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Interleukin-6 (IL-6), leukemia inhibitory factor, oncostatin M, IL-11, and ciliary neurotropic factor are a family of cytokines and neuronal differentiation factors which bind to composite plasma membrane receptors sharing the signal transducing subunit gpl30. We have shown recently that IL-6 and leukemia inhibitory factor rapidly activate a latent cytoplasmic transcription factor, acute-phase response factor (APRF), by tyrosine phosphorylation, which then binds to IL-6 response elements of various IL-6 target genes. Here we demonstrate that APRF is activated by all cytokines acting through gpl30 and is detected in a wide variety of cell types, indicating a central role of this transcription factor in gpl30-mediated signaling. APRF activation is also observed in vitro upon addition of IL-6 to cell homogenates. Protein tyrosine kinase inhibitors block both the tyrosine phosphorylation and DNA binding of APRF. The factor was purified to homogeneity from rat liver and shown to consist of a single 87-kDa polypeptide, while two forms (89 and 87 kDa) are isolated from human hepatoma cells. As reported earlier, the binding sequence specificity of APRF is shared by gamma interferon (IFN-y) activation factor, which is formed by the Stat9l protein. Partial amino acid sequence obtained from purified rat APRF demonstrated that it is likely to be related to Stat9l. In fact, an antiserum raised against the amino-terminal portion of Stat9l cross-reacted with APRF, suggesting the relatedness of APRF and Stat9l. Altogether, these data indicate that APRF belongs to a growing family of Stat-related proteins and that IFN-y and IL-6 use similar signaling pathways to activate IFN-y activation factor and APRF, respectively.Communication between cells interacting in the immune and hematopoietic systems is mediated by a class of soluble polypeptides generally referred to as cytokines. Most cytokines exert multiple effects on different cell types, a typical example being interleukin-6 (IL-6), which during injuries and infections is released by monocytes, endothelial cells, fibroblasts, and other cells. IL-6 is involved in the differentiation of B and T cells, acts as myeloma growth factor, and is the main mediator of the acute-phase response in the liver (reviewed in references 23 and 33). IL-6 specifically binds to a cell surface receptor which consists of two types of subunits, the ligand-binding glycoprotein gp8O and the signal transducer gpl3O (24,67). Binding of IL-6 to gp8O induces homodimerization and tyrosine phosphorylation of gpl3O (42)

Matrix metalloproteinase-9 (MMP-9) is the major MMP produced by B-CLL cells and contributes to their tissue infiltration by degrading extracellular and membrane-anchored substrates. Here we describe a different function for MMP-9 in B-CLL, which involves the hemopexin domain rather than its catalytic function. Binding of soluble or immobilized (pro)MMP-9, a catalytically inactive proMMP-9 mutant, or the MMP-9 hemopexin domain to its docking receptors alpha4beta1 integrin and CD44v, induces an intracellular signaling pathway that prevents B-CLL apoptosis. This pathway is induced in all B-CLL cases, is active in B-CLL lymphoid tissues, and consists of Lyn activation, STAT3 phosphorylation, and Mcl-1 upregulation. Our results establish that MMP/receptor binding induces intracellular survival signals and highlight the role of (pro)MMP-9 in B-CLL pathogenesis.

Tissue inhibitor of metalloproteinases-1 (TIMP-1) plays a crucial role in the pathogenesis of hepatic fibrosis and thus may represent an important therapeutic target in the design of anti-fibrotic strategies for chronic liver disease. We present an innovative therapy based on the assignment of inactivated enzymes acting as scavengers for TIMP-1. Hepatic fibrosis was induced in BALB/c mice by repetitive intraperitoneal CCl4 injection. The animals were treated with proteolytic inactive matrix metalloproteinase-9 mutants (E402Q, H401A, E402H/H411E) using adenovirus-mediated gene transfer. Application of these MMP-9 mutants inhibited fibrogenesis, which was indicated by decreasing portal and periportal accumulation of collagen. Total hydroxyproline of liver tissue, the morphometric stage of fibrosis as well as mRNA expression of marker proteins for hepatic fibrosis in livers of E402Q- and H401A-treated mice were significantly reduced. MMP-9 mutants suppressed transdifferentiation of hepatic stellate cells to the myofibroblast like phenotype in vitro and in vivo. Moreover, adenoviral application of the mutants MMP-9-H401A and -E402Q led to increased apoptosis of activated hepatic stellate cells, thought to be the main promoters of hepatic fibrosis. Application of MMP-9 mutants as TIMP-1 scavengers may provide a new therapeutic strategy for hepatic fibrosis.

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Liver fibrosis, a reversible wound-healing response to chronic cellular injury, reflects a balance between liver repair and progressive substitution of the liver parenchyma by scar tissue. Complex mechanisms that underlie liver fibrogenesis are summarized to provide the basis for generating targeted therapies to reverse fibrogenesis and improve the outcomes of patients with chronic liver disease. This minireview presents some pathophysiological aspects of liver fibrosis as a dynamic process and elucidates matrix metalloproteinases (MMPs) and their role within as well as beyond matrix degradation. Open questions remain, whether inhibition of fibrogenesis or induction of fibrolysis is the key mechanism to resolve fibrosis. And a point of principle might be whether regeneration of liver cirrhosis is possible. Will we ever cure fibrosis?

Matrix metalloproteinases (MMPs) are involved in the remodeling processes of the extracellular matrix and the basement membrane. Most MMPs are composed of a regulatory, a catalytic, and a hemopexin subunit. In many tumors the expression of MMP-9 correlates with local tumor growth, invasion, and metastasis. To analyze the role of the hemopexin domain in these processes, the MMP-9 hemopexin domain (MMP-9-PEX) was expressed as a glutathione S-transferase fusion protein in Escherichia coli. After proteolytic cleavage, the isolated PEX domain was purified by size exclusion chromatography. In a zymography assay, MMP-9-PEX was able to inhibit MMP-9 activity. The association and dissociation rates for the interaction of MMP-9-PEX with gelatin were determined by plasmon resonance. From the measured rate constants, the dissociation constant was calculated to be K d ‫؍‬ 2,4 ؋ 10 ؊8 M, demonstrating a high affinity between MMP-9-PEX and gelatin. In Boyden chamber experiments the recombinant MMP-9-PEX was able to inhibit the invasion of melanoma cells secreting high amounts of MMP-9 in a dose-dependent manner. These data demonstrate for the first time that the hemopexin domain of MMP-9 has a high affinity binding site for gelatin, and the particular recombinant domain is able to block MMP-9 activity and tumor cell invasion. Because MMP-9 plays an important role in metastasis, this antagonistic effect may be utilized to design MMP inhibition-based cancer therapy.Matrix metalloproteinases (MMPs) 1 are a family of zinc metallo-endopeptidases secreted by cells. They are responsible for most of the turnover of matrix components. The MMPs are produced as zymogens with a signal sequence and propeptide segment that has to be removed during activation. The propeptide domain contains a conserved cysteine that chelates the zinc in the active site. The gelatinases MMP-2 and MMP-9 contain fibronectin type II domains that are inserted in the middle of the catalytic domain, presumably to enhance substrate binding (1). MMP-9 also has a collagen type V-like domain located between the catalytic and the C-terminal hemopexin domain (Fig. 1). All but two MMPs (MMP-7 and MMP-26) contain a regulatory subunit, the hemopexin domain, separated from the catalytic domain by a variable hinge region (2). This domain is thought to confer much of the substrate specificity to the MMPs (3). It is involved in activation as well as inhibition of MMPs (3,4) and may enhance substrate binding and specificity (5). The hinge region also confers specificity to the MMPs either by direct binding of the substrate or by setting the orientation of the hemopexin domain and the catalytic domain (6). The hemopexin domain of MMP-2 is known to bind heparin (7). Heparin has been shown to potentiate the activities of some MMPs, and MMPs are often found associated with heparin sulfate glycosaminoglycans on the cell surface (8). The overall three-dimensional structure of the hemopexin domain is a four-bladed propeller with a calcium binding site nestled in the folds (3). A fragme...

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