The Study On The Role Of JNK/AP-1 And IKK/NF-κB Signaling Pathways In Mediating Arsenite-induced Apoptosis In MCF7 Cells

Objective:To explore the roles of JNK/AP-1 and IKK/NF-кB signaling pathway in mediating the apoptotic effect in human breast cancer cells exposed to arsenic trioxide (As₂O₃, arsenite).Methods:MCF7 cells were treated with arsenite. The cell cycle distribution and the apoptosis were detected by flow cytometric analysis with PI staining of the nuclei. Luciferase assay was used to detect the activation of the transcriptional factor of AP-land NF-кB in the MCF7 cells. The induced activation of JNK, p38K, ERK, MEK1/2, c-Jun and the expression of GADD45α, IKKα, IKKβ, IKKγ, p50, p65 and Fra-1 were detected by Western blot assay.Results:1. The role of JNK/AP-1 signaling pathway in the apoptotic effect of MCF7 cells induced by arsenite.(1) Arsenite treatment induced a growth arrest response at G2/M phase. Under the same conditions, an increase of cell death incidence was observed.(2) Persistent JNK phosporylation was observed in MCF7 cells by the treatment of arsenite.(3) Persistent increase of AP-1 transactivity was observed in the MCF7 cells induced by arsenite.(4) Under arsenite stimulation, we detected a remarkable phosphorylation of c-Jun and induction of Fra-1 expression in the MCF7 cells.(5) After inhibited arsenite-induced phosporylation of c-Jun and induction of Fra-1, arsenite-induced cell death was partially attenuated in the cells.(6) Pretreatment of the MCF7 cells with SP600125 dramatically suppressed arsenite-induced AP-1 transactivation, accompanied by a substantial decrease of cell apoptosis under the same arsenite treatment conditions.2. The role of IKK/NF-кB signaling pathway in the apoptotic effect of MCF7 cells induced by arsenite.(1) Persistent decrease of NF-кB transactivity was observed in the MCF7 cells by the treatment of arsenite.(2) Arsenite exposure induced a significant decrease of both IKKαand IKKβproteins expression in MCF7 cells.(3) Inhibition of NF-кB transactivation can be partially recovered in the IKKα- and IKKβ-overexpressed MCF7 cells.(4) Cell death incidence induced by arsenite can be partially recovered in the IKKα- and IKKβ-overexpressed MCF7 cells.Conclusions:1. JNK/AP-1 pathway plays an important role in mediating the apoptotic response of the MCF7 cells under arsenite exposure.2. C-Jun and Fra-1 are major AP-1 components in MCF7 cells to mediate the arsenite-induced apoptotic response, which may be used as the potential targets in treating of breast cancer.3. Arsenite exposure inhibits NF-кB transactivatin by downregulating both IKKαand IKKβproteins expression, which constitutes the novel regulation mechanism of NF-кB activation and contributes to the apoptotic response in the MCF7 cells induced by arsenite..