Cathepsin D links TNF-induced acid sphingomyelinase to Bid-mediated caspase-9 and -3 activation.
Acidic noncaspase proteases-like cathepsins have been introduced as novel mediators of apoptosis. A clear role for these proteases and the acidic endolysosomal compartment in apoptotic signalling is not yet defined. To understand the role and significance of noncaspases in promoting and mediating cell death, it is important to determine whether an intersection of these proteases and the caspase pathway exists. We recently identified the endolysosomal aspartate protease cathepsin D (CTSD) as a target for the proapoptotic lipid ceramide. Here, we show that tumor necrosis factor (TNF)-induced CTSD activation depends on functional acid sphingomyelinase (A-SMase) expression. Ectopic expression of CTSD in CTSD-deficient fibroblasts results in an enhanced TNF-mediated apoptotic response. Intracellular colocalization of CTSD with the proapoptotic bcl-2 protein family member Bid in HeLa cells, and the ability of CTSD to cleave directly Bid in vitro as well as the lack of Bid activation in cathepsin-deficient fibroblasts indicate that Bid represents a direct downstream target of CTSD. Costaining of CTSD and Bid with Rab5 suggests that the endosomal compartments are the common 'meeting point'. Caspase-9 and -3 activation also was in part dependent on A-SMase and CTSD expression as revealed in the respective deficiency models. Our results link as novel endosomal intermediates the A-SMase and the acid aspartate protease CTSD to the mitochondrial apoptotic TNF pathway.
Heinrich
M
M
Institute of Immunology, University of Kiel, Kiel D-24105, Germany.
Neumeyer
J
J
Jakob
M
M
Hallas
C
C
Tchikov
V
V
Winoto-Morbach
S
S
Wickel
M
M
Schneider-Brachert
W
W
Trauzold
A
A
Hethke
A
A
Schütze
S
S
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism*; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D002402:Cathepsin D / Q000378:metabolism*; D002478:Cells, Cultured; D002518:Ceramides / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; C494815:Bid protein, mouse; D002352:Carrier Proteins; D002518:Ceramides; D014409:Tumor Necrosis Factor-alpha; D013108:Sphingomyelin Phosphodiesterase; C505407:CASP3 protein, human; C506433:CASP9 protein, human; C505409:Casp3 protein, mouse; C506434:Casp9 protein, mouse; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D002402:Cathepsin D