Novel intracellular effects of human connective tissue growth factor expressed in Cos-7 cells

Embracing the complexity of matricellular proteins: the functional and clinical significance of splice variation

Matricellular proteins influence wide-ranging fundamental cellular processes including cell adhesion, migration, growth and differentiation. They achieve this both through interactions with cell surface receptors and regulation of the matrix environment. Many matricellular proteins are also associated with diverse clinical disorders including cancer and diabetes. Alternative splicing is a precisely regulated process that can produce multiple isoforms with variable functions from a single gene. To date, the expression of alternate transcripts for the matricellular family has been reported for only a handful of genes. Here we analyse the evidence for alternative splicing across the matricellular family including the secreted protein acidic and rich in cysteine (SPARC), thrombospondin, tenascin and CCN families. We find that matricellular proteins have double the average number of splice variants per gene, and discuss the types of domain affected by splicing in matricellular proteins. We also review the clinical significance of alternative splicing for three specific matricellular proteins that have been relatively well characterised: osteopontin (OPN), tenascin-C (TNC) and periostin. Embracing the complexity of matricellular splice variants will be important for understanding the sometimes contradictory function of these powerful regulatory proteins, and for their effective clinical application as biomarkers and therapeutic targets.

Connective Tissue Metabolism and Gingival Overgrowth

Gingival overgrowth occurs mainly as a result of certain anti-seizure, immunosuppressive, or antihypertensive drug therapies. Excess gingival tissues impede oral function and are disfiguring. Effective oral hygiene is compromised in the presence of gingival overgrowth, and it is now recognized that this may have negative implications for the systemic health of affected patients. Recent studies indicate that cytokine balances are abnormal in drug-induced forms of gingival overgrowth. Data supporting molecular and cellular characteristics that distinguish different forms of gingival overgrowth are summarized, and aspects of gingival fibroblast extracellular matrix metabolism that are unique to gingival tissues and cells are reviewed. Abnormal cytokine balances derived principally from lymphocytes and macrophages, and unique aspects of gingival extracellular matrix metabolism, are elements of a working model presented to facilitate our gaining a better understanding of mechanisms and of the tissue specificity of gingival overgrowth.

Matricellular proteins in drug delivery: Therapeutic targets, active agents, and therapeutic localization

Extracellular matrix is composed of a complex array of molecules that together provide structural and functional support to cells. These properties are mainly mediated by the activity of collagenous and elastic fibers, proteoglycans, and proteins such as fibronectin and laminin. ECM composition is tissue-specific and could include matricellular proteins whose primary role is to modulate cell-matrix interactions. In adults, matricellular proteins are primarily expressed during injury, inflammation and disease. Particularly, they are closely associated with the progression and prognosis of cardiovascular and fibrotic diseases, and cancer. This review aims to provide an overview of the potential use of matricellular proteins in drug delivery including the generation of therapeutic agents based on the properties and structures of these proteins as well as their utility as biomarkers for specific diseases.

Evolutionary emergence of a novel splice variant with an opposite effect on the cell cycle

Alternative splicing contributes greatly to the diversification of mammalian proteomes, but the molecular basis for the evolutionary emergence of splice variants remains poorly understood. We have recently found a novel class of splicing regulatory elements between the polypyrimidine tract (Py) and 3' AG (REPA) at intron ends in many human genes, including the multifunctional PRMT5 (for protein arginine methyltransferase 5) gene. The PRMT5 element is comprised of two G tracts that arise in most mammals and accompany significant exon skipping in human transcripts. The G tracts inhibit splicing by recruiting heterogeneous nuclear ribonucleoprotein (hnRNP) H and F (H/F) to reduce U2AF65 binding to the Py, causing exon skipping. The resulting novel shorter variant PRMT5S exhibits a histone H4R3 methylation effect similar to that seen with the original longer PRMT5L isoform but exhibits a distinct localization and preferential control of critical genes for cell cycle arrest at interphase in comparison to PRMT5L. This report thus provides a molecular mechanism for the evolutionary emergence of a novel splice variant with an opposite function in a fundamental cell process. The presence of REPA elements in a large group of genes implies their wider impact on different cellular processes for increased protein diversity in humans.

Cellular and molecular actions of CCN2/CTGF and its role under physiological and pathological conditions

CCN family protein 2 (CCN2), also widely known as connective tissue growth factor (CTGF), is one of the founding members of the CCN family of matricellular proteins. Extensive investigation on CCN2 over decades has revealed the novel molecular action and functional properties of this unique signalling modulator. By its interaction with multiple molecular counterparts, CCN2 yields highly diverse and context-dependent biological outcomes in a variety of microenvironments. Nowadays, CCN2 is recognized to conduct the harmonized development of relevant tissues, such as cartilage and bone, in the skeletal system, by manipulating extracellular signalling molecules involved therein by acting as a hub through a web. However, on the other hand, CCN2 occasionally plays profound roles in major human biological disorders, including fibrosis and malignancies in major organs and tissues, by modulating the actions of key molecules involved in these clinical entities. In this review, the physiological and pathological roles of this unique protein are comprehensively summarized from a molecular network-based viewpoint of CCN2 functionalities.

CCN family protein 2 (CCN2) promotes the early differentiation, but inhibits the terminal differentiation of skeletal myoblasts

Many studies have reported that CCN family protein 2 (also known as connective tissue growth factor) induces fibrotic response in skeletal muscle, thus emphasizing the pathological role of CCN2 in muscle tissues. However, the physiological role of CCN2 in myogenesis is still unknown. This study clarified the CCN2 functions during myogenesis. Recombinant CCN2 (rCCN2) promoted proliferation and MyoD production in C2C12 cells and primary myoblasts, but inhibited myogenin production. In accordance with these findings, the gene expression levels of myosin heavy chain, which is a marker of terminally differentiated myoblasts and desmin, which is the main intermediate filament protein of muscle cells, were decreased by rCCN2 treatment. In vivo analyses with Ccn2-deficient skeletal muscle revealed decreased proliferating cell nuclear antigen (PCNA)/MyoD double positive cells and muscle hypoplasia. Consistent with this finding, myogenic marker genes and myotube formation were repressed in Ccn2-deficient myoblasts. The protein production of CCN2 was increased in C2C12 myoblasts treated with tumor necrosis factor-α, which is a pro-inflammatory cytokine, suggesting its role in muscle regeneration after inflammation. These findings indicate that CCN2 promotes proliferation and early differentiation but inhibits the terminal differentiation of myoblasts, thus suggesting that CCN2 plays a physiological role in myogenesis.

Compressive force-produced CCN2 induces osteocyte apoptosis through ERK1/2 pathway

Osteocytes produce various factors that mediate the onset of bone formation and resorption and play roles in maintaining bone homeostasis and remodeling in response to mechanical stimuli. One such factor, CCN2, is thought to play a significant role in osteocyte responses to mechanical stimuli, but its function in osteocytes is not well understood. Here, we showed that CCN2 induces apoptosis in osteocytes under compressive force loading. Compressive force increased CCN2 gene expression and production, and induced apoptosis in osteocytes. Application of exogenous CCN2 protein induced apoptosis, and a neutralizing CCN2 antibody blocked loading-induced apoptosis. We further examined how CCN2 induces loaded osteocyte apoptosis. In loaded osteocytes, extracellular signal-regulated kinase 1/2 (ERK1/2) was activated, and an ERK1/2 inhibitor blocked loading-induced apoptosis. Furthermore, application of exogenous CCN2 protein caused ERK1/2 activation, and the neutralizing CCN2 antibody inhibited loading-induced ERK1/2 activation. Therefore, this study demonstrated for the first time to our knowledge that enhanced production of CCN2 in osteocytes under compressive force loading induces apoptosis through activation of ERK1/2 pathway.

Impaired glycolytic metabolism causes chondrocyte hypertrophy-like changes via promotion of phospho-Smad1/5/8 translocation into nucleus

OBJECTIVE

Hypertrophy-like changes are often observed in chondrocytes during the development of osteoarthritis (OA). These changes play a crucial part in the OA-associated cartilage degradation and osteophyte formation. However, the pathogenesis leading to such changes is still unknown. In this study, we investigated the mechanism by which these hypertrophy-like changes are induced from the viewpoint of impaired glycolytic metabolism.

METHODS

The effect of sodium fluoride (NaF) on glycolytic metabolism of cultured chondrocytes was confirmed by measurement of intracellular adenosine triphosphate (ATP) production. Translocation of phosphorylated Smad1/5/8 to the nucleus was evaluated by subcellular fractionation and Western blotting. Chondrocyte hypertrophy-like changes were investigated by real-time RT-PCR and Western blot analysis of differentiation markers.

RESULTS

ATP production was dose-dependently decreased by NaF in the human chondrocytic cell line HCS-2/8. In addition, both chondrocyte proliferation and differentiation were inhibited, whereas cell death was promoted by treatment with NaF. Interestingly, combinational treatment with NaF and lactate enhanced translocation of phospho-Smad1/5/8 to the nucleus, as well as gene expression of ALP, VEGF, COL10a1, and matrix metalloproteinase13 (MMP13), which were the markers of late mature and hypertrophic chondrocytes. Furthermore, the production of type X collagen and activation of MMP9 were also promoted under the same conditions.

CONCLUSIONS

These findings suggest that decreased ATP production by NaF promotes hypertrophy-like changes via activation of phospho-Smad1/5/8 in the presence of lactate. Novel metabolic aspects of OA pathogenesis are indicated herein.

Connective tissue growth factor in tumor pathogenesis

Key roles for connective tissue growth factor (CTGF/CCN2) are demonstrated in the wound repair process where it promotes myofibroblast differentiation and angiogenesis. Similar mechanisms are active in tumor-reactive stroma where CTGF is expressed. Other potential roles include prevention of hypoxia-induced apoptosis and promoting epithelial-mesenchymal transistion (EMT). CTGF expression in tumors has been associated to both tumor suppression and progression. For example, CTGF expression in acute lymphoblastic leukemia, breast, pancreas and gastric cancer correlates to worse prognosis whereas the opposite is true for colorectal, lung and ovarian cancer. This discrepancy is not yet understood. High expression of CTGF is a hallmark of ileal carcinoids, which are well-differentiated endocrine carcinomas with serotonin production originating from the small intestine and proximal colon. These tumors maintain a high grade of differentiation and low proliferation. Despite this, they are malignant and most patients have metastatic disease at diagnosis. These tumors demonstrate several phenotypes potentially related to CTGF function namely: cell migration, absent tumor cell apoptosis, as well as, reactive and well vascularised myofibroblast rich stroma and fibrosis development locally and in distal organs. The presence of CTGF in other endocrine tumors indicates a role in the progression of well-differentiated tumors.

CCN2 promotes cigarette smoke-induced proliferation of rat pulmonary artery smooth muscle cells through upregulating cyclin D1 expression

Cigarette smoke has been demonstrated to induce pulmonary vascular remodeling, which is characterized by medial thickening of the pulmonary arteries mainly resulting from the abnormal proliferation of pulmonary artery smooth muscle cells (PASMCs). However, the molecular mechanism underlying this process is still unclear. In the present study, we investigated whether CCN2 regulated rat PASMCs (rPASMCs) proliferation induced by cigarette smoke extract (CSE) and nicotine by upregulating cyclin D1 in vitro. CCN2 siRNA or cyclin D1 siRNA were transfected to rPASMCs which were then exposed to CSE and nicotine. Both mRNA and protein expressions of CCN2 were significantly increased in rPASMCs treated with 2% CSE or 1 µM nicotine, which markedly promoted the proliferation of rPASMCs. CCN2 siRNA inhibited the proliferation of rPASMCs induced by CSE or nicotine. Furthermore, CCN2 siRNA markedly suppressed the mRNA and protein expressions of cyclin D1 in rPASMCs and led to cell cycle arrest in G0/G1 phase resulting in reduced rPASMCs proliferation. These findings suggest that CCN2 contributes to the CSE and nicotine-induced proliferation of rPASMCs at least in part by upregulating cyclin D1 expression.

CCN family 2/connective tissue growth factor (CCN2/CTGF) promotes osteoclastogenesis via induction of and interaction with dendritic cell-specific transmembrane protein (DC-STAMP)

CCN family 2/connective tissue growth factor (CCN2/CTGF) promotes endochondral ossification. However, the role of CCN2 in the replacement of hypertrophic cartilage with bone is still unclear. The phenotype of Ccn2 null mice, having an expanded hypertrophic zone, indicates that the resorption of the cartilage extracellular matrix is impaired therein. Therefore, we analyzed the role of CCN2 in osteoclastogenesis because cartilage extracellular matrix is resorbed mainly by osteoclasts during endochondral ossification. Expression of the Ccn2 gene was upregulated in mouse macrophage cell line RAW264.7 on day 6 after treatment of glutathione S transferase (GST) fusion mouse receptor activator of NF-κB ligand (GST-RANKL), and a combination of recombinant CCN2 (rCCN2) and GST-RANKL significantly enhanced tartrate-resistant acid phosphatase (TRACP)-positive multinucleated cell formation compared with GST-RANKL alone. Therefore, we suspected the involvement of CCN2 in cell-cell fusion during osteoclastogenesis. To clarify the mechanism, we performed real-time PCR analysis of gene expression, coimmunoprecipitation analysis, and solid-phase binding assay of CCN2 and dendritic cell-specific transmembrane protein (DC-STAMP), which is involved in cell-cell fusion. The results showed that CCN2 induced and interacted with DC-STAMP. Furthermore, GST-RANKL-induced osteoclastogenesis was impaired in fetal liver cells from Ccn2 null mice, and the impaired osteoclast formation was rescued by the addition of exogenous rCCN2 or the forced expression of DC-STAMP by a retroviral vector. These results suggest that CCN2 expressed during osteoclastogenesis promotes osteoclast formation via induction of and interaction with DC-STAMP.

Suppression of radiation-induced testicular germ cell apoptosis by 2,5-hexanedione pretreatment. II. Gene array analysis reveals adaptive changes in cell cycle and cell death pathways

Sertoli cells are essential for testicular germ cell maintenance and survival. We made the unexpected observation that x-radiation (x-ray)-induced germ cell loss is attenuated by co-exposure with the Sertoli cell toxicant 2,5-hexanedione (HD). The mechanisms underlying this attenuation of germ cell apoptosis with reduced Sertoli cell support are unknown. The current study was performed to examine alterations in testicular gene expression with co-exposure to HD and x-ray. Adult male rats were exposed to HD (0.33 or 1%) in the drinking water for 18 days followed by x-ray (2 or 5 Gy), resulting in nine treatment groups. Testis samples were collected after 3 h and total messenger RNA was analyzed using Affymetrix Rat Genome 230 2.0 arrays. Normalized log2-expression values were analyzed using LIMMA and summarized using linear contrasts designed to summarize the aggregated effect, in excess of x-ray alteration, of HD across all treatment groups. These contrasts were compared with the overall linear trend expression for x-ray, to determine whether HD effects were agonistic or antagonistic with respect to x-ray damage. Overrepresentation analysis to identify biological pathways where HD modification of gene expression was the greatest was performed. HD exerted a significant influence on genes involved in cell cycle and cell death/apoptosis. The results of this study provide insight into the mechanisms underlying attenuated germ cell toxicity following HD and x-ray co-exposure through the analysis of co-exposure effects on gene expression, and suggest that HD pre-exposure reduces Sertoli cell supported germ cell proliferation thereby reducing germ cell vulnerability to x-rays.

Thrombopoietic-mesenchymal interaction that may facilitate both endochondral ossification and platelet maturation via CCN2

CCN2 plays a central role in the development and growth of mesenchymal tissue and promotes the regeneration of bone and cartilage in vivo. Of note, abundant CCN2 is contained in platelets, which is thought to play an important role in the tissue regeneration process. In this study, we initially pursued the possible origin of the CCN2 in platelets. First, we examined if the CCN2 in platelets was produced by megakaryocyte progenitors during differentiation. Unexpectedly, neither megakaryocytic CMK cells nor megakaryocytes that had differentiated from human haemopoietic stem cells in culture showed any detectable CCN2 gene expression or protein production. Together with the fact that no appreciable CCN2 was detected in megakaryocytes in vivo, these results suggest that megakaryocytes themselves do not produce CCN2. Next, we suspected that mesenchymal cells situated around megakaryocytes in the bone marrow were stimulated by the latter to produce CCN2, which was then taken up by platelets. To evaluate this hypothesis, we cultured human chondrocytic HCS-2/8 cells with medium conditioned by differentiating megakaryocyte cultures, and then monitored the production of CCN2 by the cells. As suspected, CCN2 production by HCS-2/8 was significantly enhanced by the conditioned medium. We further confirmed that human platelets were able to absorb/uptake exogenous CCN2 in vitro. These findings indicate that megakaryocytes secrete some unknown soluble factor(s) during differentiation, which factor stimulates the mesenchymal cells to produce CCN2 for uptake by the platelets. We also consider that, during bone growth, such thrombopoietic-mesenchymal interaction may contribute to the hypertrophic chondrocyte-specific accumulation of CCN2 that conducts endochondral ossification.

Connective tissue growth factor: structure-function relationships of a mosaic, multifunctional protein

Connective tissue growth factor (CTGF) is a member of the CCN family of six small secreted, cysteine-rich growth factors. The unique modular structure encompasses distinct functional domains which enable CTGF to interact with growth factors, surface receptors and matrix components. Widely expressed, CTGF has critical roles in embryonic development and the maintenance of normal cell and connective tissue function. It is also important for tissue repair following injury, and has been implicated in common diseases including atherosclerosis, pulmonary and renal fibrotic disorders and cancer. Factors that regulate CTGF transcription in response to exogenous stimuli, as well as downstream signalling pathways, have been described. However, only recently have studies begun to unravel how the functional domains within the CTGF modules orchestrate signals and control key biological processes. This article highlights how the structural and functional domains of CTGF and CTGF cleavage fragments integrate multiple extracellular events into cell signals.

Gene expression and distribution of connective tissue growth factor (CCN2/CTGF) during secondary ossification center formation

CCN2/connective tissue growth factor (CCN2/CTGF) is a critical signaling modulator of mesenchymal tissue development. This study investigated the localization and expression of CCN2/CTGF as a factor supporting angiogenesis and chondrogenesis during development of secondary ossification centers in the mouse tibial epiphysis. Formation of the secondary ossification center was initiated by cartilage canal formation and blood vessel invasion at 7 days of age, and onset of ossification was observed at 14 days. In situ hybridization showed that CCN2/CTGF mRNA was distinctively expressed in the region of the cartilage canal and capsule-attached marginal tissues at 7 days of age, and distinct expression was also observed in proliferating chondrocytes around the marrow space at 14 days of age. Immunostaining showed that CCN2/CTGF was distributed broadly around the expressed cells located in the central region of the epiphysis, where the chondrocytes become hypertrophic and the cartilage canal enters into the hypertrophic mass. Furthermore, an overlapping distribution of metalloproteinase (MMP)9 and CCN2/CTGF was found in the secondary ossification center. These findings suggest that the CCN2/CTGF is involved in establishing epiphyseal vascularization and remodeling, which eventually determines the secondary ossification center in the developing epiphysial cartilage.

CCN2 (Connective Tissue Growth Factor) is essential for extracellular matrix production and integrin signaling in chondrocytes

The matricellular protein CCN2 (Connective Tissue Growth Factor; CTGF) is an essential mediator of ECM composition, as revealed through analysis of Ccn2 deficient mice. These die at birth due to complications arising from impaired endochondral ossification. However, the mechanism(s) by which CCN2 mediates its effects in cartilage are unclear. We investigated these mechanisms using Ccn2 ( -/- ) chondrocytes. Expression of type II collagen and aggrecan were decreased in Ccn2 (-/-) chondrocytes, confirming a defect in ECM production. Ccn2 ( -/- ) chondrocytes also exhibited impaired DNA synthesis and reduced adhesion to fibronectin. This latter defect is associated with decreased expression of alpha5 integrin. Moreover, CCN2 can bind to integrin alpha5beta1 in chondrocytes and can stimulate increased expression of integrin alpha5. Consistent with an essential role for CCN2 as a ligand for integrins, immunofluorescence and Western blot analysis revealed that levels of focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK)1/2 phosphorylation were reduced in Ccn2 ( -/- ) chondrocytes. These findings argue that CCN2 exerts major effects in chondrocytes through its ability to (1) regulate ECM production and integrin alpha5 expression, (2) engage integrins and (3) activate integrin-mediated signaling pathways.

Role of CCN2/CTGF/Hcs24 in bone growth

Our bones mostly develop through a process called endochondral ossification. This process is initiated in the cartilage prototype of each bone and continues through embryonic and postnatal development until the end of skeletal growth. Therefore, the central regulator of endochondral ossification is the director of body construction, which is, in other words, the determinant of skeletal size and shape. We suggest that CCN2/CTGF/Hcs24 (CCN2) is a molecule that conducts all of the procedures of endochondral ossification. CCN2, a member of the CCN family of novel modulator proteins, displays multiple functions by manipulating the local information network, using its conserved modules as an interface with a variety of other biomolecules. Under a precisely designed four-dimensional genetic program, CCN2 is produced from a limited population of chondrocytes and acts on all of the mesenchymal cells inside the bone callus to promote the integrated growth of the bone. Furthermore, the utility of CCN2 as regenerative therapeutics against connective tissue disorders, such as bone and cartilage defects and osteoarthritis, has been suggested. Over the years, the pathological action of CCN2 has been suggested. Nevertheless, it can also be regarded as another aspect of the physiological and regenerative function of CCN2, which is discussed as well.

Multiple activation of mitogen-activated protein kinases by purified independent CCN2 modules in vascular endothelial cells and chondrocytes in culture

CCN2 consists of 4 distinct modules that are conserved among various CCN family protein members. From the N-terminus, insulin-like growth factor binding protein (IGFBP), von Willebrand factor type C repeat (VWC), thrombospondin type 1 repeat (TSP1) and C-terminal cysteine-knot (CT) modules are all aligned tandem therein. The multiple functionality of CCN2 is thought to be enabled by the differential use of these modules when interacting with other molecules. In this study, we independently prepared all 4 purified module proteins of human CCN2, utilizing a secretory production system with Brevibacillus choshinensis and thus evaluated the cell biological effects of such single modules. In human umbilical vascular endothelial cells (HUVECs), VWC, TSP and CT modules, as well as a full-length CCN2, were capable of efficiently activating the ERK signal transduction cascade, whereas IGFBP was not. In contrast, the IGFBP module was found to prominently activate JNK in human chondrocytic HCS-2/8 cells, while the others showed similar effects at lower levels. In addition, ERK1/2 was modestly, but significantly activated by IGFBP and VWC in those cells. No single module, but a mixture of the 4 modules provoked a significant activation of p38 MAPK in HCS-2/8 cells, which was activated by the full-length CCN2. Therefore, the signals emitted by CCN2 can be highly differential, depending upon the cell types, which are thus enabled by the tetramodular structure. Furthermore, the cell biological effects of each module on these cells were also evaluated to clarify the relationship among the modules, the signaling pathways and biological outcomes. Our present results not only demonstrate that single CCN2 modules were potent activators of the intracellular signaling cascade to yield a biological response per se, while also providing new insight into the module-wise structural and functional relationship of a prototypic CCN family member, CCN2.

Roles of PKC, PI3K and JNK in multiple transduction of CCN2/CTGF signals in chondrocytes

CCN2/connective tissue growth factor (CCN2/CTGF) is known to promote both the proliferation and differentiation of chondrocytes, which actions are mediated by ERK and p38 MAPK, respectively. In this study, we first re-evaluated the involvement of multiple MAPKs therein and found that JNK also mediated such CCN2 signals. Thereafter, we further analyzed the roles of upstream kinases. The involvement of PKC, PI3K and PKA in the CCN2 signaling to promote the maturation, proliferation and terminal differentiation of a human chondrocytic cell line, HCS-2/8 and rabbit primary growth cartilage cells was investigated. As a result, the PKC inhibitor calphostin C repressed all of the effects of CCN2, which were represented by increased synthesis of DNA and proteoglycans and the display of alkaline phosphatase activity. In addition, evaluation of the effect of the PI3K inhibitor wortmannin disclosed the contribution of PI3K in transducing CCN2 signals to promote chondrocyte hypertrophy. This signal was known to be mediated by PKB, which was translocated into the nucleus upon CCN2 stimulation. Of note, calphostin C showed inhibitory effects on the activation of p38 MAPK, ERK and also PKB, whereas it exerted no effect on JNK activation. These results suggest that PKC is a driver of multiple signal transducing kinases that promote the proliferation and differentiation of chondrocytes. The requirement of PI3K in transmitting the signal for terminal differentiation and PKC-independent signaling pathways for the promotion of chondrocytic growth and differentiation, which was mediated by JNK, were also uncovered.

Induction and function of CYR61 (CCN1) in prostatic stromal and epithelial cells: CYR61 is required for prostatic cell proliferation

BACKGROUND

CYR61 is an extracellular matrix-associated protein that promotes adhesion, migration, and proliferation of endothelial cells and fibroblasts. Prostate enlargement, which frequently causes the urethral compression, is often histologically observed as stromal and epithelial hyperplasia in an enlarged gland. To determine whether or not CYR61 has relevance to the progression of benign prostatic hyperplasia (BPH), we investigated the induction of CYR61, and also examined its function in both prostatic stromal and epithelial cells.

METHODS

Recombinant CYR61 protein was used for the examination of the activity of CYR61 as to cell adhesion and proliferation. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) was utilized to screen for inducers of the CYR61 gene in prostatic cells. Finally, the effects of an anti-sense oligonucleotide, which could reduce the production of CYR61, on the morphology and growth of prostatic cells were also examined.

RESULTS

Recombinant CYR61 protein promotes prostatic cell adhesion and proliferation. The mRNA for CYR61, a growth factor-inducible immediate early gene, was markedly induced by fetal bovine serum (FBS) within 1 hr, and strongly induced by transforming growth factor-beta1 (TGF-beta) for at least 19 hr following stimulation. The suppression of CYR61 production with an anti-sense oligonucleotide causes obvious morphological changes of prostatic cells. Furthermore, we have shown that CYR61 is necessary, at least in part, for FBS-induced prostatic cell proliferation, because dramatic inhibition of cellular growth was caused by the suppression of CYR61 production with the addition of the anti-sense oligonucleotide before FBS stimulation.

CONCLUSIONS

In this study, we demonstrate that serum growth factors induce the CYR61 gene in both stromal and epithelial cells, and that CYR61 plays functional roles in cell adhesion, morphology, and proliferation, supporting its involvement in benign prostatic enlargement. These results strongly suggest that CYR61 is a key molecule, and therefore could be a potential therapeutic target in prostatic hyperplastic growth.

Connective tissue growth factor [CTGF]/CCN2 stimulates mesangial cell migration through integrated dissolution of focal adhesion complexes and activation of cell polarization

Connective tissue growth factor [CTGF]/CCN2 is a prototypic member of the CCN family of regulatory proteins. CTGF expression is up-regulated in a number of fibrotic diseases, including diabetic nephropathy, where it is believed to act as a downstream mediator of TGF-beta function; however, the exact mechanisms whereby CTGF mediates its effects remain unclear. Here, we describe the role of CTGF in cell migration and actin disassembly in human mesangial cells, a primary target in the development of renal glomerulosclerosis. The addition of CTGF to primary mesangial cells induced cell migration and cytoskeletal rearrangement but had no effect on cell proliferation. Cytoskeletal rearrangement was associated with a loss of focal adhesions, involving tyrosine dephosphorylation of focal adhesion kinase and paxillin, increased activity of the protein tyrosine phosphatase SHP-2, with a concomitant decrease in RhoA and Rac1 activity. Conversely, Cdc42 activity was increased by CTGF. These functional responses were associated with the phosphorylation and translocation of protein kinase C-zeta to the leading edge of migrating cells. Inhibition of CTGF-induced protein kinase C-zeta activity with a myristolated PKC-zeta inhibitor prevented cell migration. Moreover, transient transfection of human mesangial cells with a PKC-zeta kinase inactive mutant (dominant negative) expression vector also led to a decrease in CTGF-induced migration compared with wild-type. Furthermore, CTGF stimulated phosphorylation and activation of GSK-3beta. These data highlight for the first time an integrated mechanism whereby CTGF regulates cell migration through facilitative actin cytoskeleton disassembly, which is mediated by dephosphorylation of focal adhesion kinase and paxillin, loss of RhoA activity, activation of Cdc42, and phosphorylation of PKC-zeta and GSK-3beta. These changes indicate that the initial stages of CTGF mediated mesangial cell migration are similar to those involved in the process of cell polarization. These findings begin to shed mechanistic light on the renal diabetic milieu, where increased CTGF expression in the glomerulus contributes to cellular dysfunction.

CTGF/Hcs24, hypertrophic chondrocyte-specific gene product, interacts with perlecan in regulating the proliferation and differentiation of chondrocytes

Connective tissue growth factor/hypertrophic chondrocyte-specific gene product 24 (CTGF/Hcs24) plays important roles in the control of the proliferation and differentiation of chondrocytes in vitro. To clarify the mechanisms of regulation by CTGF/Hcs24 with respect to cartilage metabolism, we investigated the interaction between CTGF/Hcs24 and heparan sulfate proteoglycan perlecan. An immunofluorescence study showed that CTGF/Hcs24 was colocalized with heparan sulfate and perlecan in human chondrosarcoma-derived chondrocytic cell line HCS-2/8 in vitro. Northern blot analysis showed that perlecan, syndecan-1, -2, and -4 transcripts were detected in HCS-2/8 cells. Particularly, expression of the perlecan gene increased markedly in HCS-2/8 cells by recombinant CTGF/Hcs24 (rCTGF/Hcs24) treatment. We also found that CTGF/Hcs24 interacted with perlecan from HCS-2/8 cells in vitro. Furthermore, CTGF/Hcs24-stimulated gene expression of the aggrecan gene, as well as DNA/proteoglycan synthesis, was diminished when HCS-2/8 cells were pretreated with heparinase, indicating that the effects of CTGF/Hcs24 on chondrocytes occurred through the interaction between CTGF/Hcs24 and heparan sulfate on the cells. An in vivo study using mouse growth plate revealed that CTGF/Hcs24 produced by hypertrophic chondrocytes was localized from the proliferative to the hypertrophic zone, whereas perlecan was predominantly localized in the prehyphertrophic zone. Consistent with such findings in vivo, the binding of (125)I-rCTGF/Hcs24 to maturing chondrocytes was at higher levels than that to chondrocytes in hypertrophic stages. These findings suggest that CTGF/Hcs24 produced in the hypertrophic region may act on chondrocytes in the proliferative and maturative zone via some heparan sulfate proteoglycan, such as perlecan.

Suppressive effect of overexpressed connective tissue growth factor on tumor cell growth in a human oral squamous cell carcinoma-derived cell line

Connective tissue growth factor (CTGF) is known to be a multifunctional growth factor that is overexpressed in several types of malignancies. In this study, effects of CTGF gene overexpression on the phenotypes of oral squamous cell carcinoma cells were investigated by using a cell line with undetectable endogenous CTGF expression. Surprisingly, our results indicated that CTGF-overexpressed clones were characterized by attenuated cell growth and less potent tumorigenicity, with coincidental downregulation of prothymosin alpha gene. Although CTGF is known to promote cell proliferation in mesenchymal cells, our present results suggest that CTGF acts as a negative regulator of the cell growth in oral squamous cell carcinoma possibly through its interaction with growth modifiers inside the cell.

Role of CTGF/HCS24/ecogenin in skeletal growth control

Connective tissue growth factor/hypertrophic chondrocyte-specific gene product 24 (CTGF/Hcs24) is a multifunctional growth factor for chondrocytes, osteoblasts, and vascular endothelial cells. CTGF/Hcs24 promotes the proliferation and maturation of growth cartilage cells and articular cartilage cells in culture and hypertrophy of growth cartilage cells in culture. The factor also stimulates the proliferation and differentiation of cultured osteoblastic cells. Moreover, CTGF/Hcs24 promotes the adhesion, proliferation, and migration of vascular endothelial cells, as well as induces tube formation by the cells and strong angiogenesis in vivo. Because angiogenesis is critical for the replacement of cartilage with bone at the final stage of endochondral ossification and because gene expression of CTGF/Hcs24 predominates in hypertrophic chondrocytes in the physiological state, a major physiological role for this factor should be the promotion of the entire process of endochondral ossification, with the factor acting on the above three types of cells as a paracrine factor. Thus, CTGF/Hcs24 should be called "ecogenin: endochondral ossification genetic factor." In addition to hypertrophic chondrocytes, osteoblasts activated by various stimuli including wounding also express a significantly high level of CTGF/Hcs24. These findings in conjunction with in vitro findings about osteoblasts mentioned above suggest the involvement of CTGF/Hcs24 in intramembranous ossification and bone modeling/remodeling. Because angiogenesis is also critical for intramembranous ossification and bone remodeling, CTGF/Hcs24 expressed in endothelial cells activated by various stimuli including wounding may also play important roles in direct bone formation. In conclusion, although the most important physiological role of CTGF/Hcs24 is ecogenin action, the factors also play important roles in skeletal growth and modeling/remodeling via its direct action on osteoblasts under both physiological and pathological conditions.

CTGF/Hcs24 interacts with the cytoskeletal protein actin in chondrocytes

Connective tissue growth factor/hypertrophic chondrocyte-specific gene product 24 (CTGF/Hcs24) displays multiple functions in several types of mesenchymal cells, including the promotion of proliferation and differentiation of chondrocytes. Recently, the internalization and intracellular function of CTGF/Hcs24 were indicated as well. In this study, a binding protein for this factor was purified from the cytosolic fraction of human chondrosarcoma-derived chondrocytic cell line (HCS-2/8) by CTGF/Hcs24-affinity chromatography. The apparent molecular weight of the protein was 42kDa and determination of the internal amino acid sequence revealed this protein to be beta- or gamma-actin. An in vitro competitive binding assay of 125I-labeled recombinant CTGF/Hcs24 with cold-rCTGF/Hcs24 showed that the binding between actin and 125I-CTGF/Hcs24 was specific. Immunoprecipitation analysis also showed that CTGF/Hcs24 bound to actin in HCS-2/8 cells. However, rCTGF/Hcs24 had no effects on the expression level of gamma-actin mRNA or total actin protein. These findings suggest that a significant portion of intracellular CTGF/Hcs24 may regulate certain cell biological events in chondrocytes through the interaction with this particular cytoskeletal protein.

Connective tissue growth factor as a major angiogenic agent that is induced by hypoxia in a human breast cancer cell line

Connective tissue growth factor (CTGF) is known to be a potent angiogenic factor. Here, we present the evidence that the hypoxic induction of angiogenesis by human breast cancer cells (MDA-231) can be ascribed at least in part to CTGF. Our results indicate that (i) CTGF is abundantly present in MDA-231 cells in vitro and in vivo, (ii) its secretion is up-regulated by hypoxia, and (iii) its gene expression is enhanced in MDA-231 cells cultured under hypoxic conditions. These data suggest CTGF may stimulate angiogenesis by paracrine mechanisms, thereby contributing to the invasion of breast cancer cells. This is the first evidence that human cancer cells differentially express CTGF protein and mRNA under the control of hypoxic conditions.

CTGF/Hcs24 induces chondrocyte differentiation through a p38 mitogen-activated protein kinase (p38MAPK), and proliferation through a p44/42 MAPK/extracellular-signal regulated kinase (ERK)

Connective tissue growth factor/hypertrophic chondrocyte specific gene product 24 (CTGF/Hcs24) promotes proliferation and differentiation of chondrocytes in culture. We investigated the roles of two major types of mitogen activated protein kinase (MAPK) in the promotion of proliferation and differentiation by CTGF/Hcs24. Here we report the effects of the MAPKK/MEK 1/2 inhibitor, PD098059, and p38 MAPK inhibitor, SB203580, in a human chondrosarcoma-derived chondrocytic cell line (HCS-2/8) and rabbit growth cartilage (RGC) cells treated with CTGF/Hcs24. In the proliferation phase, CTGF/Hcs24 induced a approximately fivefold increase in the phosphorylation of p44/42 MAPK/ERK and a approximately twofold increase in that of p38 MAPK in an in vivo kinase assay. These inhibitors of MAPKK and MAPK suppressed phosphorylation of ets-like gene-1 (Elk-1) and nuclear activating transcription factor-2 (Atf-2) induced by CTGF/Hcs24 in a dose-dependent manner, respectively. Western blot analysis showed that phosphorylation of ERK was induced from 30 to 60 min and phosphorylation of p38 MAPK from 10 to 15 min after the addition of CTGF/Hcs24 in confluence HCS-2/8 cells. PD098059 suppressed the DNA synthesis of HCS-2/8 cells and RGC cells, while SB203580 did not. On the other hand, the p38 MAPK inhibitor, SB203580, completely inhibited the CTGF/Hcs24-induced synthesis of proteoglycans in HCS-2/8 cells and RGC cells but the MEK1/2 inhibitor, PD098059, did not. These results suggest that ERK mediates the CTGF/Hcs24-induced proliferation of chondrocytes, and that p38 MAPK mediates the CTGF/Hcs24-induced differentiation of chondrocytes.

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

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

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

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

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

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

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

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

Connective tissue growth factor: what's in a name?

Connective tissue growth factor (CTGF) is a member of the recently described CCN gene family which contains CTGF itself, cyr61, nov, elm1, Cop1, and WISP-3. CTGF is transcriptionally activated by several factors although its stimulation by transforming growth factor beta (TGF-beta) has attracted considerable attention. CTGF acts to promote fibroblast proliferation, migration, adhesion, and extracellular matrix formation, and its overproduction is proposed to play a major role in pathways that lead to fibrosis, especially those that are TGF-beta-dependent. This includes fibrosis of major organs, fibroproliferative diseases, and scarring. CTGF also appears to play a role in the extracellular matrix remodeling that occurs in normal physiological processes such as embryogenesis, implantation, and wound healing. However, recent advances have shown that CTGF is involved in diverse autocrine or paracrine actions in several other cell types such as vascular endothelial cells, epithelial cells, neuronal cells, vascular smooth muscle cells, and cells of supportive skeletal tissues. Moreover, in some circumstances CTGF has negative effects on cell growth in that it can be antimitotic and apoptotic. In light of these discoveries, CTGF has been implicated in a diverse variety of processes that include neovascularization, transdifferentiation, neuronal scarring, atherosclerosis, cartilage differentiation, and endochondral ossification. CTGF has thus emerged as a potential important effector molecule in both physiological and pathological processes and has provided a new target for therapeutic intervention in fibrotic diseases.