Expression and physiological role of CCN4/Wnt-induced secreted protein 1 mRNA splicing variants in chondrocytes

An overview of CCN4 (WISP1) role in human diseases

CCN4 (cellular communication network factor 4), a highly conserved, secreted cysteine-rich matricellular protein is emerging as a key player in the development and progression of numerous disease pathologies, including cancer, fibrosis, metabolic and inflammatory disorders. Over the past two decades, extensive research on CCN4 and its family members uncovered their diverse cellular mechanisms and biological functions, including but not limited to cell proliferation, migration, invasion, angiogenesis, wound healing, repair, and apoptosis. Recent studies have demonstrated that aberrant CCN4 expression and/or associated downstream signaling is key to a vast array of pathophysiological etiology, suggesting that CCN4 could be utilized not only as a non-invasive diagnostic or prognostic marker, but also as a promising therapeutic target. The cognate receptor of CCN4 remains elusive till date, which limits understanding of the mechanistic insights on CCN4 driven disease pathologies. However, as therapeutic agents directed against CCN4 begin to make their way into the clinic, that may start to change. Also, the pathophysiological significance of CCN4 remains underexplored, hence further research is needed to shed more light on its disease and/or tissue specific functions to better understand its clinical translational benefit. This review highlights the compelling evidence of overlapping and/or diverse functional and mechanisms regulated by CCN4, in addition to addressing the challenges, study limitations and knowledge gaps on CCN4 biology and its therapeutic potential.

WNT1 Inducible Signaling Pathway Protein 1 Is a Stroma-Specific Secreting Protein Inducing a Fibroblast Contraction and Carcinoma Cell Growth in the Human Prostate

The WNT1 inducible signaling pathway protein 1 (WISP1), a member of the connective tissue growth factor family, plays a crucial role in several important cellular functions in a highly tissue-specific manner. Results of a RT-qPCR indicated that WISP1 expressed only in cells of the human prostate fibroblasts, HPrF and WPMY-1, but not the prostate carcinoma cells in vitro. Two major isoforms (WISP1v1 and WISP1v2) were identified in the HPrF cells determined by RT-PCR and immunoblot assays. The knock-down of a WISP1 blocked cell proliferation and contraction, while treating respectively with the conditioned medium from the ectopic WISP1v1- and WISPv2-overexpressed 293T cells enhanced the migration of HPrF cells. The TNFα induced WISP1 secretion and cell contraction while the knock-down of WISP1 attenuated these effects, although TNFα did not affect the proliferation of the HPrF cells. The ectopic overexpression of WISP1v1 but not WISP1v2 downregulated the N-myc downstream regulated 1 (NDRG1) while upregulating N-cadherin, slug, snail, and vimentin gene expressions which induced not only the cell proliferation and invasion in vitro but also tumor growth of prostate carcinoma cells in vivo. The results confirmed that WISP1 is a stroma-specific secreting protein, enhancing the cell migration and contraction of prostate fibroblasts, as well as the proliferation, invasion, and tumor growth of prostate carcinoma cells.

CCN proteins in the musculoskeletal system: current understanding and challenges in physiology and pathology

The acronym for the CCN family was recently revised to represent “cellular communication network”. These six, small, cysteine-enriched and evolutionarily conserved proteins are secreted matricellular proteins, that convey and modulate intercellular communication by interacting with structural proteins, signalling factors and cell surface receptors. Their role in the development and physiology of musculoskeletal system, constituted by connective tissues where cells are interspersed in the cellular matrix, has been broadly studied. Previous research has highlighted a crucial balance of CCN proteins in mesenchymal stem cell commitment and a pivotal role for CCN1, CCN2 and their alter ego CCN3 in chondrogenesis and osteogenesis; CCN4 plays a minor role and the role of CCN5 and CCN6 is still unclear. CCN proteins also participate in osteoclastogenesis and myogenesis. In adult life, CCN proteins serve as mechanosensory proteins in the musculoskeletal system providing a steady response to environmental stimuli and participating in fracture healing. Substantial evidence also supports the involvement of CCN proteins in inflammatory pathologies, such as osteoarthritis and rheumatoid arthritis, as well as in cancers affecting the musculoskeletal system and bone metastasis. These matricellular proteins indeed show involvement in inflammation and cancer, thus representing intriguing therapeutic targets. This review discusses the current understanding of CCN proteins in the musculoskeletal system as well as the controversies and challenges associated with their multiple and complex roles, and it aims to link the dispersed knowledge in an effort to stimulate and guide readers to an area that the writers consider to have significant impact and relevant potentialities.

Molecular Mechanisms of Obesity-Linked Cardiac Dysfunction: An Up-Date on Current Knowledge

Obesity is defined as excessive body fat accumulation, and worldwide obesity has nearly tripled since 1975. Excess of free fatty acids (FFAs) and triglycerides in obese individuals promote ectopic lipid accumulation in the liver, skeletal muscle tissue, and heart, among others, inducing insulin resistance, hypertension, metabolic syndrome, type 2 diabetes (T2D), atherosclerosis, and cardiovascular disease (CVD). These diseases are promoted by visceral white adipocyte tissue (WAT) dysfunction through an increase in pro-inflammatory adipokines, oxidative stress, activation of the renin-angiotensin-aldosterone system (RAAS), and adverse changes in the gut microbiome. In the heart, obesity and T2D induce changes in substrate utilization, tissue metabolism, oxidative stress, and inflammation, leading to myocardial fibrosis and ultimately cardiac dysfunction. Peroxisome proliferator-activated receptors (PPARs) are involved in the regulation of carbohydrate and lipid metabolism, also improve insulin sensitivity, triglyceride levels, inflammation, and oxidative stress. The purpose of this review is to provide an update on the molecular mechanisms involved in obesity-linked CVD pathophysiology, considering pro-inflammatory cytokines, adipokines, and hormones, as well as the role of oxidative stress, inflammation, and PPARs. In addition, cell lines and animal models, biomarkers, gut microbiota dysbiosis, epigenetic modifications, and current therapeutic treatments in CVD associated with obesity are outlined in this paper.

Adipokines: New Potential Therapeutic Target for Obesity and Metabolic, Rheumatic, and Cardiovascular Diseases

Besides its role as an energy storage organ, adipose tissue can be viewed as a dynamic and complex endocrine organ, which produces and secretes several adipokines, including hormones, cytokines, extracellular matrix (ECM) proteins, and growth and vasoactive factors. A wide body of evidence showed that adipokines play a critical role in various biological and physiological functions, among which feeding modulation, inflammatory and immune function, glucose and lipid metabolism, and blood pressure control. The aim of this review is to summarize the effects of several adipokines, including leptin, diponectin, resistin, chemerin, lipocalin-2 (LCN2), vaspin, omentin, follistatin-like 1 (FSTL1), secreted protein acidic and rich in cysteine (SPARC), secreted frizzled-related protein 5 (SFRP5), C1q/TNF-related proteins (CTRPs), family with sequence similarity to 19 member A5 (FAM19A5), wingless-type inducible signaling pathway protein-1 (WISP1), progranulin (PGRN), nesfatin-1 (nesfatin), visfatin/PBEF/NAMPT, apelin, retinol binding protein 4 (RPB4), and plasminogen activator inhibitor-1 (PAI-1) in the regulation of insulin resistance and vascular function, as well as many aspects of inflammation and immunity and their potential role in managing obesity-associated diseases, including metabolic, osteoarticular, and cardiovascular diseases.

Aging differentially modulates the Wnt pro-survival signalling pathways in vascular smooth muscle cells

We previously reported pro-survival effects of Wnt3a and Wnt5a proteins in vascular smooth muscle cells (VSMCs). Wnt5a achieved this through induction of Wnt1-inducible signalling pathway protein-1 (WISP-1) consequent to β-catenin/CREB-dependent, TCF-independent, signalling. However, we found that as atherosclerosis advances, although Wnt5a protein was increased, WISP-1 was reduced. We hypothesized this disconnect could be due to aging. In this study, we elucidate the mechanism underlying Wnt3a pro-survival signalling and demonstrate the differential effect of age on Wnt3a- and Wnt5a-mediated survival. We show Wnt3a protein was expressed in human atherosclerotic coronary arteries and co-located with macrophages and VSMCs. Meanwhile, Wnt3a stimulation of primary mouse VSMCs increased β-catenin nuclear translocation and TCF, but not CREB, activation. Wnt3a increased mRNA expression of the pro-survival factor WISP-2 in a TCF-dependent manner. Functionally, β-catenin/TCF inhibition or WISP-2 neutralization significantly impaired Wnt3a-mediated VSMC survival. WISP-2 was upregulated in human atherosclerosis and partly co-localized with Wnt3a. The pro-survival action of Wnt3a was effective in VSMCs from young (2 month) and old (18-20 month) mice, whereas Wnt5a-mediated rescue was impaired with age. Further investigation revealed that although Wnt5a induced β-catenin nuclear translocation in VSMCs from both ages, CREB phosphorylation and WISP-1 upregulation did not occur in old VSMCs. Unlike Wnt5a, pro-survival Wnt3a signalling involves β-catenin/TCF and WISP-2. While Wnt3a-mediated survival was unchanged with age, Wnt5a-mediated survival was lost due to impaired CREB activation and WISP-1 regulation. Greater understanding of the effect of age on Wnt signalling may identify targets to promote VSMC survival in elderly patients with atherosclerosis.

The emerging role of WISP proteins in tumorigenesis and cancer therapy

Accumulated evidence has demonstrated that WNT1 inducible signaling pathway protein (WISP) genes, which belong to members of the CCN growth factor family, play a pivotal role in tumorigenesis and progression of a broad spectrum of human cancers. Mounting studies have identified that WISP proteins (WISP1-3) exert different biological functions in various human malignancies. Emerging evidence indicates that WISP proteins are critically involved in cell proliferation, apoptosis, invasion and metastasis in cancers. Because the understanding of a direct function of WISP proteins in cancer development and progression has begun to emerge, in this review article, we describe the physiological function of WISP proteins in a variety of human cancers. Moreover, we highlight the current understanding of how the WISP protein is involved in tumorigenesis and cancer progression. Furthermore, we discuss that targeting WISP proteins could be a promising strategy for the treatment of human cancers. Hence, the regulation of WISP proteins could improve treatments for cancer patients.

The role of CCN4/WISP-1 in the cancerous phenotype

CCN proteins are secreted into the extracellular environment where they interact with both components of the extracellular matrix and with cell surface receptors to regulate cellular function. Through these interactions, CCNs act as extracellular ligands to activate intracellular signal transduction pathways. CCN4/WISP-1, like other CCNs, plays multiple physiologic roles in development and also participates in pathogenesis. CCN4 is of particular interest with respect to cancer, showing promise as a biomarker or prognostic factor as well as a potential therapeutic target. This review focuses on recent work addressing the role of CCN4 in cancer. While CCN4 has been identified as an oncogene in a number of cancers, where it enhances cell migration and promoting epithelial-mesenchymal transition, there are other cancers where CCN4 appears to play an inhibitory role. The mechanisms underlying these differences in cellular response have not yet been delineated, but are an active area of investigation. The expression and activities of CCN4 splice variants are likewise an emerging area for study. CCN4 acts as an autocrine factor that regulates the cancer cells from which it is secreted. However, CCN4 is also a paracrine factor that is secreted by stromal fibroblasts, and can affect the function of vascular endothelial cells. In summary, current evidence is abundant in regard to establishing potential roles for CCN4 in oncogenesis, but much remains to be learned about the functions of this fascinating protein as both an autocrine and paracrine regulator in the tumor microenvironment.

Assessment of circulating Wnt1 inducible signalling pathway protein 1 (WISP-1)/CCN4 as a novel biomarker of obesity

WNT1 inducible signaling pathway protein 1 (WISP-1/CCN4) is a novel adipokine, which is upregulated in obesity, and induces a pro-inflammatory response in macrophages in-vitro. Preclinical observations suggested WISP-1/CCN4 as a potential candidate for novel obesity therapy targeting adipose tissue inflammation. Whether circulating levels of WISP-1/CCN4 in humans are altered in obesity and/or type 2 diabetes (T2DM) and in the postprandial state, however, is unknown. This study assessed circulating WISP-1/CCN4 levels in a) paired liquid meal tests and hyperinsulinemic- euglycemic clamps (cohort I, n = 26), b) healthy individuals (cohort II, n = 207) and c) individuals with different stages of obesity and glucose tolerance (cohort III, n = 253). Circulating plasma and serum WISP-1/CCN4 concentrations were measured using a commercially available ELISA. WISP-1/CCN4 levels were not influenced by changes in insulin and/or glucose during the tests. In healthy individuals, WISP-1/CCN4 was detectable in 13% of plasma samples with the intraclass correlation coefficient of 0.93 (95% CI: 0.84-0.96) and in 58.1% of the serum samples in cohort III. Circulating WISP-1/CCN4 positively correlated with body mass index, body fat percentage, leptin and triglyceride levels, hip circumference and fatty liver index. No differences in WISP-1/CCN4 levels between individuals with normal glucose tolerance, impaired glucose tolerance and T2DM were found. The circulating concentrations of WISP-1/CCN4 showed no acute regulation in postprandial state and correlated with anthropometrical obesity markers and lipid profiles. In healthy individuals, WISP-1/CCN4 levels are more often below the detection limit. Thus, serum WISP-1/CCN4 levels may be used as a suitable biomarker of obesity.

Immunohistochemical Analysis of CCN Proteins in Calcified Tissues

Immunohistochemistry is a major technique to determine the distribution and localization of differentially produced proteins in the context of an intact tissue. It exploits one of the properties of antibodies, specific binding to an antigen, i.e., to the epitope of its target protein, in combination with a color-developing enzymatic reaction or tagged fluorophore. We have clarified the spatial and temporal expression patterns of CCN family proteins in several different types of animal tissues by using this immunohistochemical technique to support our corresponding data obtained in vitro. In this chapter, we provide our protocol for immunohistochemistry optimized for paraffin-embedded sections after having determined the optimal conditions for the use of antibodies against each member of the CCN family.

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.

CCN4/WISP-1 positively regulates chondrogenesis by controlling TGF-β3 function

The CCN family of proteins plays important roles in development and homeostasis of bone and cartilage. To understand the role of CCN4 in chondrogenesis, human bone marrow stromal cells (hBMSCs) were transduced with CCN4 adenovirus (adCCN4) or siRNA to CCN4 (siCCN4) in the presence or absence of transforming growth factor-β3 (TGF-β3). Overexpression of CCN4 enhanced TGF-β3-induced SMAD2/3 phosphorylation and chondrogenesis of hBMSCs in an in vitro assay using a micromass culture model. On the other hand, knockdown of CCN4 inhibited the TGF-β3-induced SMAD2/3 phosphorylation and synthesis of cartilage matrix in micromass cultures of hBMSCs. Immunoprecipitation-western blot analysis revealed that CCN4 bound to TGF-β3 and regulated the ability of TGF-β3 to bind to hBMSCs. In vivo analysis confirmed there was a significant decrease in the gene expression levels of chondrocyte markers in cartilage samples from Ccn4-knock out (KO) mice, compared to those from wild type (WT) control. In order to investigate the regenerative properties of the articular cartilage in Ccn4-KO mice, articular cartilage defects were surgically performed in the knee joints of young mice, and the results showed that the cartilage was partially repaired in WT mice, but not in Ccn4-KO mice. In conclusion, these results show, for the first time, that CCN4 has a positive influence on chondrogenic differentiation by modulating the effects of TGF-β3.

Dual effect of WISP-1 in diverse pathological processes

Wnt-1 inducible signaling pathway-1 (WISP-1), also known as CCN-4, belongs to the connective tissue growth factor (CTGF) family. WISP-1 is primarily expressed in embryonic stem cells and is involved in adult organ development. WISP-1 participates in many cellular processes, including proliferation, differentiation, apoptosis and adhesion. In addition, WISP-1 plays an important role in diverse pathophysiological processes, such as embryonic development, inflammation, injury repairs and cancers. Recent studies showed that WISP-1 was highly correlated with tumor progression and malignant transformation, whereas it played an oncogenic role in colorectal cancer, cholangiocarcinoma, hepatocellular carcinoma and breast cancer. However, interestingly, WISP-1 exerts a tumor-suppressing role in lung and prostate cancers. WISP-1 promotes cell proliferation, adhesion, motility, invasion, metastasis and epithelial-to-mesenchymal transition via particular signaling pathways. In this review, we discussed the structure, expression profile, functions, clinical significance and potential mechanisms of WISP-1 in cancer and non-neoplastic diseases.

Eyeing the Cyr61/CTGF/NOV (CCN) group of genes in development and diseases: highlights of their structural likenesses and functional dissimilarities

“CCN” is an acronym referring to the first letter of each of the first three members of this original group of mammalian functionally and phylogenetically distinct extracellular matrix (ECM) proteins [i.e., cysteine-rich 61 (CYR61), connective tissue growth factor (CTGF), and nephroblastoma-overexpressed (NOV)]. Although “CCN” genes are unlikely to have arisen from a common ancestral gene, their encoded proteins share multimodular structures in which most cysteine residues are strictly conserved in their positions within several structural motifs. The CCN genes can be subdivided into members developmentally indispensable for embryonic viability (e.g., CCN1, 2 and 5), each assuming unique tissue-specific functions, and members not essential for embryonic development (e.g., CCN3, 4 and 6), probably due to a balance of functional redundancy and specialization during evolution. The temporo-spatial regulation of the CCN genes and the structural information contained within the sequences of their encoded proteins reflect diversity in their context and tissue-specific functions. Genetic association studies and experimental anomalies, replicated in various animal models, have shown that altered CCN gene structure or expression is associated with “injury” stimuli—whether mechanical (e.g., trauma, shear stress) or chemical (e.g., ischemia, hyperglycemia, hyperlipidemia, inflammation). Consequently, increased organ-specific susceptibility to structural damages ensues. These data underscore the critical functions of CCN proteins in the dynamics of tissue repair and regeneration and in the compensatory responses preceding organ failure. A better understanding of the regulation and mode of action of each CCN member will be useful in developing specific gain- or loss-of-function strategies for therapeutic purposes.

The role of CCN family genes in haematological malignancies

Haematological malignancies, although a broad range of specific disease types, continue to show considerable overlap in classification, and patients are treated using similar chemotherapy regimes. In this review we look at the role of the CCN family of matricellular proteins and indicate their role in nine haematological malignancies including both myeloid and lymphoid neoplasms. The potential for further haematological neoplasms with CCN family associations is argued by summarising the demonstrated role of CCN family genes in the differentiation of haematopoietic stem cells (HSC) and mesenchymal stem cells. The expanding field of knowledge encompassing CCN family genes and cancers of the HSC-lineage highlights the importance of extracellular matrix-interactions in both normal physiology and tumorigenesis of the blood, bone marrow and lymph nodes.

CCN4/WISP1 (WNT1 inducible signaling pathway protein 1): a focus on its role in cancer

The matricellular protein WISP1 is a member of the CCN protein family. It is induced by WNT1 and is a downstream target of β-catenin. WISP1 is expressed during embryonic development, wound healing and tissue repair. Aberrant WISP1 expression is associated with various pathologies including osteoarthritis, fibrosis and cancer. Its role in tumor progression and clinical outcome makes WISP1 an emerging candidate for the detection and treatment of tumors.

WISP1 is a novel adipokine linked to inflammation in obesity

WISP1 (Wnt1-inducible signaling pathway protein-1, also known as CCN4) is a member of the secreted extracellular matrix-associated proteins of the CCN family and a target gene of the Wingless-type (WNT) signaling pathway. Growing evidence links the WNT signaling pathway to the regulation of adipogenesis and low-grade inflammation in obesity. We aimed to validate WISP1 as a novel adipokine. Human adipocyte differentiation was associated with increased WISP1 expression and secretion. Stimulation of human macrophages with WISP1 led to a proinflammatory response. Circulating WISP1 and WISP1 subcutaneous adipose tissue expression were regulated by weight changes in humans and mice. WISP1 expression in visceral and subcutaneous fat tissue was associated with markers of insulin resistance and inflammation in glucose-tolerant subjects. In patients with nonalcoholic fatty liver disease, we found no correlation among disease activity score, liver fat content, and WISP1 expression. Insulin regulated WISP1 expression in adipocytes in vitro but had no acute effect on WISP1 gene expression in subcutaneous fat tissue in overweight subjects who had undergone hyperinsulinemic clamp experiments. The data suggest that WISP1 may play a role in linking obesity to inflammation and insulin resistance and could be a novel therapeutic target for obesity.

A functional analysis of Wnt inducible signalling pathway protein -1 (WISP-1/CCN4)

Wnt-1 inducible signalling pathway protein 1 (WISP-1/CCN4) is an extracellular matrix protein that belongs to the Cyr61 (cysteine-rich protein 61), CTGF (connective tissue growth factor) and NOV (CCN) family and plays a role in multiple cellular processes. No specific WISP-1 receptors have been identified but emerging evidence suggests WISP-1 mediates its downstream effects by binding to integrins. Here we describe a functional analysis of integrin receptor usage by WISP-1. Truncated WISP-1 proteins were produced using a baculovirus expression system. Full length WISP-1 and truncated proteins were evaluated for their ability to induce adhesion in A549 epithelial cells and β-catenin activation and CXCL3 secretion in fibroblasts (NRK49-F cells). Subsequent inhibition of these responses by neutralising integrin antibodies was evaluated. A549 cells demonstrated adhesion to full-length WISP-1 whilst truncated proteins containing VWC, TSP or CT domains also induced adhesion, with highest activity observed with proteins containing the C-terminal TSP and CT domains. Likewise the ability to induce β-catenin activation and CXCL3 secretion was retained in truncations containing C-terminal domains. Pre-treatment of A549s with either integrin αVβ5, αVβ3 or β1 neutralising antibodies partially inhibited full length WISP-1 induced adhesion whilst combining integrin αVβ5 and β1 antibodies increased the potency of this effect. Incubation of NRK49-F cells with integrin neutralising antibodies failed to effect β-catenin translocation or CXCL3 secretion. Analysis of natural WISP-1 derived from human lung tissue showed the native protein is a high order oligomer. Our data suggest that WISP-1 mediated adhesion of A549 cells is an integrin-driven event regulated by the C-terminal domains of the protein. Activation of β-catenin signalling and CXCL3 secretion also resides within the C-terminal domains of WISP-1 but are not regulated by integrins. The oligomeric nature of native WISP-1 may drive a high avidity interaction with these receptors in vivo.

WISP 1 is an important survival factor in human mesenchymal stromal cells

WNT-induced secreted protein 1 (WISP1/CCN4), a member of the CCN protein family, acts as a downstream factor of the canonical WNT signaling pathway. Its expression is known to affect proliferation and differentiation of human mesenchymal stromal cells (hMSCs), which are fundamental for the development and maintenance of the musculoskeletal system. Whereas a dysregulated, excessive expression of WISP1 often reflects its oncogenic potential via the inhibition of apoptosis, our study emphasizes the importance of WISP1 signaling for the survival of primary human cells. We have established the efficient and specific down-regulation of endogenous WISP1 transcripts by gene silencing in hMSCs and observed cell death as a consequence of WISP1 deficiency. This was confirmed by Annexin V staining for apoptotic cells. DNA microarray analyses of WISP1 down-regulated versus control samples revealed several clusters of differentially expressed genes important for apoptosis induction such as TNF-related apoptosis-inducing ligand 1 (TRAIL) and the corresponding apoptosis-inducing receptors TRAIL-R1 and -R2. An increased expression of TRAIL and its receptors TRAIL-R1 and -R2 in WISP1-deficient hMSCs was confirmed by immunocytofluorescence. Accordingly, WISP1 deficiency is likely to cause TRAIL-induced apoptosis. This is an important novel finding, which suggests that WISP1 is indispensable for the protection of healthy hMSCs against TRAIL-induced apoptosis.

Core binding factor beta functions in the maintenance of stem cells and orchestrates continuous proliferation and differentiation in mouse incisors

Rodent incisors grow continuously throughout life, and epithelial progenitor cells are supplied from stem cells in the cervical loop. We report that epithelial Runx genes are involved in the maintenance of epithelial stem cells and their subsequent continuous differentiation and therefore growth of the incisors. Core binding factor β (Cbfb) acts as a binding partner for all Runx proteins, and targeted inactivation of this molecule abrogates the activity of all Runx complexes. Mice deficient in epithelial Cbfb produce short incisors and display marked underdevelopment of the cervical loop and suppressed epithelial Fgf9 expression and mesenchymal Fgf3 and Fgf10 expression in the cervical loop. In culture, FGF9 protein rescues these phenotypes. These findings indicate that epithelial Runx functions to maintain epithelial stem cells and that Fgf9 may be a target gene of Runx signaling. Cbfb mutants also lack enamel formation and display downregulated Shh mRNA expression in cells differentiating into ameloblasts. Furthermore, Fgf9 deficiency results in a proximal shift of the Shh expressing cell population and ectopic FGF9 protein suppresses Shh expression. These findings indicate that Shh as well as Fgf9 expression is maintained by Runx/Cbfb but that Fgf9 antagonizes Shh expression. The present results provide the first genetic evidence that Runx/Cbfb genes function in the maintenance of stem cells in developing incisors by activating Fgf signaling loops between the epithelium and mesenchyme. In addition, Runx genes also orchestrate continuous proliferation and differentiation by maintaining the expression of Fgf9 and Shh mRNA.

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.

Roles of heparan sulfate sulfation in dentinogenesis

Cell surface heparan sulfate (HS) is an essential regulator of cell signaling and development. HS traps signaling molecules, like Wnt in the glycosaminoglycan side chains of HS proteoglycans (HSPGs), and regulates their functions. Endosulfatases Sulf1 and Sulf2 are secreted at the cell surface to selectively remove 6-O-sulfate groups from HSPGs, thereby modifying the affinity of cell surface HSPGs for its ligands. This study provides molecular evidence for the functional roles of HSPG sulfation and desulfation in dentinogenesis. We show that odontogenic cells are highly sulfated on the cell surface and become desulfated during their differentiation to odontoblasts, which produce tooth dentin. Sulf1/Sulf2 double null mutant mice exhibit a thin dentin matrix and short roots combined with reduced expression of dentin sialophosphoprotein (Dspp) mRNA, encoding a dentin-specific extracellular matrix precursor protein, whereas single Sulf mutants do not show such defective phenotypes. In odontoblast cell lines, Dspp mRNA expression is potentiated by the activation of the Wnt canonical signaling pathway. In addition, pharmacological interference with HS sulfation promotes Dspp mRNA expression through activation of Wnt signaling. On the contrary, the silencing of Sulf suppresses the Wnt signaling pathway and subsequently Dspp mRNA expression. We also show that Wnt10a protein binds to cell surface HSPGs in odontoblasts, and interference with HS sulfation decreases the binding affinity of Wnt10a for HSPGs, which facilitates the binding of Wnt10a to its receptor and potentiates the Wnt signaling pathway, thereby up-regulating Dspp mRNA expression. These results demonstrate that Sulf-mediated desulfation of cellular HSPGs is an important modification that is critical for the activation of the Wnt signaling in odontoblasts and for production of the dentin matrix.

Differential roles of CCN family proteins during osteoblast differentiation: Involvement of Smad and MAPK signaling pathways

CCN family proteins play diverse roles in many aspects of cellular processes such as proliferation, differentiation, adhesion, migration, angiogenesis and survival. In the bone tissue of vertebrate species, the expression of most CCN family members has been observed in osteoblasts. However, their spatial and temporal distributions, as well as their functions, are still only partially understood. In this study, we evaluated the localization of CCN family members in skeletal tissue in vivo and comparatively analyzed the gene expression patterns and functions of the members in murine osteoblasts in primary culture. Immunofluorescent analyses revealed that the CCN family members were differentially produced in osteoblasts and osteocytes. The presence of all Ccn transcripts was confirmed in those osteoblasts. Among the members, CCN1, CCN2, CCN4 and CCN5 were found in osteocytes. CCN4 and CCN5 were distributed in osteocytes located inside of bone matrix as well. Next, we investigated the expression pattern of Ccn family members during osteoblast differentiation. Along with differentiation, most of the members followed proper gene expression patterns; whereas, Ccn4 and Ccn5 showed quite similar patterns. Furthermore, we evaluated the effects of CCN family members on the osteoblastic activities by using recombinant CCN proteins and RNA interference method. Five members of this family displayed positive effects on osteoblast proliferation or differentiation. Of note, CCN3 drastically inhibited the osteoblast activities. Each Ccn specific siRNA could modulate osteoblast activities in a manner expected by the observed effect of respective recombinant CCN protein. In addition, we found that extracellular signal-regulated kinase1/2 and p38 mitogen-activated protein kinase pathways were critically involved in the CCN family member-mediated modification of osteoblast activities. Collectively, all Ccn family members were found to be differentially expressed along with differentiation and therefore could participate in progression of the osteoblast lineage.

Novel effects of CCN3 that may direct the differentiation of chondrocytes

Identification and characterization of local molecules directing the differentiation of chondrocytes to either transient or permanent cartilage are major issues in cartilage biology. Here, we found CCN family protein 3 (CCN3) was abundantly produced in rat developing epiphyseal cartilage. Evaluations in vitro showed that CCN3 repressed epiphyseal chondrocyte proliferation, while promoting matrix production in multiple assays performed. Furthermore, CCN3 enhanced the articular chondrocytic phenotype; whereas it repressed the one representing endochondral ossification. Additionally, the phenotype of growth plate chondrocytes and chondrogenic progenitors also appeared to be affected by CCN3 in a similar manner. These findings suggest a significant role of CCN3 in inducing chondrocytes to articular ones during joint formation.

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.

Association of the metastatic phenotype with CCN family members among breast and oral cancer cells

The CCN family of proteins consists of six members with conserved structural features. These proteins play several roles in the physiology and pathology of cells. Among the pathological roles of the CCN family, one of the most important and controversial ones is their role in the expansion and metastasis of cancer. Up to now a number of reports have described the possible role of each CCN family member independently. In this study, we comprehensively analyzed the roles of all six CCN family members in cell growth, migration and invasion of breast cancer cells in vitro and in vivo. As a result, we found the CCN2/CCN3 ratio to be a parameter that is associated with the metastatic phenotype of breast cancer cells that are highly metastatic to the bone. The same analysis with cell lines from oral squamous carcinomas that are not metastatic to the bone further supported our notion. These results suggest the functional significance of the interplay between CCN family members in regulating the phenotype of cancer cells.

WNT1 inducible signaling pathway protein 1 (WISP1): a novel mediator linking development and disease

WISP1 is a secreted, matricellular protein allocated to the CCN protein family. The CCN protein family consists of six, modular structured, secreted proteins. WISP1 is mainly expressed during organ development and under diseased conditions, such as fibrosis or cancer. Its expression is associated with proliferation, cytoprotection, as well as extracellular matrix production, thereby representing a highly attractive therapeutical target for future applications.

The CCN proteins: important signaling mediators in stem cell differentiation and tumorigenesis

The CCN proteins contain six members, namely CCN1 to CCN6, which are small secreted cysteine-rich proteins. The CCN proteins are modular proteins, containing up to four functional domains. Many of the CCN members are induced by growth factors, cytokines, or cellular stress. The CCNs show a wide and highly variable expression pattern in adult and in embryonic tissues. The CCN proteins can integrate and modulate the signals of integrins, BMPs, VEGF, Wnts, and Notch. The involvement of integrins in mediating CCN signaling may provide diverse context-dependent responses in distinct cell types. CCN1 and CCN2 play an important role in development, angiogenesis and cell adhesion, whereas CCN3 is critical to skeletal and cardiac development. CCN4, CCN5 and CCN6 usually inhibit cell growth. Mutations of Ccn6 are associated with the progressive pseudorheumatoid dysplasia and spondyloepiphyseal dysplasia tarda. In stem cell differentiation, CCN1, CCN2, and CCN3 play a principal role in osteogenesis, chondrogenesis, and angiogenesis. Elevated expression of CCN1 is associated with more aggressive phenotypes of human cancer, while the roles of CCN2 and CCN3 in tumorigenesis are tumor type-dependent. CCN4, CCN5 and CCN6 function as tumor suppressors. Although CCN proteins may play important roles in fine-tuning other major signaling pathways, the precise function and mechanism of action of these proteins remain undefined. Understanding of the biological functions of the CCN proteins would not only provide insight into their roles in numerous cellular processes but also offer opportunities for developing therapeutics by targeting CCN functions.

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.

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.

Differential transcriptome analysis of intraarticular lesional vs intact cartilage reveals new candidate genes in osteoarthritis pathophysiology

OBJECTIVE

To elucidate disease-specific molecular changes in osteoarthritis (OA) by analyzing the differential gene expression profile of damaged vs intact cartilage areas within the same joint of patients with OA of the knee using a combination of a novel RNA extraction technique and whole-genome oligonucleotide arrays.

METHODS

The transcriptome of macroscopically affected vs intact articular cartilage as determined by visual assessment was analyzed using an optimized mill-based total RNA isolation directly from the tissue and high density synthetic oligonucleotide arrays. Articular cartilage samples were obtained from patients with OA of the knee. Expression of differentially regulated genes was validated by real-time quantitative polymerase chain reaction and immunohistochemistry.

RESULTS

The amount of RNA obtained by the optimized extraction procedure was at least 1 microg per 500 mg of cartilage and fulfilled the common quality requirements. After hybridization onto HG-U133 Plus 2.0 GeneChips (Affymetrix), 28.6-51.7% of the probe sets on the microarray showed a detectable signal above the signal threshold in the individual samples. A subset of 411 transcripts, which appeared to be differentially expressed, was obtained when applying predefined filtering criteria. Of these, six genes were found to be up-regulated in the affected cartilage of all patients, including insulin-like growth factor binding protein 3 (IGFBP-3), wnt-1-inducible signaling protein 1 (WISP-1), aquaporin 1 (AQP-1), delta/notch-like EGF-repeat containing transmembrane (DNER), decay accelerating factor (DAF), complement factor I (IF).

CONCLUSION

The optimized methodical approach reported here not only allows to determine area-specific gene expression profiles of intraindividually different low-RNA containing OA cartilage specimens. In addition, this study also revealed novel genes not yet reported to play a role in the pathophysiology of joint destruction in OA.

Regulation of chondrocytic phenotype by micro RNA 18a: involvement of Ccn2/Ctgf as a major target gene

We searched for miRNAs that were down-regulated in chondrocytic cells and predicted to target CCN2/connective tissue growth factor (CCN2/CTGF) that promotes endochondral ossification. Among them, expression of miR-18a was most strongly repressed in chondrocytic cells. Reporter gene analysis confirmed the functionality of an miR-18a target in the 3'-untranslated region of Ccn2 mRNA, which was predicted in silico. Indeed, introduction of miR-18a efficiently repressed the CCN2 production from chondrocytic cells. Finally, transfected miR-18a significantly repressed the mature chondrocytic phenotype. Our present study revealed a regulatory role for miR-18a in chondrocytic differentiation through CCN2.

Cooperative regulation of chondrocyte differentiation by CCN2 and CCN3 shown by a comprehensive analysis of the CCN family proteins in cartilage

CCN2 is best known as a promoter of chondrocyte differentiation among the CCN family members, and its null mice display skeletal dysmorphisms. However, little is known concerning roles of the other CCN members in chondrocytes. Using both in vivo and in vitro approaches, we conducted a comparative analysis of CCN2-null and wildtype mice to study the roles of CCN2 and the other CCN proteins in cartilage development. Immunohistochemistry was used to evaluate the localization of CCN proteins and other chondrocyte-associated molecules in the two types of mice. Moreover, gene expression levels and the effects of exogenous CCN proteins on chondrocyte proliferation, differentiation, and the expression of chondrocyte-associated genes in their primary chondrocytes were evaluated. Ccn3 was dramatically upregulated in CCN2-null cartilage and chondrocytes. This upregulation was associated with diminished cell proliferation and delayed differentiation. Consistent with the in vivo findings, CCN2 deletion entirely retarded chondrocyte terminal differentiation and decreased the expression of several chondrocyte-associated genes in vitro, whereas Ccn3 expression drastically increased. In contrast, the addition of exogenous CCN2 promoted differentiation strongly and induced the expression of the associated genes, whereas decreasing the Ccn3 expression. These findings collectively indicate that CCN2 induces chondrocyte differentiation by regulating the expression of chondrocyte-associated genes but that these effects are counteracted by CCN3. The lack of CCN2 caused upregulation of CCN3 in CCN2-null mice, which resulted in the observed phenotypes, such as the resultant delay of terminal differentiation. The involvement of the PTHrP-Ihh loop in the regulation of CCN3 expression is also suggested.

TGF-beta1 and WISP-1/CCN-4 can regulate each other's activity to cooperatively control osteoblast function

Wnt-induced secreted protein-1 (WISP-1), like other members of the CCN family, is expressed in skeletal tissues. Its mechanism of action remains unknown. Expression of WISP-1 was analyzed in human bone marrow stroma cells (hBMSC) by RT-PCR. We identified two major transcripts corresponding to those of full-length WISP-1, and of the splice variant WISP-1va which lacks a putative BMP/TGF-beta binding site. To investigate the function of WISP-1 in bone, hBMSC cultures were treated with recombinant human (rh)WISP-1 and analyzed for proliferation and osteogenic differentiation. WISP-1 treatment increased both BrdU incorporation and alkaline phosphatase (AP) activity. Considering the known functional synergy found between the TGF-beta super-family and members of the CCN family, we next tested the effect of WISP-1 on TGF-beta1 activity. We found that rhWISP-1 could reduce rhTGF-beta1 induced BrdU incorporation. Similarly, rhTGF-beta1 inhibited rhWISP-1 induction of AP activity. To explore functional differences between the WISP-1 variants, WISP-1 or WISP-1va were transfected into hBMSC. Both variants could strongly induce BrdU incorporation. However, there were no effects of either variant on AP activity without an additional osteogenic stimulus such as TGF-beta1. Taken together our results suggest a functional relationship between WISP-1 and TGF-beta1. To further define this relationship we analyzed the effect of WISP-1 on TGF-beta signaling. rhWISP-1 significantly reduced TGF-beta1 induced phosphorylation of Smad-2. Our data indicates that full-length WISP-1 and its variant WISP-1va are modulators of proliferation and osteogenic differentiation, and may be novel regulators of TGF-beta1 signaling in osteoblast-like cells.

Posttranscriptional regulation of chicken ccn2 gene expression by nucleophosmin/B23 during chondrocyte differentiation

CCN2/CTGF is a multifunctional factor that plays a crucial role in the growth and differentiation of chondrocytes. The chicken ccn2 gene is regulated not only at the transcriptional level but also by the interaction between a posttranscriptional element in the 3' untranslated region (3'-UTR) and a cofactor. In the present study, we identified a nucleophosmin (NPM) (also called B23) as this cofactor. Binding of NPM to the element was confirmed, and subsequent analysis revealed a significant correlation between the decrease in cytosolic NPM and the increased stability of the ccn2 mRNA during chondrocyte differentiation in vivo. Furthermore, recombinant chicken NPM enhanced the degradation of chimeric RNAs containing the posttranscriptional cis elements in a chicken embryonic fibroblast extract in vitro. It is noteworthy that the RNA destabilization effect by NPM was far more prominent in the cytosolic extract of chondrocytes than in that of fibroblasts, representing a chondrocyte-specific action of NPM. Stimulation by growth factors to promote differentiation changed the subcellular distribution of NPM in chondrocytes, which followed the expected patterns from the resultant change in the ccn2 mRNA stability. Therefore, the present study reveals a novel aspect of NPM as a key player in the posttranscriptional regulation of ccn2 mRNA during the differentiation of chondrocytes.

CCN3-mutant mice are distinct from CCN3-null mice

A recent manuscript reported phenotypic alterations associated to the expression of a CCN3 protein deleted for the Von Willebrand type C repeat that is common to the various members of the CCN family of proteins. In this comment, the biological significance of these alterations is briefly discussed.

Functional requirement of CCN2 for intramembranous bone formation in embryonic mice

CCN2 is best known as a promoter of chondrocyte differentiation among the CCN family members, and Ccn2 null mutant mice display skeletal dysmorphisms. However, little is known concerning the roles of CCN2 during bone formation. We herein present a comparative analysis of wild-type and Ccn2 null mice to investigate the roles of CCN2 in bone development. Multiple histochemical methods were employed to analyze the effects of CCN2 deletion in vivo, and effects of CCN2 on the osteogenic response were evaluated with the isolated and cultured osteoblasts. As a result, we found a drastic reduction of the osteoblastic phenotype in Ccn2 null mutants. Importantly, addition of exogenous CCN2 promoted every step of osteoblast differentiation and rescued the attenuated activities of the Ccn2 null osteoblasts. These results suggest that CCN2 is required not only for the regulation of cartilage and subsequent events, but also for the normal intramembranous bone development.

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

CCN3 is a member of the CCN family of cell growth and differentiation regulators that play key roles during embryonic development, and are associated with severe human pathologies. The level of CCN genes' expression is of prognostic value in several types of tumors. In the present manuscript, we report the isolation and characterization of a new set of antibodies targeted against each individual module of the human CCN3 protein. The need for module-specific antibodies stemmed from recent reports indicating that the expression of truncated CCN variant proteins was associated with development of cancers. Each of the four CCN3 modules were expressed as GST fusion proteins and used for rabbits immunization. Polyclonal IgGs purified by two rounds of affinity-chromatography specifically detected both the individual CCN3 domains and the full length CCN3 protein expressed in mammalian cell lines and tissues, as well as recombinant full length and truncated CCN3 proteins. The purified module-specific antibodies were successfully used for Western blotting, immunoprecipitation, immunofluorescence and immunocytochemistry. These antibodies permitted the detection of CCN3 proteins under native and denaturing conditions, and confirmed the sublocalisation of CCN3 proteins in the extracellular compartment, at the cell membrane, in the cytoplasm and in the nucleus of positive cells. Immunocytochemistry and Western blotting studies performed with the module-specific antibodies identified truncated CCN3 proteins in kidney tumor samples. The detection of these rearranged variants provides clues for their involvement in tumorigenesis. Therefore, these antibodies constitute unique tools for the identification of truncated CCN3 proteins in human tissues and may be of great interest in molecular medicine.