[Inhibition of caspase-9 activity in cisplatin-resistant head and neck squamous cell carcinoma].
We have previously reported that cisplatin induces caspase-9 activation in head and neck squamous cell carcinoma cells (HNSCCs) in vitro, and the use of a specific inhibitor of caspase-9 blocks cisplatin-induced apoptosis in HNSCCs. Our purpose here was to determine whether HNSCCs selected for resistance to cisplatin fail to exhibit caspase-9 activation in response to cisplatin. Cisplatin-resistant HNSCCs (CRHNSCCs) were selected for growth in the presence of cisplatin. Following cisplatin treatment, no protelyzed caspase-9 subunits were detected in the CRHNSCCs, whereas proteolytic degradation of procaspase-9 was observed in parental cisplatin-sensitive HNSCCs (CSHNSCCs). Using a direct enzymatic assay measuring cleavage of the synthetic peptide substrate (LEHD-AFC), caspase-9 activity in cisplatin-treated CRHNSCCs was less than that in cisplatin-treated CSHNSCCs. Because caspase-9 activation requires the release of mitochondorial cytochrome c (Cyt c) into the cytoplasm, we determined the level of cytoplasmic Cyt c in response to cisplatin treatment. Interestingly, following cisplatin treatment, the same extent of increase in cytoplasmic Cyt c was evident and the expression of Bcl-2 family proteins (Bcl-2 and Bcl-XL) remained unchanged in both CRHNSCCs and CSHNSCCs. These results suggest that in certain HNSCC cell types, inhibition of caspase-9 activity represents another mechanism of acquired cisplatin resistance. This inhibition mechanism may be independent of the release of Cyt c into the cytoplasm.
Kuwahara
Daisuke
D
Department of Otolaryngology, St. Marianna University School of Medicine, Kawasaki.
Tsutsumi
Kouichiro
K
Kobayashi
Takehiko
T
Hyoudou
Makoto
M
Koizuka
Izumi
I
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002294:Carcinoma, Squamous Cell / Q000201:enzymology* / Q000473:pathology; D053453:Caspase 9; D061945:Caspase Inhibitors; D002945:Cisplatin / Q000494:pharmacology*; D003574:Cytochrome c Group / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D006258:Head and Neck Neoplasms / Q000201:enzymology* / Q000473:pathology; D006801:Humans; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D061945:Caspase Inhibitors; D003574:Cytochrome c Group; C506433:CASP9 protein, human; D053453:Caspase 9; D002945:Cisplatin