Rapid induction of p62 and GABARAPL1 upon proteasome inhibition promotes survival before autophagy activation

Area of Science:

• Cellular Biology
• Molecular Biology
• Neuroscience

Background:

• Proteasome inhibitors are vital research tools and treatments for multiple myeloma.
• Diminished proteasome activity is implicated in neurodegenerative diseases.
• Understanding cellular compensation mechanisms for proteasome inhibition is crucial.

Purpose of the Study:

• To investigate how cells adapt and survive under proteasome inhibition.
• To identify key molecular players involved in cellular response to proteasome dysfunction.
• To elucidate the role of p62 and GABARAPL1 in cellular survival pathways.

Main Methods:

• Treatment of cells with proteasome inhibitors.
• Quantitative analysis of gene expression, including GABARAPL1 and p62.
• Gene knockdown experiments using siRNA for p62 and GABARAPL1.
• Analysis of protein aggregation and degradation pathways.

Main Results:

• Proteasome inhibitor treatment rapidly induced GABARAPL1 and p62 expression within 4 hours.
• Knockdown of p62 or GABARAPL1 significantly reduced cell survival under proteasome inhibition.
• p62 induction is dependent on the transcription factor Nrf1, which also upregulates proteasome genes.
• Extended exposure (20 hours) activated autophagy via an Nrf1-independent pathway.
• p62 knockdown prevented the accumulation of ubiquitinated proteins in aggresomes and sumoylated proteins in nuclear inclusions, but did not affect protein degradation.

Conclusions:

• Cells rapidly induce p62 expression as a primary survival mechanism against proteasome inhibition.
• p62 enhances cell survival by sequestering ubiquitinated proteins into inclusions.
• The Nrf1 transcription factor plays a dual role in early response to proteasome inhibition, inducing both p62 and proteasome genes.
• Autophagy is activated through a distinct, Nrf1-independent mechanism upon prolonged proteasome inhibition.