Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) in combination with a chemotherapeutic agent, cis-diammine dichloroplatinum (CDDP) or doxorubicin (DXR), has recently been demonstrated to result in enhanced apoptotic cell death in the sarcoma cell lines MG-63 and SaOS-2. DNA-damaging agents, such as CDDP induced sustained activation of c-Jun N-terminal kinase (JNK), probably leading to apoptosis. In the present study, whether JNK activation is involved in apoptotic cell death induced by combined treatment with CDDP/DXR and TRAIL was addressed.
MG-63 or SaOS-2 cells overexpressing the dominant-negative (dn) form of JNK (dnJNK1) were established by transfection with dnJNK1 cDNA. Following stimulation with the chemotherapeutic agent CDDP or TRAIL, both MG-63 and SaOS-2 cells demonstrated enhanced cell death compared with stimulation by either agent alone, as assayed for apoptosis using annexin V staining or mitochondrial membrane potential using DiOC6 staining. Interestingly, partial inhibition of the cell death induced by the combined treatment with CDDP/DXR and TRAIL was found in MG-63 or SaOS-2 cells overexpressing dnJNK1, suggesting that JNK activation is required for the combined treatment. Moreover, induction of caspase-8 activation by TRAIL or TRAIL plus CDDP/DXR was substantially prevented by dnJNK.
Efficient cell death induced by combined treatment with the chemotherapeutic agents CDDP/DXR and TRAIL is involved in JNK activation in the sarcoma cell lines MG-63 and SaOS-2. These results would be useful for treatment modalities of patients with sarcoma.