Tissue inhibitors of metalloproteinases: structure, regulation and biological functions

Four members of the tissue inhibitor of metalloproteinases (TIMP) family have been characterized so far, designated as TIMP-1, TIMP-2, TIMP-3, and TIMP-4. TIMP-1 and TIMP-2 are capable of inhibiting the activities of all known matrix metalloproteinases (MMPs) and as such play a key role in maintaining the balance between extracellular matrix (ECM) deposition and degradation in different physiological processes. Accelerated breakdown of ECM occurs in various pathological processes, including inflammation, chronic degenerative diseases and tumor invasion. TIMP-1 and TIMP-2 can inhibit tumor growth, invasion, and metastasis in experimental models which has been associated with their MMP inhibitory activity. Recent developments in TIMP research suggest that TIMP-1 and TIMP-2 are multifunctional proteins with diverse actions. Both inhibitors exhibit growth factor-like activity and can inhibit angiogenesis. Structure-function studies have separated the MMP inhibitory activity of TIMP-1 from its growth promoting effect. TIMP-1 has also been implicated in gonadal steroidogenesis and as a cellular elongation factor. TIMP-3 is the only member of the TIMP family which is found exclusively in the extracellular matrix (ECM). It is regulated in a cell cycle-dependent fashion in certain cell types and may serve as a marker for terminal differentiation. The most recently discovered TIMP, TIMP-4, may function in a tissue-specific fashion in extracellular matrix hemostasis. The main aim of this article is to review recent literature on TIMPs with special emphasis on their biological activities and the possibility that they may have paradoxical roles in tumor progression.