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)

Transforming growth factor-beta (TGF beta) is produced by most cultured cells in an inactive form. Potential activation mechanisms of latent TGF beta were studied using fibroblastic (NRK-49F and AKR-MCA) cell-conditioned medium as a model. Active TGF beta was monitored by radioreceptor and soft agar assays as well as by antibody inhibition and immunoprecipitation. Little or no TGF beta was detected in untreated conditioned medium. Treatment of the medium with extremes of pH (1.5 or 12) resulted in significant activation of TGF beta as shown by radioreceptor assays, while mild acid treatment (pH 4.5) yielded only 20-30% of the competition achieved by pH 1.5. In an effort to define more physiological means of TGF beta activation, the effects of some proteases were tested. Plasmin and cathepsin D were found to generate 25-kD bands corresponding to the active form of TGF beta as shown by immunoprecipitation analysis of radiolabeled cell-conditioned medium. Plasmin treatment of the medium resulted in activity that was quantitatively similar to that of mild acid treatment as measured by radioreceptor and soft agar assays. In addition, the plasmin-generated activity was inhibited by anti-TGF beta antibodies. Sequential treatments of AKR-MCA cell-conditioned medium with mild acid followed by plasmin or plasmin followed by mild acid gave activation comparable to either treatment alone. The data suggest that conditioned medium may contain at least two different pools of latent TGF beta. One pool is resistant to mild acid and/or plasmin and requires strong acid or alkali treatment for activation. A second pool is activated by mild pH change and/or plasmin. Activation of this form of latent TGF beta may take place by dissociation or proteolytic digestion from a precursor molecule or hypothetical TGF beta-binding protein complex.
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PMID:Proteolytic activation of latent transforming growth factor-beta from fibroblast-conditioned medium. 296 99

It has been shown that some types of tumour cells produce activated transforming growth factor beta-1 (TGF-beta 1). However, the mechanism for the activation of TGF-beta 1 derived from tumour cells has not been fully elucidated. The present study was undertaken to characterise an activator of latent TGF-beta 1 secreted from a human gastric cancer cell line, KATO-III. Western blot analyses using antibodies for TGF-beta 1, latency associated peptide (LAP) and latent TGF-beta 1-binding protein (LTBP) revealed that, in the cell lysate of KATO-III, TGF-beta 1 protein was expressed as a small latent complex of TGF-beta 1 and LAP. This was also confirmed by a gel chromatographic analysis of the cell lysate obtained from KATO-III. A 2.5 kb transcript of TGF-beta 1 mRNA was detected in KATO-III cells by Northern blot analysis. A gel chromatographic analysis of the conditioned medium from KATO-III cells revealed, in addition to the active form of TGF-beta 1, a factor which activated latent TGF-beta 1 from NRK-49F cells at fractions near a molecular size of 65,000. This factor was inactivated by heat (100 degrees C), acidification, trypsin and serine protease inhibitors. TGF-beta 1 activity in KATO-III cell lysate was not detected in the untreated state, but potent TGF-beta 1 activity was detected after acid treatment. These results suggest that KATO-III releases not only a latent TGF-beta 1 complex but also a type of serine protease, different from plasmin, plasminogen activator, cathepsin D, endoglycosidase F or sialidase, which activates the latent TGF-beta 1 complex as effectively as acid treatment.
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PMID:Identification of a transforming growth factor beta-1 activator derived from a human gastric cancer cell line. 766 80

Lysosomes are acidic intracellular compartments and are regarded as degradative and the end point, of the endocytic pathway. Here we provide evidence for the generation of acid hydrolase poor and non-acidic post-lysosomal compartments in NRK cells that have accumulated non-digestible macromolecules, Texas red-dextran (TR-Dex), within lysosomes. When TR-Dex was fed to the cells for 6h, most of the internalized TR-Dex colocalized with a lysosomal enzyme, cathepsin D. With an increase in the chase period, however, the internalized TR-Dex gradually accumulated in cathepsin D-negative vesicles. These vesicles were positive for a lysosomal membrane protein, LGP85, and their formation was inhibited by treatment of the cells with U18666A, which impairs membrane transport out of late endosomal/lysosomal compartments, thereby suggesting that the vesicles are derived from lysosomes. Interestingly, these compartments are non-acidic as judged for the DAMP staining. The results, therefore, suggest that the excess accumulation of non-digestible macromolecules within lysosomes induces the formation of acid hydrolase poor and non-acidic post-lysosomal compartments. The fact that treatment of the cells with lysosomotropic amines or a microtubule-depolymerization agent resulted in extensive colocalization of TR-Dex with cathepsin D further indicates that the formation of the post-lysosomal compartments depends on the lysosomal acidification and microtubule organization. Furthermore, these results suggest bi-directional membrane transport between lysosomes and the post-lysosomal compartments, which implies that the latter are not resting compartments.
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PMID:Analysis of post-lysosomal compartments. 1473 6