Constitutive activation of T cells by γ2-herpesviral GPCR through the interaction with cellular CXCR4

Area of Science:

• Virology
• Immunology
• Cellular Signaling

Background:

• Pathogenic herpesviruses utilize virally-encoded G protein-coupled receptors (vGPCRs) for pathogenesis and immune evasion.
• The precise molecular mechanisms by which vGPCRs continuously activate host cell signaling remain largely unelucidated.

Purpose of the Study:

• To investigate the molecular interactions and signaling pathways employed by herpesvirus saimiri (HVS) vGPCR in T cell activation.
• To determine the role of cellular chemokine receptors, specifically CXCR4, in mediating vGPCR-induced T cell activation.

Main Methods:

• Co-expression of HVS vGPCR with cellular CXCR4 in T cells.
• Proximity ligation assay and immunoprecipitation to demonstrate physical association between vGPCR and CXCR4.
• RNA interference (shRNA) to silence CXCR4 expression and assess its impact on T cell activation.
• Analysis of T cell receptor (TCR) signaling molecules (TCRβ, Lck, ZAP70) in vGPCR-mediated activation.

Main Results:

• HVS vGPCR constitutively activates T cells through heteromeric interaction with cellular CXCR4.
• Expression of HVS and Kaposi's sarcoma-associated herpesvirus (KSHV) vGPCRs, but not Epstein-Barr virus vGPCR, leads to constitutive T cell activation.
• HVS vGPCR down-regulates surface CXCR4 without inducing degradation, suggesting sustained signaling.
• vGPCR/CXCR4 interaction is essential for T cell activation, independent of proximal TCR signaling components.
• Inactive vGPCR mutants demonstrate a failure to interact with CXCR4.

Conclusions:

• Herpesvirus vGPCRs exploit cellular CXCR4 via heteromerization to achieve constitutive T cell activation.
• This vGPCR-CXCR4 interaction is a critical mechanism for viral pathogenesis, influencing immune evasion and cellular proliferation.
• The findings highlight the significance of GPCR heteromerization in mediating viral hijacking of host cell signaling pathways.