Upregulation of the expression of prodeath serine/threonine protein kinase for programmed cell death by steroid hormone 20-hydroxyecdysone.

Serine/threonine protein kinases phosphorylate protein substrates to initiate further cellular events. Different serine/threonine protein kinases have varied functions despite their highly conserved homology. We propose prodeath-S/TK, a prodeath serine/threonine protein kinase from the lepidopteran insect Helicoverpa armigera, promotes programmed cell death (PCD) during metamorphosis. Prodeath-S/TK is expressed in various tissues with a high expression level during molting and metamorphosis by 20-hydroxyecdysone (20E) induction. Prodeath-S/TK is localized in the larval midgut during metamorphosis. Prodeath-S/TK knockdown by injecting dsRNA into larval hemocoel suppresses the 20E-induced metamorphosis and PCD, as well as downregulates a set of genes involved in the PCD and 20E signaling pathway. 20E upregulates prodeath-S/TK expression through its nuclear receptor EcR-B1 and USP1. Prodeath-S/TK overexpression in the epidermal cell line leads to PCD with DNA fragmentation and the activation of caspases 3 and 7. Prodeath-S/TK plays role in the cytoplasm. The N-terminal and C-terminal sequences of prodeath-S/TK determine its subcellular location. These data indicate that prodeath-S/TK participates in PCD by regulating gene expression in the 20E signaling pathway.