No abstract

CD4 is the primary receptor for the human immunodeficiency virus (HIV). Nef is an accessory protein of HIV that decreases the expression of CD4 on the surface of infected cells. In this study, we identified the Nef binding protein 1 (NBP1), which interacts specifically with Nef in vitro and in vivo. Since it shares sequence similarity with the catalytic subunit of the vacuolar ATPase (V-ATPase) and complements the loss of this VMA13 gene in yeast, NBP1 is the human homolog of Vma13p. Direct interactions between Nef and NBP1 were correlated with the ability of Nef to internalize CD4. The expression of the antisense NBP1 abrogated these effects. We conclude that NBP1 helps to connect Nef with the endocytic pathway.

rev-regulated expression of HIV-1 envelope proteins from a simian virus 40 late replacement vector was found to be dependent on the presence of a 5' splice site in the env mRNA in spite of the fact that this mRNA remains unspliced. When the 5' splice site upstream of the env open reading frame was deleted or mutated, expression of envelope protein was lost. RNA analysis of cells transfected with 5' splice-site mutants showed a dramatic reduction in the steady-state levels of env mRNA whether or not rev was present. Envelope expression could be restored in one of the 5' splice-site mutants by cotransfection with a plasmid expressing a suppressor U1 small nuclear RNA containing a compensatory mutation. These experiments show that U1 small nuclear RNA plays a direct and essential role in the formation of an unspliced RNA that is subject to regulation by rev.

By activating NAK via small GTPases and their downstream effectors, Nef interacts with regulatory pathways required for cell growth, cytoskeletal rearrangement and endocytosis. Thus, NAK could participate in the budding of new virions, the modification of viral proteins and the increased endocytosis of surface molecules such as CD4. Moreover, blocking the activity of these GTPases could lead to new therapeutic interventions against AIDS.