Substrate screening identifies a novel target sequence for the proteasomal activity regulated by ionizing radiation

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Research

Background:

• Enzyme activity screening can uncover regulatory mechanisms and anti-cancer drug targets.
• Ionizing radiation (IR) influences cellular processes, including enzyme regulation in tumor cells.

Purpose of the Study:

• To develop and apply a novel screening technique to identify IR-regulated proteolytic activities in tumor cells.
• To characterize a specific IR-down-regulated protease and its substrate.

Main Methods:

• A novel screening technique was used to identify substrate peptide sequences with altered proteolytic activity upon IR exposure.
• Protease-class-specific inhibitors and cleavage site analysis were employed to identify the enzyme responsible.
• A warhead-inhibitor was synthesized to pinpoint the protease.
• In vitro assays were performed to confirm substrate cleavage.

Main Results:

• A specific substrate peptide showed reduced cleavage in IR-treated cell extracts compared to controls.
• The proteasome was identified as the key protease responsible for cleaving the substrate.
• The substrate sequence shares homology with a regulatory site on nucleoporin 50 (NUP50).
• Site-specific cleavage of NUP50 by the proteasome was confirmed in vitro.

Conclusions:

• Ionizing radiation modulates proteasome activity, affecting the cleavage of specific substrates.
• The proteasome's interaction with nucleoporin 50 suggests a new regulatory pathway linking IR, proteasome function, and nuclear transport.