G-protein-coupled receptor participates in 20-hydroxyecdysone signaling on the plasma membrane

BACKGROUND: Animal steroid hormones are conventionally known to initiate signaling via a genomic pathway by binding to the nuclear receptors. The mechanism by which 20E initiates signaling via a nongenomic pathway is unclear. RESULTS: We illustrate that 20E triggered the nongenomic pathway through a plasma membrane G-protein-coupled receptor (named ErGPCR) in the lepidopteran insect Helicoverpa armigera. The transcript of ErGPCR was increased at the larval molting stage and metamorphic molting stage by 20E regulation. Knockdown of ErGPCR via RNA interference in vivo blocked larval–pupal transition and suppressed 20E-induced gene expression. ErGPCR overexpression in the H. armigera epidermal cell line increased the 20E-induced gene expression. Through ErGPCR, 20E modulated Calponin nuclear translocation and phosphorylation, and induced a rapid increase in cytosolic Ca(2+) levels. The inhibitors of T-type voltage-gated calcium channels and canonical transient receptor potential calcium channels repressed the 20E-induced Ca(2+) increase. Truncation of the N-terminal extracellular region of ErGPCR inhibited its localization on the plasma membrane and 20E-induced gene expression. ErGPCR was not detected to bind with the steroid hormone analog [(3)H]Pon A. CONCLUSION: These results suggest that ErGPCR participates in 20E signaling on the plasma membrane.