Identification and characterization of human MT5-MMP, a new membrane-boundactivator of progelatinase A overexpressed in brain tumors

A cDNA encoding a new member of the membrane-type (MT) matrix metalloprotei nase (MMP) family has been identified and cloned from a human brain cDNA li brary, The isolated cDNA encodes a polypeptide of 645 amino acids that disp lays a similar domain organization as other MMPs, including a predomain wit h the activation locus, a zinc-binding site; and a hemopexin domain. The de duced amino acid sequence contains a COOH-terminal extension, rich in hydro phobic residues and similar in size to the equivalent domains identified in MT-MMPs. Immunofluorescence and Western blot analysis of COS-7 cells trans fected with the isolated cDNA revealed that the encoded protein is localize d in the plasma membrane. On the basis of these features, this novel human MMP has been called MT5-MMP because it represents the fifth member of the M T-MMP subfamily of MMPs. Fluorescent in sitre hybridization experiments sho wed that the human MT5-MMP gene (MMP-24) maps to 20q11.2, a region frequent ly amplified in tumors from diverse sources; Northern blot analysis demonst rated that MT5-MMP IP is predominantly expressed in brain, kidney, pancreas , and lung. In addition, MTS-MMP transcripts were detected at high levels c ompared to normal brain tissue in a series of brain tumors, including astro cyomas and glioblastomas. The catalytic domain of MT5-MMP, produced in Esch erichia coli as a fusion protein with glutathione S-transferase, exhibits a potent proteolytic activity against progelatinase A, leading to the genera tion of the M-r,62,000 active form of this enzyme. These data suggest that MTS-MMP may contribute to the activation of progelatinase A in tumor tissue s, in which it is overexpressed, thereby facilitating tumor-progression.