A negative feedback loop between miR-200b and the nuclear factor-κB pathway via IKBKB/IKK-β in breast cancer cells

MicroRNAs (miRNAs) act as important post-transcriptional regulators of gene expression in diverse signalling pathways. However, the relationship between miR-200b and the nuclear factor-kappa B (NF-kappa B) signalling pathway remains poorly understood in breast cancer cells. In the current study, we show that IKBKB is a direct target of miR-200b, and that miR-200b downregulates IKBKB expression via directly binding to its 3 '-UTR. miR-200b inhibits I kappa B alpha phosphorylation, nuclear p50/p65 expression, NF-kappa B-binding activity, and the translocation of p65 to the nucleus. In addition, miR-200b also suppresses tumour necrosis factor (TNF)-alpha-induced NF-kappa B activation and the expression of NF-kappa B target genes. Importantly, IKBKB overexpression attenuates the inhibitory roles of miR-200b in NF-kappa B expression, NF-kappa B-binding activity, and the nuclear translocation of p65. We also show that NF-kappa B p65 knockdown reduces the binding of NF-kappa B to the miR-200b promoter and miR-200b promoter activity. Furthermore, p65 knockdown or inhibition of I kappa B alpha phosphorylation suppresses miR-200b expression. Finally, functional studies show that IKBKB overexpression can restore the cell growth and migration that are suppressed by miR-200b. In conclusion, our results demonstrate that miR-200b, a transcriptional target of NF-kappa B, suppresses breast cancer cell growth and migration, and NF-kappa B activation, through downregulation of IKBKB, indicating that miR-200b has potential as a therapeutic target in breast cancer patients.