Background: 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.
Aim: 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).
Methods: 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.
Results: 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%.
Conclusions: Cell-cell contact activation of fibroblasts induced MMP-1, -10, and MT1-MMP expression, suggesting similar signaling to that in inflammation and cancer.