cytochrome-c-t and mannose-6-phosphate

Whereas caspases are essential components in apoptosis, other proteases seem to be involved in programmed cell death. This study investigated the role of lysosomal mannose 6-phosphorylated proteins in tumor necrosis factor (TNF)-induced apoptosis. We report that fibroblasts isolated from patients affected with inclusion-cell disease (ICD), having a deficient activity of almost all lysosomal hydrolases, are resistant to the toxic effect of TNF. These mutant cells exhibited a defect in TNF-induced caspase activation, Bid cleavage, and release of cytochrome c. In contrast, TNF-induced p42/p44 MAPK activation and CD54 expression remained unaltered. Human ICD lymphoblasts and fibroblasts derived from mice nullizygous for Igf2 and the two mannose 6-phosphate (M6P) receptors, Mpr300 and Mpr46, which develop an ICD-like phenotype, were also resistant to CD95 ligand and TNF, respectively. Moreover, correction of the lysosomal enzyme defect of ICD fibroblasts, using a medium enriched in M6P-containing proteins, enabled restoration of sensitivity to TNF. This effect was blocked by exogenous M6P but not by cathepsin B or L inhibitors. Altogether, these findings suggest that some M6P-bearing glycoproteins modulate the susceptibility to TNF-induced apoptosis. As a matter of fact, exogenous tripeptidyl peptidase 1, a lysosomal carboxypeptidase, could sensitize ICD fibroblasts to TNF. These observations highlight the hitherto unrecognized role of some mannose 6-phosphorylated proteins such as tripeptidyl peptidase 1 in the apoptotic cascade triggered by TNF.

Topics: Aminopeptidases; Animals; Apoptosis; Carboxypeptidases; Cathepsin B; Cathepsin L; Cathepsins; Cell Death; Cell Line, Transformed; Cell Survival; Coloring Agents; Culture Media; Cysteine Endopeptidases; Cytochromes c; Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; Dose-Response Relationship, Drug; Endopeptidases; Fas Ligand Protein; fas Receptor; Fibroblasts; Flow Cytometry; Golgi Apparatus; Humans; Intercellular Adhesion Molecule-1; Lymphocytes; Lysosomes; Mannosephosphates; Membrane Glycoproteins; Mice; Microscopy, Fluorescence; Mucolipidoses; Phenotype; Phosphorylation; Recombinant Proteins; Signal Transduction; Skin; Tetrazolium Salts; Thiazoles; Time Factors; Tumor Necrosis Factor-alpha