CD4 phosphorylation partially reverses Nef down-regulation of CD4

J Immunol. 2004 Nov 1;173(9):5495-500. doi: 10.4049/jimmunol.173.9.5495.

Abstract

HIV Nef down-regulates CD4 from the cell surface in the absence of CD4 phosphorylation, whereas PMA down-regulates CD4 through a phosphorylation-dependent pathway. In this study we show that the down-regulation of CD4 in human Jurkat T cells expressing Nef was nearly complete (approximately 95%), whereas that induced by PMA was partial (approximately 40%). Unexpectedly, treating T cells expressing Nef with PMA restored the surface CD4 up to 35% of the steady state level. Both mutating the phosphorylation sites in the CD4 cytoplasmic tail (Ser408 and Ser415) and the use of a protein kinase C inhibitor, bisindolylmaleimide1, abolished the restoration of surface CD4, suggesting that the restoration required CD4 phosphorylation. CD4 and Nef could be cross-linked by a chemical cross-linker, 3,3-dithiobis[sulfosuccinimidyl-propionate], in control T cell membranes, but not in PMA-treated T cell membrane, suggesting that CD4 and Nef interacted with each other in T cells, and the phosphorylation disrupted the CD4-Nef interaction. We propose that this dissociation switches CD4 internalization from the Nef-mediated, nearly complete down-regulation to a phosphorylation-dependent, partial down-regulation, resulting in a net gain of CD4 on the T cell surface.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • CD4 Antigens / biosynthesis
  • CD4 Antigens / metabolism*
  • Cell Fractionation
  • Cell Membrane / chemistry
  • Cell Membrane / genetics
  • Cell Membrane / immunology
  • Clone Cells
  • Cross-Linking Reagents / metabolism
  • Down-Regulation / genetics
  • Down-Regulation / immunology*
  • Drug Synergism
  • Gene Products, nef / antagonists & inhibitors
  • Gene Products, nef / biosynthesis
  • Gene Products, nef / genetics
  • Gene Products, nef / physiology*
  • HIV / immunology*
  • Humans
  • Jurkat Cells
  • Phosphorylation
  • Serine / genetics
  • Serine / metabolism
  • Staining and Labeling
  • T-Lymphocyte Subsets / immunology
  • T-Lymphocyte Subsets / metabolism
  • T-Lymphocyte Subsets / virology
  • Tetradecanoylphorbol Acetate / pharmacology
  • nef Gene Products, Human Immunodeficiency Virus

Substances

  • CD4 Antigens
  • Cross-Linking Reagents
  • Gene Products, nef
  • nef Gene Products, Human Immunodeficiency Virus
  • Serine
  • Tetradecanoylphorbol Acetate