Tissue inhibitors of metalloproteinases (TIMPs) are a family of closely related secreted proteins that limit matrix metalloproteinase (MMP) activity and also have direct effects on cell growth. We used the highly efficient adenoviral delivery system to overexpress individual TIMPs from the cytomegalovirus immediate early promoter in rat aortic smooth muscle cells. Overexpression of TIMP-1, -2, or -3, or a synthetic MMP inhibitor similarly inhibited SMC chemotaxis and invasion through reconstituted basement membrane. TIMP-1 overexpression did not effect cell proliferation. By contrast, TIMP-2 caused a dose-dependent reduction in proliferation, an effect not mimicked by a synthetic MMP inhibitor. TIMP-3 overexpression induced DNA synthesis, and promoted SMC death by apoptosis, a phenotype reproduced by adding TIMP-3 to uninfected cells, but not by a synthetic MMP inhibitor. Our study is the first to compare systematically the effect of overexpression of three TIMPs in any cell. We found similar effects on invasion mediated by inhibition of MMP activity, but widely divergent effects on proliferation and death through actions of TIMP-2 and -3 independent of MMP inhibition. These findings have important implications for the physiological roles of TIMPs and their use in gene therapy.
A H Baker, A B Zaltsman, S J George, A C Newby