Connective tissue growth factor: a cysteine-rich mitogen secreted by human vascular endothelial cells is related to the SRC-induced immediate early gene product CEF-10

Kinetics of expression of connective tissue growth factor gene during liver regeneration after partial hepatectomy and D-galactosamine-induced liver injury in rats

Connective tissue growth factor (CTGF) is up-regulated by TGF-beta1 during wound healing. The present study examined the expression of CTGF during regeneration after 70% partial hepatectomy (PH) or d-galactosamine (GalN)-injured liver in rats. CTGF, TGF-beta1, and type I collagen mRNAs were semiquantified by a ribonuclease protection assay. After PH, TGF-beta1 and type I collagen were increased at 2-6 h and at 12-48 h. CTGF increased at 6 h and returned to the control level thereafter. The ribonuclease protection assay of cultured hepatic stellate cells (HSC) and in situ hybridization suggest that the cells express CTGF along sinusoid might be HSCs. After GalN administration, CTGF increased at 2-96 h with a shoulder peak at 6-12 h followed by a main peak at 24 h. TGF-beta1 and type I collagen were up-regulated with kinetics similar to those of CTGF. The different kinetics between PH and GalN regenerations indicate that regulation of CTGF in the two processes is different. Higher TGF-beta1 expression after inflammatory/necrotic process in the GalN regeneration may caused the prolonged CTGF expression.

CTGF expression is induced by TGF- beta in cardiac fibroblasts and cardiac myocytes: a potential role in heart fibrosis

Connective tissue growth factor (CTGF) is a cysteine-rich protein induced by transforming growth factor beta (TGF- beta) in connective tissue cells. CTGF can trigger many of the cellular processes underlying fibrosis, such as cell proliferation, adhesion, migration and the synthesis of extracellular matrix; however, its role in acute and chronic cardiac injury is not fully understood. Here, we show that TGF- beta is a specific inducer of CTGF expression in both cardiac fibroblasts and cardiac myocytes. The activity of a CTGF promoter-based reporter construct correlated with endogenous CTGF expression, suggesting that TGF- beta induces CTGF expression most likely by activating its promoter. Upregulation of CTGF coincided with an increase in fibronectin, collagen type I and plasminogen activator inhibitor-1 production. Forskolin, a stimulator of cyclic AMP, blocked TGF- beta induced CTGF expression and reduced the basal level of CTGF, whereas an inhibitor that blocks the MAP kinase signaling pathway (PD 98059) significantly enhanced TGF- beta induced CTGF expression. Furthermore, we found that both TGF- beta and CTGF mRNAs were significantly elevated in the left ventricles and septa of rat hearts 2-16 weeks following myocardial infarction. This correlated well with concomitant increases in fibronectin, and type I and type III collagen mRNA levels in these animal hearts. Significant upregulation of CTGF was also detected in human heart samples derived from patients diagnosed with cardiac ischemia. Based on these findings, we propose that CTGF is an important mediator of TGF- beta signaling in the heart and abnormal expression of this gene could be used as a diagnostic marker for cardiac fibrosis.

Connective tissue growth factor: potential role in glomerulosclerosis and tubulointerstitial fibrosis

Transforming growth factor beta (TGF-beta) is a pivotal driver of glomerulosclerosis and tubulointerstitial fibrosis in renal diseases. Because TGF-beta also plays important anti-inflammatory and antiproliferative roles in mammalian systems, there has been a recent drive to elucidate downstream mediators of TGF-beta's pro-fibrotic effects with the ultimate goal of developing new anti-fibrotic strategies for treatment of chronic diseases. Connective tissue growth factor (CTGF) belongs to the CCN family of immediate early response genes. Several lines of evidence suggest that CTGF is an important pro-fibrotic molecule in renal disease and that CTGF contributes to TGF-beta bioactivity in this setting. CTGF expression is increased in the glomeruli and tubulointerstium in a variety of renal disease in association with scarring and sclerosis of renal parenchyma. In model systems in vitro, mesangial cell CTGF expression is induced by high extracellular glucose, cyclic mechanical strain and TGF-beta. Recombinant human CTGF augments the production of fibronectin and type IV collagen by mesangial cells and the effects of high glucose on mesangial cell CTGF expression and matrix production are attenuated, in part, by anti-TGF-beta antibody. In aggregate, these observations identify CTGF as an attractive therapeutic target in fibrotic renal diseases.

Identification of an RNA element that confers post-transcriptional repression of connective tissue growth factor/hypertrophic chondrocyte specific 24 (ctgf/hcs24) gene: similarities to retroviral RNA-protein interactions

The repressive effect of the 3'-untranslated region (3'-UTR) in human connective tissue growth factor/ hypertrophic chondrocyte specific 24 (ctgf/hcs24) mRNA on gene expression had been demonstrated in our previous study. Here, we identified a minimal RNA element in the 3'-UTR, which acts as a cis-acting element of structure-anchored repression (CAESAR). Deletion analyses of the 3'-UTR led us to minimize the element of 84 bases at the junction of the coding region and the 3'-UTR. The minimized RNA segment is predicted, and actually capable of forming a stable secondary structure in vitro. Mutational analyses disclosed a significant relationship between the predicted structure and repressive effect. The utility of CAESAR as a post-transcriptional regulatory element was represented by the fact that steady-state mRNA levels were not affected by CAESAR linked in cis, while protein levels from such a chimeric gene were markedly reduced. Of note, the CAESAR sequence exerted no effect, when it was placed upstream of the promoter. Finally, RNA gel electromobility-shift analyses demonstrated a nuclear factor that interacts with the folded CAESAR. Taken together, it was uncovered that CAESAR of ctgf is a novel post-transcriptional structured RNA regulatory element, probably acting through direct interactions with a nuclear factor as observed in retroviral RNA elements with certain proteins.

CTGF (IGFBP-rP2) is specifically expressed in malignant lymphoblasts of patients with acute lymphoblastic leukaemia (ALL)

Connective tissue growth factor (CTGF) is a major chemotactic and mitogenic factor for connective tissue cells. The amino acid sequence shares an overall 28-38% identity to IGFBPs and contains critical conserved sequences in the amino terminus. It has been demonstrated that human CTGF specifically binds IGFs with low affinity and is considered to be a member of the IGFBP superfamily (IGFBP-rP2). In the present study, the expression of CTGF (IGFBP-rP2) in human leukaemic lymphoblasts from children with acute lymphoblastic leukaemia (ALL) was investigated. RNA samples from tumour clones enriched by ficoll separation of bone marrow or peripheral blood mononuclear cells (MNC) from 107 patients with childhood ALL at diagnosis and 57 adult patients with chronic myeloid leukaemia (CML) were studied by RT-PCR. In addition MNC samples from children with IDDM and cord blood samples from healthy newborns were investigated as control groups. Sixty-one percent of the patients with ALL (65 of 107) were positive for CTGF (IGFBP-rP2) expression. In the control groups, no expression of CTGF (IGFBP-rP2) in peripheral MNC was detected, and in the group of adult CML patients only 3.5% (2 of 57) were positive for this gene. The role of CTGF (IGFBP-rP2) in lymphoblastic leukaemogenesis requires further evaluation, as does its potential utility as a tumour marker.

Connective tissue growth factor: what's in a name?

Connective tissue growth factor (CTGF) is a member of the recently described CCN gene family which contains CTGF itself, cyr61, nov, elm1, Cop1, and WISP-3. CTGF is transcriptionally activated by several factors although its stimulation by transforming growth factor beta (TGF-beta) has attracted considerable attention. CTGF acts to promote fibroblast proliferation, migration, adhesion, and extracellular matrix formation, and its overproduction is proposed to play a major role in pathways that lead to fibrosis, especially those that are TGF-beta-dependent. This includes fibrosis of major organs, fibroproliferative diseases, and scarring. CTGF also appears to play a role in the extracellular matrix remodeling that occurs in normal physiological processes such as embryogenesis, implantation, and wound healing. However, recent advances have shown that CTGF is involved in diverse autocrine or paracrine actions in several other cell types such as vascular endothelial cells, epithelial cells, neuronal cells, vascular smooth muscle cells, and cells of supportive skeletal tissues. Moreover, in some circumstances CTGF has negative effects on cell growth in that it can be antimitotic and apoptotic. In light of these discoveries, CTGF has been implicated in a diverse variety of processes that include neovascularization, transdifferentiation, neuronal scarring, atherosclerosis, cartilage differentiation, and endochondral ossification. CTGF has thus emerged as a potential important effector molecule in both physiological and pathological processes and has provided a new target for therapeutic intervention in fibrotic diseases.

Activation of protein kinase C inhibits the expression of connective tissue growth factor

Connective tissue growth factor (CTGF) is a member of a protein family in which 38 cysteine residues are conserved. Although a wide variety of important biological functions have been ascribed to these proteins in recent years, the regulation of their gene expression for most members is virtually unknown. We studied the effects of protein kinase C (PKC) and tyrosine kinase on the expression of CTGF and observed that at the mRNA level CTGF expression is inhibited by the activation of PKC, but stimulated by the inhibition of PKC and tyrosine kinase. We further determined that the novel and the classical PKC isoforms are needed for the inhibition, but the atypical isoforms are not involved. Our data suggest that phosphorylation on serine/threonine and tyrosine by PKC and by tyrosine kinase are all inhibitory to the expression of CTGF.

Autocrine overexpression of CTGF maintains fibrosis: RDA analysis of fibrosis genes in systemic sclerosis

We have used representational difference analysis (RDA) to identify up-regulated genes in skin fibroblasts from fibrotic lesions obtained from patients with systemic sclerosis (scleroderma). RDA of cDNA libraries derived from fibroblasts from involved and uninvolved skin detected several differentially expressed genes. One such gene consistently up-regulated in scleroderma cells coded for human connective tissue growth factor (CTGF). Other studies described here show that the CTGF protein is readily detected in cultures of systemic sclerosis fibroblasts but was not detected in comparable normal cells. High levels of CTGF are also evident in biological fluids from patients with systemic sclerosis. TGFbeta stimulates CTGF production in both normal and systemic sclerosis fibroblasts with the latter found to be higher producers. Moreover, an analysis of constitutive and TGFbeta-induced CTGF gene activation showed altered and elevated transcriptional responses in systemic sclerosis cells compared with controls. CTGF stimulated a two- to threefold increase in proalpha1(I) collagen and fibronectin synthesis by both dermal and lung fibroblasts in culture and promoted significant matrix remodeling of fibroblast-populated three-dimensional collagen lattices. A direct relation between the overexpression of CTGF and elevated collagen synthesis was suggested by the observation that transfection of a CMV-CTGF cDNA construct and protein expression in fibroblasts increased the transcription of a Col 1alpha2 promoter-reporter construct to levels seen in systemic sclerosis fibroblasts. Using Col 1alpha2 promoter deletion constructs the CTGF responsive element was localized to the first 379 bp upstream of the transcriptional start site. These data indicate that there is an overexpression of CTGF in the systemic sclerosis cells, probably due to increased gene transcription, and suggest that the dysregulation of CTGF production is an important factor in fibroblast activation and the excessive deposition of collagen in systemic sclerosis.

Genes expressed in human tumor endothelium

To gain a molecular understanding of tumor angiogenesis, we compared gene expression patterns of endothelial cells derived from blood vessels of normal and malignant colorectal tissues. Of over 170 transcripts predominantly expressed in the endothelium, 79 were differentially expressed, including 46 that were specifically elevated in tumor-associated endothelium. Several of these genes encode extracellular matrix proteins, but most are of unknown function. Most of these tumor endothelial markers were expressed in a wide range of tumor types, as well as in normal vessels associated with wound healing and corpus luteum formation. These studies demonstrate that tumor and normal endothelium are distinct at the molecular level, a finding that may have significant implications for the development of anti-angiogenic therapies.

Effects of CTGF/Hcs24, a hypertrophic chondrocyte-specific gene product, on the proliferation and differentiation of osteoblastic cells in vitro

Connective tissue growth factor/hypertrophic chondrocyte-specific gene product Hcs24 (CTGF/Hcs24) promotes the proliferation and differentiation of chondrocytes and endothelial cells which are involved in endochondral ossification (Shimo et al., 1998, J Biochem 124:130-140; Shimo et al., 1999, J Biochem 126:137-145; Nakanishi et al., 2000, Endocrinology 141:264-273). To further clarify the role of CTGF/Hcs24 in endochondral ossification, here we investigated the effects of CTGF/Hcs24 on the proliferation and differentiation of osteoblastic cell lines in vitro. A binding study using (125)I-labeled recombinant CTGF/Hcs24 (rCTGF/Hcs24) disclosed two classes of specific binding sites on a human osteosarcoma cell line, Saos-2. The apparent dissociation constant (Kd) value of each binding site was 17.2 and 391 nM, respectively. A cross-linking study revealed the formation of (125)I-rCTGF/Hcs24-receptor complex with an apparent molecular weight of 280 kDa. The intensity of (125)I-rCTGF/Hcs24-receptor complex decreased on the addition of increasing concentrations of unlabeled rCTGF/Hcs24, but not platelet-derived growth factor-BB homodimer or basic fibroblast growth factor. These findings suggest that osteoblastic cells have specific receptor molecules for CTGF/Hcs24. rCTGF/Hcs24 promoted the proliferation of Saos-2 cells and a mouse osteoblast cell line MC3T3-E1 in a dose- and time-dependent manner. rCTGF/Hcs24 also increased mRNA expression of type I collagen, alkaline phosphatase, osteopontin, and osteocalcin in both Saos-2 cells and MC3T3-E1 cells. Moreover, rCTGF/Hcs24 increased alkaline phosphatase activity in both cells. It also stimulated collagen synthesis in MC3T3-E1 cells. Furthermore, rCTGF/Hcs24 stimulated the matrix mineralization on MC3T3-E1 cells and its stimulatory effect was comparable to that of bone morphogenetic protein-2. These findings indicate that CTGF/Hcs24 is a novel, potent stimulator for the proliferation and differentiation of osteoblasts in addition to chondrocytes and endothelial cells. Because of these functions, we are re-defining CTGF/Hcs24 as a major factor to promote endochondral ossification to be called "ecogenin: endochondral ossification genetic factor."

Connective tissue growth factor expression in the rat remnant kidney model and association with tubular epithelial cells undergoing transdifferentiation

Connective tissue growth factor (CTGF) has been shown to mediate many actions of transforming growth factor-beta (TGF-beta) in the fibrotic response in several diseases. We compared expression of CTGF, TGF-beta, platelet-derived growth factor (PDGF), TNF-alpha, and interleukin-1 (IL-1) by in situ hybridization in Sprague-Dawley rats euthanized at 0, 2, 4, and 8 weeks after 5/6 nephrectomy using the rat remnant kidney model of renal failure. Collagen was evaluated by trichrome stains, immunohistochemistry, and electron microscopy. We compared expression patterns to cells undergoing metaplasia. Tubular epithelial regeneration and transdifferentiation to myofibroblasts were assessed morphologically and by proliferating cell nuclear antigen, smooth muscle actin, desmin, and vimentin immunohistochemistry. CTGF expression was minimal in controls, mild at 2 weeks and marked by 4 to 8 weeks in interstitial fibroblasts, coinciding with damage, regeneration, and fibrosis. TGF-beta expression was increased in many cell types at 2 weeks, increased further by 4 weeks, then remained constant. PDGF-B messenger RNA was found in many stromal cells at 2-4 weeks, but expression decreased at 8 weeks. No significant IL-1 or TNF-alpha staining was detected. We conclude that CTGF and interacting factors are associated with development or progression of chronic interstitial fibrosis. Proximity of CTGF, TGF-beta, and PDGF mRNA expression to regenerative epithelial cells and those transdifferentiating to myofibroblasts suggests that growth factors may modulate renal tubular epithelial differentiation.

Pseudoscleroderma associated with lung cancer: correlation of collagen type I and connective tissue growth factor gene expression

Pseudoscleroderma as a paraneoplastic syndrome is a rare disease. We report here a patient with lung cancer (undifferentiated squamous cell carcinoma), who developed acrosclerosis. Using in situ hybridization, marked expression of alpha1(I)-collagen and connective tissue growth factor (CTGF) mRNA was found in fibroblasts scattered throughout the dermis. However, transforming growth factor (TGF)-beta1 expression was not detected. The pattern of CTGF gene expression and collagen synthesis was similar to that in systemic scleroderma. The absence of TGF-beta1 mRNA could indicate that tumour-derived factors induce the expression of CTGF.

The thrombospondin type 1 repeat (TSR) superfamily: diverse proteins with related roles in neuronal development

The thrombospondins are a family of proteins found widely in the embryonic extracellular matrix. Like most matrix proteins, thrombospondins are modular and contain a series of repeated domains arrayed between globular amino and carboxyl terminal domains. In recent years, other proteins that share thrombospondin type 1 repeats, or TSRs, have been identified. These include the F-spondin gene family, the members of the semaphorin 5 family, UNC-5, SCO-spondin, and others. Most of these are expressed in the developing nervous system, and many have expression patterns and in vitro properties that suggest potential roles in the guidance of cell and growth cone migration. Both cell- and matrix-binding motifs have been identified in the TSRs of thrombospondin-1, so it has been hypothesized that the properties of these diverse proteins may also depend on the presence of these repeats. Here, we review the cell biology of the TSR module, the extensive literature regarding the distribution and functions of thrombospondins and other TSR superfamily proteins, and evaluate their possible roles during the development of the nervous system.

Pathogenesis of liver fibrosis: role of oxidative stress

In the liver, the progressive accumulation of connective tissue, a complex and dynamic process termed fibrosis, represents a very frequent event following a repeated or chronic insult of sufficient intensity to trigger a "wound healing"-like reaction. The fibrotic process recognises the involvement of various cells and different factors in bringing about an excessive fibrogenesis with disruption of intercellular contacts and interactions and of extracellular matrix composition. However, Kupffer cells, together with recruited mononuclear cells, and hepatic stellate cells are by far the key-players in liver fibrosis. Their cross-talk is triggered and favoured by a series of chemical mediators, with a prominent role played by the transforming growth factor beta. Both expression and synthesis of this inflammatory and pro-fibrogenic cytokine are mainly modulated through redox-sensitive reactions. Further, involvement of reactive oxygen species and lipid peroxidation products can be clearly demonstrated in other fundamental events of hepatic fibrogenesis, like activation and effects of stellate cells, expression of metalloproteinases and of their specific inhibitors. The important outcome of such findings as regards the pathogenesis of liver fibrosis derives from the observation of a consistent and marked oxidative stress condition in many if not all chronic disease processes affecting hepatic tissue. Hence, reactive oxidant species likely contribute to both onset and progression of fibrosis as induced by alcohol, viruses, iron or copper overload, cholestasis, hepatic blood congestion.

Distribution of IGFBP-rP1 in normal human tissues

IGFBP-rP1/mac25 is a recently described member of the insulin-like growth factor binding protein (IGFBP) family. It has structural homology to the other members of the IGFBP family but has a lower affinity for insulin-like growth factors (IGFs). In previous studies using RNA blot hybridization, it was shown that the expression of IGFBP-rP1/mac25 was ubiquitous in normal human tissues. In this report we show by immunohistochemistry that the expression of IGFBP-rP1/mac25 is actually restricted to certain organs and specific cell types. We used an antibody raised against a decapeptide of the C-terminal part of the protein that recognizes a approximately 37-kD protein under reduced conditions. The immunohistochemistry performed on normal human tissues showed a ubiquitous intense staining of peripheral nerves and a variable degree of positive staining in smooth muscle cells, including those from blood vessel walls, gut, bladder, and prostate. Cilia from the respiratory system, epididymis, and fallopian tube showed intense immunoreactivity. Most endothelial cells showed some positivity, whereas fat cells, plasma cells, and lymphocytes were negative. There was specific expression limited to certain cell types in the kidney, adrenal gland, and skeletal muscle, indicating a possible specialized function of IGFBP-rP1/mac25 in these organs. We further noted an opposite pattern of staining in the lining epithelium of breast (typically positive) and prostate glands (largely negative). The specific localization of IGFBP-rP1/mac25 as described implies a function of the protein. However, its regulation within the IGF axis or a possible direct action of IGFBP-rP1/mac25 remains to be demonstrated.

Novel intracellular effects of human connective tissue growth factor expressed in Cos-7 cells

To clarify the multiple functionality of connective tissue growth factor (CTGF), we examined the effects of nascent CTGF within the cell by transient expression. In Cos-7 cells, expression of human CTGF induced an altered cell morphology. It was associated with an increased cellular DNA content and loose attachment, indicating the cells were in G2/M phase. Overexpression of CTGF did not induce cell growth, whereas recombinant CTGF efficiently stimulated the proliferation extracellularly. These results indicate that intracellular CTGF may act as an antimitotic agent, thus it should also be noted that nascent CTGF was found to accumulate around the central mitotic machinery.

Tumor necrosis factor alpha suppresses the induction of connective tissue growth factor by transforming growth factor-beta in normal and scleroderma fibroblasts

Connective tissue growth factor (CTGF) is overexpressed in a variety of fibrotic disorders, presumably secondary to the activation and production of transforming growth factor-beta (TGF-beta), a key inducer of fibroblast proliferation and matrix synthesis. The CTGF gene promoter has a TGF-beta response element that regulates its expression in fibroblasts but not epithelial cells or lymphocytes. Recent studies have shown that the macrophage-produced cytokine tumor necrosis factor alpha (TNFalpha) is necessary to promote inflammation and to induce genes, such as matrix metalloproteinases, involved with the early stages of wound healing. In this study, we examined the ability of TNFalpha to modulate CTGF gene expression. TNFalpha was found to suppress the TGF-beta-induced expression of CTGF protein in cultured normal fibroblasts. The activity of TNFalpha was blocked by NF-kappaB inhibitors. We showed that sequences between -244 and -166 of the CTGF promoter were necessary for both TGF-beta and TNFalpha to modulate CTGF expression. There was a constitutive expression of CTGF by scleroderma fibroblasts that was increased by TGF-beta treatment. Although TNFalpha was able to repress TGF-beta-induced CTGF and collagen synthesis both in normal and scleroderma skin fibroblasts, fibroblasts cultured from scleroderma patients were more resistant to TNFalpha as TNFalpha was unable to suppress the basal level of CTGF expression in scleroderma fibroblasts. Thus, we suspect that the high level of constitutive CTGF expression in scleroderma fibroblasts and its inability to respond to negative regulatory cytokines may contribute to the excessive scarring of skin and internal organs in patients with scleroderma.

Increased expression of connective tissue growth factor in fibrotic human liver and in activated hepatic stellate cells

BACKGROUND/AIMS

Connective tissue growth factor is a recently described mitogenic protein implicated in a variety of fibrotic disorders. Connective tissue growth factor may be a downstream mediator of the pro-fibrotic and mitogenic actions of transforming growth factor-beta, promoting extracellular matrix deposition and fibrogenesis. As transforming growth factor-beta is considered important to the pathogenesis of hepatic fibrosis, we examined the possible contribution of connective tissue growth factor to this process.

METHODS

Connective tissue growth factor expression was examined in normal and fibrotic human and rat livers using RT-PCR and ribonuclease protection assays, and in primary cultures of rat hepatic stellate cells by Northern and Western blotting.

RESULTS

Ribonuclease protection assays demonstrated connective tissue growth factor mRNA was increased 3-5-fold in human fibrotic liver compared with normal. RT-PCR showed this mRNA was increased in carbon-tetrachloride-treated rat liver. Northern analysis showed connective tissue growth factor mRNA was increasingly expressed during progressive activation of cultured rat hepatic stellate cells. Western analysis confirmed that freshly isolated hepatic stellate cells secreted relatively little connective tissue growth factor compared with hepatic stellate cells activated in culture. Hepatic stellate cells stimulated with transforming growth factor-beta showed increased expression of connective tissue growth factor mRNA and protein.

CONCLUSIONS

Connective tissue growth factor mRNA is consistently upregulated in human liver cirrhosis of various aetiologies, supporting a role for this growth factor in hepatic fibrogenesis. Our studies suggest that hepatic stellate cells may be an important source of hepatic connective tissue growth factor in vivo, particularly following stimulation with transforming growth factor-beta.

Des-Arg(10)-kallidin engagement of the B1 receptor stimulates type I collagen synthesis via stabilization of connective tissue growth factor mRNA

Expression of the kinin B1 receptor is up-regulated in chronic inflammatory and fibrotic disorders; however, little is known about its role in fibrogenesis. We examined human embryonic lung fibroblasts that constitutively express the B1 receptor and report that engagement of the B1 receptor by des-Arg(10)-kallidin stabilized connective tissue growth factor (CTGF) mRNA, stimulated an increase in alpha1(I) collagen mRNA, and stimulated type I collagen production. These events were not observed in B2 receptor-activated fibroblasts. In addition, B1 receptor activation by des-Arg(10)-kallidin induced a rise in cytosolic Ca(2+) that is consistent with B1 receptor pharmacology. Our results show that the des-Arg(10)-kallidin-stimulated increase in alpha1(I) collagen mRNA was time- and dose-dependent, with a peak response observed at 20 h with 100 nM des-Arg(10)-kallidin. The increase in CTGF mRNA was also time- and dose-dependent, with a peak response observed at 4 h with 100 nM des-Arg(10)-kallidin. The increase in CTGF mRNA was blocked by the B1 receptor antagonist des-Arg(10),Leu(9)-kallidin. Inhibition of protein synthesis by cycloheximide did not block the des-Arg(10)-kallidin-induced increase in CTGF mRNA. These results suggest that engagement of the kinin B1 receptor contributes to fibrogenesis through increased expression of CTGF.

Characterization of pig connective tissue growth factor (CTGF) cDNA, mRNA and protein from uterine tissue

Connective tissue growth factor (CTGF) is a 38kDa mitogen and chemotactic factor for fibroblasts that is transcriptionally activated by serum or transforming growth factor-beta and may play a role in wound healing and various skin diseases. In these studies, pig endometrium was shown to contain a single CTGF transcript of 2.4kb and to produce a 38kDa CTGF-immunoreactive protein. Cloning and sequencing of a 1.5kb pig uterine CTGF cDNA revealed that the predicted pCTGF primary translation product displayed 92% identity to human CTGF and 93% identity to mouse CTGF. The pCTGF cDNA encoded a 26 amino acid signal peptide followed by a 323-residue sequence containing 38 highly conserved cysteine residues. In common with mouse and human CTGF proteins, pCTGF is predicted to resemble a multi-functional mosaic protein that contains four distinct modules.

Effects of p21Waf1/Cip1/Sdi1 on cellular gene expression: implications for carcinogenesis, senescence, and age-related diseases

Induction of cyclin-dependent kinase inhibitor p21(Waf1/Cip1/Sdi1) triggers cell growth arrest associated with senescence and damage response. Overexpression of p21 from an inducible promoter in a human cell line induces growth arrest and phenotypic features of senescence. cDNA array hybridization showed that p21 expression selectively inhibits a set of genes involved in mitosis, DNA replication, segregation, and repair. The kinetics of inhibition of these genes on p21 induction parallels the onset of growth arrest, and their reexpression on release from p21 precedes the reentry of cells into cell cycle, indicating that inhibition of cell-cycle progression genes is a mechanism of p21-induced growth arrest. p21 also up-regulates multiple genes that have been associated with senescence or implicated in age-related diseases, including atherosclerosis, Alzheimer's disease, amyloidosis, and arthritis. Most of the tested p21-induced genes were not activated in cells that had been growth arrested by serum starvation, but some genes were induced in both forms of growth arrest. Several p21-induced genes encode secreted proteins with paracrine effects on cell growth and apoptosis. In agreement with the overexpression of such proteins, conditioned media from p21-induced cells were found to have antiapoptotic and mitogenic activity. These results suggest that the effects of p21 induction on gene expression in senescent cells may contribute to the pathogenesis of cancer and age-related diseases.

Connective tissue growth factor induces apoptosis via caspase 3 in cultured human aortic smooth muscle cells

Connective tissue growth factor (CTGF) stimulates proliferation of fibroblasts and endothelial cells, but nothing is known about its role in smooth muscle cells. In this study, the effects of recombinant human CTGF (r-hCTGF, 0.5-10 microgram/ml) on cultured human aortic vascular smooth muscle cells were investigated. r-hCTGF significantly reduced cell viability, increased apoptosis, and augmented caspase 3 activity. Moreover, r-hCTGF-induced apoptosis was significantly inhibited by an antibody to CTGF and a caspase-3 inhibitor, Z-Asp(Ome)-Glu-(Ome)Val-Asp(Ome)-FMK. These results suggest that r-hCTGF activates caspase 3 and induces apoptosis.

Antiangiogenic domains shared by thrombospondins and metallospondins, a new family of angiogenic inhibitors

The growth of solid tumors has been shown to depend on neovascularization. By understanding the mechanisms that control the neovascular response, it may be possible to design therapeutic strategies to selectively prevent or halt pathologic vascular growth and restrain cancer progression. Thrombospondin-1 is an extracellular matrix protein that among several functions suppresses capillary growth in angiogenesis assays. We have demonstrated that within the context of the mammary gland TSP1 can modulate normal development of blood vessels. Expression of TSP1 in transgenic animals under the control of the MMTV promoter was associated with a 50-72% reduction in capillary growth. In addition, TSP1 reduced tumor size in transgenic overexpressors. The data suggest an important role for TSP1 in modulating vascular growth in both normal and pathologic tissues. The antiangiogenic region of TSP1 has been mapped to the type I (properdin) repeats. To identify novel proteins with such a domain, we have cloned two cDNAs (METH-1 and METH-2) which also have antiangiogenic properties. In addition to carboxyterminal thrombospondin-like domains they also contain metalloproteinase and disintegrin sequences. Expression of both proteins is broad but nonoverlapping. Recombinant fragments from these sequences have strong antiangiogenic potential in the CAM and cornea pocket assays. At the same molar ratio, METH-1 and METH-2 are about 20-fold more potent than TSP1. We predict that these proteins are likely endogenous modulators of vascular growth with relevant therapeutic potential in cancer and other disease states.

Cloning the full-length cDNA for rat connective tissue growth factor: implications for skeletal development

The mammalian osteopetroses represent a pathogenetically diverse group of skeletal disorders characterized by excess bone mass resulting from reduced osteoclastic bone resorption. Abnormalities involving osteoblast function and skeletal development have also been reported in many forms of the disease. In this study, we used the rat mutation, osteopetrosis (op), to examine differences in skeletal gene expression between op mutants and their normal littermates. RNA isolated from calvaria and long bones was used as a template for mRNA-differential display. Sequence information for one of the many cDNA that were selectively expressed in either normal or mutant bone suggested that it is the rat homologue of connective tissue growth factor (CTGF) previously cloned in the human, mouse, and other species. A consensus sequence was assembled from overlapping 5'-RACE clones and used to confirm the rat CTGF cDNA protein coding region. Northern blot analysis confirmed that this message was highly (8- to 10-fold) over-expressed in op versus normal bone; it was also upregulated in op kidney but none of the other tissues (brain, liver, spleen, thymus) examined. In primary rat osteoblast cultures, the CTGF message exhibits a temporal pattern of expression dependent on their state of differentiation. Furthermore, CTGF expression is regulated by prostaglandin E(2), a factor known to modulate osteoblast differentiation. Since members of the CTGF family regulate the expression of specific genes, such as collagen and fibronectin, we propose that CTGF may play a previously unreported role in normal skeletal modeling/remodeling. Its dramatic over-expression in the op mutant skeleton may be secondary to the uncoupling of bone resorption and bone formation resulting in dysregulation of osteoblast gene expression and function.

Effects of CTGF/Hcs24, a product of a hypertrophic chondrocyte-specific gene, on the proliferation and differentiation of chondrocytes in culture

Recently, we cloned a messenger RNA (mRNA) predominantly expressed in chondrocytes from a human chondrosarcoma-derived chondrocytic cell line, HCS-2/8, by differential display PCR and found that its gene, named hcs24, was identical with that of connective tissue growth factor (CTGF). Here we investigated CTGF/Hcs24 function in the chondrocytic cell line HCS-2/8 and rabbit growth cartilage (RGC) cells. HCS-2/8 cells transfected with recombinant adenoviruses that generate CTGF/Hcs24 sense RNA (mRNA) proliferated more rapidly than HCS-2/8 cells transfected with control adenoviruses. HCS-2/8 cells transfected with recombinant adenoviruses that generate CTGF/Hcs24 sense RNA expressed more mRNA of aggrecan and type X collagen than the control cells. To elucidate the direct action of CTGF/Hcs24 on the cells, we transfected HeLa cells with CTGF/Hcs24 expression vectors, obtained stable transfectants, and purified recombinant CTGF/Hcs24 protein from conditioned medium of the transfectants. The recombinant CTGF/Hcs24 effectively promoted the proliferation of HCS-2/8 cells and RGC cells in a dose-dependent manner and also dose dependently increased proteoglycan synthesis in these cells. In addition, these stimulatory effects of CTGF/Hcs24 were neutralized by the addition of anti-CTGF antibodies. Furthermore, the recombinant CTGF/Hcs24 effectively increased alkaline phosphatase activity in RGC cells in culture. Moreover, RT-PCR analysis revealed that the recombinant CTGF/Hcs24 stimulated gene expression of aggrecan and collagen types II and X in RGC cells in culture. These results indicate that CTGF/Hcs24 directly promotes the proliferation and differentiation of chondrocytes.

Connective tissue growth factor: a novel player in tissue reorganization after brain injury?

Recent studies have suggested a role of connective tissue growth factor (CTGF) in repair processes of the skin as well as in various types of fibrotic disease. However, a function of this molecule in central nervous system (CNS) repair has not been demonstrated yet. In this study we analysed the temporal and spatial expression pattern of CTGF after unilateral kainic acid lesions of the hippocampal CA3 region in mice. We found a strong induction of CTGF mRNA and protein expression in neurons and glial cells of the lesioned hippocampus. Interestingly, increased expression of this mitogen was accompanied by elevated levels of the extracellular matrix molecule fibronectin, which is a known target of CTGF action. Therefore, our data indicate a novel function of CTGF in postlesional restructuring of the hippocampus, where it possibly participates in glial scar formation.

CTGF modulates cell cycle progression in cAMP-arrested NRK fibroblasts

Connective tissue growth factor (CTGF) is a 38-kDa cysteine-rich peptide, whose synthesis and secretion are selectively induced by transforming growth factor beta (TGF-beta) in connective tissue cells. Previous studies have demonstrated that CTGF functions as a downstream mediator of TGF-beta mitogenic activity, where it controls cell cycle progression through late G1 and S-phase entry of NRK fibroblast suspension cultures. Here we report that CTGF induces this S-phase entry by upregulating cyclin A levels. The molecular mechanism for cyclin A induction appears to be via reduction of p27(Kip1) levels, which results in hyperphosphorylation of pRb and release of E2F, a known modulator of cyclin A gene transcription. These data indicate that CTGF acts as a mediator of TGF-beta-induced fibroblast proliferation in suspension cultures by regulating cdk activities.

Regulation of connective tissue growth factor activity in cultured rat mesangial cells and its expression in experimental diabetic glomerulosclerosis

Connective tissue growth factor (CTGF) is a peptide secreted by cultured endothelial cells and fibroblasts when stimulated by transforming growth factor-beta (TGF-beta), and is overexpressed during fibrotic processes in coronary arteries and in skin. To determine whether CTGF is implicated in the pathogenesis of diabetic glomerulosclerosis, cultured rat mesangial cells (MC) as well as kidney cortex and microdissected glomeruli were examined from obese, diabetic db/db mice and their normal counterparts. Exposure of MC to recombinant human CTGF significantly increased fibronectin and collagen type I production. Furthermore, unstimulated MC expressed low levels of CTGF message and secreted minimal amounts of CTGF protein (36 to 38 kD) into the media. However, sodium heparin treatment resulted in a greater than fourfold increase in media-associated CTGF, suggesting that the majority of CTGF produced was cell- or matrix-bound. Exposure of MC to TGF-beta, increased glucose concentrations, or cyclic mechanical strain, all causal factors in diabetic glomerulosclerosis, markedly induced the expression of CTGF transcripts, while recombinant human CTGF was able to autoinduce its own expression. TGF-, and high glucose, but not mechanical strain, stimulated the concomitant secretion of CTGF protein, the former also inducing abundant quantities of a small molecular weight form of CTGF (18 kD) containing the heparin-binding domain. The induction of CTGF protein by a high glucose concentration was mediated by TGF-beta, since a TGF-beta-neutralizing antibody blocked this stimulation. In vivo studies using quantitative reverse transcription-PCR demonstrated that although CTGF transcripts were low in the glomeruli of control mice, expression was increased 28-fold after approximately 3.5 mo of diabetes. This change occurred early in the course of diabetic nephropathy when mesangial expansion was mild, and interstitial disease and proteinuria were absent. A substantially reduced elevation of CTGF mRNA (twofold) observed in whole kidney cortices indicated that the primary alteration of CTGF expression was in the glomerulus. These results suggest that CTGF upregulation is an important factor in the pathogenesis of mesangial matrix accumulation and progressive glomerulosclerosis, acting downstream of TGF-beta.

Connective tissue growth factor induces apoptosis in human breast cancer cell line MCF-7

Connective tissue growth factor (CTGF) is a member of an emerging CCN gene family that is implicated in various diseases associated with fibro-proliferative disorder including scleroderma and atherosclerosis. The function of CTGF in human cancer is largely unknown. We now show that CTGF induces apoptosis in the human breast cancer cell line MCF-7. CTGF mRNA was completely absent in MCF-7 but strongly induced by treatment with transforming growth factor beta (TGF-beta). TGF-beta by itself induced apoptosis in MCF-7, and this effect was reversed by co-treatment with CTGF antisense oligonucleotide. Overexpression of CTGF gene in transiently transfected MCF-7 cells significantly augmented apoptosis. Moreover, recombinant CTGF protein significantly enhanced apoptosis in MCF-7 cells as evaluated by DNA fragmentation, Tdt-mediated dUTP biotin nick end-labeling staining, flow cytometry analysis, and nuclear staining using Hoechst 33258. Finally, recombinant CTGF showed no effect on Bax protein expression but significantly reduced Bcl2 protein expression. Taken together, these results suggest that CTGF is a major inducer of apoptosis in the human breast cancer cell line MCF-7 and that TGF-beta-induced apoptosis in MCF-7 cells is mediated, in part, by CTGF.

Enhanced insulin-like growth factor binding protein-related protein 2 (Connective tissue growth factor) expression in patients with idiopathic pulmonary fibrosis and pulmonary sarcoidosis

Connective tissue growth factor is a recently described chemoattractant and fibroblast mitogen which, because of sequence homology and weak binding to insulin-like growth factor (IGF)-1, has been proposed as the eighth member of the IGF binding protein (IGFBP) superfamily, named IGFBP-related protein 2 (IGFBP-rP2). Previous studies have implicated IGFBP-rP2 in a number of heterogeneous fibrotic pathologies, including renal fibrosis, dermal scleroderma, and bleomycin-induced pulmonary fibrosis in mice. Because profibrogenic cytokines may be produced by inflammatory cells, we developed a multiplex competitive reverse transcription/polymerase chain reaction to quantify IGFBP-rP2 transcripts in bronchoalveolar lavage cells from healthy subjects and patients with idiopathic pulmonary fibrosis (IPF) and pulmonary sarcoidosis. IGFBP-rP2 messenger RNA expression was enhanced > 10-fold (P < 0.003) in patients with IPF; > 40-fold (P < 0.006) in stage I/II sarcoidosis patients, and > 90-fold (P < 0.005) in stage III/IV sarcoidosis patients by comparison with healthy nonsmoking control subjects. We suggest these increases are predominantly associated with lymphocyte- and neutrophil-driven IGFBP-rP2 production. These findings, together with previous reports implicating other IGFBPs in the pathogenesis of pulmonary fibrosis, suggest that the complex network of IGFBPs within the human lung is an important determinant of the outcome of the fibroproliferative response to injury.

Regulation of connective tissue growth factor expression by prostaglandin E(2)

Transforming growth factor-beta (TGF-beta) stimulates alpha(1)(I) collagen mRNA synthesis in human lung fibroblasts through a mechanism that is partially sensitive to cycloheximide and that may involve synthesis of connective tissue growth factor (CTGF). Northern blot analyses indicate that TGF-beta stimulates time- and dose-dependent increases in CTGF mRNA. In TGF-beta-stimulated fibroblasts, maximal levels of CTGF mRNA (3.7-fold above baseline) occur at 6 h. The TGF-beta-stimulated increase in CTGF mRNA was not blocked by cycloheximide. Nuclear run-on analysis indicates that TGF-beta increases the CTGF transcription rate. The TGF-beta-stimulated increases in CTGF transcription and steady-state levels of CTGF mRNA are attenuated in prostaglandin E(2) (PGE(2))-treated fibroblasts. PGE(2) fails to attenuate luciferase activity induced by TGF-beta in fibroblasts transfected with the TGF-beta-responsive luciferase reporter construct p3TP-LUX. In amino acid-deprived fibroblasts, PGE(2) and insulin regulate alpha(1)(I) collagen mRNA levels without affecting CTGF mRNA levels. The data suggest that the regulation of alpha(1)(I) collagen mRNA levels by TGF-beta and PGE(2) may function through both CTGF-dependent and CTGF-independent mechanisms.

The insulin-like growth factor-binding protein (IGFBP) superfamily

Over the last decade, the concept of an IGFBP family has been well accepted, based on structural similarities and on functional abilities to bind IGFs with high affinities. The existence of other potential IGFBPs was left open. The discovery of proteins with N-terminal domains bearing striking structural similarities to the N terminus of the IGFBPs, and with reduced, but demonstrable, affinity for IGFs, raised the question of whether these proteins were "new" IGFBPs (22, 23, 217). The N-terminal domain had been uniquely associated with the IGFBPs and has long been considered to be critical for IGF binding. No other function has been confirmed for this domain to date. Thus, the presence of this important IGFBP domain in the N terminus of other proteins must be considered significant. Although these other proteins appear capable of binding IGF, their relatively low affinity and the fact that their major biological actions are likely to not directly involve the IGF peptides suggest that they probably should not be classified within the IGFBP family as provisionally proposed (22, 23). The conservation of this single domain, so critical to high-affinity binding of IGF by the six IGFBPs, in all of the IGFBP-rPs, as well, speaks to its biological importance. Historically, and perhaps, functionally, this has led to the designation of an "IGFBP superfamily". The classification and nomenclature for the IGFBP superfamily, are, of course, arbitrary; what is ultimately relevant is the underlying biology, much of which still remains to be deciphered. The nomenclature for the IGFBP related proteins was derived from a consensus of researchers working in the IGFBP field (52). Obviously, a more general consensus on nomenclature, involving all groups working on each IGFBP-rP, has yet to be reached. Further understanding of the biological functions of each protein should help resolve the nomenclature dilemma. For the present, redesignating these proteins IGFBP-rPs simplifies the multiple names already associated with each IGFBP related protein, and reinforces the concept of a relationship with the IGFBPs. Beyond the N-terminal domain, there is a lack of structural similarity between the IGFBP-rPs and IGFBPs. The C-terminal domains do share similarities to other internal domains found in numerous other proteins. For example, the similarity of the IGFBP C terminus to the thyroglobulin type-I domain shows that the IGFBPs are also structurally related to numerous other proteins carrying the same domain (87). Interestingly, the functions of the different C-terminal domains in members of the IGFBP superfamily include interactions with the cell surface or ECM, suggesting that, even if they share little sequence similarities, the C-terminal domains may be functionally related. The evolutionary conservation of the N-terminal domain and functional studies support the notion that IGFBPs and IGFBP-rPs together form an IGFBP superfamily. A superfamily delineates between closely related (classified as a family) and distantly related proteins. The IGFBP superfamily is therefore composed of distantly related families. The modular nature of the constituents of the IGFBP superfamily, particularly their preservation of an highly conserved N-terminal domain, seems best explained by the process of exon shuffling of an ancestral gene encoding this domain. Over the course of evolution, some members evolved into high-affinity IGF binders and others into low-affinity IGF binders, thereby conferring on the IGFBP superfamily the ability to influence cell growth by both IGF-dependent and IGF-independent means (Fig. 10). A final word, from Stephen Jay Gould (218): "But classifications are not passive ordering devices in a world objectively divided into obvious categories. Taxonomies are human decisions imposed upon nature--theories about the causes of nature's order. The chronicle of historical changes in classification provides our finest insight into conceptual revolutions

Overexpression of connective tissue growth factor gene induces apoptosis in human aortic smooth muscle cells

BACKGROUND

Connective tissue growth factor (CTGF) is expressed at very high levels particularly in the shoulder of human atherosclerotic lesions but not in normal blood vessels. Thus, CTGF may be important in the regulation of vascular smooth muscle cell function in atherosclerosis, but its precise role remains elusive.

METHODS AND RESULTS

Full-length CTGF cDNA driven by a cytomegalovirus promoter was transiently transfected into cultured human aortic smooth muscle cells (HASCs). Northern and Western analysis demonstrated that CTGF was overexpressed in these cells 48 hours after transfection. The effects of CTGF overexpression on cell proliferation were evaluated by [(3)H]thymidine uptake and cell count in quiescent HASCs or those stimulated with platelet-derived growth factor (PDGF). Although mock transfection showed no effect, CTGF overexpression significantly inhibited cell proliferation in cells stimulated by PDGF. Moreover, CTGF overexpression, but not mock transfection, significantly increased apoptosis as assessed by DNA fragmentation associated with histone, TdT-mediated dUTP biotin nick end-labeling, and appearance of hypodiploid cells by flow cytometry.

CONCLUSIONS

Our results for the first time demonstrate that CTGF can also act as a growth inhibitor in human aortic smooth muscle cells at least in part by inducing apoptosis. This may be important for the formation and composition of lesions and plaque stability in atherosclerosis.

Expression of connective tissue growth factor in experimental rat and human liver fibrosis

Connective tissue growth factor (CTGF) stimulates in vitro fibroblast proliferation and extracellular matrix synthesis. The aim of this study was to assess the role of CTGF in liver fibrogenesis. CTGF expression was investigated both at the protein and mRNA level in biopsies of chronic liver diseases, in experimental models of liver fibrosis, and in hepatic stellate cells in culture. CTGF immunostaining was observed in most human liver biopsies with significant fibrosis. An increase of CTGF immunostaining was associated with a higher score of fibrosis both in the group of chronic hepatitis C (chi(2) = 9.3; P <.01) and in the non-hepatitis C group (chi(2) = 7.2; P <.02). In situ hybridization showed CTGF mRNA expression in spindle cells in both the fibrous septa and sinusoidal lining. In experimental models of liver fibrosis, CTGF accumulated in parallel with the development of septal fibrosis and cirrhosis. Quantification of CTGF mRNA by a real-time reverse-transcription polymerase chain reaction (RT-PCR) assay showed a significant increase of CTGF mRNA in both CCl(4)-induced and bile duct-ligated rat models of liver fibrosis. Expression of CTGF protein and mRNA was definitively assigned to hepatic stellate cells, because CTGF was detected by Western blot both in lysate and supernatant of a hepatic stellate cell line derived from rats. These cells also displayed CTGF protein and mRNA as shown by immunohistochemistry and in situ hybridization. In conclusion, this study shows that CTGF is strongly expressed during liver fibrogenesis, and hepatic stellate cells seem to be the major cellular sources of CTGF in the liver.

Novel aspects of the insulin-like growth factor binding proteins

The insulin-like growth factors (IGFs), IGF binding proteins (IGFBPs), and IGFBP proteases regulate somatic growth and cellular proliferation both in vivo and in vitro. IGFs are potent mitogens whose actions are determined by the availability of free IGFs to interact with IGF receptors. IGFBPs comprise a family of six proteins that bind IGFs with high affinity and specificity and thereby regulate IGF-dependent actions. IGFBPs have also recently emerged as IGF-independent regulators of cell growth. Several IGFBP association proteins have been discovered recently which can affect IGFBP action. Cleavage of IGFBPs by specific proteases modulates levels of free IGFs and IGFBPs and thereby their actions. IGFBP-related proteins (IGFBP-rPs) are an emerging group of proteins which bind IGFs with low affinity and also play important roles in cell growth and differentiation. The IGFBPs appear to have emerging roles in the mechanisms underlying human cancer. The GH-IGF-IGFBP axis is complex and powerful. Future research on its physiology promises exciting insights into cell biology as well as advancements in the treatment of a wide range of disease states including cancer, diabetes, vascular disease, asthma, and growth disorders.

Role and interaction of connective tissue growth factor with transforming growth factor-beta in persistent fibrosis: A mouse fibrosis model

Skin fibrotic disorders are understood to develop under the influence of some growth factors, such as transforming growth factor-beta (TGF-beta), basic fibroblast growth factor (bFGF), or connective tissue growth factor (CTGF). To establish an appropriate animal model of skin fibrosis by exogenous application of growth factors, we investigated the in vivo effects of growth factors by injecting TGF-beta, CTGF, and bFGF into the subcutaneous tissue of newborn mice. A single application of TGF-beta or bFGF resulted in the formation of transient granulated tissue that disappeared despite 7 days of consecutive injections. A single CTGF injection also caused slight granulation. However, injecting TGF-beta plus CTGF produced long-term fibrotic tissue, which persisted for at least 14 days. Also, fibrotic tissue was observed when CTGF was injected from 4 to 7 days after TGF-beta injections for the first 1-3 days. In situ hybridization analysis revealed the expression of CTGF mRNA in the fibroblasts at least in a few fibrotic conditions. These findings suggest that either CTGF mRNA or an application of exogenous CTGF protein is required for the development of persistent fibrosis. From our study, it appears that interaction of several growth factors is required for persistent fibrotic tissue formation, with TGF-beta causing the induction and CTGF needed for maintenance of skin fibrosis. The animal model on skin fibrosis by exogenous application of growth factors developed in this study may prove useful for future studies on fibrotic disorders.

Nephroblastoma overexpressed gene (NOV) codes for a growth factor that induces protein tyrosine phosphorylation

NOV (nephroblastoma overexpressed gene) is a member of the CCN (connective tissue growth factor [CTGF], Cyr61/Cef10, NOV) family of proteins. These proteins are cysteine-rich and are noted for having growth-regulatory functions. We have isolated the rat NOV gene, and the DNA sequence shares 90% identity with the mouse and 80% identity with the human sequences. The rat NOV gene was expressed in all rat tissues examined, including brain, lung, heart, kidney, liver, spleen, thymus and skeletal muscle. Higher levels of rat NOV mRNA were seen in the brain, lung and skeletal muscle compared to the other tissues. Examination of NOV expression in various human cell lines revealed that NOV was expressed in U87, 293, T98G, SK-N-MC and Hs683 but not in HepG2, HL60, THP1 and Jurkat. The human NOV gene was transfected into 293 cells and the expressed protein purified. When 3T3 fibroblasts were treated with this recombinant NOV protein, a dose-dependent increase in proliferation was observed. Analysis of tyrosine-phosphorylated proteins revealed that when 3T3 cells were treated with NOV, a 221 kDa protein was phosphorylated. These data suggest that NOV can act as a growth factor for some cells and binds to a specific receptor that leads to the phosphorylation of a 221 kDa protein.

Role and interaction of connective tissue growth factor with transforming growth factor-beta in persistent fibrosis: A mouse fibrosis model

Skin fibrotic disorders are understood to develop under the influence of some growth factors, such as transforming growth factor-beta (TGF-beta), basic fibroblast growth factor (bFGF), or connective tissue growth factor (CTGF). To establish an appropriate animal model of skin fibrosis by exogenous application of growth factors, we investigated the in vivo effects of growth factors by injecting TGF-beta, CTGF, and bFGF into the subcutaneous tissue of newborn mice. A single application of TGF-beta or bFGF resulted in the formation of transient granulated tissue that disappeared despite 7 days of consecutive injections. A single CTGF injection also caused slight granulation. However, injecting TGF-beta plus CTGF produced long-term fibrotic tissue, which persisted for at least 14 days. Also, fibrotic tissue was observed when CTGF was injected from 4 to 7 days after TGF-beta injections for the first 1-3 days. In situ hybridization analysis revealed the expression of CTGF mRNA in the fibroblasts at least in a few fibrotic conditions. These findings suggest that either CTGF mRNA or an application of exogenous CTGF protein is required for the development of persistent fibrosis. From our study, it appears that interaction of several growth factors is required for persistent fibrotic tissue formation, with TGF-beta causing the induction and CTGF needed for maintenance of skin fibrosis. The animal model on skin fibrosis by exogenous application of growth factors developed in this study may prove useful for future studies on fibrotic disorders.

Mutations in the CCN gene family member WISP3 cause progressive pseudorheumatoid dysplasia

Members of the CCN (for CTGF, cyr61/cef10, nov) gene family encode cysteine-rich secreted proteins with roles in cell growth and differentiation. Cell-specific and tissue-specific differences in the expression and function of different CCN family members suggest they have non-redundant roles. Using a positional-candidate approach, we found that mutations in the CCN family member WISP3 are associated with the autosomal recessive skeletal disorder progressive pseudorheumatoid dysplasia (PPD; MIM 208230). PPD is an autosomal recessive disorder that may be initially misdiagnosed as juvenile rheumatoid arthritis. Its population incidence has been estimated at 1 per million in the United Kingdom, but it is likely to be higher in the Middle East and Gulf States. Affected individuals are asymptomatic in early childhood. Signs and symptoms of disease typically develop between three and eight years of age. Clinically and radiographically, patients experience continued cartilage loss and destructive bone changes as they age, in several instances necessitating joint replacement surgery by the third decade of life. Extraskeletal manifestations have not been reported in PPD. Cartilage appears to be the primary affected tissue, and in one patient, a biopsy of the iliac crest revealed abnormal nests of chondrocytes and loss of normal cell columnar organization in growth zones. We have identified nine different WISP3 mutations in unrelated, affected individuals, indicating that the gene is essential for normal post-natal skeletal growth and cartilage homeostasis.

Activation-dependent adhesion of human platelets to Cyr61 and Fisp12/mouse connective tissue growth factor is mediated through integrin alpha(IIb)beta(3)

Cyr61 and connective tissue growth factor (CTGF), members of a newly identified family of extracellular matrix-associated signaling molecules, are found to mediate cell adhesion, promote cell migration and enhance growth factor-induced cell proliferation in vitro, and induce angiogenesis in vivo. We previously showed that vascular endothelial cell adhesion and migration to Cyr61 and Fisp12 (mouse CTGF) are mediated through integrin alpha(v)beta(3). Both Cyr61 and Fisp12/mCTGF are present in normal blood vessel walls, and it has been demonstrated that CTGF is overexpressed in advanced atherosclerotic lesions. In the present study, we examined whether Cyr61 and Fisp12/mCTGF could serve as substrates for platelet adhesion. Agonist (ADP, thrombin, or U46619)-stimulated but not resting platelets adhered to both Cyr61 and Fisp12/mCTGF, and this process was completely inhibited by prostaglandin I(2), which prevents platelet activation. The specificity of Cyr61- and Fisp12/mCTGF-mediated platelet adhesion was demonstrated by specific inhibition of this process with polyclonal anti-Cyr61 and anti-Fisp12/mCTGF antibodies, respectively. The adhesion of ADP-activated platelets to both proteins was divalent cation-dependent and was blocked by RGDS, HHLGGAKQAGDV, or echistatin, but not by RGES. Furthermore, this process was specifically inhibited by the monoclonal antibody AP-2 (anti-alpha(IIb)beta(3)), but not by LM609 (anti-alpha(v)beta(3)), indicating that the interaction is mediated through integrin alpha(IIb)beta(3). In a solid phase binding assay, activated alpha(IIb)beta(3), purified by RGD affinity chromatography, bound to immobilized Cyr61 and Fisp12/mCTGF in a dose-dependent and RGD-inhibitable manner. In contrast, unactivated alpha(IIb)beta(3) failed to bind to either protein. Collectively, these findings identify Cyr61 and Fisp12/mCTGF as two novel activation-dependent adhesive ligands for the integrin alpha(IIb)beta(3) on human platelets, and implicate a functional role for these proteins in hemostasis and thrombosis.

Immunohistochemical localization of connective tissue growth factor in the rat central nervous system

Connective tissue growth factor (CTGF) is an immediate early growth-responsive gene but its distribution and significance in the central nervous system (CNS) are unknown. We investigated the distribution of CTGF-like immunoreactivity (CTGF-IR) in the rat CNS using a specific antiserum against CTGF oligopeptide. The majority of CTGF-IR was observed in astrocytes. Ependymal cells lining the wall of the cerebral ventricle and tanycytes lining the central canal of the spinal cord showed the strongest CTGF-IR, while there was a diffuse but weak signal in the gray matter of the spinal cord. CTGF-IR was also detected in the cytoplasm of a subpopulation of pyramidal neurons in the cerebral cortex. Our results showed that CTGF-IR is widely distributed in the CNS at both regional and cellular levels, suggesting a complex functional role in the CNS.

Connective tissue growth factor is a regulator for fibrosis in human chronic pancreatitis

OBJECTIVE

To evaluate the parameters that mediate fibrogenesis in chronic pancreatitis (CP).

BACKGROUND

Connective tissue growth factor (CTGF), which is regulated by transforming growth factor beta (TGF-beta), has recently been implicated in skin fibrosis and atherosclerosis. In the present study, the authors analyzed the concomitant presence of TGF-beta1 and its signaling receptors-TGF-beta receptor I, subtype ALK5 (TbetaR-I(ALK5)), and TGF-beta receptor II (TbetaR-II)-as well as CTGF and collagen type I in the pancreatic tissue of patients undergoing surgery for chronic pancreatitis.

PATIENTS AND METHODS

CP tissue samples were obtained from 40 patients (8 women, 32 men) undergoing pancreatic resection. Tissue samples of 25 previously healthy organ donors (12 women, 13 men) served as controls. The expression of TGF-beta1, TbetaR-I(ALK5), TbetaR-II, CTGF, and collagen type I was studied by Northern blot analysis. By in situ hybridization and immunohistochemistry, the respective mRNA moieties and proteins were localized in the tissue samples.

RESULTS

Northern blot analysis showed that CP tissue samples exhibited concomitant enhanced mRNA expression of TGF-beta1 (38-fold), TbetaR-II (5-fold), CTGF (25-fold), and collagen type I (24-fold) compared with normal controls. In addition, TbetaR-I(ALK5) mRNA was increased in 50% of CP tissue samples (1.8-fold). By in situ hybridization, TGF-beta1, TbetaR-I(ALK5), and TbetaR-II mRNA were often seen to be colocalized, especially in the ductal cells and in metaplastic areas where atrophic acinar cells appeared to dedifferentiate into ductal structures. In contrast, CTGF was located in degenerating acinar cells and principally in fibroblasts surrounding these areas. Moreover, CTGF mRNA expression levels correlated positively with the degree of fibrosis in CP tissues.

CONCLUSION

The concomitant overexpression of CTGF, collagen type I, TGF-beta1, and its signaling receptors in CP suggests that these proteins contribute to enhanced extracellular matrix synthesis and accumulation, resulting finally in the fibrogenesis observed in CP.

Myofibroblasts. I. Paracrine cells important in health and disease

Myofibroblasts are a unique group of smooth-muscle-like fibroblasts that have a similar appearance and function regardless of their tissue of residence. Through the secretion of inflammatory and anti-inflammatory cytokines, chemokines, growth factors, both lipid and gaseous inflammatory mediators, as well as extracellular matrix proteins and proteases, they play an important role in organogenesis and oncogenesis, inflammation, repair, and fibrosis in most organs and tissues. Platelet-derived growth factor (PDGF) and stem cell factor are two secreted proteins responsible for differentiating myofibroblasts from embryological stem cells. These and other growth factors cause proliferation of myofibroblasts, and myofibroblast secretion of extracellular matrix (ECM) molecules and various cytokines and growth factors causes mobility, proliferation, and differentiation of epithelial or parenchymal cells. Repeated cycles of injury and repair lead to organ or tissue fibrosis through secretion of ECM by the myofibroblasts. Transforming growth factor-beta and the PDGF family of growth factors are the key factors in the fibrotic response. Because of their ubiquitous presence in all tissues, myofibroblasts play important roles in various organ diseases and perhaps in multisystem diseases as well.

Identification and cloning of a connective tissue growth factor-like cDNA from human osteoblasts encoding a novel regulator of osteoblast functions

We have identified and cloned a novel connective tissue growth factor-like (CTGF-L) cDNA from primary human osteoblast cells encoding a 250-amino acid single chain polypeptide. Murine CTGF-L cDNA, encoding a polypeptide of 251 amino acids, was obtained from a murine lung cDNA library. CTGF-L protein bears significant identity ( approximately 60%) to the CCN (CTGF, Cef10/Cyr61, Nov) family of proteins. CTGF-L is composed of three distinct domains, an insulin-like growth factor binding domain, a von Willebrand Factor type C motif, and a thrombospondin type I repeat. However, unlike CTGF, CTGF-L lacks the C-terminal domain implicated in dimerization and heparin binding. CTGF-L mRNA ( approximately 1.3 kilobases) is expressed in primary human osteoblasts, fibroblasts, ovary, testes, and heart, and a approximately 26-kDa protein is secreted from primary human osteoblasts and fibroblasts. In situ hybridization indicates high expression in osteoblasts forming bone, discrete alkaline phosphatase positive bone marrow cells, and chondrocytes. Specific binding of 125I-labeled insulin-like growth factors to CTGF-L was demonstrated by ligand Western blotting and cross-linking experiments. Recombinant human CTGF-L promotes the adhesion of osteoblast cells and inhibits the binding of fibrinogen to integrin receptors. In addition, recombinant human CTGF-L inhibits osteocalcin production in rat osteoblast-like Ros 17/2.8 cells. Taken together, these results suggest that CTGF-L may play an important role in modulating bone turnover.