CDC42 AND RAC1 ARE IMPLICATED IN THE ACTIVATION OF THE NEF-ASSOCIATEDKINASE AND REPLICATION OF HIV-1

Background: The negative factor (Nef) of human and simian immunodefici ency viruses (HIV-1, HIV-2 and SIV) is required for high levels of vir emia and progression to AIDS. Additionally, Nef leads to cellular acti vation, increased viral infectivity and decreased expression of CD4 on the cell surface. Previously, we and others demonstrated that Nef ass ociates with a cellular serine kinase (NAK) activity. Recently, it was demonstrated that NAK bears structural and functional similarity to p 21-activated kinases (PAKs). Results: In this study, we demonstrate th at Nef not only binds to but also activates NAK via the small GTPases CDC42 and Rad. First, the dominant-negative PAK (PAKR), via its GTPase -binding domain, and dominant-negative GTPases (CDC42Hs-N17 and Rac1-N 17) block the ability of Nef to associate with and activate NAK. Secon d, constitutively active small GTPases (CDC42Hs-V12 and Rac1-V12) pote ntiate the effects of Nef. Third, interactions between Nef and NAK res ult in several cellular effector functions, such as activation of the serum-response pathway. And finally, PAKR, CDC42Hs-N17 and Rac1-N17 de crease levels of HIV-1 production to those of virus from which the nef gene is deleted. Conclusions: By activating NAK via small GTPases and their downstream effecters, Nef interacts with regulatory pathways re quired for cell growth, cytoskeletal rearrangement and endocytosis. Th us, NAK could participate in the budding of new virions, the modificat ion of viral proteins and the increased endocytosis of surface molecul es such as CD4. Moreover, blocking the activity of these GTPases could lead to new therapeutic interventions against AIDS.