Endocytic Control of Cell-Autonomous and Non-Cell-Autonomous Functions of p53

Area of Science:

• Cell Biology
• Molecular Oncology
• Protein Trafficking

Background:

• NUMB is an endocytic protein exhibiting tumor suppressor activity by inhibiting p53 degradation.
• The precise mechanism linking NUMB's endocytic function to p53 regulation, particularly the role of alternatively spliced exon 3 (Ex3), is not fully understood.

Purpose of the Study:

• To elucidate the mechanism by which the Ex3-encoded sequence of NUMB influences p53 regulation and cellular trafficking.
• To investigate the role of NUMB and SNX9 in the formation and secretion of exosomes containing p53.

Main Methods:

• Investigated the subcellular localization of NUMB variants.
• Utilized co-immunoprecipitation to identify protein complexes.
• Employed live-cell imaging and electron microscopy to track protein trafficking.
• Analyzed exosome content and function in recipient cells.

Main Results:

• The Ex3 sequence directs NUMB to the plasma membrane, forming a complex with SNX9.
• This NUMB-SNX9 complex recruits p53, leading to internalization and exosomal secretion dependent on both proteins.
• Exosomes containing p53 are internalized by recipient cells, translocating p53 to the nucleus and activating p53-dependent pathways.

Conclusions:

• NUMB's Ex3 exon is crucial for recruiting p53 into exosomes for intercellular transfer.
• Exosome-mediated transfer of p53 by NUMB suggests a novel mechanism for establishing a tumor-suppressive microenvironment.