Effects of growth factors on cell cycle arrest in dolichyl phosphate-depleted cultures

Polymeric mesh and insulin-like growth factor 1 delivery enhance cell homing and graft-cartilage integration

Cartilage injury, such as full-thickness lesions, predisposes patients to the premature development of osteoarthritis, a degenerative joint disease. While surgical management of cartilage lesions has improved, long-term clinical efficacy has stagnated, owing to the lack of hyaline cartilage regeneration and inadequate graft-host integration. This study tests the hypothesis that integration of cartilage grafts with native cartilage can be improved by enhancing the migration of chondrocytes across the graft-host interface via the release of chemotactic factor from a degradable polymeric mesh. To this end, a polylactide-co-glycolide/poly-ε-caprolactone mesh was designed to localize the delivery of insulin-like growth factor 1 (IGF-1), a well-established chondrocyte attractant. The release of IGF-1 (100 ng/mg) enhanced cell migration from cartilage explants, and the mesh served as critical structural support for cell adhesion, growth, and production of a cartilaginous matrix in vitro, which resulted in increased integration strength compared with mesh-free repair. Further, this neocartilage matrix was structurally contiguous with native and grafted cartilage when tested in an osteochondral explant model in vivo. These results demonstrate that this combined approach of a cell homing factor and supportive matrix will promote cell-mediated integrative cartilage repair and improve clinical outcomes of cartilage grafts in the treatment of osteoarthritis.

Effect of simvastatin on cholesterol metabolism in C2C12 myotubes and HepG2 cells, and consequences for statin-induced myopathy

The mechanism of statin-induced skeletal muscle myopathy is poorly understood. We investigated how simvastatin affects cholesterol metabolism, ubiquinone levels, and the prenylation and N-linked glycosylation of proteins in C2C12 myotubes. We used liver HepG2 cells for comparison, as their responses to statins are well-characterized in terms of their cholesterol metabolism (in contrast to muscle cells), and statins are well-tolerated in the liver. Differences between the two cell lines could indicate the mechanism behind statin-induced myopathy. Simvastatin reduced de novo cholesterol production in C2C12 myotubes by 95% after 18h treatment. The reduction was 82% in the HepG2 cells. Total cholesterol pools, however, remained constant in both cell lines. Simvastatin treatment similarly did not affect total ubiquinone levels in the myotubes, unlike in HepG2 cells (22% reduction in CoQ10). Statin treatment reduced levels of Ras and Rap1 prenylation in both cell lines, whereas N-linked glycosylation was only affected in C2C12 myotubes (21% reduction in rate). From these observations, we conclude that total cholesterol and ubiquinone levels are unlikely to be involved in statin-mediated myopathy, but reductions in protein prenylation and especially N-linked glycosylation may play a role. This first comparison of the responses to simvastatin between liver and skeletal muscle cell lines may be important for future research directions concerning statin-induced myopathy.

Up-regulation of functionally impaired insulin-like growth factor-1 receptor in scrapie-infected neuroblastoma cells

A growing body of evidence suggests that an altered level or function of the neurotrophic insulin-like growth factor-1 receptor (IGF-1R), which supports neuronal survival, may underlie neurodegeneration. This study has focused on the expression and function of the IGF-1R in scrapie-infected neuroblastoma cell lines. Our results show that scrapie infection induces a 4-fold increase in the level of IGF-1R in two independently scrapie-infected neuroblastomas, ScN2a and ScN1E-115 cells, and that the increased IGF-1R level was accompanied by increased IGF-1R mRNA levels. In contrast to the elevated IGF-1R expression in ScN2a, receptor binding studies revealed an 80% decrease in specific (125)I-IGF-1-binding sites compared with N2a cells. This decrease in IGF-1R-binding sites was shown to be caused by a 7-fold decrease in IGF-1R affinity. Furthermore, ScN2a showed no significant difference in IGF-1 induced proliferative response, despite the noticeable elevated IGF-1R expression, putatively explained by the reduced IGF-1R binding affinity. Additionally, IGF-1 stimulated IGF-1Rbeta tyrosine phosphorylation showed no major change in the dose-response between the cell types, possibly due to altered tyrosine kinase signaling in scrapie-infected neuroblastoma cells. Altogether these data indicate that scrapie infection affects the expression, binding affinity, and signal transduction mediated by the IGF-1R in neuroblastoma cells. Altered IGF-1R expression and function may weaken the trophic support in scrapie-infected neurons and thereby contribute to neurodegeneration in prion diseases.

Effect of simvastatin on vascular smooth muscle responsiveness: involvement of Ca(2+) homeostasis

This report is focused on the study of simvastatin-induced relaxation of rat aorta through its effects on vascular smooth muscle and Ca(2+) signalling. The presence of endothelium affected only the simvastatin-induced relaxation of aortic rings precontracted with noradrenaline, but not by depolarization with KCl 80 mM. Blockade of Ca(2+) entry through voltage-operated Ca(2+) channels (VOCCs) by diltiazem abolished the endothelium-dependent and direct relaxation, whereas Ca(2+)-ATPase inhibition by cyclopiazonic acid (3 x 10(-5) M) only affected the endothelium-dependent relaxation. In KCl-depolarised arteries concentration-response curves for CaCl(2) were shifted to the right in the presence of simvastatin (3 x 10(-6) and 3 x 10(-5) M) or diltiazem (10(-6) and 10(-7) M). The transient contraction caused by noradrenaline in Ca(2+)-free medium, which is mainly due to intracellular Ca(2+) release, was inhibited by simvastatin (3 x 10(-5) M) or cyclopiazonic acid (3 x 10(-5) M) and the contraction induced by CaCl(2) (2 x 10(-3) M) added after noradrenaline was inhibited by diltiazem and simvastatin. All the reported effects of simvastatin were inhibited by the product of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, mevalonate (10(-3) M). These findings demonstrate that the vascular effects of simvastatin may involve both Ca(2+) release from intracellular stores, which could promote activation of endothelial factors, and blockade of extracellular Ca(2+) entry, which promote relaxations independent of the presence of endothelium. This action on Ca(2+) could be related to the inhibition of isoprenoid synthesis, which subsequently affects the function of G-proteins involved in communication among intracellular Ca(2+) pools and capacitative Ca(2+) entry.

Simvastatin and Ca(2+) signaling in endothelial cells: involvement of rho protein

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor simvastatin is able to produce endothelium-dependent relaxation in addition to its lipid-lowering properties. The underlying mechanisms were investigated in bovine aortic endothelial cells (BAEC). Simvastatin induced an increase in cytosolic calcium ([Ca(2+)](i)) in BAEC, by releasing Ca(2+) from intracellular stores sensitive to thapsigargin and ryanodine, and increasing Ca(2+) entry. Simvastatin response was not altered by the phospholipase A(2) inhibitor ONO-RS-082, or the combination of superoxide dismutase plus catalase. However, the response to simvastatin was reduced by the product of HMG-CoA reductase, mevalonate or by the inhibitor of small G proteins of the Rho family, Clostridium botulinum C3 toxin. Thus, increase in [Ca(2+)](i) involving the activation of Rho protein through mevalonate-dependent pathway is essential for the action of simvastatin and might contribute to its beneficial effects against vascular diseases. This study helps elucidate the mechanisms of endothelial factor generation by simvastatin in BAEC.

Quantitation by (1)H-NMR of dolichol, cholesterol and choline-containing lipids in extracts of normal and phathological thyroid tissue

Proton magnetic resonance spectroscopy at 1.9 T was used to quantify dolichols, cholesterols, choline-containing phospholipids and double bonds in unsaturated acyl chains in lipid extracts of four types of thyroid tissue [normal (n = 27), papillary cancer (n = 15), adenoma (n = 13) and Basedow disease (n = 6)]. In normal thyroid the mean concentrations of dolichol, cholesterol and phospholipids were 1.2, 3.6 and 2.1 micromol/g wet weight, respectively. The concentrations of these lipids exhibited positive mutual correlations and positive correlations with patient age. The increase in dolichol in elderly human thyroid may be due to the accumulation of lysosomes and may help to compensate for the decrease in the activity of lysosomal enzymes and in thyroid hormone production and release. Dolichol concentrations were significantly lower in papillary cancer (0.4 micromol/g) and Basedow disease (0.3 micromol/g) compared to normal thyroid (p < 0.01 and p < 0.05, respectively), while cholesterol was enhanced only in cancer tissue (10.7 micromol/g). Benign adenoma exhibited normal levels of both dolichol and cholesterol. These results suggest that the synthesis and accumulation of isoprenoids are normal in adenoma but not in cancer.

Characterization of endothelial factors involved in the vasodilatory effect of simvastatin in aorta and small mesenteric artery of the rat

1. Vascular effects of the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, simvastatin, were studied in conductance (aorta) and resistance vessels (branch II or III of superior mesenteric artery, SMA) of the rat (12 - 14 weeks old). 2. Simvastatin produced relaxation of both aorta and SMA, with and without functional endothelium. These responses were inhibited by the product of HMG-CoA reductase, mevalonate (1 mmol l(-1)). 3. In vessels with functional endothelium, the NO-synthase inhibitor, L-N(G)-nitroarginine (L-NOARG, 30 micromol l(-1)), inhibited simvastatin-induced relaxation. In the presence of L-NOARG, relaxation to simvastatin was lower in vessels with endothelium than in endothelium-denuded arteries without L-NOARG. 4. The cyclo-oxygenase inhibitor, indomethacin (10 micromol l(-1)), abolished endothelium-dependent component of the response to simvastatin in both arteries. The combination of L-NOARG plus indomethacin did not produce further inhibition. The T(p) receptor antagonist, GR 32191B (3 micromol l(-1)), did not affect relaxation in aorta but it reduced response to low concentrations of simvastatin in SMA. However, the inhibitory effect of L-NOARG was less marked in the presence of GR 32191B in aorta but not in SMA. 5. The endothelium-dependent relaxation to simvastatin was inhibited by the superoxide dismutase (SOD, 100 u ml(-1)) or by the tyrosine kinase inhibitor, genistein (30 micromol l(-1)) in the two arteries. 6. The present study shows that simvastatin produces relaxation of conductance and small arteries through mevalonate-sensitive pathway. The endothelium-dependent relaxation to simvastatin involves both NO and vasodilator eicosanoids by a mechanism sensitive to SOD, and to genistein. Also, the results highlighted participation in the aorta of endothelial vasoconstrictor eicosanoids acting on the T(p) receptor after blockage of NO synthase only.

A link between basic fibroblast growth factor (bFGF) and EWS/FLI-1 in Ewing's sarcoma cells

The EWS/FLI-1 fusion gene is characteristic of most cases of Ewing's sarcoma and has been shown to be crucial for tumor transformation and cell growth. In this study we demonstrate a drastic down-regulation of the EWS/FLI-1 protein, and a growth arrest, following serum depletion of Ewing's sarcoma cells. This indicates that growth factor circuits may be involved in regulation of the fusion gene product. Of four different growth factors tested, basic fibroblast growth factor (bFGF) was found to be of particular significance. In fact, upon treatment of serum-depleted cells with bFGF, expression of the EWS/FLI-1 protein and growth of the Ewing's sarcoma cells were restored. In addition, a bFGF-neutralizing antibody, which was confirmed to inhibit FGF receptor (FGFR) phosphorylation, caused down-regulation of EWS/FLI-1. Experiments using specific cell cycle blockers (thymidine and colcemide) suggest that EWS/FLI-1 is directly linked to bFGF stimulation, and not indirectly to cell proliferation. We also demonstrated expression of FGFRs in several tumor samples of Ewing's sarcoma. Taken together, our data suggest that expression of FGFR is a common feature of Ewing's sarcoma and, in particular, that the bFGF pathway may be important for the maintenance of a malignant phenotype of Ewing's sarcoma cells through up-regulating the EWS/FLI-1 protein. Oncogene (2000) 19, 4298 - 4301

Regulatory role of mevalonate and N-linked glycosylation in proliferation and expression of the EWS/FLI-1 fusion protein in Ewing's sarcoma cells

The Ewing's sarcoma cell line RD-ES, which carries the EWS/FLI-1 fusion gene, responded to the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor lovastatin with growth arrest. Replenishment of mevalonate (MVA) to the arrested cells restored cell growth. However, if tunicamycin (TM), which is an inhibitor of N-linked glycosylation, was present together with MVA the cells remained arrested, indicating that N-linked glycosylation is of importance for growth of Ewing's sarcoma cells. Inhibition of the biosynthesis of EWS/FLI-1 fusion protein by treatment with antisense oligonucleotides also led to growth arrest, suggesting that this protein is of importance for cell growth. We investigated whether MVA synthesis and N-linked glycosylation could be involved in regulation of the expression of the EWS/FLI-1 fusion protein, which in fact contains four potential sites for N-linked glycosylation. We found that inhibition of both HMG-CoA reductase and N-linked glycosylation drastically decreased the expression of the fusion protein, which mainly appears in the cell nuclei. There was no significant difference in the inhibitory effect on the fusion protein between the cytoplasm and the cell nuclei, indicating that the transport of the fusion protein to the cell nucleus is not affected. The fusion protein did not exhibit any gel electrophoretic mobility shift after treatment of the cells with lovastatin or TM, and it did not incorporate [3H]glucosamine. Therefore we can conclude that the fusion protein is not a glycoprotein. The decreased expression of the fusion protein following lovastatin or TM treatment was found to be due to a lowered stability of de novo-synthesized fusion protein. The down-regulation of the fusion protein was correlated to growth arrest. Furthermore, the kinetics between the expression of EWS/FLI-1 fusion protein and the initiation of DNA synthesis in MVA-stimulated cells were similar. Taken together, our data suggest that the regulatory role of N-linked glycosylation in the expression of the EWS/FLI-1 fusion protein is important for growth of Ewing's sarcoma cells. Possible mechanisms underlying TM-induced decrease in EWS/FLI-1 expression may involve the breaking of growth factor receptor pathways.

CPP32 activation during dolichyl phosphate-induced apoptosis in U937 leukemia cells

Treatment of U937 cells with dolichyl phosphate led to an increase in the activity of the ICE family protease CPP32, accompanied with cleavage of pre-CPP32 to generate p17. Peptide inhibitors YVAD-cmk and Z-Asp-CH2-DCB (specific to ICE) and DEVD-CHO (specific to CPP32) blocked the dolichyl phosphate-induced apoptosis. The dolichyl phosphate-induced increase of CPP32 activity was inhibited by adenylate cyclase inhibitors, SQ 22536 and 2',5'-dideoxyadenosine. Dolichyl phosphate caused a transient increase of intracellular cAMP concentration. The results suggest that modulation of cAMP synthesis due to the stimulation of adenylate cyclase by dolichyl phosphate plays a critical role in CPP32 activation and apoptosis.

Mevalonic acid is limiting for N-linked glycosylation and translocation of the insulin-like growth factor-1 receptor to the cell surface. Evidence for a new link between 3-hydroxy-3-methylglutaryl-coenzyme a reductase and cell growth

Depletion of mevalonic acid (MVA), obtained by inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase using lovastatin, depressed the biosynthesis of dolichyl-phosphate and the rate of N-linked glycosylation and caused growth arrest in the melanoma cell line SK-MEL-2. The growth arrest was partially prevented by addition of high concentrations of insulin-like growth factor-1 (IGF-1) to the cells, indicating that MVA depletion may inhibit cell growth through decreasing the number of IGF-1 receptors (IGF-1R) at the cell surface. Such a decrease in receptor number might be a result of a lowered translocation of de novo synthesized receptors to the cell membrane which in turn might be a result of a decreased N-linked glycosylation of the receptor proteins. We could also demonstrate that IGF-1R became underglycosylated and that the amount of de novo synthesized IGF-1R proteins at the cell membrane was drastically decreased upon MVA depletion. Analysis of receptor proteins cross-linked with IGF-1, as well as binding assays and immunocytostaining confirmed that the number of functional membrane-bound IGF-1R was substantially reduced. The N-linked glycosylation and the expression of de novo synthesized IGF-1R proteins at the cell surface as well as the number of IGF-1 binding sites were completely restored upon replenishment of MVA. These effects of MVA were efficiently abrogated by the glycosylation inhibitor tunicamycin. The translocation of IGF-1R to the cell membrane was shown to take place just prior to initiation of DNA synthesis in arrested cells stimulated with MVA. Additionally, there was a clear correlation between IGF-1 binding and initiation of DNA synthesis with regard to the MVA dose requirement. It was confirmed that inhibition of HMG-CoA reductase activity and N-linked glycosylation also depressed the expression of functional IGF-1R in other cell types (i.e. hepatoblastoma cells and colon cancer cells). Our data suggest that this mechanism is involved in MVA-regulated cell growth.