Ecdysone-induced expression of the caspase DRONC during hormone-dependent programmed cell death in Drosophila is regulated by Broad-Complex

Abstract

he steroid hormone ecdysone regulates both cell differentiation and cell death during insect metamorphosis, by hierarchical transcriptional regulation of a number of genes, including the Broad-Complex ( BR-C ), the zinc finger family of transcription factors. These genes in turn regulate the transcription of a number of downstream genes. DRONC, a key apical caspase in Drosophila , is the only known caspase that is transcriptionally regulated by ecdysone during development. We demonstrate that dronc T gene expression is ablated or reduced in BR-C mutant flies. Using RNA interference in an ecdysone-responsive Drosophila cell line, we show that DRONC is essential for ecdysone-mediated cell death, and that dronc upregulation in these cells is controlled by BR-C. Finally, we show that the dronc promoter has BR-C interaction sites, and that it can be transactivated by a specific isoform of BR-C. These results indicate that BR-C plays a key role in ecdysonemediated caspase regulation.

Autophagic programmed cell death in Drosophila

“…36 E74A mutants exhibit reduced levels of hid, crq, buffy, drice, and dream. 36,59 Studies of apoptosis gene promoters indicate that rpr is a direct target of the ecdysone receptor 54 and that dronc is a direct target of BR-C. 61 These data suggest that the ecdysone-regulated early genes BR-C, E74A, and E93 have overlapping and distinct target apoptosis genes that they regulate. Significantly, it appears that proper transciption of apoptosis genes is essential for autophagic cell death, since animals with mutations in BR-C, E74A, and E93 prevent destruction of salivary glands.…”

Caspase function in programmed cell death

“…17,26,29 Furthermore, in cultured cells, dronc ablation by RNA interference (RNAi) inhibits cell death induced by ecdysone. 37,38 However, surprisingly, midgut removal and downstream caspase activation in larval midguts occur normally in dronc mutant animals, 26 suggesting that alternative ways of activating effector caspases exists in some cases ( Figure 3). Gene expression and promoter analysis indicate that the dronc gene is regulated by the heterodimeric nuclear receptor EcR/Usp (ecdysone receptor/ultraspiracle) directly in response to ecdysone and also via the ecdysoneinduced transcription factor BR-C. 37,38 CARMER, the fly homologue of the mammalian CARM1 histone methyl transferase, is also recruited to the dronc promoter via the EcR/Usp complex and positively regulates ecdysone-induced dronc expression.…”

kep1 interacts genetically with dredd / Caspase-8 , and kep1 mutants alter the balance of dredd isoforms

“…Dronc, another group III caspase with substantial IETDase activity despite its active site, which is very divergent from that of Dredd (39), may be responsible for this additional activity. Dronc is induced by ecdysone (23,40), and ecdysone inhibits apoptosis of nurse cells (41,42); so in developing ovaries, Dronc, although present, must be in an inactive form. In our ovary extracts, however, we may have diluted out any short-lived inhibitory proteins, for example Diap1, which can bind Dronc (43).…”