LACK OF SUPPRESSION OF TUMOR-CELL PHENOTYPE BY OVEREXPRESSION OF TIMP-3 IN MOUSE JB6 TUMOR-CELLS - IDENTIFICATION OF A TRANSFECTANT WITH INCREASED TUMORIGENICITY AND INVASIVENESS

Background: We have recently cloned mouse tissue inhibitor of metallop roteinases-3 (mTIMP-3) by the differential display technique and found that mTIMP-3 was expressed in preneoplastic but not in neoplastic mou se JB6 epidermal cells (Sun et al. Cancer Res. 54:11139, 1994). This d own regulation of the gene is attributable at least in part to alterna tion in gene methylation (Sun et al., J. Biol. Chem., 270:19312, 1995) . Methods: To examine the potential role of TIMP-3 in this tumor model , we overexpressed mouse TIMP-3 in two JB6 tumor cell lines lacking en dogenous mTIMP-3 expression. Stable transfectants from each line were selected and assayed for possible changes in tumor cell phenotype. Res ults: Our results showed that overexpression of mTIMP-3 in these two t umor lines did not change their ability to grow in soft agar, an assay for anchorage-independent growth, nor in nude mice, an in vivo tumori genicity assay, nor to penetrate matrigel, an assay for invasiveness. We, however, isolated a clone which is highly malignant as demonstrate d by a) very short latent period for tumor formation; b) very fast tum or growth; and c) highly invasive in the matrigel assay. Conclusion: W e conclude from this study that although TIMP-3 is not expressed in mo use JB6 tumor cells, overexpression by DNA transfection did not revers e tumor cell phenotype, suggesting a complex role for TIMP-3 in tumori genesis. The highly malignant transfectant isolated by this study can be used as a tool for the cloning of dominant oncogenes as well as tum or suppressor genes.