This article discusses the transformation of epithelial Madin-Durby canine kidney (MDCK) cells with v-src induced expression of membrane-type 1-matrix metalloproteinase (MT1-MMP) and metastatic growth in nude mice (Kadono Y et al., Cancer Res 1998; 58: 2240-44). To analyze genes associated with invasive phenotype of v-src MDCK cells, mRNA differential display was performed between control and the transformed cells. A clone 12', the expression of which was clearly up-regulated in the transformed cells, encoded a protein 81% homologous to human tissue inhibitor of matrix metalloproteinases-1 (TIMP-1). Northern hybridization showed that only MT1-MMP expression was enhanced and other matrix metalloproteinases (MMPs) were undetectable or rather repressed in the transformed cells. Proteolytic activity against type I gelatin was observed in v-src MDCK cells, which was inhibited only by TIMP-2 but not by TIMP-1. MDCK cells stably transfected with the MT1-MMP gene also degraded gelatin, which was selectively inhibited by TIMP-2. These results suggest that MT1-MMP, the expression of which is induced in v-src MDCK cells, degrades extracellullar matrix by itself rather than through the activation of progelatinase A, which in turn contributes to the metastasis of the transformed cells.