No abstract

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.