Celastrol Blocks Interleukin-6 Gene Expression via Downregulation of NF-κB in Prostate Carcinoma Cells

Interleukin-6 (IL-6), a multifunctional cytokine, contributes to proliferation or differentiation of prostate carcinoma cells in a highly cell type-specific manner. Celastrol (3-hydroxy-24-nor-2oxo-1(10), 3,5,7-friedelatetrane-29-oic acid), also named as tripterine, is extracted from root of Chinese traditional herb Tripterygiumwilfordii Hook f with potent anti-inflammatory and anti-cancer activities. In this study, we evaluated the molecular mechanisms of celastrol on cell proliferation and IL-6 gene expression in prostate carcinoma cells. 3 H-thymidine incorporation and flow cytometric analysis indicated that celastrol treatments arrested the cell cycle at the G0/ G1 phase, thus attenuating cell proliferation in prostate carcinoma PC-3 cells; moreover, celastrol induced cell apoptosis at higher dosage. Knockdown of IL-6 attenuated the anti-proliferative effect of celastrol on PC-3 cells. Results from ELISA and 5'-deletion transient gene expression assays indicated that celastrol treatment decreased IL-6 secretion and gene expression, and this effect is dependent on the NF-kappa B response element within IL-6 promoter area since mutation of the NF-kappa B response element from AAATGTCCCATTTTCCC to AAATGTTACATTTTCCC by site-directed mutagenesis abolished the inhibition of celastrol on the IL-6 promoter activity. Celastrol also attenuated the activation of PMA and TNF alpha on the gene expression and secretion of IL-6 in PC-3 cells. Immunoblot assays revealed that celastrol treatment downregulated the expressions of IKK alpha, p50 and p65, supporting the 5'-deletion transient gene expression assay result that celastrol blocked IL-6 expression through the NF-kappa B pathway in PC-3 cells. For the first time, our results concluded that celastrol attenuates PC-3 cell proliferation via downregulation of IL-6 gene expression through the NF-kappa B-dependent pathway.