Assembly of the CD8alpha/p56(lck) protein complex in stably expressing rat epithelial cells

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 SIV_mac239 EnvCDs were described to trigger nuclear translocation of NF-κB (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-κB. To that aim, we evaluated the ability of primary HIV-1 Envs from subtypes B and C to activate the NF-κB pathway. Primary subtype B and C Envs all failed to activate the NF-κB pathway. In contrast, when the EnvCD of HIV-1 Envs was fused to the the CD8-α chain, it induced ~ 10-fold increase in NF-κB 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-κB pathway in its native trimeric form.

The carboxyl-terminal valine is required for transport of glycoprotein CD8 alpha from the endoplasmic reticulum to the intermediate compartment

There is evidence that a carboxyl-terminal valine residue is an anterograde transport signal for type I transmembrane proteins. Removal of the signal would either delay glycosylation in the Golgi complex of proteins destined to recycle to the endoplasmic reticulum or determine accumulation in the endoplasmic reticulum of newly synthesized proteins destined for the plasma membrane. We used the human CD8 alpha glycoprotein to investigate the role of the carboxyl-terminal valine in the exocytic pathway. Using immunofluorescence light microscopy, metabolic labeling, and cell fractionation, we demonstrate that removal of the carboxyl-terminal valine residue delays transport of CD8 alpha from the endoplasmic reticulum to the intermediate compartment. Removal of the residue did not affect the other steps of the exocytic pathway or the folding/dimerization and glycosylation processes. Therefore, it is likely that this signal plays a role in the transport of CD8 alpha from the endoplasmic reticulum to the intermediate compartment either before or during the formation of the transport vesicles that drive the exit the protein from the endoplasmic reticulum.