Specialized Surface Protrusions of Invasive Cells, Invadopodia and Lamellipodia, Have Differential MT1‐MMP, MMP‐2, and TIMP‐2 Localization

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Abstract
Surface protrusions, invadopodia, and analogous lamellipodia at the leading edge of an invasive cell, which make contact with the underlying extracellular matrix (ECM), are the main motor for cellular locomotion and invasion. Previous studies have demonstrated that invadopodia, but not lamellipodia, are sites of ECM degradation on the cell surface. Such degradative activity is in part due to the localization of latent matrix metalloproteinase‐2 (MMP‐2) and membrane type‐1 MMP (MT1‐MMP) to invadopodia, where MMP activation occurs. Although lamellipodia exhibit similar structure and mobility to invadopodia, lamellipodia, by virtue of their location at the cellular periphery, are readily accessible to the soluble tissue inhibitor of matrix metalloproteinase‐2 (TIMP‐2) and blood‐borne inhibitors. We show here that TIMP‐2 co‐localizes with MT1‐MMP and MMP‐2 at lamellipodia but not with that of invadopodia. Thus, the MMP‐TIMP localization at lamellipodia may be a key mechanism for the regulation of MMP activation on the cell surface, which in turn governs expression of the cell‐invasive phenotype.