HIV-1 Nef disrupts MHC-I trafficking by recruiting AP-1 to the MHC-I cytoplasmic tail

Abstract

To avoid immune recognition by cytotoxic T lymphocytes (CTLs), human immunodeficiency virus (HIV)-1 Nef disrupts the transport of major histocompatibility complex class I molecules (MHC-I) to the cell surface in HIV-infected T cells. However, the mechanism by which Nef does this is unknown. We report that Nef disrupts MHC-I trafficking by rerouting newly synthesized MHC-I from the trans-Golgi network (TGN) to lysosomal compartments for degradation. The ability of Nef to target MHC-I from the TGN to lysosomes is dependent on expression of the μ1 subunit of adaptor protein (AP) AP-1A, a cellular protein complex implicated in TGN to endolysosomal pathways. We demonstrate that in HIV-infected primary T cells, Nef promotes a physical interaction between endogenous AP-1 and MHC-I. Moreover, we present data that this interaction uses a novel AP-1 binding site that requires amino acids in the MHC-I cytoplasmic tail. In sum, our evidence suggests that binding of AP-1 to the Nef–MHC-I complex is an important step required for inhibition of antigen presentation by HIV.

HIV Type 1 Nef Is Released from Infected Cells in CD45+Microvesicles and Is Present in the Plasma of HIV-Infected Individuals

“…Nef has been shown to upregulate the endosomal pathway and actually increase the numbers of endosomes within the cell. 36,37,54,[69][70][71][72] Given Nef interactions with the endosomal pathway it is not unlikely that Nef could be released into exosome-like microvesicles.…”

HIV-1 Nef Binds PACS-2 to Assemble a Multikinase Cascade That Triggers Major Histocompatibility Complex Class I (MHC-I) Down-regulation

“…This Nef-activated SFK then stimulates tyrosine phosphorylation of ZAP-70/Syk, recruiting class I PI3K by an unknown mechanism to increase endocytosis of MHC-I through an ARF6-regulated pathway (7,8). MHC-I molecules internalized by this signaling pathway are then redistributed to paranuclear endosomal compartments by a process that requires Nef Met 20 , which mediates interaction with AP-1 (7,11). This Nef-assembled signaling-based pathway that triggers MHC-I down-regulation was elucidated using PACS and SFK interfering mutants, siRNA knockdown of ZAP-70 or Syk, and isoform-directed inhibitors of class I PI3Ks (8).…”

“…This MHC-I down-regulation requires the action of three motifs (1, 2) as follows: an N-proximal ␣-helical region (residues 7-26) (9) containing a critical methionine (Met 20 ) that promotes association of MHC-I with the heterotetrameric adaptor AP-1 (10,11); an acidic cluster (EEEE 65 ) required for binding to phosphofurin acidic cluster sorting protein-1 (PACS-1) (12,13); and an SH3-binding domain formed by a type II polyproline helix (PXXP 75 ) (9,12) that promotes association of Nef with Src family tyrosine kinases (SFKs) (14 -17). The conservation of these three motifs in the pandemic M group HIV-1, which accounts for over 90% of all AIDS cases worldwide, suggests they control an essential pathway required for HIV-1 pathogenesis (18,19).…”

“…This ligation is similar to the mechanism used by phagocytic cells to trigger ARF6-mediated Fc receptor internalization, which is stimulated by the binding of class I PI3K to SFK-phosphorylated ZAP-70/Syk (39). The recruited class I PI3K then triggers the ARF6-controlled down-regulation of cell-surface MHC-I to TGN/endosomal compartments, a process that requires Nef Met 20 (7), which mediates the interaction of MHC-I with AP-1 (11). In the absence of PACS-2, Nef is unable to bind SFKs, recruit and direct ZAP-70 Tyr 292 phosphorylation, or stimulate class I PI3K, thereby preventing MHC-I down-regulation (Figs.…”

Human Immunodeficiency VirusnefSignature Sequences Are Associated with Pulmonary Hypertension

“…4 27 where x is any amino acid), the L 58 V CD4 down-regulation domain, 28 the E 63 G acidic cluster mediating the sequestration of MHC-1 in the trans-Golgi network, 29 and the M 79 I/T 80 N/Y 81 F phosphorylation site for protein kinase C. 30 We also found changes near M 20 whose functional role is to interact with the adaptor protein 1 (AP-1) and efficiently prevent MHC-1 trafficking to the membrane. 31 Importantly, 7 of these 10 nef polymorphisms were validated in the San Francisco group with HIV-PH (Fig. 1, Supplementary Table S1).…”