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

Connective tissue growth factor is secreted through the Golgi and is degraded in the endosome

Connective tissue growth factor (CTGF) is a cysteine-rich heparin-binding polypeptide that promotes proliferation, collagen synthesis, and chemotaxis in mesanchymal cells. When coinjected subcutaneously with transforming growth factor beta (TGFbeta), CTGF promotes sustained fibrosis in rats. However, little is known about the cell biology and structure/functional relationship of CTGF. In particular, no detailed characterization of the subcellular localization of CTGF has occurred, nor have sequences been identified within this protein required for this localization. In this report, using immunofluorescence and Western blot analysis, we show that CTGF is localized to the Golgi apparatus both in dermal fibroblasts and activated hepatic stellate cells. Using these methods, no CTGF was detected in endosomal, plasma membrane, cytosolic or nuclear fractions. Addition of brefeldin A, a drug that disrupts the Golgi, blocks the secretion of CTGF. We further show that the amino-terminal 37 amino acids of CTGF are sufficient to localize a heterologous protein (red fluorescent protein, RFP) to the Golgi. Although within this region of human CTGF is a N-glycosylation site, tunicamycin, which blocks N-linked glycosylation, has no significant effect on CTGF secretion. Surprisingly, mutation of a single amino acid residue, CYS-34, to alanine prevents localization of a CTGF-RFP fusion protein to the Golgi. These results are the first proof that endogenous CTGF is localized to the Golgi apparatus. Furthermore, using exogenously added (125)I-labeled CTGF, we show that CTGF is internalized and rapidly degraded in the endosome. That is, CTGF is quantitatively secreted through the golgi and is degraded in the endosome.

The low density lipoprotein receptor-related protein/alpha2-macroglobulin receptor is a receptor for connective tissue growth factor

Connective tissue growth factor (CTGF) expression is regulated by transforming growth factor-beta (TGF-beta) and strong up-regulation occurs during wound healing; in situ hybridization data indicate that there are high levels of CTGF expression in fibrotic lesions. Recently the binding parameters of CTGF to both high and lower affinity cell surface binding components have been characterized. Affinity cross-linking and SDS-polyacrylamide gel electrophoresis analysis demonstrated the binding of CTGF to a cell surface protein with a mass of approximately 620 kDa. We report here the purification of this protein by affinity chromatography on CTGF coupled to Sepharose and sequence information obtained by mass spectroscopy. The binding protein was identified as the multiligand receptor, low density lipoprotein receptor-related protein/alpha2-macroglobulin receptor (LRP). The identification of LRP as a receptor for CTGF was validated by several studies: 1) binding competition with many ligands that bind to LRP, including receptor-associated protein; 2) immunoprecipitation of CTGF-receptor complex with LRP antibodies; and 3) cells that are genetically deficient for LRP were unable to bind CTGF. Last, CTGF is rapidly internalized and degraded and this process is LRP-dependent. In summary, our data indicate that LRP is a receptor for CTGF, and may play an important role in mediating CTGF biology.

Transforming growth factor-beta and connective tissue growth factor: key cytokines in scleroderma pathogenesis

Evidence for a role for members of the transforming growth factor beta (TGF-beta) family of cytokines in the pathogensis of systemic sclerosis and other fibrotic conditions is provided from studies of TGF-beta protein and gene expression in lesional biopsy specimens, from altered responses of explanted fibroblasts to TGF-beta stimulation which are associated with increased receptor expression on these cells and from genetic data linking TGF-beta gene loci to the disease. Of the many effects of TGF-beta on fibroblast properties induction of the connective tissue growth factor/Cyr61/NOV (CCN) family members, connective tissue growth factor (CTGF) may be particularly relevant to fibrosis. Moreover, systemic sclerosis (SSc) fibroblasts demonstrate constitutive over expression of CTGF that promotes migration, proliferation and matrix production. Studies of mechanisms regulating constitutive expression of CTGF by SSc fibroblasts are currently being undertaken and indicate that a TGF-beta responsive element in the CTGF promoter is involved, although this appears to function independent of the Smad proteins, suggesting that other TGF-beta-regulated pathways may be involved. TGF-neutralizing strategies have now been shown to abrogate many animal models of fibrosis, and will soon reach the clinical arena for SSc. These agents will further clarify the role of this ligand in initiating or sustaining fibrosis and offer the exciting possibility of targeted therapy for this disease.

Pathogenesis of diabetic nephropathy: focus on transforming growth factor-beta and connective tissue growth factor

Although considerable improvement in the prognosis of diabetic nephropathy has been achieved in recent years due to intensive insulin and angiotensin-converting enzyme inhibitor treatment, these approaches do not provide complete protection against progression of diabetic nephropathy. An urgent need for additional novel therapies to prevent or further slow the progression of diabetic nephropathy motivated us to provide an up-to-date review with particular emphasis on the potential role of two growth factors--transforming growth factor-beta and connective tissue growth factor--in the pathogenesis of diabetic nephropathy. The most intensively studied to date, transforming growth factor-beta appears to play a central role in the pathogenesis of diabetic nephropathy. Recently, attention has focused on connective tissue growth factor, which mimics the biological activity of transforming growth factor-beta in profibrotic tissue formation. Thus, acting as a downstream mediator of the profibrotic activity of transforming growth factor-beta, connective tissue growth factor may constitute a more specific target for future antifibrotic therapies.

Role of connective tissue growth factor in profibrotic action of transforming growth factor-beta: a potential target for preventing renal fibrosis

Tubulointerstitial fibrosis is a crucial process determining the progression and prognosis of various renal diseases. Connective tissue growth factor (CTGF), a novel fibrogenic protein induced by transforming growth factor-beta (TGF-beta), is upregulated in various clinical and experimental nephropathies, but the significance of CTGF in the profibrotic action of TGF-beta is still poorly defined. To explore the implication of CTGF in renal fibrosis, we investigated gene expression of CTGF, fibronectin, and alpha1(I) collagen in an obstructive nephropathy model in rats. Furthermore, to elucidate the role of CTGF in TGF-beta-stimulated extracellular matrix accumulation, we analyzed the effects of blockade of endogenous CTGF using antisense oligodeoxynucleotides (ODNs) in cultured rat renal fibroblasts. After unilateral ureteral obstruction, TGF-beta1 and CTGF messenger RNA (mRNA) expression in the obstructed kidney was coordinately upregulated from the early stage of interstitial fibrosis, followed by marked induction of fibronectin and alpha1(I) collagen mRNA expression. In cultured normal rat kidney fibroblast (NRK-49F) cells, CTGF antisense ODN transfection significantly attenuated TGF-beta1-induced fibronectin and alpha1(I) collagen mRNA expression compared with control reverse ODNs. These results indicate that CTGF has a crucial role in the profibrotic action of TGF-beta in renal fibroblasts, providing a potential therapeutic target against tubulointerstitial fibrosis.

Identification and initial characterization of 5000 expressed sequenced tags (ESTs) each from adult human normal and osteoarthritic cartilage cDNA libraries

OBJECTIVE

To prepare, sequence and analyse adult human cartilage cDNA libraries to study the gene expression pattern between normal and osteoarthritic cartilage.

METHODS

Poly A(+)RNA from adult human normal and osteoarthritic articular cartilage was isolated and used to prepare cDNA libraries. Approximately 5000 ESTs from each library were sequenced and analysed using bioinformatic tools. The expression of select genes was confirmed by Northern blot and in situ hybridization analysis.

RESULTS

Multiple gene families including several classical cartilage matrix protein encoding genes were identified. Approximately 28-40% of the genes sequenced from these libraries were novel, while half of the genes encoded known proteins and 4-6% of the genes encoded novel homologs of known proteins. Several known genes, whose expression has not been reported previously in cartilage, were also identified. We have confirmed the cartilage expression of three known (CTGF, CTGF-L and clusterin) and two novel homologs of known genes (PCPE-2 and Gal-Nac transferase) by Northern blot and in situ hybridization analysis.

CONCLUSION

This is the first report of the preparation and sequencing of cDNA libraries from adult human normal and osteoarthritic articular cartilage. Further analysis of genes identified from these libraries may provide molecular targets for diagnosis and/or treatment of osteoarthritis (OA).

Uptake and intracellular transport of the connective tissue growth factor: a potential mode of action

Connective tissue growth factor (CTGF) is a secreted cysteine-rich protein now considered as an important effector molecule in both physiological and pathological processes. An increasing amount of evidence indicates that CTGF plays a key role in the pathogenesis of different fibrotic disorders including diabetic nephropathy. However, the molecular mechanisms by which CTGF exerts its effects are not known. Here we provide the first evidence for the existence of an intracellular transport pathway for the growth factor in human mesangial cells. Our results demonstrate that CTGF is internalized from the cell surface in endosomes and accumulates in a juxtanuclear organelle from which the growth factor is then translocated into the cytosol. In the cytosol CTGF is phosphorylated by protein kinase C and PMA treatment can enhance this phosphorylation. Phosphorylated CTGF may have an important role in the cytosol, but it is also translocated into the nucleus where it may directly affect transcription.

Inhibition of glioma cell growth and tumorigenic potential by CCN3 (NOV)

AIMS

To establish whether the ectopic expression of CCN3 (NOV) in glioma cells can interfere with their tumorigenic potential and assess its potential value in molecular medicine.

METHODS

Glioma cell lines were used to assess whether differences in the degree of intracellular communication induced by the expression of the gap junction protein connexin 43 (Cx43) is related to the differential expression of CCN3 (NOV). The antiproliferative activity of rat CCN3 (rCCN3; NOV) in glioma cells, has been assessed both in vitro and in vivo with glioma cell lines expressing different amounts of CCN3 (NOV).

RESULTS

Upon ectopic expression of Cx43, the growth of C6 glioma cells is decreased. An increase of CCN3 (NOV) expression matches the reduced tumorigenic potential of these transfected cells. The localisation of CCN3 (NOV) is affected by the increased expression of Cx43 in the Cx-13 transfected cells, in which it is detected at areas of cell-cell contact. In a xenograft model, CCN3 (NOV) transfected glioma cells were found to induce tumours to a lesser degree than their parental counterparts, which do not express detectable amounts of CCN3 (NOV).

CONCLUSIONS

Previous observations had suggested an inverse relation between CCN3 (NOV) expression in glioma cells and their tumorigenicity. These results establish a direct association between the establishment of functional gap junctional intercellular communication and the expression of rCCN3 (NOV). In addition to a negative effect on murine and human cell growth, CCN3 (NOV) has antiproliferative activity on tumour cells in vivo. Thus, the antiproliferative activity of the CCN3 (NOV) protein might involve reorganisation of cellular contacts that play a crucial role in tumorigenesis. The antiproliferative activity of CCN3 (NOV) established in this work sets the stage for the potential use of CCN proteins in molecular oncology.

Fibroblasts in mechanically stressed collagen lattices assume a "synthetic" phenotype

Fibroblasts are subjected to changes of the mechanical force balance during physiological as well as pathological situations, such as wound healing, development of hypertrophic scars, and fibrogenesis. However, the molecular response and the changes in fibroblast gene expression upon mechanical stimulation remain poorly understood. As an in vitro model, human dermal fibroblasts were cultured within a three-dimensional network of fibrillar collagen either under high (stressed) or low tension (relaxed). cDNA microarray technology in combination with Northern blot analysis led to identification of mechano-responsive genes coding for extracellular matrix proteins, fibrogenic growth factors, protease inhibitors, components of focal adhesions, and the cytoskeleton. Application of biaxial strain to fibroblasts cultured on flexible silicone membranes revealed that the type of strain as well as the properties of the substrate induced different patterns of gene regulation. The transcriptional profile of mechanically induced genes in collagen lattices suggests that mechanical stimuli lead to a "synthetic" fibroblast phenotype characterized by induction of connective tissue synthesis while simultaneously inhibiting matrix degradation.

Expression of connective tissue growth factor in human renal fibroblasts: regulatory roles of RhoA and cAMP

The induction of connective tissue growth factor (CTGF) was investigated in a human renal fibroblast cell line that exhibited many characteristics of primary human renal fibroblasts. Induction of CTGF mRNA was observed after treatment of the cells with transforming growth factor-beta (TGF-beta) or, even more prominently, lysophosphatidic acid (LPA). LPA induced a rapid transient increase in CTGF mRNA expression, with maximal levels being observed after 1 to 2 h. This increase was accompanied by CTGF protein synthesis. Induction of CTGF was insensitive to pertussis toxin and was not dependent on the activation of p42/44 mitogen-activated protein kinases. Inhibition of the proteins of the Rho family with toxin B from Clostridium difficile abrogated basal and LPA-mediated induction of CTGF. Specific targeting of RhoA with C3 exotoxin or of the Rho kinases with the inhibitor Y-27632 similarly prevented induction of CTGF, implicating RhoA as a signaling module downstream of LPA. Inhibition of RhoA depolymerized the actin cytoskeleton, as did treatment with cytochalasin D. Preincubation of the human renal fibroblasts with cytochalasin D prevented induction of CTGF by LPA, indicating a strong contribution of an intact cytoskeleton. Interference with RhoA signaling similarly inhibited the induction of CTGF by TGF-beta. Elevation of intracellular levels of cAMP and thus activation of protein kinase A prevented induction of CTGF expression. The cytoskeletal effects of cAMP, however, were reversed by LPA. These data indicate complex interactions involving LPA-mediated activation of RhoA- and protein kinase A-dependent signaling pathways. The data thus demonstrate the regulatory functions of the small GTPase RhoA and of an intact cytoskeleton in the expression of CTGF after stimulation with LPA or TGF-beta. Analogous signal transduction pathways were previously demonstrated in rat mesangial cells, suggesting a more general role for RhoA in the regulation of CTGF expression.

Expression and characterisation of the thrombospondin type I repeats of human properdin

Properdin, an upregulator of the alternative complement pathway, is central to deposition of the activated complement fragment C3b on the surfaces of the pathogens, which it achieves by preventing the dissociation of the Bb catalytic subunit from the inherently labile C3bBb complexes. It is also known to bind sulphated glycoconjugates, such as sulphatides. Properdin has an unusual structure formed by oligomerisation of a rod-like monomer into cyclic dimers, trimers and tetramers. The monomer (approximately 53 kDa) contains an N-terminal region of no known homology, followed by six non-identical repeats of 60 amino acids (based on exon/intron boundaries), called 'thrombospondin type I repeats' or TSR modules. We have expressed and purified the N-terminal region and each of the individual TSR repeats in Escherichia coli. Although the individual recombinant TSRs, after a denaturation-renaturation cycle, appeared to be correctly folded modules, as judged by the one-dimensional (1D)- and 2D-nuclear magnetic resonance spectra of TSR3, they did not show binding to either C3b or sulphatide. Polyclonal antibodies were raised against each TSR and were found to be module-specific. The anti-TSR5 polyclonal antibody was found to inhibit binding of native human properdin to solid-phase C3b, or sulphatides. It could also block properdin-dependent haemolysis of rabbit erythrocytes. These results are consistent with the view that the TSR5 contains the major site in properdin which is involved in both C3b and sulphatide binding. It also suggests that a co-operative intramolecular interaction between TSRs, as found in the native molecule, is required for TSR5 to bind either C3b or sulphatides.

Novel mode of processing and secretion of connective tissue growth factor/ecogenin (CTGF/Hcs24) in chondrocytic HCS-2/8 cells

The synthesis, processing, and secretion of human connective tissue growth factor (CTGF/Hcs24) in a human chondrocytic cell line, HCS-2/8, were analyzed immunochemically. By metabolic pulse-labeling, chasing, and subsequent immunoprecipitation analyses, active synthesis of CTGF was observed not only in growing HCS-2/8 cells, but also in confluent cells. However, secretion and processing of CTGF were found to be regulated differentially, depending upon the growth status. During phases of growth, HCS-2/8 cells released CTGF molecules immediately without sequestering them within the cell layer. In contrast, after the cells reached confluence, the secretion slowed, resulting in an accumulation of CTGF in the cells or extracellular matrices (ECMs). Also, in confluent cell layers, a 10 kDa protein that was reactive to an anti-CTGF serum was observed. This CTGF-related small protein was not detected immediately after labeling, but gradually appeared within 6 h after chase, which suggests its entity as a processed subfragment of CTGF. Surprisingly, the 10 kDa protein was stable even 48 h after synthesis, and was not released by ECM digestion, suggesting an intracellular maintenance and function. Taken together, the behavior of CTGF in HCS-2/8 cells is remarkably different from that reported in fibroblasts, which may represent unique roles for CTGF in the growth and differentiation of chondrocytes.

Connective tissue growth factor: an attractive therapeutic target in fibrotic renal disease

Despite diverse initiating insults, glomerulosclerosis and tubulointerstitial fibrosis are pathological features common to most forms of progressive renal disease. Control of systemic hypertension and blockade of the renin-angiotensin system ameliorate the rate of progression of chronic renal disease; however they generally fail to completely arrest the scarring process. While the chain of events leading to scarring are still being defined, TGF-beta is a cytokine that plays a pivotal role in the pathogenesis of glomerulosclerosis and tubulointerstitial fibrosis [1]. Given the pleiotropic effects of TGF-beta, significant attention has focused on the potential of its downstream mediators as therapeutic targets. Connective tissue growth factor (CTGF) is a member of the CCN gene family, which includes CyR61 (cysteine rich 61), Nov (Nephroblastoma overexpressed) and the WISP family (for review see [2,3,4]). These immediate-early genes coordinate complex biologic processes during differentiation and tissue repair [5]. Increased expression of CTGF has been detected in experimental and human renal fibrosis where it correlates with glomerulosclerosis and the degree of tubulointerstitial fibrosis [6]. In these settings CTGF expression is regulated at least in part by TGF-beta. This review details the biology of CTGF with specific reference to its potential as a therapeutic target in renal fibrosis.

Differential expression of the ccn3 (nov) proto-oncogene in human prostate cell lines and tissues

AIMS

To investigate the expression of the human ccn3 (hccn3; nov) proto-oncogene, a member of the CCN family of proteins, in prostate epithelial cells and prostate tissue samples.

METHODS

Normal adult prostate luminal epithelial cells immortalised by SV40 large T (PNT1A and PNT1B), metastatic tumours (LNCaP, DU-145, and PC-3), and prostate tissue samples from patients with benign prostatic hyperplasia (BPH) and prostatic adenocarcinoma were used. hccn3 (nov) mRNA was measured by the reverse transcription polymerase chain reaction (RT-PCR) and hCCN3 (NOV) protein expression was determined by immunochemistry.

RESULTS

hccn3 (nov) RNA values were higher in PC-3 cells than in the other prostate cell lines. The immortalised normal cell lines either did not express hccn3 (nov) RNA (PNT1B) or expressed very low amounts (PNT1A). BPH samples expressed variable amounts of hccn3 (nov) RNA. With the use of immunocytochemistry, all cell lines except PNT1A and PNT1B were shown to contain hCCN3 (NOV) protein. hCCN3 (NOV) was localised mainly in the epithelial compartment of BPH and adenocarcinoma samples, and there was evidence of luminal secretion.

CONCLUSION

The overexpression of hccn3 (nov) RNA in cancer cell lines compared with other cell lines and its epithelial localisation in human prostate samples are consistent with a role for hCCN3 (NOV) in prostatic tumorigenesis.

The control of ccn2 (ctgf) gene expression in normal and scleroderma fibroblasts

Although the role of transforming growth factor beta (TGFbeta) in initiating fibrosis is well established, the role that TGFbeta plays in maintaining fibrosis is unclear. The gene encoding connective tissue growth factor (ccn2; ctgf), which promotes fibrosis, is not normally expressed in dermal fibroblasts unless TGFbeta is present. However, in dermal fibroblasts cultured from lesional areas of scleroderma, ccn2 (ctgf) is expressed constitutively. The contribution of several elements in the ccn2 (ctgf) promoter to basal and TGFbeta induced ccn2 (ctgf) expression in normal and scleroderma fibroblasts has been investigated. A functional SMAD binding site in the ccn2 (ctgf) promoter that is necessary for the TGFbeta mediated induction of this gene has been identified. The previously termed TGFbeta responsive enhancer (TGFbetaRE) in the ccn2 (ctgf) promoter has been found to be necessary for basal promoter activity in normal fibroblasts. The SMAD element is not necessary for the high ccn2 (ctgf) promoter activity seen in scleroderma fibroblasts. However, mutation of the previously termed TGFbetaRE reduces ccn2 (ctgf) promoter activity in scleroderma fibroblasts to that seen in normal fibroblasts. Thus, the maintenance of the scleroderma phenotype, as assessed by a high degree of ccn2 (ctgf) promoter activity, appears to be relatively independent of SMAD action and seems to reflect increased basal promoter activity.

5' flanking sequence of the human immediate early responsive gene ccn1 (cyr61) and mapping of polymorphic CA repeat sequence motifs in the human ccn1 (cyr61) locus

AIMS

The human ccn1 (hccn; hcyr61) gene has been identified previously at the mRNA and protein level as a 1,25-dihydroxyvitamin D(3) and growth factor regulated gene in human osteoblasts. This study aimed to analyse genomic clones containing the human ccn1 (cyr61) gene and to provide the 5' flanking region.

METHODS

Genomic clones were isolated by screening a lambda library and by array filter hybridisations of a genomic library. Sequencing was performed using the dye terminator method. Promoter activity was measured after transient transfection using a beta galactosidase assay. CA repeat motifs were studied by a combined PCR/fragment analysis protocol.

RESULTS

The human 5' flanking region of 870 nucleotides contains several stretches with high homology to the mouse promoter as well as CA repeat motifs. This first report on the human 5' flanking sequence of the hccn1 (hcyr61) gene provides important insights into regulation pathways for the expression of this 1,25-dihydroxyvitamin D(3) and growth factor responsive early gene. A genomic clone containing the hccn1 (hcyr61) gene region also yielded a CA sequence located 3' of the ccn1 (cyr61) gene. This CA repeat and one of the CA repeat motifs in the promoter were studied in detail and found to be polymorphic.

CONCLUSIONS

The 5' flanking sequence of the hccn1 (hcyr61) gene provides insights into the mechanisms of regulation of this immediate early gene product. The CA repeat polymorphisms within the gene region will be useful in the genetic study of disorders affecting bone metabolism.

Iloprost suppresses connective tissue growth factor production in fibroblasts and in the skin of scleroderma patients

Patients with scleroderma receiving Iloprost as a treatment for severe Raynaud's phenomenon report a reduction in skin tightness, suggesting that this drug inhibits skin fibrosis. Connective tissue growth factor (CTGF), a recently described profibrotic cytokine, acts downstream and in concert with TGF-beta to stimulate the fibrotic process and is involved in the fibrosis seen in scleroderma. Here we show that Iloprost, acting by elevation of cAMP, blocks the induction of CTGF and the increase in collagen synthesis in fibroblasts exposed to TGF-beta. The potency of Iloprost with respect to suppression of CTGF far exceeds that of other prostanoid receptor agonists, suggesting that its effect is mediated by the prostacyclin receptor IP. By sampling dermal interstitial fluid using a suction blister device, we show that CTGF levels are greatly elevated in the dermis of scleroderma patients compared with healthy controls and that Iloprost infusion causes a marked decrease in dermal CTGF levels. These studies suggest that Iloprost could be reducing the level of a key profibrotic cytokine in scleroderma patients and that endogenous production of eicosanoids may limit the fibrotic response to TGF-beta.

COP-1, a member of the CCN family, is a heparin-induced growth arrest specific gene in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) hyperplasia is responsible for the failure of 15-30% of vascular surgical procedures such as coronary artery bypass grafts and angioplasties. We and others have shown that heparin suppresses VSMC proliferation in vivo and in cell culture. We hypothesize that heparin inhibits VSMC proliferation by binding to cell surface receptors, resulting in selective modulation of mitogenic signal transduction pathways and altered transcription of a specific subset of growth regulatory genes. To test this idea, we used subtractive hybridization to identify differentially expressed mRNAs in heparin-treated and untreated VSMC. We identified a heparin induced mRNA identical to Cop-1, a member of the CCN family of proteins which are secreted, cysteine-rich modular proteins involved in growth regulation and migration. Cop-1 from smooth muscle cells appears to have a different expression pattern and possibly different functions than Cop-1 from other cells. Cop-1 mRNA is expressed at high levels in quiescent VSMC and at low levels in proliferating VSMC, an expression pattern highly characteristic of growth arrest specific genes. Cop-1 mRNA is expressed at high levels in heparin treated VSMC and COP-1 protein is secreted into culture medium. In tissues, Cop-1 expression is observed in the uninjured rat aorta suggesting a possible role for Cop-1 in vivo. We found PDGF, but not EGF, inhibits the expression of Cop-1 in VSMC. Neither TGF-beta nor interferon-beta, two inhibitors of VSMC proliferation, were able to induce Cop-1 expression. In addition, heparin does not induce Cop-1 mRNA in endothelial cells and VSMC resistant to the antiproliferative effect of heparin. Conditioned medium from cells over-expressing COP-1 protein inhibits VSMC proliferation in culture. Together, our data indicate that COP-1 may play a role in the antiproliferative mechanism of action of heparin.

Connective tissue growth factor in tubulointerstitial injury of diabetic nephropathy

BACKGROUND

Chronic interstitial fibrosis, which follows the onset of glomerular proteinuria, importantly contributes to progressive renal failure in diabetic nephropathy. The present studies examine the potential role of tubular connective tissue growth factor (CTGF).

METHODS

The expression of CTGF was examined in rats with diabetic nephropathy. Regulation and actions of CTGF were studied in in vitro cell culture models.

RESULTS

CTGF mRNA levels were increased in the renal cortex of rats with streptozotocin-induced diabetes compared with controls. Immunohistology indicated that CTGF was expressed in renal cortex of diabetic rats, in contrast to controls in some tubular cross-sections, particularly dilated-appearing proximal tubules, in which it tended to colocalize with insulin-like growth factor-I (IGF-I). Glomerular ultrafiltrate from diabetic rats, which contained bioactive transforming growth factor-beta (TGF-beta) and hepatocyte growth factor (HGF), induced increased CTGF expression in tubular cells. TGF-beta1 and, to a lesser extent, HGF also raised CTGF expression in cultured proximal tubular cells. In contrast, high glucose (25 mmol/L) did not increase the secretion of CTGF. In cultured tubular cells, rhCTGF moderately increased fibronectin but not collagen (Col) type I and type III expression. In NRK-49F renal interstitial fibroblasts, CTGF raised Col alpha1III and thrombospondin-1 levels. CTGF has an IGF-binding domain and binds to IGF-I. In NRK-49F cells, IGF-I increased the activity of CTGF towards the expression of Col alpha1III.

CONCLUSIONS

CTGF is expressed and regulated downstream from TGF-beta and HGF in proximal tubular cells, is induced by diabetic rat glomerular ultrafiltrate, and has moderate profibrogenic activity in tubular cells and renal interstitial fibroblasts, where its activity is IGF-I dependent. By these means, CTGF may act downstream of TGF-beta and HGF and may contribute to chronic tubulointerstitial fibrosis in diabetic nephropathy.

Connective tissue growth factor in drug-induced gingival overgrowth

BACKGROUND

Drug-induced gingival overgrowth is a known side effect of certain chemotherapeutic agents used for the treatment of systemic disorders. The pathogenesis and mechanisms responsible for this condition are not fully understood. This study assesses for the presence and localization of connective tissue growth factor (CTGF) in drug-induced gingival overgrowth tissues. CTGF immunostaining was compared with sections stained with transforming growth factor (TGF)-beta1 and CD31 antibodies in order to investigate possible pathogenic mechanisms.

METHODS

Gingival overgrowth samples were obtained from patients undergoing therapy with phenytoin (n = 9), nifedipine (n = 4), cyclosporin A (n = 5), and control tissues from systemically healthy donors (n = 9). Tissue sections were subjected to peroxidase immunohistochemistry and were stained with CTGF and TGF-beta1 polyclonal primary antibodies. Possible relationships between CTGF staining and angiogenesis were also studied using an anti-CD31 antibody as a marker for endothelial cells. Staining was analyzed by computer-assisted quantitative and semiquantitative methodology at 5 defined sites in all samples based on the location of specific landmarks including epithelium and underlying connective tissues.

RESULTS

Cellular and extracellular CTGF content in phenytoin gingival overgrowth tissues was significantly (P<0.05) higher compared to the other gingival overgrowth tissues and the controls. Higher CTGF staining in phenytoin gingival overgrowth tissues was accompanied by an increased abundance of fibroblasts and connective tissue fibers. No strong association of CTGF staining with TGF-beta1 or CD31 staining was found.

CONCLUSIONS

The data from the present study show significantly higher CTGF staining in phenytoin-induced gingival overgrowth tissues compared to controls, cyclosporin A-, or nifedipine-induced gingival overgrowth. Moreover, semiquantitative analyses of histologic samples support the concept that the phenytoin overgrowth tissues are fibrotic. These associations suggest a possible role for CTGF in promoting development of fibrotic lesions in phenytoin-induced gingival overgrowth.

Hydrogen peroxide is a novel inducer of connective tissue growth factor

Connective tissue growth factor (CTGF) has recently been described as a fibrogenic factor and is greatly induced by various extracellular stimuli, such as transforming growth factor-beta (TGF-beta), dexamethasone, and serotonin. CTGF induces collagen type I and fibronectin, and the deposition of such molecules leads to fibrotic disease in many tissues. Intracellular reactive oxygen species (ROS) are generated by extracellular stress conditions and are produced as by-products of cellular metabolism. Imbalanced cellular redox status is a potent pathogenic factor that leads to various degenerative diseases, including tissue fibrosis. Since CTGF is believed to play a crucial role in fibrotic disease formation in many tissues, we examined the role of ROS in CTGF gene expression in human lens epithelial cell line B3. The results showed that CTGF was induced by reactive oxygen species such as hydrogen peroxide and hydroxyl radicals. Next, we examined whether CTGF induction by ROS is via newly synthesized TGF-beta. The results showed that ROS directly induced CTGF mRNA not via the increased TGF-beta synthesis or activation. Next, we treated AG490, which is the well-known inhibitor of Janus kinase (JAK), with hydrogen peroxide. AG490 abrogated the CTGF induction by ROS in a dose-dependent manner. The results suggest that JAK-2/-3 seems to be involved in the enhanced CTGF mRNA expression by hydrogen peroxide. In this report, we present that hydrogen peroxide is a novel inducer of CTGF gene expression and that JAK-2/-3 activation seems to play a role in CTGF induction.

CYR61 stimulates human skin fibroblast migration through Integrin alpha vbeta 5 and enhances mitogenesis through integrin alpha vbeta 3, independent of its carboxyl-terminal domain

CYR61, an angiogenic factor and a member of the CCN protein family, is an extracellular matrix-associated, heparin-binding protein that mediates cell adhesion, promotes cell migration, and enhances growth factor-stimulated cell proliferation. CYR61 induces angiogenesis and promotes tumor growth in vivo and is expressed in dermal fibroblasts during cutaneous wound healing. It has been demonstrated recently that adhesion of primary skin fibroblasts to CYR61 is mediated through integrin alpha(6)beta(1) and cell surface heparan sulfate proteoglycans, resulting in adhesive signaling and up-regulation of matrix metalloproteinases 1 and 3. CYR61 is composed of four discrete structural domains that bear sequence similarities to the insulin-like growth factor-binding proteins, von Willebrand factor type C repeat, thrombospondin type 1 repeat, and a carboxyl-terminal (CT) domain that resembles cysteine knots found in some growth factors. In this study, we show that a CYR61 mutant (CYR61DeltaCT) that has the CT domain deleted is unable to support adhesion of primary human skin fibroblasts but is still able to stimulate chemotaxis and enhance basic fibroblast growth factor-induced mitogenesis similar to wild type. In addition, fibroblast migration to CYR61 is mediated through integrin alpha(v)beta(5) but not integrins alpha(6)beta(1) or alpha(v)beta(3). Furthermore, we show that CYR61 binds directly to purified integrin alpha(v)beta(5) in vitro. By contrast, CYR61 enhancement of basic fibroblast growth factor-induced DNA synthesis is mediated through integrin alpha(v)beta(3), a known receptor for CYR61 that mediates CYR61-dependent cell adhesion and chemotaxis in vascular endothelial cells. Thus, CYR61 promotes primary human fibroblast adhesion, migration, and mitogenesis through integrins alpha(6)beta(1), alpha(v)beta(5), and alpha(v)beta(3), respectively. Together, these findings establish CYR61 as a novel ligand for integrin alpha(v)beta(5) and show that CYR61 interacts with distinct integrins to mediate disparate activities in a cell type-specific manner.

Type II alveolar epithelial cells and interstitial fibroblasts express connective tissue growth factor in IPF

Connective tissue growth factor (CTGF) is a growth and chemotactic factor for fibroblasts encoded by an immediate early gene that is transcriptionally activated by transforming growth factor-beta. Previous studies have shown that both CTGF messenger ribonuclear acid (mRNA) and protein are expressed in renal fibrosis and bleomycin-induced pulmonary fibrosis in mice. The aim of the present study was to investigate the localization of CTGF protein and its mRNA expression in the fibrotic lung tissue of patients with idiopathic pulmonary fibrosis (IPF). Using human fibrotic lung tissue obtained from eight autopsy cases and four biopsy cases with IPF, immunohistochemical staining, in situ hybridization, and reverse transcription-polymerase chain reaction (RT-PCR) were performed. The cellular immunoreactivity for CTGF was markedly increased in the lung tissue of patients with IPF, compared to normal lungs. The immunolocalization of CTGF was confined predominantly to proliferating type II alveolar epithelial cells and activated fibroblasts. In the normal lung, type II alveolar epithelial cells stained for CTGF were sparsely distributed. CTGF mRNA was localized in proliferating type II alveolar epithelial cells and activated fibroblasts in the interstitium of fibrotic lung tissues. RT-PCR analysis showed that CTGF mRNA was expressed at a higher level in fibrotic lungs than in normal lungs. In both an autocrine and a paracrine manner, type II alveolar epithelial cells and activated fibroblasts may play a critical role in pulmonary fibrosis by producing connective tissue growth factor which modulates fibroblast proliferation and extracellular matrix production.

Cyclosporine induces myocardial connective tissue growth factor in spontaneously hypertensive rats on high-sodium diet

BACKGROUND

The introduction of cyclosporine (CsA) has led to an improvement in the prognosis of solid organ transplantation. However, drug-induced hypertension and nephrotoxicity, associated with the development of atherosclerosis and coronary heart disease, still worsen the long-term outcome of CsA-treated patients. Whether the CsA-induced myocardial changes are associated with the induction of connective tissue growth factor (CTGF), a recently found polypeptide implicated in extracellular matrix synthesis, is not known.

METHODS

Spontaneously hypertensive rats (8-9 weeks old) were treated with CsA (5 mg x kg(-1) x d(-1) subcutaneously) for 6 weeks. The influence of angiotensin-converting enzyme inhibition (enalapril 30 mg x kg(-1) x d(-1) orally) and angiotensin-1 receptor blockade (valsartan 3 and 30 mg x kg(-1) x d(-1) orally) on CsA toxicity was also investigated. Myocardial morphology was examined, and vascular lesions were scored. Localization and the quantitative expression of CTGF, as well as collagen I and collagen III, mRNA were evaluated by in situ hybridization and Northern blot.

RESULTS

CsA-induced hypertension and nephrotoxicity were associated with myocardial infarcts and vasculopathy of the coronary arteries. CsA increased myocardial CTGF, collagen I, and collagen III mRNA expressions by 91%, 198%, and 151%, respectively. CTGF mRNA expression colocalized with the myocardial lesions. Blockade of the renin-angiotensin system prevented vascular damage and the CsA-induced CTGF, collagen I, and collagen III mRNA overexpressions in the heart.

CONCLUSIONS

CsA increases CTGF, collagen I, and collagen III mRNA expressions in the heart. The induction of CTGF gene is mediated, at least in part, by angiotensin II.

Static pressure regulates connective tissue growth factor expression in human mesangial cells

Connective tissue growth factor (CTGF) is overexpressed in a variety of fibrotic disorders such as renal fibrosis and atherosclerosis. Fibrosis is a common final pathway of renal diseases of diverse etiology, including inflammation, hemodynamics, and metabolic injury. Mechanical strains such as stretch, shear stress, and static pressure are possible regulatory elements in CTGF expression. In this study, we examined the ability of static pressure to modulate CTGF gene expression in cultured human mesangial cells. Low static pressure (40-80 mm Hg) stimulated cell proliferation via a protein kinase C-dependent pathway. In contrast, high static pressure (100-180 mm Hg) induced apoptosis in human mesangial cells. This effect was reversed by treatment with CTGF antisense oligonucleotide but not with transforming growth factor beta1-neutralizing antibody or protein kinase C inhibitor. High static pressure not only up-regulated the expression of CTGF, but also the expression of extracellular matrix proteins (collagen I and IV, laminin). This up-regulation of extracellular matrix proteins was also reversed by treatment with CTGF antisense oligonucleotide. As judged by mRNA expression of a total of 1100 genes, including apoptosis-associated genes using DNA microarray techniques, recombinant CTGF protein induced apoptosis by down-regulation of a number of anti-apoptotic genes. Overexpression of CTGF in mesangial cells by transient transfection had similar effects. Taken together, these results suggest that high blood pressure up-regulates CTGF expression in mesangial cells. High levels of CTGF in turn enhance extracellular matrix production and induce apoptosis in mesangial cells, and may contribute to remodeling of mesangium and ultimately glomerulosclerosis.

Gene induction by coagulation factor Xa is mediated by activation of protease-activated receptor 1

Cell signaling by coagulation factor Xa (Xa) contributes to pro-inflammatory responses in vivo. This study characterizes the signaling mechanism of Xa in a HeLa cell line that expresses protease-activated receptor 1 (PAR-1) but not PAR-2, -3, or -4. Xa induced NF-kappaB in HeLa cells efficiently but with delayed kinetics compared to thrombin. This delay caused no difference in gene expression patterns, as determined by high-density microarray analysis. Both proteases prominently induced the angiogenesis-promoting gene Cyr61 and connective tissue growth factor. Inhibition of PAR-1 cleavage abolished MAP kinase phosphorylation and gene induction by Xa, demonstrating that Xa signals through PAR-1 and not through a novel member of the PAR family. Activation of cell surface prothrombin with the snake venom enzyme Ecarin also produced PAR-1-dependent signaling. However, though the response to Ecarin was completely blocked by the thrombin inhibitor hirudin, the response to Xa was not. This suggests that the Xa response is not mediated by locally generated thrombin. The concentration dependence of Xa for PAR-1 activation is consistent with previously characterized Xa-mediated PAR-2 signaling, suggesting that local concentration of Xa on the cell surface, rather than sequence-specific recognition of the PAR scissile bond, determines receptor cleavage. This study demonstrates that PAR-1 cleavage by Xa can elicit the same cellular response as thrombin, but mechanistic differences in receptor recognition may be crucial for specific roles for Xa in signaling during spatial or temporal separation from thrombin generation.

Connective tissue growth factor and its regulation: a new element in diabetic glomerulosclerosis

Connective tissue growth factor (CTGF), a member of the closely related CCN family of cytokines appears to be fibrotic in skin. To determine whether CTGF is implicated in diabetic glomerulosclerosis we studied cultured rat mesangial cells (MC) as well as kidney cortex and microdissected glomeruli from obese, diabetic db/db mice and their normal counterparts. Exposure of MC to rhCTGF significantly increased fibronectin and collagen type I secretion. Further, unstimulated MC expressed low levels of CTGF message and secreted minimal amounts of CTGF protein (36-38 kDa). However, exposure to TGF-beta, increased glucose concentrations, or cyclic mechanical strain, all causal factors in glomerulosclerosis, markedly induced the expression of CTGF transcripts. With all but mechanical strain there was a concomitant stimulation of CTGF protein secretion. TGF-beta also induced abundant quantities of a small molecular weight form of CTGF (18 kDa). 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 RT-PCR demonstrated that while CTGF transcripts were low in the glomeruli of control mice, expression was increased 27-fold after approximately 3.5 months of diabetes. These changes occurred early in diabetic nephropathy when mesangial expansion was mild, and interstitial disease and proteinuria were absent. A substantially reduced elevation of CTGF mRNA (2-fold) observed in whole kidney cortices indicted 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 in both diabetic and non-diabetic glomerulosclerosis, acting downstream of TGF-beta.

Breast cancer. Cyr61 is overexpressed, estrogen-inducible, and associated with more advanced disease

To identify genes involved in breast cancer, polymerase chain reaction-selected cDNA subtraction was utilized to construct a breast cancer-subtracted library. Differential screening of the library isolated the growth factor-inducible immediate-early gene Cyr61, a secreted, cysteine-rich, heparin binding protein that promotes endothelial cell adhesion, migration, and neovascularization. Northern analysis revealed that Cyr61 was expressed highly in the invasive breast cancer cell lines MDA-MB-231, T47D, and MDA-MB-157; very low levels were found in the less tumorigenic MCF-7 and BT-20 breast cancer cells and barely detectable amounts were expressed in the normal breast cells, MCF-12A. Univariate analysis showed a significant or borderline significant association between Cyr61 expression and stage, tumor size, lymph node positivity, age, and estrogen receptor levels. Interestingly, expression of Cyr61 mRNA increased 8- to 12-fold in MCF-12A and 3- to 5-fold in MCF-7 cells after 24- and 48-h exposure to estrogen, respectively. Induction of Cyr61 mRNA was blocked by tamoxifen and ICI182,780, inhibitors of the estrogen receptor. Stable expression of Cyr61 cDNA under the regulation of a constitutive promoter in MCF-7 cells enhanced anchorage-independent cell growth in soft agar and significantly increased tumorigenicity and vascularization of these tumors in nude mice. Moreover, overexpression of Cyr61 in MCF-12A normal breast cells induced their tumor formation and vascularization in nude mice. In summary, these results suggest that Cyr61 may play a role in the progression of breast cancer and may be involved in estrogen-mediated tumor development.

CTGF and SMADs, maintenance of scleroderma phenotype is independent of SMAD signaling

In normal adult fibroblasts, transforming growth factor-beta (TGFbeta) induces the expression of connective tissue growth factor (CTGF). CTGF independently promotes fibroblast proliferation and matrix deposition, and in acute models of fibrosis promotes cell proliferation and collagen deposition acting synergistically with TGFbeta. In contrast to normal fibroblasts, fibroblasts cultured from fibrotic tissues express high basal levels of CTGF, even in the absence of added TGFbeta. Induction of transcription by TGFbeta requires the action of SMAD proteins. In this report we have investigated the role of SMADs in the TGFbeta-induction of CTGF in normal fibroblasts and in the elevated levels of CTGF expression found in dermal fibroblasts cultured from lesional areas of patients with scleroderma, a progressive fibrotic disorder that can affect all organs of the body. We have identified a functional SMAD binding site in the CTGF promoter. TGFbeta-induction of CTGF is dependent on SMAD3 and SMAD4 but not SMAD2 and is p300-independent. However, mutation of the SMAD binding site does not reduce the high level of CTGF promoter activity observed in dermal fibroblasts cultured from lesional areas of scleroderma patients. Conversely, the previously termed TGFbetaRE in the CTGF promoter is required for basal CTGF promoter activity in normal fibroblasts and for the elevated level of CTGF promoter activity in scleroderma fibroblasts. Thus, the maintenance of the fibrotic phenotype in scleroderma fibroblasts, as visualized by excess CTGF expression, appears to be independent of SMAD-dependent TGFbeta signaling. Furthermore, given CTGF's activities, the high level of CTGF expression observed in scleroderma lesions may contribute to the excessive scarring observed in this disorder.

NOV (nephroblastoma overexpressed) and the CCN family of genes: structural and functional issues

The CCN family of genes presently consists of six distinct members encoding proteins that participate in fundamental biological processes such as cell proliferation, attachment, migration, differentiation, wound healing, angiogenesis, and several pathologies including fibrosis and tumorigenesis. Whereas CYR61 and CTGF were reported to act as positive regulators of cell growth, NOV (nephroblastoma overexpressed) provided the first example of a CCN protein with negative regulatory properties and the first example of aberrant expression being associated with tumour development. The subsequent discovery of the ELM1, rCOP1, and WISP proteins has broadened the variety of functions attributed to the CCN proteins and has extended previous observations to other biological systems. This review discusses fundamental questions regarding the regulation of CCN gene expression in normal and pathological conditions, and the structural basis for their specific biological activity. After discussing the role of nov and other CCN proteins in the development of a variety of different tissues such as kidney, nervous system, muscle, cartilage, and bone, the altered expression of the CCN proteins in various pathologies is discussed, with an emphasis on the altered expression of nov in many different tumour types such as Wilms's tumour, renal cell carcinomas, prostate carcinomas, osteosarcomas, chondrosarcomas, adrenocortical carcinomas, and neuroblastomas. The possible use of nov as a tool for molecular medicine is also discussed. The variety of biological functions attributed to the CCN proteins has led to the proposal of a model in which physical interactions between the amino and carboxy portions of the CCN proteins modulate their biological activity and ensure a proper balance of positive and negative signals through interactions with other partners. In this model, disruption of the secondary structure of the CCN proteins induced by deletions of either terminus is expected to confer on the truncated polypeptide constitutive positive or negative activities.

Proliferating bile duct epithelial cells are a major source of connective tissue growth factor in rat biliary fibrosis

Connective tissue growth factor (CTGF) is a downstream mediator of transforming growth factor-beta1 (TGF-beta1) and thus a potential target for antifibrotic treatment strategies. CTGF is up-regulated in disorders such as atherosclerosis, scleroderma, and fibrosis of kidneys and lungs. We investigated the temporospatial expression patterns of CTGF and TGF-beta1 mRNA in rat livers with acute fibrogenesis (after a single dose of CCl(4)) and with advanced fibrosis (6 weeks after complete bile duct occlusion). Multiprobe ribonuclease protection assay revealed increasing TGF-beta1 and CTGF mRNA levels 6 hours after injection of CCl(4), with peak levels after 72 hours. In biliary fibrosis TGF-beta1 and CTGF mRNA levels increased fourfold and sevenfold, respectively (P: < 0.001). In situ hybridization combined with cell-specific markers revealed CTGF transcripts in desmin-positive cells after a single dose of carbon tetrachloride, whereas no transcripts were found in normal livers. In biliary fibrosis, however, proliferating bile duct epithelial cells were the predominant source of CTGF mRNA. We conclude that in rat liver fibrogenesis CTGF is up-regulated in close association with TGF-beta1 and that, contrary to a previous report, not solely hepatic stellate cells but activated bile duct epithelial cells are the main source of this profibrogenic factor.

The angiogenic factors Cyr61 and connective tissue growth factor induce adhesive signaling in primary human skin fibroblasts

The angiogenic inducers cysteine-rich angiogenic protein 61 (Cyr61) and connective tissue growth factor (CTGF) are structurally related, extracellular matrix-associated heparin-binding proteins. Both can stimulate chemotaxis and promote proliferation in endothelial cells and fibroblasts in culture and induce neovascularization in vivo. Encoded by inducible immediate early genes, Cyr61 and CTGF are synthesized upon growth factor stimulation in cultured fibroblasts and during cutaneous wound healing in dermal fibroblasts. Recently, we have shown that adhesion of primary human fibroblasts to immobilized Cyr61 is mediated through integrin alpha(6)beta(1) and cell surface heparan sulfate proteoglycans (HSPGs) (Chen, N., Chen, C.-C., and Lau, L.F. (2000) J. Biol. Chem. 275, 24953-24961), providing the first demonstration of an absolute requirement for HSPGs in integrin-mediated cell attachment. We show in this study that CTGF also mediates fibroblast adhesion through the same mechanism and demonstrate that fibroblasts adhesion to immobilized Cyr61 or CTGF induces distinct adhesive signaling responses consistent with their biological activities. Compared with fibroblast adhesion to fibronectin, laminin, or type I collagen, cell adhesion to Cyr61 or CTGF induces 1) more extensive and prolonged formation of filopodia and lamellipodia, concomitant with formation of integrin alpha(6)beta(1)-containing focal complexes localized at leading edges of pseudopods; 2) activation of intracellular signaling molecules including focal adhesion kinase, paxillin, and Rac with similar rapid kinetics; 3) sustained activation of p42/p44 MAPKs lasting for at least 9 h; and 4) prolonged gene expression changes including up-regulation of MMP-1 (collagenase-1) and MMP-3 (stromelysin-1) mRNAs and proteins sustained for at least 24 h. Together, these results establish Cyr61 and CTGF as bona fide adhesive substrates with specific signaling capabilities, provide a molecular basis for their activities in fibroblasts through integrin alpha(6)beta(1) and HSPG-mediated signaling during attachment and indicate that these proteins may function in matrix remodeling through the activation of metalloproteinases during angiogenesis and wound healing.

Overexpression of connective tissue growth factor/hypertrophic chondrocyte-specific gene product 24 decreases bone density in adult mice and induces dwarfism

Connective tissue growth factor/hypertrophic chondrocyte-specific gene product 24 (CTGF/Hcs24) is a multifunctional growth factor for fibroblasts, chondrocytes, and vascular endothelial cells. In the present study, we established transgenic (Tg) mice that overproduce CTGF/Hcs24 under the control of mouse type XI collagen promoter. Tg mice could develop and their embryonic and neonatal growth occurred normally. But they showed dwarfism within a few months of birth. X-ray analysis revealed that their bone density was decreased compared with normal mice. The femurs in the hindlimbs in particular showed an apparent low density. These results indicated that overexpression of CTGF/Hcs24 affects certain steps of endochondral ossification. In addition, the testes were much smaller than normal and fertility was affected in Tg mice, indicating that CTGF/Hcs24 may also regulate the embryonic development of the testis.

Differentiation-dependent expression of connective tissue growth factor and lysyl oxidase messenger ribonucleic acids in rat granulosa cells

Searching for novel genes involved in tissue remodeling during ovarian folliculogenesis, we carried out differential display RT-PCR (DDRT-PCR) on RNA from gonadotropin-stimulated rat granulosa cells (GC). GC from preantral and early antral follicles in immature rat ovaries were cultured in serum-free medium containing no hormone (control), recombinant human FSH (10 ng/ml), 5alpha-dihydrotestosterone (DHT; 10(-6) M), or FSH plus DHT. Total cellular RNA was extracted from cells at 6, 12, 24, and 48 h of treatment for DDRT-PCR analysis, corresponding to an estimated 60% saturation of the messenger RNA (mRNA) population. Six distinct complementary DNA clones were obtained that reproduced the DDRT-PCR profile on a Northern blot of the corresponding RNA samples. Two of these clones detected transcripts that were strongly down-regulated by FSH. One corresponded to connective tissue growth factor (CTGF), a cysteine-rich secreted protein related to platelet-derived growth factor that is implicated in mitogenesis and angiogenesis, and a second was identical to lysyl oxidase (LO), a key participant in extracellular matrix deposition. In detailed expression studies, Northern analysis revealed a single, approximately 2.5-kb CTGF transcript maximally suppressed within 3 h of exposure to FSH with or without DHT and two LO transcripts ( approximately 3.8 and approximately 5.2 kb) maximally suppressed at 6 h. DHT alone did not affect CTGF mRNA, but strongly enhanced LO mRNA relative to the control value. In vivo, CTGF and LO transcripts were significantly suppressed in GC 48 h after equine CG injection (10 IU, ip) compared with untreated controls and were further reduced 12 h after administration of additional 10 IU hCG to induce luteinization. In situ hybridization confirmed GC in preantral/early antral follicles as principal sites of CTGF and LO mRNA expression. We conclude that expression of CTGF and LO mRNAs is inversely related to GC differentiation. The encoded proteins probably have roles in the regulation of tissue remodeling and extracellular matrix formation during early follicular development.

Kinetics of connective tissue growth factor expression during experimental proliferative glomerulonephritis

Connective tissue growth factor (CTGF) is a member of the CCN family of immediate early genes, which are involved in cell proliferation, migration, and matrix production. Recently, CTGF was observed to be strongly upregulated in human proliferative and fibrogenic renal disease. By in situ hybridization and reverse transcriptase-PCR, the expression of CTGF was investigated in experimental proliferative glomerulonephritis induced by injection of anti-Thy-1.1 antibody in the rat. CTGF expression in cultured rat mesangial cells and glomerular visceral epithelial cells (GVEC) was studied in response to transforming growth factor beta (TGF-beta), an essential pathogenetic factor in this model. In normal rat kidneys, only some GVEC expressed CTGF mRNA. In anti-Thy-1.1 nephritis, CTGF mRNA expression was strongly increased in extracapillary and mesangial proliferative lesions and in areas of periglomerular fibrosis. Early glomerular CTGF overexpression in GVEC coincided with a striking upregulation of TGF-beta2 and to a lesser extent of TGF-beta3. Glomerular CTGF mRNA expression was maximal at day 7, in association with increased TGF-beta1 mRNA and protein expression. CTGF mRNA overexpression by parietal epithelial cells preceded the periglomerular appearance of alpha-smooth muscle actin-positive fibroblasts. In cultured mesangial cells, TGF-beta1, -beta2, and -beta3 transiently increased the CTGF/glyceraldehyde phosphate dehydrogenase mRNA ratio up to threefold versus control at 4 h. In GVEC, upregulation of CTGF mRNA by these TGF-beta isoforms was more sustained, being 8- to 16-fold versus control at 24 h. The kinetics of CTGF expression strongly suggest a role in glomerular repair, possibly downstream of TGF-beta, in this model of transient renal injury.

Mechanical stimulation induces CTGF expression in rat osteocytes

Connective tissue growth factor (CTGF), which is encoded by an immediate early gene and a member of the CCN family, has been shown to be expressed in osteoblasts, fibroblasts, and chondrocytes. Although CTGF is expressed in bone and cartilage tissues, we tested the hypothesis that CTGF is regulated in mechanotransduction. In the alveolar bone during experimental tooth movement, CTGF mRNA was expressed in osteoblasts and in osteocytes localized around the periodontal ligament under control conditions. Interestingly, 12 hrs after the start of experimental tooth movement, the expression of CTGF mRNA in osteocytes and osteoblasts became more intense around the periodontal ligament, and the intense expression of CTGF extended to osteocytes situated deep in alveolar bone matrix apart from periodontal ligament in both tension and compression sides. Our present findings indicate that CTGF could play a role in regulation of osteocyte function during the mechanical stimulation of bone.

Establishment of cell lines with high- and low-metastatic potential from PC-14 human lung adenocarcinoma

This article reports the establishment of variant cell lines with high and low metastatic potential by repeated selection and the dilution plating technique. Five clones with high metastatic potential, Lu-2, Lu-7, Lu-4, Lu-1 and Lu-5, and four clones with low metastatic potential, 3S, 7S, 8S and 13S, were established from PC-14 human lung adenocarcinoma. The high-metastatic cell lines produced enhanced lung metastases, but the low-metastatic cell lines did not produce lung metastasis by injection into the tail vein of 5-week-old BALB / c nude mice. The high-metastatic cell lines produced enhanced tumors on both visceral and parietal pleurae, and enhanced metastases to the mediastinum and contralateral pleural cavity. The low-metastatic cell lines produced reduced tumors on both visceral and parietal pleurae and reduced metastases to the mediastinum and contralateral pleural cavity after injection into the left preceral cavity of the nude mice. When the nine variant cell lines and original PC-14 cells were embedded in collagen gels, the PC-14 cells and the low-metastatic cell lines gave rise to colonies with a dendritic morphology, and cells were tightly associated. The high-metastatic cell lines were more loosely associated and scattered into three-dimensional colonies. These nine cloned cell lines originated from heterogeneous populations of the parental PC-14 cells should be useful tools for studying the process of metastasis of lung cancer.

Isolation of a novel actin-related gene expressed in low-metastatic PC-14 human lung adenocarcinoma

In this article, we report the identification of differentially expressed genes associated with the metastatic potential of PC-14 human lung adenocarcinoma. The mRNA differential display method was applied to compare mRNAs from six cloned PC-14 cell lines representing different metastatic potentials. A novel gene was identified as being expressed in low-metastatic cells but not in high-metastatic cells. Sequence analysis revealed that this novel gene has an open reading frame of 210 amino acid residues showing 89% amino acid identity with human Arp3, which is one of the actin-related proteins. This gene was designated the Arp11 gene (the 11th Actin-related gene). The Arp11 gene was mapped to human chromosome 7q32-36. Southern blot and PCR analyses show that all of the high-metastatic variant cells have not rearrangements and deletions of Arp11 allele. Expression of the Arp11 gene may regulate the metastatic potential of PC-14 human lung adenocarcinoma.

Connective tissue growth factor expression in pediatric myofibroblastic tumors

Human connective tissue growth factor (CTGF) is a secreted cysteine-rich peptide and a member of the peptide family that includes serum-induced immediate gene products such as a v-src-induced peptide and a putative proto-oncogene, c-src. CTGF is secreted by endothelial cells, fibroblasts, smooth muscle cells, and myofibroblasts. Its expression is increased in various human and animal fibrotic diseases. We hypothesized that tumors with significant fibrous and vascular components would exhibit increased expression of CTGF. We examined the expression of CTGF mRNA by in situ hybridization in 12 pediatric tumors and tumor-like conditions, including angiofibroma, malignant fibrous histiocytoma, infantile myofibromatosis, and malignant hemangiopericytoma. All the tumors showed moderate to intense CTGF expression in tumor cells and/or endothelial cells of the associated vasculature. Angiofibromas expressed CTGF only in factor VIII-positive endothelial cells and vascular smooth muscle cells. In contrast, infantile myofibromatosis, malignant hemangiopericytomas, and fibrous histiocytomas expressed CTGF in both endothelial cells and in vimentin-positive tumor cells, particularly those around the blood vessels. CTGF mRNA was not detected in the inflammatory cells observed in many of the tumors. The presence of CTGF in the endothelial cells and tumor cells around blood vessels raises the possibility that CTGF is involved in the pathogenesis of these myofibroblastic tumors.

Physical characterization of the procollagen module of human thrombospondin 1 expressed in insect cells

Thrombospondin 1 (TSP1) is a homotrimeric glycoprotein composed of 150-kDa subunits connected by disulfide bridges. The procollagen module of thrombospondin 1 has been implicated in antiangiogenic activity. Procollagen modules are found in a number of extracellular proteins and are identifiable by 10 cysteines with characteristic spacing. We expressed and studied the procollagen module (C) of human TSP1, both by itself and in the context of the adjoining oligomerization sequence (o) and N-terminal module (N). The coding sequences were introduced into baculoviruses along with an N-terminal signal sequence and C-terminal polyhistidine tag. Proteins were purified from conditioned medium of infected insect cells by nickel-chelate chromatography. NoC is a disulfide bonded trimer and cleaves readily at a site of preferential proteolysis to yield monomeric N and trimeric oC. These are known properties of full-length TSP1. Mass spectroscopy indicated that C is N-glycosylated, and all 10 cysteine residues of C are in disulfides. By equilibrium ultracentrifugation, C is a monomer in physiological salt solution. Circular dichroism, intrinsic fluorescence, and differential scanning calorimetry experiments suggest that the stability of C is determined by the disulfides. The two tryptophans of C are in a polar, exposed environment as assessed by iodide fluorescence quenching and solvent perturbation. The oC far UV circular dichroism spectrum could be modeled as the sum of C and a coiled-coil oligomerization domain. The results indicate that the recombinant C folds autonomously into its native structure, and trimerization of the modules in TSP1 does not perturb their structures.

Vascular endothelial growth factor induces expression of connective tissue growth factor via KDR, Flt1, and phosphatidylinositol 3-kinase-akt-dependent pathways in retinal vascular cells

Fibroblastic proliferation accompanies many angiogenesis-related retinal and systemic diseases. Since connective tissue growth factor (CTGF) is a potent mitogen for fibrosis, extracellular matrix production, and angiogenesis, we have studied the effects and mechanism by which vascular endothelial growth factor (VEGF) regulates CTGF gene expression in retinal capillary cells. In our study, VEGF increased CTGF mRNA levels in a time- and concentration-dependent manner in bovine retinal endothelial cells and pericytes, without the need of new protein synthesis and without altering mRNA stability. VEGF activated the tyrosine receptor phosphorylation of KDR and Flt1 and increased the binding of phosphatidylinositol 3-kinase (PI3-kinase) p85 subunit to KDR and Flt1, both of which could mediate CTGF gene induction. VEGF-induced CTGF expression was mediated primarily by PI3-kinase activation, whereas PKC and ERK pathways made only minimal contributions. Furthermore, overexpression of constitutive active Akt was sufficient to induce CTGF gene expression, and inhibition of Akt activation by overexpressing dominant negative mutant of Akt abolished the VEGF-induced CTGF expression. These data suggest that VEGF can increase CTGF gene expression in bovine retinal capillary cells via KDR or Flt receptors and the activation of PI3-kinase-Akt pathway independently of PKC or Ras-ERK pathway, possibly inducing the fibrosis observed in retinal neovascular diseases.

Identification of connective tissue growth factor as a target of WT1 transcriptional regulation

The Wilms tumor suppressor WT1 has transcription-activating and -suppressing capabilities. WT1-responsive promoters have been described; however, in large part, it remains unclear which potential downstream genes are physiologically relevant and mediate the function of WT1 in tumorigenesis and development. To identify genes regulated by WT1 in vivo, we used a dominant-negative version of WT1 to modulate WT1 activity in a Wilms tumor cell line. Screening oligonucleotide arrays with RNA from these cells uncovered a number of genes whose expression was altered by abrogation of WT1 function. Several of the genes encode members of the CCN family of growth regulators. The promoter of one of these genes, connective tissue growth factor (CTGF), is suppressed by WT1 both in its endogenous location and in reporter constructs. WT1 regulation of CTGF expression is not mediated by previously identified WT1 recognition elements and may therefore involve a novel mechanism. Our results indicate that CTGF is a bona fide target of WT1 transcriptional suppression and likely plays a role in Wilms tumorigenesis and associated disease syndromes.

Connective tissue growth factor (CTGF) stimulates vascular smooth muscle cell growth and migration in vitro

Connective tissue growth factor (CTGF) was first identified as a 38-kDa cysteine-rich protein which can be specifically induced by TGF-beta and was recently found to be expressed abundantly in atherosclerotic lesions, but only marginally in normal vascular tissues. It was hypothesized that CTGF is one of the factors involved in the development of atherosclerotic lesions. In this study, we investigated the functions of CTGF protein in regulating the growth and migration of vascular smooth muscle cells (VSMC) and found that by overexpressing CTGF in VSMC, proliferation and migration rates were significantly increased. The accelerated growth and migration can be reversed by an anti-CTGF antibody. In addition, overexpression of CTGF also promotes VSMC to express more extracellular matrix protein collagen I and fibronectin. Our results indicate that CTGF is a growth factor for VSMC and it may play a similar role in promoting VSMC proliferation, migration, and formation of extracellular matrix, in vivo.

Induction of connective tissue growth factor by activation of heptahelical receptors. Modulation by Rho proteins and the actin cytoskeleton

Expression of connective tissue growth factor (CTGF) was induced in renal mesangial cells by activation of heptahelical receptors by serotonin (5-HT) and lysophosphatidic acid (LPA). Induction of CTGF mRNA was transient with maximal expression after 1 to 2 h, whereas induction of CTGF by transforming growth factor beta (TGF-beta) increased over time. In contrast to the induction of other early response genes (Egr-1 and cyclooxygenase-2), LPA-mediated induction of CTGF was pertussis toxin-insensitive and independent of p42/44 MAP kinase activation. 5-HT-mediated CTGF induction was due to activation of 5-HT(2A) receptors and likewise independent of p42/44 MAP kinase activation. Upon stimulation, enhanced levels of CTGF protein were detected in cellular homogenates, whereas no protein was detectable in cell culture supernatants. Inhibition of proteins of the Rho family by toxin B abrogated basal as well as CTGF expression stimulated by LPA, 5-HT, and TGF-beta. Inhibition of the downstream mediator of RhoA, the Rho kinase by Y-27632 partially reduced induction of CTGF by LPA and TGF-beta. Toxin B not only affected gene expression, but disrupted the actin cytoskeleton similarly as observed after treatment with cytochalasin D. Disassembly of actin stress fibers by cytochalasin D partially reduced basal and stimulated CTGF expression. These data indicate that an intact actin cytoskeleton is critical for the expression of CTGF. Elimination of the input of Rho proteins by toxin B, however, was significantly more effective and their effect on CTGF expression thus goes beyond disruption of the cytoskeleton. These findings thus establish activation of heptahelical receptors coupled to pertussis toxin-insensitive G proteins as a novel signaling pathway to induce CTGF. Proteins of the Rho family and an intact cytoskeleton were identified as critical determinants of CTGF expression induced by LPA and 5-HT, and also by TGF-beta.

Growth regulation of skin fibroblasts

The growth of skin fibroblasts is regulated in a complex manner by various growth factors. Representative growth factors are platelet-derived growth factor (PDGF), basic fibroblast growth factor (b-FGF), transforming growth factor-beta (TGF-beta), and connective tissue growth factor (CTGF). These growth factors have various biological activities besides growth regulation of skin fibroblasts, and are involved in wound healing and in the pathogenesis of various disorders. For example, PDGF and CTGF stimulate chemotaxis of skin fibroblasts, b-FGF stimulates angiogenesis, and TGF-beta stimulates production of matrix proteins. First, the properties of these growth factors are reviewed briefly. Our skin fibrosis model in newborn mice are also described here. In 1986, Roberts et al. reported that subcutaneous injection of TGF-beta in newborn mice caused granulation tissue formation followed by fibrosis (Roberts et al. Proc Natl Acad Sci USA 1986;83:4167-71). We conducted similar experiments, and found that TGF-beta1, beta2 or beta3 caused skin fibrosis after 3 consecutive days of injection; this change was transient and disappeared after 7 consecutive days of injection. In contrast, irreversible fibrosis was observed upon stimultaneous injection of TGF-beta and b-FGF or TGF-beta and CTGF, or TGF-beta injection for the first 3 days and b-FGF or CTGF injection for the next 4 days (Shinozaki et al. Biochem Biophys Res Commun 1997;237:292-7; Mori et al. J Cell Physiol 1999;181:153-9). These observations suggest that TGF-beta induces skin fibrosis and b-FGF or CTGF maintains it in various skin fibrotic disorders. In the 21st century, we speculate that cocktails of various growth factors may permit subtle growth regulation of skin fibroblasts; such technology would have applications in the treatment of many skin diseases.

Characterization of a mouse ctgf 3'-UTR segment that mediates repressive regulation of gene expression

We isolated a small segment of the 3'-untranslated region (3'-UTR) in the mouse connective tissue growth factor (ctgf/fisp12) gene and evaluated its functionality. Comparison of the nucleotide sequences of human and mouse ctgf 3'-UTRs revealed a conserved small segment of 91 bases. The corresponding segments of the 3'-UTRs shared as much as 82.4% homology, whereas the overall homology between the 3'-UTRs was 71.8%. To study the functionality of the conserved segment, the corresponding region of mouse ctgf cDNA was amplified from NIH3T3 cells. When it was fused downstream of a marker gene, it showed remarkable repressive effects on gene expression. The repressive effect of the sense form was more prominent than that of the antisense form. Computer analyses of these sequence predicted stable secondary structures, suggesting that they act at the RNA level. The predicted structures of the sense and antisense forms appeared to be slightly different, which is consistent with the difference in repressive function. These findings defined the conserved small element in the mouse ctgf gene as a potent negative regulator of gene expression, which may act at a posttranscriptional level.

Thrombin is a potent inducer of connective tissue growth factor production via proteolytic activation of protease-activated receptor-1

The coagulation protease thrombin plays a critical role in hemostasis and exerts pro-inflammatory and pro-fibrotic effects via proteolytic activation of the major thrombin receptor, protease-activated receptor-1 (PAR-1). Connective tissue growth factor (CTGF) is a novel fibroblast mitogen and also promotes extracellular matrix protein production. It is selectively induced by transforming growth factor beta (TGF-beta) and is thought to be the autocrine agent responsible for mediating its pro-fibrotic effects. CTGF is up-regulated during tissue repair and in fibrotic conditions associated with activation of the coagulation cascade. We therefore hypothesized that coagulation proteases promote the production of CTGF by cells at sites of tissue injury. To begin to address this hypothesis, we assessed the effect of coagulation proteases on fibroblast CTGF expression in vitro, and we show that thrombin, at physiological concentrations, up-regulated CTGF mRNA levels 5-fold relative to base line (p < 0.01) in fetal fibroblasts and 7-fold in primary adult fibroblasts (p < 0.01). These effects were cycloheximide-insensitive and were not blocked with a pan-specific TGF-beta-neutralizing antibody. They were further paralleled by a concomitant increase in CTGF protein production and could be mimicked with selective PAR-1 agonists. In addition, fibroblasts derived from PAR-1 knockout mice were unresponsive to thrombin but responded normally to TGF-beta(1). Finally, factor Xa, which is responsible for activating prothrombin during blood coagulation, exerted similar stimulatory effects. We propose that coagulation proteases and PAR-1 may play a role in promoting connective tissue formation during normal tissue repair and the development of fibrosis by up-regulating fibroblast CTGF expression.

Characterization of insulin-like growth factor-binding protein-related proteins (IGFBP-rPs) 1, 2, and 3 in human prostate epithelial cells: potential roles for IGFBP-rP1 and 2 in senescence of the prostatic epithelium

Insulin-like growth factor (IGF)-binding protein (IGFBP)-related proteins (IGFBP-rPs) are newly described cysteine-rich proteins that share significant aminoterminal structural similarity with the conventional IGFBPs and are involved in a diversity of biological functions, including growth regulation. IGFBP-rP1 (MAC25/Angiomodulin/prostacyclin-stimulating factor) is a potential tumor-suppressor gene that is differentially expressed in meningiomas, mammary and prostatic cancers, compared with their malignant counterparts. We have previously shown that IGFBP-rP1 is preferentially produced by primary cultures of human prostate epithelial cells (HPECs) and by poorly tumorigenic P69SV40T cells, compared with the cancerous prostatic LNCaP, DU145, PC-3, and M12 cells. We now show that IGFBP-rP1 increases during senescence of HPEC. IGFBP-rP2 (also known as connective tissue growth factor), a downstream effector of transforming growth factor (TGF)-beta and modulator of growth for both fibroblasts and endothelial cells, was detected in most of the normal and malignant prostatic epithelial cells tested, with a marked up-regulation of IGFBP-rP2 during senescence of HPEC. Moreover, IGFBP-rP2 noticeably increased in response to TGF-beta1 and all-trans retinoic acid (atRA) in HPEC and PC-3 cells, and it decreased in response to IGF-I in HPEC. IGFBP-rP3 [nephroblastoma overexpressed (NOV)], the protein product of the NOV protooncogene, was not detected in HPEC but was expressed in the tumorigenic DU145 and PC-3 cells. It was also synthesized by the SV40-T antigen-transformed P69 and malignant M12 cells, where it was down-regulated by atRA. These observations suggest biological roles of IGFBP-rPs in the human prostate. IGFBP-rP1 and IGFBP-rP2 are likely to negatively regulate growth, because they seem to increase during senescence of the prostate epithelium and in response to growth inhibitors (TGF-beta1 and atRA). Although the data collected on IGFBP-rP3 in prostate are modest, its role as a growth stimulator and/or protooncogene is supported by its preferential expression in cancerous cells and its down-regulation by atRA.