20-hydroxyecdysone via upregulating 4EBP expression and inhibiting its phosphorylation represses cell proliferation to permit insect larval molting.

The eukaryotic translation initiation factor 4E binding protein (4EBP) represses protein translation as a nonphosphorylated form by interacting with the eukaryotic translation initiation factor 4E (eIF4E). However, the upstream regulator of 4EBP is unclear. Using the major agricultural pest, Helicoverpa armigera, cotton bollworm, as a research model, we observed higher expression levels of 4Ebp at the 5th instar molting stage and metamorphosis. 20-hydroxyecdysone (20E) significantly upregulated the expression of 4Ebp and inhibited its phosphorylation. 20E promoted the binding of ecdysone receptor B (EcRB) to the ecdysone response element (EcRE) in the promoter sequence of 4Ebp, thus facilitating 4Ebp transcription. Knocked down 4Ebp by RNA interference caused abnormal molting of the 5th instar larvae, and overexpression of 4EBP in the H. armigera epidermal cell line inhibited cell proliferation. These data suggested that 20E repressed cell proliferation temporarily by upregulating 4Ebp expression level and inhibiting its phosphorylation, which is necessary for insect larval molting.