A protein from the cabbage looper, Trichoplusia ni, regulated by a bacterial infection is homologous to 3-dehydroecdysone 3β-reductase

Abstract During the screening of immune-regulated genes from the cabbage looper, Trichoplusia ni , a 3-dehydroecdysone 3β-reductase homologue (DERH) was cloned. In the course of development, 3-dehydroecdysone 3β-reductase mediates the conversion of 3-dehydroecdysone (3dE) secreted from the prothoracic glands to ecdysone (E), which is subsequently converted to 20-hydroxyecdysone (20E), the major insect molting hormone. The cloned gene is upregulated in fat body during development and is strongly induced after the larva is challenged with bacteria. The gene codes for a 308 amino acid residue protein which shows 42.5% identity to Spodoptera littoralis 3-dehydroecdysone 3β-reductase. Using the baculovirus expression system, the recombinant DERH was expressed. The purified protein mediates the reduction of 3-dehydromakisterone A to makisterone A, and requires NADPH as a cofactor. Western blots using an antiserum to T. ni DERH revealed the presence of the protein in larval hemolymph and integument. The data indicate that the protein is regulated developmentally and is induced after a challenge with bacteria. Immunohistochemical studies localized the enzyme exclusively in the epidermis and the cuticle.