IMPLICATION OF COLLAGEN TYPE-1-INDUCED MEMBRANE-TYPE-1 MATRIX METALLOPROTEINASE EXPRESSION AND MATRIX METALLOPROTEINASE-2 ACTIVATION IN THEMETASTATIC PROGRESSION OF BREAST-CARCINOMA

We have previously demonstrated that fibroblasts and invasive human br east carcinoma (HBC) cells specifically activate matrix metalloprotein ase-2 (MMP-2) when cultured on 3-dimensional gels of type I collagen b ut not a range of other substrates. We show here the constitutive expr ession of membrane-type 1 (MT1)-MMP in both fibroblasts, and invasive HBC cell lines, that have fibroblastic attributes presumably acquired through an epithelial-to-mesenchymal transition (EMT). Treatment with collagen type I increased the steady-state MT1-MMP mRNA levels in thes e cells but did not induce either MT1-MMP expression or MMP-2 activati on in noninvasive breast carcinoma cell lines, which retain epithelial features. Basal MT3-MMP mRNA expression had a pattern similar to that of MT1-MMP but was not up-regulated by collagen. MT4-MMP mRNA was see n in both invasive and noninvasive HBC cell lines and was also not col lagen-regulated, and MT2-MMP mRNA was not detected in any of the HBC c ell lines tested. These data support a role for MT1-MMP in the collage n-induced MMP-2-activation seen in these cells. In situ hybridization analysis of archival breast cancer specimens revealed a close parallel in expression of both collagen type I and MT1-MMP mRNA in peritumoral fibroblasts, which was correlated with aggressiveness of the lesion. Relatively high levels of expression of both mRNA species were seen in fibroblasts close to invasive tumor nests and, although only focally, in certain areas close to preinvasive tumors. These foci may represen t hot spots for local degradation and invasive progression. Collective ly, these results implicate MT1-MMP in collagen-stimulated MMP-2 activ ation and suggest that this mechanism may be employed in vivo by both tumor-associated fibroblasts and EMT-derived carcinoma cells to facili tate increased invasion and/or metastasis.