Connective Tissue Growth Factor (CCN2) Induces Adhesion of Rat Activated Hepatic Stellate Cells by Binding of Its C-terminal Domain to Integrin αvβ3 and Heparan Sulfate Proteoglycan

Abstract

Connective tissue growth factor (CCN2, also known as CTGF) is a matricellular protein that appears to play an important role in hepatic stellate cell (HSC)-mediated fibrogenesis. After signal peptide cleavage, the fulllength CCN2 molecule comprises four structural modules (CCN2 1-4 ) and is susceptible to proteolysis by HSC yielding isoforms comprising essentially modules 3 and 4 (CCN2 3-4 ) or module 4 alone (CCN2 4 ). In this study we show that rat activated HSC are capable of adhesion to all three CCN2 isoforms via the binding of module 4 to integrin ␣ v ␤ 3 , a process that is dependent on interactions between module 4 and cell surface heparan sulfate proteoglycans (HSPGs). These findings are based on several lines of evidence. First, integrin ␣ v ␤ 3 was detected in HSC lysates by immunoprecipitation and Western blot, and CCN2 4 -mediated HSC adhesion was blocked by anti-integrin ␣ v ␤ 3 antibody. Second, as assessed by immunoprecipitation and solid phase binding assay, CCN2 4 bound directly to integrin ␣ v ␤ 3 in cell-free systems. Third, destruction or inhibition of synthesis of cell surface HSPGs with, respectively, heparinase or sodium chlorate abrogated HSC adhesion to CCN2 4 . Fourth, prior occupancy of heparin-binding sites on CCN2 4 with soluble heparin completely blocked HSC adhesion. These findings indicate that integrin ␣ v ␤ 3 functions as a co-receptor with HSPGs for CCN2 4 -mediated HSC adhesion. Furthermore, by peptide mapping and site-directed mutagenesis we demonstrated that the sequence IRTPKISKPIKFELSG within CCN2 4 is a unique binding domain for integrin ␣ v ␤ 3 that is sufficient to mediate integrin ␣ v ␤ 3 -and HSPG-dependent HSC adhesion. These findings offer the possibility of developing novel antifibrotic therapies that target the integrin-binding domain.

MMP‐13 deletion decreases profibrogenic molecules and attenuates N‐nitrosodimethylamine‐induced liver injury and fibrosis in mice

“…Previous studies have suggested the implications of CTGF in the pathogenesis of hepatic fibrosis characterized by deposition of fibrillar collagens in the liver 21, 44, 45, 46. The full‐length CTGF molecule comprises four structural domains, that is modules 1–4, which are susceptible to proteolysis by hepatic stellate cells, yielding C‐terminal fragments composed of the modules 3 and 4 or the module 4 alone 46.…”

Inhibition of β-catenin signaling protects against CTGF-induced alveolar and vascular pathology in neonatal mouse lung

“…Interestingly, we have also found that CTGFinduced lung pathology is associated with activation of β-catenin signaling, whereas treatment with CTGF antibody inhibits hyperoxia-activated β-catenin signaling. It is known that CTGF can activate β-catenin signaling by binding to cell surface integrins and lipoprotein receptor-related protein (LRP) 5/6, coreceptors of wingless/Int (Wnt) (13)(14)(15)(16). It is unknown, however, whether activation of β-catenin signaling mediates CTGF-induced alveolar and vascular pathology in neonatal mice.…”

“…The transcription complex formed by β-catenin and its DNA-binding partners known as LEF/TCF is able to promote chromatin remodeling and transcriptional initiation in a cell type-specific and context-specific manner, thus playing a key role in embryonic development, cell proliferation, differentiation, and survival. CTGF can directly bind to cell surface integrin complexes thus activating ILK signaling (13,14). CTGF can also directly bind to LRP5/6, coreceptors of Wnt (15,16).…”

The absence of the human platelet antigen polymorphism effect on fibrosis progression in human immunodeficiency virus-1/hepatitis C virus coinfected patients

“…The activation of the liver stellate cells has been associated with regulation by the integrin family of proteins (8) (9) , and some of these are expressed on hepatic stellate cells (6) (7) .…”

“…Similarly, the expression of some integrins, which are present in a variety of cell types, including platelets (5) and liver stellate cells (6) (7) , has been associated with the development of fi brosis (8) (9) . The integrins that are present on platelet membranes express different types of antigens, and, of these, the human platelet antigens (HPA) have received considerable attention (10) .…”