DDX3 interacts with USP9X and participates in deubiquitination of the anti-apoptotic protein MCL1

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• The RNA helicase DDX3 and deubiquitinase USP9X are crucial proteins involved in various cellular processes.
• Understanding their interaction is key to elucidating their distinct and potentially cooperative roles in cellular regulation.

Purpose of the Study:

• To investigate the novel interaction between DDX3 and USP9X in human cells.
• To determine the functional consequences of this interaction on protein stability and cellular processes, particularly apoptosis.

Main Methods:

• Domain mapping to identify interaction sites between DDX3 and USP9X.
• Cellular localization studies using microscopy.
• Overexpression and depletion experiments in HeLa cells.
• Luciferase reporter assays to assess translational effects.
• Western blotting to analyze protein ubiquitination and stability.

Main Results:

• DDX3 interacts with USP9X via their C-terminal and N-terminal regions, respectively, primarily in the cytoplasm.
• Overexpression of DDX3 induces cytoplasmic stress granule formation and recruits USP9X.
• USP9X depletion does not affect DDX3-mediated translation, and DDX3 is not a substrate for USP9X.
• Depletion of USP9X and/or DDX3 leads to accumulation of ubiquitinated MCL1, indicating a role in MCL1 protein stability.

Conclusions:

• DDX3 and USP9X interact physically and functionally in human cells.
• The DDX3-USP9X complex plays a significant role in regulating the stability and anti-apoptotic function of MCL1.
• DDX3 likely exerts anti-apoptotic effects by collaborating with USP9X to promote MCL1 deubiquitination.