Unlike most other matrix metalloproteinases (MMPs) MMP-19 is expressed in undifferentiated basal keratinocytes of healthy human skin. The human keratinocyte cell line HaCaT, which like basal keratinocytes constitutively expresses MMP-19, down-regulated the expression of MMP-19 at high calcium concentrations. Calcium-regulation occurred through E-cadherin mediated cell-cell contacts because neutralizing anti-E-cadherin antibodies restored MMP-19 expression in high calcium. Overexpression of MMP-19 in HaCaT cells (HaCaT-WT) increased cellular proliferation, as well as migration and adhesion on type I collagen. This was due to proteolysis of the insulin-like growth factor (IGF) binding protein-3 by MMP-19, which augmented signaling through the IGF-I receptor, as evidenced by its increased autophosphorylation. Conversely, these effects were not observed in cells transfected with MMP-2 or a catalytically inactive MMP-19 mutant. As further proof that increased IGF-signaling promoted adhesion and migration in HaCaT-WT cells, we reproduced these effects by treating parental HaCaT with IGF-I. We observed dephosphorylation of the focal adhesion kinase in HaCaT-WT as well as IGF-I-treated HaCaT cells, suggesting that inactivating focal adhesion kinase is a mechanism by which IGF-I enhances adhesion. Furthermore, IGF-I-triggered motility on type I collagen was mediated by MMP activity, which, however, was distinct from MMP-19. Considering the coexpression of IGFBP-3 and MMP-19 in the skin, we conclude that MMP-19 is a likely candidate to be the major IGFBP-3 degrading MMP in the quiescent epidermis. This activity might have widespread consequences for the behavior of epidermal keratinocytes.

In this study we analyzed the proteolytic activity of MMP-19 and its impact on keratinocyte migration. In the HaCaT keratinocyte cell line overexpressing wild-type MMP-19 (HaCaT-WT), transmigration through fibrin and type IV collagen matrices was significantly increased compared to cells harboring a catalytically inactive mutant (HaCaT-EA). Studying the expression of MMP-19 in early stages of squamous cell cancer (SCC), we found co-localization of MMP-19 and laminin 5 at the invading tumor front but not in suprabasal epidermis of the tumor. Examination of laminin 5 processing revealed increased processing of the gamma2 chain in the medium and matrix of HaCaT-WT cells and degradation by recombinant human MMP-19 to 105-kDa and 80-kDa fragments. Parental HaCaT grown on the matrix of HaCaT-WT and HaCaT-EA cells displayed differential tyrosine phosphorylation. Using integrin blocking and stimulating antibodies we could attribute these differences to a shift from beta4-integrin-dependent signaling on the HaCaT-EA matrix toward alpha3-integrin-dependent signaling on the HaCaT-WT matrix. As a consequence, parental HaCaT showed increased migration on the matrix of HaCaT-WT cells. These data suggest that the MMP-19-dependent processing of the gamma2 chains leads to the integrin switch favoring epithelial migration and that MMP-19 actively participates in the early stages of SCC invasion.