The SH3 domain-binding surface and an acidic motif in HIV-1 Nef regulate trafficking of class I MHC complexes.
Nef, a regulatory protein of human and simian immunodeficiency viruses, downregulates cell surface expression of both class I MHC and CD4 molecules in T cells by accelerating their endocytosis. Fibroblasts were used to study alterations in the traffic of class I MHC complexes induced by Nef. We found that Nef downregulates class I MHC complexes by a novel mechanism involving the accumulation of endocytosed class I MHC in the trans-Golgi, where it colocalizes with the adaptor protein-1 complex (AP-1). This effect of Nef on class I MHC traffic requires the SH3 domain-binding surface and a cluster of acidic amino acid residues in Nef, both of which are also required for Nef to downregulate class I MHC surface expression and to alter signal transduction in T cells. Downregulation of class I MHC complexes from the surface of T cells also requires a tyrosine residue in the cytoplasmic domain of the class I MHC heavy chain molecule. The requirement of the same surfaces of the Nef molecule for downregulation of surface class I MHC complexes in T cells and for their accumulation in the trans-Golgi of fibroblasts indicates that the two effects of Nef involve similar interactions with the host cell machinery and involve a molecular mechanism regulating class I MHC traffic that is common for both of these cell types. Interestingly, the downregulation of class I MHC does not require the ability of Nef to colocalize with the adaptor protein-2 complex (AP-2). We showed previously that the ability of Nef to colocalize with AP-2 correlates with the ability of Nef to downregulate CD4 expression. Our observations indicate that Nef downregulates class I MHC and CD4 surface expression via different interactions with the protein sorting machinery, and link the sorting and signal transduction machineries in the regulation of class I MHC surface expression by Nef.
Greenberg
M E
ME
Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
Iafrate
A J
AJ
Skowronski
J
J
D033965:Adaptor Protein Complex alpha Subunits; D033942:Adaptor Proteins, Vesicular Transport; D001665:Binding Sites; D015704:CD4 Antigens / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D015536:Down-Regulation; D015870:Gene Expression; D015693:Gene Products, nef / Q000235:genetics / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D015497:HIV-1 / Q000378:metabolism*; D015793:HLA-B7 Antigen / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D008565:Membrane Proteins / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D054311:nef Gene Products, Human Immunodeficiency Virus; D018909:src Homology Domains
D033965:Adaptor Protein Complex alpha Subunits; D033942:Adaptor Proteins, Vesicular Transport; D015704:CD4 Antigens; D015693:Gene Products, nef; D015793:HLA-B7 Antigen; D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus; D014443:Tyrosine