Down-modulation of B cell signal transduction by ligation of mucins to CD22

Biochem Biophys Res Commun. 2008 Jul 18;372(1):45-50. doi: 10.1016/j.bbrc.2008.04.175. Epub 2008 May 12.

Abstract

Epithelial cancer cells secrete mucins carrying carbohydrate antigens such as a sialyl-Tn antigen into cancer tissues and/or the bloodstream, in which mucins may interact with CD22 (Siglec-2). Mucins isolated from colon cancer cells and bovine submaxillary mucins bound to CD22 cDNA transfectants and a human B cell line, Daudi cell, and the binding of soluble recombinant CD22 to the mucins was confirmed by means of a plate assay. The binding specificity was demonstrated by the fact that the mucins bound to the recombinant CD22 with an intact ectodomain but not to that with a mutated ectodomain. Daudi cells were stimulated with anti-IgM F(ab')(2) in the presence or absence of mucins. Ligation of mucins to CD22 decreased the phosphorylation of CD22 and SHP-1 recruitment, and the phosphorylation of ERK-1/2 prominently. The in vivo effect of mucins on splenic B cells in the tumor-bearing state was investigated using mucin-producing (TA3-Ha) and non-producing (TA3-St) mammary adenocarcinoma-bearing mice. When fluorescence-labeled epiglycanins were administered to normal mice, a portion of them was taken up by the spleen and became associated with splenic B cells. We found that splenic B cells were reduced in TA3-Ha-bearing mice but not in TA3-St-bearing ones. These results suggest that in the tumor-bearing state a portion of the mucins in the bloodstream was taken up by the spleen and ligated to CD22 expressed on splenic B cells, which may have led to down-regulation of signal transduction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • B-Lymphocytes / immunology*
  • Cattle
  • Cell Line, Tumor
  • Colonic Neoplasms / immunology*
  • Down-Regulation
  • Humans
  • Immune Tolerance
  • Immunoglobulin Fab Fragments / immunology
  • Immunoglobulin M / immunology
  • Mice
  • Mice, Inbred Strains
  • Mitogen-Activated Protein Kinase 1 / metabolism
  • Mitogen-Activated Protein Kinase 3 / metabolism
  • Mucins / metabolism*
  • Phosphorylation
  • Protein Tyrosine Phosphatase, Non-Receptor Type 6 / metabolism
  • Receptors, Antigen, B-Cell / metabolism
  • Sialic Acid Binding Ig-like Lectin 2 / genetics
  • Sialic Acid Binding Ig-like Lectin 2 / metabolism*
  • Signal Transduction*
  • Spleen / immunology

Substances

  • Immunoglobulin Fab Fragments
  • Immunoglobulin M
  • Mucins
  • Receptors, Antigen, B-Cell
  • Sialic Acid Binding Ig-like Lectin 2
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Protein Tyrosine Phosphatase, Non-Receptor Type 6