Interaction of MT1-MMP and laminin-5γ2 chain correlates with metastasis and invasiveness in human esophageal squamous cell carcinoma

To gain insights into metastatic mechanisms in esophageal squamous cell carcinoma (ESCC), we established sublines (MLuB1 and MLuC1) with different capacity of spontaneous lung metastasis by subcutaneous injection of a human ESCC cell line (EC 9706) into nude mices. The incidence of the mice with lung metastasis produced by MLuC1 (87%) was significantly higher than that of MLuB1 (22%). The gene expression profiles of the two sublines were compared with cDNA arrays containing 5,000 known genes, and 47 genes were differentially expressed >= 2.0 fold. Laminin-5 gamma 2 chain (Ln-5 gamma 2) was one of the up-regulated genes in MLuC1 cells. Proteolytically processed forms of gamma 2 are known to promote migration of a multitude of epithelial cells in vitro. Western-blotting analysis revealed that degraded fragments of Ln-5 gamma 2 and active form of membrane-type matrix metalloproteinase-1 (MT1-MMP) in MLuC1 was significantly higher than those in MLuB1. Expression of MT1-MMP was observed in 60 of 75 Ln-5 gamma 2-positive carcinoma tissues (80%). Co-expression of the two proteins was significantly associated with depth of invasion (P = 0.012). Moreover, proteolytic fragments of Ln-5 gamma 2 and active forms of MT1-MMP were frequently found in tumor tissues, whereas in the corresponding normal esophageal tissues there were only intact forms of gamma 2 and MT1-MMP. siRNA-mediated silencing of MT1-MMP significantly reduced production of gamma 2' and gamma 2x in MLuC1 cells and inhibited cell migration. The results suggest that MT1-MMP is an enzyme responsible for Ln-5 gamma 2 cleavage in ESCC, and interaction between them may play a critical role in promoting invasion and metastasis of human ESCC.