A novel member of human tissue inhibitor of metalloproteinases (TIMP) gene family is regulated during G1 progression, mitogenic stimulation, differentiation, and senescence.

We have identified in the human diploid fibroblast cell line WI-38 a novel serum-inducible gene, mitogen-inducible gene 5 (mig-5), of the delayed-early class, which represents a new member of the family of human tissue inhibitors of metalloproteinases (TIMPs). The deduced Mig-5 protein shares the highest degree of homology with chicken TIMP-3 (74% identity) and is more distantly related to human TIMP-1 and TIMP-2 (30-38% identity), indicating that mig-5 may represent the human homolog of chicken TIMP-3. In contrast to TIMP-1 and TIMP-2, mig-5 mRNA expression is not only induced in response to mitogenic stimulation but also is subject to cell cycle regulation in normally proliferating WI-38 fibroblasts and HL-60 myeloid cells, showing a clear peak around mid-G1. In agreement with this observation, differentiation of HL-60 cells to either granulocytic or macrophage-like cells leads to increased levels of mig-5 mRNA concomitant with a block in G1. In contrast, mig-5 expression is decreased in senescent human fibroblasts, suggesting that these cells may be blocked at a stage in G1 before or after the phase of maximum mig-5 expression. Since in contrast to the vast majority of other known mitogen-inducible genes, mig-5 expression is periodically up-regulated in G1, this gene should represent an invaluable tool for the analysis of cell cycle progression, terminal differentiation, and replicative senescence.