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      A Novel Enediynyl Peptide Inhibitor of Furin That Blocks Processing of proPDGF-A, B and proVEGF-C

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          Furin represents a crucial member of secretory mammalian subtilase, the Proprotein Convertase (PC) or Proprotein Convertase Subtilisin/Kexin (PCSK) superfamily. It has been linked to cancer, tumorgenesis, viral and bacterial pathogenesis. As a result it is considered a major target for intervention of these diseases.

          Methodology/Principal Findings

          Herein, we report, for the first time, the synthesis and biological evaluation of a newly designed potent furin inhibitor that contains a highly reactive beta-turn inducing and radical generating “enediynyl amino acid” (Eda) moiety. “Eda” was inserted between P1 and P1′ residues of hfurin 98–112 peptide, derived from the primary cleavage site of furin's own prodomain. The resulting hexadecapeptide derivative inhibited furin in vitro with IC 50 ∼40 nM when measured against the fluorogenic substrate Boc-RVRR-MCA. It also inhibited furin-mediated cleavage of a fluorogenic peptide derived from hSARS-CoV spike protein with IC 50 ∼193 nM. Additionally it also blocked furin-processing of growth factors proPDGF-A, B and VEGF-C that are linked to tumor genesis and cancer. Circular dichroism study showed that this inhibitor displayed a predominantly beta-turn structure while western blots confirmed its ability to protect furin protein from self degradation.


          These findings imply its potential as a therapeutic agent for intervention of cancer and other furin-associated diseases.

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          Most cited references 52

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          The activation and physiological functions of the proprotein convertases.

          The mammalian secretory proprotein convertases are part of a family of nine serine proteinases of the subtilisin-type. Seven of them cleave after basic amino acids and are called PC1/3, PC2, furin, PC4, PC5/6, PACE4 and PC7. The two other convertases SKI-1/S1P and PCSK9 are implicated in cholesterol and/or fatty acid metabolism. The convertases PC5/6 and PACE4 are activated at the cell surface where they are tethered to heparan sulfate proteoglycans. This activation pathway is unique and differs from that of furin and PC7, which are activated in the trans-Golgi network and from PC1/3 and PC2 that are activated in dense core secretory granules. While some of the basic amino acid-specific convertases may display redundant cleavages of substrates, they uniquely process certain substrates in vivo. Indeed, the conditional knockout of the PC5/6 gene in the embryo proper in mice led to severe malformations, bone morphogenic defects and death at birth. This is likely due to the absence of processing of the growth differentiating factor 11 (Gdf11). Both complete and liver-specific knockout of Pcsk9 revealed that it is a major convertase that regulates the level of circulating low-density lipoproteins (LDL) via the degradation of the hepatic LDL-receptor. This apparently non-enzymatic mechanism implicates the enhanced degradation of the LDLR in endosomes/lysosomes. These data provide evidence that an inhibitor of PCSK9-LDLR interaction is a viable target for the development of a novel cholesterol lowering drug in conjunction with the classical statins.
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            The crystal structure of the proprotein processing proteinase furin explains its stringent specificity.

            In eukaryotes, many essential secreted proteins and peptide hormones are excised from larger precursors by members of a class of calcium-dependent endoproteinases, the prohormone-proprotein convertases (PCs). Furin, the best-characterized member of the mammalian PC family, has essential functions in embryogenesis and homeostasis but is also implicated in various pathologies such as tumor metastasis, neurodegeneration and various bacterial and viral diseases caused by such pathogens as anthrax and pathogenic Ebola virus strains. Furin cleaves protein precursors with narrow specificity following basic Arg-Xaa-Lys/Arg-Arg-like motifs. The 2.6 A crystal structure of the decanoyl-Arg-Val-Lys-Arg-chloromethylketone (dec-RVKR-cmk)-inhibited mouse furin ectodomain, the first PC structure, reveals an eight-stranded jelly-roll P domain associated with the catalytic domain. Contoured surface loops shape the active site by cleft, thus explaining furin's stringent requirement for arginine at P1 and P4, and lysine at P2 sites by highly charge-complementary pockets. The structure also explains furin's preference for basic residues at P3, P5 and P6 sites. This structure will aid in the rational design of antiviral and antibacterial drugs.
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              Proprotein convertases in tumor progression and malignancy: novel targets in cancer therapy.

              The mammalian subtilisin/kexin-like proprotein convertase (PC) family has been implicated in the activation of a wide spectrum of proteins. These proteins are usually synthesized as inactive precursors before their conversion to fully mature bioactive forms. A large majority of these active proteins such as matrix metalloproteases, growth factors, and adhesion molecules are crucial in the processes of cellular transformation, acquisition of the tumorigenic phenotype, and metastases formation. Inhibition of PCs significantly affects the malignant phenotype of various tumor cells. In addition to direct tumor cell proliferation and migration blockade, PC inhibitors can also be used to target tumor angiogenesis. In this Review article we discuss a number of recent findings on the clinical relevance of PCs in cancer patients, their implication in the regulation of multiple cellular functions that impact on the invasive/metastatic potential of cancer cells. Thus, PC inhibitors may constitute new promising agents for the treatment of multiple tumors and/or in adjuvant therapy to prevent recurrence.

                Author and article information

                Role: Editor
                PLoS One
                PLoS ONE
                Public Library of Science (San Francisco, USA )
                26 November 2009
                : 4
                : 11
                [1 ]Chronic Diseases Program, Regional Protein Chemistry Center, Ottawa Hospital Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottowa, Ottawa, Canada
                [2 ]INSERM, UMRS940, Equipe AVENIR. Institut de Génétique Moléculaire, Hospital St-Louis, Paris, France
                [3 ]Université Paris 7, Paris, France
                [4 ]Department of Chemistry, Indian Institute of Technology, Kharagpur, West Bengal, India
                [5 ]Department of Chemistry, Indian Institute of Technology, Guwahati, Assam, India
                University of Helsinki, Finland
                Author notes

                Conceived and designed the experiments: AB. Performed the experiments: AB DM SB MK SSB. Analyzed the data: AB AMK. Contributed reagents/materials/analysis tools: AB. Wrote the paper: AB. Took part in discussion and formatting: SB.

                Basak et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                Page count
                Pages: 14
                Research Article
                Chemical Biology/Biocatalysis



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