Nef-mediated lipid raft exclusion of UbcH7 inhibits Cbl activity in T cells to positively regulate signaling

Immunity. 2005 Dec;23(6):621-34. doi: 10.1016/j.immuni.2005.11.003.

Abstract

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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blotting, Western
  • CD4-Positive T-Lymphocytes / cytology
  • CD4-Positive T-Lymphocytes / immunology*
  • Cell Cycle Proteins / metabolism
  • Cell Line
  • Enzyme-Linked Immunosorbent Assay
  • Gene Products, nef / immunology
  • Gene Products, nef / metabolism*
  • Guanine Nucleotide Exchange Factors / metabolism
  • HIV*
  • Humans
  • Immunoprecipitation
  • Membrane Microdomains / immunology
  • Membrane Microdomains / metabolism*
  • Microscopy, Confocal
  • Proto-Oncogene Proteins c-cbl / immunology
  • Proto-Oncogene Proteins c-cbl / metabolism*
  • RNA, Small Interfering / genetics
  • Rho Guanine Nucleotide Exchange Factors
  • Signal Transduction / immunology*
  • Ubiquitin-Conjugating Enzymes / immunology
  • Ubiquitin-Conjugating Enzymes / metabolism*
  • Virus Replication / immunology*
  • cdc42 GTP-Binding Protein / metabolism
  • nef Gene Products, Human Immunodeficiency Virus

Substances

  • Cell Cycle Proteins
  • Gene Products, nef
  • Guanine Nucleotide Exchange Factors
  • RNA, Small Interfering
  • Rho Guanine Nucleotide Exchange Factors
  • nef Gene Products, Human Immunodeficiency Virus
  • UBE2L3 protein, human
  • Ubiquitin-Conjugating Enzymes
  • Proto-Oncogene Proteins c-cbl
  • cdc42 GTP-Binding Protein
  • CBL protein, human