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)

The transport of proteins from the secretory to the endocytic pathway is mediated by carrier vesicles coated with the AP-1 Golgi assembly proteins and clathrin. The mannose 6-phosphate receptors (MPHs) are two major transmembrane proteins segregated into these transport vesicles. Together with the GTPase ARF-1, these cargo proteins are essential components for the efficient translocation of the cytosolic AP-1 onto membranes of the trans-Golgi network, the first step of clathrin coat assembly, MPR-negative fibroblasts have a low capacity of recruiting AP-1 which can be restored by re-expressing the MPRs in these cells. This property was used to identify the protein motif of the cation-dependent mannose 6-phosphate receptor (CD-MPR) cytoplasmic domain that is essential for these interactions. Thus, the affinity of AP-1 for membranes and in vivo transport of cathepsin D were measured for MPR-negative cells re-expressing various CD-MPR mutants. The results indicate that the targeting of lysosomal enzymes requires the CD-PDR cytoplasmic domain that are different from tyrosine-based endocytosis motifs. The first is a casein kinase II phosphorylation site (ESEER) that is essential for high affinity binding of AP-1 and therefore probably acts as a dominant determinant controlling CD-MPR sorting in the trans-Golgi network. The second is the adjacent di-leucine motif (HLLPM), which, by itself, is not critical for AP-1 binding, but is absolutely required for a downstream sorting event.
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PMID:A casein kinase II phosphorylation site in the cytoplasmic domain of the cation-dependent mannose 6-phosphate receptor determines the high affinity interaction of the AP-1 Golgi assembly proteins with membranes. 856 75

The GGAs (Golgi-localizing, gamma-adaptin ear homology domain, ARF-binding) are a multidomain family of proteins implicated in protein trafficking between the Golgi and endosomes. Recent evidence has established that the cation-independent (CI) and cation-dependent (CD) mannose 6-phosphate receptors (MPRs) bind specifically to the VHS domains of the GGAs through acidic cluster-dileucine motifs at the carboxyl ends of their cytoplasmic tails. However, the CD-MPR binds the VHS domains more weakly than the CI-MPR. Alignment of the C-terminal residues of the two receptors revealed a number of non-conservative differences in the acidic cluster-dileucine motifs and the flanking residues. Mutation of these residues in the CD-MPR cytoplasmic tail to the corresponding residues in the CI-MPR conferred either full binding (H63D mutant), intermediate binding (R60S), or unchanged binding (E56F/S57H) to the GGAs as determined by in vitro glutathione S-transferase pull-down assays. Furthermore, the C-terminal methionine of the CD-MPR, but not the C-terminal valine of the CI-MPR, inhibited GGA binding. Addition of four alanines to the C-terminal valine of the CI-MPR also severely reduced GGA binding, demonstrating the importance of the spacing of the acidic cluster-dileucine motif relative to the C terminus for optimal GGA interaction. Mouse L cells stably expressing CD-MPRs with mutations that enhance GGA binding sorted cathepsin D more efficiently than wild-type CD-MPR. These studies provide an explanation for the observed differences in the relative affinities of the two MPRs for the GGA proteins. Furthermore, they indicate that the GGAs participate in lysosomal enzyme sorting mediated by the CD-MPR.
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PMID:Interaction of the cation-dependent mannose 6-phosphate receptor with GGA proteins. 1188 74

We have used GST pulldowns from A431 cell cytosol to identify three new binding partners for the gamma-adaptin appendage: Snx9, ARF GAP1, and a novel ENTH domain-containing protein, epsinR. EpsinR is a highly conserved protein that colocalizes with AP-1 and is enriched in purified clathrin-coated vesicles. However, it does not require AP-1 to get onto membranes and remains membrane-associated in AP-1-deficient cells. Moreover, although epsinR binds AP-1 via its COOH-terminal domain, its NH(2)-terminal ENTH domain can be independently recruited onto membranes, both in vivo and in vitro. Brefeldin A causes epsinR to redistribute into the cytosol, and recruitment of the ENTH domain requires GTPgammaS, indicating that membrane association is ARF dependent. In protein-lipid overlay assays, the epsinR ENTH domain binds to PtdIns(4)P, suggesting a possible mechanism for ARF-dependent recruitment onto TGN membranes. When epsinR is depleted from cells by RNAi, cathepsin D is still correctly processed intracellularly to the mature form. This indicates that although epsinR is likely to be an important component of the AP-1 network, it is not necessary for the sorting of lysosomal enzymes.
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PMID:EpsinR: an ENTH domain-containing protein that interacts with AP-1. 1258 59

Three mammalian GGAs (Golgi-localized, gamma-ear-containing, ARF-binding proteins), GGA1, 2, and 3 have been implicated in the sorting of mannose 6-phosphate receptor (MPR). To investigate the distinct roles of GGA2 in lysosomal enzyme transport, we established two stable cell lines that had a reduced expression of GGA2 by RNA interference. The expression levels of GGA2 were approximately 5% of the control levels, whereas those of non-targeted GGA1 and GGA3 were not apparently reduced. The depletion of GGA2 did not cause changes in the overall distribution of GGA1, GGA3, cation-dependent MPR, or cation-independent MPR. However, the cell lines showed increased secretion of a lysosomal enzyme, cathepsin D. In addition, a moderate expression of the dominant negative VHS-GAT domain of GGA2 had no effect on the trans-Golgi network (TGN) signal of three GGAs, nor was the GGA2 signal affected by the expression of VHS-GAT domain of GGA1 or 3. These results suggest that GGA2 is recruited to the TGN independently of the other GGAs and is required for the efficient sorting of lysosomal enzymes.
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PMID:Specific depletion of GGA2 causes cathepsin D missorting in HeLa cells. 1843 Oct 31