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MT1-MMP1 (MMP-14) is a member of a large family of zinc endoproteinases, matrixins or matrix metalloproteinases (MMPs) (1, 2). There are several structural features such as the modular domain structure and the existence of an N-terminal propeptide domain, a zinc-coordinating active site domain, and a C-terminal hemopexin-like domain that are characteristic for most MMPs (1-3). A subfamily of membrane type (MT)-MMPs including MT1-MMP is distinguished by a relatively short transmembrane domain and a cytoplasmic tail, which associate these enzymes with discrete regions of the plasma membrane and the intracellular compartment. MT1-MMP expression has been documented in many tumor cell types and strongly implicated in malignant progression (3, 4). In addition to its ability to directly cleave certain components of the extracellular matrix (5, 6), MT1-MMP initiates the activation pathway of the most widespread MMP, MMP-2, by converting pro-MMP-2 into an activation intermediate that further undergoes autocatalytic conversion to generate the mature enzyme of MMP-2 (7-9). Structure-function relationships of MT1-MMP (10 -16) and the mechanisms of pro-MMP-2 activation to the mature enzyme (9,(17)(18)(19)(20) are not understood in detail (21)(22)(23)). An immediate proximity of at least two molecules of MT1-MMP (an "activator" and a "receptor") on the cell surface is required for in trans activation of MMP-2 to the mature form (17,19,20,24). However, there is no direct biochemical evidence to support the existence of MT1-MMP oligomers on cell surfaces. In addition, mechanisms involved in activation and trafficking of MT1-MMP are not well elucidated and remain controversial (10,(13)(14)(15)(25)(26)(27)(28). Thus, furin, a serine proteinase of the trans-Golgi network, has been earlier assumed to function as a unique activator of MT1-MMP (25). However, evidence is emerging that there could be alternative pathways of 28). In this respect, it is not possible to rule out certain autocatalytic steps in MT1-MMP activation such as those involved in the activation pathway of pro-MMP-2 and pro- [29][30][31].To better understand functions of MT1-MMP, we con-* This work was supported by National Institutes of Health Grants CA83017 and CA77470, California Breast Cancer Program Grant 5JB0094, and Susan G. Komen Breast Cancer Foundation Grant 9849 (to A. Y. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.¶ To whom correspondence and reprint requests should be addressed: The Burnham Institute, 10901 North Torrey Pines Rd., La Jolla, CA 92037. Tel.: 858-713-6271; Fax: 858-646-3192; E-mail: strongin@ burnham.org 1 The abbreviations used are: MT, membrane type; MMP, matrix metalloproteinase; BSA, bovine serum albumin; PBS, phosphate-buffered saline; DPBS, Dulbecco's phosphate-buffered saline; DMEM, Dulbecco's modified Eagle's medium; TIMP, tissue inhibitor of me...

Identification of expanding roles for matrix metalloproteinases (MMPs) in complex regulatory processes of tissue remodelling has stimulated the search for genes encoding proteinases with unique functions, regulation and expression patterns. By using a novel cloning strategy, we identified three previously unknown human MMPs, i.e. MMP-21, MMP-26 and MMP-28, in comprehensive gene libraries. The present study is focused on the gene and the protein of a novel MMP, MMP-26. Our findings show that MMP-26 is specifically expressed in cancer cells of epithelial origin, including carcinomas of lung, prostate and breast. Several unique structural and regulatory features, including an unusual 'cysteine-switch' motif, discriminate broad-spectrum MMP-26 from most other MMPs. MMP-26 efficiently cleaves fibrinogen and extracellular matrix proteins, including fibronectin, vitronectin and denatured collagen. Protein sequence, minimal modular domain structure, exon-intron mapping and computer modelling demonstrate similarity between MMP-26 and MMP-7 (matrilysin). However, substrate specificity and transcriptional regulation, as well as the functional role of MMP-26 and MMP-7 in cancer, are likely to be distinct. Despite these differences, matrilysin-2 may be a suitable trivial name for MMP-26. Our observations suggest an important specific function for MMP-26 in tumour progression and angiogenesis, and confirm and extend the recent findings of other authors [Park, Ni, Gerkema, Liu, Belozerov and Sang (2000) J. Biol. Chem. 275, 20540--20544; Uría and López-Otín (2000) Cancer Res. 60, 4745--4751; de Coignac, Elson, Delneste, Magistrelli, Jeannin, Aubry, Berthier, Schmitt, Bonnefoy and Gauchat (2000) Eur. J. Biochem. 267, 3323--3329].

No abstract

Identification of expanding roles for matrix metalloproteinases (MMPs) in complex regulatory processes of tissue remodelling has stimulated the search for genes encoding proteinases with unique functions, regulation and expression patterns. By using a novel cloning strategy, we identified three previously unknown human MMPs, i.e. MMP-21, MMP-26 and MMP-28, in comprehensive gene libraries. The present study is focused on the gene and the protein of a novel MMP, MMP-26. Our findings show that MMP-26 is specifically expressed in cancer cells of epithelial origin, including carcinomas of lung, prostate and breast. Several unique structural and regulatory features, including an unusual ' cysteine-switch ' motif, discriminate broadspectrum MMP-26 from most other MMPs. MMP-26 efficiently cleaves fibrinogen and extracellular matrix proteins, including fibronectin, vitronectin and denatured collagen. Protein sequence, minimal modular domain structure, exon-intron map-