Down-regulation of the c-myc proto-oncogene in inhibition of vascular smooth-muscle cell proliferation: a signal for growth arrest?

Ending Restenosis: Inhibition of Vascular Smooth Muscle Cell Proliferation by cAMP

Increased vascular smooth muscle cell (VSMC) proliferation contributes towards restenosis after angioplasty, vein graft intimal thickening and atherogenesis. The second messenger 3′ 5′ cyclic adenosine monophosphate (cAMP) plays an important role in maintaining VSMC quiescence in healthy vessels and repressing VSMC proliferation during resolution of vascular injury. Although the anti-mitogenic properties of cAMP in VSMC have been recognised for many years, it is only recently that we gained a detailed understanding of the underlying signalling mechanisms. Stimuli that elevate cAMP in VSMC inhibit G₁-S phase cell cycle progression by inhibiting expression of cyclins and preventing S-Phase Kinase Associated Protein-2 (Skp2-mediated degradation of cyclin-dependent kinase inhibitors. Early studies implicated inhibition of MAPK signalling, although this does not fully explain the anti-mitogenic effects of cAMP. The cAMP effectors, Protein Kinase A (PKA) and Exchange Protein Activated by cAMP (EPAC) act together to inhibit VSMC proliferation by inducing Cyclic-AMP Response Element Binding protein (CREB) activity and inhibiting members of the RhoGTPases, which results in remodelling of the actin cytoskeleton. Cyclic-AMP induced actin remodelling controls proliferation by modulating the activity of Serum Response Factor (SRF) and TEA Domain Transcription Factors (TEAD), which regulate expression of genes required for proliferation. Here we review recent research characterising these mechanisms, highlighting novel drug targets that may allow the anti-mitogenic properties of cAMP to be harnessed therapeutically to limit restenosis.

Gene therapy with antisense oligonucleotides silencing c-myc reduces neointima formation and vessel wall thickness in a mouse model of vein graft disease

Gene therapy for avoiding intimal hyperplasia of vein grafts after coronary artery bypass grafting is still discussed controversially. A promising application of gene therapy in vein grafts is the use of antisense oligonucleotides to block the expression of genes encoding cell cycle regulatory proteins in vascular smooth muscle cells. C-myc, either directly or by regulating the expression of other proteins, controls cell proliferation, apoptosis and cell survival, tissue remodeling, angiogenesis, cell metabolism, production of inflammatory and anti-inflammatory cytokines, and also participates in cell transformation. Forty C57BL/6J mice underwent interposition of the inferior vena cava from isogenic donor mice into the common carotid artery using a previously described cuff technique. Twenty mice received periadventitial administration of antisense oligonucleotides directed against c-myc (treatment group), the other twenty mice received no treatment (control group). All vein grafts were harvested two weeks after surgery, dehydrated, wax embedded, cut into slides of 2 μm thickness, stained and histologically and immunohistochemically examined under light microscope. In our study, we could show the promising effects of antisense oligonucleotide treatment in a mouse model of vein graft disease including the significant reduction of neointimal, media and total vessel wall thickness with a significantly lower percentage of SMA positive cells, elastic fibres and acid mucopolysaccharides in the neointima and media, a decreased vascularization, and a lower expression of PDGFR ß, MMP-9 and VEGF-A positive cells throughout the whole vein graft wall.

The role of androgen receptors in atherosclerosis

Male disadvantage in cardiovascular health is well recognised. However, the influence of androgens on atherosclerosis, one of the major causes of many life-threatening cardiovascular events, is not well understood. With the dramatic increase in clinical prescription of testosterone in the past decade, concerns about the cardiovascular side-effects of androgen supplementation or androgen deprivation therapy are increasing. Potential atheroprotective effects of testosterone could be secondary to (aromatase-mediated) conversion into oestradiol or, alternatively, to direct activation of androgen receptors (AR). Recent development of animal models with cell-specific AR knockout has indicated a complex role for androgen action in atherosclerosis. Most studies suggest androgens are atheroprotective but the precise role of AR remains unclear. Increased use of AR knockout models should clarify the role of AR in atherogenesis and, thus, lead to exploitation of this pathway as a therapeutic target.

Upregulation of let-7a inhibits vascular smooth muscle cell proliferation in vitro and in vein graft intimal hyperplasia in rats

BACKGROUND

Proliferation of vascular smooth muscle cells (VSMCs) is a crucial event in the pathogenesis of intimal hyperplasia, which is the main cause of restenosis after vascular reconstruction. In this study, we assessed the impact of let-7a microRNA (miRNA) on the proliferation of VSMCs.

METHODS

Using miRNA microarrays analysis for miRNA expression in the vein graft model. Lentiviral vector-mediated let-7a was transfected into the vein grafts. In situ hybridization was performed to detect let-7a. Cultured rat VSMCs were transfected with let-7a mimics for different periods of time. Cell proliferation, migration and cell cycle activity were monitored following transfection of the let-7a mimics. Immunohistochemical and Western blotting analysis the expression levels of c-myc and K-ras.

RESULTS

We found that let-7a was the most downregulated miRNA in the vein graft model. In vivo proliferation of VSMCs was assessed in a rat model of venous graft intimal hyperplasia. Let-7a was found to localize mainly to the VSMCs. Let-7a miRNA expression was increased in VSMCs in the neointima of the let-7a treated group. Intimal hyperplasia was suppressed by upregulation of let-7a via lentiviral vector-mediated mimics. In cultured VSMCs, the expression of let-7a increased upon starving, and the upregulation of let-7a miRNA significantly decreased cell proliferation and migration. Immunohistochemical and Western blotting analysis demonstrated that treatment with let-7a mimics resulted in decreased expression levels of c-myc and K-ras.

CONCLUSIONS

The results indicate that let-7a miRNA is a novel regulator of VSMC proliferation in intimal hyperplasia. These findings suggest that let-7a miRNA is a promising therapeutic target for the prevention of intimal hyperplasia.

Redox control of the cell cycle in health and disease

The cellular oxidation and reduction (redox) environment is influenced by the production and removal of reactive oxygen species (ROS). In recent years, several reports support the hypothesis that cellular ROS levels could function as ''second messengers'' regulating numerous cellular processes, including proliferation. Periodic oscillations in the cellular redox environment, a redox cycle, regulate cell-cycle progression from quiescence (G(0)) to proliferation (G(1), S, G(2), and M) and back to quiescence. A loss in the redox control of the cell cycle could lead to aberrant proliferation, a hallmark of various human pathologies. This review discusses the literature that supports the concept of a redox cycle controlling the mammalian cell cycle, with an emphasis on how this control relates to proliferative disorders including cancer, wound healing, fibrosis, cardiovascular diseases, diabetes, and neurodegenerative diseases. We hypothesize that reestablishing the redox control of the cell cycle by manipulating the cellular redox environment could improve many aspects of the proliferative disorders.

Mechanisms of resistance to interferon-gamma-mediated cell growth arrest in human oral squamous carcinoma cells

Interferon-gamma (IFNgamma) has an antiproliferative effect on a variety of tumor cells. However, many tumor cells resist treatment with IFNs. Here, we show that IFNgamma fails to inhibit the growth of some types of oral squamous cell carcinoma (OSCC) cells that possess a fully functional IFNgamma/STAT1 (signal transducer and activator of transcription-1) signaling pathway. IFNgamma inhibited the growth of the HSC-2, HSC-3, and HSC-4 OSCC cell lines. However, Ca9-22 cells were resistant to IFNgamma despite having intact STAT1-dependent signaling, such as normal tyrosine phosphorylation, DNA binding activity, and transcriptional activity of STAT1. The growth inhibition of HSC-2 cells resulted from S-phase arrest of the cell cycle. IFNgamma inhibited cyclin A2 (CcnA2)-associated kinase activity, which correlated with the IFNgamma-mediated down-regulation of CcnA2 and Cdk2 expression at both the transcriptional and post-transcriptional level in HSC-2 cells but not in Ca9-22 cells. RNAi-mediated knockdown of CcnA2 and Cdk2 resulted in growth inhibition in both cell lines. These results indicate that the resistance of OSCC to IFNgamma is not due simply to the deficiency in STAT1-dependent signaling but results from a defect in the signaling component that mediates this IFNgamma-induced down-regulation of CcnA2 and Cdk2 expression at the transcriptional and post-transcriptional levels.

Inhibitory effects of emodin on the proliferation of cultured rat vascular smooth muscle cell-induced by angiotensin II

Rhubarb, used as a traditional Chinese medicine for centuries, offers therapeutic potential for cardiovascular and other diseases. Emodin, extracted from the root extract of rhubarb has sparked increasing interest for therapeutic application. The main objective was to study the effect of emodin on cultured vascular smooth muscle cells (VSMCs) proliferation induced by angiotensin II (Ang II) and the expression of proto-oncogene c-myc. VSMCs were cultured by the explant method, then incubated for 24, 48 and 72 h with emodin (10-80 microm) and Ang II, or were left untreated (control). Cell proliferation was measured by MTT assay and immunohistochemical staining for proliferating cell nuclear antigen (PCNA), respectively. The expression of c-myc was measured by immunohistochemical staining and image analysis technique. Ang II increased the cell proliferation compared with the control group (p < 0.01). The expression of PCNA and c-myc was increased compared with the control group (p < 0.01). After pretreatment with emodin, the above indexes were obviously reduced compared with the Ang II group (p < 0.01). These findings suggested that emodin inhibited VSMCs proliferation induced by Ang II. Inhibition of the expression of c-myc might be correlated with the inhibitory effects.

Effect of heparin on production of transforming growth factor (TGF)-beta1 and TGF-beta1 mRNA expression by human normal skin and hyperplastic scar fibroblasts

Heparin affects both dermal fibroblast proliferation and collagen and may mediate these effects by altering the levels of transforming growth factor-beta1 (TGF-beta1) production and TGF-beta1 mRNA expression as a wound healing modulator. The purpose of this study is to probe the effect of heparin on TGF-beta1 and TGF-beta1 mRNA production by human normal skin and hyperplastic scar fibroblasts. This research investigates the effect of heparin on TGF-beta1 and TGF-beta1 mRNA production by human normal skin and hyperplastic scar fibroblasts with exposure to 0 microg/mL, 100 microg/mL, 300 microg/mL, or 600 microg/mL heparin for 24, 48, 72, or 96 hours in a serum-free in vitro model. Levels of TGF-beta1 in the supernatants and TGF-beta1 mRNA expression of fibroblasts were determined by enzyme-linked immunosorbent assay (ELISA) and real time RT-PCR, respectively. Heparin (300 microg/mL and 600 microg/mL) stimulated TGF-beta1 production by normal skin (26% to 83%) and hyperplastic scar fibroblasts (63% to 85%), with statistical significance (P < 0.05) at various time points. Heparin (300 microg/mL and 600 microg/mL) also stimulated TGF-beta1 mRNA expression by normal skin (12% to 53%) and hyperplastic scar fibroblasts (33% to 52%), with statistical significance (P < 0.05) at various time points. These effects of heparin on normal skin and hyperplastic scar fibroblasts may have implications for hyperplastic scar formation and wound healing in vivo.

Effect of heparin on production of basic fibroblast growth factor and transforming growth factor-beta1 by human normal skin and hyperplastic scar fibroblasts

Heparin affects both dermal fibroblast proliferation and collagen and may mediate these effects by altering the levels of basic fibroblast growth factor (bFGF) and transforming growth factor-beta1 (TGF-beta1) production as a wound healing modulator. The purpose of this study is to probe the effect of heparin on bFGF and TGF-beta1 production by human normal skin and hyperplastic scar fibroblasts. This research investigates the effect of heparin on bFGF and TGF-beta1 production by human normal skin and hyperplastic scar fibroblasts with exposure to 0, 100, 300, or 600 microg/ml heparin for 24, 48, 72, or 96 hours in a serum-free in vitro model. Levels of bFGF and TGF-beta1 in the supernatants were determined by enzyme-linked immunosorbant assay. All doses of heparin significantly stimulated production of bFGF by normal skin (393% to 1019% increase) and hyperplastic scar fibroblasts (405% to 899% increase) at all time points (P < .05). Heparin (300 and 600 microg/ml) also stimulated TGF-beta1 production by normal skin (26% to 83%) and hyperplastic scar fibroblasts (63% to 85%) with statistical significance (P < .05) at various time points. These effects of heparin on normal skin and hyperplastic scar fibroblasts may have implications for hyperplastic scar formation and wound healing in vivo.

Effects of ouabain on proliferation, intracellular free calcium and c-myc mRNA expression in vascular smooth muscle cells

Ouabain, a newly discovered mammalian steroid hormone, has been shown to correlate directly with mean blood pressure. In the present study, the mechanism by which ouabain may act on blood pressure was investigated using primary cultures of bovine vascular smooth muscle cells. 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay showed a biphasic effect on cell proliferation: at low concentrations ouabain stimulated cell growth while at higher concentrations it inhibited cell growth, which is similar to angiotensin II, an octapeptide hormone. Confocal laser scanning microscopy assay also indicated a biphasic nature on intracellular free calcium, which was decreased by low concentration of ouabain and increased by higher concentration of ouabain. Simultaneously, an increase of c-myc mRNA expression by low concentration of ouabain was obtained with reverse transcription-polymerase chain reaction (RT-PCR) assay. It is important to note that the low concentrations (10(-15)-10(-12) M) are under the normal circulating levels (2.5-8.0 x 10(-11) M) of endogenous ouabain. These results suggest that ouabain-induced proliferation might be attributed, at least in part, to the decrease of intracellular free calcium and the increase of c-myc mRNA expression, and that may be directly or indirectly involved in the regulation of blood pressure.

Concerted effect of transforming growth factor-β, cyclin inhibitor p21, and c-mycon smooth muscle cell proliferation

Increased aortic smooth muscle cell (SMC) proliferation is a key event in the pathogenesis of atherosclerosis. Transforming growth factor-β (TGF-β) is one of the potent inhibitors of SMC proliferation. The purpose of this study was 1) to explore the effect of TGF-β inhibition on proliferation of SMC and expression of growth regulatory molecules like p21 and c- myc and 2) to determine whether restoration of cell cycle regulatory molecules normalizes the altered proliferation. To test the role of TGF-β in SMC proliferation, using antisense plasmid DNA, we inhibited TGF-β gene from aortic SMC, which resulted in a significant increase ( P < 0.03) in proliferation (studied by quantifying new DNA synthesis with [3H]thymidine uptake assay). In TGF-β-altered SMC (TASMC), the mRNA expression (studied by RT-PCR) of c- myc was increased whereas that of the cyclin inhibitor p21 was completely inhibited. Using p21 sense plasmid DNA, we transfected p21 gene in TASMC, which restored p21 mRNA and protein expression and decreased proliferation ( P < 0.002) in TASMC. Similar treatment with c- myc antisense oligonucleotides significantly ( P < 0.001) decreased the proliferation of TASMC. TASMC also exhibited alteration in morphological changes in SMC but returned to normal with treatment of p21 and TGF-β sense plasmid DNA. Two-dimensional gel electrophoresis analysis of SMC and TASMC demonstrated differential expression of proteins relevant to cellular proliferation and atherosclerosis. This study uniquely analyzes the effect of TGF-β at the molecular level on proliferation of SMC and on cell cycle regulatory molecules, implicating their potential role in the pathogenesis of atherosclerosis.

Gene expression profiling of human stenotic aorto-coronary bypass grafts by cDNA array analysis

OBJECTIVE

Aorto-coronary bypass graft disease with its increasing clinical signification represents an unsolved problem in cardiological and heart surgery practice. Late occlusion of autologous saphenous vein grafts is due to medial and neointimal thickening secondary to migration and proliferation of smooth muscle cells (SMCs) and the subsequent formation of atherosclerotic plaques. This study is aimed at identifying differentially expressed genes in human stenotic bypass grafts to detect unknown pathomechanism and to identify novel targets for prophylactic treatment options.

METHODS

Stenotic saphenous aorto-coronary bypass grafts (n=5) were retrieved during re-do aorto-coronary bypass surgery. Ungrafted saphenous vein segments (n=5) were taken from the same group of patients and served as internal controls. cDNA samples were prepared and hybridized to cDNA arrays.

RESULTS

Some of the differentially expressed genes complied with expected gene expression including upregulation of c-jun and CDK10. In addition, previously unidentified gene expression patterns were detected such as upregulation of HSP70, fibronectin1, erbB3 proto-oncogene and c-myc. To confirm the latter finding, upregulation of c-myc in neointimal and medial SMCs of stenotic graft segments was confirmed by in situ hybridization studies and by immunohistochemistry.

CONCLUSION

Gene expression patterns of human stenotic bypass grafts retrieved by re-do operations can be reliably analyzed by cDNA array technology. With this technique, new therapeutic targets in patients could be identified as shown by the findings regarding c-myc. c-myc is a proto-oncogene acting as a transcription factor and blocking c-myc has shown a reduction of neointima formation in animal models. Our study yields a rational for the use of antisense c-myc oligonucleotides to reduce neointima formation and to avoid stenosis in patients.

Expression of the proto-oncogene c-myc in human stenotic aortocoronary bypass grafts

Proliferation and differentiation of vascular smooth muscle cells (VSMC) are central events in vascular pathobiology and play a major role in the development of stenotic and restenotic lesions. The proto-oncogene c-myc and other early cell cycle-regulating genes have been implicated in the induction of cell proliferation and differentiation under diverse pathophysiological conditions. In the present study we analyzed c-myc mRNA expression by indirect nonradioactive in situ hybridization technique (NISH) in human stenotic venous bypass grafts (n = 32) retrieved during re-do operations of coronary artery disease and compared the results with 28 native veins (vena saphena magna) from the same patients. Stenotic bypass grafts showed enhanced c-myc expression located predominantly in VSMC in the media and neointima (severity score: ++-+++, 32/32 stenotic veins). In native veins we observed only low levels of c-myc mRNA (severity score: +, 28/28 native veins), all signals were restricted to endothelial cells of either the innermost intimal layer or of the vasa vasorum. Our in situ hybridization studies demonstrate enhanced mRNA expression of the proto-oncogene c-myc in stenotic venous bypass grafts. These results suggest that--in analogy to other pathophysiological conditions--c-myc exerts essential regulatory functions in cellular events operative during the initiation and progression of venous bypass graft disease.

c-Myc oncoprotein: a dual pathogenic role in neoplasia and cardiovascular diseases?

A growing body of evidence indicates that c-Myc can play a pivotal role both in neoplasia and cardiovascular diseases. Indeed, alterations of the basal machinery of the cell and perturbations of c-Myc-dependent signaling network are involved in the pathogenesis of certain cardiovascular disorders. Down-regulation of c-Myc induced by intervention with antioxidants or by antisense technology may protect the integrity of the arterial wall as well as neoplastic tissues. Further intervention studies are necessary to investigate the effects of tissue-specific block of c-Myc overexpression in the development of cardiovascular diseases.

Influence of Class I interferons on performance of vascular cells on stent material in vitro

PURPOSE

Numerous reports suggest that Class 1 interferons (IFNs), particularly IFN-gamma, inhibit migration and proliferation of different types of human cells. The objective of the present study was to determine the effect of Class I IFNs on viability and growth characteristics of human aortic endothelial cells (ECs), smooth muscle cells (SMC) and fibroblasts (FBs) in vitro.

METHODS

Stainless-steel (316-l) disks were coated with fibrin meshwork containing IFN-gamma or IFN-alpha. The discs and IFN embedded meshwork were incubated with human EC, SMC and FB, and then cultured, whereas control cells were seeded onto uncoated surfaces or plain fibrin meshwork. Concentrations of recombinant IFN varied from 5 to 20 ng/cm(2). Assessment of effect on cell viability, growth and attachment was performed utilizing Alamar Blue (AB) assay. Cell morphology was assessed by scanning electron microscopy (SEM).

RESULTS

We have now shown inhibitory capacity of IFN-gamma on all three types of unstimulated cells. The growth-inhibitory effect was maximal with SMC, while it was minimal with FB and EC. IFN-gamma abrogated mitogenic responses of SMC but not EC and partially FB to VEGF and FGF stimulation. IFN-alpha was able to inhibit EC growth and, to a lesser extent, FB, and did influence growth rates of SMC. Biochemical analysis of lactate dehydrogenase activity suggested that IFN was not toxic to vascular cells. We also measured the expression of cell adhesive molecules: P- and E-selections, PECAM and ICAM-1. These molecules were upregulated by IFN in EC. Media derived from quiescent human SMC displayed low immunoreactive elastase activity, while conditional media after IFN-gamma treatment but not IFN-alpha treatment had approximately a threefold greater activity.

CONCLUSION

These data suggest that IFN-gamma significantly inhibits SMC growth in the absence of significant endothelial toxicity and is dose-dependent; however, animal experiments are needed to further explore the antirestenotic effects of IFNs.

Decrease in carotid intima media thickness after 1 year of cilostazol treatment in patients with type 2 diabetes mellitus

A multicenter exploratory study at three university hospitals was performed to evaluate the effect of oral cilostazol on intima media thickness (IMT) in diabetic patients. A total of 141 patients was recruited in this study and randomized into a cilostazol group and a placebo (control) group. One hundred and twenty patients completed the study (i.e. 60 on cilostazol and 60 on placebo). Biochemical profiles and the IMT of the common carotid artery (CCA) determined by high-resolution B-mode ultrasonography were measured at 0, 6, and 12 months after the oral administration of 100--200 mg of cilostazol or placebo (i.e. two or four times daily for 12 months). Clinical and biochemical characteristics, the treatment modality, and microvascular diabetic complications after randomization were not significantly different between the two groups after the study. In the cilostazol treatment group, left CCA average IMT significantly decreased from 0.94+/-0.03 to 0.91+/-0.02 mm at 6 months (P<0.05), and thereafter increased to 0.92+/-0.01 mm (P>0.05) at 12 months, whereas in the control group, it increased from 0.92+/-0.03 to 0.93+/-0.01 mm at 6 months (P>0.05), and to 0.94+/-0.01 mm at 12 months (P>0.05). As for the right CCA average IMT, it decreased from 0.83+/-0.03 to 0.82+/-0.01 mm at 6 months (P<0.05), and to 0.81+/-0.01 mm at 12 months (P<0.05) in the cilostazol group, whereas it increased from 0.87+/-0.03 to 0.89+/-0.01 mm at 6 months (P<0.05), and to 0.90+/-0.01 mm at 12 months (P<0.05) in the control group (P<0.05). After correction for risk factors such as blood pressure, smoking, and lipid profiles, there were significant changes in left and right CCA average IMT for both groups (P<0.05). Left and right CCA average IMT was significantly different between the two groups (P<0.05). After making statistical corrections for blood pressure, smoking, and lipid profiles, the differences between these two groups remained significant (P<0.05). Meanwhile, there were no differences between the groups in the change of risk factors such as BMI, blood pressure, blood sugar, HbA(1c), and lipid profiles. Generally, cilostazol was well tolerated and the most common side effect in the cilostazol group was headache (12/60), mostly early in the treatment regimen. The results suggest that oral cilostazol may be helpful in the treatment of atherosclerosis in type 2 diabetic patients, although conventional cardiovascular risk factors remained unmodified.

Safety of intracoronary administration of c-myc antisense oligomers after percutaneous transluminal coronary angioplasty (PTCA)

We wished to assess the clinical safety and pharmacokinetics of ascending doses of a synthetic oligodeoxynucleotide (LR-3280) administered after coronary angioplasty. Antisense oligodeoxynucleotides designed to hybridize with target messenger ribonucleic acid (mRNA) in a complementary fashion to inhibit the expression of corresponding protein also have the ability to bind to extracellular growth factors. LR-3280 has been shown to reduce c-myc expression, inhibit growth and collagen biosynthesis in human vascular cells, and reduce neointimal formation in animal models of vascular injury. After successful percutaneous transluminal coronary angioplasty (PTCA), 78 patients were randomized to receive either standard care (n = 26) or standard care and escalating doses of LR-3280 (n = 52) (doses from 1 to 24 mg), administered into target vessel through a guiding catheter. Overall safety was evaluated by clinical adverse events, laboratory tests, and electrocardiograms. Patency was evaluated by quantitative coronary angiography. There were no clinically significant differences between treated and control patients. No adverse effects of LR-3280 on the patency of dilated coronary arteries were observed. Pharmacokinetic data revealed that peak plasma concentrations of LR-3280 occurred at 1 minute over the studied dose range and rapidly decreased after approximately1 hour, with little LR-3280 detected in the urine between 0-6 hours and 12-24 hours. The intracoronary administration of LR-3280 is well tolerated at doses up to 24 mg and produces no adverse effects in dilated coronary arteries. These results provide the basis for the evaluation of local delivery of this phosphorothioate oligodeoxynucleotide for the prevention of human vasculoproliferative disease.

Apoptotic proteins. p53 and c-myc related pathways

c-Myc and p53 are two proteins that have critical roles in the regulation of apoptosis and the cell cycle. The authors review how these two proteins are thought to control the opposing events of proliferation and apoptosis and examine whether their well-documented biological roles in tumorigenesis can be applied to the vascular system.

Serum regulates the expression of complement receptor 2 on human B cell lines

Complement receptor 2 (CR2) participates in the regulation of B cell responses to antigen. In this study we report that treatment of IM-9 B lymphoblastoid cells or Raji Burkitt's lymphoma cells with 10% heat-inactivated fetal bovine serum for 24 hr increased both the CR2 mRNA level and CR2 surface protein expression more than two-fold. No change in the CR2 expression level was observed if cells were cultured in serum-free medium. The CD19 mRNA level decreased after 24 hr independently of the presence of serum. The serum-stimulated increase in CR2 expression was not due to changes in the proliferative capacity of the cells and could not be mimicked by various cytokines. However, IFN-gamma as well as OKB7, a CR2-specific monoclonal antibody, blocked the serum-induced increase in CR2 expression at the mRNA level. Our data show for the first time that factors in serum induce the expression of the CR2 gene and that signals initiated by IFN-gamma and OKB7 interfere with the serum-induced changes. Because stimuli that alter CR2 expression can influence the extent of the B cell response to antigen-C3d complexes, serum factors may play a role in regulating the responsiveness of B cells.

Molecular mechanisms in intimal hyperplasia

Intimal hyperplasia is the process by which the cell population increases within the innermost layer of the arterial wall, such as occurs physiologically during closure of the ductus arteriosus and during involution of the uterus. It also occurs pathologically in pulmonary hypertension, atherosclerosis, after angioplasty, in transplanted organs, and in vein grafts. The underlying causes of intimal hyperplasia are migration and proliferation of vascular smooth muscle cells provoked by injury, inflammation, and stretch. This review discusses, at a molecular level, both the final common pathways leading to smooth muscle migration and proliferation and their (patho)-physiological triggers. It emphasizes the key roles played by growth factors and extracellular matrix-degrading metalloproteinases, which act in concert to remodel the extracellular matrix and permit cell migration and proliferation.

Differential regulation of extracellular signal-regulated protein kinases (ERKs) 1 and 2 by cAMP and dissociation of ERK inhibition from anti-mitogenic effects in rabbit vascular smooth muscle cells

The inhibition of extracellular signal-regulated protein kinases (ERKs) is implicated in the negative regulation of vascular smooth muscle cell (VSMC) mitogenesis by cAMP-elevating agents and transforming growth factor beta(1) (TGF-beta(1)). These factors inhibited rabbit aortic VSMC mitogenesis induced by platelet-derived growth factor (PDGF)-BB by preventing the entry of cells into S-phase. cAMP-elevating agents partly inhibited the late phase (1-4 h) of activation of ERKs 1 and 2 induced by PDGF-BB without inhibiting the early phase of activity (5-15 min) and had no effect on activity induced by basic fibroblast growth factor (bFGF). In contrast, cAMP elevation caused a marked inhibition of early ERK activation induced by angiotensin II and thrombin. TGF-beta(1) had no inhibitory effect on ERK activation induced by PDGF-BB or bFGF. The inhibition of PDGF-BB-stimulated DNA synthesis by either forskolin/3-isobutyl-1-methylxanthine (IBMX) or TGF-beta(1) was not decreased when the agents were added up to 8 h after growth factor. In contrast, the selective ERK kinase inhibitor PD98059 was a weak inhibitor of DNA synthesis; a combination of PD98059 and forskolin/IBMX had an additive inhibitory effect on DNA synthesis. Forskolin/IBMX inhibited the growth factor-induced expression of c-myc mRNA and cyclin D(1) protein, and enhanced the protein expression of p27(kip1). TGF-beta(1) had no effect on the expression of c-myc or p27(kip1) and weakly attenuated the expression of cyclin D(1). These findings support the conclusion that the suppression of VSMC mitogenesis by cAMP and TGF-beta(1) is independent of ERK inhibition. Anti-mitogenic effects of cAMP might be primarily mediated by events in late G(1).

C-myc antisense oligodeoxynucleotides can induce apoptosis and down-regulate Fas expression in rheumatoid synoviocytes

OBJECTIVE

To investigate the role of c-myc in the pathogenesis of rheumatoid arthritis (RA) and the mechanism of synovial apoptosis.

METHODS

Using cultured human synoviocytes from patients with RA and c-myc antisense oligodeoxynucleotides (AS ODN), we examined the inhibition of cell proliferation by the MTT assay and the induction of apoptosis with TUNEL staining and fluorescence microscopy. In addition, the effect of c-myc on down-regulation of Fas expression was analyzed by flow cytometry, cytotoxicity assay, and reverse transcriptase-polymerase chain reaction.

RESULTS

Treatment with c-myc AS ODN induced inhibition of cell proliferation, along with down-regulation of c-Myc protein and c-myc messenger RNA (mRNA) expression. The morphologic changes of synovial cell death were typical of apoptosis. In addition, c-myc AS ODN treatment down-regulated expression of Fas mRNA but not Fas antigen. Analysis of the involvement of the caspase cascade revealed that the cytotoxic activity of c-myc AS ODN was completely blocked by inhibitors of both caspase 1 (YVAD-FMK) and caspase 3 (DEVD-FMK).

CONCLUSION

Our results strongly suggest that c-myc AS ODN might be a useful therapeutic tool in RA and clarify that cell death by c-myc AS ODN is induced through the caspase cascade, similar to Fas-induced apoptosis. In addition, combination therapy with anti-Fas antibody and c-myc AS ODN reduced Fas-dependent cytotoxicity.

Interferon-gamma-mediated inhibition of cyclin A gene transcription is independent of individual cis-acting elements in the cyclin A promoter

Interferons (IFNs) affect cellular functions by altering gene expression. The eukaryotic cell cycle is governed in part by the periodic transcription of cyclin genes, whose protein products associate with and positively regulate the cyclin-dependent kinases. To understand better the growth inhibitory effect of IFN-gamma on vascular smooth muscle cells (VSMCs), we compared the expression and activity of G1 and S phase cyclins in control and IFN-gamma-treated VSMCs. IFN-gamma treatment did not inhibit the G1 cyclins but did decrease cyclin A protein, mRNA, and associated kinase activity by 85, 90, and 90%, respectively. Nuclear run-on and mRNA stability determinations indicated that this decrease was the result of transcriptional inhibition. To investigate the molecular basis of this inhibition, we examined protein-DNA interactions involving the cyclin A promoter. Electromobility shift assays showed little change with IFN-gamma treatment in the binding of nuclear proteins to isolated ATF, NF-Y, and CDE elements. In vivo genomic footprinting indicated that IFN-gamma treatment changed the occupancy of chromosomal NF-Y and CDE sites slightly and did not affect occupancy of the ATF site. In a previous study of transforming growth factor-beta1-mediated inhibition of the cyclin A promoter, we mapped the inhibitory effect to the ATF site; in the present study of IFN-gamma treatment, functional analysis by transient transfection showed that inhibition of the cyclin A promoter persisted despite mutation of the ATF, NF-Y, or CDE elements. We hypothesize that IFN-gamma inhibits cyclin A transcription by modifying co-activators or general transcription factors within the complex that drives transcription of the cyclin A gene.

cdc25A is necessary but not sufficient for optimal c-myc-induced apoptosis and cell proliferation of vascular smooth muscle cells

Increasing evidence indicates that the control of cell proliferation and apoptosis are linked. The c-myc proto-oncogene is induced early after cell-cycle entry in vascular smooth muscle cells (VSMCs) in vitro and after arterial injury and regulates both cell proliferation and apoptosis. Although both proliferation and apoptosis are likely to be mediated via transcriptional activation of target genes, few c-myc targets have been identified. Therefore, the recent identification that cdc25A, a cell-cycle phosphatase involved in G1 progression, is transcriptionally activated by c-myc and regulates c-myc-induced apoptosis has suggested that cdc25A may be the principal mediator of c-myc in VSMCs. We examined cdc25A regulation of c-myc-induced proliferation and apoptosis by expressing cdc25A or antisense cdc25A in primary rat VSMCs or in VSMCs expressing deregulated c-myc or adenovirus E1A. Ectopic c-myc increased cdc25A expression, but cdc25A was still responsive to serum components, which indicated that c-myc alone is not the main determinant of cdc25A expression. Antisense cdc25A inhibited c-myc-induced proliferation and apoptosis; however, drug and metabolic blocks indicated that this effect was limited to G1. Ectopic cdc25A augmented the proproliferative and proapoptotic action of c-myc but did not increase cell proliferation or apoptosis in the absence of ectopic c-myc. In contrast, E1A/E2F-induced apoptosis was independent of cdc25A. We conclude that cdc25A expression modulates the ability of c-myc to induce apoptosis in G1. However, cdc25A alone does not induce apoptosis and cannot substitute for c-myc in VSMCs. Additional targets of c-myc are therefore involved in apoptosis of both G1 and post-G1 VSMCs.

Effects of a single local administration of cilostazol on neointimal formation in balloon-injured rat carotid artery

To elucidate if locally administered cilostazol, an inhibitor of cyclic AMP phosphodiesterase III, suppresses neointimal formation in balloon-injured carotid artery of the rat, 20 mg of cilostazol was topically applied using pluronic gel at the time of balloon injury. Rats were sacrificed 14 days after balloon injury to measure the extent of neointimal formation. Plasma and tissue concentrations of cilostazol were also measured at 1, 3, 7 and 14 days after topical application. The 5-bromo-2'-deoxyuridine (BrdU, a thymidine analogue) was given intraperitoneally to detect proliferation of smooth muscle cells in the injured media at 3 days after balloon injury. At 1 day after injury, plasma and tissue concentrations were 0.147+/-0.043 microg/ml and 1380 microg/g tissue. Although the plasma concentration of cilostazol was undetectable ( < 0.02 microg/ml), a significant amount of cilostazol (46 microg/g tissue) was still detected in the tissue at the site of application even after 2 weeks. The intimal area of the injured carotid after 2 weeks was significantly smaller in the cilostazol-treated group than in the gel-treated control group (0.06+/-0.01 vs 0.15+/-0.02 mm2, P<0.001). BrdU-positive smooth muscle cells in the injured media after 3 days were also significantly fewer in the cilostazol-treated group than in the gel-treated control group (4.3+/-0.5 vs 9.1+/-0.9% of total cells, P < 0.001). These results suggest that local administration of cilostazol using pluronic gel maintains a high concentration of the drug at the application site, has an anti-proliferative effect on smooth muscle cells, and may have potential for clinical therapeutic use for the prevention of restenosis following arterial intervention.

Sustained reduction of neointima with c-myc antisense oligonucleotides in saphenous vein grafts

BACKGROUND

Treatment of saphenous veins with c-myc antisense oligomers during preparation for grafting reduces medial cellular proliferation and macrophage infiltration, and preserves medial smooth muscle content at 3 days. Accordingly, the purpose of this study was to examine whether c-myc antisense oligomers have an impact on late vein graft remodeling.

METHODS

Sixty-two pigs underwent unilateral saphenous vein-carotid artery interposition grafting. Harvested veins were incubated either in saline (control group) or 20-micromol/L or 200-micromol/L concentrations of c-myc antisense oligomers (treated groups) for 30 minutes intraoperatively. Three months after surgery, vein graft histology was assessed.

RESULTS

Forty-five of 62 randomized animals survived the experiment; no differences in animal survival or graft patency among the groups were observed (p = NS, chi2). C-myc antisense oligomers significantly decreased neointimal and wall thickness, as well as increased lumenal index, in treated groups (p<0.04, p<0.03, and p<0.001, respectively, analysis of variance). In contrast, there was no difference in medial thickness or perivascular wound healing.

CONCLUSION

Intraoperative treatment of saphenous veins with c-myc antisense oligomers decreased neointimal formation at 3 months after grafting. In conjunction with our previous reports, these findings suggest that early inhibition of cellular proliferation and inflammatory infiltration results in a sustained reduction in neointimal formation and favorable graft remodeling.

Heparin sensitive and resistant vascular smooth muscle cells: biology and role in restenosis

Vascular smooth muscle cells (VSMC)s are characterized by their acute growth inhibition by heparin and heparan sulfates; however, recently the isolation of VSMCs which display greatly diminished sensitivity to the antiproliferative action of heparin have been reported. These heparin resistant (HR) VSMCs have been derived through multiple passage of normal rat VSMCs in culture media containing high heparin doses, by transformation of VSMCs with oncogene-containing vectors, or have been isolated from vascular tissues of spontaneously hypertensive rats, healthy humans, or humans with restenosis where their presence is not limited to sites of injury. Initial characterizations of HR VSMCs are reviewed, and here we propose a definition of HR VSMCs. To date the mechanisms underlying heparin insensitivity remain elusive. Further study of HR VSMCs may expand our understanding of cell growth regulation by heparin, establish whether HR VSMCs contribute to the reported failure of heparin to combat restenosis in humans, and identify cellular mechanisms driving certain vascular proliferative diseases.

Characteristics of smooth muscle cell lipoprotein binding proteins (p105/p130) as T-cadherin and regulation by positive and negative growth regulators

Smooth muscle cells (SMC) express atypical surface low density lipoprotein (LDL) binding proteins of M(r)105 and M(r)130 (p105 and p130) which have been putatively identified as the cell adhesion glycoprotein T-cadherin. Using cultured human and rat aortic SMC and analysis by ligand (LDL)- and immuno-blotting techniques we now confirm identity of p105 and p130 as T-cadherin, as adjudged by sensitivity to PI-PLC cleavage, insensitivity to trypsin degradation in the presence of calcium, and immunoreactivity to anti-T-cadherin peptide antisera. The function of T-cadherin (p105/p130) in the vasculature is unknown. The proteins were downmodulated by the peptide growth factors PDGF-BB, IGF, EGF, and bFGF, but not by vasoactive peptide hormones (angiotensin II, vasopressin, bradykinin, and endothelin). TGF beta, a recognized inhibitor of SMC proliferation, per se had no effect but inhibited growth factor-induced p105/p130 downmodulation. Expression of p105/p130 in quiescent SMC and growth-stimulated SMC (respectively, in serum-free and serum or PDGF-BB containing culture conditions) was increased by forskolin and 8-Br-cyclic GMP, both anti-mitogenic substances, but was unaffected by phorbol ester, calcium ionophores, or calcium antagonists. The findings are compatible with a function for the lipoprotein binding proteins (T-cadherin) in negative regulation of SMC growth.

Saphenous vein graft protection: effects of c-myc antisense

OBJECTIVE

Saphenous vein grafting is associated with extensive medial remodeling, characterized by cellular proliferation, loss of smooth muscle cells, and an inflammatory response. In this study, we examined whether unfavorable responses to vein grafting could be modified by the intraoperative application of c-myc antisense oligomers.

METHODS

The intragraft cell proliferation, macrophage infiltration, and medial preservation were examined in a porcine model in the control and antisense-treated groups (n = 36).

RESULTS

Saphenous veins showed transmural distribution of oligomers within 30 minutes of the ex vivo incubation. A concentration-dependent inhibition of cell proliferation in the media of saphenous grafts was noted 3 days later (0 to 200 mumol/L, p = 0.005). The growth inhibition was sequence-specific, because control oligomers produced only insignificant effects (20 mumol/L). Vascular effects of c-myc antisense were associated with a significant attenuation of macrophage infiltration in saphenous grafts. A concentration-dependent decrease in tissue edema (p = 0.0005) and the attenuated loss of smooth muscle cells (p = 0.002) were noted in the media of the arterialized venous conduits after c-myc antisense.

CONCLUSIONS

Direct application of synthetic DNA to harvested saphenous veins resulted in a rapid transmural distribution. The inhibition of the intragraft cell proliferation in vivo after c-myc antisense was sequence dependent. Decrease in vein graft injury resulted in an attenuated inflammatory response and better medial preservation. These findings provide a rationale for assessment of the long-term effects of vein graft protection with c-myc antisense.

Control of vascular smooth-muscle cell growth by macrophage-colony-stimulating factor

Since in several vascular diseases abnormal vascular smooth-muscle cell (VSMC) proliferation is often associated with the presence of macrophages, we examined whether macrophage-colony-stimulating factor (M-CSF) might play a role in the control of VSMC growth. VSMCs were isolated from rat aorta and maintained in culture. Using a bioassay, a macrophage-colony-stimulating activity was detected in the serum-free supernatant of VSMCs, which could be inhibited by the addition of specific anti-M-CSF antibodies. The presence of M-CSF receptor protein and of M-CSF and M-CSF receptor gene transcripts was demonstrated by immunocytochemistry, using a specific anti-c-Fms antibody and Northern blot analysis respectively. [3H]Thymidine incorporation was measured following the addition to quiescent VSMCs of various dilutions of L929 cell supernatant (as a source of M-CSF) or of recombinant M-CSF. Both exogenous M-CSF and serum-free VSMC conditioned medium promoted DNA synthesis in a concentration-dependent manner, and this effect could be abrogated by the presence of a specific anti-M-CSF antibody. Under similar experimental conditions, L929 cell supernatant modulated proto-oncogene expression, as assessed by Northern blot analysis of c-fos, c-myc, egr-1 and junB. It was further demonstrated that M-CSF could act in synergy with thrombin, platelet-derived growth factor or basic fibroblast growth factor in promoting VSMC DNA synthesis. These results support the hypothesis that M-CSF affects the growth of cultured rat VSMCs through paracrine/autocrine mechanisms. Its effects at both the macrophage and the VSMC level confer to M-CSF a central role in the development of vascular lesions that occurs during atherosclerotic progression.

Depolymerized holothurian glycosaminoglycan (DHG) prevents neointimal formation in balloon-injured rat carotid artery

The in vivo activity of depolymerized holothurian glycosaminoglycan (DHG), a newly developed polysaccharide anticoagulant, on neointimal formation induced by a balloon catheter in the left common carotid artery of rats was investigated. In every Sprague-Dawley rat weighing approximately 400 g, a Forgaty 2Fr balloon catheter was inserted from the left femoral artery to the left common carotid artery, and was passed through three times in order to denude the endothelium of the artery. These rats were divided into four groups by the following treatment protocols; DHG was given to rats by daily subcutaneous injection into their abdomens at a dose of 3 mg/kg or 10 mg/kg (D3 or D10 group). For controls, 250 microl saline was injected daily (C group). Furthermore, 1 mg/kg of unfractionated heparin was also injected daily as a comparison to DHG (H group). Each treatment was performed in six rats, and the injections were continued for two weeks after the catheterization. The area ratio of thickened intima/media (I/M ratio) treated with DHG decreased in a dose-dependent manner compared to the control. In addition, the ratio in the D10 group was significantly lower than in the control (P < 0.01). However, the ratio in the H group did not decrease. By anti-a smooth muscle actin antibody staining the intimal thickening layers were seen to be completely occupied by proliferated smooth muscle cells, and their amount in these layers was attenuated by the DHG treatment. This indicated that DHG has an inhibitory effect on intimal thickening induced by balloon catheterization, and that this might be due to the inactivation of aberrant smooth muscle cells by this agent.

Heparin-induced overexpression of basic fibroblast growth factor, basic fibroblast growth factor receptor, and cell-associated proteoheparan sulfate in cultured coronary smooth muscle cells

Basic fibroblast growth factor (bFGF), a potent mitogen for arterial smooth muscle cells (SMCs), plays a pivotal role in the pathogenesis of arteriosclerosis and restenosis. Heparin in nanogram quantities may promote or even be required for binding of bFGF to its cognate receptor. Conversely, heparin in microgram doses is a strong inhibitor of arterial SMC replication in vitro and in vivo. Bovine coronary SMCs (cSMCs) express bFGF, bFGF receptor (FGF-R1), and cell membrane-integrated proteoheparan sulfate (HSPG). These three molecules are known to form a trimolecular complex that promotes signal transduction and mitogenesis. The bFGF synthesized by cSMCs is distributed to an intracellular and a pericellular compartment. Resting cultured cells retain about 80% of their bFGF intracellularly; 20% is found in the pericellular region. During proliferation, 70% to 80% of total bFGF is expressed in the pericellular compartment. Trypsinization generates soluble forms of the complex of bFGF with the ectodomains of the bFGF receptor and cell membrane-integrated HSPG in the pericellular compartment, thus allowing quantification of pericellular bFGF by a highly specific enzyme immunoassay. Standard heparin inhibits the proliferation of cSMCs by up to 80% in a concentration range between 10 and 100 micrograms/mL medium in a dose-dependent manner but increases the protein content of cSMCs compared with proliferating control cells. The heparin-induced increase in cellular protein content includes a 60% to 100% increase in the expression of pericellular bFGF, FGF-R1, and cell membrane-integrated HSPG. Thus, under heparin treatment, the heparan sulfate side chains of cell membrane-integrated HSPG incorporate more [35S]sulfate, and the proportion of [35S]heparan sulfate among total glycosaminoglycans increases from 36% to 52%. Fluorescence-activated cell sorting analysis and [3H]thymidine incorporation experiments provide evidence for multiple effects of heparin, including blocks at early and late checkpoints of the cell cycle in heparin-treated cells. These results indicate that heparin, despite its anti-proliferative potency, stimulates the expression of all components of the bFGF system even in coronary SMCs in which growth is inhibited.

Apoptosis of rat vascular smooth muscle cells is regulated by p53-dependent and -independent pathways

Apoptosis of vascular smooth muscle cells has recently been described in culture and also in remodeling of the artery after birth. However, the genes that regulate apoptosis in smooth muscle cells are mostly unknown. We studied the regulation of apoptosis in rat smooth muscle cells stably infected with retrovirus constructs containing c-myc, adenovirus E1A, bcl-2, and a temperature-sensitive mutant of the tumor suppressor gene p53. Apoptosis was verified by electron microscopy and quantified by time-lapse videomicroscopy. Death was induced by c-myc and E1A when cells were deprived of serum survival factors, bcl-2 suppressed apoptosis of cells infected with c-myc and E1A and also normal smooth muscle cells. Overexpression of wild-type p53 induced apoptosis of cells infected with E1A and c-myc but not normal cells. In contrast, expression of mutant p53, which blocks wild-type p53 function, suppressed apoptosis of cells infected with E1A or c-myc but not normal cells. Both adenovirus E1A and c-myc increased the expression of endogenous p53 protein but not p53 mRNA. Although bcl-2 suppressed apoptosis induced by E1A and c-myc, upregulation of p53 protein induced by these agents was unaffected. We conclude that apoptosis of vascular smooth muscle cells is regulated by p53-dependent and -independent pathways. Death induced by c-myc and E1A is mediated by, and dependent on, p53. However, the suppression of apoptosis by bcl-2 is not mediated by changes in p53 expression, and the low level of apoptosis seen in normal VSMCs upon removal of survival factors is independent of p53.