Mitochondrial ubiquitin ligase MARCH5 promotes TLR7 signaling by attenuating TANK action

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Toll-like receptors (TLRs) are crucial for innate immune defense against pathogens.
• Mitochondria are increasingly recognized as central hubs for antiviral signaling pathways.
• The specific role of mitochondria in regulating TLR signaling remains largely uncharacterized.

Purpose of the Study:

• To investigate the regulatory role of mitochondria in Toll-like receptor (TLR) signaling.
• To identify mitochondrial proteins that modulate TLR signaling pathways.
• To elucidate the molecular mechanisms by which mitochondria influence innate immune responses.

Main Methods:

• Utilized ectopic expression and knockdown of MARCH5 to assess its impact on NF-κB-mediated gene expression.
• Performed co-immunoprecipitation assays to identify protein interactions between MARCH5 and TANK.
• Analyzed the ubiquitylation status of TANK upon MARCH5 interaction using mass spectrometry.
• Investigated the functional consequences of MARCH5-TANK interaction on TRAF6 inhibition.

Main Results:

• The mitochondrial protein MARCH5 was identified as a positive regulator of Toll-like receptor 7 (TLR7) signaling.
• MARCH5 directly interacts with TANK, an inhibitor of TRAF6, and this interaction is enhanced by R837 stimulation.
• MARCH5 catalyzes K63-linked poly-ubiquitination of TANK, impairing its inhibitory function on TRAF6.
• Mislocalization of MARCH5 from mitochondria abrogated its regulatory effect on TANK, highlighting the importance of mitochondrial localization.

Conclusions:

• Mitochondria critically modulate innate immunity through proteins like MARCH5.
• MARCH5 enhances TLR7 signaling by ubiquitinating TANK on mitochondria, thereby promoting immune activation.
• This study establishes a novel link between mitochondria and TLR signaling, opening new avenues for understanding innate immune regulation.