Background: Tumor hypoxia, one of the features of solid tumors, is associated with chemo-resistance. Recently, nuclear factor-κB (NF-κB) was found to be activated during hypoxia. However, the impact of NF-κB activation on chemo-resistance during hypoxia remains unknown.
Methods: Human lung adenocarcinoma A549 cells were transfected with NF-κB p65siRNA and treated with cobalt chloride (CoCl2) to mimic hypoxia in the presence or absence of cisplatin. NF-κB expression was measured by Western blotting, immune-fluorescence and real-time PCR. Hypoxia-inducible factor-1α (HIF-1α) and Bcl-2 expression were determined by Western blotting. Cell apoptosis and survival with half-maximum inhibitory concentration (IC50) of cisplatin were determined by Annexin V-FITC/PI and 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT), respectively.
Results: Exposure of A549 cells to CoCl2 increased nuclear HIF-1a protein expression, and enhanced NF-κB p65 protein nuclear accumulation (the mark of NF-κB activation) in a time and dose dependant manner. CoCl2 did not promote apoptosis in A549 cells; on the contrary, it reduced cisplatin-induced apoptosis and increased the IC50 of cisplatin. However, when we inhibited CoCl2-induced activation of NF-κB through NF-κB p65siRNA, cisplatin-induced apoptosis was increased and IC50 of cisplatin was reduced to levels similar to those in control cells. Meanwhile, CoCl2-induced Bcl-2 overexpression was down-regulated in the presence of cisplatin when NF-κB activity was inhibited.
Conclusion: Up-regulating Bcl-2 might be involved in NF-κB activation induced resistance to cisplatin in A549 cells under CoCl2-induced chemical hypoxia.