CELL GROWTH-PROMOTING ACTIVITY OF TISSUE INHIBITOR OF METALLOPROTEINASES-2 (TIMP-2)

Human tissue inhibitor of metalloproteinases-2 (TIMP-2) has a potent g rowth-promoting activity for wide range of human, bovine and mouse cel ls, having an optimal concentration (10 ng/ml, 0.46 nM) that is ten-ti mes lower than that of TIMP-1 (Hayakawa et al. (1992) FEBS Lett. 298, 29). Neither TIMP-1 complexed with progelatinase B nor TIMP-2 complexe d with progelatinase A, both of which have full inhibitory activity ag ainst active forms of matrix metalloproteinases (MMPs), showed any cel l growth-promoting activity. On the contrary, both reductively alkylat ed TIMPs had no MMP inhibitory activity, but significantly stimulated cell proliferation. These facts clearly indicate that the cell-prolife rating activity of TIMPs is independent of MMP inhibitory activity. We also demonstrated that [H-3]thymidine was significantly incorporated into Raji cells, a Burkitt lymphoma cell line, in the presence of eith er 4 ng/ml of TIMP-1 or 0.1 ng/ml of TIMP-2. Under steady-state condit ions at 4 degrees C, high-(K-d=0.15 nM) and low (35 nM) affinity bindi ng sites for TIMP-2 were identified on Raji cells with 20,000 and 1.4x 10(5) sites/cell, respectively. Both high- and low-affinity binding of I-125-TIMP-2 to Raji cells were competitively inhibited by unlabeled TIMP-2 but not by unlabeled TIMP-1, suggesting the presence of recepto rs for TIMP-2 independent from those for TIMP-1. TIMP-2 seems to be an other new TIMP cell-growth factor in serum, besides TIMP-1.