Proteins of the matrix metalloproteinase (MMP) family are involved in the breakdown of extracellular matrix in normal physiological processes, such as embryonic development, reproduction, and tissue remodeling, as well as in disease processes, such as arthritis and metastasis. Most MMP's are secreted as inactive proproteins which are activated when cleaved by extracellular proteinases.
MMP26, also known as Matrilysin 2, was first cloned from human fetal cells, and identified as an MMP most closely related to MMP7 (Matrilysin 1). The homology between MMP7 and MMP26 is low (only 38% identical), thus the functions are unlikely to be similar. Homology is much higher (48% identical) for the comparable region of MMP12, but MMP26 appears to have broader substrate specificity than does MMP12. MMP26, like MMP7, lacks the hemopexin domain common to the other MMPs, but contains a Propeptide domain, cysteine switch activation site, followed by a catalytic domain, and a short vestige of the hinge region. MMP26 is apparently not glycosylated, and is a secreted MMP. Tissue analysis shows MMP26 most strongly in placenta and uterus, but also in kidney cells, lung cells, lymphocytes and lung or endometrial carcinoma cells. MMP26 is proteolytically active, cleaving casein in zymograms, and gelatin, a1PI, fibrinogen, fibronectin, vitronectin, type IV collagen, and apparently activating MMP9. The proteolytic activity was blocked by TIMP1 and TIMP2. MMP26 does not appear to be produced by most normal quiescent cells, but treatment of many cell types with the phorbol ester TPA, or IL1 stimulates production of MMP26.