Platelet-derived growth factor induces collagenase 3 transcription in osteoblasts through the activator protein 1 complex

Host-Pathogen Interactions in Progressive Chronic Periodontitis

Periodontitis is an infection characterized by the occurrence of supporting tissue destruction with an episodic nature. Disease progression is often determined by the loss of attachment level or alveolar bone, and sequential probing of periodontal attachment remains the most commonly utilized method to diagnose progressive destruction of the periodontium. The tolerance method has been the most extensive clinical method used in recent years to determine site-specific attachment level changes. There is abundant evidence that major tissue destruction in periodontal lesions results from the recruitment of immune cells. Considerable effort has been made to study the host cell and mediator profiles involved in the pathogenesis of chronic periodontitis, but the definition of active sites, where current periodontal breakdown occurs, and consecutive characterization of the mediators involved are still among the main concerns. In the present review, we summarize periodontopathic bacteria and host factors, including infiltrating cell populations, cytokines, and host matrix metalloproteinases, associated with under-going episodic attachment loss that could partly explain the mechanisms involved in destruction of the supporting tissues of the tooth.

Chloramphenicol causes mitochondrial stress, decreases ATP biosynthesis, induces matrix metalloproteinase-13 expression, and solid-tumor cell invasion

Overuse and abuse of antibiotics can increase the risk of cancer. Chloramphenicol can inhibit both bacterial and mitochondrial protein synthesis, causing mitochondrial stress and decreased ATP biosynthesis. Chloramphenicol can accelerate cancer progression; however, the underlying mechanisms of chloramphenicol in carcinogenesis and cancer progression are still unclear. We found that chloramphenicol can induce matrix metalloproteinase (MMP)-13 expression and increase MMP-13 protein in conditioned medium, resulting in an increase in cancer cell invasion. Chloramphenicol also activated c-Jun N-terminal kinases (JNK) and phosphatidylinositol 3-kinase (PI-3K)/Akt signaling, leading to c-Jun protein phosphorylation. The activated c-Jun protein has been proven to activate binding to the MMP-13 promoter and also upregulate the amount of MMP-13. Both the SP 600125 (JNK inhibitor) and LY 294002 (PI-3K/Akt inhibitor) can inhibit chloramphenicol-induced c-Jun phosphorylation, MMP-13 expression, and cell invasion. Overexpression of the dominant-negative JNK and PI-3K p85 subunit also negate chloramphenicol-induced responses. Other antibiotics that cause mitochondrial stress and a decrease in ATP biosynthesis also induce MMP-13 expression. These findings suggest that chloramphenicol-induced PI-3K/Akt, JNK phosphorylation, and activator protein 1 activation might function as a novel mitochondrial stress signal that result in an increase of MMP-13 expression and MMP-13-associated cancer cell invasion. The findings of this study confirms that chloramphenicol, and other 70S ribosomal inhibitors, should be administered with caution, especially during cancer therapy.

Protein kinase C-delta transactivates platelet-derived growth factor receptor-alpha in mechanical strain-induced collagenase 3 (matrix metalloproteinase-13) expression by osteoblast-like cells

Matrix metalloproteinase-13 (MMP-13, or collagenase 3) has been shown to degrade intact collagen and to participate in situations where rapid and effective remodeling of collagenous ECM is required. Mechanical strain induction of MMP-13 is an example of how osteoblasts respond to high mechanical forces and participate in the bone-remodeling mechanism. Using MC3T3-E1 osteoblast-like cells, we dissected the signaling molecules involved in MMP-13 induction by mechanical strain. Reverse transcription-PCR and zymogram analysis showed that platelet-derived growth factor receptor (PDGFR) inhibitor, AG1296, inhibited the mechanical strain-induced MMP-13 gene and activity. However, the induction was not affected by anti-PDGF-AA serum. Immunoblot analysis revealed time-dependent phosphorylation of PDGFR-alpha up to 2.7-fold increases within 3 min under strain. Transfection with shPDGFR-alpha (at 4 and 8 microg/ml) abolished PDGFR-alpha and reduced MMP-13 expression. Moreover, time-dependent recruitments of phosphoinositide 3-kinase (PI3K) by PDGFR-alpha were detected by immunoprecipitation with anti-PDGFR-alpha serum followed by immunoblot with anti-PI3K serum. AG1296 inhibited PDGFR-alpha/PI3K aggregation and Akt phosphorylation. Interestingly, protein kinase C-delta (PKC-delta) inhibitor, rottlerin, inhibited not only PDGFR-alpha/PI3K aggregation but PDGFR-alpha phosphorylation. The sequential activations were further confirmed by mutants DeltaPKC-delta, DeltaAkt, and DeltaERK1. Consistently, the primary mouse osteoblast cells used the same identified signaling molecules to express MMP-13 under mechanical strain. These results demonstrate that, in osteoblast-like cells, the MMP-13 induction by mechanical strain requires the transactivation of PDGFR-alpha by PKC-delta and the cross-talk between PDGFR-alpha/PI3K/Akt and MEK/ERK pathways.

MMP-13 and TIMP-1 determinations in progressive chronic periodontitis

Matrix metalloproteinase (MMP)-13 is a collagenase involved in extracellular matrix degradation either by its direct degradative effects or by processing bioactive substrates. The aim of this study was to determine the levels of MMP-13 and tissue inhibitor of metalloproteinase (TIMP)-1 in gingival crevicular fluid (GCF) and gingival biopsies obtained from active and inactive sites during chronic periodontitis progression.

MATERIALS AND METHODS

This was a longitudinal study in which chronic periodontitis patients with moderate to severe disease were included and followed until they developed progression determined by the tolerance method. GCF samples were obtained from periodontitis, active, inactive and healthy sites and additional gingival biopsies were taken from active and inactive sites. MMP-13 and TIMP-1 determinations were carried out by immunodot blots and immunowestern blots.

RESULTS

In progressive periodontitis, MMP-13 and TIMP-1 remained unchanged between active and inactive sites, but as the TIMP-1 relative levels increased together with MMP-13 elevation in inactive samples, an inverse correlation was observed in active sites. Besides, MMP-13 was undetectable in healthy controls.

CONCLUSION

Chronic periodontitis is characterized by increased MMP-13 expression. During disease progression, active sites tended to decrease TIMP-1 levels in association with MMP-13 elevation.

Differential and synergistic effects of platelet-derived growth factor-BB and transforming growth factor-beta1 on activated pancreatic stellate cells

OBJECTIVE

The cytokines platelet-derived growth factor (PDGF) and transforming growth factor (TGF)-beta1 are major factors influencing the transformation from the quiescent to the activated phenotype of pancreatic stellate cells (PSC), a process involved in the pathogenesis of chronic pancreatitis. Albeit much effort has been made to study the effects of PDGF and TGF-beta1 on PSCs, their interaction is still unclear, because these cytokines show both differential and synergistic effects as outlined by this study.

METHODS

Culture-activated PSCs of rats were treated with PDGF-BB and TGF-beta1. Subsequent changes of cell proliferation and migration were determined by cell counting, (+)-bromo-2'-deoxyuridine enzyme-linked immunosarbant assay (ELISA), and migration assay. Gene expression, synthesis of proteins, and activation of kinases were further studied by reverse transcription-polymerase chain reaction, real-time polymerase chain reaction, ELISA, and Western blot.

RESULTS

PDGF-BB increased PSC proliferation and migration, accompanied by elevated expression of matrix metalloproteinases (MMP)-13 and MMP-3. The mRNA amount of procollagen alpha2(I), alpha-smooth muscle actin (alpha-SMA), tissue inhibitor of metalloproteinase (TIMP)-1, and TGF-beta1 was also increased by PDGF-BB. In contrast, PDGF-BB reduced collagen type I in culture medium and synthesis of alpha-SMA. Treatment of PSC with TGF-beta1 decreased proliferation, had no significant effect on migration and MMP expression, but increased expression and synthesis of procollagen alpha2(I) and alpha-SMA. Both cytokines induced phosphorylation of extracellular signal regulated kinase (ERK)-1/2 and p38, but only PDGF-BB activated the protein kinase B signaling pathway.

CONCLUSION

PDGF-BB augments effects of TGF-beta1 on the mRNA level presumably because of up-regulation of TGF-beta1 synthesis and common signaling pathways of the 2 cytokines. However, at the protein level, PDGF-BB impairs typical TGF-beta1 effects such as increased synthesis of collagen (type I) and alpha-SMA. Moreover, PDGF-BB facilitates degradation of extracellular matrix proteins by enhancement of MMP synthesis, but MMP activity was probably limited because of elevated tissue inhibitor of metalloproteinase 1 expression.

Bone morphogenetic protein-2 suppresses collagenase-3 promoter activity in osteoblasts through a runt domain factor 2 binding site

Transforming growth factor-beta (TGFbeta) superfamily of growth factors, which include bone morphogenetic proteins (BMPs), have multiple effects in osteoblasts. In this study, we examined the regulation of collagenase-3 promoter activity by BMP-2 in osteoblast-enriched (Ob) cells from fetal rat calvariae. BMP-2 suppressed the activity of a -2 kb collagenase-3 promoter/luciferase recombinant in a time- and dose-dependent manner. The BMP-2 effect on the collagenase-3 promoter was further tested in several collagenase-3 promoter deletion constructs and it was narrowed down to a -148 to -94 nucleotide segment of the promoter containing a runt domain factor 2 (Runx2) site at nucleotide -132 to -126. The effect of BMP-2 was obliterated in a collagenase-3 promoter/luciferase construct containing a mutated Runx2 (mRunx2) sequence indicating that the Runx2 site mediates the BMP-2 response. Electrophoretic mobility shift assays, using nuclear extracts from control and BMP-2-treated Ob cells, indicated that the Runx2 protein is a component of the specific DNA-protein complex formed on the Runx2 site and that the BMP-2 effect may be associated with minor protein modifications rather than major changes in the composition of specific proteins interacting with the Runx2 site. We confirmed that other members of the TGFbeta family can down-regulate the collagenase-3 promoter by showing that TGFbeta1 also suppresses the promoter activity in a time- and dose-dependent manner. In conclusion, this study demonstrates that BMP-2 and TGFbeta1 suppress collagenase-3 promoter activity in osteoblasts and establishes a link between BMP-2 action and collagenase-3 expression via Runx2, a major regulator of osteoblast formation and function.

Phosphorylation of the carboxyl-terminal transactivation domain of c-Fos by extracellular signal-regulated kinase mediates the transcriptional activation of AP-1 and cellular transformation induced by platelet-derived growth factor

Polypeptide growth factors, such as platelet-derived growth factor (PDGF), promote the reinitiation of DNA synthesis and cell growth through multiple intracellular signaling pathways that converge in the nucleus to regulate the activity of transcription factors, thereby controlling the expression of growth-promoting genes. Among them, the AP-1 (activating protein-1) family of transcription factors, including c-Fos and c-Jun family members, plays a key role, as AP-1 activity is potently activated by PDGF and is required to stimulate cell proliferation. However, the nature of the pathways connecting PDGF receptors to AP-1 is still poorly defined. In this study, we show that PDGF regulates AP-1 by stimulating the expression and function of c-Fos through extracellular signal-regulated kinase (ERK). The latter involves the direct phosphorylation by ERK of multiple residues in the carboxyl-terminal transactivation domain of c-Fos, which results in its increased transcriptional activity. Interestingly, the phosphorylation of c-Fos by ERK was required for the ability of PDGF and serum to stimulate the activity of c-Fos as well as AP-1-dependent transcription. Furthermore, we provide evidence that the ERK-dependent activation of c-Fos is an integral component of the mitogenic pathway by which PDGF regulates normal and aberrant cell growth.

Platelet-derived growth factor up-regulates the expression of transcription factors NF-E2, GATA-1 and c-Fos in megakaryocytic cell lines

Platelet-derived growth factor (PDGF) is a platelet alpha-granule protein. In previous reports, we demonstrated the expression of PDGF receptors on platelets and megakaryocytic cells and that PDGF enhanced the proliferation of megakaryocytic progenitor cells. In this study, we investigated the effects of PDGF on mRNA and protein expressions of megakaryocyte-associated transcription factors, c-Fos, GATA-1, NF-E2 and PU.1, in two human megakaryocytic cell lines CHRF-288-11 and DAMI. RT-PCR/Southern blot analysis and Real-time PCR demonstrated that PDGF increased the mRNA expression of c-Fos, GATA-1 and NF-E2, but not PU.1 in a dose- and time-dependent manner. The activation was confirmed at the protein level by Western blot analysis of both total cell and nuclear lysates. The addition of increasing concentrations of Tyrphostin AG1295, an inhibitor of PDGF receptor kinase, blocked the stimulatory effect of PDGF on the mRNA and protein expressions of these transcription factors. The up-regulation of c-Fos, GATA-1 and NF-E2 protein by PDGF was inhibited by actinomycin D and cycloheximide, suggesting that mRNA and protein synthesis might be involved in the mechanism. Our data suggest a direct stimulatory effect of PDGF on c-Fos, GATA-1 and NF-E2 expressions and we speculate that these transcription factors might be involved in the signal transduction of PDGF on the regulation of megakaryocytopoiesis.

Functional analysis of aortic endothelial cells expressing mutant PDGF receptors with respect to expression of matrix metalloproteinase-3

Platelet-derived growth factor (PDGF) stimulates expression of matrix metalloproteinases (MMPs), including stromelysin-1 (MMP-3). Induction of these expressions is known to occur during the course of atherosclerosis, tumor invasion, and metastasis. We investigated PDGF-alpha receptor (alphaR)- and beta receptor (betaR)-mediated signaling pathways for the expression of MMP-3 and invasion activity using porcine aortic endothelial (PAE) cells with stable expression of normal or mutated PDGF receptors. RT-PCR and Western blot analyses revealed that PDGF-BB induces MMP-3 expression in PAE cells that exclusively express either the PDGF-alphaR or the -betaR, but not in non-transfected control cells. To identify the signals necessary for PDGF receptor-mediated induction of MMP-3 expression, several lines of PAE cells expressing mutant PDGF receptors were further analyzed. Cells expressing mutant PDGF receptors unable to associate with Src or PLCgamma, retained the ability to induce MMP-3 expression as a result of PDGF-BB stimulation. However, incubation with PDGF-BB did not induce MMP-3 expression in cells expressing a mutant PDGF-betaR unable to associate with phosphatidylinositol 3(')-kinase (PI3K). LY294002, a PI3K inhibitor, reduced PDGF-BB-stimulated MMP-3 expression in PAE cells expressing wild-type PDGF receptors. In contrast, PDGF-BB induced MMP-3 expression in the presence of U-73122, a PLCgamma inhibitor. Moreover, PDGF-BB enhanced the invasiveness of cells expressing wild type PDGF-beta receptors, but not of cells expressing mutant PDGF-betaRs impaired in their ability to associate with PI3K. In light of these results, it appears that PDGF-BB is capable of inducing MMP-3 expression through both the PDGF-alphaR and the -betaR, and the effects are contributed by the PI3K-mediated transduction pathways.

Macrophage migration inhibitory factor up-regulates matrix metalloproteinase-9 and -13 in rat osteoblasts. Relevance to intracellular signaling pathways

Neutral matrix metalloproteinases (MMPs) play an important role in bone matrix degradation accompanied by bone remodeling. We herein show for the first time that macrophage migration inhibitory factor (MIF) up-regulates MMP-13 (collagenase-3) mRNA of rat calvaria-derived osteoblasts. The mRNA up-regulation was seen at 3 h in response to MIF (10 microg/ml), reached the maximum level at 6-12 h, and returned to the basal level at 36 h. MMP-13 mRNA up-regulation was preceded by up-regulation of c-jun and c-fos mRNA. Tissue inhibitor of metalloproteinase (TIMP)-1 and MMP-9 (92-kDa type IV collagenase) were also up-regulated, but to a lesser extent. The MMP-13 mRNA up-regulation was significantly suppressed by genistein, herbimycin A and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine. Similarly, a selective mitogen-activated protein kinase (MAPK) kinase (MEK)1/2 inhibitor (PD98059) and c-jun/activator protein (AP)-1 inhibitor (curcumin) suppressed MMP-13 mRNA up-regulation induced by MIF. The mRNA levels of c-jun and c-fos in response to MIF were also inhibited by PD98059. Consistent with these results, MIF stimulated phosphorylation of tyrosine, autophosphorylation of Src, activation of Ras, activation of extracellular signal-regulated kinases (ERK) 1/2, a MAPK, but not c-Jun N-terminal kinase or p38, and phosphorylation of c-Jun. Osteoblasts obtained from calvariae of newborn JunAA mice, defective in phosphorylation of c-Jun, or newborn c-Fos knockout (Fos -/- ) mice, showed much less induction of MMP-13 with the addition of MIF than osteoblasts obtained from wild-type or littermate control mice. Taken together, these results suggest that MIF increases the MMP-13 mRNA level of rat osteoblasts via the Src-related tyrosine kinase-, Ras-, ERK1/2-, and AP-1-dependent pathway.

Platelet-derived growth factor BB secreted from osteoclasts acts as an osteoblastogenesis inhibitory factor

Osteoclasts and osteoblasts are responsible for strict bone maintenance with a balance between bone formation and resorption by interacting with each other. Recently, it has been revealed that osteoblasts/stromal cells regulate differentiation of osteoclasts/hematopoietic cells by two factors, the receptor activator of nuclear factor-kappaB (NF-kappaB) ligand (RANKL) on the plasma membrane, and secreted osteoprotegerin (OPG). However, no factors have yet been reported by which osteoclasts/hematopoietic cells regulate osteoblasts/stromal cells. To elucidate the possibility of signal transduction from osteoclasts to osteoblasts, we studied the conditioned medium of mouse osteoclast-like myeloma cell line RAW264.7 treated with RANKL. We found that this medium contains a factor that inhibits differentiation of mouse osteoblast precursor-like cell line MC3T3-E1 to osteoblasts induced by bone morphogenetic protein 4 (BMP-4) and named this factor osteoblastogenesis inhibitory factor (OBIF). OBIF was purified by successive three-step chromatography by heparin affinity, anion exchange, and reversed-phase columns. Osteoblastogenesis inhibitory activity made one peak in each chromatography step, showing the factor is a single entity. Active fractions were loaded on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and bands of proteins were excised, digested by trypsin, and analyzed by liquid chromatography equipped with tandem mass spectrometry (LC/MS/MS). Consequently, we have identified this factor to be platelet-derived growth factor BB (PDGF BB) homodimer. Furthermore, this identification of PDGF BB as OBIF was confirmed by neutralization of the inhibitory activity of the medium with anti-PDGF antibody. These results show, for the first time, that osteoclasts regulate osteoblasts directly and suggest that PDGF BB is a key factor in bone remodeling.

Induction of c-jun and TGF-beta 1 in Fischer 344 rats during amiodarone-induced pulmonary fibrosis

Amiodarone (AM) is an antidysrhythmic agent with a propensity to cause pulmonary toxicity, including potentially fatal fibrosis. In the present study, the potential roles of c-Jun and transforming growth factor (TGF)-beta 1 in AM-induced inflammation and fibrogenesis were examined after intratracheal administration of AM (1.83 micromol/day on days 0 and 2) or an equivalent volume (0.4 ml) of distilled water to male Fischer 344 rats. Northern and immunoblot analyses demonstrated that lung TGF-beta 1 (mRNA and protein) expression was increased 1.5- to 1.8-fold relative to control during the early inflammation period and 1 day, 1 wk, and 2 wk post-AM treatment. Lung c-Jun protein expression was increased concomitantly with evidence of AM-induced fibrosis; at 5 wk post-AM treatment, c-Jun protein was increased 3.3-fold relative to control. The results indicate a role for induction of c-jun and TGF-beta 1 expression in the development of AM-induced pulmonary fibrosis in the Fischer 344 rat and provide potential targets for therapeutic intervention.