Celastrol induces apoptosis and autophagy via the ROS/JNK signaling pathway in human osteosarcoma cells: an in vitro and in vivo study.

H-Y Li,Z-M Ye,N Zhang,T Xie,L-L Sun,H-L Gao,J Zhang,B-H Li

doi:10.1038/cddis.2014.543

H-Y Li, Z-M Ye + Show 6 more

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https://doi.org/10.1038/cddis.2014.543

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Abstract

Osteosarcoma is the most common primary malignant tumor of bone, the long-term survival of which has stagnated in the past several decades. Celastrol, a triterpene from traditional Chinese medicine, has been proved to possess potent anti-tumor effect on various cancers. However, the effect of celastrol on human osteosarcoma and the underlying mechanisms remains to be elucidated. We reported here that celastrol could inhibit cell proliferation by causing G2/M phase arrest. Exposure to celastrol resulted in the activation of caspase-3, -8, and -9, indicating that celastrol induced apoptosis through both extrinsic and intrinsic pathways. Autophagy occurred in celastrol-treated cells as evidenced by formation of autophagosome and accumulation of LC3B-II. The celastrol-induced cell death was remarkably restored by the combination of autophagy and apoptosis inhibitors. Furthermore, inhibition of apoptosis enhanced autophagy while suppression of autophagy diminished apoptosis. Celastrol also induced JNK activation and ROS generation. The JNK inhibitor significantly attenuated celastrol-triggered apoptosis and autophagy while ROS scavenger could completely reverse them. The ROS scavenger also prevented G2/M phase arrest and phosphorylation of JNK. Importantly, we found that celastrol had the similar effects on primary osteosarcoma cells. Finally, in vivo, celastrol suppressed tumor growth in the mouse xenograft model. Taken together, our results revealed that celastrol caused G2/M phase arrest, induced apoptosis and autophagy via the ROS/JNK signaling pathway in human osteosarcoma cells. Celastrol is therefore a promising candidate for development of antitumor drugs targeting osteosarcoma.

Highlights

Celastrol, a triterpenoid isolated from the traditional Chinese medicine ‘Thunder of God Vine’, has been used in the treatment of autoimmune and neurodegenerative diseases.[3,4,5] Recently, celastrol has attracted great attention for its potent anticancer effects and its diverse molecular targets involved in tumorigenesis have been reported.[6,7,8,9,10,11,12] these molecular targets have positive correlations with inhibition of tumors, it is not clear which, if any, is the direct target or the principal mediator
We further explored the molecular mechanisms, that is, induction of G2/M phase arrest, apoptosis and autophagy mediated by the Reactive oxygen species (ROS)/JNK signaling pathway
Our results presented here confirm that celastrol could inhibit proliferation of human osteosarcoma in vitro and in vivo through G2/M arrest, apoptosis and autophagy mediated by the ROS/JNK signaling pathway

Summary

Introduction

A triterpenoid isolated from the traditional Chinese medicine ‘Thunder of God Vine’, has been used in the treatment of autoimmune and neurodegenerative diseases.[3,4,5] Recently, celastrol has attracted great attention for its potent anticancer effects and its diverse molecular targets involved in tumorigenesis have been reported.[6,7,8,9,10,11,12] these molecular targets have positive correlations with inhibition of tumors, it is not clear which, if any, is the direct target or the principal mediator. Cell death could be classified into apoptosis, autophagy, necrosis, cornification and tentative definitions of atypical cell death modalities.[17] Apoptosis, as the type-I programmed cell death (PCD), plays a key role in chemotherapies against a variety of cancers.[18] Autophagy is regarded as type-II PCD and the caspase-independent cell death pathway.[19] In some cellular settings, autophagy serves as a cell survival pathway, suppressing apoptosis, and, in others, it can lead to cell death itself, either in collaboration with apoptosis or as a back-up mechanism when the former is defective.[20] Whether celastrol can induce apoptosis or autophagy, what roles do they have and the interplay between each other in celastrol-induced cell death of osteosarcoma remain to be determined. We further explored the molecular mechanisms, that is, induction of G2/M phase arrest, apoptosis and autophagy mediated by the ROS/JNK signaling pathway

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