The Expression of GB Virus C Envelope E2 Protein Inhibits HIV-1 Assembly and Release
Christine Timmons*1, Q Shao1, C Wang2, H Wei1, H Liu2, and B Liu1
1Meharry Med Coll, Nashville, TN, US and 2Sun Yat-sen Univ, Guangzhou, China
Background: GB virus C (GBV-C) is a single-stranded positive-sense RNA virus which is classified in the Flaviviridae family. This nonpathogenic lymphotropic virus shares the same transmission pathway as HIV-1 and primarily replicates in CD4+ T cells. In HIV-1 infected individuals, persistent co-infection with GBV-C is associated with lower HIV-1 viral load, higher CD4 T cell counts and also prolonged survival through mechanisms such as induction of anti-HIV-1 chemokines and decreased expression of HIV-1 co-receptors. However, the direct interactions between GBV-C and HIV in the co-infected cells remain to be elucidated.
Methods: GBV-C E2 and HIV-1 gag-pol expression plasmids were co-transfected into 293T cells. Ultracentrifugation was used to pellet down viral-like particles (VLP) released from the transfected cells. Western blot analysis was used to measure HIV-1 gag precursor processing, assembly and release. Membrane floatation gradient analysis and indirect immunofluorescence /confocal microscopy were used to determine HIV-1 gag intracellular trafficking and plasma membrane targeting.
Results: The expression of glycosylated GBV-C E2 inhibits HIV-1 gag precursor processing resulting in less CAp24 and MAp17 being produced while the overall expression level of gag precursor Pr55 remains unchanged. The viral particle release is also impaired in cells expressing glycosylated E2 when compared to cells expressing gag alone. Confocal images and membrane floatation gradient analysis show that glycosylated E2 disrupt HIV-1 gag trafficking to the plasma membrane, resulting in gag accumulation in subcellular compartments.
Conclusions: Taken together, studies in our lab show that GBV-C Envelope E2 interferes with HIV-1 gag precursor processing, assembly and release. GBV-C E2 causes gag to accumulate in subcellular compartments, leading to a disruption in gag trafficking to the plasma membrane and release. This diminishes HIV-1 infection by decreasing HIV-1 assembly, maturation and release which is required for virions to infect a new host cell. Further elucidation of the mechanism of inhibition will shed light on novel HIV/AIDS therapeutic options.