Membrane type 6-matrix metalloproteinase (MT6-MMP) is highly expressed in colon cancer and promotes tumor growth of human colon cancer cells in mouse xenografts. Free

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The membrane type-matrix metalloproteinases (MT-MMPs) are a family of membrane-anchored MMPs, which mediate pericellular proteolysis in cancer. MT6-MMP (MMP25) is a glycosylphosphatidylinositol (GPI)-anchored MT-MMP, whose expression and role in cancer have not been studied. Here we investigated the biological and biochemical properties of human MT6-MMP expressed in mammalian cells using a vaccinia expression system and in stably transfected human colorectal carcinoma cell lines. We also investigated MT6-MMP expression in human colon cancer and its role in tumor growth in mice. Subcellular fractionation studies demonstrated that MT6-MMP is targeted to lipid rafts and is found on the cell surface in a monomeric and a homodimeric form, the latter held by disulfide bonds, which may regulate enzyme function. MT6-MMP, either cell-associated or released by phosphatidylinositol-specific phospholipase C (PI-PLC), does not activate pro-gelatinases (pro-MMP-2 and pro-MMP-9) even in the presence of tissue inhibitors of metalloproteinases (TIMP)-2 or TIMP-1. In fact, neither GPI-anchored nor soluble MT6-MMP showed TIMP-1 or TIMP-2 binding with several approaches whereas surface MT1-MMP readily bound TIMP-2 under the same conditions. Immunohistochemical analysis of 69 human colon cancer specimens showed marked increases in MT6-MMP expression within in situ dysplasia and invasive cancer (p<0.01). Transgenic expression of human MT6-MMP in HCT 116 and HT-29 colon cancer cell lines did not lead to activation of pro-gelatinases or enhancement of in vitro cell invasion or migration. However, in subcutaneous tumors in nude mice, transgenic MT6-MMP expression resulted in increased tumor sizes of both HT-29 (p<0.01) and HCT 116 xenografts (P<0.02). Histologically, these MT6-MMP-expressing tumors demonstrated an infiltrative leading edge in contrast to a rounded leading edge in vector controls (p=0.05). In conclusion, our studies indicate that MT6-MMP exhibits unique biological and biochemical properties among the members of the MMP family. MT6-MMP is highly expressed in human colon cancer cells where it may play a role in promotion of tumor growth and invasion.