Article

LRP1 regulates remodeling of the extracellular matrix by fibroblasts.

Department of Pathology, University of California San Diego, La Jolla, California 92093, USA.
Matrix biology: journal of the International Society for Matrix Biology (impact factor: 3.56). 09/2009; 29(1):22-30. DOI:10.1016/j.matbio.2009.08.003 pp.22-30
Source: PubMed

ABSTRACT Low density lipoprotein receptor-related protein (LRP1) is an endocytic receptor for diverse proteases, protease inhibitors, and other plasma membrane proteins, including the urokinase receptor (uPAR). LRP1 also functions in cell-signaling and regulates gene expression. The goal of this study was to determine whether LRP1 regulates remodeling of provisional extracellular matrix (ECM) by fibroblasts. To address this problem, we utilized an in vitro model in which type I collagen was reconstituted and overlaid with fibronectin. Either the collagen or fibronectin was fluorescently-labeled. ECM remodeling by fibroblasts deficient in LRP1, uPAR, or MT1-MMP was studied. MT1-MMP was required for efficient remodeling of the deep collagen layer but not involved in fibronectin remodeling. Instead, fibronectin was remodeled by a system that required urokinase-type plasminogen activator (uPA), uPAR, and exogenously-added plasminogen. LRP1 markedly inhibited fibronectin remodeling by regulating cell-surface uPAR and plasminogen activation. LRP1 also regulated remodeling of the deep collagen layer but not by controlling MT1-MMP. Instead, LRP1 deficiency or inhibition de-repressed a secondary pathway for collagen remodeling, which was active in MT1-MMP-deficient cells but not in uPAR-deficient cells. These results demonstrate that LRP1 regulates ECM remodeling principally by repressing pathways that require plasminogen activation by uPA in association with uPAR.

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  • Article: Down-regulation of monocyte tissue factor mediated by tissue factor pathway inhibitor and the low density lipoprotein receptor-related protein.
    A Hamik, H Setiadi, G Bu, R P McEver, J H Morrissey
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    ABSTRACT: Inflammatory mediators like bacterial lipopolysaccharide induce monocytes to express tissue factor (TF), the cell-surface protein that triggers the blood clotting cascade in hemostasis and thrombotic disease. The physiologic ligand for TF is the serine protease, factor VIIa (FVIIa), and the resulting bimolecular enzyme, TF/FVIIa, can be reversibly inhibited by tissue factor pathway inhibitor (TFPI). Culturing monocytic cells in the presence of both FVIIa and TFPI caused down-regulation of TF expression via reducing its half-life. To exert this effect, FVIIa had to be competent to bind both TF and TFPI, and TFPI had to contain the C-terminal domain required for binding to other cell-surface receptors, including the low density lipoprotein receptor-related protein (LRP). TF down-regulation by FVIIa plus TFPI was abrogated by the 39-kDa receptor-associated protein, which blocks binding of all known ligands to LRP. Furthermore, treatment with FVIIa plus TFPI caused monocyte TF to colocalize with alpha-adaptin, a component of clathrin-coated pits. Thus, in addition to reversibly inhibiting TF/FVIIa catalytic activity, TFPI also mediates the permanent down-regulation of cell-surface TF in monocytic cells via LRP-dependent internalization and degradation. This represents an unusual mechanism for receptor internalization, requiring ligand-dependent bridging of one cell-surface receptor (TF) to a second cell-surface receptor (LRP), the latter being capable of clathrin-mediated internalization.
    Journal of Biological Chemistry 03/1999; 274(8):4962-9. · 4.77 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

Keywords

collagen layer
 
diverse proteases
 
exogenously-added plasminogen
 
fibroblasts deficient
 
inhibition de-repressed
 
Low density lipoprotein receptor-related protein
 
LRP1 regulates
 
LRP1 regulates ECM
 
MT1-MMP-deficient cells
 
plasma membrane proteins
 
plasminogen activation
 
provisional extracellular matrix
 
regulates gene expression
 
regulating cell-surface uPAR
 
require plasminogen activation
 
required urokinase-type plasminogen activator
 
secondary pathway
 
uPAR
 
uPAR-deficient cells
 
vitro model
 

Alban Gaultier