Degradation of 3H-non-mineralized (A) and 3H-mineralized (B) bone matrix by breast cancer cells. Breast cancer cells (105 cells/well) stimulated with TGFβ (10-10 M) were cultured for 24 h on 3H-labelled extracellular matrices in the presence (+) and absence (-) of 2 μg/ml of human plasminogen. After 24-h incubation, bone matrix degradation was measured as described in Materials and methods. 8–800 mU (Ploug units) of pure human uPA in 1 ml of serum-free medium with or without 2 μg/ml of plasminogen, incubated as a control in parallel wells in the absence of cells, released 3–4% of the total radioactivity. This experiment was repeated twice. The results are expressed as percentage release of 3H labelled bone matrix. Each bar is the mean ± S.E.M. of six wells. The stimulatory effects of TGFβ on breast cancer cell mediated 3H release were statistically significant ***P < 0.001 compared with the unstimulated controls and the HME cells.