TIMP-2, a growth-stimulatory protein from SV40-transformed human fibroblasts

The mechanisms by which the early genes of simian virus 40 (SV40) transform human cells are unclear; however, this is clearly a multistep process involving a number of cellular and genetic changes. An early change following expression of the SV40 genes is growth under reduced serum conditions, which could be consistent with the production of autocrine/paracrine growth factors. HSF4-T12 is a human fibroblast cell line produced by transfection of primary cells with the genes for large T and small t antigens. A progressive stepwise transformation was observed with in vitro culture, eventually resulting in a tumorigenic cell line. Serum-free defined medium conditioned by HSF4-T12 was able to stimulate growth of normal human fibroblasts as determined by growth curve and [3H]-thymidine incorporation assays. Purification of this activity by heparin affinity chromatography and nondenaturing polyacrylamide gel electrophoresis resulted in a single band of approximately 21 kDa on a nonreducing, denaturing gel. A partial 14-amino acid sequence was found to share 100% homology with a region of tissue inhibitor of metalloproteinases-2 (TIMP-2). Western blot analysis with anti-TIMP-2 antiserum confirmed this identification, and addition of this same antiserum to HSF4-T12-conditioned medium resulted in inhibition of stimulatory activity.