Eriocalyxin B Inhibits STAT3 Signaling by Covalently Targeting STAT3 and Blocking Phosphorylation and Activation of STAT3
Fig 4
DTT and GSH abolished the EB-caused JAK-STAT3 inhibition.
(A) A549 cells were pretreated with DTT (0.5 mM), GSH (2 mM), EB (20 μM) or their mixture (EB and DTT/GSH were pre-incubated at RT for 30 min) for 2 h and then stimulated with IL-6 for 15 min. Whole cell lysates were processed for western blot analysis using antibodies as indicated. (B) A549 cells were cultured in the presence of indicated concentrations of EB or EB + DTT (0.5 mM) for 48 h and then the viability of A549 cells was analyzed by MTT assay. (C) EB (50 μM) was incubated with GSH (250 μM) at 37°C for 2 h, and the products were resolved by mass spectrometry. A possible Michael addition reaction between EB and GSH is illustrated. The black arrows indicated the molecular weights of EB+GSH and EB+2GSH.