Investigating the p21 Ubiquitin-Independent Degron Reveals a Dual Degron Module Regulating p21 Degradation and...

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Intrinsically disordered proteins (IDPs) undergo ubiquitin-independent degradation via the 20S proteasome.
• The PSMA3 Trapper domain on the 20S proteasome mediates interactions with IDPs.
• The role of specific IDP interaction sites in proteasomal degradation and cellular function is not fully understood.

Purpose of the Study:

• To investigate the biological significance of the interaction between IDPs and the PSMA3 Trapper.
• To identify the specific region of the IDP p21 responsible for PSMA3 Trapper interaction and its role in degradation.
• To elucidate the functional consequences of altered p21 degradation on cell cycle and senescence.

Main Methods:

• Split luciferase reporter assay to detect protein interactions.
• Site-directed mutagenesis to identify the p21 RRLIF box.
• CRISPR-Cas9 genome editing in HEK293 and HeLa cells to modify the p21 RRLIF box.
• Analysis of p21 half-life, cell cycle progression, and senescence marker gene expression.

Main Results:

• The p21 RRLIF box was identified as the key mediator of PSMA3 Trapper interaction.
• Deletion or mutation of the p21 RRLIF box significantly increased p21 half-life.
• Edited cells exhibited aberrant cell cycle patterns and enhanced senescence hallmark gene expression post-DNA damage.
• Increased p21 half-life, rather than protein level, was found to regulate senescence.

Conclusions:

• The p21 RRLIF box functions as a ubiquitin-independent degron, interacting with the PSMA3 Trapper.
• p21 possesses a dual degron module, combining ubiquitin-dependent and independent degradation pathways.
• This dual degron system plays a critical role in regulating p21 degradation and its impact on cellular processes like senescence.