20-hydroxyecdysone upregulates Atg genes to induce autophagy in the Bombyx fat body

• Published in: Autophagy 2013-08, Vol.9 (8), p.1172-1187
• Main Authors: Tian, Ling, Ma, Li, Guo, Enen, Deng, Xiaojuan, Ma, Sanyuan, Xia, Qingyou, Cao, Yang, Li, Sheng
• Format: Article
• Language: English
• Subjects: 20-hydroxyecdysone; Animals; Atg genes; Atg1; ATG8; autophagy; Autophagy - drug effects; Autophagy - genetics; Base Sequence; Basic Research Paper; Bombyx - drug effects; Bombyx - genetics; Bombyx - growth & development; Bombyx - ultrastructure; Bombyx mori; Down-Regulation - drug effects; Down-Regulation - genetics; Ecdysterone - pharmacology; fat body; Fat Body - drug effects; Fat Body - growth & development; Fat Body - metabolism; Fat Body - ultrastructure; Gene Expression Profiling; Gene Expression Regulation, Developmental - drug effects; Gene Knockdown Techniques; Genes, Insect - genetics; HEK293 Cells; Humans; Insect Proteins - genetics; Insect Proteins - metabolism; Models, Biological; Molecular Sequence Data; Response Elements - genetics; RNA Interference - drug effects; TORC1; Transcription, Genetic - drug effects; transcriptional regulation; Up-Regulation - drug effects; Up-Regulation - genetics
• ISSN: 1554-8627; 1554-8635
• DOI: 10.4161/auto.24731

Autophagy is finely regulated at multiple levels and plays crucial roles in development and disease. In the fat body of the silkworm, Bombyx mori, autophagy occurs and Atg gene expression peaks during the nonfeeding molting and pupation stages when the steroid hormone (20-hydroxyecdysone; 20E) is high. Injection of 20E into the feeding larvae upregulated Atg genes and reduced TORC1 activity resulting in autophagy induction in the fat body. Conversely, RNAi knockdown of the 20E receptor partner (USP) or targeted overexpression of a dominant negative mutant of the 20E receptor (EcR DN ) in the larval fat body reduced autophagy and downregulated the Atg genes, confirming the importance of 20E-induction of Atg gene expression during pupation. Moreover, in vitro treatments of the larval fat body with 20E upregulated the Atg genes. Five Atg genes were potentially 20E primary-responsive, and a 20E response element was identified in the Atg1 (ortholog of human ULK1) promoter region. Furthermore, RNAi knockdown of 4 key genes (namely Br-C, E74, HR3 and βftz-F1) in the 20E-triggered transcriptional cascade reduced autophagy and downregulated Atg genes to different levels. Taken together, we conclude that in addition to blocking TORC1 activity for autophagosome initiation, 20E upregulates Atg genes to induce autophagy in the Bombyx fat body.