Celastrol enhances TRAIL-induced apoptosis in human glioblastoma via the death receptor pathway
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Glioblastoma is the most common, malignant and devastating type of primary brain tumor. Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) is characterized by its lethality to precancerous and cancerous cells. However, many kinds of tumor cells, including most glioma cells, tend to evade TRAIL-induced apoptosis. Celastrol is a pleiotropic compound from a traditional Chinese medicine that has proven to be useful as a sensitizer for TRAIL treatment. However, the underlying mechanism and role of celastrol in the sensitization of glioma cells remain to be elucidated.
The viability of glioma cell lines was examined by the CCK-8 assay. The expression of DR5 was detected by reverse transcriptase quantitative real-time PCR. The protein expression of DR5, cleaved caspase-8, cleaved caspase-3 and PARP were measured by western blot. The apoptosis rates and the sub-G1 population were detected by flow cytometry. The cellular morphological changes were assessed by TUNEL apoptosis and Hoechst 33258 staining assays. The knockdown of DR5 expression was conducted by siRNA.
In this study, we observed that celastrol treatment inhibited cell viability in a dose-dependent manner, while glioma and normal human astroglial cell lines were resistant to TRAIL treatment. We also observed that the antiproliferative effects of TRAIL in combination with a noncytotoxic concentration of celastrol were significantly greater than those of celastrol or TRAIL alone. In addition, cell death induced by the combination treatment was apoptotic and occurred through the death receptor pathway via activation of caspase-8, caspase-3, and PARP. Furthermore, celastrol upregulated death receptor 5 (DR5) at the mRNA and protein levels, and siRNA-mediated DR5 knockdown reduced the killing effect of the combination drug treatment on glioma cells and reduced the activation of caspase-3, caspase-8 and PARP.
Taken together, the results of our study demonstrate that celastrol sensitizes glioma cells to TRAIL via the death receptor pathway and that DR5 plays an important role in the effects of this cotreatment. The results indicate that this cotreatment is a promising tumor-killing therapeutic strategy with high efficacy and low toxicity.
KeywordsCelastrol TRAIL U87-MG DR5 Apoptosis
Tumor necrosis factor-related apoptosis-induced ligand
Death receptor 5
Fetal bovine serum
Central nervous system
Death receptor 4
Fas-associated death domain
Death-inducing signaling complex
Short tandem repeat
Cell Counting Kit-8
Small interfering RNA
Tris-buffered saline with Tween
Reverse transcriptase quantitative real-time PCR
Coefficient of drug interaction
This study was funded by the Chongqing Fundamental Research Funds for nonprofit public scientific research institutions from the Chongqing Science and Technology Commission (Grant number 2015CSTC-JBKY-01702).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflicts of interest.
This article does not contain any studies with human participants or animals performed by any of the authors. The manuscript does not contain clinical studies or patient data.
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