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MDA-MB-231 breast cancer cells have a high invasive potential, yet the mechanisms involved are not known. This study showed that Toll-like receptor 2 (TLR2) was highly expressed in MDA-MB-231 cells and played a critical role in cell invasion. Compared with the poorly invasive MCF-7 cells, MDA-MB-231 cells expressed 10.5-fold more TLR2. Using TLR2 agonist pg-LPS and TLR2 neutralizing antibody, we found that TLR2 activation significantly promoted MDA-MB-231 invasion, whereas TLR2 blockade diminished this capacity. TLR2 activation enhanced the activity of NF-kappaB and induced phosphorylation of TAK1 and IkappaBalpha in the TLR2/NF-kappaB signaling pathway in MDA-MB-231, but not in MCF-7 cells. TLR2 activation increased IL-6, TGF-beta, VEGF and MMP9 secretion, which are associated with TLR2-NF-kappaB signaling. We demonstrated that TLR2 is a critical receptor responsible for NF-kappaB signaling activity and highly invasive capacity of MDA-MB-231 cells.