Nef-mediated lipid raft exclusion of UbcH7 inhibits Cbl activity in T cells to positively regulate signaling.
Lentiviral Nef increases T cell signaling activity, but the molecular nature of the stimulus involved is incompletely described. We explored CD4 T cell lipid raft composition in the presence and absence of Nef. Here, the E2 ubiquitin-conjugating enzyme UbcH7, which acts in conjunction with c-Cbl, is absent from lipid rafts. This Nef-mediated exclusion is associated with failure of ubiquitination of activated Vav. In the presence of Nef, lipid raft Cdc42 is activated and forms a ternary complex between the c-Cbl-interacting protein p85Cool-1/betaPix and c-Cbl, displacing UbcH7 from rafts. Suppression of p85Cool-1/betaPix expression restores UbcH7 raft localization and Vav ubiquitination and diminishes Cdc42 activity. Moreover, p85Cool-1/betaPix knockdown attenuates HIV replication. Thresholds for activation of signaling involve the intricate balance of positive and negative regulators. Here we provide evidence for Nef disruption of a negative regulator of T cell signaling in promoting HIV replication.
Pubmed ID: 16356860 RIS Download
Blotting, Western | CD4-Positive T-Lymphocytes | Cell Cycle Proteins | Cell Line | Enzyme-Linked Immunosorbent Assay | Gene Products, nef | Guanine Nucleotide Exchange Factors | HIV | Humans | Immunoprecipitation | Membrane Microdomains | Microscopy, Confocal | Proto-Oncogene Proteins c-cbl | RNA, Small Interfering | Rho Guanine Nucleotide Exchange Factors | Signal Transduction | Ubiquitin-Conjugating Enzymes | Virus Replication | cdc42 GTP-Binding Protein | nef Gene Products, Human Immunodeficiency Virus