MicroRNA-26b suppresses the NF-κB signaling and enhances the chemosensitivity of hepatocellular carcinoma cells by targeting TAK1 and TAB3.

BACKGROUND: Abnormal activation of the NF-κB pathway is closely related to tumorigenesis and chemoresistance. Therefore, microRNAs that possess the NF-κB inhibitory activity may provide novel targets for anti-cancer therapy. miR-26 family members have been shown to be frequently downregulated in hepatocellular carcinoma (HCC) and correlated with the poor survival of HCC patients. To date, there is no report disclosing the regulatory role of miR-26 on the NF-κB pathway and its biological significance.

METHODS: The effects of miR-26b on the NF-κB signaling pathway and the chemosensitivity of cancer cells were examined in two HCC cell lines, QGY-7703 and MHCC-97H, using both gain- and loss-of-function studies. The correlation between miR-26b level and apoptosis rate was further investigated in clinical HCC specimens.

RESULTS: Both TNFα and doxorubicin treatment activated the NF-κB signaling pathway in HCC cells. However, the restoration of miR-26b expression significantly inhibited the phosphorylation of IκBα and p65, blocked the nuclear translocation of NF-κB, reduced the NF-κB reporter activity, and consequently abrogated the expression of NF-κB target genes in TNFα or doxorubicin-treated HCC cells. Furthermore, the ectopic expression of miR-26b dramatically sensitized HCC cells to the doxorubicin-induced apoptosis, whereas the antagonism of miR-26b attenuated cell apoptosis. Consistently, the miR-26b level was positively correlated with the apoptosis rate in HCC tissues. Subsequent investigations revealed that miR-26b inhibited the expression of TAK1 and TAB3, two positive regulators of NF-κB pathway, by binding to their 3'-untranslated region. Moreover, knockdown of TAK1 or TAB3 phenocopied the effects of miR-26b overexpression.

CONCLUSIONS: These data suggest that miR-26b suppresses NF-κB signaling and thereby sensitized HCC cells to the doxorubicin-induced apoptosis by inhibiting the expression of TAK1 and TAB3. Our findings highlight miR-26b as a potent inhibitor of the NF-κB pathway and an attractive target for cancer treatment.