4356

experimental and clinical evidence has demonstrated that MT1-MMP may serve as a master regulator of cancer dissemination. The mechanism underlying this process remains to be defined. While, recent reports on the role of MT1-MMP in cell migration and invasion in three dimensional (3D) type I collagen gels have expanded our understanding of cancer cell invasion, some of the data appear contradictory. Epithelial-to-mesenchymal transition (EMT) has emerged as a critical step in the conversion of early stage tumors into invasive malignancies. Employing our previously established stable cell lines {human prostate cancer (LNCaP), breast cancer (MCF-7) and fibrosarcoma (HT1080) cells} expressing “pathophysiologic” level of MT1-MMP-GFP (MT1-GFP) chimera as well as GFP control cells cultivated in either 2D plastic dishes or 3D native type I collagen gels, we examined the role of MT1-MMP in promoting epithelial cancer cell EMT. expression of MT1-MMP in all three cell lines promotes cell proliferation in 3D cultures, but not in 2D cultures. Enzymatic activity of MT1-MMP is a prerequisite for enhanced cell proliferation suggesting that cellular degradation of surrounding collagen is a prerequisite for enhanced cell proliferation. GFP-expressing LNCaP and MCF-7 cells cultivated in 3D type I collagen gels gradually formed spherical aggregates, whereas cells expressing MT1-GFP display a scattered growth pattern. MT1-MMP-induced cell scattering was abrogated by targeted inhibition of either the catalytic domain (TIMP-2, but not TIMP-1) or the hemopexin domain (recombinant MT1-hemopexin protein), indicating a specific role for each domain of MT1-MMP in cancer cell scattering. Inhibition of MT1-MMP-induced phenotypic changes (fibroblast-like morphology and cell scattering), however, was reversed upon withdrawal of inhibitors. MT1-MMP transfected LNCaP and MCF-7 cells also degraded the cell-cell adherins junction molecule, E-cadherin. In contrast to epithelial cells (LNCaP, MCF-7), HT1080 cells which are mesenchymal in origin displayed a scattered growth pattern in 3D collagen gels. Transfection of HT1080 cells with MT1-MMP or treatment with high dose TIMP-2, did not alter the scattered growth pattern of HT1080 cells, thus consistent with previous observations that mesenchymal cell invasion is independent of MMP activity. Given these data, it appears that MT1-MMP is responsible for converting LNCaP and MCF-7 cells (epithelial origin) to a mesenchymal phenotype. We hypothesize that MT1-MMP degradation of E-cadherin and collagen leads to mesenchymal-associated morphologic changes in 3-D collagen gels and promotes cancer cell migration and proliferation, thus recapitulating EMT. The central role of MT1-MMP in epithelial cancer progression provides a stimulus for development of specific inhibitors as treatment of early stage cancer.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]