SUPPRESSION OF IN-VIVO TUMOR-GROWTH AND INDUCTION OF SUSPENSION CELL-DEATH BY TISSUE INHIBITOR OF METALLOPROTEINASES (TIMP)-3

Tissue inhibitor of metalloproteinases-3(TIMP-3), a novel member of TI MP family genes, has been recently cloned and shown to be expressed in preneoplastic but not in neoplastic mouse JB6 epidermal cells (Sun ed al. 1994 Cancer Res., 54, 11139), This down regulation of the gene ap pears to be attributable at least in part to alteration of gene methyl ation (Sun et al, 1995 J. Biol. Chem., 270, 19312), Little is known, h owever, about the role of TIMP-3 in human cancers, We screened several human tumor cell lines for TIMP-3 expression and found that a colon c arcinoma line, DLD-1, did not express TIMP-3, If down regulation of TI MP-3 is causally related to carcinogenesis, re-expression by transfect ion may reverse the tumor cell phenotype, We therefore overexpressed h uman TIMP-3 in DLD-1 cells, TIMP-3 transfectants showed a serum-depend ent growth inhibition in monolayer culture and a decreased growth pote ntial in nude mice in a manner dependent on the level of TIMP-3 expres sion, A transfectant expressing a high level of active hTIMP-3 complet ely lost the ability to form tumors following s.c. injection into nude mice, We also tested TIMP-3 expressing cells and neocontrol TIMP-3 ne gative cells for their ability to grow in liquid suspension culture, s ince both cells grew in semi-solid soft agar, As compared to neocontro l cells, TIMP-3 overexpressors formed large aggregates, followed by ce ll death, This effect was not mimicked by BB94, a broad MMP inhibitor, We conclude from this study that (i) TIMP-3 overexpression in human c olon carcinoma cells induces growth arrest in low serum conditions and inhibits in vivo tumor growth and (ii) the TIMP-3-induced large aggre gate formation and subsequent cell death under suspension growth canno t be explained by its MMP inhibitory activity.