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J. Biol. Chem., Vol. 279, Issue 24, 25143-25148, June 11, 2004

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A Cellular Metalloproteinase Activates Vibrio cholerae Pro-cytolysin^*

Angela Valeva, Ivan Walev, Silvia Weis, Fatima Boukhallouk, Trudy M. Wassenaar¶, Kristina Endres||, Falk Fahrenholz||, Sucharit Bhakdi, and Alexander Zitzer

From the Institute of Medical Microbiology and Hygiene, University of Mainz, D55101 Mainz, Germany, ^¶Molecular Microbiology and Genomics Consultants, D55576 Zotzenheim, Germany, and ^||Institute of Biochemistry, University of Mainz, D55099 Mainz, Germany

Many strains of Vibrio cholerae produce a cytolysin (VCC) that forms oligomeric transmembrane pores in animal cells. The molecule is secreted as a procytolysin (pro-VCC) of 79 kDa that must be cleaved at the N terminus to generate the active 65-kDa toxin. Processing can occur in solution, and previous studies have described the action of mature VCC thus generated. However, little is known about the properties of pro-VCC itself. In this study, it is shown that pro-VCC exist as a monomer in solution and binds as a monomer to eukaryotic cells. Bound pro-VCC can then be activated either by exogenous, extracellular, or by endogenous, cell-bound proteases. In both cases, cleavage generates the 65-kDa VCC that oligomerizes to form transmembrane pores. A wide variety of exogenous proteinases can mediate activation. In contrast, the activating cellular protease is selectively inhibited by the hydroxamate inhibitor TAPI, and thus probable candidates are members of the ADAM-metalloproteinase family. Furin, MMP-2, MMP-9, and serine proteinases were excluded. Cells over-expressing ADAM-17, also known as tumor necrosis factor converting enzyme, displayed increased activation of VCC, and knockout cells lacking ADAM-17 had a markedly decreased capacity to cleave the protoxin. The possibility is raised that pro-VCC is targeted to membrane sites that selectively contain or are accessible to cellular ADAM-metalloproteinases. Although many microbial toxins are activated by furin, this is the first evidence for processing by a cellular metalloproteinase. We identified ADAM-17 as a potent activator of pro-VCC.

Received for publication, December 19, 2003 , and in revised form, March 31, 2004.

^* This work was supported by Deutsche Forschungsgemeinschaft Grant SFB 490, project C1. 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 should be addressed: Institute of Medical Microbiology and Hygiene, University of Mainz, Augustusplatz, D55101 Mainz, Germany. Tel.: 49-6131-39-36363; Fax: 49-6131-39-32359; E-mail: avaleva{at}uni-mainz.de.

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