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)

Molecular heterogeneity of fibronectins (FNs) isolated from plasma, cultured fibroblasts, and placenta was studied with site-specific antibodies recognizing alternatively spliced peptide segments, termed ED-A and IIICS/delta 2. The antibodies were raised in rabbits by immunization with synthetic peptides. Neither the ED-A nor the IIICS/delta 2 extra peptide segment was present in the major subunits of plasma FN, although a minor subunit contained the latter extra segment. Cellular FN consisted of at least four subunits differing in size of the fragments generated by cleavage of the C-terminal region with cathepsin D. These fragments were distinct from each other in the reactivity with anti-ED-A and anti-IIICS/delta 2 antibodies, suggesting that all combinations of the presence or absence of the extra segments were produced by cultured fibroblasts. Placental FN was more heterogeneous than plasma and cellular FNs, consisting of five, or probably more, subunits. Among these, the two smaller subunits appeared to be closely similar to the major subunits of plasma FN, whereas the other subunits were more related to those of cellular FN in the size of cathepsin D cleaved C-terminal fragments and in the reactivity with anti-peptide antibodies. These results, taken together, indicate that the FNs produced by different tissues or cell types are distinct from each other in the number and types of subunits, which are partly, if not all, defined by alternative splicing at the ED-A and IIICS regions.
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PMID:Probing molecular polymorphism of fibronectins with antibodies directed to the alternatively spliced peptide segments. 274 38

The alternatively spliced type III connecting segment (IIICS) of fibronectin (Fn) contains an amino acid sequence, CS-1, which is recognized by the integrin receptor, alpha 4 beta 1. Plasma Fn inhibits alpha 4 beta 1-dependent binding of lymphocytes and monocytes to CS-1 containing Fn derivatives poorly, suggesting limited exposure of the CS-1 sequence in Fn. To test the availability of CS-1 in plasma Fn, an antibody was raised to the synthetic peptide CS-1. The CS-1 sequence was found to be minimally exposed in plasma Fn; and immobilization of Fn, a model of matrix deposition, caused only a modest increase in its exposure. Digestion of Fn with selected proteases, however, induced substantial expression of the CS-1 sequence. The acid protease cathepsin D generated fragments of 31-33.5 kDa from the COOH-terminal heparin-binding domain of Fn which possessed high immunoreactivity with anti-CS-1. Digestion of Fn with cathepsin B also resulted in the exposure of CS-1 sequence in a 140 kDa fragment. Although the digestion of Fn with neutral proteases (neutrophil elastase, cathepsin G, chymotrypsin, trypsin) generated fragments from the COOH-terminal heparin-binding domain of similar molecular weight as with cathepsin D, the exposure of CS-1 did not occur. Exposure of the CS-1 region by the cathepsins was supported by cell adhesion experiments; digestion of Fn with cathepsins D and B transformed inert plasma Fn to an effective inhibitor of adhesion of lymphoblastoid B and T cells (Ramos, Jurkat, Molt-4) to an immobilized CS-1 conjugate. These results suggest that exposure of the CS-1 sequence in plasma Fn by proteolysis with cathepsins D and B, enzymes implicated in several pathological processes, may serve a regulatory function in cell adhesion. The adhesive function of the CS-1 region in intact Fn appears to be suppressed by the native conformation of the molecule.
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PMID:Proteolysis regulates exposure of the IIICS-1 adhesive sequence in plasma fibronectin. 871 84

Alternative splicing of precursor mRNA is a fundamental mechanism to generate multiple proteins from a single gene. Although constitutive and alternative mRNA splicing is temporally and spatially regulated, deregulation of mRNA splicing could cause development, progression, and metastasis of tumors. Through yeast two-hybrid screening of a human breast cDNA library using estrogen receptor-alpha (ERalpha) as bait, we identified a novel nuclear receptor box containing full-length protein, nuclear protein E3-3 (NPE3-3). Our results revealed that NPE3-3 associates with not only ERalpha but also with splicing factors, serine/arginine-rich protein (SRp)-30c, SRp40, and splicing factor SC-35, suggesting that NPE3-3 is likely to be involved in regulation of mRNA splicing. Accordingly, transient expression of NPE3-3 in cells resulted in expected splicing of the CD44 control minigene. We also discovered that NPE3-3-overexpressing clones produced a novel, previously unrecognized, alternatively spliced variant of ERalpha (termed ERalphaV), which had a molecular size of 37 kDa composed of only exons 1, 2, 7, and 8. ERalphaV was expressed and sequestered in the cytoplasm in MCF-7 cells stably overexpressing NPE3-3, suggesting its involvement in nongenomic hormone signaling. NPE3-3 clones exhibited up-regulation of ERK1/2 signaling, cyclin D1, and cathepsin D and enhanced tumor cell proliferation, migration, and tumorigenicity. Moreover, direct expression of the ERalphaV in breast cancer cells stimulated ERK1/2 up-regulation and cyclin D1 expression. We found that ERalphaV physically interacted with MAPK kinase (MEK)-1/2, and thus, an ERalphaV and MEK1/2 complex could lead to the activation of the ERK1/2 pathway. Interestingly, NPE3-3 was up-regulated in human breast tumors. These findings revealed a role for NPE3-3 in alternative splicing and suggest that ERalpha is a physiological target of NPE3-3, leading to a constitutive nongenomic signaling pathway in breast cancer cells.
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PMID:Identification of a novel estrogen receptor-alpha variant and its upstream splicing regulator. 2030 96