The Vpu-interacting protein ATP6V0C regulates expression of tetherin and HIV-1 release

The HIV-1 accessory protein Vpu enhances virus release by down-regulating cell surface expression of the host restriction factor tetherin. To further understand the role of host proteins in Vpu function, 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 a defect in HIV-1 release. We also observed that overexpression of ATP6V0C stabilizes tetherin expression. This stabilization is 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 studies showed that the ATP6V0C-stabilized tetherin is sequestered in a CD63- and LAMP1-positive intracellular compartment. These data demonstrate that the Vpu-interacting protein ATP6V0C plays a role in regulating tetherin expression and HIV-1 assembly and release.