CD4 down-regulation by HIV-1 Nef reveals distinct roles for γ1 and γ2 subunits of AP-1 complex in protein trafficking

Abstract

The HIV accessory protein Nef is a major determinant of viral pathogenesis that facilitates viral particle release, prevents viral antigen presentation and increases infectivity of new virus particles. These functions of Nef involve its ability to remove specific host proteins from the surface of infected cells, including the CD4 receptor. Nef binds to the adaptor protein 2 (AP-2) and CD4 in clathrin-coated pits, forcing CD4 internalization and subsequent target to lysosomes. Herein, we report that this lysosomal targeting requires a variant of the AP-1 comprising the isoform 2 of γ-adaptin. Depletion of γ2 or μ1A subunits of AP-1, but not of γ1, precludes Nef-mediated lysosomal degradation of CD4. In γ2-depleted cells, CD4 internalized by Nef accumulates in early endosomes and this alleviates CD4 removal from the cell surface. Depletion of γ2 also hinders EGFR-EGF complex targeting to lysosomes, an effect that is not observed upon γ1 depletion. Altogether, our data provide evidence that γ1 and γ2 subunits compose two distinct variants of AP-1 complexes, with different functions in protein sorting.