Matrix metalloproteinases (MMPs) are zinc-dependent and calcium-dependent proteases that cleave within a polypeptide (endopeptidases). They degrade most components of the extracellular matrix (such as growth factors, their binding proteins, and other bioactive molecules, as well as binding sites for cell-surface molecules) and some non-extracellular-matrix molecules []. Two categories of MMPs can be recognised based on their cellular localisation: soluble vs. membrane-bound. The soluble MMPs are divided into the collagenases (MMP1, MMP8 and MMP13), gelatinases (MMP2 and MMP9), stromelysins (MMP3, MMP12) and those yet to be classified. The membrane-bound MMPs include MT1, 2, 3, 4, 5 and their hallmark is the presence of plasma membrane anchoring domains []. MMPs are highly expressed in various cancers, both by tumour cells and in surrounding stromal cells such as macrophages []. Matrix metalloproteinase-16 (MMP16; MEROPS identifier M10.016), also called MT3-MMP, degrades various components of the extracellular matrix, such as collagen type III and fibronectin. It has no effect on type I, II, IV and V collagen. However, upon interaction with CSPG4, it may be involved in degradation and invasion of type I collagen by melanoma cells []. MMP-16 can not only directly degrade some matrix molecules, but can also activate pro-MMP-2 (gelatinase A), one of the most important MMPs in tissue remodelling and cell migration [, ].
