HIV Nef-mediated major histocompatibility complex class I down-modulation is independent of Arf6 activity.
HIV Nef has a number of important biological effects, including the down-modulation of several immunological important molecules (CD4, major histocompatibility complex [MHC] class I). Down-modulation of CD4 seems to be via clathrin-dependent endocytosis, whereas down-modulation of MHC class I remains unexplained. Several mutant proteins, including mutations in the small GTPase Arf6, have been used to probe membrane traffic pathways. One such mutant has recently been used to propose that Nef acts through Arf6 to activate the endocytosis of MHC class I. Here, we show that MHC class I down-modulation is unaffected by other Arf6 mutants that provide more specific perturbations in the GDP-GTP cycling of Arf6. Inhibition of phosphatidylinositol-3-phosphate kinase, an upstream activator of Arf6, also had no effect on the internalization step, but its activity is required to direct MHC class I to the trans-Golgi network. We conclude that the apparent Arf6 dependency of Nef-mediated MHC class I down-modulation is due to nonspecific perturbations in membrane traffic.
Larsen
Jakob E
JE
Department of Cell Biology and The Center for Blood Research, Harvard Medical School, Boston, Massachusetts 02115, USA.
Massol
Ramiro H
RH
Nieland
Thomas J F
TJ
Kirchhausen
Tomas
T
D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D002478:Cells, Cultured; D002966:Clathrin / Q000378:metabolism*; D003001:Cloning, Molecular; D015536:Down-Regulation / Q000502:physiology; D004705:Endocytosis / Q000502:physiology; D004789:Enzyme Activation / Q000502:physiology; D005434:Flow Cytometry; D005805:Genes, MHC Class I / Q000502:physiology*; D015754:Genes, nef / Q000502:physiology*; D006056:Golgi Apparatus / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006678:HIV / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology
D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors; D002966:Clathrin; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D019869:Phosphatidylinositol 3-Kinases; C000715348:ARF6 protein, human