Reaper is regulated by IAP-mediated ubiquitination

Area of Science:

• Cellular biology
• Molecular biology
• Apoptosis research

Background:

• Apoptotic cell death involves caspase activation, while Inhibitors of Apoptosis (IAPs) counteract caspases, increasing the threshold for cell death.
• Pro-apoptotic proteins like Drosophila RHG proteins (Reaper, HID, Grim) and mammalian Smac/DIABLO disrupt IAP function.
• In Drosophila, RHG proteins can trigger IAP ubiquitination and degradation via IAP's own ubiquitin ligase activity.

Purpose of the Study:

• To investigate the role of IAP-mediated ubiquitination on Drosophila RHG proteins.
• To elucidate the mechanism and biological significance of Reaper ubiquitination by IAPs.
• To explore the reciprocal regulation between IAPs and Reaper-like proteins.

Main Methods:

• Investigating the ubiquitination of Drosophila RHG proteins (Reaper, HID, Grim) by IAPs.
• Analyzing the requirement of IAP ubiquitin-ligase activity and Reaper-IAP interaction for ubiquitination.
• Mutational analysis of potential Reaper ubiquitination sites to assess degradation.
• Evaluating the impact of Reaper ubiquitination on its biological activity.

Main Results:

• Drosophila RHG proteins, specifically Reaper, are substrates for IAP-mediated ubiquitination.
• Reaper ubiquitination necessitates IAP ubiquitin-ligase activity and a stable Reaper-IAP interaction.
• Mutating potential ubiquitination sites on Reaper prevents its degradation.
• Ubiquitination significantly influences Reaper's biological activity, demonstrating its regulatory role.

Conclusions:

• IAPs possess a novel function in ubiquitylating and degrading Reaper.
• The ubiquitination of Reaper by IAPs is a critical mechanism controlling Reaper's abundance and biological activity.
• IAPs and Reaper-like proteins engage in a mutual regulatory relationship, controlling each other's levels.