Introduction: Host cell proteins are specifically incorporated into HIV-1 envelope during budding. Virionic HLA-C reduces HIV-1 susceptibility to neutralizing antibodies (Cosma 1999). A polymorphism in the 5' region of the HLA-C gene has been associated to individual variations in set point viral loads (Fellay 2007), suggesting a role of HLA-C expression levels in modulating HIV-1 infectivity. We have reported (Matucci 2008; Baroni 2010) that HLA-C in the HIV-1 envelope associates to Env increasing viral infectivity of both R5 and X4 tropic viruses. The purpose of this study is to elucidate this interaction and exploit it for generating new immunogens capable of conferring protective immunity.
Methods: Using recombinant HLA-C and Env molecules fused to fluorescent tags, we are studying their association using the bimolecular fluorescence complementation (BiFC) technique. BiFC allows the analysis of the interaction between associated proteins in living cells and to study their co-localization into cellular compartments. Env-deletion mutants and Env swapped domain recombinants are being tested to identify protein domains involved in their association. HLA-C coded by different alleles will be analyzed for their association with Env to study the influence of HLA-C polymorphisms in increasing HIV-1 infectivity.
Results: Preliminary results on Env-HLA-C association and sub-cellular compartmentalization, using a specific marker for ER, reveal a direct proximity between these proteins, suggesting an early association at the ER level. Similarly, analysis of co-localization between Golgi apparatus and Env-HLA-C reveal the presence of the complementation signal between the two proteins in Golgi vesicles.
Conclusions: BiFC assays allows an efficient visualization of HLA-C and HIV-1 Env association in living cells. Preliminary results obtained suggest an association between the two proteins at the ER and Golgi level. Understanding the interaction between HLA-C and HIV-1 Env might give valuable information for the design of new immunogens and/or compounds that, by reducing viral infectivity, may help controlling HIV-1 infection.