Celastrol targets IRAKs to block Toll-like receptor 4-mediated nuclear factor-kappa B activation

OBJECTIVE: Celastrol has been established as a nuclear factor-kappa B (NF-kappa B) activation inhibitor; however, the exact mechanism behind this action is still unknown. Using text-mining technology, the authors predicted that interleukin-1 receptor-associated kinases (IRAKs) are potential celastrol targets, and hypothesized that targeting IRAKs might be one way that celastrol inhibits NF-kappa B. This is because IRAKs are key molecules for some crucial pathways to activate NF-kappa B (e.g., the interleukin-1 receptor (IL-1R)/Toll-like receptor (TLR) superfamily). METHODS: The human hepatocellular cell line (HepG2) treated with palmitic acid (PA) was used as a model for stimulating TLR4/NF-kappa B activation, in order to observe the potential effects of celastrol in IRAK regulation and NF-kappa B inhibition. The transfection of small interfering RNA was used for down-regulating TLR4, IRAK1 and IRAK4, and the Western blot method was used to detect changes in the protein expressions. RESULTS: The results showed that celastrol could effectively inhibit PA-caused TLR4-dependent NF-kappa B activation in the HepG2 cells; PA also activated IRAKs, which were inhibited by celastrol. Knocking down IRAKs abolished PA-caused NF-kappa B activation. CONCLUSION: The results for the first time show that targeting IRAKs is one way in which celastrol inhibits NF-kappa B activation.