Cell growth-promoting activity of tissue inhibitor of metalloproteinases-2 (TIMP-2)

Abstract

Human tissue inhibitor of metalloproteinases-2 (TIMP-2) has a potent growth-promoting activity for wide range of human, bovine and mouse cells, having an optimal concentration (10 ng/ml, 0.46 nM) that is ten-times lower than that of TIMP-1 (Hayakawa et al. (1992)FEBS Lett. 298, 29). Neither TIMP-1 complexed with progelatinase B nor TIMP-2 complexed with progelatinase A, both of which have full inhibitory activity against active forms of matrix metalloproteinases (MMPs), showed any cell growthpromoting activity. On the contrary, both reductively alkylated TIMPs had no MMP inhibitory activity, but significantly stimulated cell proliferation. These facts clearly indicate that the cell-proliferating activity of TIMPs is independent of MMP inhibitory activity. We also demonstrated that [3H]thymidine was significantly incorporated into Raji cells, a Burkitt lymphoma cell line, in the presence of either 4 ng/ml of TIMP-1 or 0.1 ng/ml of TIMP-2. Under steady-state conditions at 4°C, high-(Kd=0.15 nM) and low-(35 nM) affinity binding sites for TIMP-2 were identified on Raji cells with 20,000 and 1.4×105 sites/cell, respectively. Both high- and low-affinity binding of 125I-TIMP-2 to Raji cells were competitively inhibited by unlabeled TIMP-2 but not by unlabeled TIMP-1, suggesting the presence of receptors for TIMP-2 independent from those for TIMP-1. TIMP-2 seems to be another new TIMP cell-growth factor in serum, besides TIMP-1.