Contribution of fibroblast-derived matrix metalloproteinase-3 (MMP-3) activity to tumor cell invasion. (a) Reverse transcription-polymerase chain reaction for housekeeping gene GAPDH, MMP-1, and MMP-3 in tumor cell and fibroblast populations, indicating that MDA MB 468 tumor cells do not express MMP-1 or MMP-3, even following culture with fibroblast conditioned media (CM), whereas both primary fibroblasts and the hfff2 cell line are a source of these MMPs. (1) MDA MB 468; (2) MDA MB 468 + fibroblast CM; (3) hfff2 fibroblast cell line; (4) primary fibroblasts; (5) water blank. M, molecular weight markers. (b) Effect of human recombinant MMP-3 on invasion of MDA MB 468 cells. Increasing invasion is observed in the presence of increasing concentrations of MMP-3, with a doubling of invasion at 100 ng/mL MMP-3 compared with control (p = 0.014). (c) Effect of the MMP-3 inhibitor on fibroblast-stimulated tumor invasion: (i) shows tumor invasion generated by three separate donors, and (ii) shows mean invasion in the presence of MMP-3 inhibitor relative to control. There is a significant reduction in tumor cell invasion in the presence of MMP-3 inhibitor (p = 0.005). * p =< 0.05.