Vav exchange factor counteracts the HIV-1 Nef-mediated decrease of plasma membrane GM1 and NF-AT activity in T cells.

Area of Science:

• Immunology
• Cell Biology
• Virology

Background:

• GM1-enriched lipid microdomains and Vav are crucial for T cell activation.
• A link exists between lipid microdomains, Vav, and HIV Nef protein.
• Nef may alter plasma membrane GM1, impacting T cell antigen recognition and Vav function.

Purpose of the Study:

• To investigate how HIV Nef affects GM1 levels in T cells.
• To determine the impact of Nef on T cell activation pathways, specifically NF-AT and NF-kappaB.
• To explore the role of Vav in counteracting Nef-induced changes.

Main Methods:

• Assessing GM1 levels in T cells with and without Nef expression.
• Analyzing NF-AT and NF-kappaB activation via T cell receptor (TCR) engagement.
• Investigating the Ca(2+)/calcineurin and JNK signaling pathways.
• Evaluating the effect of Vav overexpression on Nef-induced alterations.

Main Results:

• Nef expression significantly down-regulates plasma membrane GM1 in unstimulated T cells.
• Nef inhibits NF-AT activation but not NF-kappaB activation following TCR engagement.
• Nef specifically inhibits the Ca(2+)/calcineurin cascade, leaving JNK and AP-1 unaffected.
• Vav overexpression counteracted both Nef-induced GM1 decrease and NF-AT inhibition.

Conclusions:

• HIV Nef interferes with T cell activation by down-regulating GM1 levels.
• Nef disrupts the Ca(2+)/calcineurin signaling pathway essential for NF-AT activation.
• Vav plays a role in mitigating Nef's effects on GM1 and T cell activation.
• Nef may modulate GM1 microdomain trafficking and clustering to impair TCR-mediated activation.