CCN Family Of Proteins Research Articles

The CCN Family of Proteins: A Critical Approach to the Multi-Modular Structure of the CCN Domains

The CCN family of proteins is composed of six members (CCN1-CCN6) sharing a tetra-modular organization and a striking conservation of their primary structure. The CCN acronym was originally assigned in 1993 by P. Bork to three newly discovered factors (originally called CTGF, CYR61, and NOV), which he proposed to constitute a new family of proteins on the basis of their common physical features. Six years later, three other proteins (Wisp1-3), sharing the same tetramodular organization, joined the family (figure 1). The HUGO-recognized acronyms for the CCN proteins were officialized in 2018[1]. The CCN family turned out to contain positive and negative regulators of cell proliferation and differentiation, with pro- and anti-tumorigenic activities. A significant amount of work has been performed to identify the participation of the constitutive modules in these biological features. The aim of this review is to briefly examine the potential roles assigned to the constitutive modules of CCN proteins and propose a critical view of the structural basis for their interactions and functions.

The regulation and functions of the matricellular CCN proteins induced by shear stress.

Shear stress is a frictional drag generated by the flow of fluid, such as blood or interstitial fluid, and plays a critical role in regulating cellular gene expression and functional phenotype. The matricellular CCN family proteins are dynamically regulated by shear stress of different flow patterns, and their expression significantly alters the microenvironment of cells. Secreted CCN proteins mainly bind to several cell surface integrin receptors to mediate their diverse functions in regulating cell survival, function, and behavior. Gene-knockout studies indicate major functions of CCN proteins in the cardiovascular and skeletal systems, the two primary systems in which CCN expressions are regulated by shear stress. In the cardiovascular system, the endothelium is directly exposed to vascular shear stress. Unidirectional laminar blood flow generates laminar shear stress, which promotes a mature endothelial phenotype and upregulates anti-inflammatory CCN3 expression. In contrast, disturbed flow generates oscillatory shear stress, which induces endothelial dysfunction through the induction of CCN1 and CCN2. Shear-induced CCN1 binds to integrin α6β1 and promotes superoxide production, NF-κB activation, and inflammatory gene expression in endothelial cells. Although the interaction between shear stress and CCN4-6 is not clear, CCN 4 exhibits a proinflammatory property and CCN5 inhibits vascular cell growth and migration. The crucial roles of CCN proteins in cardiovascular development, homeostasis, and disease are evident but not fully understood. In the skeletal system, mechanical loading on bone generates shear stress from interstitial fluid in the lacuna-canalicular system and promotes osteoblast differentiation and bone formation. CCN1 and CCN2 are induced and potentially mediate fluid shear stress mechanosensing in osteocytes. However, the exact roles of interstitial shear stress-induced CCN1 and CCN2 in bone are still not clear. In contrast to other CCN family proteins, CCN3 inhibits osteoblast differentiation, although its regulation by interstitial shear stress in osteocytes has not been reported. The induction of CCN proteins by shear stress in bone and their functions remain largely unknown and merit further investigation. This review discusses the expression and functions of CCN proteins regulated by shear stress in physiological conditions, diseases, and cell culture models. The roles between CCN family proteins can be compensatory or counteractive in tissue remodeling and homeostasis.

Protocols for Screening Peptides Binding to CCN Family Proteins and Their Extended Utility.

The function of CCN family proteins is determined by their interactions with multiple cofactors that are present in the microenvironment. Therefore, determining these cofactors is critically important in understanding the molecular function of CCN family members. For this objective, a bacteriophage random peptide display library is a suitable tool. In this library, each filamentous bacteriophage is designed to display an oligopeptide of 7-20 random amino acid residues on its surface. Bacteriophage clones that possess peptides that bind to a CCN family protein are selected through several cycles of a process called biopanning or affinity selection. By determining the nucleotide sequence of the DNA that encodes the displayed peptide, the oligopeptides that specifically bind to the CCN family member can be specified. The obtained peptide sequences can be utilized to design peptide aptamers for CCN family proteins, or as a key sequence to determine new CCN family cofactor candidates in silico. Instead of a random peptide cDNA library, an antibody cDNA library from naïve lymphocytes or from B cells immunized by a CCN family protein can be used in order to obtain a highly specific CCN family detection or functional modulation tool.

Cellular Fluorescence Imaging for the Evaluation of Bioactivity of CCN Family Proteins.

The method of labeling proteins of interest with fluorescent dyes that can specifically stain organelles in living cells provides a tool for investigating various cellular processes under a microscope. Visualization (imaging) of the cells using fluorescence has many advantages, including the ability to stain multiple cell organelles and intracellular proteins simultaneously and discriminately, and is used in many research fields. In this chapter, we describe the observation of cell organelles using fluorescence staining to analyze the functions of CCN family proteins involved in various cellular events.

The role of CCNs in controlling cellular communication in the tumor microenvironment.

The Cellular communication network (CCN) family of growth regulatory factors comprises six secreted matricellular proteins that promote signal transduction through cell-cell or cell-matrix interaction. The diversity of functionality between each protein is specific to the many aspects of healthy and cancer biology. For example, CCN family proteins modulate cell adhesion, proliferation, migration, invasiveness, apoptosis, and survival. In addition, the expression of each protein regulates many biological and pathobiological processes within its microenvironment to regulate angiogenesis, inflammatory response, chondrogenesis, fibrosis, and mitochondrial integrity. The collective range of CCN operation remains fully comprehended; however, understanding each protein's microenvironment may draw more conclusions about the abundance of interactions and signaling cascades occurring within such issues. This review observes and distinguishes the various roles a CCN protein may execute within distinct tumor microenvironments and the biological associations among them. Finally. We also review how CCN-family proteins can be used in nano-based therapeutic implications.

Association between WNT-1-inducible signaling pathway protein-1 (WISP1) genetic polymorphisms and the risk of gastric cancer in Guangxi Chinese

BackgroundWNT1-inducible signaling pathway protein 1 (WISP1) is a member of the CCN protein family and a downstream target of β-catenin. Aberrant WISP1 expression may be involved in carcinogenesis. To date, no studies have investigated the association between single-nucleotide polymorphisms (SNPs) of WISP1 and gastric cancer. Therefore, we conducted this study to explore their relationship.MethodsPolymerase chain reaction-restriction fragment length polymorphism assay was used to analyze three SNPs of WISP1 in 204 gastric cancer patients and 227 controls.ResultsOverall, we could not identify a significant association between WISP1 SNPs and gastric cancer risk. However, the subgroup analysis demonstrated that the presence of the rs7843546 T allele was associated with a significantly decreased risk of gastric cancer in those of Han Chinese ethnicity (CT vs. CC: OR = 0.33, 95%CI 0.14–0.78; TT vs. CC: OR = 0.29, 95%CI 0.11–0.76; CT + TT vs. CC: OR = 0.32, 95%CI 0.14–0.74). In addition, patients with the rs7843546 TT genotype display a 0.34-fold lower risk of developing stage I/II gastric cancer than those with the CC genotype Furthermore, individuals ≥ 50 years old who carried the rs10956697 AC genotype had a significantly decreased risk of gastric cancer (OR = 0.58, 95%CI 0.35–0.98). Smokers with the rs10956697 AC and AC + AA genotypes exhibited a 0.28-fold lower and 0.32-fold lower risk of gastric cancer, respectively.ConclusionsThe WISP1 SNPs rs7843546 and rs10956697 were, for the first time, found to reduce susceptibility to gastric cancer in various subgroups of Guangxi Chinese.

CTGF regulates cell proliferation, migration, and glucose metabolism through activation of FAK signaling in triple-negative breast cancer.

Connective tissue growth factor (CTGF), also known as CCN2, is a member of the CCN protein family of secreted proteins with roles in diverse biological processes. CTGF regulates biological functions such as cell proliferation, migration, adhesion, wound healing, and angiogenesis. In this study, we demonstrate a mechanistic link between CTGF and enhanced aerobic glycolysis in triple-negative breast cancer (TNBC). We found that CTGF is overexpressed in TNBC and high CTGF expression is correlated with a poor prognosis. Also, CTGF was required for in vivo tumorigenesis and in vitro proliferation, migration, invasion, and adhesion of TNBC cells. Our results indicate that extracellular CTGF binds directly to integrin αvβ3, activating the FAK/Src/NF-κB p65 signaling axis, which results in transcriptional upregulation of Glut3. Neutralization of CTGF decreased cell proliferation, migration, and invasion through downregulation of Glut3-mediated glycolytic phenotypes. Overall, our work suggests a novel function for CTGF as a modulator of cancer metabolism, indicating that CTGF is a potential therapeutic target in TNBC.

Expression of Cyr61 in ApoE\u2212/\u2212 mice with chronic unilateral renal artery ligation

Cyr61 is a member of the CCN family of proteins that is expressed in atherosclerotic lesions and regulated by angiotensin II. It is unknown whether renal artery stenosis (RAS) increases Cyr61 expression. Male ApoE−/− mice were randomized to surgically induced RAS, RAS + treatment with either irbesartan, aliskiren or amlodipine or sham-surgery. RAS resulted in increased plasma angiotensin II levels, a mild, sustained increase in systolic blood pressure and increased aortic lipid deposition compared to sham-surgery. Surgically induced RAS led to the formation of atheroma in the infrarenal aorta and there was consistent and intense staining for Cyr61 within the atheroma. Treatment with irbesartan, aliskiren and amlodipine were associated with decreased aortic lipid deposition and decreased staining for Cyr61 in aortic atheroma. Serum levels of Cyr61 were not increased in mice or humans with RAS. In summary, Cyr61 expression in aortic atheroma but not serum is increased by RAS in ApoE−/− mice and is reduced by agents that lower blood pressure.

CCN2 Facilitates IL-17 Production and Osteoclastogenesis in Human Osteoarthritis Synovial Fibroblasts by Inhibiting miR-655 Expression.

Osteoarthritis (OA) is associated with extensive upregulation of osteoclastogenesis and subsequent bone breakdown. The CCN family protein connective tissue growth factor (CCN2, also called CCN2) enhances inflammatory cytokine production in OA disease. The cytokine interleukin (IL)-17 is known to induce osteoclastogenesis and bone erosion in arthritic disease. Our retrieval of data from the Gene Expression Omnibus (GEO) data set and clinical tissues exhibited higher CCN2 and IL-17 expression in OA synovial sample than in normal healthy samples. We observed the same phenomenon in synovial tissue from rats with anterior cruciate ligament transaction (ACLT)-elicited OA compared with synovial tissue from control healthy rats. We also found that CCN2 facilitated increases in IL-17 synthesis in human OA synovial fibroblasts (OASFs) and promoted osteoclast formation. CCN2 affected IL-17 production by reducing miR-655 expression through the ILK and Syk signaling cascades. Our findings improve our understanding about the effect of CCN2 in OA pathogenesis and, in particular, IL-17 production and osteoclastogenesis, which may help with the design of more effective OA treatments. © 2022 American Society for Bone and Mineral Research (ASBMR).

Emerging role of CCN family proteins in fibrosis.

Fibrosis is a common pathological change characterized by the excessive accumulation of fibrous connective tissue. Once uncontrolled, this pathological progress can lead to irreversible damage to the structure and function of organs, which is a serious threat to human health and life. Actually, the disability and death of patients caused by many chronic diseases have a closed relationship with fibrosis. The CCN protein family, including six members, is a small group of matrix proteins exhibiting structurally similar features. In the past 20 years, different biological functions of CCN proteins have been identified in various diseases. Of note, it has been recently shown that they are implicated in the key pathological process of fibrosis. In this review, we summarize the current status of knowledge regarding the role of CCN proteins involved in the pathogenesis of fibrosis diseases in detail. Furthermore, we highlight some of the underlying interaction mechanisms of CCN protein acting in fibrosis that helps to develop new drugs and determine appropriate clinical strategies for fibrotic diseases.

The 2019 FASEB Science Research Conference on Matricellular Proteins in Inflammation and Tissue Remodeling, July 14-19, 2019, Lisbon, Portugal.

The 2019 FASEB Science Research Conference on Matricellular Proteins in Inflammation and Tissue Remodeling, July 14-19, 2019, Lisbon, Portugal.

Suppression of adipocyte differentiation by low-intensity pulsed ultrasound via inhibition of insulin signaling and promotion of CCN family protein 2.

Adipocyte differentiation is regulated by several transcription factors such as the CCAAT/enhancer-binding proteins (C/EBPs) and peroxisome proliferator-activated receptor-γ (PPARγ). Here, we demonstrate that low-intensity pulsed ultrasound (LIPUS) suppressed differentiation into mature adipocytes via multiple signaling pathways. When C3H10T1/2, a mesenchymal stem cell line, was treated with LIPUS (3.0 MHz, 60 mW/cm2 ) for 20 minutes once a day for 4 days during adipogenesis, and both the number of lipid droplets and the gene expression of PPARγ and C/EBPα were significantly decreased. Furthermore, LIPUS treatment decreased the phosphorylation of the insulin receptor and also that of Akt and ERK1/2, which are located downstream of this receptor. Next, we showed that LIPUS suppressed the gene expression of angiotensinogen (AGT), which is an adipokine produced by mature adipocytes, as well as that of angiotensin-converting enzyme1 (ACE1) and angiotensin receptor type 1 (AT1 R) during adipogenesis of pre-adipogenic 3T3-L1 cells. Next, the translocation of Yes-associated protein (YAP) into the nucleus of 3T3-L1 cells was promoted by LIPUS, leading to upregulation of CCN family protein 2 (CCN2), a cellular communication network factor. Moreover, forced expression of CCN2 in 3T3-L1 cells decreased PPARγ gene expression, but it did not increase alkaline phosphatase and osterix gene expression. Finally, gene silencing of CCN2 in C3H10T1/2 cells diminished the effect of LIPUS on the gene expression of PPARγ and C/EBPα. These findings suggest that LIPUS suppressed adipogenesis through inhibition of insulin signaling and decreased PPARγ expression via increased CCN2 production, resulting in a possible decrease of mature adipocytes.

The Roles of a Matricellular CCN Family Protein CCN5 in Cardiac Fibrosis of Heart Failure

Cardiac fibrosis is a major player in cardiovascular disease, both as a contributor to the development of disease and a post-injury response that drives progression to heart failure. Despite the identification of many mechanisms responsible for cardiovascular fibrosis, such as angiotensin II, TGF-[Formula: see text] and endothelin-1, to date no treatments have emerged that have effectively reduced the excess deposition of extracellular matrix associated with fibrotic conditions. Matricellular CCN proteins spatiotemporally regulated nonstructural components of the extracellular matrix (ECM) and participated in many essential biological functions, including wound healing and fibrotic diseases. CCN5 exhibited the opposing effects of CCN2 on the development of cardiac hypertrophy and fibrosis, and overexpression of matricellular protein CCN5 in the heart by adenoviral deliver significantly improved cardiac fibrosis in severe heart failure. Future time- and cell-specific study of CCN5 effect and its domain-specific function on fibrotic development and progression will advance our understanding of cardiac fibrosis, and meanwhile provide opportunities for therapeutic intervention of heart failure.

Diabetic Foot Ulcer as a Cause of Significant Decline in the Renal Function Among South Indian Population With Type 2 Diabetes: Role of TGF-β1 and CCN Family Proteins.

In the present study, a total of 428 South Indian subjects were divided into four different groups, consisting of individuals with type 2 diabetes without any other complications (T2DM), T2DM subjects with stage 2 and 3 diabetic kidney disease (CKD), T2DM subjects with grade 2 or 3 diabetic foot ulcer (DFU) and T2DM subjects having both diabetic kidney disease and diabetic foot ulcer (CKDDFU). The study was conducted ambispectively by comparing the changes in renal function among two consecutive periods, i.e., the period prior to the development of grade 2 and 3 diabetic foot ulcer (retrospectively) and after the development of DFU (prospectively). A gradual and uniform reduction of eGFR was observed throughout the study period in the subjects affected with either CKD or DFU alone. Whereas in subjects with both CKD and DFU, there was a sharp decline in the eGFR during the six months prior to the baseline, i.e., the period in which the development of ulcer and its progression to grade 2 or 3 happened. Remarkable elevations in the levels of TGF-β1 and CCN2 (CTGF), as well as a significant reduction in the level of CCN3 (NOV), were observed in the serum of CKDDFU group subjects, compared to the other groups. Increased production of TGF-β1 in response to the inflammatory stimulus from multiple sites in CKDDFU subjects caused a subsequent down-regulation of CCN3, followed by the activation of a large quantity of CCN2.

Effects of Fibroblast Growth Factor 1 (FGF‐1) on CCN2 Gene Expression in Chondrocytic Cells

Cartilage and bone are developed by chondrocytes and osteoblasts differentiated from mesenchymal stem cells under the multiple interactions of extracellular signaling molecules. Among such molecules, CCN family protein 2 (CCN2) plays a critical role in the development and regeneration of the cartilage and bone to promote proliferation, differentiation and chondrocyte maturation as well as matrix remodeling during chondrogenesis. CCN2 interacts with several growth factors involved in endochondral ossification, which include fibroblast growth factor 1 (FGF‐1) showing a specific binding with this CCN2. However, the role of FGF‐1 in chondrocyte metabolism has not been investigated well. Therefore, in this study, we evaluated the effect of FGF‐1 on chondrocytes and its role on CCN2 regulation. The effect of FGF‐1 on CCN2 in human chondrocytic HCS‐2/8 cells and the cellular phenotype was estimated by the gene expression of chondrocytic markers. Addition of FGF‐1 to chondrocytic cell culture drastically repressed the mRNA levels of CCN2, with significant repression of other chondrocytic markers in those cells. The ELISA experiments revealed consistent results, in which the protein level of CCN2 was drastically down‐regulated by the addition of FGF‐1. Next, reporter gene assay was used to examine whether the CCN2 regulation by FGF‐1 is mediated by genetic elements involved in the proximal promoter, or not. However, the negative effect of FGF‐1 on CCN2 promoter activity appears to have been too weak to account for the observed decrease at mRNA and protein levels. Another reporter gene assay was performed with a plasmid containing multiple post‐transcriptional regulatory elements in the 3′‐untranslated region of the CCN2 gene. Surprisingly, FGF‐1 has no effect on these elements. Degradation fate of CCN2 mRNA after the addition of actinomycin D was tested, in the presence or absence of FGF‐1, showing unexpected results. Suspecting a regulation at a chromatin level, the effect of a histone deacetylase inhibitor, valproic acid (VPA), on the FGF‐1 function was evaluated, but VPA did not prevent the repressive effect of FGF‐1 on CCN2 gene expression. Further investigation is underway, suspecting a transcriptional regulation through a silencer located outside of the proximal promoter region.Support or Funding InformationJapan Society for the Promotion of Science (JSPS)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Protein PEGylation for cancer therapy: bench to bedside.

PEGylation is a biochemical modification process of bioactive molecules with polyethylene glycol (PEG), which lends several desirable properties to proteins/peptides, antibodies, and vesicles considered to be used for therapy or genetic modification of cells. However, PEGylation of proteins is a complex process and can be carried out using more than one strategy that depends on the nature of the protein and the desired application. Proteins of interest are covalently conjugated or non-covalently complexed with inert PEG strings. Purification of PEGylated protein is another critical step, which is mainly carried out based on electrostatic interactions or molecular sizes using chromatography. Several PEGylated drugs are being used for diseases like anemia, kidney disease, multiple sclerosis, hemophilia and cancers. With the advancement and increased specificity of the PEGylation process, the world of drug therapy, and specifically cancer therapy could benefit by utilizing this technique to create more stable and non-immunogenic therapies. In this article we describe the structure and functions of PEGylation and how this chemistry helps in drug discovery. Moreover, special emphasis has been given to CCN-family proteins that can be targeted or used as therapy to prevent or block cancer progression through PEGylation technology.

Role of the CCN protein family in cancer

The CCN protein family is composed of six matricellular proteins, which serve regulatory roles rather than structural roles in the extracellular matrix. First identified as secreted proteins which are induced by oncogenes, the acronym CCN came from the names of the first three members: CYR61, CTGF, and NOV. All six members of the CCN family consist of four cysteine-rich modular domains. CCN proteins are known to regulate cell adhesion, proliferation, differentiation, and apoptosis. In addition, CCN proteins are associated with cardiovascular and skeletal development, injury repair, inflammation, and cancer. They function either through binding to integrin receptors or by regulating the expression and activity of growth factors and cytokines. Given their diverse roles related to the pathology of certain diseases such as fibrosis, arthritis, atherosclerosis, diabetic nephropathy, retinopathy, and cancer, there are many emerging studies targeting CCN protein signaling pathways in attempts to elucidate their potentials as therapeutic targets.

YAP/TAZ Are Essential for TGF-β2-Mediated Conjunctival Fibrosis.

To investigate the roles of Yes-associated protein (YAP)/transcriptional co-activator with PDZ-binding motif (TAZ), the major effector molecules of the Hippo pathway, in TGF-β2-mediated conjunctival fibrosis. Primary human conjunctival fibroblasts were treated with TGF-β2. The expression of YAP/TAZ was examined by Western blot analyses and immunocytochemistry. The expression of fibrotic proteins and genes were evaluated by Western blot analyses and quantitative real-time PCR, respectively. The effects of YAP/TAZ on fibrotic changes were examined by knockdown experiments and the YAP/TAZ inhibitor, verteporfin. TGF-β2 stabilized YAP/TAZ and subsequently activated Smad2/3, which led to the transcription of fibrotic genes in human primary conjunctival fibroblasts. These fibrotic genes were differently regulated by YAP/TAZ. Notably, α-smooth muscle actin, fibronectin, collagen I, and collagen IV were primarily regulated by YAP. In contrast, CCN family proteins (CTGF and CYR61) depended on both YAP and TAZ. Mechanistically, YAP/TAZ were located in close proximity to Smad2/3, and in particular, YAP was required for TGF-β2-mediated phosphorylation and the nuclear translocation of Smad2/3. Furthermore, a YAP/TAZ inhibitor markedly suppressed TGF-β2-mediated fibrotic changes in conjunctival fibroblasts. YAP/TAZ acted as a molecular hub of TGF-β2 signaling in a cellular model of conjunctival fibrosis. Moreover, verteporfin, a YAP/TAZ inhibitor exerted potent antifibrosis effects by suppressing TGF-β2-YAP/TAZ-Smad signaling. Our study highlights YAP/TAZ as essential regulators of conjunctival fibrosis and shows that inhibition of YAP/TAZ might potentially improve the outcomes of glaucoma filtration surgery.

Impacts of WNT1-inducible signaling pathway protein 1 polymorphism on hepatocellular carcinoma development.

BackgroundWNT1-inducible signaling pathway protein 1 (WISP1) is a member of CCN protein family and a downstream target of β-catenin. Aberrant WISP1 expression is associated with carcinogenesis. In the current study, we focused on examining WISP1 single nucleotide polymorphisms (SNPs) to elucidate hepatocellular carcinoma (HCC) clinicopathologic characteristics.Methodology/Principal findingsThe WISP1 SNPs rs2977530, rs2977537, rs2929973, rs2929970, rs62514004, and rs16893344 were analyzed by real-time polymerase chain reaction in 332 patients with HCC and 664 cancer-free controls.ResultsThe patients with higher frequencies of WISP1 rs62514004 (AG + GG) and rs16893344 (CT + TT) variants revealed a lower risk to reach a later clinical stage compared with their wild-type carriers. Furthermore, individuals who carried WISP1 rs62514004 and rs16893344 haplotype G-T showed a greater synergistic effect combined with alcohol drinking on HCC development (AOR = 26.590, 95% CI = 9.780–72.295).ConclusionsOur results demonstrated that the HCC patients with WISP1 SNPs are associated with HCC development, and WISP1 SNPs may serve as markers or therapeutic targets for HCC.

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.