Transcriptional cross-talk between Smad, ERK1/2, and p38 mitogen-activated protein kinase pathways regulates transforming growth factor-beta-induced aggrecan gene expression in chondrogenic ATDC5 cells

Signal transduction and metabolism in chondrocytes is modulated by lactoferrin

OBJECTIVE

Activation of granulocytes causes a considerable rise in the concentration of lactoferrin (Lf) in synovial fluid (SF). We here investigate consequences thereof on signal transduction and the balance between catabolic and anabolic metabolism in chondrocytes.

METHODS

Signal transduction was analysed in cultured chondrocytes by immunodetection of mitogen activated protein kinases (MAPK) and analysis of Smad2 translocation to the nucleus. Expression levels of matrix metalloproteinases (MMPs) and of aggrecan were measured by reverse-transcription-PCR. The proteolytic activity of MMPs was ascertained by zymography. Expression of the low-density-lipoprotein-receptor-related-protein-1 (LRP-1), a Lf receptor for signalling, was assayed by immunohistochemistry in cartilage and in cultured chondrocytes by immunoblotting.

RESULTS

We found LRP-1 expressed in dedifferentiated chondrocytes in culture and in cartilage tissue preferentially on the articular surface where it can encounter Lf within SF. Lf stimulated proliferation of chondrocytes, comparable to transforming growth factor-beta1 (TGFbeta1) and activated p38 and the extracellular-signal regulated-kinases 1/2 (ERK1/2) within minutes. Surprisingly, Lf induced nuclear Smad2 translocation, a signal pathway ascribed to TGFbeta receptor activation. Lf significantly increased the levels of catabolic indicators such as MMP1, MMP2, MMP3 and MMP13 and inhibited aggrecan synthesis.

CONCLUSION

Lf is a robust regulator of chondrocyte metabolism, comparable to TGFbeta1. The catabolic influence together with the proliferative stimulus indicates a function as an early phase cytokine, enhancing MMPs, necessary for degradation of damaged tissue and stimulating proliferation of chondrocytes, necessary for reconstruction.

Synergistic effects of growth and differentiation factor-5 (GDF-5) and insulin on expanded chondrocytes in a 3-D environment

OBJECTIVE

To investigate the effects of growth and differentiation factor-5 (GDF-5) alone or in combination with insulin on engineered cartilage from primary or expanded chondrocytes during 3-dimensional in vitro culture.

DESIGN

Juvenile bovine chondrocytes were seeded either as primary or as expanded (passage 2) cells onto polyglycolic acid fiber meshes and cultured for 3 weeks in vitro. Additionally, adult human chondrocytes were grown in pellet culture after expansion (passage 2). The culture medium was supplemented either with GDF-5 in varying concentrations or insulin alone, or with combinations thereof.

RESULTS

For primary chondrocytes, the combination of GDF-5 and insulin led to increased proliferation and construct weight, as compared to either factor alone, however, the production of glycosaminoglycans (GAG) and collagen per cell were not affected. With expanded bovine chondrocytes, the use of GDF-5 or insulin alone led to only very small constructs with no type II collagen detectable. However, the combination of GDF-5 (0.01 or 0.1 microg/ml) and insulin (2.5 microg/ml) yielded cartilaginous constructs and, in contrast to the primary cells, the observed redifferentiating effects were elicited on the cellular level independent of proliferation (increased production of GAG and collagen per cell, clear shift in collagen subtype expression with type II collagen observed throughout the construct). The synergistic redifferentiating effects of the GDF-5/insulin combination were confirmed with expanded adult human cells, also exhibiting a clear shift in collagen subtype expression on the mRNA and protein level.

CONCLUSIONS

In combination with insulin, GDF-5 appears to enable the redifferentiation of expanded chondrocytes and the concurrent generation of cartilaginous constructs. The demonstration of these synergistic effects also for adult human chondrocytes supports the clinical relevance of the findings.

TGF-beta3: A potential biological therapy for enhancing chondrogenesis

BACKGROUND

TGF-beta has been proposed to stimulate chondrogenesis through intracellular pathways involving small mothers against decapentaplegic proteins (Smads).

OBJECTIVE

To examine the use of exogenous TGF-beta3 to promote new hyaline cartilage formation.

METHODS

An overview of in vitro and in vivo evidence on the effects of TGF-beta3 on cartilage regeneration.

RESULTS/CONCLUSION

There is robust in vitro evidence suggesting a positive dose- and time-dependent effect of TGF-beta3 on anabolic chondrogenic gene markers such as alpha1-collagen type II and cartilage oligomeric matrix protein in human mesenchymal stem cells. TGF-beta3 cultured with silk elastin-like polymer scaffold carrier exhibits significantly increased glycosaminoglycan and collagen content. In vivo data showed that TGF-beta3 cultured with ovine mesenchymal stem cells in a chitosan scaffold stimulated the growth of hyaline cartilage that was fully integrated into host cartilage tissue of sheep. We highlight the potential for the clinical enhancement of cartilage formation through the use of TGF-beta3 with a suitable dose and scaffold carrier.

The promotion of chondrogenesis in adipose-derived adult stem cells by an RGD-chimeric protein in 3D alginate culture

The dynamic regulation of integrin-binding peptides is crucial for chondrogenic differentiation. Here, we revealed the feasibility for flexible modification of RGD by embedding a large molecular weight and slightly charged (isoelectric point, 6-6.25) RGD-chimeric protein (CBD-RGD) with cellulose-binding domain (CBD) in three dimensional (3D) alginate beads to evaluate the chondrogenesis of adipose-derived adult stem cells (ADAS). The binding of CBD-RGD with cells and its diffusion from alginate beads were studied on fluorescein isothiocyanate (FITC)-conjugated CBD-RGD. The increases in gene expression (Sox9, Aggrecan, fibronectin and collagen II), accumulation of chondrogenic matrices and decrease of collagen X gene expression during TGF-beta3 induction were only observed for those beads containing 10mg/g CBD-RGD initially, with 20.18+/-0.73% of that released in a week. The contrary was observed for beads with CBD-RGD 20mg/g initially and having higher persistence (only 8.6+/-2.17% released in a week). The 10mg/g CBD-RGD-mediated enhancement was demonstrated via the activation of integrin alpha5 and beta1-dependent pathway, and especially related to the upregulation of Sox9 gene and the temporary block of fibronectin expression as well as sustained inhibition of RhoA activity in the early differentiation stage. Thus, we speculated that the dynamic mobility of CBD-RGD may account for the enhanced chondrogenesis. It was concluded that the CBD-RGD-alginate culture system promoted the chondrogenesis of mesenchymal stem cells coordinated with TGF-beta3 induction in an RGD dose-dependent manner.

Hyperosmolarity regulates SOX9 mRNA posttranscriptionally in human articular chondrocytes

The transcription factor SOX9 regulates cartilage extracellular matrix gene expression and is essential for chondrocyte differentiation. We previously showed that activation of p38 MAPK by cycloheximide in human chondrocytes leads to stabilization of SOX9 mRNA (Tew SR and Hardingham TE. J Biol Chem 281: 39471–39479, 2006). In this study we investigated whether regulation of p38 MAPK caused by changes in osmotic pressure could control SOX9 mRNA levels expression by a similar mechanism. Primary human articular chondrocytes isolated from osteoarthritic cartilage at passage 2-4 showed significantly raised SOX9 mRNA levels when exposed to hyperosmotic conditions for 5 h. The effect was strongest and most reproducible when actin stress fibers were disrupted by the Rho effector kinase inhibitor Y27632, or by culturing the cells within alginate beads. Freshly isolated chondrocytes, used within 24–48 h of isolation, did not contain actin stress fibers and upregulated SOX9 mRNA in response to hyperosmolarity in the presence and absence of Y27632. In these freshly isolated chondrocytes, hyperosmolarity led to an increase in the half-life of SOX9 mRNA, which was sensitive to the p38 MAPK inhibitor SB202190. SOX9 protein levels were increased by hyperosmotic culture over 24 h, and, in passaged chondrocytes, the activity of a COL2A1 enhancer driven luciferase assay was upregulated. However, in freshly isolated chondrocytes, COL2A1 mRNA levels were reduced by hyperosmotic conditions and the half-life was decreased. The results showed that the osmotic environment regulated both SOX9 and COL2A1 mRNA posttranscriptionally, but in fresh cells resulted in increased SOX9, but decreased COL2A1.

SMAD-proteins as a molecular switch from hypertrophy to apoptosis induction in adult ventricular cardiomyocytes

Heart failure development goes along with a transition from hypertrophic growth to apoptosis induction. In adult cardiomyocytes SMAD proteins are only activated under apoptotic, but not under hypertrophic conditions and are increased at the transition to heart failure. Therefore, SMADs could be candidates that turn the balance from hypertrophic growth to apoptosis resulting in heart failure development. To test this hypothesis we infected isolated rat ventricular cardiomyocytes with adenovirus encoding SMAD4 (AdSMAD4) and investigated the impact of SMAD4 overexpression on the development of apoptosis and hypertrophy under stimulation with phenylephrine (PE). Infection of cardiomyocytes with AdSMAD4 significantly enhanced SMAD-binding activity while apoptosis after 24 and 36 h infection did not rise. But when SMAD4 overexpressing cardiomyocytes were incubated with PE (10 microM), the number of apoptotic cells increased (Ctrl: 94.97 +/- 6.91%; PE: 102.48 +/- 4.78% vs. AdSMAD4 + PE: 118.64 +/- 3.28%). Furthermore expression of caspase 3 as well as bax/bcl2 ratio increased in SMAD4 overexpressing, PE-stimulated cardiomyocytes. In addition, the effects of SMAD4 overexpression on PE-induced hypertrophic growth were analyzed. Protein synthesis 36 h after AdSMAD4 infection was comparable to control cells, whereas the increase in protein synthesis stimulated by phyenylephrine was significantly reduced in SMAD4 overexpressing cells (134.28 +/- 10.02% vs. 100.57 +/- 8.86%). SMAD4 triggers the transition from hypertrophy to apoptosis in ventricular cardiomyocytes. Since SMADs are increased under several pathophysiological conditions in the heart, it can be assumed that it triggers apoptosis induction and therefore contributes to negative remodeling and heart failure progression.

Mechanical compression of articular cartilage induces chondrocyte proliferation and inhibits proteoglycan synthesis by activation of the ERK pathway: implications for tissue engineering and regenerative medicine

Articular cartilage is recalcitrant to endogenous repair and regeneration and is thus a focus of tissue engineering and regenerative medicine strategies. A prerequisite for articular cartilage tissue engineering is an understanding of the signal transduction pathways involved in mechanical compression during trauma or disease. We sought to explore the role of the extracellular signal-regulated kinase 1/2 (ERK 1/2) pathway in chondrocyte proliferation and proteoglycan synthesis following acute mechanical compression. Bovine articular cartilage explants were cultured with and without the ERK 1/2 pathway inhibitor PD98059. Cartilage explants were statically loaded to 40% strain at a strain rate of 1/s for 5 s. Control explants were cultured under similar conditions but were not loaded. There were four experimental groups: (a) no load, without inhibitor; (b) no load, with the inhibitor PD98059; (c) loaded, without the inhibitor; and (d) loaded, with the inhibitor PD98059. The explants were cultured for varying durations from 5 min to 5 days and were then analysed by biochemical and immunohistochemical methods. Mechanical compression induced phosphorylation of ERK 1/2, and this was attenuated with the ERK 1/2 pathway inhibitor PD98059 in a dose-dependent manner. Chondrocyte proliferation was increased by mechanical compression. This effect was blocked by the inhibitor of the ERK 1/2 pathway. Mechanical compression also led to a decrease in proteoglycan synthesis that was reversed with inhibitor PD98059. In conclusion, the ERK 1/2 pathway is involved in the proliferative and biosynthetic response of chondrocytes following acute static mechanical compression.

Galectin-9 accelerates transforming growth factor beta3-induced differentiation of human mesenchymal stem cells to chondrocytes

Galectin-9 (Gal-9), a beta-galactoside binding lectin, plays a crucial role in innate and adaptive immunity. In the rat collagen-induced arthritis model, administration of Gal-9 induced repair of existing cartilage injury even when joints were already swollen with cartilage destruction. We thus attempted to explore the role of Gal-9 in chondrocyte differentiation utilizing human mesenchymal stem cell (MSC) pellet cultures. During chondrogenesis induced by transforming growth factor beta3 (TGFbeta3), MSCs strongly expressed endogenous Gal-9. Expression of Gal-9 peaked on day 14 and the neutralization of endogenous Gal-9 resulted in the reduced chondrogenesis, indicating possible involvement of Gal-9 in TGFbeta-mediated chondrogenesis. In pellets, addition of Gal-9 significantly enhanced TGFbeta3-induced chondrogenesis, as evidenced by increasing proteoglycan content, but not cell proliferation. In the absence of Gal-9, collagen expression by MSCs switched from type I to type II on 28 days after stimulation with TGFbeta3. When MSCs were co-stimulated with Gal-9, the class switch occurred on day 21. In addition, Gal-9 synergistically enhanced TGFbeta3-induced phosphorylation of Smad2, though Gal-9 did not itself induce detectable Smad2 phosphorylation. These results suggest that Gal-9 has a beneficial effect on cartilage repair in injured joints by induction of differentiation of MSCs into chondrocytes.

Transforming growth factor-beta induces CD44 cleavage that promotes migration of MDA-MB-435s cells through the up-regulation of membrane type 1-matrix metalloproteinase

CD44, a transmembrane receptor for hyaluronic acid, is implicated in various adhesion-dependent cellular processes, including cell migration, tumor cell metastasis and invasion. Recent studies demonstrated that CD44 expressed in cancer cells can be proteolytically cleaved at the ectodomain by membrane type 1-matrix metalloproteinase (MT1-MMP) to form soluble CD44 and that CD44 cleavage plays a critical role in cancer cell migration. Here, we show that transforming growth factor-beta (TGF-beta), a multifunctional cytokine involved in cell proliferation, differentiation, migration and pathological processes, induces MT1-MMP expression in MDA-MB-435s cells. TGF-beta-induced MT1-MMP expression was blocked by the specific extracellular regulated kinase-1/2 (ERK1/2) inhibitor PD98059 and the specific phosphoinositide 3-OH kinase (PI3K) inhibitor LY294002. In addition, treatment with SP600125, an inhibitor for c-Jun NH(2)-terminal kinase (JNK), resulted in a significant inhibition of MT1-MMP production. These data suggest that ERK1/2, PI3K, and JNK likely play a role in TGF-beta-induced MT1-MMP expression. Interestingly, treatment of MDA-MB-435s cells with TGF-beta resulted in a colocalization of MT1-MMP and CD44 in the cell membrane and in an increased level of soluble CD44. Using an electric cell-substrate impedance sensing cell-electrode system, we demonstrated that TGF-beta treatment promotes MDA-MB-435s cell migration, involving MT1-MMP-mediated CD44 cleavage. MT1-MMP siRNA transfection-inhibited TGF-beta-induced cancer cell transendothelial migration. Thus, this study contributes to our understanding of molecular mechanisms that play a critical role in tumor cell invasion and metastasis.

Inhibition of JNK enhances TGF-beta1-activated Smad2 signaling in mouse embryonic lung

The Smad2/3 pathway plays a key role in mediating TGF-beta1 inhibition of branching morphogenesis and induction of connective tissue growth factor (CTGF) expression in embryonic lungs. Because a number of cell-specific interactions have been described between TGF-beta1-driven Smad signaling and the c-Jun N-terminal kinase (JNK) pathway, we have investigated the effects of JNK inhibition on TGF-beta1 activation of Smad2, inhibition of branching, induction of CTGF expression, and apoptosis in mouse embryonic lung explants. Mouse embryonic day 12.5 (E12.5) lung explants were treated with TGF-beta1 in the presence or absence of a specific pharmacologic JNK inhibitor (SP600125) and a specific JNK peptide inhibitor (JNKI). We found that TGF-beta1 activated the JNK pathway by stimulating c-Jun phosphorylation, which was blocked by JNK inhibitors. Treatment with SP600125 stimulated Smad2 phosphorylation and enhanced TGF-beta1-induced Smad2 phosphorylation. Treatment with JNK inhibitors also decreased normal branching morphogenesis and induced CTGF expression as well as augmented TGF-beta1 inhibition of branching and induction of CTGF expression. Furthermore, JNK inhibition-induced apoptosis. Our results demonstrate that inhibition of the JNK pathway promotes TGF-beta1-driven Smad2 responses in lung branching morphogenesis. These data suggest that the JNK pathway may antagonize TGF-beta1 dependent Smad2 signaling during mouse embryonic lung development.

The type III transforming growth factor-beta receptor negatively regulates nuclear factor kappa B signaling through its interaction with beta-arrestin2

Transforming growth factor-beta (TGF-beta) increases or decreases nuclear factor kappa B (NFkappaB) signaling in a context-dependent manner through mechanisms that remain to be defined. The type III transforming growth factor-beta receptor (TbetaRIII) is a TGF-beta superfamily co-receptor with emerging roles in both mediating and regulating TGF-beta superfamily signaling. We have previously reported a novel interaction of TbetaRIII with the scaffolding protein, beta-arrestin2, which results in TbetaRIII internalization and downregulation of TGF-beta signaling. beta-arrestin2 also scaffolds interacting receptors with the mitogen-activated protein kinase and NFkappaB-signaling pathways. Here, we demonstrate that TbetaRIII, through its interaction with beta-arrestin2, negatively regulates NFkappaB signaling in MCF10A breast epithelial and MDA-MB-231 breast cancer cells. Increasing TbetaRIII expression reduced NFkappaB-mediated transcriptional activation and IkappaBalpha degradation, whereas a TbetaRIII mutant unable to interact with beta-arrestin2, TbetaRIII-T841A, had no effect. In a reciprocal manner, short hairpin RNA-mediated silencing of either TbetaRIII expression or beta-arrestin2 expression increased NFkappaB-mediated transcriptional activation and IkappaBalpha degradation. Functionally, TbetaRIII-mediated repression of NFkappaB signaling is important for TbetaRIII-mediated inhibition of breast cancer cell migration. These studies define a mechanism through which TbetaRIII regulates NFkappaB signaling and expand the roles of this TGF-beta superfamily co-receptor in regulating epithelial cell homeostasis.

Modulation of xylosyltransferase I expression provides a mechanism regulating glycosaminoglycan chain synthesis during cartilage destruction and repair

Osteoarthritis and rheumatoid arthritis are characterized by loss of proteoglycans (PGs) and their glycosaminoglycan (GAG) chains that are essential for cartilage function. Here, we investigated the role of glycosyltransferases (GTs) responsible for PG-GAG chain assembly during joint cartilage destruction and repair processes. At various times after antigen-induced arthritis (AIA) and papain-induced cartilage repair in rats, PG synthesis and deposition, expression of GTs, and GAG chain composition were analyzed. Our data showed that expression of the GT xylosyltransferase I (XT-I) gene initiating PG-GAG chain synthesis was significantly reduced in AIA rat cartilage and was associated with a decrease in PG synthesis. Interestingly, interleukin-1beta, the main proinflammatory cytokine incriminated in joint diseases, down-regulated the XT-I gene expression with a concomitant decrease in PG synthesis in rat cartilage explants ex vivo. However, cartilage from papain-injected rat knees showed up-regulation of XT-I gene expression and increased PG synthesis at early stages of cartilage repair, a process associated with up-regulation of TGF-beta1 gene expression and mediated by p38 mitogen-activated protein kinase activation. Consistently, silencing of XT-I expression by intraarticular injection of XT-I shRNA in rat knees prevented cartilage repair by decreasing PG synthesis and content. These findings show that GTs play a key role in the loss of PG-GAGs in joint diseases and identify novel targets for stimulating cartilage repair.

TGF-beta1 modulates focal adhesion kinase expression in rat intestinal epithelial IEC-6 cells via stimulatory and inhibitory Smad binding elements

TGF-beta and FAK modulate cell migration, differentiation, proliferation and apoptosis, and TGF-beta promotes FAK transcription in intestinal epithelial cells via Smad-dependent and independent pathways. We utilized a 1320 bp FAK promoter-luciferase construct to characterize basal and TGF-beta-mediated FAK gene transcription in IEC-6 cells. Inhibiting JNK or Akt negated TGF-beta-stimulated promoter activity; ERK inhibition did not block the TGF-beta effect but increased basal activity. Co-transfection with Co-Smad4 enhanced the TGF-beta response while the inhibitory Smad7 abolished it. Serial deletions sequentially removing the four Smad binding elements (SBE) in the 5' untranslated region of the promoter revealed that the two most distal SBE's are positive regulators while SBE3 exerts a negative influence. Mutational deletion of two upstream p53 sites enhanced basal but did not affect TGF-beta-stimulated increases in promoter activity. TGF-beta increased DNA binding of Smad4, phospho-Smad2/3 and Runx1/AML1a to the most distal 435 bp containing 3 SBE and 2 AML1a sites by ChIP assay. However, although point mutation of SBE1 ablated the TGF-beta-mediated rise in SV40-promoter activity, mutation of AML1a sites did not. TGF-beta regulation of FAK transcription reflects a complex interplay between positive and negative non-Smad signals and SBE's, the last independent of p53 or AML1a.

Involvement of Gas7 along the ERK1/2 MAP kinase and SOX9 pathway in chondrogenesis of human marrow-derived mesenchymal stem cells

OBJECTIVE

The growth-arrest-specific protein, Gas7, has been shown to be involved in reorganization of the cytoskeleton and for inducing changes in cell shape during cell differentiation. The goals of this study were to investigate the novel role of human Gas7 (hGas7) in chondrogenic differentiation of human mesenchymal stem cells (hMSCs) and to identify the relationship between hGas7, extracellular signal-regulated kinase (ERK1/2) and SOX9 in the chondrogenic pathway.

METHODS

Bone marrow-derived hMSCs were induced to undergo chondrogenic differentiation with transforming growth factor-beta1 (TGF-beta1) in an aggregate culture system. The expression of hGas7 and SOX9 and phosphorylation of ERK1/2 at multiple time points were investigated. Chondrogenic capacity was evaluated by the size of aggregates, by glycosaminoglycan content, and by type II collagen and proteoglycan deposition after interfering with expression of hGas7, ERK1/2 or SOX9. To delineate the functional role of these genes in chondrogenesis, inhibition of individual gene's expression in hMSCs, by antisense oligonucleotides or interference RNA (siRNA), and the effect on chondrogenic differentiation were also investigated.

RESULTS

Treatment of hMSCs with TGF-beta1 resulted in a transient up-regulation of hGas7b, one of the hGas7 isoforms (day 3-day 5), a transient phosphorylation of ERK1/2 (0.5-4 h) and an up-regulation of SOX9 (2 h to day 14). Transient expression of hGas7b was also detected in hMSCs by reverse transcription-polymerase chain reaction at day 2 and day 3 following TGF-beta1 treatment. Interference with hGas7b production by hGas7b-specific antisense oligonucleotide or inhibition of p-ERK with PD98059, a specific inhibitor of ERK signaling pathway, or interference with SOX9 production by SOX9 siRNA all caused adverse effects of chondrogenic differentiation of hMSCs. Meanwhile, inhibition of p-ERK or SOX9 both blocked the expression of hGas7b. However, the p-ERK and SOX9 pathway was not affected by inhibition of hGas7b.

CONCLUSION

These results provide evidence that the transient expression of hGas7b, regulated by activation of ERK1/2 and SOX9 pathway, is essential for chondrogenic differentiation of hMSCs.

Type III transforming growth factor-beta (TGF-beta) receptor mediates apoptosis in renal cell carcinoma independent of the canonical TGF-beta signaling pathway

PURPOSE

Alterations in transforming growth factor-beta (TGF-beta) signaling occur early during malignant transformation of renal epithelial cells and are associated with loss of type III TGF-beta receptor (TbetaRIII) expression. We evaluated the role of TbetaRIII in mediation of apoptosis using in vitro cell culture and in vivo animal models of clear cell renal cell carcinoma.

EXPERIMENTAL DESIGN

TbetaR3 expression was manipulated with adenoviral gene vector delivery system in vitro and in vivo. Induction of apoptosis and signaling through the Smad and mitogen-activated protein kinase (MAPK) pathways were examined at various time points after infection. To study viral oncolysis in vivo, human renal cell carcinoma cells were implanted s.c. in the flanks of nude mice and treated with intratumoral injections of adenovirus.

RESULTS

Restoring TbetaRIII expression in clear cell renal cell carcinoma resulted in a marked induction of apoptosis using in vitro cell culture and in vivo animal models. The expression of the cytoplasmic domain, but not the extracellular domain, of TbetaRIII mimicked the induction of apoptosis by full-length TbetaRIII in cell culture and the growth inhibition of tumors in athymic nude mice. TbetaRIII-associated apoptosis was not dependent on signaling through the canonical TGF-beta/Smad pathway but was mediated through p38 MAPK.

CONCLUSION

These findings indicate a novel mechanistic antitumor function for TbetaRIII and further support its role as an important tumor suppressor in clear cell renal cell carcinoma.

Regulation of cartilage formation and maturation by mitogen-activated protein kinase signaling

The majority of bones comprising the adult vertebrate skeleton are generated from hyaline cartilage templates that form during embryonic development. A process known as endochondral ossification is responsible for the conversion of these transient cartilage anlagen into mature, calcified bone. Endochondral ossification is a highly regulated, multistep cell specification program involving the initial differentiation of prechondrogenic mesenchymal cells into hyaline chondrocytes, terminal differentiation of hyaline chondrocytes into hypertrophic chondrocytes, and finally, apoptosis of hypertrophic chondrocytes followed by bone matrix deposition. Recently, extensive research has been carried out describing roles for the three major mitogen-activated protein kinase (MAPK) signaling pathways, the extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and c-jun N-terminal kinase (JNK) pathways, in the successive stages of chondrogenic differentiation. In this review, we survey this research examining the involvement of ERK1/2, p38, and JNK pathway signaling in all aspects of the chondrogenic differentiation program from embryonic through postnatal stages of development. In addition, we summarize evidence from in vitro studies examining MAPK function in immortalized chondrogenic cell lines and adult mesenchymal stem cells. We also provide suggestions for future studies that may help ameliorate existing confusion concerning the specific roles of MAPK signaling at different stages of chondrogenesis.

Tumor necrosis factor-alpha inhibits chondrogenic differentiation of synovial fibroblasts through p38 mitogen activating protein kinase pathways

We previously reported that synovial fibroblast-like cells (SFs) can be differentiated into chondrocytes through activin receptor-like kinase (ALK) 3 activation. The aim of this study was to clarify the effect and signaling pathways of tumor necrosis factor (TNF)-alpha on the chondrogenic differentiation of SFs. Primary SFs from patients with rheumatoid arthritis (RA) were treated with recombinant human bone morphogenetic protein-2 or transduced with a constitutively active mutant of the ALK3 gene (ALK3CA) with or without TNF-alpha, and then cultured in pellets. Expression of chondrocyte-specific genes was analyzed by real-time polymerase chain reaction or by histological analysis. Inhibitors of mitogen-activating protein kinase (MAPK) pathways or adenovirus vectors carrying a dominant-negative mutant of the IkappaB kinase 2 gene (AxIKK2DN) were used to analyze the signaling pathways of TNF-alpha. Expression of chondrocyte-specific genes was induced in SFs either by rhBMP-2 treatment or by ALK3CA transduction, which was strongly suppressed by TNF-alpha treatment. TNF-alpha markedly increased the p38 MAPK pathways in SFs, and inhibition of p38 MAPK activation partially restored the inhibitory effect of TNF-alpha on the chondrogenic differentiation of SFs. Combination therapy BMP-2 and anti-TNF-alpha agents especially targeting p38 MAPK might be a good approach to stimulating neochondrogenesis in the damaged joints in RA.

Sphingosine kinases and sphingosine-1-phosphate are critical for transforming growth factor beta-induced extracellular signal-regulated kinase 1 and 2 activation and promotion of migration and invasion of esophageal cancer cells

Transforming growth factor beta (TGFbeta) plays a dual role in oncogenesis, acting as both a tumor suppressor and a tumor promoter. These disparate processes of suppression and promotion are mediated primarily by Smad and non-Smad signaling, respectively. A central issue in understanding the role of TGFbeta in the progression of epithelial cancers is the elucidation of the mechanisms underlying activation of non-Smad signaling cascades. Because the potent lipid mediator sphingosine-1-phosphate (S1P) has been shown to transactivate the TGFbeta receptor and activate Smad3, we examined its role in TGFbeta activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and promotion of migration and invasion of esophageal cancer cells. Both S1P and TGFbeta activate ERK1/2, but only TGFbeta activates Smad3. Both ligands promoted ERK1/2-dependent migration and invasion. Furthermore, TGFbeta rapidly increased S1P, which was required for TGFbeta-induced ERK1/2 activation, as well as migration and invasion, since downregulation of sphingosine kinases, the enzymes that produce S1P, inhibited these responses. Finally, our data demonstrate that TGFbeta activation of ERK1/2, as well as induction of migration and invasion, is mediated at least in part by ligation of the S1P receptor, S1PR2. Thus, these studies provide the first evidence that TGFbeta activation of sphingosine kinases and formation of S1P contribute to non-Smad signaling and could be important for progression of esophageal cancer.

Inorganic pyrophosphate generation by transforming growth factor-beta-1 is mainly dependent on ANK induction by Ras/Raf-1/extracellular signal-regulated kinase pathways in chondrocytes

ANK is a multipass transmembrane protein transporter thought to play a role in the export of intracellular inorganic pyrophosphate and so to contribute to the pathophysiology of chondrocalcinosis. As transforming growth factor-beta-1 (TGF-β1) was shown to favor calcium pyrophosphate dihydrate deposition, we investigated the contribution of ANK to the production of extracellular inorganic pyrophosphate (ePPi) by chondrocytes and the signaling pathways involved in the regulation of Ank expression by TGF-β1. Chondrocytes were exposed to 10 ng/mL of TGF-β1, and Ank expression was measured by quantitative polymerase chain reaction and Western blot. ePPi was quantified in cell supernatants. RNA silencing was used to define the respective roles of Ank and PC-1 in TGF-β1-induced ePPi generation. Finally, selective kinase inhibitors and dominant-negative/overexpression plasmid strategies were used to explore the contribution of several signaling pathways to Ank induction by TGF-β1. TGF-β1 strongly increased Ank expression at the mRNA and protein levels, as well as ePPi production. Using small interfering RNA technology, we showed that Ank contributed approximately 60% and PC-1 nearly 20% to TGF-β1-induced ePPi generation. Induction of Ank by TGF-β1 required activation of the extracellular signal-regulated kinase (ERK) pathway but not of p38-mitogen-activated protein kinase or of protein kinase A. In line with the general protein kinase C (PKC) inhibitor calphostin C, Gö6976 (a Ca²⁺-dependent PKC inhibitor) diminished TGF-β1-induced Ank expression by 60%, whereas a 10% inhibition was observed with rottlerin (a PKCδ inhibitor). These data suggest a regulatory role for calcium in TGF-β1-induced Ank expression. Finally, we demonstrated that the stimulatory effect of TGF-β1 on Ank expression was inhibited by the suppression of the Ras/Raf-1 pathway, while being enhanced by their constitutive activation. Transient overexpression of Smad 7, an inhibitory Smad, failed to affect the inducing effect of TGF-β1 on Ank mRNA level. These data show that TGF-β1 increases ePPi levels, mainly by the induction of the Ank gene, which requires activation of Ras, Raf-1, ERK, and Ca²⁺-dependent PKC pathways in chondrocytes.

Tyrosine kinase and cooperative TGFβ signaling in the reproductive organs of Schistosoma mansoni

Drug-induced suppression of female schistosome sexual maturation is an auspicious strategy to combat schistosomiasis since the eggs are the causative agent. The establishment of drug targets requires knowledge about the molecular mechanisms that regulate the development of the female reproductive organs, which include vitellarium and ovary. This review summarizes recent studies suggesting tyrosine kinases as important factors for the regulation of female gonad development. In this context, especially cytoplasmatic tyrosine kinases of the Src class seem to play dominant roles. Moreover, experimental data and theoretical concepts are provided supporting a crosstalk between tyrosine kinase and TGFbeta signaling in the production of vitellocytes. Finally, we take advantage from the schistosome genome project to propose a model for the regulation of vitelline-cell production and differentiation.

Protective effect of hyaluronic acid on interleukin-1-induced deregulation of beta1-integrin and insulin-like growth factor-I receptor signaling and collagen biosynthesis in cultured human chondrocytes

The mechanism of protective action of hyaluronic acid (HA) on collagen metabolism disturbances in tissues during inflammation is not known. Insulin-like growth factor-I (IGF-I) receptor and beta1-integrin receptor signaling plays an important role in the regulation of collagen biosynthesis at both transcriptional and post-transcriptional levels. The present study was undertaken to evaluate the effect of IL-1beta (inductor of experimental inflammation) on the signaling pathways as well as on collagen biosynthesis, gelatinases and prolidase activity in cultured human chondrocytes and the effect of HA on these processes. It was found that IL-1beta-dependent inhibition of collagen biosynthesis was accompanied by increase in beta1-integrin receptor, NF-kB expressions, and increase in phosphorylation of FAK, that resulted in stimulation of metalloproteinase MMP-2 and MMP-9 activities, but not prolidase activity and expression. Simultaneously, decrease in expression of IGF-I receptor and phosphorylation of Akt and p38 were found. All those processes were counteracted by HA. This suggests that cross talk between beta1-integrin and IGF-I receptors is disturbed by IL-1beta, and HA recovers their proper signaling in cultured chondrocytes. We propose that IGF-I receptor and beta1-integrin signaling may play an important role in protective effect of hyaluronic acid on interleukin-1-induced inhibition of collagen biosynthesis in cultured human chondrocytes.

Lead induces chondrogenesis and alters transforming growth factor-beta and bone morphogenetic protein signaling in mesenchymal cell populations

BACKGROUND

It has been established that skeletal growth is stunted in lead-exposed children. Because chondrogenesis is a seminal step during skeletal development, elucidating the impact of Pb on this process is the first step toward understanding the mechanism of Pb toxicity in the skeleton.

OBJECTIVES

The aim of this study was to test the hypothesis that Pb alters chondrogenic commitment of mesenchymal cells and to assess the effects of Pb on various signaling pathways.

METHODS

We assessed the influence of Pb on chondrogenesis in murine limb bud mesenchymal cells (MSCs) using nodule formation assays and gene analyses. The effects of Pb on transforming growth factor-beta (TGF-beta) and bone morphogenetic protein (BMP) signaling was studied using luciferase-based reporters and Western analyses, and luciferase-based assays were used to study cyclic adenosine monophosphate response element binding protein (CREB), beta-catenin, AP-1, and nuclear factor-kappa B (NF-kappaB) signaling. We also used an ectopic bone formation assay to determine how Pb affects chondrogenesis in vivo.

RESULTS

Pb-exposed MSCs showed enhanced basal and TGF-beta/BMP induction of chondrogenesis, evidenced by enhanced nodule formation and up-regulation of Sox-9, type 2 collagen, and aggrecan, all key markers of chondrogenesis. We observed enhanced chondrogenesis during ectopic bone formation in mice preexposed to Pb via drinking water. In MSCs, Pb enhanced TGF-beta but inhibited BMP-2 signaling, as measured by luciferase reporter assays and Western analyses of Smad phosphorylation. Although Pb had no effect on basal CREB or Wnt/beta-catenin pathway activity, it induced NFkappaB signaling and inhibited AP-1 signaling.

CONCLUSIONS

The in vitro and in vivo induction of chondrogenesis by Pb likely involves modulation and integration of multiple signaling pathways including TGF-beta, BMP, AP-1, and NFkappaB.

Transforming growth factor-beta inhibits telomerase through SMAD3 and E2F transcription factors

Cancer arises from multiple genetic changes within the cell, among which constitutive telomerase activity and attainment of immortality are central. Expression of hTERT, the protein component of telomerase, is increased in most cancer cells. Transforming growth factor-beta (TGFbeta), a potent tumor suppressor, has been reported to regulate hTERT expression. We found that TGFbeta represses hTERT expression in normal and cancer cells and that this effect is mediated through Smad3 but also requires Erk1/2, p38 kinase and histone deacetylase activity. Furthermore, we identified four critical E2F transcription factor binding sites within the hTERT gene promoter that confer the TGFbeta response. Finally, using the E2F-1 knockout model, we showed that loss of E2F-1 abolishes TGFbeta inhibition of telomerase expression. These findings highlight the prominent role of TGFbeta in regulating telomerase expression and identify Smad3 and E2F-1 as critical mediators of TGFbeta effects in both normal and cancer cells.

Complexity in interpretation of embryonic epithelial-mesenchymal transition in response to transforming growth factor-beta signaling

Epithelial-mesenchymal transition (EMT) is a highly conserved and fundamental process that governs morphogenesis in development and may also contribute to cancer metastasis. Transforming growth factor (TGF-beta) is a potent inducer of EMT in various developmental and tumor systems. The analysis of TGF-beta signal transduction pathways is now considered a critically important area of biology, since many defects occur in these pathways in embryonic development. The complexity of TGF-beta signal transduction networks is overwhelming due to the large numbers of interacting constituents, complicated feedforward, feedback and crosstalk circuitry mechanisms that they involve in addition to the cellular kinetics and enzymatics that contribute to cell signaling. As a result of this complexity, apparently simple but highly important questions remain unanswered, that is, how do epithelial cells respond to such TGF-beta signals? System biology and cellular kinetics play a crucial role in cellular function; omissions of such a critical contributor may lead to inaccurate understanding of embryonic EMT. In this review, we identify and explain why certain conditions need to be considered for a true representation of TGF-beta signaling in vivo to better understand the controlled, yet delicate mechanism of embryonic EMT.

Transforming Growth Factor β Is a Critical Regulator of Adult Human Islet Plasticity

Tissue plasticity is well documented in the context of pancreatic regeneration and carcinogenesis, with recent reports implicating dedifferentiated islet cells both as endocrine progenitors and as the cell(s) of origin in pancreatic adenocarcinoma. Accordingly, it is noteworthy that accumulating evidence suggests that TGFβ signaling is essential to pancreatic endocrine development and maintenance, whereas its loss is associated with the progression to pancreatic adenocarcinoma. The aim of this study was to examine the role of TGFβ in an in vitro model of islet morphogenetic plasticity. Human islets were embedded in a collagen gel and cultured under conditions that induced transformation into duct-like epithelial structures (DLS). Addition of TGFβ caused a dose-dependent decrease in DLS formation. Although it was demonstrated that collagen-embedded islets secrete low levels of TGFβ, antibody-mediated neutralization of this endogenously released TGFβ improved DLS formation rates, suggesting local TGFβ concentrations may in fact be higher. Time course studies indicated that TGFβ signaling was associated with an increase in ERK and p38 MAPK phosphorylation, although inhibitor-based studies were consistent with an islet endocrine-stabilizing effect mediated by p38 alone. Localization of TGFβ signaling molecules suggested that the action of TGFβ is directly on the β-cell to inhibit apoptosis and thus stabilize endocrine phenotype.

Splicing factor 3b subunit 4 binds BMPR-IA and inhibits osteochondral cell differentiation

Bone morphogenetic protein (BMP)-2/4 play critical roles in early embryogenesis and skeletal development. BMP-2/4 signals conduct into cells via two types of serine/threonine kinase receptors, known as BMPR-I (IA and IB) and BMPR-II. Here we identified splicing factor 3b subunit 4 (SF3b4) as a molecule that interacts with BMPR-IA, using a yeast two-hybrid screening with a human fetal brain cDNA library. Co-immunoprecipitation/immunoblot analysis confirmed their interaction in mammalian cells. By separation of the cell components, SF3b4 was present in the cell membrane fraction with BMPR-IA as well as in the nucleus. Overexpression of SF3b4 inhibited BMP-2-mediated osteogenic and chondrocytic differentiation of C2C12 and ATDC5 cells, respectively, and the endogenous expression level of SF3b4 decreased during differentiation in ATDC5 cells. By reporter gene assay, SF3b4 suppressed Id reporter gene activity, specific to the Smad1/5/8 pathway, but not TGFbeta-mediated reporter gene activity. Biotin labeling of the cell surface proteins followed by their immunoblot revealed that SF3b4 decreased the cell surface BMPRI-A levels. Further analysis by molecular modeling of the intracellular domain of BMPR-IA, coupled with binding studies of its several mutants, indicated that the site(s) for SF3b4 binding is not directly associated with the C-terminal lobe and the activation segment. Taken together, these results suggest that SF3b4, known to be localized in the nucleus and involved in RNA splicing, binds BMPR-IA and specifically inhibits BMP-mediated osteochondral cell differentiation.

A novel modulatory mechanism of transforming growth factor-beta signaling through decorin and LRP-1

Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that signals to the nucleus through cell surface transmembrane receptors with serine/threonine kinase activity and cytoplasmic effectors, including Smad proteins. Here we describe two novel modulators of this pathway, lipoprotein-receptor related protein (LRP-1) and decorin. Decorin null (Dcn null) myoblasts showed a diminished TGF-beta response that is restored by decorin re-expression. Importantly, this reactivation occurs without changes in the binding to TGF-beta receptors, Smad protein phosphorylation, or Smad-4 nuclear translocation. In wild type myoblasts, inhibition of decorin binding to LRP-1 and depletion of LRP-1 inhibited TGF-beta response to levels similar to those observed in Dcn null myoblasts. Re-expression of decorin in Dcn null myoblasts cannot restore TGF-beta response if the Smad pathway or phosphatidylinositol 3-kinase activity is inhibited, suggesting that this LRP-1-decorin modulatory pathway requires activation of the Smad pathway by TGF-beta and involves phosphatidylinositol 3-kinase activity. This work unveils a new regulatory mechanism for TGF-beta signaling by decorin and LRP-1.

Agonists of peroxisome proliferators-activated receptors (PPAR) alpha, beta/delta or gamma reduce transforming growth factor (TGF)-beta-induced proteoglycans' production in chondrocytes

OBJECTIVE

To investigate the potency of selective agonists of peroxisome proliferators-activated receptors' (PPAR) isotypes (alpha, beta/delta or gamma) to modulate the stimulating effect of transforming growth factor-beta1 (TGF-beta1) on proteoglycans' (PGs) synthesis in chondrocytes.

METHOD

Rat chondrocytes embedded in alginate beads and cultured under low serum conditions were exposed to TGF-beta1 (10 ng/ml), alone or in combination with the following agonists: Wy14643 for PPARalpha, GW501516 for PPARbeta/delta, rosiglitazone (ROSI) for PPARgamma, in the presence or absence of PPAR antagonists (GW6471 for PPARalpha, GW9662 for PPARgamma). PGs' synthesis was evaluated by radiolabelled sulphate incorporation and glycosaminoglycans' (GAGs) content by Alcian blue staining of beads and colorimetric 1.9 dimethyl-methylene blue assay after beads' solubilization. Phosphorylation of Extracellular Signal-related Kinase1/2 (ERK1/2), Smad2/3 and p38-MAPK was assessed by Western Blot and production of prostaglandin E2 (PGE2) by Enzyme immuno-assay (EIA). Levels of mRNA for PPAR target genes [acyl-CoA oxidase (ACO) for PPARalpha; mitochondrial carnitin palmitoyl transferase-1 (CPT-1) for PPARbeta/delta and adiponectin for PPARgamma], aggrecan, TGF-beta1 and genes controlling GAGs' side chains' synthesis were quantified by real time polymerase chain reaction and normalized over RP29 housekeeping gene.

RESULTS

ACO was selectively up-regulated by 100 microM of Wy14643, CPT-1 by 100 nM of GW501516 and adiponectin by 10 microM of ROSI without cell toxicity. TGF-beta1 increased PGs' synthesis by four-fold, GAGs' content and deposition by 3.5-fold and six-fold, respectively, while inducing aggrecan expression around 10-fold without modifying mRNA levels of GAGs' controlling enzymes. PPAR agonists inhibited the stimulating effect of TGF-beta1 by 24-44% on PGs' synthesis and over 75% on aggrecan, GAGs' content and deposition with the following rank order of potency: ROSI>GW501516> or =Wy14643. TGF-beta1-induced phosphorylation of Smad2/3 and ERK1/2 was reduced by ROSI over GW501516 but not by Wy14643 whereas stimulated PGE2 production was inhibited by Wy14643 over GW501516 but not by ROSI. The effect of PPAR agonists on PPAR target genes and TGF-beta1-induced aggrecan expression was reversed selectively by PPAR antagonists.

CONCLUSION

In chondrocytes' beads, PPAR agonists reduced the stimulating effect of TGF-beta1 on PGs by inhibiting TGF-beta1-induced aggrecan expression in an isotype-selective manner. Thus, PPAR agonists could be deleterious in situation of cartilage repair although being protective in situation of cartilage degradation.

Ex vivo expansion and pluripotential differentiation of cryopreserved human bone marrow mesenchymal stem cells

This study is aimed at investigating the potentials of ex vivo expansion and pluri-differentiation of cryopreservation of adult human bone marrow mesenchymal stem cells (hMSCs) into chondrocytes, adipocytes and neurocytes. Cryopreserved hMSCs were resuscitated and cultured for 15 passages, and then induced into chondrocytes, adipocytes and neurocytes with corresponding induction medium. The induced cells were observed for morphological properties and detected for expressions of type II collagen, triglyceride or neuron-specific enolase and nestin. The result showed that the resuscitated cells could differentiate into chondrocytes after exposure to transforming growth factor beta(1) (TGF-beta(1)), insulin-like growth factor I (IGF-I) and vitamin C (V(C)), and uniformly changed morphologically from a spindle-like fibroblastic appearance to a polygonal shape in three weeks. The induced cells were heterochromatic to safranin O and expressed cartilage matrix-procollagenal (II) mRNA. The resuscitated cells cultured in induction medium consisting of dexamethasone, 3-isobutyl-1-methylxanthine, indomethacin and IGF-I showed adipogenesis, and lipid vacuoles accumulation was detectable after 21 d. The resuscitated hMSCs were also induced into neurocytes and expressed nestin and neuron specific endolase (NSE) that were special surface markers associated with neural cells at different stage. This study suggested that the resuscitated hMSCs should be still a population of pluripotential cells and that it could be used for establishing an abundant hMSC reservoir for further experiment and treatment of various clinical diseases.

MS analysis of chondroitin polymerization: effects of Mn2+ ions on the stability of UDP-sugars and chondroitin synthesis

Chondroitin polymerase from Escherichia coli strain K4 (K4CP) synthesizes chondroitin (CH) polysaccharides by the alternate addition of N-acetyl-D-galactosamine (GalNAc) and D-glucuronic acid (GlcA) to acceptor CH oligosaccharides in the presence of Mn(2+) ions. In this study, we applied matrix-assisted laser desorption ionization and time-of-flight mass spectrometry (MALDI-TOF MS) for the further characterization of the products synthesized by K4CP from CH hexasaccharide as an initial acceptor and UDP-GalNAc and UDP-GlcA as donors. The analysis identified individual CH chains of various lengths and enabled the calculation of their average molecular weights. The ion peaks of the CH chains synthesized in the short-time reactions demonstrated not only the alternate addition of GlcA and GalNAc but also the more frequent transfer of GlcA and GalNAc, consistent with our previous kinetic data. In contrast, the MS spectra of the chains synthesized in the long-time reaction showed that CH chains containing GalNAc at the nonreducing ends were more abundant than those containing GlcA. We found that this inconsistency was due to the preferential decomposition of UDP-GlcA by Mn(2+) ions. We defined the optimal conditions to yield further elongation of the CH chains that have nearly equal numbers of GlcA and GalNAc residues at the nonreducing ends.

Phosphate stimulates matrix Gla protein expression in chondrocytes through the extracellular signal regulated kinase signaling pathway

Whereas increasing evidence suggests that inorganic phosphate (Pi) may act as a signaling molecule in mineralization-competent cells, its mechanisms of action remain largely unknown. The aims of the present work were to determine whether Pi regulates expression of matrix Gla protein (MGP), a mineralization inhibitor, in growth plate chondrocytes and to identify the involved signaling pathways. Chondrogenic ATDC5 cells and primary growth plate chondrocytes were used. Messenger RNA and protein analyses were performed by quantitative PCR and Western blotting, respectively. The activation and role of MAPKs were, respectively, determined by Western blotting and the use of specific inhibitors. Immunohistological detection of ERK1/2 was performed in rib organ cultures from newborn mice. The results indicate that Pi markedly stimulates expression of MGP in ATDC5 cells and primary growth plate chondrocytes. Investigation of the involved intracellular signaling pathways reveals that Pi activates ERK1/2 in a cell-specific manner, because the stimulation was observed in ATDC5 and primary chondrocytes, MC3T3-E1 osteoblasts, and ST2 stromal cells, but not in L929 fibroblasts or C2C12 myogenic cells. Accordingly, immunohistological detection of ERK1/2 phosphorylation in rib growth plates revealed a marked signal in chondrocytes. Finally, a specific ERK1/2 inhibitor, UO126, blocks Pi-stimulated MGP expression in ATDC5 cells, indicating that ERK1/2 mediates, mainly, the effects of Pi. These data demonstrate, for the first time, that Pi regulates MGP expression in growth plate chondrocytes, thereby suggesting a key role for Pi and ERK1/2 in the regulation of bone formation.

Gene therapy and wound healing

Wound repair involves the sequential interaction of various cell types, extracellular matrix molecules, and soluble mediators. During the past 10 years, much new information on signals controlling wound cell behavior has emerged. This knowledge has led to a number of novel therapeutic strategies. In particular, the local delivery of pluripotent growth factor molecules to the injured tissue has been intensively investigated over the past decade. Limited success of clinical trails indicates that a crucial aspect of the growth factor wound healing strategy is the effective delivery of these polypeptides to the wound site. A molecular approach in which genetically modified cells synthesize and deliver the desired growth factor in regulated fashion has been used to overcome the limitations associated with the (topical) application of recombinant growth factor proteins. We have summarized the molecular and cellular basis of repair mechanisms and their failure, and we give an overview of techniques and studies applied to gene transfer in tissue repair.

Rebamipide inhibits gastric cancer cell growth

Rebamipide is an antiulcer drug used in Japan, Korea, China, Philippines, and other Asian countries for treatment of gastritis and peptic ulcer. Its effect on gastric cancer cell growth and its regulatory mechanisms remain unknown. We examined whether rebamipide affects human gastric cancer cell proliferation and activation of Smad signaling pathway. Gastric cancer (AGS) cells were treated with either (a) medium (control), (b) medium-containing rebamipide (0.5-2 mg/mL), or (c) PD98059+rebamipide. We determined cell proliferation, expression of p21, phosphorylation of ERK2, JNK p38, and Smad2/3, formation of Smad2/3-Smad4 complex, and nuclear translocation of Smad2/3. Rebamipide treatment inhibited AGS cell proliferation and increased p21, Smad2/3 phosphorylation, and Smad2/3-Smad4 complex formation. Rebamipide induced phosphorylation of ERK2 but not JNK or p38. Inactivation of ERK2 by PD98059 partly attenuated rebamipide-induced p21 expression. These data demonstrate that rebamipide activates Smad signaling pathway and suppresses human gastric cancer cell growth. Inactivation of ERK2 partly inhibited rebamipide-induced p21 expression, indicating a crosstalk between ERK and Smad signaling pathways.

Loss of functional transforming growth factor (TGF)-beta type II receptor results in insensitivity to TGF-beta1-mediated apoptosis and Epstein-Barr virus reactivation

Transforming growth factor (TGF)-beta1 induces not only cell growth inhibition or apoptosis but also Epstein-Barr virus (EBV) reactivation in some Burkitt's lymphoma (BL) cell lines. The purpose of this study was to define the role of TGF-beta signaling molecules in response to TGF-beta1-mediated cell growth inhibition, apoptosis, and EBV reactivation in BL cell lines. First, we confirmed the effect of TGF-beta1 on the cell growth and EBV reactivation in six BL cell lines. TGF-beta1 induced cell growth inhibition and EBV reactivation in these cell lines but did not in Akata cells. To elucidate the mechanism of TGF-beta1 unresponsiveness in Akata cells, we studied the expression of TGF-beta receptors and the intracellular signaling molecules Smads. All cell lines expressed TGF-beta type I receptor, Smad2, Smad3, and Smad4. TGF-beta type II receptor (R-II) was expressed in all cell lines except Akata cells. Introduction of the TGF-beta R-II into Akata cells results in sensitivity to TGF-beta1-mediated growth inhibition, apoptosis, and EBV reactivation. In addition, to test a possibility to the transcriptional repression of the TGF-beta R-II gene in Akata cells, the effect of histone deacetylation (HDAC) inhibitor, trichostatin A (TSA) was examined. The expression of TGF-beta R-II in Akata cells was induced by TSA treatment. These results suggest that the lack of functional TGF-beta R-II impedes the progression of signals through TGF-beta1 and becomes a determinant of unresponsiveness to TGF-beta1-mediated growth inhibition and EBV reactivation.

Inhibition of in vitro chondrogenesis in RGD-modified three-dimensional alginate gels

The goal of this study was to investigate the effects of adhesion to the arginine-glycine-aspartic acid (RGD) sequence on the chondrogenesis of bone marrow stromal cells (BMSCs). Synthetic RGE- and RGD-containing peptides were conjugated to sodium alginate, and bovine BMSCs were seeded onto 2D alginate surfaces or encapsulated in 3D gels. BMSCs spread specifically on RGD-modified surfaces, and spreading was inhibited by a soluble RGD peptide and by anti-beta1 and anti-alpha(v)beta3 integrin blocking antibodies. After 7 days in 3D gel culture, the chondrogenic supplements (TGF-beta1 and dexamethasone) significantly stimulated chondrocytic gene expression (collagen II, aggrecan, and Sox-9) and matrix accumulation (collagen II and sGAG) in RGE-modified gels, but this response was inhibited in the RGD-modified gels. Inhibition of sGAG synthesis increased with increasing RGD density, and synthesis was partially rescued by adding a soluble RGD peptide. Addition of an anti-alpha(v)beta3 integrin blocking antibody had no effect on chondrogenesis, while an anti-alpha5 antibody reduced sGAG accumulation. Overall, this study demonstrates that interaction with the RGD motif significantly inhibits the initial chondrogenesis of BMSCs within 3D alginate gels. These results provide new insights into the role of cell-matrix interactions in regulating chondrogenesis and highlight the importance of choosing appropriate biomaterials for tissue engineering therapies.

Dynamic compression regulates the expression and synthesis of chondrocyte-specific matrix molecules in bone marrow stromal cells

The overall objective of the present study was to investigate the mechanotransduction of bovine bone marrow stromal cells (BMSCs) through the interactions between transforming growth factor beta1 (TGF-beta1), dexamethasone, and dynamic compressive loading. Overall, the addition of TGF-beta1 increased cell viability, extracellular matrix (ECM) gene expression, matrix synthesis, and sulfated glycosaminoglycan content over basal construct medium. The addition of dexamethasone further enhanced extracellular matrix gene expression and protein synthesis. There was little stimulation of ECM gene expression or matrix synthesis in any medium group by mechanical loading introduced on day 8. In contrast, there was significant stimulation of ECM gene expression and matrix synthesis in chondrogenic media by dynamic loading introduced on day 16. The level of stimulation was also dependent on the medium supplements, with the samples treated with basal medium being the least responsive and the samples treated with TGF-beta1 and dexamethasone being the most responsive at day 16. Both collagen I and collagen II gene expressions were more responsive to dynamic loading than aggrecan gene expression. Dynamic compression upregulated Smad2/3 phosphorylation in samples treated with basal and TGF-beta1 media. These findings suggest that interactions between mechanical stimuli and TGF-beta signaling may be an important mechanotransduction pathway for BMSCs, and they indicate that mechanosensitivity may vary during the process of chondrogenesis.

Inhibition of p38 MAPK signaling in chondrocyte cultures results in enhanced osteogenic differentiation of perichondral cells

Chondrocytes and osteoblasts originate from the same progenitor cell; however, both are characterized by distinct gene expression profiles once they are differentiated. Signals from differentiating chondrocytes, such as Indian hedgehog (Ihh), regulate the differentiation of osteoblast precursor cells. The MAPK pathways play important roles in controlling the differentiation of both chondrocytes and osteoblasts, with the p38 pathway being particularly relevant in skeletal cells. In the present study, we investigated the effects of p38 inhibition on osteoblastic marker gene expression in chondrocyte cultures. Using high-density micromass cultures of mesenchymal cells as well as chondrocytes that had differentiated in vivo and were maintained in short-term monolayer culture, we demonstrate elevated Runx2, Osterix and Osteocalcin transcript levels in chondrocyte cultures upon inhibition of p38 activity with the pharmacological inhibitor PD169316. Osteocalcin immunolocalization was restricted to perichondral/periosteal cells in micromass cultures, suggesting that inhibition of p38 results in increased periosteal osteogenesis. Coinciding with increased expression of these genes, we observed elevated levels of transcripts for Ihh and its target gene, Ptch, in response to p38 inhibition. Addition of recombinant hedgehog protein mimicked some effects of p38 inhibitors. We therefore suggest that p38 signaling regulates chondrocyte-perichondral cell communication during skeletal development, partially through increased Ihh signaling.

Biomechanical signals exert sustained attenuation of proinflammatory gene induction in articular chondrocytes

OBJECTIVES

Physical therapies are commonly used for limiting joint inflammation. To gain insight into their mechanisms of actions for optimal usage, we examined persistence of mechanical signals generated by cyclic tensile strain (CTS) in chondrocytes, in vitro. We hypothesized that mechanical signals induce anti-inflammatory and anabolic responses that are sustained over extended periods.

METHODS

Articular chondrocytes obtained from rats were subjected to CTS for various time intervals followed by a period of rest, in the presence of interleukin-1beta (IL-1beta). The induction for cyclooxygenase (COX-2), inducible nitric oxide synthase (iNOS), matrix metalloproteinase (MMP)-9, MMP-13 and aggrecan was analyzed by real-time polymerase chain reaction (PCR), Western blot analysis and immunofluorescence.

RESULTS

Exposure of chondrocytes to constant CTS (3% CTS at 0.25 Hz) for 4-24 h blocked more than 90% (P<0.05) of the IL-1beta-induced transcriptional activation of proinflammatory genes, like iNOS, COX-2, MMP-9 and MMP-13, and abrogated inhibition of aggrecan synthesis. CTS exposure for 4, 8, 12, 16, or 20 h followed by a rest for 20, 16, 12, 8 or 4h, respectively, revealed that 8h of CTS optimally blocked (P<0.05) IL-1beta-induced proinflammatory gene induction for ensuing 16 h. However, CTS for 8h was not sufficient to inhibit iNOS expression for ensuing 28 or 40 h.

CONCLUSIONS

Data suggest that constant application of CTS blocks IL-1beta-induced proinflammatory genes at transcriptional level. The signals generated by CTS are sustained after its removal, and their persistence depends upon the length of CTS exposure. Furthermore, the sustained effects of mechanical signals are also reflected in their ability to induce aggrecan synthesis. These findings, once extrapolated to human chondrocytes, may provide insight in obtaining optimal sustained effects of physical therapies in the management of arthritic joints.

ERK contributes to the effects of Smad signaling on oxidized LDL-induced PAI-1 expression in human mesangial cells

Oxidized low-density lipoprotein (Ox-LDL) stimulates plasminogen activator inhibitor-1 (PAI-1) expression in human mesangial cells mediated by transforming growth factor-beta (TGF-beta)/Smad signaling pathway. TGF-beta activates extracellular signal-regulated kinase (ERK) in mesangial cells, and ERK is involved in activation of Smad2/3. This study examines whether an interaction exists between Ox-LDL-induced TGF-beta/Smad signaling pathways and ERK activation leading to PAI-1 transcription in human mesangial cells. Ox-LDL (50 microg/mL) induced an acute increase in ERK activity within 15 min, which decreased to control value at 2 h. Incubation with anti-TGF-beta or SB-431542, an inhibitor of the TGF-beta type I receptor, along with Ox-LDL, inhibited the expected increase in ERK phosphorylation. Treatment with PD98059 or UO126, mitogen-activated ERK-activating kinase 1/2 inhibitors, significantly inhibited the Ox-LDL-induced increase in PAI-1 mRNA and nuclear Smad3 expression, DNA/protein complex formation, and PAI-1 promoter activity. These results suggest that phosphorylation of ERK is induced by Ox-LDL through the induction of the TGF-beta signaling pathway and that activated ERK, in turn, participates in the Ox-LDL-induced Smad3 activation and subsequent PAI-1 gene expression in mesangial cells.

cAMP inhibits transforming growth factor-beta-stimulated collagen synthesis via inhibition of extracellular signal-regulated kinase 1/2 and Smad signaling in cardiac fibroblasts

Cardiac fibroblasts produce and degrade extracellular matrix and are critical in regulating cardiac remodeling and hypertrophy. Cytokines such as transforming growth factor-beta (TGF-beta) play a fundamental role in the development of tissue fibrosis by stimulating matrix deposition and other profibrotic responses, but less is known about pathways that might inhibit fibrosis. Increased cAMP formation inhibits myofibroblast differentiation and collagen production by cardiac fibroblasts, but the mechanism of this inhibition is not known. We sought to characterize the signaling pathways by which cAMP-elevating agents alter collagen expression and myofibroblast differentiation. Treatment with 10 microM forskolin or isoproterenol increased cAMP production and cAMP response element binding protein (CREB) phosphorylation in cardiac fibroblasts and inhibited serum- or TGF-beta-stimulated collagen synthesis by 37% or more. These same cAMP-elevating agents blunted TGF-beta-stimulated expression of collagen I, collagen III, and alpha-smooth muscle actin. Forskolin or isoproterenol treatment blocked the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) induced by TGF-beta despite the fact that these cAMP-elevating agents stimulated ERK1/2 activation on their own. cAMP-elevating agents also attenuated the activation of c-Jun NH(2)-terminal kinase and reduced binding of the transcriptional coactivator CREB-binding protein 1 to transcriptional complexes containing Smad2, Smad3, and Smad4. Pharmacological inhibition of ERK completely blocked TGF-beta-stimulated collagen gene expression, but expression of an active mutant of MEK was additive with TGF-beta treatment. Thus, cAMP-elevating agents inhibit the profibrotic effects of TGF-beta in cardiac fibroblasts largely through inhibiting ERK1/2 phosphorylation but also by reducing Smad-mediated recruitment of transcriptional coactivators.