Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.23.5 (cathepsin D)
 4,130 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have investigated the effect of a glycosylphosphatidylinositol anchor on the distribution of the soluble lysosomal enzyme cathepsin D. Only 10% of the chimeric protein (CD-GPI) could be detected on the plasma membrane after transfection in CHO cells. Similarly to endogenous cathepsin D, intracellular CD-GPI was detected in vesicular structures, suggesting that CD-GPI is targeted to lysosomes. CD-GPI is present as three forms with M(r) 55, 50 and 37 kD which could correspond to the precursor, intermediate and mature forms of cathepsin D, respectively. CD-GPI was shown to be GPI anchored by differential extractability with Triton X-114 before and after phosphatidylinositol phospholipase C hydrolysis. Intracellular CD-GPI is mainly substituted with oligosaccharides containing uncovered mannose 6-phosphate residues whereas these residues are covered in the cell surface precursor form of CD-GPI. Ammonium chloride treatment reduces the lysosomal delivery of CD-GPI and increases the cell surface expression of its precursor form.
 ...
PMID:Localization and processing of glycosylphosphatidylinositol anchored cathepsin D. 759 25

Both freshly-isolated rat hepatocytes and Morris hepatoma 7777 cells synthesized cathepsin D as a precursor that was either processed intracellular to smaller mature forms or secreted into the medium. The pattern of mature enzyme forms was different in the 2 cell types. In addition, the relative amount of precursor secreted was much higher for hepatoma cells. Monensin strongly enhanced the secretion and also impaired the intracellular transport-linked maturation of procathepsin D in hepatocytes, while it markedly inhibited intracellular maturation and only slightly increased secretion of the pro-enzyme in hepatoma cells. Ammonium chloride influenced the intralysosomal segregation and maturation of procathepsin D in hepatocytes but not in hepatoma cells. Our observations indicate that (i) the lysosomal segregation of cathepsin D was less efficient and its fractional secretion higher in hepatoma cells than in hepatocytes; (ii) in the 2 cell types, delivery to lysosomes and processing of procathepsin D were differently sensitive to increases in the vacuolar pH.
 ...
PMID:Altered intracellular processing and enhanced secretion of procathepsin D in a highly deviated rat hepatoma. 781 53

Synthesis, processing and sorting of pro-cathepsin D (proCD), the precursor of a lysosomal protease involved in tumor-cell proliferation and invasion, were compared in various human tumor cell lines. In cultures of HepG2, HT29 and MCF7 cells the extracellular CD activity was up to 10 times higher than in cultures of U937 and MG63 cells. Ammonium chloride, which disrupts the pH-dependent receptor-mediated transport of lysosomal enzymes, exerted a differential effect on the secretion of CD activity in these cells. As judged by metabolic labeling and immunoprecipitation, the secretion of CD synthesized in 24 hr in MG63 and U937 cells was enhanced 4- to 10-fold by ammonium chloride, while it was only slightly increased in HepG2, HT29 and MCF7 cells. In all tumor cells examined, a portion of proCD was segregated into the endosomal-lysosomal pathway in the presence of ammonium chloride. However, the intralysosomal maturation of CD was only inhibited by this drug in HT29 and MCF7 cells. The Golgi-associated processing of proCD, leading to the synthesis of uncovered phosphomannosyl groups, proceeded with comparable efficiency in all tumor cells examined. These results suggest that hypersecretion of proCD in HepG2, HT29 and MCF7 cells is linked to transport mechanisms, as yet unidentified, which are independent of mannose-6-phosphate.
 ...
PMID:Mis-sorting of procathepsin D in metastogenic tumor cells is not due to impaired synthesis of the phosphomannosyl signal. 905 56

BHK cells transfected with human cathepsin D (CD) cDNA normally segregate the autologous hamster cathepsin D while secreting a large proportion of the human proenzyme. In the present work, we have utilized these transfectants to examine to what extent the mannose-6-phosphate-dependent pathway for lysosomal enzyme segregation contributes to the differential sorting of human and hamster CD. We report that, in recipient control BHK cells, the rate of mannose-6-phosphate-dependent endocytosis of human procathepsin D secreted by transfected BHK cells is lower than that of hamster procathepsin D and much lower than that of human arylsulphatase A. The missorted human enzyme bears phosphorylated oligosaccharides and most of its phosphate residues are "uncovered", like the autologous enzyme. Thus, despite both the Golgi-associated modifications of oligosaccharides, i.e. the phosphorylation of mannose and the uncovering of mannose-6-phosphate residues, which proceed on human and hamster procathepsin D with comparable efficiency, only the latter is accurately packaged into lysosomes. Ammonium chloride partially affects the lysosomal targeting of cathepsin D in control BHK cells, whereas in transfected cells, this drug strongly inhibits the maturation of human procathepsin D and slightly enhances its secretion. These data indicate that: (1) over-expression of a lysosomal protein does not saturate the Golgi-associated reactions leading to the synthesis of mannose-6-phosphate; (2) a portion of cathepsin D is targeted independently of mannose-6-phosphate receptors in the transfected BHK cells; and (3) whichever mechanism for lysosomal delivery of autologous procathepsin D is involved, this is not saturated by the high rate of expression of human cathepsin D.
 ...
PMID:Human and hamster procathepsin D, although equally tagged with mannose-6-phosphate, are differentially targeted to lysosomes in transfected BHK cells. 956 Apr 73