HSP70 regulates cell proliferation and apoptosis in actinomycin-D-treated lung cancer cells

BACKGROUND: Heat-shock protein 70 (HSP70) is a member of the heat-shock protein family which is expressed in various types of cancer and associated with apoptosis in cancer cells. However, the role of HSP70 in the regulation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38MAPK)-dependent growth and apoptosis in lung cancer cells remains largely unknown. METHODS: In this study, we conducted in vitro experiments. First, we examined the effect of HSP70 by treatment with mild heat and JNK/p38 MAPK inhibitors on cell proliferation in A549 cells by MTT assay. And then, through the use of flow cytometric assay, we examined the effect of HSP70 by treatment with mild heat and JNK/p38 MAPK inhibitors on cell apoptosis in A549 cells. Finally, we determined the role of HSP70 in the regulation of JNK and p38 MAPK-dependent growth and apoptosis in A549 cells by siRNA HSPAIA-2009 and Western blot. RESULTS: We found that treatment of the cells with mild heat and JNK/p38 MAPK pathway inhibitors (SP600125 and SB203580) promoted cell proliferation in the presence of actinomycin D (ActD) in A549 cells. We also showed that treatment with mild heat or SP600125 and SB203580 significantly slowed the steps of apoptosis induced by ActD in A549 cells. Moreover, we found that HSP70 overexpression induced by mild heat markedly decreased the expression of cell growth and apoptosis-related protein p-JNK, p38 and caspase-3. By contrast, knockdown of HSP70 by siRNA HSPAIA-2009 effectively promoted the expression of the JNK and p38 MAPK. CONCLUSIONS: Our results indicate that HSP70 plays an important role in lung cancer growth and apoptosis through the activation of JNK and p38 MAPK signaling in actinomycin-D-treated lung cancer A549 cells.