Overexpression of both catalytically active and -inactive cathepsin D by cancer cells enhances apoptosis-dependent chemo-sensitivity.
The aspartic protease cathepsin D (cath-D) is a key mediator of induced-apoptosis and its proteolytic activity has been generally involved in this event. During apoptosis, cath-D is translocated to the cytosol. Because cath-D is one of the lysosomal enzymes that requires a more acidic pH to be proteolytically active relative to the cysteine lysosomal enzymes such as cath-B and -L, it is therefore open to question whether cytosolic cath-D might be able to cleave substrate(s) implicated in the apoptotic cascade. Here, we have investigated the role of wild-type cath-D and its proteolytically inactive counterpart overexpressed by 3Y1-Ad12 cancer cells during chemotherapeutic-induced cytotoxicity and apoptosis, as well as the relevance of cath-D catalytic function. We demonstrate that wild-type or mutated catalytically inactive cath-D strongly enhances chemo-sensitivity and apoptotic response to etoposide. Both wild-type and mutated inactive cath-D are translocated to the cytosol, increasing the release of cytochrome c, the activation of caspases-9 and -3 and the induction of a caspase-dependent apoptosis. In addition, pretreatment of cells with the aspartic protease inhibitor, pepstatin A, does not prevent apoptosis. Interestingly therefore, the stimulatory effect of cath-D on cell death is independent of its catalytic activity. Overall, our results imply that cytosolic cath-D stimulates apoptotic pathways by interacting with a member of the apoptotic machinery rather than by cleaving specific substrate(s).
Beaujouin
M
M
INSERM U540 Endocrinologie Moléculaire et Cellulaire des Cancers, Université Montpellier 1, Montpellier, France.
Baghdiguian
S
S
Glondu-Lassis
M
M
Berchem
G
G
Liaudet-Coopman
E
E
D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002402:Cathepsin D / Q000096:biosynthesis*; D003600:Cytosol / Q000737:chemistry; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D006801:Humans; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D002402:Cathepsin D