Expression of microRNA-146 suppresses NF-κB activity with reduction of metastatic potential in breast cancer cells

Cancer cells often acquire a constitutively active nuclear factor-kappa B (NF-kappa B) program to promote survival, proliferation and metastatic potential by mechanisms that remain largely unknown. Extending observations from an immunologic setting, we demonstrate that microRNA-146a and microRNA-146b (miR-146a/b) when expressed in the highly metastatic human breast cancer cell line MDA-MB-231 function to negatively regulate NF-kappa B activity. Lentiviral-mediated expression of miR-146a/b significantly downregulated interleukin (IL)-1 receptor-associated kinase and TNF receptor-associated factor 6, two key adaptor/scaffold proteins in the IL-1 and Toll-like receptor signaling pathway, known to positively regulate NF-kappa B activity. Impaired NF-kappa B activity was evident from reduced phosphorylation of the NF-kappa B inhibitor I kappa B alpha, reduced NF-kappa B DNA-binding activity and suppressed expression of the NF-kappa B target genes IL-8, IL-6 and matrix metalloproteinase-9. Functionally, miR-146a/b-expressing MDA-MB-231 cells showed markedly impaired invasion and migration capacity relative to control cells. These findings implicate miR-146a/b as a negative regulator of constitutive NF-kappa B activity in a breast cancer setting and suggest that modulating miR-146a/b levels has therapeutic potential to suppress breast cancer metastases.