title: Caspase-8 and caspase-7 sequentially mediate proteolytic activation of acid sphingomyelinase in TNF-R1 receptosomes.
abstract: We previously demonstrated that tumour necrosis factor (TNF)-induced ceramide production by endosomal acid sphingomyelinase (A-SMase) couples to apoptosis signalling via activation of cathepsin D and cleavage of Bid, resulting in caspase-9 and caspase-3 activation. The mechanism of TNF-mediated A-SMase activation within the endolysosomal compartment is poorly defined. Here, we show that TNF-induced A-SMase activation depends on functional caspase-8 and caspase-7 expression. The active forms of all three enzymes, caspase-8, caspase-7 and A-SMase, but not caspase-3, colocalize in internalized TNF receptosomes. While caspase-8 and caspase-3 are unable to induce activation of purified pro-A-SMase, we found that caspase-7 mediates A-SMase activation by direct interaction resulting in proteolytic cleavage of the 72-kDa pro-A-SMase zymogen at the non-canonical cleavage site after aspartate 253, generating an active 57 kDa A-SMase molecule. Caspase-7 down modulation revealed the functional link between caspase-7 and A-SMase, confirming proteolytic cleavage as one further mode of A-SMase activation. Our data suggest a signalling cascade within TNF receptosomes involving sequential activation of caspase-8 and caspase-7 for induction of A-SMase activation by proteolytic cleavage of pro-A-SMase.
authors.affiliation: Institute of Immunology, Christian-Albrechts-University of Kiel, Kiel, Germany.
authors.forename: Bärbel
authors.initials: B
authors.lastname: Edelmann
authors.forename: Uwe
authors.initials: U
authors.lastname: Bertsch
authors.forename: Vladimir
authors.initials: V
authors.lastname: Tchikov
authors.forename: Supandi
authors.initials: S
authors.lastname: Winoto-Morbach
authors.forename: Cristiana
authors.initials: C
authors.lastname: Perrotta
authors.forename: Marten
authors.initials: M
authors.lastname: Jakob
authors.forename: Sabine
authors.initials: S
authors.lastname: Adam-Klages
authors.forename: Dieter
authors.initials: D
authors.lastname: Kabelitz
authors.forename: Stefan
authors.initials: S
authors.lastname: Schütze
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D053179:Caspase 7 / Q000378:metabolism*; D053181:Caspase 8 / Q000378:metabolism*; D002460:Cell Line; D002518:Ceramides / Q000378:metabolism; D002855:Chromatography, Thin Layer; D003001:Cloning, Molecular; D011992:Endosomes / Q000378:metabolism*; D004789:Enzyme Activation / Q000235:genetics / Q000502:physiology*; D005434:Flow Cytometry; D055785:Gene Knockdown Techniques; D006801:Humans; D019169:Jurkat Cells; D051379:Mice; D018613:Microscopy, Confocal; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D002518:Ceramides; D014409:Tumor Necrosis Factor-alpha; C112980:acid sphingomyelinase-1; D013108:Sphingomyelin Phosphodiesterase; D053179:Caspase 7; D053181:Caspase 8