The viral protein U (Vpu)-interacting host protein ATP6V0C down-regulates cell-surface expression of tetherin and thereby contributes to HIV-1 release

Abstract

Host proteins with antiviral activity have evolved as first-line defenses to suppress viral replication. The HIV-1 accessory protein viral protein U (Vpu) enhances release of the virus from host cells by down-regulating the cell-surface expression of the host restriction factor tetherin. However, the exact mechanism of Vpu-mediated suppression of antiviral host responses is unclear. To further understand the role of host proteins in Vpu's function, here we carried out yeast two-hybrid screening and identified the V0 subunit C of vacuolar ATPase (ATP6V0C) as a Vpu-binding protein. To examine the role of ATP6V0C in Vpu-mediated tetherin degradation and HIV-1 release, we knocked down ATP6V0C expression in HeLa cells and observed that ATP6V0C depletion impairs Vpu-mediated tetherin degradation, resulting in defective HIV-1 release. We also observed that ATP6V0C overexpression stabilizes tetherin expression. This stabilization effect was specific to ATP6V0C, as overexpression of another subunit of the vacuolar ATPase, ATP6V0C″, had no effect on tetherin expression. ATP6V0C overexpression did not stabilize CD4, another target of Vpu-mediated degradation. Immunofluorescence localization experiments revealed that the ATP6V0C-stabilized tetherin is sequestered in a CD63– and lysosome-associated membrane protein 1 (LAMP1)–positive intracellular compartment. These results indicate that the Vpu-interacting protein ATP6V0C plays a role in down-regulating cell-surface expression of tetherin and thereby contributes to HIV-1 assembly and release.

Reduced vacuolar ATPase protects mice from Friend virus infection – an unintended but instructive effect in Hif-2afl mice

“…Other retroviruses, like HIV-1 or -2 or human T-cell leukemia virus type 1 (HTLV-1) or 2, enter the cells pH independently, indicating that vacuolar ATPase is not required for HIV or HTLV entry ( McClure et al, 1988 ; Stein et al, 1987 ). Interestingly, a recent report has suggested that the V o subunit C of the vacuolar ATPase, which forms the proton transporting channel, plays a role in regulating tetherin expression and therefore regulates the assembly and release of HIV ( Waheed et al, 2020 ). Thus, it seems that apart from its role in viral entry by lysosomal acidification, the vacuolar ATPase is also important for the release of newly synthesized virions.…”

HIV–Host Cell Interactions

“…By degrading tetherin, Vpu enhances the release of viral particles from infected cells [100,101]. However, recent studies have shown that tetherin also plays a role in the transport of MHC I molecules to the cell surface [102]. Tetherin interacts with newly synthesized MHC I molecules and promotes their transport to the cell surface, where they can present viral antigens to the immune system [103].…”

Human TRIM5α: Autophagy Connects Cell-Intrinsic HIV-1 Restriction and Innate Immune Sensor Functioning

“…For example, tetherin has been shown to interact with autophagy via multiple different pathways. In the context of HIV-1 infection, HIV-1 Vpu has been reported to downregulate tetherin expression on the cell surface by promoting its ubiquitination and subsequent intracellular sequestration and/or degradation within autophagosomes or lysosomes, thus potentially hijacking the autophagy pathway for the benefit of the virus [ 188 , 189 ]. Strikingly, breast cancer-associated gene 2 (BCA2, also known as Rabring7, ZNF364, or RNF115), a RING-type E3 ubiquitin ligase, was shown to interact with tetherin to promote HIV-1 packaging into CD63 + endosomes, with the end result being lysosomal degradation of HIV-1 virions and tetherin in a manner reminiscent of tetherin-dependent autophagic degradation of damaged mitochondria in uninfected cells [ 190 , 191 ].…”