title: The proteasome regulates caspase-dependent and caspase-independent protease cascades during apoptosis of MO7e hematopoietic progenitor cells.
abstract: Withdrawal of trophic support from growth factor-dependent MO7e human myeloid progenitor cells induces apoptosis characterized by DNA fragmentation and degradation of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs). Inhibitors of caspase (ICE) protease family members did not inhibit apoptosis or DNA fragmentation induced by factor withdrawal, but blocked degradation of DNA-PKcs. Thus, caspase activity accounts for only a component of the apoptotic program in MO7e hematopoietic cells. The protease inhibitor TPCK, but not other protease inhibitors, blocked DNA fragmentation, but not degradation of DNA-PKcs during apoptosis of MO7e cells. Thus, caspase-independent and caspase-dependent protease cascades mediate distinct features of MO7e cell apoptosis. The proteasome inhibitors calpain inhibitor I and lactacystin promoted DNA fragmentation, degradation of DNA-PKcs and apoptosis of MO7e cells. The ability of lactacystin to promote DNA fragmentation was abrogated by TPCK, but not by caspase inhibitors, whereas the ability of lactacystin to promote degradation of DNA-PKcs was blocked by caspase inhibitors, but not by TPCK. Thus, caspase-dependent and caspase-independent protease cascades are downstream of and regulated by the proteasome, which plays a central role in regulating the multiple protease cascades that induce apoptosis.
authors.affiliation: Department of Microbiology and Immunology and the Walther Oncology Center, Indiana University School of Medicine, Indianapolis 46202, USA.
authors.forename: L W
authors.initials: LW
authors.lastname: Wu
authors.forename: S
authors.initials: S
authors.lastname: Reid
authors.forename: A
authors.initials: A
authors.lastname: Ritchie
authors.forename: H E
authors.initials: HE
authors.lastname: Broxmeyer
authors.forename: D B
authors.initials: DB
authors.lastname: Donner
mesh_terms: D017209:Apoptosis; D020169:Caspases / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D006412:Hematopoietic Stem Cells / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D009097:Multienzyme Complexes / Q000378:metabolism*; D009687:Nuclear Proteins; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
chemical_list: D004268:DNA-Binding Proteins; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex