title: Cysteine cathepsins trigger caspase-dependent cell death through cleavage of bid and antiapoptotic Bcl-2 homologues.
abstract: As a model for defining the role of lysosomal cathepsins in apoptosis, we characterized the action of the lysosomotropic agent LeuLeuOMe using distinct cellular models. LeuLeuOMe induces lysosomal membrane permeabilization, resulting in release of lysosomal cathepsins that cleave the proapoptotic Bcl-2 family member Bid and degrade the antiapoptotic member Bcl-2, Bcl-xL, or Mcl-1. The papain-like cysteine protease inhibitor E-64d largely prevented apoptosis, Bid cleavage, and Bcl-2/Bcl-xL/Mcl-1 degradation. The pancaspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(OMe)fluoromethyl ketone failed to prevent Bid cleavage and degradation of anti-apoptotic Bcl-2 homologues but substantially decreased cell death, suggesting that cathepsin-mediated apoptosis in these cellular models mostly follows a caspase-dependent pathway. Moreover, in vitro experiments showed that one or more of the cysteine cathepsins B, L, S, K, and H could cleave Bcl-2, Bcl-xL, Mcl-1, Bak, and BimEL, whereas no Bax cleavage was observed. On the basis of inhibitor studies, we demonstrate that lysosomal disruption triggered by LeuLeuOMe occurs before mitochondrial damage. We propose that degradation of anti-apoptotic Bcl-2 family members by lysosomal cathepsins synergizes with cathepsin-mediated activation of Bid to trigger a mitochondrial pathway to apoptosis. Moreover, XIAP (X-chromosome-linked inhibitor of apoptosis) was also found to be a target of cysteine cathepsins, suggesting that cathepsins can mediate caspase-dependent apoptosis also downstream of mitochondria.
authors.affiliation: Department of Biochemistry, Molecular and Structural Biology, J. Stefan Institute, Sl-1000 Ljubljana, Slovenia.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Droga-Mazovec
authors.forename: Lea
authors.initials: L
authors.lastname: Bojic
authors.forename: Ana
authors.initials: A
authors.lastname: Petelin
authors.forename: Saska
authors.initials: S
authors.lastname: Ivanova
authors.forename: Rok
authors.initials: R
authors.lastname: Romih
authors.forename: Urska
authors.initials: U
authors.lastname: Repnik
authors.forename: Guy S
authors.initials: GS
authors.lastname: Salvesen
authors.forename: Veronika
authors.initials: V
authors.lastname: Stoka
authors.forename: Vito
authors.initials: V
authors.lastname: Turk
authors.forename: Boris
authors.initials: B
authors.lastname: Turk
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D018938:Caco-2 Cells; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006801:Humans; D008247:Lysosomes / Q000201:enzymology*; D008565:Membrane Proteins / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D011480:Protease Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C494772:BAK1 protein, human; C494811:BCL2L1 protein, human; C000606775:BCL2L11 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D000072224:Bcl-2-Like Protein 11; D008565:Membrane Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D011480:Protease Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051020:bcl-X Protein; D002403:Cathepsins