MT1-MMP CORRELATES WITH MMP-2 ACTIVATION POTENTIAL SEEN AFTER EPITHELIAL TO MESENCHYMAL TRANSITION IN HUMAN BREAST-CARCINOMA CELLS

We have previously reported that human breast carcinoma (HBC) cell lin es expressing the mesenchymal intermediate filament protein vimentin ( VIM+) are highly invasive in vitro, and highly metastatic in nude mice , when compared to their VIM- counterparts. Since only VIM+ cell lines can be induced to activate matrix metalloproteinase-2 (MMP-2) upon st imulation,vith Concanavalin A (Con A), we have examined here membrane type 1 MMP (MT1-MMP), a cell surface activator of MMP-2. Northern anal ysis reveals baseline expression of MT1-MMP in five of the six VIM+ ce ll Lines studied (MDA-MB-231, MDA-MB-435, BT-549, Hs578T, MCF-7(ADR)), each of which showed variable activation of exogenous MMP-2 after tre atment with Con A. In contrast, the four VIM-, poorly invasive HBC cel l lines studied (MCF-7, T47D, MDA-MB 468, ZR-75-1) lacked baseline MT1 -MMP mRNA expression, and showed no induction of either MT1-MMP expres sion or MMP-2-activation with Con A. Such differential MT1-MMP express ion was confirmed in vivo using in situ hybridization analysis of nude mouse tumor xenografts of representative cell lines. Western analysis of the MDA-MB-231 cells revealed baseline membrane expression of a 60 kDa species, which was strongly induced by Con A treatment along with a weaker band co-migrating with that from MT1-MMP-transfected COS-1 c ells (63 kDa), presumably representing latent MT1-MMP. MT1-MMP immunof luorescence strongly decorated Con A-stimulated MDA-MB-231 cells in a manner consistent with membranous staining, but did not decorate the u nstimulated MDA-MB-231 cells or MCF-7 cells under either condition. Co llectively, the results suggest the constitutive production of active MT1-MMP which is unavailable for either MMP-2 activation or immune-dec oration until Con A treatment. Since VIM expression arises by virtue o f the so-called epithelial to mesenchymal transition (EMT) in invasive embryonic epithelia, we propose that this represents a major metastas is mechanism in breast carcinomas. MT1-MMP on the surface of such 'fib roblastoid' carcinoma cells may mediate a paracrine loop for the utili zation of stromally produced MMP-2, and contribute to the poorer survi val associated with VIM+ breast carcinomas.