title: Aspartic cathepsin D degrades the cytosolic cysteine cathepsin inhibitor stefin B in the cells.
abstract: Stefin B is the major general cytosolic protein inhibitor of cysteine cathepsins. Its main function is to protect the organism against the activity of endogenous potentially hazardous proteases accidentally released from lysosomes. In this study, we investigated the possible effect of endosomal/lysosomal aspartic cathepsins D and E on stefin B after membrane permeabilization. Loss of membrane integrity of lysosomes and endosomes was induced by a lysosomotropic agent L-Leucyl-L-leucine methyl ester (Leu-Leu-OMe). The rat thyroid cell line FRTL-5 was selected as a model cell line owing to its high levels of proteases, including cathepsin D and E. Permeabilization of acid vesicles from FRTL-5 cells induced degradation of stefin B. The process was inhibited by pepstatin A, a potent inhibitor of aspartic proteases. However, degradation of stefin B was prevented by siRNA-mediated silencing of cathepsin D expression. In contrast, cathepsin E silencing had no effect on stefin B degradation. These results showed that cathepsin D and not cathepsin E degrades stefin B. It can be concluded that the presence of cathepsin D in the cytosol affects the inhibitory potency of stefin B, thus preventing the regulation of cysteine cathepsin activities in various biological processes.
authors.affiliation: Department of Biochemistry and Molecular and Structural Biology, J. Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Tajana Zajc
authors.initials: TZ
authors.lastname: Železnik
authors.affiliation: Department of Biochemistry and Molecular and Structural Biology, J. Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia; Jožef Stefan International Postgraduate School, Jamova 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Andrey
authors.initials: A
authors.lastname: Kadin
authors.affiliation: Department of Biochemistry and Molecular and Structural Biology, J. Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia; Jožef Stefan International Postgraduate School, Jamova 39, SI-1000 Ljubljana, Slovenia.
authors.forename: Vito
authors.initials: V
authors.lastname: Turk
authors.affiliation: Department of Biochemistry and Molecular and Structural Biology, J. Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia. Electronic address: iztok.dolenc@ijs.si.
authors.forename: Iztok
authors.initials: I
authors.lastname: Dolenc
mesh_terms: D000818:Animals; D002402:Cathepsin D / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020059:Cathepsin E / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002463:Cell Membrane Permeability / Q000187:drug effects; D055313:Cystatin B / Q000378:metabolism* / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology*; D004151:Dipeptides / Q000494:pharmacology; D011992:Endosomes / Q000187:drug effects / Q000201:enzymology; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D007694:Killer Cells, Natural / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D008247:Lysosomes / Q000187:drug effects / Q000201:enzymology; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D051379:Mice; D010436:Pepstatins / Q000494:pharmacology; D059748:Proteolysis / Q000187:drug effects; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051381:Rats; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects / Q000201:enzymology
chemical_list: D004151:Dipeptides; D010436:Pepstatins; D034741:RNA, Small Interfering; C045139:leucyl-leucine-methyl ester; D055313:Cystatin B; D020059:Cathepsin E; D002402:Cathepsin D; C031375:pepstatin
keywords: Cathepsin D; Cathepsin E; Endosomes; Lysosomes; Membrane permeabilization; Stefin B