ARF1 regulates Nef-induced CD4 degradation.
BACKGROUND
The HIV Nef protein downregulates CD4 through sequential connection with clathrin-coated pits and the COP1 coatomer, resulting in accelerated endocytosis and lysosomal targeting.


RESULTS
Here we report that the small GTPase ARF1 controls the Nef-induced, COP-mediated late-endosomal targeting of CD4. We find that Nef binds ARF1 directly and can recruit the GTPase onto endosomal membranes. Furthermore, a complex comprising Nef, ARF1, and betaCOP can be immunoprecipitated from cells expressing the viral protein. Residues in a C-terminal loop of the viral protein facilitate both these interactions and the targeting of Nef and CD4 to acidic late endosomes, whereas other residues primarily involved in mediating CD4 endocytosis are dispensable for this process. Finally, a dominant-negative ARF1 mutant blocks the migration of the Nef-CD4 complex to lysosomes.


CONCLUSIONS
Our results support a model in which ARF1 is the immediate downstream partner of Nef for CD4 lysosomal targeting.
Fauré
Julien
J
Department of Biochemistry, University of Geneva, 1211 Geneva, Switzerland.
Stalder
Romaine
R
Borel
Christelle
C
Sobo
Komla
K
Piguet
Vincent
V
Demaurex
Nicolas
N
Gruenberg
Jean
J
Trono
Didier
D
D020823:ADP-Ribosylation Factor 1 / Q000378:metabolism*; D000818:Animals; D015704:CD4 Antigens / Q000378:metabolism*; D002478:Cells, Cultured; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism*; D006224:Cricetinae; D004705:Endocytosis / Q000502:physiology; D011992:Endosomes / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015693:Gene Products, nef / Q000378:metabolism*; D005822:Genetic Vectors; D006678:HIV; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal; D009154:Mutation / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D011233:Precipitin Tests; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D014760:Viral Fusion Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus
D015704:CD4 Antigens; D015693:Gene Products, nef; D014760:Viral Fusion Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus; C471981:COP1 protein, human; D044767:Ubiquitin-Protein Ligases; D020823:ADP-Ribosylation Factor 1