Domain-specific CCN3 antibodies as unique tools for structural and functional studies

Cooperation is the key: the CCN biological system as a gate to high complex protein superfamilies' signaling

Cellular signaling is generally understood as the support of communication between contiguous cells belonging to the same tissue or cells being far apart of each other, at a molecular scale, when the message emitted by the transmitters is traveling in liquid or solid matter to reach recipient targets. Subcellular signaling is also important to ensure the proper cell constitution and functioning. However cell signaling is mostly used in the first understanding, to describe how the message sent from one point to another one, will reach a target where it will be interpreted. The Cellular Communication Network (CCN) factors (Perbal et al. 2018) constitute a family of biological regulators thought to be responsible for signaling pathways coordination (Perbal 2018). Indeed, these proteins interact with a diverse group of cell receptors, such as integrins, low density lipoprotein receptors, heparan sulfate proteoglycan receptors (HSPG), and the immunoglobulin superfamily expressed exclusively in the nervous system, or with soluble factors such as bone morphogenetic proteins (BMPS) and other growth factors such as vascular endothelial growth factor, fibroblastic growth factor, and transforming growth factor (TGFbeta). Starting from the recapitulation of basic concepts in enzymology and protein-ligands interactions, we consider, in this manuscript, interpretations of the mechanistic interactions that have been put forward to explain the diversity of CCN proteins biological activities. We suggest that the cross-talks between superfamilies of proteins under the control of CCNs might play a central role in the coordination of developmental signaling pathways.

Single nucleotide mutation changes the capability of CCN3 in osteosarcoma cell invasion and differentiation

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The frequency of G-to-A mutation in CCN3 is higher than para-carcinoma tissue.

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Mutation in CCN3 change its capacity of osteosarcoma invasion and differentiation.

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Mutant CCN3 decrease nuclear ratio of glycosylated/non-glycosylated isoforms.

This study aimed to identify significant mutations in CCN3 gene in osteosarcoma, and to explore the influence of this gene on cell invasion and differentiation and the underlying mechanism. Sanger sequencing was used to identify CCN3 gene sequence in human osteosarcoma cell lines, peripheral blood mononuclear cells (PBMC), and osteosarcoma tissues. Wild-type and mutant CCN3 (mCCN3) were ectopically expressed by lentivirus in human osteosarcoma cell lines. Tumor cell invasion was measured by trans-well assay. Osteogenic differentiation was induced by osteogenic differentiating medium and evaluated based on alkaline phosphatase activity and collagen type I alpha 1 chain and osteocalcin expression. Western blotting was used to detect protein levels of CCN3 and mCCN3 in cytoplasmic, nuclear and secreted fractions of cells. A G-to-A single nucleotide mutation in the coding region of CCN3 was found in both osteosarcoma cells and tissues. The frequency of this mutation in osteosarcoma tissue was much higher than that in para-carcinoma tissue and PBMC of healthy people. This nucleotide mutation decreased nuclear glycosylated full length protein level of CCN3 and affected osteosarcoma cell invasion and differentiation. A lower nuclear ratio of glycosylated/non-glycosylated isoforms accounted for the different behavior of mCCN3 compared with CCN3. The G-to-A mutation identified in CCN3 resulted in differential glycosylated full-length protein levels and altered the functional role of CCN3 in osteosarcoma cell invasion and differentiation.

The CCN axis in cancer development and progression

Since the authors first reviewed this subject in 2016 significant progress has been documented in the CCN field with advances made in the understanding of how members of the CCN family of proteins, CCN1-6, contribute to the pathogenesis and progression, positive and negative, of a larger variety of cancers. As termed matricellular proteins, and more recently the connective communication network, it has become clearer that members of the CCN family interact complexly with other proteins in the extracellular microenvironment, membrane signaling proteins, and can also operate intracellularly at the transcriptional level. In this review we expand on this earlier information providing new detailed information and insights that appropriate a much greater involvement and importance of their role in multiple aspects of cancer. Despite all the new information many more questions have been raised and intriguing results generated that warrant greater investigation. In order to permit the reader to smoothly integrate the new information we discuss all relevant CCN members in the context of cancer subtypes. We have harmonized the nomenclature with CCN numbering for easier comparisons. Finally, we summarize what new has been learned and provide a perspective on how our knowledge about CCN1-6 is being used to drive new initiatives on cancer therapeutics.

CCN3 is dynamically regulated by treatment and disease state in multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is an immune-mediated disease that damages myelin in the central nervous system (CNS). We investigated the profile of CCN3, a known regulator of immune function and a potential mediator of myelin regeneration, in multiple sclerosis in the context of disease state and disease-modifying treatment.

METHODS

CCN3 expression was analysed in plasma, immune cells, CSF and brain tissue of MS patient groups and control subjects by ELISA, western blot, qPCR, histology and in situ hybridization.

RESULTS

Plasma CCN3 levels were comparable between collective MS cohorts and controls but were significantly higher in progressive versus relapsing-remitting MS and between patients on interferon-β versus natalizumab. Higher body mass index was associated with higher CCN3 levels in controls as reported previously, but this correlation was absent in MS patients. A significant positive correlation was found between CCN3 levels in matched plasma and CSF of MS patients which was absent in a comparator group of idiopathic intracranial hypertension patients. PBMCs and CD4+ T cells significantly upregulated CCN3 mRNA in MS patients versus controls. In the CNS, CCN3 was detected in neurons, astrocytes and blood vessels. Although overall levels of area immunoreactivity were comparable between non-affected, demyelinated and remyelinated tissue, the profile of expression varied dramatically.

CONCLUSIONS

This investigation provides the first comprehensive profile of CCN3 expression in MS and provides rationale to determine if CCN3 contributes to neuroimmunological functions in the CNS.

The concept of the CCN protein family revisited: a centralized coordination network

The wide array of biological properties attributed to the CCN family of proteins (Perbal in Lancet 363(9402):62-64, 2004) led me to reconsider the possible relationship and roles that these proteins may play as a team, instead of acting on their own as individual regulators in various signaling pathways. The dynamic model which I present in this review stems from the contribution of the biological properties that we established for CCN3, one of the three founding members of the CCN family, which was identified by our group as the first CCN protein showing growth inhibitory properties (1992), expressed mainly in quiescent cells (1996), and showing anti-tumor activities in several cellular models both ex vivo and in vivo. At the present time CCN3 is the only member of the family that has been reported to negatively act on the progression of the cell cycle. The unique dual localisation of CCN3 in the nucleus and outside cells, either at the membrane or in the extracellular matrix, that I first established in 1999, and that now appears to be shared by several other CCN proteins, is a unique essential feature which can no longer be ignored. Based on the structural and functional properties of CCN3, shared by most of the CCN family members, I propose an « all in one » concept in which CCN proteins are team members with specific functions that are aimed at the same goal. This model accounts both for the functional specificity of the various CCN proteins, their sequential and opposite or complementary effects in various biological context, and for the biological consequences of their physical interaction and biological cross-regulation.

The concept of the CCN protein family revisited: a centralized coordination network

The wide array of biological properties attributed to the CCN family of proteins (Perbal in Lancet 363(9402):62-64, 2004) led me to reconsider the possible relationship and roles that these proteins may play as a team, instead of acting on their own as individual regulators in various signaling pathways. The dynamic model which I present in this review stems from the contribution of the biological properties that we established for CCN3, one of the three founding members of the CCN family, which was identified by our group as the first CCN protein showing growth inhibitory properties (1992), expressed mainly in quiescent cells (1996), and showing anti-tumor activities in several cellular models both ex vivo and in vivo. At the present time CCN3 is the only member of the family that has been reported to negatively act on the progression of the cell cycle. The unique dual localisation of CCN3 in the nucleus and outside cells, either at the membrane or in the extracellular matrix, that I first established in 1999, and that now appears to be shared by several other CCN proteins, is a unique essential feature which can no longer be ignored. Based on the structural and functional properties of CCN3, shared by most of the CCN family members, I propose an « all in one » concept in which CCN proteins are team members with specific functions that are aimed at the same goal. This model accounts both for the functional specificity of the various CCN proteins, their sequential and opposite or complementary effects in various biological context, and for the biological consequences of their physical interaction and biological cross-regulation.

Preparation of Module-Specific Antibodies Against CCN Family Members

Specific antibodies against biomolecules are conventional, but robust tools for the structural and functional analysis of target molecules. Since CCN family proteins are composed of four distinct modules that together determine the functionalities as full-length molecules depending upon extracellular microenvironment, specific antibody against independent modules are quite useful in CCN family research. Three distinct strategies are considerable for raising antibodies specific to four modules: IGFBP, VWC, TSP1, and CT modules. In the first strategy, full-length CCN family proteins are used to immunize mice to obtain a number of hybridoma clones producing different monoclonal antibodies, which are to be characterized to locate the epitopes in particular modules. Second methodology is a straightforward one, in which each modular protein fragment or synthetic peptide is prepared and is used for the immunization of animals independently. Finally, DNA immunization technology is recently known to be useful in developing module-specific antibodies against CCN family proteins as well. Preparation of antibodies is a quite classical and established technique, and thus nowadays is managed mostly by professional and commercial facilities. Therefore in this chapter, essentials of each strategy are introduced, rather than experimental details in each process.

A novel, dual role of CCN3 in experimental glomerulonephritis: pro-angiogenic and antimesangioproliferative effects

In contrast to factors that promote mesangial cell proliferation, little is known about their endogenous inhibitors. During experimental mesangioproliferative nephritis, expression of the glomerular CCN3 (nephroblastoma overexpressed gene [NOV]) gene is reduced before the proliferative phase and increased in glomeruli and serum when mesangial cell proliferation subsides. To further elucidate its role in mesangioproliferative glomerulonephritis, CCN3 systemically was overexpressed by muscle electroporation in healthy or nephritic rats. This increased CCN3 serum concentrations more than threefold for up to 56 days. At day 5 after disease induction, CCN3-transfected rats showed an increase in glomerular endothelial area and in mRNA levels of the pro-angiogenic factors vascular endothelial growth factor and PDGF-C. At day 7, CCN3 overexpression decreased mesangial cell proliferation, including expression of α-smooth muscle actin and matrix accumulation of fibronectin and type IV collagen. In progressive nephritis (day 56), overexpression of CCN3 resulted in decreased albuminuria, glomerulosclerosis, and reduced cortical collagen type I accumulation. In healthy rat kidneys, overexpression of CCN3 induced no morphologic changes but regulated glomerular gene transcripts (reduced transcription of PDGF-B, PDGF-D, PDGF-receptor-β, and fibronectin, and increased PDGF-receptor-α and PDGF-C mRNA). These data identify a dual role for CCN3 in experimental glomerulonephritis with pro-angiogenic and antimesangioproliferative effects. Manipulation of CCN3 may represent a novel approach to help repair glomerular endothelial damage and mesangioproliferative changes.

CCN3 modulates bone turnover and is a novel regulator of skeletal metastasis

The CCN family of proteins is composed of six secreted proteins (CCN1-6), which are grouped together based on their structural similarity. These matricellular proteins are involved in a large spectrum of biological processes, ranging from development to disease. In this review, we focus on CCN3, a founding member of this family, and its role in regulating cells within the bone microenvironment. CCN3 impairs normal osteoblast differentiation through multiple mechanisms, which include the neutralization of pro-osteoblastogenic stimuli such as BMP and Wnt family signals or the activation of pathways that suppress osteoblastogenesis, such as Notch. In contrast, CCN3 is known to promote chondrocyte differentiation. Given these functions, it is not surprising that CCN3 has been implicated in the progression of primary bone cancers such as osteosarcoma, Ewing’s sarcoma and chondrosarcoma. More recently, emerging evidence suggests that CCN3 may also influence the ability of metastatic cancers to colonize and grow in bone.

Transforming growth factor β controls CCN3 expression in nucleus pulposus cells of the intervertebral disc

OBJECTIVE

To investigate transforming growth factor β (TGFβ) regulation of CCN3 expression in cells of the nucleus pulposus.

METHODS

Real-time reverse transcription-polymerase chain reaction and Western blot analyses were used to measure CCN3 expression in the nucleus pulposus. Transfections were used to measure the effect of Smad3, MAPKs, and activator protein 1 (AP-1) on TGFβ-mediated CCN3 promoter activity. Lentiviral knockdown of Smad3 was performed to assess the role of Smad3 in CCN3 expression.

RESULTS

CCN3 was expressed in embryonic and adult intervertebral discs. TGFβ decreased the expression of CCN3 and suppressed its promoter activity in nucleus pulposus cells. DN-Smad3, Smad3 small interfering RNA, or DN-AP-1 had little effect on TGFβ suppression of CCN3 promoter activity. However, p38 and ERK inhibitors blocked suppression of CCN3 by TGFβ, suggesting involvement of these signaling pathways in the regulation of CCN3. Interestingly, overexpression of Smad3 in the absence of TGFβ increased CCN3 promoter activity. We validated the role of Smad3 in controlling CCN3 expression in Smad3-null mice and in nucleus pulposus cells transduced with lentiviral short hairpin Smad3. In terms of function, treatment with recombinant CCN3 showed a dose-dependent decrease in the proliferation of nucleus pulposus cells. Moreover, CCN3-treated cells showed a decrease in aggrecan, versican, CCN2, and type I collagen expression.

CONCLUSION

The opposing effect of TGFβ on CCN2 and CCN3 expression and the suppression of CCN2 by CCN3 in nucleus pulposus cells further the paradigm that these CCN proteins form an interacting triad, which is possibly important in maintaining extracellular matrix homeostasis and cell numbers.

CCN3-mediated promotion of sulfated proteoglycan synthesis in rat chondrocytes from developing joint heads

Chondrocytes forming articular cartilage are embedded in a vast amount of extracellular matrix having physical stiffness and elasticity, properties that support the mechanical load from bones and enable the flexible movement of synovial joints. Unlike chondrocytes that conduct the growth of long bones by forming the growth plate, articular chondrocytes show suppressed cell proliferation, unless these cells are exposed to pathological conditions such as mechanical overload. In the present study, we found that one of the members of the CCN family, CCN3, was significantly expressed in chondrocytes isolated from the epiphyseal head in developing rat synovial joints. Evaluation of the effect of recombinant CCN3 on those chondrocytes revealed that CCN3 promoted proteoglycan synthesis, whereas this factor repressed the proliferation of the same cells. These results suggest a critical role for CCN3 in the regulation of the biological properties of articular chondrocytes.

Impact of CCN3 (NOV) glycosylation on migration/invasion properties and cell growth of the choriocarcinoma cell line Jeg3

BACKGROUND

Recently we have shown that the matricellular CCN3 protein expressed in invasive extravillous trophoblast cells (EVTs) is decreased in early-onset pre-eclampsia and is regulated by oxygen tension. Pathogenesis of pre-eclampsia relies on a shallow invasion of EVTs into the spiral arteries, which leads to hypoxia accompanied by uteroplacental insufficiency. Here we investigated the function of glycosylated and non-glycosylated CCN3 protein on cell growth as well as migration and invasion properties of the malignant trophoblast cell line Jeg3 which is a widely used model for the invasive trophoblast.

METHODS AND RESULTS

Stable transfection of Jeg3 choriocarcinoma cells with full length CCN3 resulted in high expression of secreted glycosylated and cellular non-glycosylated CCN3. These cells revealed significantly reduced growth in cell numbers combined with a significantly increased migratory and invasive capacity. Matrix metalloprotease (MMP)-2 and MMP-9 activities were enhanced dependent on CCN3 expression, which could be confirmed by CCN3 knockdown studies. Using recombinant glycosylated and non-glycosylated CCN3, we revealed that CCN3 decreased growth in Jeg3 cell numbers independent of its glycosylation status, whereas only non-glycosylated CCN3 was able to enhance migration and invasion properties.

CONCLUSIONS

The present results suggest that CCN3 protein regulates the decrease in Jeg3 cell numbers independent of its glycosylation status, whereas migratory and invasive properties are influenced only by non-glycosylated CCN3. An impaired balance in the expression of glycosylated and non-glycosylated CCN3 could contribute to the shallow invasion of EVTs observed in pre-eclampsia.

ALK5 inhibition blocks TGFß-induced CCN2 expression in gingival fibroblasts

Connective tissue growth factor (CCN2/CTGF) is not normally expressed in gingival fibroblasts, but is induced by the potent profibrotic cytokine TGFβ and is overexpressed in gingival fibrosis. Since CCN2 is a marker and mediator of fibrosis, targeting CCN2 expression in gingival fibroblasts may provide new insights into the future development of novel therapeutic opportunities to treat oral fibrosis. Herein we used real-time polymerase chain-reaction, Western blot, and indirect immunofluorescence analysis to evaluate whether SB-431542, a specific pharmacological inhibitor of TGFβ type I receptor (ALK5), blocks the ability of TGFβ to induce CCN2 mRNA and protein expression in human gingival fibroblasts. Our results indicate that CCN2 mRNA and protein are induced by TGFβ in gingival fibroblasts in a SB-431542-sensitive fashion. These results suggest that blocking ALK5 may be useful in blocking the profibrotic effects of TGFβ in gingival fibroblasts.

Matricellular protein CCN3 (NOV) regulates actin cytoskeleton reorganization

CCN3 (NOV), a putative ligand for integrin receptors, is tightly associated with the extracellular matrix and mediates diverse cellular functions, including cell adhesion and proliferation. CCN3 has been shown to negatively regulate growth although it promotes migration in a cell type-specific manner. In this study, overexpression of CCN3 reduces growth and increases intercellular adhesion of breast cancer cells. Interestingly, CCN3 overexpression also led to the formation of multiple pseudopodia that are enriched in actin, CCN3, and vinculin. Breast cancer cells preincubated with exogenous CCN3 protein also induced the same phenotype, indicating that secreted CCN3 is sufficient to induce changes in cell morphology. Surprisingly, extracellular CCN3 is internalized to the early endosomes but not to the membrane protrusions, suggesting pseudopodia-enriched CCN3 may derive from a different source. The presence of an intracellular variant of CCN3 will be consistent with our finding that the cytoplasmic tail of the gap junction protein connexin43 (Cx43) associates with CCN3. Cx43 is a channel protein permitting intercellular communication to occur. However, neither the channel properties nor the protein levels of Cx43 are affected by the CCN3 protein. In contrast, CCN3 proteins are down-regulated in the absence of Cx43. Finally, we showed that overexpression of CCN3 increases the activity of the small GTPase Rac1, thereby revealing a pathway that links Cx43 directly to actin reorganization.

Prognostic relevance of CCN3 in Ewing sarcoma

Ewing sarcoma is a highly aggressive malignant bone tumor occurring preferentially in children and young adults. At present, only clinical features, such as patient age, presence of clinically evident metastases at diagnosis, and poor response to neoadjuvant chemotherapy, are widely accepted as prognostic indicators in Ewing sarcoma. In this study, we assessed the prognostic value of CCN3 (Nov), a matricellular protein that play crucial roles in bone formation. Polyclonal antibodies directed against each of the different CCN3 modules were used to identify variant CCN3 proteins in tumors and to draw potential relationships between the expression of these variants and the outcome of patients with Ewing sarcoma. Our results confirmed that expression of the full-length CCN3 in Ewing sarcoma is associated to a worse prognostic. Furthermore, we report a possible relationship between the expression of a CCN3 protein lacking an internal module (von Willebrand factor type C) and sensitivity to radiotherapy. We hypothesize that the increased level of variant CCN3 in the tumor cells reduces their tumorigenic potential and results in better outcome.

Domain-and species-specific monoclonal antibodies recognize the Von Willebrand Factor-C domain of CCN5

The CCN family of proteins typically consists of four distinct peptide domains: an insulin-like growth factor binding protein-type (IGFBP) domain, a Von Willebrand Factor C (VWC) domain, a thrombospondin type 1 repeat (TSP1) domain, and a carboxy-terminal (CT) domain. The six family members participate in many processes, including proliferation, motility, cell-matrix signaling, angiogenesis, and wound healing. Accumulating evidence suggests that truncated and alternatively spliced isoforms are responsible for the diverse functions of CCN proteins in both normal and pathophysiologic states. Analysis of the properties and functions of individual CCN domains further corroborates this idea. CCN5 is unique among the CCN family members because it lacks the CT-domain. To dissect the domain functions of CCN5, we are developing domain-specific mouse monoclonal antibodies. Monoclonal antibodies have the advantages of great specificity, reproducibility, and ease of long-term storage and production. In this communication, we injected mixtures of GST-fused rat CCN5 domains into mice to generate monoclonal antibodies. To identify the domains recognized by the antibodies, we constructed serial expression plasmids that express dual-tagged rat CCN5 domains. All of the monoclonal antibodies generated to date recognize the VWC domain, indicating it is the most highly immunogenic of the CCN5 domains. We characterized one particular clone, 22H10, and found that it recognizes mouse and rat CCN5, but not human recombinant CCN5. Purified 22H10 was successfully applied in Western Blot analysis, immunofluorescence of cultured cells and tissues, and immunoprecipitation, indicating that it will be a useful tool for domain analysis and studies of mouse-human tumor models.

Alternative splicing of CCN mRNAs .... it has been upon us

Variant CCN proteins have been identified over the past decade in several normal and pathological situations. The production of CCN truncated proteins have been reported in the case of CCN2(ctgf), CCN3(nov), CCN4(wisp-1) and CCN6(wisp-3). Furthermore, the natural CCN5 is known to miss the C-terminal domain that is present in all other members of the CCN family of proteins. In spite of compelling evidence that assign important biological activities to these truncated CCN variants, their potential regulatory functions have only recently begun to be widely accepted. The report of CCN1(cyr61) intron 3 retention in breast cancer cells now confirms that, in addition to well documented post-translational processing of full length CCN proteins, alternative splicing is to be regarded as another effective way to generate CCN variants. These observations add to a previous bulk of evidence that support the existence of alternative splicing for other CCN genes. It has become clearly evident that we need to recognize these mechanisms as a means to increase the biological diversity of CCN proteins.

What's in an intron? CCN1 mRNA splicing in cancer

The CCN family of matricellular signaling regulators shares a common domain structure. Variants of individual CCN proteins exist, which contain different combinations of these domains. Although mRNA splicing is likely to play a key role on CCN biology, this hypothesis has not been thoroughly tested. In a recent report, Hirschfeld and colleagues (Cancer Res 69:2082-90, 2009), show that CCN1 (cyr61) mRNA is normally present in a form in which intron 3 is retained. In cancers, or upon hypoxia, intron 3 is removed resulting in the appearance of CCN1 protein. The significance of this paper is discussed.

Regulatory role of CCN3 in melanoma cell interaction with the extracellular matrix

It is increasingly clear that melanoma cells modify their environment not only through the release of growth factors (GFs) and cytokines that have autocrine or paracrine effects and strongly modulate the immune response, but also by secreting proteins that become structural or transient components of the extracellular matrix (ECM). Melanoma cell secreted proteins play a significant role in cell-ECM interactions, helping tumor cells to invade neighbouring stroma, disseminate and survive in other tissue contexts. CCN3/NOV (nephroblastoma overexpressed) is a matricellular protein that belongs to the CCN family of proteins containing six members in humans. Its structure consists of modules related to functional domains previously identified in major regulatory proteins: insulin-like growth factor-binding protein (IGFBP), von Willebrand factor type C repeats (VWC), thrombospondin type 1 repeats, and secreted regulatory factors containing cysteine knot motifs. Extensive studies have indicated that the biological properties of CCN3 are dependent upon the cellular context, and its role in melanoma seems to recapitulate cell context functions.

The CCN family of proteins: structure-function relationships

The CCN proteins are key signalling and regulatory molecules involved in many vital biological functions, including cell proliferation, angiogenesis, tumourigenesis and wound healing. How these proteins influence such a range of functions remains incompletely understood but is probably related to their discrete modular nature and a complex array of intra- and inter-molecular interactions with a variety of regulatory proteins and ligands. Although certain aspects of their biology can be attributed to the four individual modules that constitute the CCN proteins, recent results suggest that some of their biological functions require cooperation between modules. Indeed, the modular structure of CCN proteins provides important insight into their structure-function relationships.

The CCN family of proteins: structure-function relationships

The CCN proteins are key signalling and regulatory molecules involved in many vital biological functions, including cell proliferation, angiogenesis, tumourigenesis and wound healing. How these proteins influence such a range of functions remains incompletely understood but is probably related to their discrete modular nature and a complex array of intra- and inter-molecular interactions with a variety of regulatory proteins and ligands. Although certain aspects of their biology can be attributed to the four individual modules that constitute the CCN proteins, recent results suggest that some of their biological functions require cooperation between modules. Indeed, the modular structure of CCN proteins provides important insight into their structure-function relationships.

The CCN family of genes: a perspective on CCN biology and therapeutic potential

The CCN family of genes currently comprises six secreted proteins (designated CCN1-6 after Cyr61/CCN1; ctgf/CCN2; Nov/CCN3; WISP1/CCN4; WISP2/CCN5, WISP3/CCN6) with a similar mosaic primary structure. It is now well accepted that CCN proteins are not growth factors but matricellular proteins that modify signaling of other molecules, in particular those associated with the extracellular matrix. CCN proteins are involved in mitosis, adhesion, apoptosis, extracellular matrix production, growth arrest and migration of multiple cell types. Since their first identification as matricellular factors, the CCN proteins now figure prominently in a variety of major diseases and are now considered valid candidates for therapeutic targeting. Dissection of the molecular mechanisms governing the biological properties of these proteins is being actively pursued by an expanding network of scientists around the globe who will meet this year at the 5th International Workshop on the CCN family of Genes, organized by the International CCN Society ( http://ccnsociety.com ), home for an international cadre of collaborators working in the CCN field.

CCN3/nephroblastoma overexpressed matricellular protein regulates integrin expression, adhesion, and dissemination in melanoma

CCN3/nephroblastoma overexpressed belongs to the CCN family of genes that encode secreted proteins associated with the extracellular matrix (ECM) and exert regulatory effects at the cellular level. Overexpression of CCN3 was shown in metastatic melanoma cells compared with cells of the primary tumor from the same patient. Analysis of short-term cultures from 50 primary and metastatic melanomas revealed a heterogeneous expression pattern of both the 46-kDa full-length cytoplasmic/secreted protein and the 32-kDa nuclear-truncated form. The different protein expression patterns were not associated with gene alterations or polymorphisms. Like the metastatic cells expressing high levels of the 46-kDa CCN3, cells transfected to overexpress CCN3 showed increased adhesion to ECM proteins, whereas inhibition of CCN3 expression by small interfering RNA decreased adhesion to laminin and vitronectin. CCN3 overexpression induced increased expression of laminin and vitronectin integrin receptors alpha 7 beta 1 and alpha v beta 5 by increasing their mRNA production. Moreover, CCN3 secreted by melanoma cells acted as an adhesion matrix protein for melanoma cells themselves. Analysis of CCN3 protein expression with respect to melanoma progression detected the protein in all visceral metastases tested and in most nodal metastases from relapsing patients but in only a few nodal metastases from nonrelapsing patients and cutaneous metastases. Consistently, xenotransplantation in immunodeficient mice showed a higher metastatic potential of melanoma cells overexpressing CCN3. Together, these data indicate a role for CCN3 in melanoma cell interaction with the ECM by regulating integrin expression, resulting in altered cell adhesion and leading melanoma progression to aggressive disease.