Arsenic trioxide promotes ERK1/2-mediated phosphorylation and degradation of BIMEL to attenuate apoptosis in BEAS-2B cells

Inorganic arsenic is highly toxic, widely distributed in the human environment and may result in multisystem diseases and several types of cancers. The BCL-2-interacting mediator of cell death protein (BIM) is a key modulator of the intrinsic apoptosis pathway. Interestingly, in the present study, we found that arsenic trioxide (As2O3) decreased BIMEL levels in human bronchial epithelial cell line BEAS-2B and increased BIMEL levels in human lung carcinoma cell line A549 and mouse Sertoli cell line TM4. Mechanismly, the 26S proteasome inhibitors MG132 and bortezomib could effectively inhibit BIMEL degradation induced by As2O3 in BEAS-2B cells. As2O3 activated extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) signaling pathways, but only the ERK1/2 MAPK inhibitor PD98059 blocked BIMEL degradation induced by As2O3. Furthermore, As2O3 induced-phosphorylation of BIMEL at multiple sites was inhibited by ERK1/2 MAPK inhibitor PD98059. Inhibition of As2O3-induced ERK1/2 MAPK phosphorylation increased the levels of BIMEL and cleaved-caspase-3 proteins and decreased BEAS-2B cell viability. As2O3 also markedly mitigated tunicamycin-induced apoptosis of BEAS-2B cells by increasing ERK1/2 phosphorylation and BIMEL degradation. Our results suggest that As2O3-induced activation of the ERK1/2 MAPK pathway increases phosphorylation of BIMEL and promotes BIMEL degradation, thereby alleviating the role of apoptosis in As2O3-induced cell death. This study provides new insights into how to maintain the survival of BEAS-2B cells before malignant transformation induced by high doses of As2O3.