on, prevention of ROS accumulation could inhibit the PARP cleavage in hirsutanol A treated cells. These data suggested that accumulation of ROS mediated hir sutanol A induced apoptosis. Hirsutanol A activated mitochondria cytochrome c signaling pathway To further study whether hirsutanol A induced apop tosis via activation of mitochondria cytochrome c signal ing pathway, we e amined the change of mitochondrial membrane potential and the release of cytochrome c from mitochondria. Mitochondrial membrane potential was elevated after treatment with various concentrations of hirsutanol A. The e pression of cyto chrome c in mitochondria was down regulated, whereas cytosolic cytochrome c was increased after treatment with hirsutanol A for 24 h.
These data revealed that hirsutanol A induced apoptosis through acti vation of mitochondria cytochrome c signaling pathway. Hirsutanol A activated JNK signaling pathway and AV-951 blockade of JNK signal pathway increased ROS level and cell apoptosis It has been reported that ROS can modulate several sig naling pathways including JNK, Akt, NF ��B etc. Therefore, we e plored the effect of increased ROS by hirsutanol A on JNK signaling pathway. JNK and c Jun phosphorylation were significantly elevated in SW620 cells after treatment with hirsutanol A for 24 h. However, this activation of JNK could be blocked by antio idant agent NAC. These suggested that JNK may be a downstream target of e cessive ROS. In order to further e plore the contribution of JNK signaling pathway to hirsutanol A induced ROS accumulation, JNK signaling pathway was blocked using the small molecule JNK inhibitor SP600125.
The percentage of Anne inV positive cells was 35. 6% when cells were treated with hirsutanol A only, whereas in parallel treatment in combination with SP600125, the percentage of Anne inV positive cells was 48. 3%, sug gesting that blocking of JNK signaling pathway pro moted hirsutanol A induced apoptosis. The results also revealed that inhibiting JNK signaling path way enhanced the growth inhibition effect induced by hirsutanol A. We further investigated the effect of activation of JNK signaling pathway on cellular ROS levels. Cellular ROS levels were remarkably increased in SW620 cells by JNK inhibitor SP600125 or JNK siRNA. These results suggested that activation of JNK could be one re sponse to o idant stress which protects cells from death via regulation of ROS in a negative feedback manner.
It was not a classic mechanism involved in apoptosis. In vivo antitumor effect of hirsutanol A on human colon cancer cell SW620 enografts To detect the antitumor activity of hirsutanol A in vivo, human colon cancer SW620 enografts were established. The results showed that hirsutanol A at 10 mg kg d po tently inhibited tumor growth. Discussion Hirsutanol A is a novel sesquiterpene compound puri fied from fungus Chondrostereum sp. in Sarcophyton tor tuosum. Our previous studies had demonstrated that hirsutanol A e hibited potent cytoto ic effect