Active roles for inhibitory κB kinases α and β in nuclear factor-κB-mediated chemoresistance to doxorubicin

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