Rapaprotin, an Endopeptidase-Activated Proteasome Inhibitor that Induces 26S Disassembly

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Research

Background:

• The 26S proteasome, a crucial holoenzyme, regulates cellular protein homeostasis and is implicated in cancer.
• Current proteasome inhibitors target the 20S core particle, offering therapeutic benefits for various cancers.

Purpose of the Study:

• To discover novel inhibitors of 26S proteasome assembly.
• To investigate the anticancer potential and mechanism of action of rapaprotin.

Main Methods:

• Genome-wide CRISPR-Cas9 screening to identify factors required for rapaprotin's activity.
• Mechanistic studies involving biochemical assays and cell-based experiments.
• Time-resolved cryogenic electron microscopy (cryo-EM) to elucidate structural mechanisms.

Main Results:

• Rapaprotin, a 26S proteasome assembly inhibitor, induces apoptosis in myeloma and leukemia cells.
• Prolyl endopeptidase (PREP) is essential for rapaprotin's pro-apoptotic effect, converting it to an active linear form (rapaprotin-L).
• Rapaprotin-L disrupts 26S proteasome holoenzyme integrity by causing 19S regulatory particle dissociation and demonstrates synergy with existing proteasome inhibitors.

Conclusions:

• Rapaprotin represents a novel chemical entity that targets 26S proteasome assembly through a unique activation mechanism.
• Rapaprotin shows potential as a new anticancer therapeutic, particularly in overcoming drug resistance.
• This compound serves as a valuable tool for studying proteasome assembly dynamics.