Cell type dependent inhibition of transport of cathepsin D in HepG2 cells and fibroblasts exposed to deoxy-manno-nojirimycin and deoxynojirimycin.
The synthesis, transport and processing of lysosomal enzymes was examined in human hepatoma HepG2 cells and in human fibroblasts exposed to the Golgi alpha-mannosidase I inhibitor 1-deoxy-manno-nojirimycin. In HepG2 cells cathepsin D, beta-hexosaminidase and arylsulfatase B synthesized in the presence of 5 mM 1-deoxy-manno-nojirimycin contained exclusively endo-beta-N-acetylglucosaminidase H-cleavable oligosaccharides, indicating that alpha-mannosidase I had been inhibited efficiently. The proteolytic processing of intracellularly retained cathepsin D was retarded and the fraction of secreted cathepsin D was increased two-fold. In fibroblasts neither segregation nor maturation of cathepsin D were affected by 1-deoxy-manno-nojirimycin in spite of the inhibition of oligosaccharide processing. In the presence of the glucosidase I inhibitor 1-deoxynojirimycin, the precursor of cathepsin D (larger by about 1 kDa than the secreted form) accumulated transiently in light membranes in HepG2 cells. Release from the site of accumulation was accompanied by a decrease in size by about 1 kDa. This change was attributed to the removal of glucose residues. In fibroblasts the transient accumulation of larger precursors in the presence of 1-deoxynojirimycin was more pronounced than in HepG2 cells. The differential effects of alpha-mannosidase I and glucosidase I inhibitors on the transport of cathepsin D in HepG2 cells and fibroblasts may indicate that different intermediates in the biosynthetic pathway of asparagine-linked oligosaccharides participate in the transport of lysosomal enzymes in the two cell types.
Nauerth
A
A
Lemansky
P
P
Hasilik
A
A
von Figura
K
K
Bause
E
E
Legler
G
G
D017485:1-Deoxynojirimycin; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001693:Biological Transport, Active / Q000187:drug effects; D002402:Cathepsin D / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D003470:Culture Media; D003864:Depression, Chemical; D005347:Fibroblasts / Q000378:metabolism; D005944:Glucosamine / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D008715:Methionine / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism
D000900:Anti-Bacterial Agents; D003470:Culture Media; D017485:1-Deoxynojirimycin; D008715:Methionine; D002402:Cathepsin D; D005944:Glucosamine