Tumor Necrosis Factor–Mediated E2F1 Suppression in Endothelial Cells

Compartment-specific regulation of NaV1.7 in sensory neurons after acute exposure to TNF-α

Tumor necrosis factor α (TNF-α) is a major pro-inflammatory cytokine, important in many diseases, that sensitizes nociceptors through its action on a variety of ion channels, including voltage-gated sodium (NaV) channels. We show here that TNF-α acutely upregulates sensory neuron excitability and current density of threshold channel NaV1.7. Using electrophysiological recordings and live imaging, we demonstrate that this effect on NaV1.7 is mediated by p38 MAPK and identify serine 110 in the channel's N terminus as the phospho-acceptor site, which triggers NaV1.7 channel insertion into the somatic membrane. We also show that the N terminus of NaV1.7 is sufficient to mediate this effect. Although acute TNF-α treatment increases NaV1.7-carrying vesicle accumulation at axonal endings, we did not observe increased channel insertion into the axonal membrane. These results identify molecular determinants of TNF-α-mediated regulation of NaV1.7 in sensory neurons and demonstrate compartment-specific effects of TNF-α on channel insertion in the neuronal plasma membrane.

Inhibition of specific signaling pathways rather than epigenetic silencing of effector genes is the leading mechanism of innate tolerance

Introduction

Macrophages activated through a pattern-recognition receptor (PRR) enter a transient state of tolerance characterized by diminished responsiveness to restimulation of the same receptor. Signaling-based and epigenetic mechanisms are invoked to explain this innate tolerance. However, these two groups of mechanisms should result in different outcomes. The epigenetic scenario (silencing of effector genes) predicts that activation of a PRR should broadly cross-tolerize to agonists of unrelated PRRs, whereas in the signaling-based scenario (inhibition of signaling pathways downstream of specific PRRs), cross-tolerization should occur only between agonists utilizing the same PRR and/or signaling pathway. Also, the so-called non-tolerizeable genes have been described, which acquire distinct epigenetic marks and increased responsiveness to rechallenge with the same agonist. The existence of such genes is well explained by epigenetic mechanisms but difficult to explain solely by signaling mechanisms.

Methods

To evaluate contribution of signaling and epigenetic mechanisms to innate tolerance, we tolerized human macrophages with agonists of TLR4 or NOD1 receptors, which signal via distinct pathways, and assessed responses of tolerized cells to homologous restimulation and to cross-stimulation using different signaling, metabolic and transcriptomic read-outs. We developed a transcriptomics-based approach to distinguish responses to secondary stimulation from continuing responses to primary stimulation.

Results

We found that macrophages tolerized with a NOD1 agonist lack responses to homologous restimulation, whereas LPS-tolerized macrophages partially retain the ability to activate NF-κB pathway upon LPS rechallenge, which allows to sustain low-level expression of a subset of pro-inflammatory genes. Contributing to LPS tolerance is blockade of signaling pathways required for IFN-β production, resulting in 'pseudo-tolerization' of IFN-regulated genes. Many genes in NOD1- or TLR4-tolerized macrophages are upregulated as the result of primary stimulation (due to continuing transcription and/or high mRNA stability), but do not respond to homologous restimulation. Hyperresponsiveness of genes to homologous rechallenge is a rare and inconsistent phenomenon. However, most genes that have become unresponsive to homologous stimuli show unchanged or elevated responses to agonists of PRRs signaling via distinct pathways.

Discussion

Thus, inhibition of specific signaling pathways rather than epigenetic silencing is the dominant mechanism of innate tolerance.

Reprogramming of microRNA expression via E2F1 downregulation promotes Salmonella infection both in infected and bystander cells

Cells infected with pathogens can contribute to clearing infections by releasing signals that instruct neighbouring cells to mount a pro-inflammatory cytokine response, or by other mechanisms that reduce bystander cells’ susceptibility to infection. Here, we show the opposite effect: epithelial cells infected with Salmonella Typhimurium secrete host factors that facilitate the infection of bystander cells. We find that the endoplasmic reticulum stress response is activated in both infected and bystander cells, and this leads to activation of JNK pathway, downregulation of transcription factor E2F1, and consequent reprogramming of microRNA expression in a time-dependent manner. These changes are not elicited by infection with other bacterial pathogens, such as Shigella flexneri or Listeria monocytogenes. Remarkably, the protein HMGB1 present in the secretome of Salmonella-infected cells is responsible for the activation of the IRE1 branch of the endoplasmic reticulum stress response in non-infected, neighbouring cells. Furthermore, E2F1 downregulation and the associated microRNA alterations promote Salmonella replication within infected cells and prime bystander cells for more efficient infection.

Cells infected with pathogens can release signals that instruct neighbouring cells to mount an immune response or that reduce these cells’ susceptibility to infection. Here, Aguilar et al. show the opposite effect: cells infected with Salmonella Typhimurium secrete host factors that facilitate the infection of bystander cells by activating their ER-stress response.

Resveratrol Attenuates High Glucose-Induced Vascular Endothelial Cell Injury by Activating the E2F3 Pathway

Type 2 diabetes mellitus (T2DM) is the most common metabolic disease. High glucose-induced macrovascular disease and microangiopathy are major complications of diabetes. E2F3, a member of the E2F transcription factor family, is closely related to cardiovascular diseases. Resveratrol, a nonflavonoid polyphenolic compound widely found in plants, has been shown to have cardiovascular protection. However, there are few studies on whether resveratrol can effectively treat diabetic angiopathy, and the specific mechanism involved needs further study. This study investigated whether E2F3 transcription factors are involved in the process of vascular endothelial injury induced by high glucose and observed its effects on the proliferation of vascular endothelial cells. Then, it analyzed whether resveratrol can inhibit high glucose-induced vascular endothelial cell injury by regulating the E2F3 pathway. We demonstrated that the expression level of the E2F3 transcription factor was significantly inhibited in high glucose state. Resveratrol inhibited high glucose-induced vascular endothelial cell injury by upregulating the E2F3 pathway. High glucose can induce vascular endothelial injury by inhibiting E2F3 gene expression, while resveratrol can inhibit high glucose-induced vascular endothelial injury by activating the E2F3 pathway.

Cathelicidin-related antimicrobial peptide protects against myocardial ischemia/reperfusion injury

BACKGROUND

Cathelicidins are a major group of natural antimicrobial peptides which play essential roles in regulating host defense and immunity. In addition to the antimicrobial and immunomodulatory activities, recent studies have reported the involvement of cathelicidins in cardiovascular diseases by regulating inflammatory response and microvascular dysfunction. However, the role of cathelicidins in myocardial apoptosis upon cardiac ischemia/reperfusion (I/R) injury remains largely unknown.

METHODS

CRAMP (cathelicidin-related antimicrobial peptide) levels were measured in the heart and serum from I/R mice and in neonatal mouse cardiomyocytes treated with oxygen glucose deprivation/reperfusion (OGDR). Human serum cathelicidin antimicrobial peptide (LL-37) levels were measured in myocardial infarction (MI) patients. The role of CRAMP in myocardial apoptosis upon I/R injury was investigated in mice injected with the CRAMP peptide and in CRAMP knockout (KO) mice, as well as in OGDR-treated cardiomyocytes.

RESULTS

We observed reduced CRAMP level in both heart and serum samples from I/R mice and in OGDR-treated cardiomyocytes, as well as reduced LL-37 level in MI patients. Knockdown of CRAMP enhanced cardiomyocyte apoptosis, and CRAMP KO mice displayed increased infarct size and myocardial apoptosis. In contrast, the CRAMP peptide reduced cardiomyocyte apoptosis and I/R injury. The CRAMP peptide inhibited cardiomyocyte apoptosis by activation of Akt and ERK1/2 and phosphorylation and nuclear export of FoxO3a. c-Jun was identified as a negative regulator of the CRAMP gene. Moreover, lower level of serum LL-37/neutrophil ratio was associated with readmission and/or death in MI patients during 1-year follow-up.

CONCLUSIONS

CRAMP protects against cardiomyocyte apoptosis and cardiac I/R injury via activation of Akt and ERK and phosphorylation and nuclear export of FoxO3a. Increasing LL-37 might be a novel therapy for cardiac ischemic injury.

IL-10 Accelerates Re-Endothelialization and Inhibits Post-Injury Intimal Hyperplasia following Carotid Artery Denudation

The role of inflammation on atherosclerosis and restenosis is well established. Restenosis is thought to be a complex response to injury, which includes early thrombus formation, acute inflammation and neo-intimal growth. Inflammatory cells are likely contributors in the host response to vascular injury, via cytokines and chemokines secretion, including TNF-alpha (TNF). We have previously shown that IL-10 inhibits TNF and other inflammatory mediators produced in response to cardiovascular injuries. The specific effect of IL-10 on endothelial cell (ECs) biology is not well elucidated. Here we report that in a mouse model of carotid denudation, IL-10 knock-out mice (IL-10KO) displayed significantly delayed Re-endothelialization and enhanced neo-intimal growth compared to their WT counterparts. Exogenous recombinant IL-10 treatment dramatically blunted the neo-intimal thickening while significantly accelerating the recovery of the injured endothelium in WT mice. In vitro, IL-10 inhibited negative effects of TNF on ECs proliferation, ECs cell cycle, ECs-monocyte adhesion and ECs apoptosis. Furthermore, IL-10 treatment attenuated TNF-induced smooth muscle cells proliferation. Our data suggest that IL-10 differentially regulate endothelial and vascular smooth cells proliferation and function and thus inhibits neo-intimal hyperplasia. Thus, these results may provide insights necessary to develop new therapeutic strategies to limit vascular restenosis during percutaneous coronary intervention (PCI) in the clinics.

Alcohol consumption negates estrogen-mediated myocardial repair in ovariectomized mice by inhibiting endothelial progenitor cell mobilization and function

We have shown previously that estrogen (estradiol, E2) supplementation enhances voluntary alcohol consumption in ovariectomized female rodents and that increased alcohol consumption impairs ischemic hind limb vascular repair. However, the effect of E2-induced alcohol consumption on post-infarct myocardial repair and on the phenotypic/functional properties of endothelial progenitor cells (EPCs) is not known. Additionally, the molecular signaling of alcohol-estrogen interactions remains to be elucidated. This study examined the effect of E2-induced increases in ethanol consumption on post-infarct myocardial function/repair. Ovariectomized female mice, implanted with 17β-E2 or placebo pellets were given access to alcohol for 6 weeks and subjected to acute myocardial infarction. Left ventricular functions were consistently depressed in mice consuming ethanol compared with those receiving only E2. Alcohol-consuming mice also displayed significantly increased infarct size and reduced capillary density. Ethanol consumption also reduced E2-induced mobilization and homing of EPCs to injured myocardium compared with the E2-alone group. In vitro, exposure of EPCs to ethanol suppressed E2-induced proliferation, survival, and migration and markedly altered E2-induced estrogen receptor-dependent cell survival signaling and gene expression. Furthermore, ethanol-mediated suppression of EPC biology was endothelial nitric oxide synthase-dependent because endothelial nitric oxide synthase-null mice displayed an exaggerated response to post-acute myocardial infarction left ventricular functions. These data suggest that E2 modulation of alcohol consumption, and the ensuing EPC dysfunction, may negatively compete with the beneficial effects of estrogen on post-infarct myocardial repair.

TNF-α response of vascular endothelial and vascular smooth muscle cells involve differential utilization of ASK1 kinase and p73

Atherosclerosis involves a specialized inflammatory process regulated by an intricate network of cytokine and chemokine signaling. Atherosclerotic lesions lead to the release of cytokines that can have multiple affects on various vascular cell functions either promoting lesion expansion or alternatively retard progression. Tumor necrosis factor-α (TNF-α) is one such cytokine that can activate both cell survival and cell death mechanisms simultaneously. Here we show that TNF-α induces apoptosis in human aortic endothelial cells (HAECs), while it promotes the proliferation of vascular smooth muscle cells (VSMCs). Both events involved the activation of the Rb-E2F1 transcriptional regulatory pathway. Stimulation of HAECs with TNF-α led to an increased expression of p73 protein and a reduction in the levels of p53. This involved apoptosis signal-regulating kinase 1 (ASK1)- mediated inactivation of Rb and its dissociation from the p73 promoter. In contrast, TNF-α stimulation of VSMCs enhanced the association of E2F1 with proliferative promoters like thymidylate synthase and cdc25A, while Rb was dissociated. ASK1 kinase has a critical role in the apoptotic process, as its depletion or dissociation from Rb reduced TNF-α-induced apoptosis. These results show that the cytokine TNF-α can elicit diametrically opposite responses in vascular endothelial cells and VSMCs, utilizing the Rb-E2F pathway.

p38 phosphorylates Rb on Ser567 by a novel, cell cycle-independent mechanism that triggers Rb-Hdm2 interaction and apoptosis

The retinoblastoma protein (Rb) inhibits both cell division and apoptosis, but the mechanism by which Rb alternatively regulates these divergent outcomes remains poorly understood. Cyclin dependent kinases (Cdks) promote cell division by phosphorylating and reversibly inactivating Rb by a hierarchical series of phosphorylation events and sequential conformational changes. The stress-regulated mitogen activated protein kinase (MAPK) p38 also phosphorylates Rb, but it does so in a cell cycle-independent manner that is associated with apoptosis rather than with cell division. Here, we show that p38 phosphorylates Rb by a novel mechanism that is distinct from that of Cdks. p38 bypasses the cell cycle-associated hierarchical phosphorylation and directly phosphorylates Rb on Ser567, which is not phosphorylated during the normal cell cycle. Phosphorylation by p38, but not Cdks, triggers an interaction between Rb and the human homologue of murine double minute 2 (Hdm2), leading to degradation of Rb, release of E2F1 and cell death. These findings provide a mechanistic explanation for how Rb regulates cell division and apoptosis through different kinases, and reveal how Hdm2 may functionally link the tumor suppressors Rb and p53.

Inhibition of melanoma angiogenesis by telomere homolog oligonucleotides

Telomere homolog oligonucleotides (T-oligos) activate an innate telomere-based program that leads to multiple anticancer effects. T-oligos act at telomeres to initiate signaling through the Werner protein and ATM kinase. We wanted to determine if T-oligos have antiangiogenic effects. We found that T-oligo-treated human melanoma (MM-AN) cells had decreased expression of vascular endothelial growth factor (VEGF), VEGF receptor 2, angiopoeitin-1 and -2 and decreased VEGF secretion. T-oligos activated the transcription factor E2F1 and inhibited the activity of the angiogenic transcription factor, HIF-1α. T-oligos inhibited EC tubulogenesis and total tumor microvascular density matrix invasion by MM-AN cells and ECs in vitro. In melanoma SCID xenografts, two systemic T-oligo injections decreased by 60% (P < .004) total tumor microvascular density and the functional vessels density by 80% (P < .002). These findings suggest that restriction of tumor angiogenesis is among the host's innate telomere-based anticancer responses and provide further evidence that T-oligos may offer a powerful new approach for melanoma treatment.

Transcription factor E2F1 suppresses dendritic cell maturation

Transcription factor E2F1 has been largely studied as a promoter of S-phase transition in the cell cycle and as a regulator of apoptosis. Recently, E2F1 has been shown to regulate a wide range of genes in response to inflammatory stimulation of macrophages and to contribute to T cell activation in response to pathogens, implicating an extensive immunological role for E2F1. Dendritic cells (DCs) play critical roles as professional APCs in the development of immune responses. However, it is unclear whether E2F1 has any effect on DC phenotype or function. In this paper, we report that E2F1 acts as a suppressor of DC maturation. The level of E2F1 expression was transiently downregulated in the course of LPS-induced maturation of both human monocyte-derived DCs and a mouse DC cell line, DC2.4. Knockdown of E2F1 by small interfering RNA in DC2.4 cells resulted in both phenotypic and functional maturation, even without LPS treatment. Conversely, ectopic overexpression of E2F1 suppressed LPS-induced maturation of DC2.4 cells. Furthermore, knockdown of E2F1 caused the activation of several major signaling pathways known to be activated in the course of DC maturation, including Erk1/2, NF-kappaB, and PI3K/Akt, suggesting that E2F1 may be involved in regulating multiple signaling pathways in DCs. Finally, the alteration of phenotypic maturation by E2F1 was confirmed with bone marrow-derived DCs from E2F1 knockout mice. Overall, our data demonstrate for the first time that E2F1 is a critical regulator of DC maturation.

c-Jun N-Terminal Kinase Primes Endothelial Cells at Atheroprone Sites for Apoptosis

Objective— Atherosclerosis is a focal disease that occurs predominantly at branches and bends of the arterial tree. Endothelial cells (EC) at atherosusceptible sites are prone to injury, which can contribute to lesion formation, whereas EC at atheroprotected sites are resistant. The c-Jun N-terminal kinase (JNK) is activated constitutively in EC at atherosusceptible sites but is inactivated at atheroprotected sites by mitogen-activated protein kinase phosphatase-1 (MKP-1). Here, we examined the effects of JNK activation on EC physiology at atherosusceptible sites.

Methods and Results— We identified transcriptional programs regulated by JNK by applying a specific pharmacological inhibitor to cultured EC and assessing the transcriptome using microarrays. This approach and subsequent validation by gene silencing revealed that JNK positively regulates the expression of numerous proapoptotic molecules. Analysis of aortae of wild-type, JNK1 −/− , and MKP-1 −/− mice revealed that EC at an atherosusceptible site express proapoptotic proteins and are primed for apoptosis and proliferation in response to lipopolysaccharide through a JNK1-dependent mechanism, whereas EC at a protected site expressed lower levels of proapoptotic molecules and were protected from injury by MKP-1.

Conclusion— Spatial variation of JNK1 activity delineates the spatial distribution of apoptosis and turnover of EC in arteries.

Alcohol consumption, cardiovascular health, and endothelial function markers

Cardiovascular diseases are among the worldwide leading causes of shorter life expectancy and loss of quality of life. Thus, any influence of diet or life habits on the cardiovascular system may have important implications for public health. Most world populations consume alcoholic beverages. Since alcohol may have both protective and harmful effects on cardiovascular health, the identification of biochemical mechanisms that could explain such paradoxical effects is warranted. The vascular endothelium is the target of important mediating pathways of differential ethanol concentrations, such as oxidative stress, lipoproteins, and insulin resistance. Alcohol-induced endothelial damage or protection may be related to the synthesis or action of several markers, such as nitric oxide, cortisol, endothelin-1, adhesion molecules, tumor necrosis factor alpha, interleukin-6, C-reactive protein, and haemostatic factors. The expression of these markers is consistent with the J-shaped curve between alcohol consumption and cardiovascular health. However, there is genetic and phenotypic heterogeneity in alcohol response, and despite the apparent beneficial biochemical effects of low doses of ethanol, there is not enough clinical and epidemiological evidence to allow the recommendation to consume alcoholic beverages for abstemious individuals. Considering the potential for addiction of alcoholic beverage consumption and other negative consequences of alcohol, it would be worthwhile to identify substances able to mimic the beneficial effects of low doses of ethanol without its adverse effects.

Phactr4 regulates neural tube and optic fissure closure by controlling PP1-, Rb-, and E2F1-regulated cell-cycle progression

Here we identify the humpty dumpty (humdy) mouse mutant with failure to close the neural tube and optic fissure, causing exencephaly and retinal coloboma, common birth defects. The humdy mutation disrupts Phactr4, an uncharacterized protein phosphatase 1 (PP1) and actin regulator family member, and the missense mutation specifically disrupts binding to PP1. Phactr4 is initially expressed in the ventral cranial neural tube, a region of regulated proliferation, and after neural closure throughout the dorsoventral axis. humdy embryos display elevated proliferation and abnormally phosphorylated, inactive PP1, resulting in Rb hyperphosphorylation, derepression of E2F targets, and abnormal cell-cycle progression. Exencephaly, coloboma, and abnormal proliferation in humdy embryos are rescued by loss of E2f1, demonstrating the cell cycle is the key target controlled by Phactr4. Thus, Phactr4 is critical for the spatially and temporally regulated transition in proliferation through differential regulation of PP1 and the cell cycle during neurulation and eye development.

Lysyl oxidase (LOX) down-regulation by TNFalpha: a new mechanism underlying TNFalpha-induced endothelial dysfunction

OBJECTIVE

TNFalpha is a pro-inflammatory cytokine that induces endothelial dysfunction and promotes atherosclerosis progression. Down-regulation of lysyl oxidase (LOX), a key enzyme in extracellular matrix maturation, by pro-atherogenic risk factors such as LDL and homocysteine, is associated with an impairment of endothelial barrier function. Our hypothesis is that the inflammatory cytokine TNFalpha could also modulate LOX expression/function in endothelial cells.

METHODS

The study was carried out in human umbilical vein endothelial cells (HUVEC), porcine aortic endothelial cells (PAEC) and bovine aortic endothelial cells (BAEC). LOX mRNA levels were analysed by real-time PCR and LOX activity was assessed by a high sensitive fluorescent assay. Promoter activity was determined by transient transfection using a luciferase reporter system.

RESULTS

TNFalpha decreases LOX mRNA levels in endothelial cells in a dose- and time-dependent manner. The effect of TNFalpha was observed at low concentrations (0.1-1 ng/mL) and was maximal at 2.5 ng/mL (after 21 h). In transfection assays, TNFalpha reduced LOX transcriptional activity to a similar extent than LOX mRNA. Furthermore, TNFalpha decreases endothelial LOX enzymatic activity. By using both TNF receptor (TNFR) agonist and blocking antibodies we determined the involvement of TNFR2 on LOX down-regulation. Moreover, while TNFR-associated factor-2 (TRAF-2) did not mediate signalling events leading to LOX inhibition, PKC inhibitors counteracted the TNFalpha-induced decrease of LOX mRNA levels. Finally, TNFalpha administration significantly reduced vascular LOX expression in rat aorta.

CONCLUSIONS

Endothelial dysfunction induced by TNFalpha is associated with a decrease of LOX expression/activity. Thus, LOX seems to be involved in the impairment of endothelial function triggered by different pathological conditions.

Tumor necrosis factor-alpha receptor p75 is required in ischemia-induced neovascularization

BACKGROUND

Aging is a risk factor for coronary and peripheral artery disease. Tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, is expressed in ischemic tissue and is known to modulate angiogenesis. Little is known about the role of TNF-alpha receptors (TNFR1/p55 and TNFR2/p75) in angiogenic signaling.

METHODS AND RESULTS

We studied neovascularization in the hindlimb ischemia model in young and old TNFR2/p75 knockout (p75KO) and wild-type age-matched controls. Between days 7 to 10 after hindlimb surgery, 100% of old p75KOs experienced autoamputation of the operated limbs, whereas none of the age-matched wild-type mice exhibited hindlimb necrosis. Poor blood flow recovery in p75KO mice was associated with increased endothelial cell apoptosis, decreased capillary density, and significant reductions in the expression of vascular endothelial growth factor and basic fibroblast growth factor-2 mRNA transcripts in ischemic tissue and in circulating endothelial progenitor cells. The number of circulating bone marrow-derived endothelial progenitor cells was significantly reduced in p75KO mice. Transplantation of wild-type bone marrow mononuclear cells into irradiated old p75KO mice 1 month before hindlimb surgery prevented limb loss.

CONCLUSIONS

Our present study suggests that ischemia-induced endothelial progenitor cell-mediated neovascularization is dependent, at least in part, on p75 TNF receptor expressed in bone marrow-derived cells. Specifically, endothelial cell/endothelial progenitor cell survival, vascular endothelial growth factor expression, endothelial progenitor cell mobilization from bone marrow, endothelial progenitor cell differentiation, and ultimately ischemia-induced collateral vessel development are dependent on signaling through TNFR2/p75. Furthermore, because TNFR2/p75 becomes an age-related limiting factor in postischemic recovery, it may be a potential gene target for therapeutic interventions in adult vascular diseases.

Cell cycle regulator E2F1 modulates angiogenesis via p53-dependent transcriptional control of VEGF

The transcription factor E2F1 is known to regulate cell proliferation and has been thought to modulate tumorigenesis via this mechanism alone. Here we show that mice deficient in E2F1 exhibit enhanced angiogenesis. The proangiogenic phenotype in E2F1 deficiency is the result of overproduction of vascular endothelial growth factor (VEGF) and is prevented by VEGF blockade. Under hypoxic conditions, E2F1 down-regulates the expression of VEGF promoter activity by associating with p53 and specifically down-regulating expression of VEGF but not other hypoxia-inducible genes, suggesting a promoter structure context-dependent regulation mechanism. We found that the minimum VEGF promoter mediating transcriptional repression by E2F1 features an E2F1- binding site with four Sp-1 sites in close proximity. These data disclose an unexpected function of endogenous E2F1: regulation of angiogenic activity via p53-dependent transcriptional control of VEGF expression.

CAMP-response element-binding protein mediates tumor necrosis factor-alpha-induced vascular cell adhesion molecule-1 expression in endothelial cells

Hypertension causes endothelial dysfunction, which plays an important role in atherogenesis. The vascular cell adhesion molecule-1 (VCAM-1) contributes to atherosclerotic lesion formation by recruiting leukocytes from blood into tissues. Tumor necrosis factor-alpha (TNFalpha) induces endothelial dysfunction and VCAM-1 expression in endothelial cells (ECs). We examined whether the cAMP-response element binding protein (CREB), a transcription factor that mediates cytokine expression and vascular remodeling, is involved in TNFalpha-induced VCAM-1 expression. TNFalpha induced phosphorylation of CREB with a peak at 15 min of stimulation in a dose-dependent manner in bovine aortic ECs. Pharmacological inhibition of p38 mitogen-activated protein kinase (p38-MAPK) inhibited TNFalpha-induced CREB phosphorylation. Adenovirus-mediated overexpression of a dominant-negative form of CREB suppressed TNFalpha-induced VCAM-1 and c-fos expression. Although activating protein 1 DNA binding activity was attenuated by overexpression of dominant negative CREB, nuclear factor-kappaB activity was not affected. Our results suggest that the p38-MAPK/CREB pathway plays a critical role in TNFalpha-induced VCAM-1 expression in vascular endothelial cells. The p38MAPK/CREB pathway may be a novel therapeutic target for the treatment of atherosclerosis.

Identification of p54(nrb) and the 14-3-3 Protein HS1 as TNF-alpha-inducible genes related to cell cycle control and apoptosis in human arterial endothelial cells

TNF-alpha plays a pivotal role in inflammation processes which are mainly regulated by endothelial cells. While TNF-alpha induces apoptosis of several cell types like tumor cells, endothelial cells are resistant to TNFa mediated cell death. The cytotoxic effects of TNF-alpha on most cells are only evident if RNA or protein synthesis is inhibited, suggesting that de novo RNA or protein synthesis protect cells from TNF-alpha cytotoxicity, presumably by NF-kappaB mediated induction of protective genes. However, the cytoprotective genes involved in NF-kappaB dependent endothelial cell survival have not been sufficiently identified. In the present study, the suppression subtractive hybridization (SSH) method was employed to identify rarely transcribed TNF-alpha inducible genes in human arterial endothelial cells related to cell survival and cell cycle. The TNF-alpha-induced expression of the RNA binding protein p54(nrb) and the 14-3-3 protein HS1 as shown here for the first time may contribute to the TNF-alpha mediated cell protection of endothelial cells. These genes have been shown to play pivotal roles in cell survival and cell cycle control in different experimental settings. The concerted expression of these genes together with other genes related to cell protection and cell cycle like DnaJ, p21(cip1) and the ubiquitin activating enzyme E1 demonstrates the identification of new genes in the context of TNF-alpha induced gene expression patterns mediating the prosurvival effect of TNF-alpha in endothelial cells.

Ethanol modulation of TNF-alpha biosynthesis and signaling in endothelial cells: synergistic augmentation of TNF-alpha mediated endothelial cell dysfunctions by chronic ethanol

Despite reported cardio-protective effects of low alcohol intake, chronic alcoholism remains a risk factor in the pathogenesis of coronary artery disease. Dose related bimodal effects of alcohol on cardiovascular system might reflect contrasting influences of light versus heavy alcohol consumption on the vascular endothelium. Chronic ethanol induced damage to various organs has been linked to the increased release of TNF-alpha (TNF). We have previously shown that TNF, expressed at the sites of arterial injury, suppresses re-endothelialization of denuded arteries and inhibits endothelial cell (EC) proliferation in vitro. Here we report that in vitro chronic ethanol exposure enhances agonist-induced TNF mRNA and protein expression in EC. Ethanol-mediated increment in TNF expression involves increased de novo transcription without affecting mRNA stability. DNA binding assays revealed that ethanol-induced TNF up regulation was AP1 dependent. Functionally, TNF induced EC dysfunction, including reduced proliferation, migration and cyclin A expression, were all markedly enhanced in the presence of ethanol. Additionally, expression of cyclin D1 was significantly attenuated in cells co-treated with TNF and ethanol while each treatment alone had little effect on cyclin D1 expression. Furthermore, exposure to ethanol potentiated and prolonged agonist-induced activation of JNK. Inhibition of JNK by over-expression of dominant negative JNK1 substantially reversed ethanol/TNF-mediated inhibition of cyclin A expression and EC proliferation, suggesting modulation of JNK1 signaling as the mechanism for ethanol/TNF-induced EC dysfunctions. Taken together, these data indicate that chronic ethanol consumption may negatively influence post angioplasty re-endothelialization thereby contributing to the development of restenosis.

T-oligo treatment decreases constitutive and UVB-induced COX-2 levels through p53- and NFkappaB-dependent repression of the COX-2 promoter

Chronically irradiated murine skin and UV light-induced squamous cell carcinomas overexpress the inducible isoform of cyclooxygenase (COX-2), and COX-2 inhibition reduces photocarcinogenesis in mice. We have reported previously that DNA oligonucleotides substantially homologous to the telomere 3'-overhang (T-oligos) induce DNA repair capacity and multiple other cancer prevention responses, in part through up-regulation and activation of p53. To determine whether T-oligos affect COX-2 expression, human newborn keratinocytes and fibroblasts were pretreated with T-oligos or diluent alone for 24 h, UV-irradiated, and processed for Western blotting. In both cell types, T-oligos transcriptionally down-regulated base-line and UV light-induced COX-2 expression, coincident with p53 activation. In fibroblasts with wild type versus dominant negative p53 (p53(WT) versus p53(DN)), T-oligos decreased constitutive expression of a COX-2 reporter plasmid by >50%. We then examined NFkappaB, a known positive regulator of COX-2 transcription. In p53(WT) but not in p53(DN) fibroblasts and in human keratinocytes, T-oligos decreased readout of an NFkappaB promoter-driven reporter plasmid and decreased NFkappaB binding to DNA. After T-oligo treatment and subsequent UV irradiation, binding of the transcriptional co-activator protein p300 to NFkappaB was decreased, whereas binding of p300 to p53 was increased. Human skin explants provided with T-oligos had markedly decreased COX-2 immunostaining both at base-line and post-UV light, coincident with increased p53 immunostaining. We conclude that T-oligos transcriptionally down-regulate COX-2 expression in human skin via activation and up-regulation of p53, at least in part by inhibiting NFkappaB transcriptional activation. Decreased COX-2 expression may contribute to the observed ability of T-oligos to reduce photocarcinogenesis.

Angiopoietin-1 attenuates H2O2-induced SEK1/JNK phosphorylation through the phosphatidylinositol 3-kinase/Akt pathway in vascular endothelial cells

Oxidative stress activates various signal transduction pathways, including Jun N-terminal kinase (JNK) and its substrates, that induce apoptosis. We reported here the role of angiopoietin-1 (Ang1), which is a prosurvival factor in endothelial cells, during endothelial cell damage induced by oxidative stress. Hydrogen peroxide (H2O2) increased apoptosis of endothelial cells through JNK activation, whereas Ang1 inhibited H2O2-induced apoptosis and concomitant JNK phosphorylation. The inhibition of H2O2-induced JNK phosphorylation was reversed by inhibitors of phosphatidylinositol (PI) 3-kinase and dominant-negative Akt, and constitutively active-Akt attenuated JNK phosphorylation without Ang1. These data suggested that Ang1-dependent Akt phosphorylation through PI 3-kinase leads to the inhibition of JNK phosphorylation. H2O2-induced phosphorylation of SAPK/Erk kinase (SEK1) at Thr261, which is an upstream regulator of JNK, was also attenuated by Ang1-dependent activation of the PI 3-kinase/Akt pathway. In addition, Ang1 induced SEK1 phosphorylation at Ser80, suggesting the existence of an additional signal transduction pathway through which Ang1 attenuates JNK phosphorylation. These results demonstrated that Ang1 attenuates H2O2-induced SEK1/JNK phosphorylation through the PI 3-kinase/Akt pathway and inhibits the apoptosis of endothelial cells to oxidative stress.

Activation of p38 Has Opposing Effects on the Proliferation and Migration of Endothelial Cells

Pathological conditions such as hypertension and hyperglycemia as well as abrasions following balloon angioplasty all lead to endothelial dysfunction that impacts disease morbidity. These conditions are associated with the elaboration of a variety of cytokines and increases in p38 activity in endothelial cells. However, the relationship between enhanced p38 activity and endothelial cell function remains poorly understood. To investigate the effect of enhanced p38 MAPK activity on endothelial cell function, we expressed an activated mutant of MEK6 (MEK6E), an upstream regulator of p38. Expression of MEK6E activated p38 and resulted in phosphorylation of its downstream substrate, heat shock protein 27 (Hsp27). Activation of p38 was not sufficient to induce apoptosis; however, it did induce p38-dependent cell cycle arrest. MEK6E expression was sufficient to inhibit ERK phosphorylation triggered by growth factors and integrin engagement. MAPK phosphatase-1 (MKP-1) expression was increased upon p38 activation, and expression of a "substrate-trapping" MKP-1 was sufficient to restore ERK activity. Activation of p38 was sufficient to induce cell migration, which was accompanied by alterations in actin architecture characterized by enhanced lamellipodia. Co-expression of a mutant form of Hsp27, lacking all three phosphorylation sites, reversed MEK6E-induced cell migration and altered the cytoskeletal changes induced by p38 activation. Collectively, these results suggest that cellular decisions regarding migration and proliferation are influenced by p38 activity and that prolonged activation of p38 may result in an anti-angiogenic phenotype that contributes to endothelial dysfunction.

The E2F transcriptional network: old acquaintances with new faces

The E2 factor (E2F) family of transcription factors are downstream targets of the retinoblastoma protein. E2F factors have been known for several years to be important regulators of S-phase entry. Recent studies have improved our understanding of the molecular mechanisms of action used by this transcriptional network. In addition, they have given us an appreciation of the fact that E2F has functions that reach beyond G1/S control and impact cell proliferation in several different ways. The discovery of new family members with unusual properties, the unexpected phenotypes of mutant animals, a diverse collection of biological activities, a large number of new putative target genes and the new modes of transcriptional regulation have all contributed to an increasingly complex view of E2F function. In this review, we will discuss these recent developments and describe how they are beginning to shape a new and revised picture of the E2F transcriptional program.