title: Proteasome activation as a critical event of thymocyte apoptosis.
abstract: Caspase activation may occur in a direct fashion as a result of CD95 death receptor crosslinking (exogenous pathway) or may be triggered indirectly, via a Bcl-2 inhibitable mitochondrial permeabilization event (endogenous pathway). Thymocyte apoptosis is generally accompanied by proteasome activation. If death is induced by DNA damage, inactivation of p53, overexpression of a Bcl-2 transgene, inhibition of protein synthesis, and antioxidants (N-acetylcyteine, catalase) prevent proteasome activation. Glucocorticoid-induced proteasome activation follows a similar pattern of inhibition except for p53. Caspase inhibition fails to affect proteasome activation induced by topoisomerase inhibition or glucocorticoid receptor ligation. In contrast, caspase activation (but not p53 knockout or Bcl-2 overexpression) does interfere with proteasome activation induced by CD95. Specific inhibition of proteasomes with lactacystin or MG123 blocks caspase activation at a pre-mitochondrial level if thymocyte apoptosis is induced by DNA damage or glucocorticoids. In strict contrast, proteasome inhibition has no inhibitory effect on the mitochondrial and nuclear phases of apoptosis induced via CD95. Thus, proteasome activation is a critical event of thymocyte apoptosis stimulated via the endogenous pathway yet dispensable for CD95-triggered death.
authors.affiliation: Centre National de la Recherche Scientifique, ERS1984, 19 rue Guy Môquet, F-94801 Villejuif, France.
authors.forename: B
authors.initials: B
authors.lastname: Dallaporta
authors.forename: M
authors.initials: M
authors.lastname: Pablo
authors.forename: C
authors.initials: C
authors.lastname: Maisse
authors.forename: E
authors.initials: E
authors.lastname: Daugas
authors.forename: M
authors.initials: M
authors.lastname: Loeffler
authors.forename: N
authors.initials: N
authors.lastname: Zamzami
authors.forename: G
authors.initials: G
authors.lastname: Kroemer
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002374:Catalase / Q000494:pharmacology; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000187:drug effects / Q000378:metabolism*; D003609:Dactinomycin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004789:Enzyme Activation; D005047:Etoposide / Q000494:pharmacology; D005260:Female; D051379:Mice; D008807:Mice, Inbred BALB C; D008928:Mitochondria / Q000378:metabolism; D009097:Multienzyme Complexes / Q000187:drug effects / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D019014:fas Receptor / Q000502:physiology*
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D000975:Antioxidants; D061945:Caspase Inhibitors; D009097:Multienzyme Complexes; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; D003609:Dactinomycin; D005047:Etoposide; D003907:Dexamethasone; D002374:Catalase; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine