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 gene expression in tissue sections from localized scleroderma, keloid, and other fibrotic skin disorders

Connective tissue growth factor (CTGF) is a novel peptide that exhibits platelet-derived growth factor-like activities and is produced by skin fibroblasts after activation with transforming growth factor-beta. Coordinate expression of transforming growth factor-beta followed by CTGF during wound repair suggests a cascade process for control of tissue regeneration. We recently reported a significant correlation between CTGF mRNA expression and histologic sclerosis in systemic sclerosis. To confirm the relation between CTGF and skin fibrosis, we investigated CTGF gene expression in tissue expression in tissue sections from patients with localized scleroderma, keloid, other sclerotic skin disorders using nonradioactive in situ hybridization. In localized scleroderma, the fibroblasts with positive signals for CTGF mRNA were scattered throughout the sclerotic lesions with no preferential distribution around the inflammatory cells or perivascular regions, whereas the adjacent nonaffected dermis was negative for CTGF mRNA. In keloid tissue, the fibroblasts positive for CTGF mRNA were diffusely distributed, especially in the peripheral expanding lesions. In scar tissue, however, the fibroblasts in the fibrotic lesions showed partially positive signals for CTGF mRNA. In eosinophilic fasciitis, nodular fasciitis, and Dupuytren's contracture, CTGF mRNA was also expressed partially in the fibroblasts of the fibrotic lesions. Our findings reinforce a correlation between CTGF gene expression and skin sclerosis and support the hypothesis that transforming growth factor-beta plays an important role in the pathogenesis of fibrosis, as it is the only inducer for CTGF identified to date.

Cyr61, a product of a growth factor-inducible immediate-early gene, promotes cell proliferation, migration, and adhesion

cyr61 was first identified as a growth factor-inducible immediate-early gene in mouse fibroblasts. The encoded Cyr61 protein is a secreted, cystein-rich heparin-binding protein that associates with the cell surface and the extracellular matrix, and in these aspects it resembles the Wnt-1 protein and a number of known growth factors. During embryogenesis, cyr61 is expressed most notably in mesenchymal cells that are differentiating into chondrocytes and in the vessel walls of the developing circulatory system. cyr61 is a member of an emerging gene family that encodes growth regulators, including the connective tissue growth factor and an avian proto-oncoprotein, Nov cyr61 also shares sequence similarities with two Drosophila genes, twisted gastrulation and short gastrulation, which interact with decapentaplegic to regulate dorsal-ventral patterning. In this report we describe the purification of the Cyr61 protein in a biologically active form, and we show that purified Cyr61 has the following activities: (i) it promotes the attachment and spreading of endothelial cells in a manner similar to that of fibronectin; (ii) it enhances the effects of basic fibroblast growth factor and platelet-derived growth factor on the rate of DNA synthesis of fibroblasts and vascular endothelial cells, although it has no detectable mitogenic activity by itself; and (iii) it acts as a chemotactic factor for fibroblasts. Taken together, these activities indicate that Cyr61 is likely to function as an extracellular matrix signaling molecule rather than as a classical growth factor and may regulate processes of cell proliferation, migration, adhesion, and differentiation during development.

Transcriptional down regulation of the nov proto-oncogene in fibroblasts transformed by p60v-src

We have sought to identify genes whose expression is altered as a consequence of transformation by p60v-src. Using the mRNA differential display method, we have identified the nov proto-oncogene as one gene that is down regulated in chicken embryo fibroblasts (CEFs) transformed by p60v-src. nov transcripts were also found to be present at only very low levels in proliferating CEFs in comparison with quiescent CEFs. Serum stimulation of quiescent CEFs also resulted in a decline in the steady-state level of nov transcripts. Taken together, these findings suggest that the nov gene is expressed only in quiescent fibroblasts and that its down regulation may contribute to cellular transformation by the v-src oncogene. Down regulation of the nov gene appears to occur at both the transcriptional and posttranscriptional levels. Results obtained from experiments with a protein kinase inhibitor suggest that protein kinase C may be a key downstream effector in mediating the down regulation of nov transcripts in response to activation of p60src or serum stimulation. In addition, we found that transcription of an unknown gene is required for the decline in the steady-state level of nov transcripts in response to serum stimulation.

Differential gene expression in migrating renal epithelial cells after wounding

An in vitro model of wound healing was used to study cell migration that is independent of proliferation during renal regeneration after acute tubular necrosis. Monolayer cultures of high-density, quiescent renal epithelial cells of the BSC-1 line were subjected to scrape wounding and then Northern blot analysis was employed to identify genes that mediate cell migration. After wounding the monolayer, there is maximal induction of the immediate-early genes Egr-1, c-fos, NAK-1, and gro at 1 hour, followed by peak induction of connective tissue growth factor (CTGF) and c-myc at 4 hours. Message levels of urokinase-type plasminogen activator (u-PA) and its inhibitor (PAI-1) and heat shock protein (HSP)-70 are markedly raised 4-8 hours after wounding. Constitutive expression is repressed at 1 hour for transcripts that encode receptors for fibronectin (FN), epidermal growth factor, and hepatocyte growth factor (c-met), and the secreted proteins FN and osteopontin. Expression of genes encoding transforming growth factor (TGF)-beta 1 and -beta 2, retinoic acid receptor alpha, int-1, int-2, and gap junction protein which can play a role in cell movement, appeared unchanged after wounding. Differential expression of genes was a function of cell location relative to the wound; NAK-1, PAI-1, and HSP-70 were induced or stimulated only in cells at the wound edge, u-PA was stimulated in cells away from the wound, and CTGF was induced in each of these populations suggesting that cell-to-cell communication may regulate gene expression after wounding. Adenosine diphosphate, a potent stimulator of cell migration which enhances expression of u-PA and PAI-1 in nonwounded cultures, additively stimulates these genes after wounding and may thereby potentiate wound healing. Thus scrape wounding of renal epithelial cells is followed by induction, stimulation, or repression of specific genes with distinct responses in different populations of cells.

Molecular cloning of a gene from Plasmodium falciparum that codes for a protein sharing motifs found in adhesive molecules from mammals and plasmodia

Adhesion of Plasmodium to host cells is an important phenomenon in parasite invasion and in malaria-associated pathology. We report here the molecular cloning of a putative adhesive molecule from P. falciparum that shares both sequence and structural similarities with a sporozoite surface molecule from Plasmodium termed the thrombospondin-related anonymous protein (TRAP) and, to a lesser extent, with the circumsporozoite (CS) protein. The gene, which is present on chromosome 3 as a single copy, was termed CTRP for CS protein-TRAP-related protein. The full-length CTRP encodes a protein containing a putative signal sequence followed by a long extracellular region of 1990 amino acids, a transmembrane domain, and a short cytoplasmic segment. The putative extracellular region of CTRP is defined by two separated adhesive domains. The first domain contains six 210-amino acid-long homologous repeats, the sequence of which is related to the A-type domain found in adhesive molecules including the alpha subunits of several integrins and a number of extracellular matrix glycoproteins. The second domain contains seven repeats of 87-60 amino acids in length, which share similarities with the thrombospondin type 1 domain found in a variety of adhesive molecules. Finally, CTRP also contains consensus motifs found in the superfamily of haematopoietin receptors. Interstrain analysis of eight different parasite isolates revealed that CTRP does not show size polymorphism except in repetitive regions flanking potential adhesive domains.

Significant correlation between connective tissue growth factor gene expression and skin sclerosis in tissue sections from patients with systemic sclerosis

The role of some growth factors and cytokines in the pathogenesis of systemic sclerosis (SSc) has been suggested. In particular, the contribution of transforming growth factor beta in the progression of skin sclerosis is suspected. Connective tissue growth factor (CTGF) was originally identified in human umbilical vein endothelial cells, and a recent study has revealed that human skin fibroblasts produce CTGF after stimulation with transforming growth factor beta. In the present study, the distribution of CTGF gene expression in tissue sections from patients with SSc was investigated by digoxigenin-labeled in situ hybridization. Strong CTGF mRNA signals were observed in the fibroblasts in sclerotic lesions, especially in the deep dermis, of the skin specimens from patients with SSc, whereas there was no expression in the skin from normal controls. The number of fibroblasts with positive hybridization signals was more abundant in the dermis from the sclerotic stage than in that from the inflammatory stage. Our findings indicate a correlation between CTGF gene expression and skin sclerosis and support the hypothesis that transforming growth factor-beta plays an important role in the pathogenesis of SSc, because transforming growth factor beta is the only inducer for CTGF identified to date.

Calcium oxalate monohydrate crystals stimulate gene expression in renal epithelial cells

Primary or secondary hyperoxaluria is associated with calcium oxalate nephrolithiasis, interstitial fibrosis and progressive renal insufficiency. Monolayer cultures of nontransformed monkey kidney epithelial cells (BSC-1 line) and calcium oxalate monohydrate (COM) crystals were used as a model system to study cell responses to crystal interactions that might occur in the nephrons of patients during periods of hyperoxaluria. To determine if COM crystals signal a change in gene expression, Northern blots were prepared from total renal cellular RNA after the cells were exposed to crystals. The immediate early genes c-myc, EGR-1, and Nur-77 were induced at one hour. At two to six hours stimulated expression of the genes encoding plasminogen activator inhibitor (PAI-1) and platelet-derived growth factor (PDGF)-A chain was detected, but constitutive expression of urokinase-type plasminogen activator (u-PA) was not altered. Expression of connective tissue growth factor (CTGF) was induced at one hour and persisted up to 24 hours. The stimulation of gene expression by COM crystals was relatively crystal- and renal cell-type specific. Thus the interaction of kidney epithelial cells with COM crystals alters expression of genes that encode three classes of proteins: transcriptional activators, a regulator of extracellular matrix (ECM), and growth factors. Activation of PAI-1 gene expression without a change in u-PA favors accumulation of ECM proteins, as does increased expression of PDGF and CTGF which can also stimulate fibroblast proliferation in a paracrine manner. These results suggest that COM crystal-mediated stimulation of specific genes in renal tubular cells may contribute to the development of interstitial fibrosis in hyperoxaluric states.

Growth regulation in scleroderma fibroblasts: increased response to transforming growth factor-beta 1

We investigated the responses of normal and scleroderma fibroblasts to various growth factors, especially transforming growth factor-beta 1 (TGF-beta 1). The effects of various growth factors on [3H]thymidine incorporation in normal and scleroderma fibroblasts were examined. [125I]-labeled platelet-derived growth factor (PDGF)-BB binding in scleroderma and normal fibroblasts was examined both in the presence and absence of TGF-beta 1 (1 ng/ml). Cytoplasmic protein was isolated and analyzed by Western blotting. Total RNA from fibroblasts was also isolated and analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) using specific primer sets. Mitogenic responses to TGF-beta 1 (0.33-1 ng/ml) in seven scleroderma fibroblast strains were significantly greater than those in normal controls. [125I]-PDGF-BB binding to scleroderma fibroblasts was increased after TGF-beta 1 stimulation. The increased response to TGF-beta 1 was shown to be mediated through PDGF-like protein induction; TGF-beta 1-treated scleroderma fibroblasts produced greater amounts of 36-kD PDGF-like protein, which was reported previously as connective tissue growth factor (CTGF), than did TGF-beta 1-treated normal fibroblasts. TGF-beta 1 treatment also upregulated PDGF-alpha receptor expression in scleroderma fibroblasts but not in normal dermal fibroblasts. mRNA expression of CTGF and PDGF-alpha receptor was correlated with the above protein expression. These observations suggest that the increased growth response to TGF-beta 1 in scleroderma fibroblasts is mediated through the induction of CTGF and PDGF-alpha receptor.

Dorsal-ventral patterning of the Drosophila embryo depends on a putative negative growth factor encoded by the short gastrulation gene

Pattern formation in the dorsal region of the Drosophila embryo depends on the activity of a small group of zygotically acting genes. dpp, a key gene in this group, encodes a TGF-beta-like product (Dpp) that has been proposed to function as a morphogen with peak levels of Dpp-specifying amnioserosa, the dorsal-most cell type, and lower Dpp levels specifying dorsal ectoderm. The short gastrulation gene also contributes to patterning the dorsal region, but unlike the other genes involved in this process, sog activity is only required in ventral cells. Genetic evidence indicates that sog functions to antagonize dpp activity. In this report we present further phenotypic characterization of sog mutant embryos in dorsal and lateral regions and describe the cloning of the sog locus. sog is expressed in a broad lateral stripe of cells that abuts the dorsal territory of dpp-expressing cells. sog is predicted to encode a protein with an internal signal sequence and a large extracellular domain containing four repeats of a novel motif defined by the spacing of 10 cysteine residues that is distantly related to domains present in thrombospondin and procollagen. We propose that one or more of these cysteine repeats can be liberated by proteolytic cleavage of the primary Sog protein. These putative soluble Sog peptides may then diffuse into the dorsal region to antagonize the activity of Dpp, leading to the subdivision of the dorsal territory into amnioserosa and dorsal ectoderm.

Dorsal midline fate in Drosophila embryos requires twisted gastrulation, a gene encoding a secreted protein related to human connective tissue growth factor

The twisted gastrulation (tsg) gene is one of seven known zygotic genes that specify the fate of dorsal cells in Drosophila embryos. Mutations in these genes cause at least some of the cells on the dorsal half of the embryo to adopt more ventral cell fates leading to the proposal that most of these genes participate in establishing, maintaining, or modulating a gradient of a single signaling molecule DECAPENTAPLEGIC (DPP). We have examined the effects of tsg mutations on the development of cuticule elements, expression of a region specific enhancer trap, and patterns of mitotic domains. Mutations of tsg only affect the fate of a narrow strip of dorsal midline cells and do not affect dorsal ectoderm cells. However, the pattern of tsg expression is not coincident with the territories affected by tsg mutations. Structural analysis of the tsg gene reveals features of a secreted protein suggesting an extracellular site of action. The TSG protein bears a weak resemblance to human connective tissue growth factor (CTGF), a TGF-beta-induced protein. We propose that dorsal midline cell fate is specified by the combination of both a TSG and a DPP signal to which the dorsal midline cells are uniquely competent to respond.

Variable expression of platelet-derived growth factor family proteins in acute lung injury

During acute lung injury, there is an outpouring of growth factors into the alveolar space that drive local repair and fibrosis. During the remodeling that follows the instillation of bleomycin via the trachea into the adult rat, at least two platelet-derived growth factor (PDGF)-like peptides are released sequentially into lung lining fluid. Groups of four to five animals were killed at 3, 6, 15, and 26 days after exposure to bleomycin and lungs lavaged with isotonic saline. PDGF-like peptides in epithelial lining fluid (ELF) were partially purified by cation exchange chromatography and concentrated. Isolated peptides were analyzed by immunoblotting to determine their molecular weight and immunologic identity. Western blots were probed with polyclonal antibodies to PDGF-BB and PDGF-AA. PDGF-like peptides of two distinct size classes (38-40 kD and 29 kD) were present in alveolar fluid from all rats with lung injury induced by bleomycin. No PDGF-like peptides were found in comparably prepared ELF from control animals. The 38-40 kD peptide was detected only with anti-PDGF-BB antibody; the 29 kD peptide was detected only with anti-PDGF-AA antibody. The presence of these two peptides varied independently with time after exposure to bleomycin. The 38-40 kD peptide was at peak levels at 3 to 6 days. In contrast, the 29 kD peptide was present at all times following injury but with far less variation over time. In parallel with these immunoassays for PDGF-like molecules, there was abundant growth-promoting activity for fibroblasts present in concentrated ELF during the course of injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular modelling of the Norrie disease protein predicts a cystine knot growth factor tertiary structure

The X-lined gene for Norrie disease, which is characterized by blindness, deafness and mental retardation has been cloned recently. This gene has been thought to code for a putative extracellular factor; its predicted amino acid sequence is homologous to the C-terminal domain of diverse extracellular proteins. Sequence pattern searches and three-dimensional modelling now suggest that the Norrie disease protein (NDP) has a tertiary structure similar to that of transforming growth factor beta (TGF beta). Our model identifies NDP as a member of an emerging family of growth factors containing a cystine knot motif, with direct implications for the physiological role of NDP. The model also sheds light on sequence related domains such as the C-terminal domain of mucins and of von Willebrand factor.

Density-dependent endothelial cell production of an inhibitor of smooth muscle cell growth

Embryonic data and ultrastructural analyses suggest that the primitive endothelium signals undifferentiated mesenchymal cells to migrate to the forming blood vessel and subsequently regulates mural cell growth and behavior. Upon maturation of the blood vessel, chemotactic and mitogenic signals are apparently diminished and differentiated smooth muscle cells normally remain quiescent. This homeostasis is seemingly upset in conditions which lead to pathologies characterized by smooth muscle cell hyperplasia such as atherosclerosis. By culturing endothelial cells at different densities, we attempted to re-create the various stages of vascular development. Whereas media conditioned by sparse endothelial cells stimulate smooth muscle cells, media conditioned by dense endothelial cell cultures are inhibitory. Culture of sparse smooth muscle cells in media conditioned for 3 days by postconfluent endothelial cell cultures leads to dose-dependent and reversible smooth muscle cell inhibition. Furthermore, in the presence of the endothelial cell-derived inhibitor, smooth muscle cells are rendered refractory to mitogens such as fibroblast growth factor and platelet-derived growth factor. The inhibitory activity is not attributable to the well-characterized inhibitors of smooth muscle cell growth, transforming growth factor type-beta, prostaglandin I2, or heparan sulfate proteoglycan. Partial characterization of the inhibitory conditioned media suggests that the active molecule is smaller than 1,000 da, and stable to boiling as well as proteinase K and heparinase digestion. These findings support the concept that there is intercellular communication between endothelial cells and smooth muscle cells and provide evidence for a novel endothelial cell-derived smooth muscle cell growth inhibitor.

The modular architecture of a new family of growth regulators related to connective tissue growth factor

Recently, several groups have characterized and sequenced members of a new family of growth regulators (originally called cef10, connective tissue growth factor, fisp-12, cyr61, or, alternatively, beta IG-M1 and beta IG-M2), all of which belong to immediate-early genes expressed after induction by growth factors or certain oncogenes. Sequence analysis of this family revealed the presence of four distinct modules. Each module has homologues in other extracellular mosaic proteins such as Von Willebrand factor, slit, thrombospondins, fibrillar collagens, IGF-binding proteins and mucins. Classification and analysis of these modules suggests the location of binding regions and, by analogy to better characterized modules in other proteins, sheds some light onto the structure of this new family.

Accumulation of PDGF B and cell-binding forms of PDGF A in the extracellular matrix

PDGF is a powerful mitogen initially identified within platelets, but also shown to be produced by a wide variety of cell types. PDGF is encoded on two separate genes. These give rise to three polypeptides, PDGF B and two forms of PDGF A (SA and LA), resulting from alternative splicing of the PDGF A gene primary transcript. We report that in CHO cells transfected with PDGF gene constructs and producing moderate levels of PDGF homodimers, much of the PDGF LA and B produced, but little if any SA, is found in the matrix laid down beneath the cells. Immunoreactive PDGF in cells, and in matrix below expressing cells, was visualized by laser confocal microscopy. Western blotting of protein in matrix extracts, cell extracts, and secreted into the growth medium was used to demonstrate that the range of PDGF A polypeptides seen in the matrix was overlapping with those reported previously to be cell associated in cell types such as NIH3T3 and COS 7. This suggests that attachment to matrix or cell surface may be alternative fates for these polypeptides, with fate dependent on the characteristics of the producing cells. Immunoreactive PDGF A and B could be partially released by incubation of matrix material with heparin but not with other glycosaminoglycans. Digestion of matrix with chondroitin ABC lyase but not heparitinase or collagenase displaced some PDGF from its attachment sites. The results indicate attachment of PDGF to matrix proteoglycans, at least partly through the glycosaminoglycan moieties, and perhaps to additional components. The significance of matrix deposition for PDGF action is discussed.

Regulation of connective tissue growth factor gene expression in human skin fibroblasts and during wound repair

Connective tissue growth factor (CTGF) is a cysteine-rich peptide that exhibits platelet-derived growth factor (PDGF)-like biological and immunological activities. CTGF is a member of a family of peptides that include serum-induced immediate early gene products, a v-src-induced peptide, and a putative avian transforming gene, nov. In the present study, we demonstrate that human foreskin fibroblasts produce high levels of CTGF mRNA and protein after activation with transforming growth factor beta (TGF-beta) but not other growth factors including PDGF, epidermal growth factor, and basic fibroblast growth factor. Because of the high level selective induction of CTGF by TGF-beta, it appears that CTGF is a major autocrine growth factor produced by TGF-beta-treated human skin fibroblasts. Cycloheximide did not block the large TGF-beta stimulation of CTGF gene expression, indicating that it is directly regulated by TGF-beta. Similar regulatory mechanisms appear to function in vivo during wound repair where there is a coordinate expression of TGF-beta 1 before CTGF in regenerating tissue, suggesting a cascade process for control of tissue regeneration and repair.

Capillary endothelial cells secrete a heparin-binding mitogen for pericytes

The cells of the retinal microvasculature consist predominantly of mesodermally derived pericytes and endothelial cells, and the regulatory factors which govern their co-ordinated growth and define their phenotypic characteristics in vivo may be regarded as key elements of the angiogenic process. An investigation of these cells in co-culture experiments has led to the identification of a potent mitogen for pericytes in medium conditioned by retinal endothelial cells (EC-FBS). EC-FBS activity was shown to be non-dialyzable, and stable to both heat and acid treatment. EC-FBS was inactivated by passage over a heparin-Agarose column. The column-bound activity could be eluted as a single peak at approximately 1.0 M NaCl. Stimulation of pericyte growth was also achieved with platelet-derived growth factor (PDGF), acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF) and could be blocked by using the appropriate antiserum (anti-PDGF or anti-aFGF). Neither antisera, however, blocked the activity of EC-FBS. The EC-FBS mitogen markedly altered the phenotypic behavior of pericytes compared with PDGF and the FGFs; yet, unlike them, it failed to stimulate the growth of smooth muscle cells (SMC) and Balb/c 3T3 cells.

Modularity of the slit protein. Characterization of a conserved carboxy-terminal sequence in secreted proteins and a motif implicated in extracellular protein interactions

Since our characterization of the slit cDNA sequence, encoding a protein secreted by glial cells and involved in the formation of axonal pathways in Drosophila, we have discovered that the protein contains two additional sequence motifs that are highly conserved in a variety of proteins. A search of the GenPept database with the 73 amino acids at the carboxy terminus of slit revealed that this region contains significant similarity to a carboxy-terminal domain found in six other exported proteins. This observation has allowed us to define a new carboxy-terminal protein motif. In addition, comparisons with a 202 amino acid domain residing between epidermal growth factor (EGF) repeats in slit shows this region to be conserved in laminin, agrin and perlecan and, strikingly, also to lie between EGF repeats in both agrin and perlecan. Our analysis suggests this motif is involved in mediating interactions among extracellular proteins. Consistent with our previous characterization of the slit protein, both new motifs are found only in extracellular proteins. The identification of these two conserved motifs in slit reveals that the entire 1469 amino acids of the protein are made up of modular regions similar to those conserved in other extracellular proteins.

Isolation and characterization of a novel type of growth factor derived from serum-free conditioned medium of chicken embryo fibroblasts

A strong mitogenic activity for fibroblastic cells has been found in serum-free medium of growth-arrested primary cultures of chicken embryo fibroblasts (CEF). This serum-free conditioned medium promoted growth of NIH/3T3 cells and primary as well as secondary cultures of CEF. The mitogenic activity was as potent as 5% serum. Half-maximum stimulation was obtained with 20% of the initial concentration of the conditioned medium. The activity eluted at high M(r) (1-2 x 10(5)) from a gel-filtration column under nondenaturing conditions and was trypsin insensitive and thiol insensitive. Treatment with acid or urea converted the mitogen to a low-molecular-mass form, which showed a delayed induction of DNA synthesis. Purification of this factor (10000-fold) to apparent homogeneity was achieved by preparative isoelectric focusing, gel filtration, reverse-phase HPLC and nonreducing SDS/PAGE. The factor, termed CEF-derived growth factor (CDGF) was a 32-kDa, disulfide-linked heterodimer of a 15-kDa and a 17-kDa subunit as judged by SDS/PAGE, with a pI of approximately 7 in 8 M urea. It exhibited partial stability towards heat treatment and was trypsin sensitive. CDGF was active only in its dimeric form and half-maximum stimulation of NIH/3T3 cells was obtained at approximately 10 pM. The mitogenic activity was not suppressible by an antibody neutralizing the activity of transforming growth factor beta 1, 2 and 3 (TGF-beta). The physico-chemical properties suggest that CDGF is not identical with one of the common growth factors like fibroblast growth factor, platelet-derived growth factor, epidermal growth factor, insulin-like growth factor, or TGF-beta but rather represents a novel type of growth factor.

Proviral rearrangements and overexpression of a new cellular gene (nov) in myeloblastosis-associated virus type 1-induced nephroblastomas

Histological and anatomopathological studies performed on 152 independent myeloblastosis-associated virus type 1 (MAV1)-induced nephroblastomas allowed us to precisely define the chronology of tumor development in chickens. Three tumors representing increasing developmental stages were used to construct genomic libraries and to study both the state of proviral genomes and the sites of MAV1 integration in genomic DNA. We established that increasing levels of proviral rearrangement, eventually leading to the elimination of infectious MAV genomes, were associated with tumor progression and that 22 individual tumors, representative of different developmental stages, did not contain any common MAV1 integration site. Cloning of cellular fragments flanking the MAV1-related proviruses in tumor DNA showed that each one of eight nephroblastomas tested expressed a high level of an as yet unidentified cellular gene (nov) whose transcription is normally arrested in adult kidney cells. Cloning of the normal nov gene established that in one tumor, fused long terminal repeat-truncated nov mRNA species were expressed, indicating that at least in that case, the high level of nov expression was under the control of the MAV long terminal repeat promoter. The normal nov gene encodes a putative 32-kDa secreted polypeptide, which is a member of a new family of proteins likely to be involved in cell growth regulation. We also showed that the expression of an amino-terminal-truncated nov product in chicken embryo fibroblasts was sufficient to induce their transformation.

Proviral rearrangements and overexpression of a new cellular gene (nov) in myeloblastosis-associated virus type 1-induced nephroblastomas

Histological and anatomopathological studies performed on 152 independent myeloblastosis-associated virus type 1 (MAV1)-induced nephroblastomas allowed us to precisely define the chronology of tumor development in chickens. Three tumors representing increasing developmental stages were used to construct genomic libraries and to study both the state of proviral genomes and the sites of MAV1 integration in genomic DNA. We established that increasing levels of proviral rearrangement, eventually leading to the elimination of infectious MAV genomes, were associated with tumor progression and that 22 individual tumors, representative of different developmental stages, did not contain any common MAV1 integration site. Cloning of cellular fragments flanking the MAV1-related proviruses in tumor DNA showed that each one of eight nephroblastomas tested expressed a high level of an as yet unidentified cellular gene (nov) whose transcription is normally arrested in adult kidney cells. Cloning of the normal nov gene established that in one tumor, fused long terminal repeat-truncated nov mRNA species were expressed, indicating that at least in that case, the high level of nov expression was under the control of the MAV long terminal repeat promoter. The normal nov gene encodes a putative 32-kDa secreted polypeptide, which is a member of a new family of proteins likely to be involved in cell growth regulation. We also showed that the expression of an amino-terminal-truncated nov product in chicken embryo fibroblasts was sufficient to induce their transformation.