Nef is physically recruited into the immunological synapse and potentiates T cell activation early after TCR engagement.
The HIV-1 protein Nef enhances viral pathogenicity and accelerates disease progression in vivo. Nef potentiates T cell activation by an unknown mechanism, probably by optimizing the intracellular environment for HIV replication. Using a new T cell reporter system, we have found that Nef more than doubles the number of cells expressing the transcription factors NF-kappaB and NFAT after TCR stimulation. This Nef-induced priming of TCR signaling pathways occurred independently of calcium signaling and involved a very proximal step before protein kinase C activation. Engagement of the TCR by MHC-bound Ag triggers the formation of the immunological synapse by recruiting detergent-resistant membrane microdomains, termed lipid rafts. Approximately 5-10% of the total cellular pool of Nef is localized within lipid rafts. Using confocal and real-time microscopy, we found that Nef in lipid rafts was recruited into the immunological synapse within minutes after Ab engagement of the TCR/CD3 and CD28 receptors. This recruitment was dependent on the N-terminal domain of Nef encompassing its myristoylation. Nef did not increase the number of cell surface lipid rafts or immunological synapses. Recently, studies have shown a specific interaction of Nef with an active subpopulation of p21-activated kinase-2 found only in the lipid rafts. Thus, the corecruitment of Nef and key cellular partners (e.g., activated p21-activated kinase-2) into the immunological synapse may underlie the increased frequency of cells expressing transcriptionally active forms of NF-kappaB and NFAT and the resultant changes in T cell activation.
Fenard
David
D
Gladstone Institute of Virology and Immunology, University of California, 94158, USA.
Yonemoto
Wes
W
de Noronha
Carlos
C
Cavrois
Marielle
M
Williams
Samuel A
SA
Greene
Warner C
WC
D018106:CD28 Antigens / Q000502:physiology; D020013:Calcium Signaling; D015693:Gene Products, nef / Q000737:chemistry / Q000502:physiology*; D006678:HIV / Q000502:physiology*; D006801:Humans; D019169:Jurkat Cells; D008213:Lymphocyte Activation; D021962:Membrane Microdomains / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D017434:Protein Structure, Tertiary; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D013601:T-Lymphocytes / Q000276:immunology*; D054311:nef Gene Products, Human Immunodeficiency Virus; D054462:p21-Activated Kinases
D018106:CD28 Antigens; D015693:Gene Products, nef; D016328:NF-kappa B; D050778:NFATC Transcription Factors; D011948:Receptors, Antigen, T-Cell; D054311:nef Gene Products, Human Immunodeficiency Virus; C515907:PAK2 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D011493:Protein Kinase C