The aspartyl protease DDI2 activates Nrf1 to compensate for proteasome dysfunction

Area of Science:

• Molecular Biology
• Cellular Biology
• Biochemistry

Background:

• Mammalian cells activate Nrf1 to upregulate proteasome gene expression in response to proteasome dysfunction.
• Nrf1, an ER-resident transcription factor, is normally degraded by the proteasome.
• Upon proteasome inhibition, Nrf1 is stabilized and cleaved for activation, but the processing enzyme was unknown.

Purpose of the Study:

• To identify the enzyme responsible for cleaving and activating the transcription factor Nrf1.
• To investigate the role of this enzyme in the cellular response to proteasome dysfunction and proteasome upregulation.

Main Methods:

• Utilized gene deletion and reintroduction experiments in mammalian cells.
• Assessed Nrf1 processing (cleaved vs. full-length forms) using Western blotting or similar techniques.
• Evaluated proteasome gene expression and cellular responses to proteasome inhibition.

Main Results:

• Demonstrated that the aspartyl protease DNA-damage inducible 1 homolog 2 (DDI2) is required for Nrf1 cleavage and activation.
• Deletion of DDI2 led to accumulation of full-length Nrf1 and impaired proteasome upregulation following proteasome inhibition.
• Restoration of DDI2 function rescued these defects, while protease-defective DDI2 did not.

Conclusions:

• DNA-damage inducible 1 homolog 2 (DDI2) is the processing enzyme that cleaves and activates Nrf1.
• DDI2-mediated Nrf1 activation is crucial for compensatory proteasome synthesis.
• Targeting DDI2 may offer a strategy to inhibit compensatory proteasome upregulation in cancer therapies.