Cytokines play important roles in tumorigenesis and progression of cancer cells, while their functions in drug resistance remain to be illustrated. We successfully generated doxorubicin (Dox)-resistant CRC HCT-116 and SW480 cells (namely HCT-116/Dox and SW480/Dox, respectively). Cytokine expression analysis revealed that IL-8, while not FGF-2, EGF, TGF-β, IL-6, or IL-10, was significantly increased in Dox-resistant CRC cells as compared with their corresponding parental cells. Targeted inhibition of IL-8 via siRNAs or its inhibitor reparixin can increase the Dox sensitivity of HCT-116/Dox and SW480/Dox cells. The si-IL-8 can decrease the mRNA and protein expression of multidrug resistance 1 (MDR1, encoded by ABCB1), while has no effect on the expression of multidrug resistance-associated protein 1 (ABCC1), in CRC Dox-resistant cells. IL-8 can increase the phosphorylation of p65 and then upregulate the binding between p65 and promoter of ABCB1. BAY 11-7082, the inhibitor of NF-κB, suppressed the recombination IL-8 (rIL-8) induced upregulation of ABCB1. It confirmed that NF-κB is involved in IL-8-induced upregulation of ABCB1. rIL-8 also increased the phosphorylation of IKK-β, which can further activate NF-κB, while specific inhibitor of IKK-β (ACHP) can reverse rIL-8-induced phosphorylation of p65 and upregulation of MDR1. These results suggested that IL-8 regulates the Dox resistance of CRC cells via modulation of MDR1 through IKK-β/p65 signals. The targeted inhibition of IL-8 might be an important potential approach to overcome the clinical Dox resistance in CRC patients.
Keywords: CRC; Dox resistance; IL-8; MDR1; P65.