Reassessment of the capacity of the HIV-1 Env cytoplasmic domain to trigger NF-κB activation

The cytoplasmic domain of lentiviral Envelopes (EnvCD) ensures Env incorporation into nascent virions and regulates Env trafficking to and from the plasma membrane. It has also been reported to promote transcription from the viral LTR both directly and indirectly. Noticeably, the HIV-1 and SIVmac239 EnvCDs were described to trigger nuclear translocation of NF-kappa B (Postler, Cell Host Microbes 2012). Given the paramount importance of identifying viral and host factors regulating HIV transcription, cellular signaling pathways and latency, and given that viral replication capacity is dependent on Env, we asked whether HIV EnvCDs from different HIV-1 subtypes differently modulated NF-kappa B. To that aim, we evaluated the ability of primary HIV-1 Envs from subtypes B and C to activate the NF-kappa B pathway. Primary subtype B and C Envs all failed to activate the NF-kappa B pathway. In contrast, when the EnvCD of HIV-1 Envs was fused to the the CD8-alpha chain, it induced similar to 10-fold increase in NF-kappa B induction, and this increase was much stronger with a truncated form of the HIV EnvCD lacking the 76 C-terminal residues and containing the proposed TAK-1 binding domain. Our results indicate that the HIV-1 EnvCD is unlikely to trigger the NF-kappa B pathway in its native trimeric form.