Proteolytic processing of cathepsin D in prelysosomal organelles.
The initial steps of proteolytic processing of newly synthesized cathepsin D were investigated in prelysosomal membranes, which were defined by their contents of 300 kDa mannose 6-phosphate receptor (MPR 300). MPR 300-containing vesicles were immuno-isolated from a postmitochondrial supernatant of HepG2 cells using a peptide-specific antibody directed against the 15 C-terminal amino acids of the cytoplasmic domain of MPR 300. In the immunoisolated fraction, MPR 300 was enriched 11.5-fold over [35S]polypeptides, 29-fold over the lysosomal marker beta-hexosaminidase and 4.5-fold over the trans Golgi marker galactosyltransferase, when referred to the postmitochondrial supernatant. MPR 300-containing vesicles harbored, on average, 12% of the cathepsin D precursor from the postmitochondrial supernatant, suggesting that segregation of MPR 300 and cathepsin D occurs rapidly in prelysosomal organelles. Detection of low, but significant amount of mature cathepsin D in the immunoisolated fraction suggests that proteolytic processing is initiated in MPR 300-containing vesicles or in tightly associated prelysosomal vesicles, which are distinct from mature lysosomes.
Delbrück
R
R
Georg-August-Universität, Göttingen/Germany.
Desel
C
C
von Figura
K
K
Hille-Rehfeld
A
A
D015415:Biomarkers; D006528:Carcinoma, Hepatocellular / Q000473:pathology; D002402:Cathepsin D / Q000378:metabolism*; D006801:Humans; D008113:Liver Neoplasms / Q000473:pathology; D008247:Lysosomes; D008565:Membrane Proteins / Q000378:metabolism; D009363:Neoplasm Proteins / Q000378:metabolism; D015388:Organelles / Q000201:enzymology*; D011498:Protein Precursors / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017527:Receptor, IGF Type 2 / Q000032:analysis; D014407:Tumor Cells, Cultured
D015415:Biomarkers; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D011498:Protein Precursors; D017527:Receptor, IGF Type 2; D002402:Cathepsin D