Capsular polysaccharide induction of apoptosis by intrinsic and extrinsic mechanisms

Cell Microbiol. 2008 Oct;10(10):2129-37. doi: 10.1111/j.1462-5822.2008.01196.x. Epub 2008 Jul 10.

Abstract

A purified microbial capsular polysaccharide of Cryptococcus neoformans, glucuronoxylomannan (GXM), induces Fas ligand (FasL) upregulation on macrophages and, as a consequence, apoptosis of lymphocytes. The mechanisms that lead to lymphocyte apoptosis in both in vitro and in vivo systems were investigated by cytofluorimetric analysis and Western blotting experiments. Caspase 8 cleaves caspase 3 in two different pathways: directly as well as indirectly by activation of Bcl-2 interacting domain, which initiates caspase 9 cleavage. Therefore, the caspase 8 and caspase 9 pathways cooperate in an amplification loop for efficient cell death, and noteworthily we provide evidence that they are both activated in one single cell. Furthermore, both activation of GXM-mediated caspase 8 and apoptosis were also found in in vivo systems in an experimental model of murine candidiasis. Collectively, our data show that GXM-induced apoptosis involves, in a single cell, a cross-talk between extrinsic and intrinsic pathways. Such a finding offers opportunities for the therapeutic usage of this polysaccharide in appropriate clinical settings for taming T-cell responses.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis*
  • Candidiasis / immunology
  • Caspase 8 / metabolism
  • Caspases / metabolism
  • Cryptococcus neoformans / immunology*
  • Female
  • Humans
  • Jurkat Cells
  • Mice
  • Models, Biological
  • Polysaccharides / immunology*
  • Proto-Oncogene Proteins c-bcl-2 / metabolism

Substances

  • Polysaccharides
  • Proto-Oncogene Proteins c-bcl-2
  • caspase 9s, human
  • glucuronoxylomannan
  • CASP8 protein, human
  • Caspase 8
  • Caspases