Figure 5
Activation of c-Jun N-terminal kinase (JNK) signaling pathway in MCF-7:2A cells in response to buthionine sulfoximine (BSO) and 17β-estradiol (E2) treatment. (a) MCF-7 and MCF-7:2A cells were treated with ethanol vehicle (control), 1 nM E2 or 100 μM BSO plus E2 for 48 h and protein levels of phosphorylated JNK, JNK, phosphorylated c-Jun, and c-Jun were analyzed by western blotting. β-Actin was used as a control. (b) Inhibition of JNK activation by SP600125 (SP) partially reverses the apoptotic effect of BSO and estradiol in MCF-7:2A cells. Cells were pretreated with 20 μM SP600125 or vehicle for 24 h, then further incubated for 48 h with 1 nM E2, E2 + 100 μM BSO, 20 μM SP, or E2 + BSO + SP and apoptosis was determined by annexin V-propidium iodide (PI) staining as described in Materials and methods. Columns, mean percentage of apoptotic cells from three independent experiments performed in triplicate; bars, ± standard error of the mean (SEM). **, p < 0.001 compared with control (C) cells; ##, p < 0.01 compared with E2 plus BSO-treated cells.