A NOVEL MEMBER OF HUMAN TISSUE INHIBITOR OF METALLOPROTEINASES (TIMP)GENE FAMILY IS REGULATED DURING G(1) PROGRESSION, MITOGENIC STIMULATION, DIFFERENTIATION, AND SENESCENCE

We have identified in the human diploid fibroblast cell line WI-38 a n ovel serum-inducible gene, mitogen-inducible gene 5 (mig-5), of the de layed-early class, which represents a new member of the family of huma n tissue inhibitors of metalloproteinases (TIMPs). The deduced Mig-5 p rotein 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 expres sion is not only induced in response to mitogenic stimulation but also is subject to cell cycle regulation in normally proliferating WI-38 f ibroblasts and HL-60 myeloid cells, showing a clear peak around mid-G( 1). In agreement with this observation, differentiation of HL-60 cells to either granulocytic or macrophage-like cells leads to increased le vels of mig-5 mRNA concomitant with a block in G(1). In contrast, mig- 5 expression is decreased in senescent human fibroblasts, suggesting t hat these cells may be blocked at a stage in G(1) before or after the phase of maximum mig-5 expression. Since in contrast to the vast major ity of other known mitogen-inducible genes, mig-5 expression is period ically up-regulated in G(1), this gene should represent an invaluable tool for the analysis of cell cycle progression, terminal differentiat ion, and replicative senescence.