TNF-alpha increases human melanoma cell invasion and migration in vitro: the role of proteolytic enzymes

Inflammatory mediators have been reported to promote malignant cell growth, invasion and metastatic potential. More specifically, we have recently reported that tumour necrosis factor alpha (TNF-a) increases melanoma cell attachment to extracellular matrix (ECM) substrates and invasion through fibronectin. In this study, we extend these investigations asking specifically whether the TNF-a effect on cell invasion and migration involves activation of proteolytic enzymes. We examined the effect of TNF-a on melanoma expression/activation of type IV gelatinases matrix metalloproteinases 2 and 9 (MMPs -2 and -9) and general proteolytic enzymes. Stimulation with TNF-a significantly increased both melanoma cell migration at 24 h ( þ 21%) and invasion through fibronectin ( þ 35%) but did not upregulate/activate the expression of latent MMP-2 constitutively produced by these cells and did not upregulate their general protease activity. However, the increased cell migration and invasion through fibronectin observed following stimulation with TNF-a were inhibited by the general protease inhibitor a2 macroglobulin. These findings suggest that the promigratory and proinvasive effect of TNF-a on this melanoma cell line may be mediated to some extent by induction of localised cell membrane-bound degradative enzyme activity, which is not readily detected in biochemical assays.