Cathepsin B mediates TRAIL-induced apoptosis in oral cancer cells.
OBJECTIVE
The death ligand TRAIL (tumor necrosis factor-related apoptosis inducing ligand) triggers apoptosis in a variety of cancer cells, which implies the potential for therapeutic applications. The purpose of this study was to investigate the role of the lysosomal protease cathepsin B (CB) in mediating TRAIL-induced cell death in oral squamous cell carcinoma (OSCC) cells.


METHODS
OSCC cell lines from primary tumor and lymph node metastasis were examined for expression of apoptosis markers by Western blots, enzyme activity assays, nuclear fragmentation assays, and FACS analysis. Gene-specific ribozymes or chemical inhibitors were used to inhibit CB or caspases in target cells.


RESULTS
TRAIL-induced activation of caspase-3, cleavage of Bid and poly-ADP-ribose polymerase, release of cytochrome c, and DNA fragmentation were blocked either by a pan-caspase inhibitor (zVAD-fmk) or a CB inhibitor (CA074Me), consistent with the involvement of TRAIL as well as CB in cell death. The primary tumor cells were more susceptible to apoptosis than their corresponding lymph node metastatic cells. Stable transfection of a ribozyme which inhibited CB expression also decreased the apoptotic process.


CONCLUSIONS
We conclude that TRAIL-induced apoptotic cell death in OSCC cells is mediated through CB or through caspase activation. Our data point to a new tumor-suppressive role for CB in OSCC which is opposed to the invasion- and metastasis-promoting functions of lysosomal proteases.
Nagaraj
Nagathihalli S
NS
Department of Medicine, James Graham Brown Cancer Center, University of Louisville, Louisville, KY 40202, USA.
Vigneswaran
Nadarajah
N
Zacharias
Wolfgang
W
D000368:Aged; D017209:Apoptosis / Q000502:physiology*; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000473:pathology*; D002401:Cathepsin B / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D020287:In Situ Nick-End Labeling; D008297:Male; D009062:Mouth Neoplasms / Q000378:metabolism / Q000473:pathology*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D053221:TNF-Related Apoptosis-Inducing Ligand; D002401:Cathepsin B