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-24 (MMP24; MEROPS identifier M10.023), or membrane-type matrix metalloproteinase 5 (MT5), activates progelatinase A (also known as MMP-2), which is involved in diverse functions such as remodelling of the vasculature, angiogenesis, tissue repair, tumor invasion, inflammation, and atherosclerotic plaque rupture []. MMP24 may play an important role in extracellular matrix remodelling events in the brain and during embryonic development [].
