Vav Proteins Are Key Regulators of Card9 Signaling for Innate Antifungal Immunity

Area of Science:

• Immunology
• Molecular Biology
• Microbiology

Background:

• Fungal infections pose significant health risks, particularly for immunocompromised individuals.
• The innate immune system relies on C-type lectin receptors (CLRs) and the Card9 adaptor protein for antifungal defense.
• The precise mechanisms linking CLR signaling to Card9 activation remain incompletely understood.

Purpose of the Study:

• To identify key molecular players that bridge CLR signaling to Card9 activation.
• To elucidate the role of Vav proteins in antifungal immunity.
• To investigate the functional redundancy and specific contributions of Vav family members in the Card9 pathway.

Main Methods:

• Utilized knockout mouse models (Vav1/2/3^-/- and Card9^-/-) to assess fungal susceptibility.
• Investigated signaling pathways downstream of CLRs (Dectin-1, Dectin-2, Mincle) including NF-κB activation.
• Analyzed genetic variations in human VAV3 for association with candidemia susceptibility.

Main Results:

• Vav proteins (Vav1, Vav2, Vav3) were identified as essential activators of the Card9 pathway.
• Cooperative action of Vav proteins downstream of key CLRs regulates NF-κB signaling and pro-inflammatory gene expression.
• Vav1/2/3^-/- mice exhibited severe susceptibility to fungal infections, mirroring Card9^-/- phenotypes.
• Vav3 was identified as the most critical Vav protein in mice, and a human VAV3 polymorphism correlated with candidemia risk.

Conclusions:

• Vav proteins are indispensable components of the CLR-Card9 signaling axis in innate antifungal immunity.
• This study reveals a novel molecular mechanism regulating Card9 function, crucial for host defense against fungi.
• Targeting Vav proteins or understanding VAV3 polymorphisms may offer new therapeutic strategies for fungal infections.