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)

Aftiphilin is a protein that was recently identified in database searches for proteins with motifs that interact with AP-1 and clathrin, but its function is unknown. Here we demonstrate that aftiphilin has a second, atypical clathrin binding site, YQW, that colocalizes with AP-1 by immunofluorescence, and that is enriched in clathrin-coated vesicles (CCVs), confirming that it is a bona fide component of the CCV machinery. By gel filtration, aftiphilin coelutes with two other AP-1 binding partners, p200a and gamma-synergin. Antibodies against any one of these three proteins immunoprecipitate the other two, and knocking down any of the three proteins by siRNA causes a reduction in the levels of the other two, indicating that they form a stable complex. Like AP-1-depleted cells, aftiphilin-depleted cells missort a CD8-furin chimera and the lysosomal enzyme cathepsin D. However, whereas AP-1-depleted cells recycle endocytosed transferrin more slowly than untreated cells, aftiphilin-depleted cells accumulate endocytosed transferrin in a peripheral compartment and recycle it more rapidly. These observations show that in general, the aftiphilin/p200/gamma-synergin complex facilitates AP-1 function, but the complex may have additional functions as well, because of the opposing effects of the two knockdowns on transferrin recycling.
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PMID:The aftiphilin/p200/gamma-synergin complex. 1575 25

A detailed proteolysis study of internalized diphtheria toxin (DT) within rat liver endosomes was undertaken to determine whether DT-resistant species exhibit defects in toxin endocytosis, toxin activation by cellular enzymes or toxin translocation to its cytosolic target. Following administration of a saturating dose of wild-type DT or nontoxic mutant DT (mDT) to rats, rapid endocytosis of the intact 62-kDa toxin was observed coincident with the endosomal association of DT-A (low association) and DT-B (high association) subunits. Assessment of the subsequent post-endosomal fate of internalized mDT revealed a sustained endo-lysosomal transfer of the mDT-B subunit accompanied by a net decrease in intact mDT and mDT-A subunit throughout the endo-lysosomal apparatus. In vitro proteolysis of DT, using an endosomal lysate, was observed at both neutral and acidic pH, with the subsequent generation of DT-A and DT-B subunits (pH 7) or DT fragments with low ADP-ribosyltransferase activity (pH 4). Biochemical characterization revealed that the neutral endosomal DT-degrading activity was due to a novel luminal 70-kDa furin enzyme, whereas the aspartic acid protease cathepsin D (EC 3.4.23.5) was identified as being responsible for toxin degradation at acidic pH. Moreover, an absence of in vivo association of the DT-A subunit with cytosolic fractions was identified, as well as an absence of in vitro translocation of the DT-A subunit from cell-free endosomes into the external milieu. Based on these findings, we propose that, in rat, resistance to DT may originate from two different mechanisms: the ability of free DT-A subunits to be rapidly proteolyzed by acidic cathepsin D within the endosomal lumen, and/or the absence of DT translocation across the endosomal membrane, which may arise from the absence of a functional cytosolic translocation factor previously reported to participate in the export of DT from human endosomes.
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PMID:Endosomal proteolysis of diphtheria toxin without toxin translocation into the cytosol of rat liver in vivo. 1831 97

The ubiquitin proteasome system is central to the regulation of a number of intracellular sorting pathways in mammalian cells including quality control at the endoplasmic reticulum and the internalization and endosomal sorting of cell surface receptors. Here we describe that RNF126, an E3 ubiquitin ligase, is involved in the sorting of the cation-independent mannose 6-phosphate receptor (CI-MPR). In cells transiently depleted of RNF126, the CI-MPR is dispersed into Rab4 positive endosomes and the efficiency of retrograde sorting is delayed. Furthermore, the stable knockdown of RNF126 leads to the lysosomal degradation of CI-MPR and missorting of cathepsin D. RNF126 specifically regulates the sorting of the CI-MPR as other cargo that follow the retrograde sorting route including the cholera toxin, furin and TGN38 are unaffected in the absence of RNF126. Lastly we show that the RING finger domain of RNF126 is required to rescue the decrease in CI-MPR levels, suggesting that the ubiquitin ligase activity of RNF126 is required for CI-MPR sorting. Together, our data indicate that the ubiquitin ligase RNF126 has a role in the retrograde sorting of the CI-MPR.
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PMID:The ubiquitin ligase RNF126 regulates the retrograde sorting of the cation-independent mannose 6-phosphate receptor. 2427 55