Tissue inhibitor of metalloproteinase-1 stimulates proliferation of human cancer cells by inhibiting a metalloproteinase

TIMP-1, an ∼30 kDa glycosylated protein found predominantly in extracellular compartments, is involved in the regulation of a variety of developmental, remodelling, and pathological processes. One function of TIMP-1 is to inhibit certain members of a group of extracellular and cell surface enzymes known collectively as metalloproteinases (MP). These include the matrix metalloproteinases and the adamalysin-like disintegrin and metalloproteinases (ADAMs). Additional activities of TIMP-1 include potentiating the activity of erythroid precursors and stimulating proliferation of certain cancer cell lines. Published evidence suggests that the apparent proliferative action of TIMP-1 is independent of its MP-inhibitory activity; however, reports of a cell surface receptor for TIMP-1 have not been confirmed. We have utilised a baculovirus-based system to produce TIMP-1. Data presented here show that TIMP-1 and synthetic hydroxamate (GM6001) MP inhibitors stimulate proliferation and metabolic activity of MDA-MB-435 cancer cells with similar kinetics. An inactive hydroxamate derivative was ineffective. The TIMP-1-induced increase in proliferation and metabolic activity was not the consequence of the inhibition of apoptosis by TIMP-1 in the serum-free medium. These data taken together imply that the mechanism by which TIMP-1 enhances cell growth depends on its ability to inhibit a metalloproteinase, rather than to stimulate a cell surface receptor by a process independent of its MP-inhibitory activity. Inhibitors of extracellular regulated kinase (U0126) and p38 (SB203580), and to a lesser extent the phosphatidylinositol-3-kinase inhibitor LY294002, suppressed the action of TIMP-1. Assays for ERK1/2 and p38 showed that both were activated by TIMP-1 and GM6001. Mechanisms by which TIMP-1 might act to stimulate cell proliferation are described.