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Two functional variants of AP-1 complex composed of either ³2 or ³1-subunits are independently required for MHC-I downregulation by HIV-1 Nef


The HIV-1 accessory protein Nef downregulates cell surface expression of MHC-I molecules to facilitate virus spreading. The Nef-induced downregulation of MHC-I molecules, such as HLA-A, requires the clathrin adaptor protein 1 (AP-1) complex. The cooperative interaction of Nef, AP-1, and the cytosolic tail (CT) of HLA-A leads to redirection of HLA-A targeting from the trans-Golgi network (TGN) to lysosomes for degradation. Although the ³-adaptin subunit of AP-1 has two distinct isoforms (³1 and ³2), which may form two AP-1 complex variants, so far only the importance of AP-1³1 in MHC-I downregulation by Nef has been investigated. Here we report that the AP-1³2 isoform also participates in this process. We found that AP-1³2 forms a complex with Nef and HLA-A2_CT, and that this interaction depends on Y320 residue in HLA-A2_CT and Nef expression. Moreover, Nef targets AP-1³1 and AP-1³2 to different compartments in T cells, and depletion of either AP-1 variant impairs the Nef-mediated reduction of endogenous HLA-A total levels, and rescues HLA-A levels in the cell surface. Finally, immunofluorescence and immuno-electron microscopy analyses reveal that the depletion of ³2 in T cells compromises both Nef-mediated retention of HLA-A molecules in the TGN, and targeting to multivesicular bodies/late endosomes. Altogether, these results show that in addition to AP-1³1, Nef also requires the AP-1³2 variant for efficient MHC-I downregulation. (AU)

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