Chemotherapy agents have been shown to induce the transcription factor NF-κB and subsequent chemoresistance in fibrosarcomas and other cancers. The mechanism of NF-κB-mediated chemoresistance remains unclear, with a previous report suggesting that doxorubicin induces this response independent of the inhibitory κB kinases (IKKs). Other studies have indicated that IKKβ, but not IKKα, is required. Mouse embryo fibroblasts (MEF) devoid of IKKα, IKKβ, or both subunits (DKO) were treated with doxorubicin. The absence of either IKKα or IKKβ or both kinases resulted in impaired induction of NF-κB DNA-binding activity in response to doxorubicin. To provide a valid clinical correlate, HT1080 human fibrosarcoma cells were transfected with small interference RNAs (siRNAs) specific for IKKα or IKKβ and then subsequently treated with doxorubicin. Knockdown of IKKα severely impaired the ability of doxorubicin to initiate NF-κB DNA-binding activity. However, a decrease in either IKKα or IKKβ resulted in decreased phosphorylation of p65 in response to doxorubicin. The inhibition of doxorubicin-induced NF-κB activation by the knockdown of either catalytic subunit resulted in increased cleaved caspase 3 and cleaved PARP, and increased apoptosis when compared to doxorubicin alone. The results of this study validate current approaches aimed at NF-κB inhibition to improve clinical therapies. Moreover, we demonstrate that IKKα plays a critical role in NF-κB-mediated chemoresistance in response to doxorubicin and may serve as a potential target in combinational strategies to improve chemotherapeutic response
