Stimulation of NF-κB activity by the HIV restriction factor BST2

Area of Science:

• Immunology
• Virology
• Cell Biology

Background:

• BST2 (tetherin) is an interferon-inducible protein known to restrict enveloped virus release.
• BST2 was previously identified as an inducer of NF-κB activity, a key inflammatory pathway.

Purpose of the Study:

• To investigate the mechanisms by which BST2 induces NF-κB signaling.
• To determine the relationship between BST2's NF-κB inducing activity and its antiviral function.
• To explore how HIV-1 Vpu interacts with BST2 signaling.

Main Methods:

• Site-directed mutagenesis of BST2 to identify functional domains (YxY motif, GPI anchor site, coiled-coil structure).
• Coimmunoprecipitation assays to study protein-protein interactions (BST2, TAK1, TAB1).
• Functional assays measuring NF-κB induction, viral restriction, and inhibition by HIV-1 Vpu and its mutants.

Main Results:

• BST2 induces NF-κB in a dose-dependent manner, separable from viral restriction.
• A YxY motif in BST2's cytoplasmic domain is crucial for NF-κB induction but not viral restriction.
• HIV-1 Vpu inhibits BST2-induced NF-κB signaling via interaction with the β-TrCP E3 ubiquitin ligase complex.
• BST2 can function as a virus sensor, with its signaling augmented by HIV-1 lacking Vpu.

Conclusions:

• BST2 possesses multifaceted roles in innate immunity: NF-κB signaling, viral sensing, and direct viral restriction.
• HIV-1 Vpu has evolved to counteract all these BST2 functions.
• Understanding BST2-Vpu interactions provides insights into viral evasion strategies and host antiviral responses.