Sequestration of p56(lck) by gp120, a model for TCR desensitization.
Ligation of the CD4 receptor by HIV envelope glycoprotein gp120 inhibits T cell activation and signaling through the TCR complex. Recent reports suggest CD4 ligation by gp120 + anti-gp120 Abs uncouples protein tyrosine kinases (PTKs) from the TCR signal-transduction cascade. This finding and other observations led us to hypothesize that the effects of gp120 are mediated through p56(lck), a PTK noncovalently associated with CD4. To test this hypothesis, we first examined the kinetics of gp120/anti-gp120-induced TCR signaling defects in the Jurkat T cell line. Pretreating cells with gp120/anti-gp120 for 1 to 4 h before stimulation prevented TCR-directed PTK activation. Coincident with TCR desensitization, pretreatment with gp120/anti-gp120 also decreased the amount of p56(lck) that could be immunoprecipitated from the Nonidet P-40 detergent-soluble fraction of cellular lysates, while simultaneously increasing the recovery of p56(lck) from the Nonidet P-40 detergent-insoluble fraction (or cytoskeleton). To assess the potential role of the actin in this process, experiments were conducted in the presence of cytochalasin D. Cytochalasin D restored TCR signaling in cells previously desensitized with gp120/anti-gp120 and prevented translocation of p56lck from the Nonidet P-40 detergent-soluble fraction of cell lysates. Furthermore, p56(lck) was found to coimmunoprecipitate with anti-actin. These data suggest that gp120/anti-gp120 may inhibit TCR signaling by sequestering p56(lck) to the cytoskeleton.
Goldman
F
F
Department of Pediatrics, University of Iowa Hospitals and Clinics, Iowa City 52242, USA.
Crabtree
J
J
Hollenback
C
C
Koretzky
G
G
D000199:Actins / Q000378:metabolism; D015638:Cytochalasin D / Q000494:pharmacology; D015699:HIV Envelope Protein gp120 / Q000187:drug effects / Q000276:immunology / Q000494:pharmacology*; D006801:Humans; D007106:Immune Sera / Q000187:drug effects / Q000494:pharmacology; D019169:Jurkat Cells; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D018448:Models, Immunological; D011948:Receptors, Antigen, T-Cell / Q000096:biosynthesis* / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology; D019061:src-Family Kinases / Q000187:drug effects / Q000378:metabolism*
D000199:Actins; D015699:HIV Envelope Protein gp120; D007106:Immune Sera; D011948:Receptors, Antigen, T-Cell; D015638:Cytochalasin D; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D019061:src-Family Kinases