Chrysanthemulide A induces apoptosis through DR5 upregulation via JNK‐mediated autophagosome accumulation in human osteosarcoma cells

Abstract Osteosarcoma is the most frequent malignant primary bone tumor, and it generally develops a multidrug resistance. Chrysanthemulide A (CA) is a sesquiterpenoid from the herb Chrysanthemum indicum that has demonstrated a great anti‐osteosarcoma potential. In this study, CA‐induced apoptotic cell death resulted in the activation of the caspase‐8‐mediated caspase cascade, as evidenced by the cleavage of the substrate protein Bid and the caspase‐8 inhibitor Z‐VAD‐FMK. The CA treatment upregulated the expression of death receptor 5 (DR5) in both whole cells and the cell membrane. Blocking DR5 expression by the small interfering RNA (siRNA) treatment decreased the caspase‐8‐mediated caspase cascade and efficiently attenuated CA‐induced apoptosis, suggesting the critical role of DR5 in CA‐induced apoptotic cell death. CA‐induced upregulation of the DR5 protein was accompanied by the accumulation of LC3B‐II, indicating the formation of autophagosomes. Importantly, DR5 upregulation was mediated by transcriptionally controlled autophagosome accumulation, as blockade of autophagosomes by LC3B or ATG‐5 siRNA substantially decreased DR5 upregulation. Furthermore, CA activated the c‐Jun N‐terminal kinase (JNK) signaling pathway, and treatment with JNK siRNAs or inhibitor SP600125 significantly attenuated CA‐mediated autophagosome accumulation and DR5‐mediated cell apoptosis. Finally, CA sensitized the osteosarcoma cells to the DR5 ligand tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL)‐induced apoptotic cell death. Above all, these results suggest that CA induces apoptosis through upregulating DR5 via JNK‐mediated autophagosome accumulation and that combined treatment with CA and TRAIL might be a promising therapy for osteosarcoma.