Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.7 (plasmin)
 9,023 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We studied the localization of latent transforming growth factor-beta 1 (TGF-beta 1) and its binding protein (LTBP-1) in the extracellular matrix of cultured human fibroblasts by immunofluorescence and immunoelectron microscopy. Immunofluorescence of confluent fibroblast cultures indicated that LTBP-1 localizes to extracellular fibrillar structures resembling fibronectin-collagen matrix. Similar fibrillar structures were detected in cells stained with antibodies specific for TGF-beta 1 propeptide (beta 1-LAP). Both LTBP-1 and beta 1-LAP colocalized with fibronectin in double immunofluorescence analysis. These fibrillar structures were resistant to extraction with sodium deoxycholate, which is further evidence that LTBP-1 and large latent TGF-beta 1 complexes are integral components of the extracellular matrix. SV-40-transformed human fibroblasts lacked extracellular LTBP-1 fibers. EM analysis revealed approximately 10-nm-thick microfibrils that were labeled by anti-LTBP at 90-140-nm intervals. In addition, LTBP-1 was found in structures that were heavily labeled for fibronectin. The accumulation of LTBP-1 in the fibronectin matrix could be reconstituted in vitro. When isolated matrix components were immobilized on nitrocellulose and incubated with fibroblast conditioned medium, LTBP-1 from the medium associated with cellular fibronectin but not with heparan or chondroitin sulfate, vitronectin, tenascin, laminin, or collagen I or IV. The association of LTBP-1 with cellular fibronectin was abolished by treatment of the medium with plasmin, which cleaves LTBP-1 and inhibits its assembly to matrix. The present results indicate that latent TGF-beta 1 complexes are components of the extracellular matrix and suggest that alterations of the pericellular matrix could result in aberrant TGF-beta signaling.
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PMID:Latent transforming growth factor-beta 1 and its binding protein are components of extracellular matrix microfibrils. 875 60

Transforming growth factor betas (TGF-betas) are secreted by most cell types as latent high molecular weight complexes consisting of TGF-beta and its latency associated peptide (LAP) propeptide dimers, covalently linked to latent TGF-beta-binding proteins (LTBPs). Currently, three different LTBPs are known (LTBPs 1, 2, and 3), all with highly similar protein domain structure consisting of epidermal growth factor-like and 8-Cys repeats. The 3rd 8-Cys repeat of LTBP-1 mediates its association with TGF-beta1.LAP. By using an expressed sequence tag homologous to the 3rd 8-Cys repeat of human LTBP-1 as a probe, a novel cDNA similar to known LTBPs was cloned from human heart cDNA library. This cDNA was named LTBP-4 and found to exist in at least four different forms, generated by alternative splicing at the amino terminus and at the central epidermal growth factor repeat domain. One of the alternative amino-terminal forms contained an RGD sequence, indicating possible cell-surface interactions with integrins. LTBP-4 gene was localized to chromosomal position 19q13. 1-19q13.2. The major LTBP-4 mRNA form is about 5.1 kilobase pairs in size and is predominantly expressed in the heart, aorta, uterus, and small intestine. Immunoblotting analysis indicated that LTBP-4 was secreted from cultured human lung fibroblasts both in a free form and in a disulfide bound complex with a TGF-beta. LAP-like protein. Both LTBP-4 forms were also found to be deposited in the extracellular matrix. The matrix-associated LTBP-4 was susceptible to proteolytic release with plasmin. LTBP-4 is a new member of the growing LTBP-fibrillin family of proteins and offers an alternative means for the secretion and targeted matrix deposition of TGF-betas or related proteins.
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PMID:Identification and characterization of a new latent transforming growth factor-beta-binding protein, LTBP-4. 966 Aug 15

Latent transforming growth factor beta binding protein (LTBP), a high-molecular-weight glycoprotein of the large latent TGF-beta complex is suggested to serve as an anchor for latent TGF-beta in the extracellular matrix and as a component of microfibrillar structures. Proteolytic cleavage of LTBP is supposed to be a prerequisite for the release and generation of bioactive (mature) TGF-beta. We investigated the expression of LTBP isoforms in normal and fibrotic rat liver and in cultured rat hepatic stellate cells (HSC) transdifferentiating to myofibroblasts (MFB). We further determined their interaction with the matrix and some of their basic functions. Immunostainings of normal and fibrotic livers demonstrate intense signals for LTBP-1 and -2, preferably in parenchymal, but also nonparenchymal, cells and in fibrotic extracellular matrix. However, in situ hybridization points to a restriction of transcripts to nonparenchymal cells from fibrotic livers, whereas hepatocytes were always devoid of LTBP transcripts. The findings were confirmed by real-time quantitative reverse-transcription polymerase chain reaction (RT-PCR), which showed isoform-specific increases of LTBP transcripts in cultured stellate cells transdifferentiating to MFB and by Northern blot analyses showing the absence of LTBP-1 mRNA in freshly isolated hepatocytes. Using a cell enzyme-linked immunosorbent assay (ELISA), a differential increase of partly deoxycholate (DOC)-resistant, matrix-bound LTBP-1 and -2 was measured in cultured stellate cells. Treatment with plasmin generated soluble LTBP-1 and bioactive TGF-beta, which was able to induce Smad7 expression in an autocrine fashion. Our data propose (transdifferentiating) stellate cells, respectively MFB, as the major source of LTBP in normal and fibrotic liver, which here probably fulfills structural and TGF-beta-regulating functions as suggested for nonhepatic tissues.
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PMID:Expression and matrix deposition of latent transforming growth factor beta binding proteins in normal and fibrotic rat liver and transdifferentiating hepatic stellate cells in culture. 1117 40

In mouse embryonic fibroblasts (MEF) lacking dioxin receptor (AhR), high levels of latent transforming growth factor-beta (TGF-beta)-binding protein-1 (LTBP-1) correlated with increased TGF-beta1 activity, an observation suggesting that LTBP-1 could contribute to maintain TGF-beta1 levels. Here, using small interfering RNAs (siRNA), we have first analyzed if LTBP-1 expression affected TGF-beta1 activity in MEF cells. We have then determined how LTBP-1 levels could alter the activity of extracellular proteases known to activate TGF-beta1, and finally, whether protease inhibition could reduce TGF-beta1 activation. LTBP-1 inhibition by siRNA in AhR-/- MEF decreased the amount of active TGF-beta1 and reduced plasminogen activators (PA)/plasmin and elastase activities and thrombospondin-1 (TSP-1) expression, without significantly affecting their mRNA levels. On the contrary, LTBP-1 siRNA restored matrix metalloproteinase-2 (MMP-2) activity in AhR-/- MEF. Interestingly, whereas a TGF-beta1 neutralizing antibody mimicked many of the LTBP-1 siRNA effects on extracellular proteases, addition of recombinant TGF-beta1 protein increased proteases activity over basal levels in AhR-/- MEF. These proteases contributed to TGF-beta activation since their specific inhibitors reduced active TGF-beta levels in these cells. These results suggest that LTBP-1 contributes to TGF-beta1 activation in MEF, possibly by influencing the activities of PA/plasmin, elastase, TSP-1, and MMP-2. TGF-beta1, on the other hand, could be also involved in maintaining the activity of these extracellular proteases. Thus, LTBP-1 appears to play a role in TGF-beta1 activation through a process involving extracellular protease activities, which, in turn, could be affected by TGF-beta1 levels.
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PMID:LTBP-1 blockade in dioxin receptor-null mouse embryo fibroblasts decreases TGF-beta activity: Role of extracellular proteases plasmin and elastase. 1618 95

Targeting of transforming growth factor beta (TGF-beta) to the extracellular matrix (ECM) by latent TGF-beta binding proteins (LTBPs) regulates the availability of TGF-beta for interactions with endothelial cells during their quiescence and activation. However, the mechanisms which release TGF-beta complexes from the ECM need elucidation. We find here that morphological activation of endothelial cells by phorbol 12-myristate 13-acetate (PMA) resulted in membrane-type 1 matrix metalloproteinase (MT1-MMP) -mediated solubilization of latent TGF-beta complexes from the ECM by proteolytic processing of LTBP-1. These processes required the activities of PKC and ERK1/2 signaling pathways and were coupled with markedly increased MT1-MMP expression. The functional role of MT1-MMP in LTBP-1 release was demonstrated by gene silencing using lentiviral short-hairpin RNA as well as by the inhibition with tissue inhibitors of metalloproteinases, TIMP-2 and TIMP-3. Negligible effects of TIMP-1 and uPA/plasmin system inhibitors indicated that secreted MMPs or uPA/plasmin system did not contribute to the release of LTBP-1. Current results identify MT1-MMP-mediated proteolytic processing of ECM-bound LTBP-1 as a mechanism to release latent TGF-beta from the subendothelial matrix.
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PMID:MT1-MMP releases latent TGF-beta1 from endothelial cell extracellular matrix via proteolytic processing of LTBP-1. 1860 1