CD4 is active as a signaling molecule on the human monocytic cell line Thp-1

Exp Cell Res. 2002 Sep 10;279(1):141-52. doi: 10.1006/excr.2002.5581.


CD4 is a 56-kDa membrane glycoprotein expressed by a subset of T cells, by cells of the monocyte/macrophage lineage, and by eosinophils and dendritic cells. CD4 serves as a coreceptor for HIV and IL-16. T cell CD4 mediates signal transduction by associating with the protein tyrosine kinase p56(lck); this interaction does not exist in monocytes. We wished to elucidate the mechanism(s) by which monocyte CD4 transduces signals. Stimulation of CD4 on Thp-1 monocytic cells induced a Ca(2+) flux and the time-dependent activation of phosphotyrosine proteins ranging from 35 to 180 kDa. We identified the 140- and 85-kDa proteins as phospholipase C gamma (PLC-gamma) and the regulatory subunit of phosphatidylinositol 3-kinase (PI-3K), respectively. Using immunoprecipitation/Western immunoblotting however, we were unable to show any direct association between CD4 and PLC-gamma, PI-3K, or other known signaling proteins. To identify proteins capable of associating with the cytoplasmic tail of CD4, we fused it with gluthatione S-transferase and used the fusion protein in far Western and pull-down experiments. In both types of experiments, the fusion protein routinely associated with 45- and 55-kDa proteins. Mass spectrometry analysis of the tryptic peptides generated from these two proteins indicated novel sequences.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies / pharmacology
  • CD4 Antigens / genetics
  • CD4 Antigens / immunology
  • CD4 Antigens / physiology*
  • Calcium / metabolism
  • Cell Line
  • Glutathione Transferase / genetics
  • Humans
  • Isoenzymes / metabolism
  • Kinetics
  • Models, Biological
  • Monocytes / metabolism*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phospholipase C gamma
  • Phosphorylation
  • Phosphotyrosine / metabolism
  • Recombinant Fusion Proteins / metabolism
  • Signal Transduction*
  • Type C Phospholipases / metabolism


  • Antibodies
  • CD4 Antigens
  • Isoenzymes
  • Recombinant Fusion Proteins
  • Phosphotyrosine
  • Glutathione Transferase
  • Phosphatidylinositol 3-Kinases
  • Type C Phospholipases
  • Phospholipase C gamma
  • Calcium