Cell-cell contact activation of fibroblasts increases the expression of matrix metalloproteinases

We recently found that direct homotypic cell-cell contacts between human dermal fibroblasts induce a novel form of cell activation leading to non-apoptotic programmed cell death. As the major features of this process we identified massive induction of cyclo-oxygenase-2 and production of inflammatory prostaglandins. On the surface of the decomposing spheroids, activation of the major extracellular proteolytic cascade, plasminogen activation, associated with surface exposure of alpha-enolase, took place.

To further characterize pericellular proteolysis by cell-cell contact-activated fibroblasts we studied the role of the other major extracellular proteolytic system, matrix metalloproteinases (MMPs).

MMP expression in fibroblast clusters and monolayers was compared using mRNA microarrays and immunoblot analyses. The activities of MMPs were confirmed using MMP inhibitors and caseinolysis.

In microarrays MMP-1, -10, and -14 (MT1-MMP) were induced 5.8-, 106-, and 5.6-fold, respectively. These findings were confirmed by immunoblotting. Radial caseinolysis showed low level of proteolytic activity in spheroid-conditioned media; ilomastat, a general inhibitor of MMPs, suppressed 50% of the proteolytic activity thus confirming it to be at least in part due to MMPs. A cocktail of tetracycline-derived MMP inhibitors suppressed lactate dehydrogenase (LDH) release only 11%, and if combined with aprotinin 28%.

Cell-cell contact activation of fibroblasts induced MMP-1, -10, and MT1-MMP expression, suggesting similar signaling to that in inflammation and cancer.