promote pupation. DopEcR was expressed in various tissues and its level increased during metamorphic molting under 20E regulation. The 20E titer was low during larval feeding stages and high during wandering stages. By contrast, the dopamine (DA) titer was high during larval feeding stages and low during the wandering stages. Injection of 20E or blocking dopamine receptors using the inhibitor flupentixol decreased larval food consumption and body weight. Knockdown of DopEcR repressed larval feeding, growth, and pupation. 20E, via DopEcR, promoted apoptosis; and DA, via DopEcR, induced cell proliferation. 20E opposed DA function by repressing DA-induced cell proliferation and AKT phosphorylation. 20E, via DopEcR, induced gene expression and a rapid increase in intracellular calcium ions and cAMP. 20E induced the interaction of DopEcR with G proteins αs and αq. 20E, via DopEcR, induced protein phosphorylation and binding of the EcRB1-USP1 transcription complex to the ecdysone response element. DopEcR could bind 20E inside the cell membrane or after being isolated from the cell membrane. Mutation of DopEcR decreased 20E binding levels and related cellular responses. 20E competed with DA to bind to DopEcR. The results of the present study suggested that 20E, via binding to DopEcR, arrests larval feeding and promotes pupation.
Author summary The steroid hormone 20-hydroxyecdysone (20E) represses insect larval feeding and promotes metamorphosis; however, the mechanism is unclear. The dopamine receptor plays important roles in animal motor function and reward-motivated behavior. Using the serious lepidopteran agricultural pest Helicoverpa armigera as a model, we revealed that 20E binds to DopEcR to block the dopamine pathway and initiates the 20E pathway. Dopamine (DA) binds to the dopamine receptor (DopEcR), a G protein-coupled receptor (GPCR), to regulate cell proliferation, larval feeding, and growth. However, 20E competes with DA to bind to DopEcR, which represses larval feeding and triggers the 20E-pathway, leading to metamorphosis. The results suggested that 20E, via binding to DopEcR, stops larval feeding and promotes pupation, which presented an example of the steroid hormone regulating dopamine receptor and behavior. Our study showed that GPCRs can bind 20E and function as 20E cell membrane receptors.