Oxidized phospholipids increase interleukin 8 (IL-8) synthesis by activation of the c-src/signal transducers and activators of transcription (STAT)3 pathway

PLD1-dependent PKCgamma activation downstream to Src is essential for the development of pathologic retinal neovascularization

Vascular endothelial growth factor (VEGF) appears to be an important mediator of pathologic retinal angiogenesis. In understanding the mechanisms of pathologic retinal neovascularization, we found that VEGF activates PLD1 in human retinal microvascular endothelial cells, and this event is dependent on Src. In addition, VEGF activates protein kinase C-gamma (PKCgamma) via Src-dependent PLD1 stimulation. Inhibition of Src, PLD1, or PKCgamma via pharmacologic, dominant negative mutant, or siRNA approaches significantly attenuated VEGF-induced human retinal microvascular endothelial cell migration, proliferation, and tube formation. Hypoxia also induced Src-PLD1-PKCgamma signaling in retina, leading to retinal neovascularization. Furthermore, siRNA-mediated down-regulation of VEGF inhibited hypoxia-induced Src-PLD1-PKCgamma activation and neovascularization. Blockade of Src-PLD1-PKCgamma signaling via the siRNA approach also suppressed hypoxia-induced retinal neovascularization. Thus, these observations demonstrate, for the first time, that Src-dependent PLD1-PKCgamma activation plays an important role in pathologic retinal angiogenesis.

Thrombin enhanced migration and MMPs expression of human chondrosarcoma cells involves PAR receptor signaling pathway

Thrombin is a multifunctional protease that can activate hemostasis and coagulation through the cleavage of fibrinogen to form fibrin clots. Thrombin also plays a crucial role in migration and metastasis of human cancer cells. However, the effect of thrombin on migration activity in human chondrosarcoma cells is mostly unknown. Here, we found that thrombin increased the migration and expression of matrix metalloproteinase (MMP)-2 and MMP-13 in human chondrosarcoma cells (JJ012 and SW1353 cells). By using pharmacological inhibitors or activators or genetic inhibition by the protease-activated receptor (PAR), we found that the PAR1 and PAR4 receptor but not PAR3 receptor are involved in thrombin-mediated cell migration and MMPs expression. Thrombin-mediated migration and MMPs up-regulation was attenuated by phospholipase C (PLC), protein kinase C, and c-Src inhibitor. Activations of PLCbeta, PKCalpha, c-Src, and NF-kappaB pathways after thrombin treatment was demonstrated, and thrombin-induced MMPs expression and migration activity was inhibited by the specific inhibitors and mutants of PLC, PKC, c-Src, and NF-kappaB cascades. Taken together, our results indicated that thrombin enhances the migration of chondrosarcoma cells by increasing MMP-2 and MMP-13 expression through the PAR/PLC/PKCalpha/c-Src/NF-kappaB signal transduction pathway.

Generation and biological activities of oxidized phospholipids

Glycerophospholipids represent a common class of lipids critically important for integrity of cellular membranes. Oxidation of esterified unsaturated fatty acids dramatically changes biological activities of phospholipids. Apart from impairment of their structural function, oxidation makes oxidized phospholipids (OxPLs) markers of "modified-self" type that are recognized by soluble and cell-associated receptors of innate immunity, including scavenger receptors, natural (germ line-encoded) antibodies, and C-reactive protein, thus directing removal of senescent and apoptotic cells or oxidized lipoproteins. In addition, OxPLs acquire novel biological activities not characteristic of their unoxidized precursors, including the ability to regulate innate and adaptive immune responses. Effects of OxPLs described in vitro and in vivo suggest their potential relevance in different pathologies, including atherosclerosis, acute inflammation, lung injury, and many other conditions. This review summarizes current knowledge on the mechanisms of formation, structures, and biological activities of OxPLs. Furthermore, potential applications of OxPLs as disease biomarkers, as well as experimental therapies targeting OxPLs, are described, providing a broad overview of an emerging class of lipid mediators.

Galactose specific adhesin of enteroaggregative E. coli induces IL-8 secretion via activation of MAPK and STAT-3 in INT-407 cells

BACKGROUND

Enteroaggregative Escherichia coli (EAEC) is one of the most common bacterial pathogens associated with the etiology of persistent diarrhea. A characteristic feature of EAEC-pathogenesis is the induction of profound inflammatory response in the intestinal epithelium. The present study was designed to investigate the underlying mechanism of inflammatory responses induced by a novel galactose specific adhesin of T7 strain of EAEC (EAEC-T7) in human intestinal epithelial cell line (INT-407).

METHODS

INT-407 cells were stimulated with the adhesin in the absence and presence of anti-adhesin (IgG(AD))/d-galactose/H7/staurosporin (inhibitor of PKC)/PD098059 (inhibitor of MEK)/SB203580 (inhibitor of p38-MAPkinase)/AG490 (inhibitor of JAK (-2,-3)/STAT-3 pathway). The expression of activated Raf-1, MEK-1, ERK1/2, JNK, p38-MAPK and STAT-3 was analyzed by Western immunoblot. Release of interleukin-8 (IL-8) was measured by ELISA.

RESULTS

The adhesin was found to induce activation of Raf-1, MEK-1, ERK1/2, p38-MAPK and STAT-3, which was reduced in the presence of IgG(AD)/d-galactose. The activation of Raf-1 was found to be attenuated in the presence of H7/staurosporin. The expression of phosphorylated STAT-3 was downregulated in the presence of AG490 and PD098059. Further, the adhesin induced IL-8 secretion was reduced in the presence of the inhibitors of MEK (PD098059), p38-MAPK (SB203580) and JAK (-2,-3)/STAT-3 pathway (AG490).

CONCLUSIONS

We propose that STAT-3 activation is quintessential for the galactose specific adhesin induced IL-8 secretion by INT-407 cells and must occur in concert with the activation of ERK1/2.

GENERAL SIGNIFICANCE

Our contribution regarding the galactose specific adhesin mediated signaling leads to an improved understanding of the EAEC-pathogenesis and may provide novel therapeutic approaches to combat EAEC infection.

Cyclooxygenase-2 enhances alpha2beta1 integrin expression and cell migration via EP1 dependent signaling pathway in human chondrosarcoma cells

Background

Cyclooxygenase (COX)-2, the inducible isoform of prostaglandin (PG) synthase, has been implicated in tumor metastasis. Interaction of COX-2 with its specific EP receptors on the surface of cancer cells has been reported to induce cancer invasion. However, the effects of COX-2 on migration activity in human chondrosarcoma cells are mostly unknown. In this study, we examined whether COX-2 and EP interaction are involved in metastasis of human chondrosarcoma.

Results

We found that over-expression of COX-2 or exogenous PGE₂ increased the migration of human chondrosarcoma cells. We also found that human chondrosarcoma tissues and chondrosarcoma cell lines had significant expression of the COX-2 which was higher than that in normal cartilage. By using pharmacological inhibitors or activators or genetic inhibition by the EP receptors, we discovered that the EP1 receptor but not other PGE receptors is involved in PGE₂-mediated cell migration and α2β1 integrin expression. Furthermore, we found that human chondrosarcoma tissues expressed a higher level of EP1 receptor than normal cartilage. PGE₂-mediated migration and integrin up-regulation were attenuated by phospholipase C (PLC), protein kinase C (PKC) and c-Src inhibitor. Activation of the PLCβ, PKCα, c-Src and NF-κB signaling pathway after PGE₂ treatment was demonstrated, and PGE₂-induced expression of integrin and migration activity were inhibited by the specific inhibitor, siRNA and mutants of PLC, PKC, c-Src and NF-κB cascades.

Conclusions

Our results indicated that PGE₂ enhances the migration of chondrosarcoma cells by increasing α2β1 integrin expression through the EP1/PLC/PKCα/c-Src/NF-κB signal transduction pathway.

Lipoteichoic acid enhances IL-6 production in human synovial fibroblasts via TLR2 receptor, PKCdelta and c-Src dependent pathways

Patients with rheumatoid arthritis (RA) are at increased risk of developing infections and appear to be particularly susceptible to septic arthritis. Lipoteichoic acid (LTA), a cell wall component of Gram-positive bacteria is an amphiphilic, negatively charged glycolipid. However, the effects of LTA on human synovial fibroblasts are largely unknown. We investigated the signaling pathway involved in IL-6 production stimulated by LTA in rheumatoid arthritis synovial fibroblasts (RASF). LTA caused concentration- and time-dependent increases in IL-6 production. LTA-mediated IL-6 production was attenuated by Toll-like receptor 2 (TLR2) monoclonal antibody or siRNA. Pretreatment with PKCdelta inhibitor (rottlerin), c-Src inhibitor (PP2), AP-1 inhibitor (tanshinone IIA) and NF-kappaB inhibitor (PDTC and TPCK) also inhibited the potentiating action of LTA. However, focal adhesion kinase (FAK) mutant and siRNA did not affect LTA-mediated IL-6 production. Stimulation of cells with LTA increased the PKCdelta and c-Src phosphorylation and kinase activity. LTA increased the accumulation of p-c-Jun and p-p65 in the nucleus, as well as AP-1 and NF-kappaB luciferase activity. LTA-mediated increase of AP-1 and NF-kappaB luciferase activity was inhibited by rottlerin and PP2 or TLR2 and PKCdelta siRNA or c-Src mutant. Our results suggest that LTA-increased IL-6 production in human synovial fibroblasts via the TLR2 receptor, PKCdelta, c-Src, AP-1 and NF-kappaB signaling pathways.

Src kinases as therapeutic targets for cancer

Src family kinases (SFKs) have a critical role in cell adhesion, invasion, proliferation, survival, and angiogenesis during tumor development. SFKs comprise nine family members that share similar structure and function. Overexpression or high activation of SFKs occurs frequently in tumor tissues and they are central mediators in multiple signaling pathways that are important in oncogenesis. SFKs can interact with tyrosine kinase receptors, such as EGFR and the VEGF receptor. SFKs can affect cell proliferation via the Ras/ERK/MAPK pathway and can regulate gene expression via transcription factors such as STAT molecules. SFKs can also affect cell adhesion and migration via interaction with integrins, actins, GTPase-activating proteins, scaffold proteins, such as p130(CAS) and paxillin, and kinases such as focal adhesion kinases. Furthermore, SFKs can regulate angiogenesis via gene expression of angiogenic growth factors, such as fibroblast growth factor, VEGF, and interleukin 8. On the basis of these important findings, small-molecule SFK inhibitors have been developed and are undergoing early phase clinical testing. In preclinical studies these agents can suppress tumor growth and metastases. The agents seem to be safe in humans and could add to the therapeutic arsenal against subsets of cancers.

Targeting inflammatory pathways for prevention and therapy of cancer: short-term friend, long-term foe

Chronic infections, obesity, alcohol, tobacco, radiation, environmental pollutants, and high-calorie diet have been recognized as major risk factors for the most common types of cancer. All these risk factors are linked to cancer through inflammation. Although acute inflammation that persists for short-term mediates host defense against infections, chronic inflammation that lasts for long term can predispose the host to various chronic illnesses, including cancer. Linkage between cancer and inflammation is indicated by numerous lines of evidence; first, transcription factors nuclear factor-kappaB (NF-kappaB) and signal transducers and activators of transcription 3 (STAT3), two major pathways for inflammation, are activated by most cancer risk factors; second, an inflammatory condition precedes most cancers; third, NF-kappaB and STAT3 are constitutively active in most cancers; fourth, hypoxia and acidic conditions found in solid tumors activate NF-kappaB; fifth, chemotherapeutic agents and gamma-irradiation activate NF-kappaB and lead to chemoresistance and radioresistance; sixth, most gene products linked to inflammation, survival, proliferation, invasion, angiogenesis, and metastasis are regulated by NF-kappaB and STAT3; seventh, suppression of NF-kappaB and STAT3 inhibits the proliferation and invasion of tumors; and eighth, most chemopreventive agents mediate their effects through inhibition of NF-kappaB and STAT3 activation pathways. Thus, suppression of these proinflammatory pathways may provide opportunities for both prevention and treatment of cancer.

Lovastatin inhibits oxidized L-A-phosphatidylcholine B-arachidonoyl-gamma-palmitoyl (ox-PAPC)-stimulated interleukin-8 mRNA and protein synthesis in human aortic endothelial cells by depleting stores of geranylgeranyl pyrophosphate

Human aortic endothelial cells (HAEC) exposed to 50 microg/ml oxidized L-A-phosphatidylcholine B-arachidonoyl-gamma-palmitoyl (ox-PAPC) for 6h increased in interleukin-8 mRNA and protein levels. Preincubation of HAEC with the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG CoA) inhibitor, (20 microM), significantly inhibited ox-PAPC-stimulated interleukin-8 mRNA and protein levels. Mevalonate (200 microM) reversed the inhibition of ox-PAPC-stimulated mRNA and protein levels by lovastatin, indicating the inhibitory effect of lovastatin was due to inhibition of mevalonate synthesis. Addition of the geranylgeraniol (GGOL, 10 microM) but not farnesol (FOL, 10 microM), reversed the inhibitory effect of lovastatin on interleukin-8 mRNA and protein levels stimulated by ox-PAPC, indicating that lovastatin exerted its effect by inhibiting stores of geranylgeranyl pyrophosphate (GGPP) which are necessary for geranylgeranylation of proteins. These results suggest a new mechanism for lovastatin in preventing atherosclerosis by inhibiting the inflammatory response that takes place in the vascular wall.

Oxidized phospholipids in control of inflammation and endothelial barrier

The levels of circulating oxidized phospholipids (OxPLs) become increased in chronic and acute pathologic conditions such as hyperlipidemia, atherosclerosis, increased intimamedia thickness in the patients with systemic Lupus erythematosus, vascular balloon injury, acute lung injury (ALI), and acute respiratory distress syndrome (ARDS). These pathologies are associated with inflammation and activation of endothelial cells. Depending on the biological context and the specific group of phospholipid oxidation products, OxPL may exhibit both proinflammatory and anti-inflammatory effects. This review will summarize the data showing a dual role of OxPL in modulation of chronic and acute inflammation as well as OxPL effects on pulmonary endothelial permeability. Recent reports show protective effects of OxPL in the models of endotoxin and ventilator-induced ALI and suggest a potential for using OxPL-derived cyclopenthenone-containing compounds with barrier-protective properties for drug design. These compounds may represent a new group of therapeutic agents for the treatment of lung syndromes associated with acute inflammation and lung vascular leak.

Role of Src tyrosine kinase in the atherogenic effects of the 12/15-lipoxygenase pathway in vascular smooth muscle cells

OBJECTIVE

The 12/15-Lipoxygenase (12/15-LO) and its metabolite 12(S)-Hydroxyeicosatetraenoic acid [12(S)-HETE] mediate proatherogenic responses in vascular smooth muscle cells (VSMCs). We examined the role of the nonreceptor tyrosine kinase Src in the signaling and epigenetic chromatin mechanisms involved in these processes.

METHODS AND RESULTS

Rat VSMCs (RVSMCs) were stimulated with 12(S)-HETE (0.1 micromol/L) in the presence or absence of the Src inhibitor PP2 (10 micromol/L). Src activation and downstream signaling events including inflammatory gene expression and chromatin histone H3-Lys-9/14 acetylation were examined by immunoblotting, RT-PCR, and chromatin immunoprecipitation assays, respectively. 12(S)-HETE significantly activated Src, focal adhesion kinase, Akt, p38MAPK, and CREB. Expression of monocyte chemoattractant protein-1 and interleukin-6 genes and histone H3-Lys-9/14 acetylation on their promoters were also increased by 12(S)-HETE. PP2 inhibited these responses as well as 12(S)-HETE-induced VSMC migration. Furthermore, dominant negative mutants of Src, CREB, and a histone acetyltransferase p300 significantly blocked 12(S)-HETE-induced inflammatory gene expression. In addition, growth factor induced Src signaling and downstream events including H3-Lys-9/14 acetylation and migration were significantly attenuated in VSMCs derived from 12/15-LO(-/-) mice relative to WT.

CONCLUSIONS

Src kinase signaling plays a central role in the proatherogenic responses mediated by 12/15-LO and its oxidized lipid metabolite 12(S)-HETE in VSMCs.

Ox-PAPC activation of PMET system increases expression of heme oxygenase-1 in human aortic endothelial cell

Oxidized-1-palmitoyl-2-arachidonyl-sn-glycerol-3-phosphocholine (Ox-PAPC) has been demonstrated to accumulate in atherosclerotic lesions and regulates expression of more than 1,000 genes in human aortic endothelial cell (HAEC). Among the most highly induced is heme oxygenase-1 (HO-1), a cell-protective antioxidant enzyme, which is sensitively induced by oxidative stress. To identify the pathway by which Ox-PAPC induces HO-1, we focused on the plasma membrane electron transport (PMET) complex, which contains ecto-NADH oxidase 1 (eNOX1) and NADPH:quinone oxidoreductase 1 (NQO1) and affects cellular redox status by regulating levels of NAD(P)H. We demonstrated that Ox-PAPC and its active components stimulated electron transfer through the PMET complex in HAECs from inside to outside [as determined by extracellular 2-(4-iodophenyl)-3-(44-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-1) reduction] and from outside to inside of the cell (as determined by intracellular NBT reduction). Chemical inhibitors of PMET system and siRNAs to PMET components (NQO1 and eNOX1) significantly decreased HO-1 induction by Ox-PAPC. We present evidence that Ox-PAPC activation of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) in HAEC plays an important role in the induction of HO-1 and PMET inhibitors blocked Nrf2 activation by Ox-PAPC. We hypothesized that PMET activation by Ox-PAPC causes intracellular NAD(P)H depletion, which leads to the increased oxidative stress and HO-1 induction. Supporting this hypothesis, cotreatment of cells with exogenous NAD(P)H and Ox-PAPC significantly decreased oxidative stress and HO-1 induction by Ox-PAPC. Taken together, we demonstrated that the PMET system in HAEC plays an important role in the regulation of cellular redox status and HO-1 expression by Ox-PAPC.

Clotrimazole ameliorates intestinal inflammation and abnormal angiogenesis by inhibiting interleukin-8 expression through a nuclear factor-kappaB-dependent manner

Increased interleukin (IL)-8 plays an important role not only in activation and recruitment of neutrophils but also in inducing exaggerated angiogenesis at the inflamed site. In the present study, we investigated the fact that clotrimazole (CLT) inhibits intestinal inflammation, and the inhibitory action is mediated through suppression of IL-8 expression. In the trinitrobenzene sulfonic acid (TNBS)-induced rat colitis model, CLT dose-dependently protected from the TNBS-induced weight loss, colon ulceration, and myeloperoxidase activity increase. In the lesion site, CLT also suppressed the TNBS-induced angiogenesis, IL-8 expression, and nuclear factor (NF)-kappaB activation. In a cellular model of colitis using tumor necrosis factor (TNF)-alpha-stimulated HT29 colon epithelial cells, treatment with CLT significantly suppressed TNF-alpha-mediated IL-8 induction and NF-kappaB transcriptional activity revealed by a luciferase reporter gene assay. Furthermore, cotreatment with CLT and pyrrolidine dithiocarbamate, a NF-kappaB inhibitor, synergistically reduced the NF-kappaB transcriptional activity as well as IL-8 expression. In an in vitro angiogenesis assay, CLT suppressed IL-8-induced proliferation, tube formation, and invasion of human umbilical vein endothelial cells. The in vivo angiogenesis assay using chick chorioallantoic membrane also showed that CLT significantly inhibited the IL-8-induced formation of new blood vessels. Taken together, these results suggest that CLT may prevent the progression of intestinal inflammation by not only down-regulating IL-8 expression but also inhibiting the action of IL-8 in both colon epithelial and vascular endothelial cells during pathogenesis of intestinal inflammation.

Regulation of Sox2 by STAT3 initiates commitment to the neural precursor cell fate

STAT3, a member of the signal transducer and activator or transcription (STAT) family of proteins, plays a major role in gliogenesis; however, its functions during differentiation of neural precursor cells (NPCs) are unclear. Our data demonstrate that STAT3 is present and active in the developing mouse central nervous system (CNS) as early as E7.5, several days prior to gliogenesis. We hypothesize that STAT3 is functioning very early in neural development to regulate NPC differentiation. To test this hypothesis, STAT3 dominant negative embryonic stem (ES) cells were generated and subjected to neural differentiation. The loss of STAT3 resulted in production of significantly fewer NPCs along with decreased expression of the neural stem cell marker nestin. Further investigation revealed the existence of a novel signaling pathway during early neural development in which STAT3 directly regulates the Sox2 promoter leading to Sox2 expression and subsequent nestin expression and commitment to the NPC fate.

Activation of the non-receptor tyrosine kinase cSrc in macrophage-rich atherosclerotic plaques of human carotid arteries

To determine the involvement of the non-receptor tyrosine kinase cSrc in plaque destabilization in carotid atherosclerosis (CAS), which is responsible for cerebral infarction, we performed quantitative and morphological detection of phosphorylated active cSrc (p-cSrc) and histopathological examination in CAS lesions. We examined carotid endarterectomy specimens obtained from 32 CAS patients. Each specimen was used for immunoblot and immunohistochemical analyses of p-cSrc, histopathological analysis, and image analysis of macrophage content. There was a strong positive correlation between cSrc activation on blots and macrophage content on sections. When we defined the macrophage-rich plaque (MRP) and the macrophage-poor plaque (MPP) as having macrophage content more and less than 5%, respectively, the p-cSrc density and the occurrence of plaque hemorrhage and thrombus formation were significantly increased in the MRP group (n=18) compared to the MPP group (n=14). p-cSrc immunoreactivity was localized in lesional endothelial cells, macrophages, and smooth muscle cells, which contained proinflammatory substances: the upstream oxidized low density lipoprotein, tissue factor and osteopontin, and the downstream active forms of extracellular signal-activated kinase and p38 and nuclear factor-kappaB. Our results suggest that cSrc activation in lesional cells contributes to plaque destabilization in CAS via persistent inflammation.

Thrombin-induced IL-6 production in human synovial fibroblasts is mediated by PAR1, phospholipase C, protein kinase C alpha, c-Src, NF-kappa B and p300 pathway

Thrombin is a key factor in the stimulation of fibrin deposition, angiogenesis and proinflammatory processes. Abnormalities in these processes are primary features of rheumatoid arthritis (RA) in synovial tissues. We investigated the signaling pathway involved in IL-6 production caused by thrombin in synovial fibroblasts. Thrombin caused concentration- and time-dependent increases in IL-6 production. By using pharmacological inhibitors or activators or genetic inhibition by the protease activated receptor (PAR), siRNA revealed that the PAR1 receptor but not other PAR receptors is involved in thrombin-mediated up-regulation of IL-6. Thrombin-mediated IL-6 production was attenuated by thrombin inhibitor (PPACK), phospholipase C inhibitor (U73122), protein kinase C alpha inhibitor (Ro320432), Src inhibitor (PP2), NF-kappaB inhibitor (PDTC), I kappa B protease inhibitor (TPCK), or NF-kappaB inhibitor peptide. Stimulation of synovial fibroblasts with thrombin activated I kappa B kinase alpha/beta (IKK alpha/beta), I kappa B alpha phosphorylation, I kappa B alpha degradation, p65 phosphorylation at Ser(276), p65 and p50 translocation from the cytosol to the nucleus, and kappaB-luciferase activity. Thrombin-mediated an increase of IKK alpha/beta activity, kappaB-luciferase activity and p65 and p50 binding to the NF-kappaB element was inhibited by PPACK, U73122, Ro320432 and PP2. The binding of p65 and p50 to the NF-kappaB elements, as well as the recruitment of p300 and the enhancement of p50 acetylation on the IL-6 promoter was enhanced by thrombin. Our results suggest that thrombin increased IL-6 production in synovial fibroblasts via the PAR1 receptor/PI-PLC/PKC alpha/c-Src/NF-kappaB and p300 signaling pathway.

Role of the Jak/STAT pathway in the regulation of interleukin-8 transcription by oxidized phospholipids in vitro and in atherosclerosis in vivo

Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (Ox-PAPC) and its component phospholipid, 1-palmitoyl-2-epoxyisoprostane-sn-glycero-3-phosphorylcholine, induce endothelial cells (EC) to synthesize chemotactic factors, such as interleukin 8 (IL-8). Previously, we demonstrated a role for c-Src kinase activation in Ox-PAPC-induced IL-8 transcription. In this study, we have examined the mechanism regulating IL-8 transcription by Ox-PAPC downstream of c-Src. Our findings demonstrate an important role for JAK2 in the regulation of IL-8 transcription by Ox-PAPC. Treatment of human aortic EC with Ox-PAPC and 1-palmitoyl-2-epoxyisoprostane-sn-glycero-3-phosphorylcholine induced a rapid yet sustained activation of JAK2; activation of JAK2 by Ox-PAPC was dependent on c-Src kinase activity. Furthermore, pretreatment with selective JAK2 inhibitors significantly reduced Ox-PAPC-induced IL-8 transcription. In previous studies, we also demonstrated activation of STAT3 by Ox-PAPC. Here we provide evidence that STAT3 activation by Ox-PAPC is dependent on JAK2 activation and that STAT3 activation regulates IL-8 transcription by Ox-PAPC in human EC. Transfection with small interfering RNA against STAT3 significantly reduced Ox-PAPC-induced IL-8 transcription. Using chromatin immunoprecipitation assays, we demonstrated binding of activated STAT3 to the sequence flanking the consensus gamma-interferon activation sequence (GAS) in the IL-8 promoter; site-directed mutagenesis of GAS inhibited IL-8 transcription by Ox-PAPC. Finally, these studies demonstrate a role for STAT3 activation in atherosclerosis in vivo. We found increased staining for activated STAT3 in the inflammatory regions of human atherosclerotic lesions and reduced fatty streak formation in EC-specific STAT3 knock-out mice on the atherogenic diet. Taken together, these data demonstrate an important role for the JAK2/STAT3 pathway in Ox-PAPC-induced IL-8 transcription in vitro and in atherosclerosis in vivo.

Substrate specificity and catalytic efficiency of aldo-keto reductases with phospholipid aldehydes

Phospholipid oxidation generates several bioactive aldehydes that remain esterified to the glycerol backbone ('core' aldehydes). These aldehydes induce endothelial cells to produce monocyte chemotactic factors and enhance monocyte-endothelium adhesion. They also serve as ligands of scavenger receptors for the uptake of oxidized lipoproteins or apoptotic cells. The biochemical pathways involved in phospholipid aldehyde metabolism, however, remain largely unknown. In the present study, we have examined the efficacy of the three mammalian AKR (aldo-keto reductase) families in catalysing the reduction of phospholipid aldehydes. The model phospholipid aldehyde POVPC [1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine] was efficiently reduced by members of the AKR1, but not by the AKR6 or the ARK7 family. In the AKR1 family, POVPC reductase activity was limited to AKR1A and B. No significant activity was observed with AKR1C enzymes. Among the active proteins, human AR (aldose reductase) (AKR1B1) showed the highest catalytic activity. The catalytic efficiency of human small intestinal AR (AKR1B10) was comparable with the murine AKR1B proteins 1B3 and 1B8. Among the murine proteins AKR1A4 and AKR1B7 showed appreciably lower catalytic activity as compared with 1B3 and 1B8. The human AKRs, 1B1 and 1B10, and the murine proteins, 1B3 and 1B8, also reduced C-7 and C-9 sn-2 aldehydes as well as POVPE [1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphoethanolamine]. AKR1A4, B1, B7 and B8 catalysed the reduction of aldehydes generated in oxidized C(16:0-20:4) phosphatidylcholine with acyl, plasmenyl or alkyl linkage at the sn-1 position or C(16:0-20:4) phosphatidylglycerol or phosphatidic acid. AKR1B1 displayed the highest activity with phosphatidic acids; AKR1A4 was more efficient with long-chain aldehydes such as 5-hydroxy-8-oxo-6-octenoyl derivatives, whereas AKR1B8 preferred phosphatidylglycerol. These results suggest that proteins of the AKR1A and B families are efficient phospholipid aldehyde reductases, with non-overlapping substrate specificity, and may be involved in tissue-specific metabolism of endogenous or dietary phospholipid aldehydes.

Oxidized phospholipids: From molecular properties to disease

Oxidized lipids are generated from (poly)unsaturated diacyl- and alk(en)ylacyl glycerophospholipids under conditions of oxidative stress. The great variety of reaction products is defined by the degree of modification, hydrophobicity, chemical reactivity, physical properties and biological activity. The biological activities of these compounds may depend on both, the recognition of the particular molecular structures by specific receptors and on the unspecific physical and chemical effects on their target systems (membranes, proteins). In this review, we aim at highlighting the molecular features that are essential for the understanding of the biological actions of pure oxidized phospholipids. Firstly, their chemical structures are described as a basis for an understanding of their physical and (bio)chemical properties in membrane- and protein-bound form. Secondly, the biological activities of oxidized phospholipids are discussed in terms of their unspecific effects on the membrane level as well as their potential interactions with specific targets (receptors) affecting a large set of (signaling) molecules. Finally, the role of oxidized phospholipids as important mediators in pathophysiology is discussed with emphasis on atherosclerosis.

Airway epithelial STAT3 is required for allergic inflammation in a murine model of asthma

The STAT3 transcription factor is critical for cytokine signaling and the acute phase response, but its role in allergic asthma is largely undefined. To investigate the role of STAT3 in mediating allergic inflammation, we used chemical and genetic approaches to inactivate STAT3 in the airway epithelium of mice. In a murine model of chronic asthma, we demonstrate that the administration of house dust mite (HDM) leads to robust STAT3 activation in the airway epithelium, smooth muscle, and immune cells in the lungs of C57BL/6 mice. To investigate the role of STAT3 in HDM-induced airway inflammation, a conditional knockout of STAT3 in the airway epithelium was generated, e-STAT3-/-. We determined that e-STAT3-/- mice had a significant decrease in HDM-induced airway eosinophilia, lung Th2 accumulation, and chemokines compared with wild-type animals. Importantly, the e-STAT3-/- mice had a significant decrease in airway hyperresponsiveness to methacholine. The administration of two STAT kinase inhibitors diminished STAT3 activation and markedly abrogated the HDM-induced lung inflammation. These findings suggest that STAT3 acts as a novel epithelial regulator of the allergic response by altering Th2 cell recruitment and effector function, and thus, targeting this molecule may provide the basis for a novel asthma therapy.

XB130, a Novel Adaptor Protein for Signal Transduction

Adaptor proteins are important mediators in signal transduction. In the present study, we report the cloning and characterization of a novel adaptor protein, XB130. This gene is located on human chromosome 10q25.3 and encodes a protein of 818 amino acids. It contains several Src homology (SH)2- and SH3-binding motifs, two pleckstrin homology domains, a coiled-coil region, and a number of potential tyrosine or serine/threonine phosphorylation sites. Endogenous XB130 interacts with c-Src tyrosine kinase. Their co-expression in COS-7 cells resulted in activation of c-Src and elevated tyrosine phosphorylation of multiple proteins, including XB130 itself. XB130 expression in HEK293 cells enhanced serum response element- and AP-1-dependent transcriptional activation mediated by c-Src. XB130DeltaN, an N-terminal deletion mutant lacking a putative SH3-binding motif and several putative SH2-binding sites, reduced its ability to mediate Src signal transduction. Down-regulation of endogenous XB130 with siRNA reduced c-Src activity, IL-8 production, EGF-induced phosphorylation of Akt and GSK3beta, and altered cell cycles in human lung epithelial cells. These data suggest that XB130 as an adaptor may play an important role in the regulation of signal transduction and cellular functions.

High-density lipoprotein modulates oxidized phospholipid signaling in human endothelial cells from proinflammatory to anti-inflammatory

OBJECTIVE

Oxidized 1-palmitoyl-2-arachidonyl-sn-3-glycero-phosphorylcholine (Ox-PAPC) and its component phospholipid, 1-palmitoyl-2-(5,6 epoxyisoprostanoyl)-sn-glycero-3-phosphocholine (PEIPC), which are present in atherosclerotic lesions, activate endothelial cells to induce a complex inflammatory and pro-oxidant response. Previously, we demonstrated induction of genes regulating chemotaxis, sterol biosynthesis, the unfolded protein response, and redox homeostasis by Ox-PAPC in human aortic endothelial cells (HAECs). Activation of the c-Src kinase/signal transducer and activator of transcription 3 and the endothelial nitric oxide synthase/sterol regulatory element binding protein (SREBP) pathways were shown to regulate several of these inflammatory effects of Ox-PAPC in HAECs. The goal of the current studies was to determine the role of high-density lipoprotein (HDL) in regulating Ox-PAPC signaling in HAECs.

METHODS AND RESULTS

Using quantitative real-time polymerase chain reaction, Western analysis, and functional studies, we demonstrated that pretreatment of HAECs with HDL reduced the induction of inflammatory, sterol biosynthetic, and unfolded protein response genes by Ox-PAPC and PEIPC; Ox-PAPC-induced chemotactic activity and monocyte binding were also decreased. These effects were associated with HDL inhibition of Ox-PAPC-induced c-Src, signal transducer and activator of transcription 3, and SREBP activation, alterations in endothelial nitric oxide synthase phosphorylation (previously associated with the inflammatory action of Ox-PAPC), and a decrease in superoxide formation. Finally, we demonstrated that treatment with HDL did not inhibit Ox-PAPC and PEIPC-induced activation of redox pathways, which protect the cell from the effects of oxidative stress.

CONCLUSIONS

Taken together, these studies demonstrated that HDL inhibits the pro-inflammatory effects of Ox-PAPC and PEIPC, while maintaining the antioxidant activities of these lipids.

Mycobacterium bovis bacillus Calmette–Guérin (BCG)-induced CXCL8 production is mediated through PKCα-dependent activation of the IKKαβ signaling pathway in epithelial cells

Upon contact with airway epithelial cells, mycobacteria activate several signal transduction events that are required for induction of NF-kappaB-dependent chemokine gene expression. However, downstream signaling pathways, especially that of Ca(2+)-dependent protein kinase C alpha (PKCalpha), and in particular, the identity of the IKKalphabeta signal pathway for CXCL8 secretion in Mycobacterium bovis BCG-induced epithelial cells are still unknown. In this study, we demonstrated that the phosphoinositide-phospholipase C (PI-PLC) downstream signaling pathway is involved in M. bovis BCG-induced CXCL8 release, since A549 cells pretreated with U73122, a PI-PLC inhibitor, inhibited CXCL8 release, whereas U73343 the inactive analog had no effect. In addition, our results demonstrated that M. bovis BCG-induced CXCL8 production by A549 cells was significantly blocked by using neomycin (another well-described inhibitor of PI-PLC with a different mechanism of action), Ro-32-0432 and Ro-31-8220 (two PKCalpha inhibitors), PP1 and PP2 (two potent and selective inhibitors of the Src-family tyrosine kinases), and Bay 11-7082 (an IkappaB phosphorylation inhibitor). We also demonstrated that M. bovis BCG can rapidly induce translocation of PKCalpha from the cytosol to the membrane, and that treatment of cells with M. bovis BCG caused time-dependent increases in phosphorylation of c-Src at tyrosine 416. Finally, our studies revealed that M. bovis BCG induced the association of c-Src and IKKalphabeta during the interaction of PKCalpha and IKKalphabeta. Altogether, these results represent the first evidence to date suggesting that M. bovis BCG activates the PI-PLC/PKCalpha/c-Src/IKKalphabeta signaling pathway to induce CXCL8 release in human epithelial cells.

Signaling pathways involved in OxPAPC-induced pulmonary endothelial barrier protection

Increased tissue or serum levels of oxidized phospholipids have been detected in a variety of chronic and acute pathological conditions such as hyperlipidemia, atherosclerosis, heart attack, cell apoptosis, acute inflammation and injury. We have recently described signaling cascades activated by oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (OxPAPC)in the human pulmonary artery endothelial cells (EC) and reported potent barrier-protective effects of OxPAPC, which were mediated by small GTPases Rac and Cdc42. In this study we have further characterized signal transduction pathways involved in the OxPAPC-mediated endothelial barrier protection. Inhibitors of small GTPases, protein kinase A (PKA), protein kinase C (PKC), Src family kinases and general inhibitors of tyrosine kinases attenuated OxPAPC-induced barrier-protective response and EC cytoskeletal remodeling. In contrast, small GTPase Rho, Rho kinase, Erk-1,2 MAP kinase and p38 MAP kinase and PI3-kinase were not involved in the barrier-protective effects of OxPAPC. Inhibitors of PKA, PKC, tyrosine kinases and small GTPase inhibitor toxin B suppressed OxPAPC-induced Rac activation and decreased phosphorylation of focal adhesion kinase (FAK) and paxillin. Barrier-protective effects of OxPAPC were not reproduced by platelet activating factor (PAF), which at high concentrations induced barrier dysfunction, but were partially attenuated by PAF receptor antagonist A85783. These results demonstrate for the first time upstream signaling cascades involved in the OxPAPC-induced Rac activation, cytoskeletal remodeling and barrier regulation and suggest PAF receptor-independent mechanisms of OxPAPC-mediated endothelial barrier protection.

Tiam1 and βPIX mediate Rac-dependent endothelial barrier protective response to oxidized phospholipids

Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (OxPAPC) exhibits potent barrier protective effects on pulmonary endothelium, which are mediated by small GTPases Rac and Cdc42. However, upstream mechanisms of OxPAPC-induced small GTPase activation are not known. We studied involvement of Rac/Cdc42-specific guanine nucleotide exchange factors (GEFs) Tiam1 and betaPIX in OxPAPC-induced Rac activation, cytoskeletal remodeling, and barrier protective responses in the human pulmonary endothelial cells (EC). OxPAPC induced membrane translocation of Tiam1, betaPIX, Cdc42, and Rac, but did not affect intracellular distribution of Rho and Rho-specific GEF p115-RhoGEF. Protein depletion of Tiam1 and betaPIX using siRNA approach abolished OxPAPC-induced activation of Rac and its effector PAK1. EC transfection with Tiam1-, betaPIX-, or PAK1-specific siRNA dramatically attenuated OxPAPC-induced barrier enhancement, peripheral actin cytoskeletal enhancement, and translocation of actin-binding proteins cortactin and Arp3. These results show for the first time that Tiam1 and betaPIX mediate OxPAPC-induced Rac activation, cytoskeletal remodeling, and barrier protective response in pulmonary endothelium.

Vascular endothelial growth factor receptor 2 plays a role in the activation of aortic endothelial cells by oxidized phospholipids

OBJECTIVE

Previous studies have shown that oxidized products of PAPC (Ox-PAPC) regulate cell transcription of interleukin-8, LDL receptor, and tissue factor. This upregulation takes place in part through the activation of sterol regulatory element-binding protein (SREBP) and Erk 1/2. The present studies identify vascular endothelial growth factor receptor 2 (VEGFR2) as a major regulator in the activation of SREBP and Erk 1/2 in endothelial cells activated by Ox-PAPC.

METHODS AND RESULTS

Ox-PAPC induced the phosphorylation of VEGFR2 at Tyr1175 in human aortic endothelial cells. Inhibitors and siRNA for VEGFR2 decreased the transcription of interleukin-8, LDL receptor, and tissue factor in response to Ox-PAPC and the activation of SREBP and Erk 1/2, which mediate this transcription. We provide evidence that the activation of VEGFR2 is rapid, sustained, and c-Src-dependent.

CONCLUSIONS

These data point to a major role of VEGFR2 in endothelial regulation by oxidized phospholipids which accumulate in atherosclerotic lesions and apoptotic cells.

Diesel exhaust particulate-induced activation of Stat3 requires activities of EGFR and Src in airway epithelial cells

In vivo exposure to diesel exhaust particles (DEP) elicits acute inflammatory responses in the lung characterized by inflammatory cell influx and elevated expression of mediators such as cytokines and chemokines. Signal transducers and activators of transcription (STAT) proteins are a family of cytoplasmic transcription factors that are key transducers of signaling in response to cytokine and growth factor stimulation. One member of the STAT family, Stat3, has been implicated as a regulator of inflammation but has not been studied in regard to DEP exposure. The results of this study show that DEP induces Stat3 phosphorylation as early as 1 h following stimulation and that phosphorylated Stat3 translocates into the nucleus. Inhibition of epidermal growth factor receptor (EGFR) and Src activities by the inhibitors PD-153035 and PP2, respectively, abolished the activation of Stat3 by DEP, suggesting that Stat3 activation by DEP requires EGFR and Src kinase activation. The present study suggests that oxidative stress induced by DEP may play a critical role in activating EGFR signaling, as evidenced by the fact that pretreatment with antioxidant prevented the activation of EGFR and Stat3. These findings demonstrate that DEP inhalation can activate proinflammatory Stat3 signaling in vitro.

Oxidized phospholipids alter vascular connexin expression, phosphorylation, and heterocellular communication

OBJECTIVE

In endothelial cells (EC) and vascular smooth muscle cells (VSMC) from atherosclerotic mice, connexin (Cx) expression becomes distorted. Lipoprotein-derived phospholipid oxidation products (OxPAPC) play a critical role in atherosclerosis, and we hypothesized that they may act as trigger molecules causing the changes in connexin expression.

METHODS AND RESULTS

We applied OxPAPC to murine carotid arteries in vivo and vascular cell cocultures. OxPAPC applied to carotids induced an upregulation of both Cx37 and Cx43 in the VSMC. In EC, Cx43 was upregulated and Cx37 was downregulated, whereas Cx40 in EC remained constant. In the vascular cell coculture, OxPAPC caused similar changes in Cx37 and Cx43 but caused a decrease in Cx40 in EC and an elevation of Cx40 in VSMC. In the coculture model, OxPAPC treatment led to the selective disappearance of Cx40 at the myoendothelial junction. Biocytin dye transfer between EC and VSMC coupling was dramatically reduced by OxPAPC. The decrease in dye transfer after OxPAPC treatment was correlated with an increase in tyrosine 265 phosphorylation of Cx43, especially at the in vitro myoendothelial junction.

CONCLUSIONS

We conclude that OxPAPC could be responsible for the changes in connexin expression previously reported in atherosclerosis.

Toll-like receptor 4 signalling is neither sufficient nor required for oxidised phospholipid mediated induction of interleukin-8 expression

OBJECTIVE

Toll-like receptor (TLR)-4 signalling has been shown to accelerate atherosclerosis. As oxidised phospholipids are present in atherosclerotic plaque and have been shown to modulate TLR4 signalling, we investigated the role of oxidised 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphorylcholine (OxPAPC) in the regulation of TLR 1, 2, 4 and 6 signalling.

METHODS AND RESULTS

Unlike established TLR agonists, OxPAPC did not induce NF-kappaB-dependent gene expression in monocytic THP-1 cells, human aortic endothelial cells or TLR-deficient HEK-293 cells transfected with TLRs 1, 2, 4 or 6. OxPAPC induction of IL-8 was not blocked by the TLR4 specific antagonist Rhodobacter sphaeroides LPS in human aortic endothelial cells, though OxPAPC potently inhibited TLR4 mediated IL-8 induction in these cells. OxPAPC upregulated IL-8 production in TLR4 deficient HEK-293 cells and this was not increased following TLR4 overexpression. Lipids extracted from carotid atherectomy samples did not stimulate TLR 1, 2, 4 or 6 signalling in a HEK-293 transfection assay.

CONCLUSIONS

TLR4 signalling does not contribute to OxPAPC induced IL-8 expression in human epithelial HEK-293, monocytic THP-1 or aortic endothelial cells. As lipids extracted from diseased human artery also induced no TLR signalling, it is likely that the TLR-activating materials contributing to atherosclerosis are not of endogenous lipid origin.

The unfolded protein response is an important regulator of inflammatory genes in endothelial cells

OBJECTIVE

Oxidized 1-palmitoyl-2-arachidonyl-sn-3-glycero-phosphorylcholine (oxPAPC) accumulates in atherosclerotic lesions and in vitro studies suggest that it mediates chronic inflammatory response in endothelial cells (ECs). The goal of our studies was to identify pathways mediating the induction of inflammatory genes by oxPAPC.

METHODS AND RESULTS

Using expression arrays, quantitative polymerase chain reaction (PCR), and immunoblotting we demonstrate that oxPAPC leads to endoplasmic reticulum stress and activation of the unfolded protein response (UPR) in human aortic ECs. Immunohistochemistry analysis of human atherosclerotic lesions indicated that UPR is induced in areas containing oxidized phospholipids. Using the UPR inducing agent tunicamycin and selective siRNA targeting of the ATF4 and XBP1 branches of the UPR, we demonstrate that these transcription factors are essential mediators of IL8, IL6, and MCP1 expression in human aortic ECs required for maximal inflammatory gene expression in the basal state and after oxPAPC treatment. We also identify a novel oxPAPC-induced chemokine, the CXC motif ligand 3 (CXCL3), and show that its expression requires XBP1.

CONCLUSIONS

These data suggest that the UPR pathway is a general mediator of vascular inflammation and EC dysfunction in atherosclerosis, and, likely, other inflammatory disorders.

c-Src Mediates Thrombin-Induced NF-κB Activation and IL-8/CXCL8 Expression in Lung Epithelial Cells

In this study, we examined the regulation of NF-kappaB activation and IL-8/CXCL8 expression by thrombin in human lung epithelial cells (EC). Thrombin caused a concentration-dependent increase in IL-8/CXCL8 release in a human lung EC line (A549) and primary normal human bronchial EC. In A549 cells, thrombin, SFLLRN-NH2 (a protease-activated receptor 1 (PAR1) agonist peptide), and GYPGQV-NH2 (a PAR4 agonist peptide), but not TFRGAP-NH2 (a PAR3 agonist peptide), induced an increase in IL-8/CXCL8-luciferase (Luc) activity. The thrombin-induced IL-8/CXCL8 release was attenuated by D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (a thrombin inhibitor), U73122 (a phosphoinositide-phospholipase C inhibitor), Ro-32-0432 (a protein kinsase C alpha (PKC alpha) inhibitor), an NF-kappaB inhibitor peptide, and Bay 117082 (an IkappaB phosphorylation inhibitor). Thrombin-induced increase in IL-8/CXCL8-Luc activity was inhibited by the dominant-negative mutant of c-Src and the cells transfected with the kappaB site mutation of the IL-8/CXCL8 construct. Thrombin caused time-dependent increases in phosphorylation of c-Src at tyrosine 416 and c-Src activity. Thrombin-elicited c-Src activity was inhibited by Ro-32-0432. Stimulation of cells with thrombin activated IkappaB kinase alphabeta (IKK alphabeta), IkappaB alpha phosphorylation, IkappaB alpha degradation, p50 and p65 translocation from the cytosol to the nucleus, NF-kappaB-specific DNA-protein complex formation, and kappaB-Luc activity. Pretreatment of A549 cells with Ro-32-4032 and the dominant-negative mutant of c-Src DN inhibited thrombin-induced IKK alphabeta activity, kappaB-Luc activity, and NF-kappaB-specific DNA-protein complex formation. Further studies revealed that thrombin induced PKC alpha, c-Src, and IKK alphabeta complex formation. These results show for the first time that thrombin, acting through PAR1 and PAR4, activates the phosphoinositide-phospholipase C/PKC alpha/c-Src/IKK alphabeta signaling pathway to induce NF-kappaB activation, which in turn induces IL-8/CXCL8 expression and release in human lung EC.

Identification of inflammatory gene modules based on variations of human endothelial cell responses to oxidized lipids

Oxidized phospholipids are thought to promote atherogenesis by stimulating endothelial cells (ECs) to produce inflammatory cytokines, such as IL-8. In studies with mouse models, we previously demonstrated that genetic variation in inflammatory responses of endothelial cells to oxidized lipids contributes importantly to atherosclerosis susceptibility. We now show that similar variations occur in cultured aortic ECs derived from multiple heart transplant donors. These variations were stably maintained between passages and, thus, reflect either genetic or epigenetic regulatory differences. Expression array analysis of aortic EC cultures derived from 12 individuals revealed that >1,000 genes were regulated by oxidized phospholipids. We have used the observed variations in the sampled population to construct a gene coexpression network comprised of 15 modules of highly connected genes. We show that several identified modules are significantly enriched in genes for known pathways and confirm a module enriched for unfolded protein response (UPR) genes using siRNA and the UPR inducer tunicamycin. On the basis of the constructed network, we predicted that a gene of unknown function (MGC4504) present in the UPR module is a target for UPR transcriptional activator ATF4. Our data also indicate that IL-8 is present in the UPR module and is regulated, in part, by the UPR. We validate these by using siRNA. In conclusion, we show that interindividual variability can be used to group genes into pathways and predict gene-gene regulatory relationships, thus identifying targets potentially involved in susceptibility to common diseases such as atherosclerosis.

Src activation of Stat3 is an independent requirement from NF-kappaB activation for constitutive IL-8 expression in human pancreatic adenocarcinoma cells

Human pancreatic tumors often overexpress the angiogenesis-promoting factor Interleukin 8 (IL-8), in part due to overexpression of NF-kappaB, a frequent occurrence in pancreatic adenocarcinoma. In this study, we demonstrate that reducing c-Src kinase activity, through either pharmacologic inhibition or small interfering RNA-targeted reduction of Src expression, significantly decreased IL-8 expression (P < 0.05) without affecting NF-kappaB-mediated transcription, but by decreasing phosphorylation of STAT3. To ascertain whether Src-mediated expression of IL-8 was dependent on STAT3, we used stable clones expressing a dominant-negative isoform of STAT3 that inhibits endogenous STAT3 phosphorylation and subsequent DNA binding and STAT3-mediated gene expression or a constitutively activated isoform of STAT3. IL-8 expression was significantly lower in clones expressing the dominant-negative isoform and significantly increased in clones expressing the activated isoform (P < 0.05 for both). Pharmacologic inhibition of NF-kappaB activity significantly reduced basal IL-8 expression and tumor necrosis factor-induced IL-8 expression (P < 0.05 for both), yet NF-kappaB activity was not dependent on Src. We therefore suggest that Src activation, through phosphorylation of STAT3, and NF-kappaB are all required for expression of IL-8 a critical angiogenic-promoting factor in pancreatic adenocarcinomas.

STAT3 attenuates EGFR-mediated ERK activation and cell survival during oxidant stress in mouse proximal tubular cells

We have shown that renal epithelial cell survival depends on the sustained activation of the extracellular signal-regulated protein kinase (ERK) and lack of this activation was associated with death during oxidative stress. ERK is activated via the canonical epidermal growth factor receptor (EGFR)-Ras-MEK pathway, which could be attenuated by oxidants. We now show that the failure to activate ERK in a sustained manner during severe oxidative stress is owing to the activation of the signal transducer and activator of transcription-3 (STAT3) rather than the failure to activate the EGFR. Tyrosine phosphorylation of the EGFR and STAT3 was studied in hydrogen peroxide (H(2)O(2))-treated mouse proximal tubule (TKPTS) cells or in mouse kidney after ischemia/reperfusion (I/R) injury by Western blotting. STAT3 activation was inhibited by either pharmacologically (AG490) through its upstream janus kinase (JAK2) or by a dominant-negative STAT3 adenovirus. EGFR was inhibited by AG1478. Survival was determined by fluorescence-activated cell sorter analysis and trypan blue exclusion. We found that the EGFR was phosphorylated on its major autophosphorylation site (Tyr1173) regardless of the H(2)O(2) dose. On the other hand, both I/R and severe oxidative stress - but not moderate stress - increased tyrosine phosphorylation of STAT3 in an EGFR and JAK2-dependent manner. Inhibition of JAK2 or STAT3 lead to increased ERK activation and survival of TKPTS cells during severe oxidative stress. Our data suggest a role of tyrosine-phosphorylated STAT3 in the suppression of ERK activation. These data suggest that the STAT3 pathway might represent a new target for improved survival of proximal tubule cells exposed to severe oxidant injury.

Oxidized lipids: The two faces of vascular inflammation

Elevated plasma levels of low-density lipoprotein and generation of oxidized low-density lipoprotein have been directly associated with the pathogenesis of atherosclerosis, and lipid oxidation products have been directly linked with induction and propagation of monocytic subendothelial accumulation and other inflammatory reactions associated with chronic vascular inflammation. However, accumulating data suggest that oxidized lipids may also exhibit anti-inflammatory potential and serve as potent inhibitors of nuclear factor-kappaB-dependent proinflammatory cascade. In addition, we have characterized a group of bioactive components of oxidized phospholipids with barrier-protective effects towards endothelial cells in the models of agonist-induced endothelial permeability and lipopolysaccharide-induced lung dysfunction. This review discusses the role of oxidized lipids in the progression of atherosclerosis as well as the important anti-inflammatory effects of oxidized phospholipids and their potential role in the modulation of vascular barrier integrity.

c-Src is the primary signaling mediator of polychlorinated biphenyl-induced interleukin-8 expression in a human microvascular endothelial cell line

Interleukin-8/CXCL8 (IL-8) is a prominent factor that modulates endothelial cell proliferation, migration, and angiogenesis. Therefore, the present study focused on the regulatory mechanisms of IL-8 expression induced by environmental pollutants such as polychlorinated biphenyls (PCBs). Treatment of human microvascular endothelial cells (HMECs) with specific PCB congener, 2,2',4,6,6'-pentachlorobiphenyl (PCB 104), dose dependently increased levels of IL-8 mRNA and secreted protein. IL-8-neutralizing antibody inhibited migration of endothelial cells stimulated by conditioned media derived from PCB 104-treated HMECs. Site-directed mutagenesis of the IL-8 promoter- and DNA-binding assays revealed that activator protein 1 (AP-1) and nuclear factor kappaB (NF-kappaB) sites are required for PCB 104-induced IL-8 transcription. Most importantly, pharmacological inhibition of Src kinase activity or overexpression of dominant-negative c-src in HMECs resulted in a significant decrease in IL-8 expression and promoter activity. In contrast, ectopic expression of activated c-Src markedly increased promoter activity of IL-8. These stimulatory effects of dominant-positive c-src were abrogated by mutagenesis of AP-1- and NF-kappaB-binding sites in the IL-8 promoter.

Cytokines in Atherosclerosis: Pathogenic and Regulatory Pathways

Atherosclerosis is a chronic disease of the arterial wall where both innate and adaptive immunoinflammatory mechanisms are involved. Inflammation is central at all stages of atherosclerosis. It is implicated in the formation of early fatty streaks, when the endothelium is activated and expresses chemokines and adhesion molecules leading to monocyte/lymphocyte recruitment and infiltration into the subendothelium. It also acts at the onset of adverse clinical vascular events, when activated cells within the plaque secrete matrix proteases that degrade extracellular matrix proteins and weaken the fibrous cap, leading to rupture and thrombus formation. Cells involved in the atherosclerotic process secrete and are activated by soluble factors, known as cytokines. Important recent advances in the comprehension of the mechanisms of atherosclerosis provided evidence that the immunoinflammatory response in atherosclerosis is modulated by regulatory pathways, in which the two anti-inflammatory cytokines interleukin-10 and transforming growth factor-β play a critical role. The purpose of this review is to bring together the current information concerning the role of cytokines in the development, progression, and complications of atherosclerosis. Specific emphasis is placed on the contribution of pro- and anti-inflammatory cytokines to pathogenic (innate and adaptive) and regulatory immunity in the context of atherosclerosis. Based on our current knowledge of the role of cytokines in atherosclerosis, we propose some novel therapeutic strategies to combat this disease. In addition, we discuss the potential of circulating cytokine levels as biomarkers of coronary artery disease.

Role of Endothelial Nitric Oxide Synthase in the Regulation of SREBP Activation by Oxidized Phospholipids

Oxidized-1-palmitoyl-2-arachidonyl- sn -glycero-3-phosphorylcholine (Ox-PAPC), found in atherosclerotic lesions and other sites of chronic inflammation, activates endothelial cells (EC) to synthesize chemotactic factors, such as interleukin (IL)-8. Previously, we demonstrated that the sustained induction of IL-8 transcription by Ox-PAPC was mediated through the activation of sterol regulatory element–binding protein (SREBP). We now present evidence for the role of endothelial nitric oxide synthase (eNOS) in the activation of SREBP by Ox-PAPC. Ox-PAPC treatment of EC induced a dose- and time-dependent activation of eNOS, as measured by phosphorylation of serine 1177, dephosphorylation of threonine 495, and the conversion of l -arginine to l -citrulline. Activation of eNOS by Ox-PAPC was regulated through a phosphatidylinositol-3-kinase/Akt-mediated mechanism. These studies also demonstrated that pretreatment of EC with NOS inhibitor, N ω -nitro- l -arginine-methyl ester (L-NAME), significantly inhibited Ox-PAPC–induced IL-8 synthesis. Because SREBP activation had been previously shown to regulate IL-8 transcription by Ox-PAPC, we examined the effects of L-NAME on Ox-PAPC–induced SREBP activation. Our data demonstrated that Ox-PAPC–induced SREBP activation and expression of SREBP target genes were significantly reduced by pretreatment with L-NAME. Interestingly, treatment of EC with NO donor, S -nitroso- N -acetylpenicillamine, did not activate SREBP, suggesting that NO alone was not sufficient for SREBP activation. Rather, our findings indicated that superoxide (O 2 ·− ), in combination with NO, regulated SREBP activation by Ox-PAPC. We found that Ox-PAPC treatment generated O 2 ·− through an eNOS-mediated mechanism and that mercaptoethylguanidine, a peroxynitrite scavenger, reduced SREBP activation by Ox-PAPC. Taken together, these findings propose a novel role for eNOS in the activation of SREBP and SREBP-mediated inflammatory processes.

Oxidized phospholipids as triggers of inflammation in atherosclerosis

Chronic inflammatory diseases including atherosclerosis are major causes of morbidity and mortality worldwide. However, the factors, which trigger processes that determine the outcome of an inflammatory response, are still poorly understood. Accumulating evidence suggests that certain lipid oxidation products, such as oxidized phospholipids (OxPL), may represent endogenously formed factors that are capable of triggering vascular inflammation. This review will address important questions regarding mechanisms involved in acute and chronic inflammation, and discuss the role of OxPL as key players in triggering the inflammatory response in atherosclerosis. Better understanding of how OxPL contribute to vascular inflammation should lead to new strategies in the treatment of chronic inflammatory disorders.

Specific monocyte adhesion to endothelial cells induced by oxidized phospholipids involves activation of cPLA2 and lipoxygenase

Oxidized phospholipids stimulate endothelial cells to bind monocytes, but not neutrophils, an initiating event in atherogenesis. Here, we investigate intracellular signaling events induced by oxidized phospholipids in human umbilical vein endothelial cells (HUVECs) that lead to specific monocyte adhesion. In a static adhesion assay, oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine and one of its components, 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphorylcholine, stimulated HUVECs to bind U937 cells and human peripheral blood monocytes but not HL-60 cells or blood neutrophils. Monocyte adhesion was dependent on protein kinases A and C, extracellular signal-regulated kinase 1/2, p38 mitogen activated protein kinases (MAPKs), and cytosolic phospholipase A(2) (cPLA(2)). Inhibition of 12-lipoxygenase (12-LOX), but not cyclooxygenases, blocked monocyte adhesion, and addition of 12-hydroxyeicosatetraenoic acid (12-HETE) mimicked the effects of oxidized phospholipids. Peroxisome proliferator-activated receptor alpha (PPARalpha) was excluded as a possible target for 12-HETE, because monocyte adhesion was still induced in endothelial cells from PPARalpha null mice. Together, our results suggest that oxidized phospholipids stimulate HUVECs to specifically bind monocytes involving MAPK pathways, which lead to the activation of cPLA(2) and 12-LOX. Further analysis of signaling pathways induced by oxidized phospholipids that lead to specific monocyte adhesion should ultimately lead to the development of novel therapeutic approaches against chronic inflammatory diseases.

Oxidized phospholipid: POVPC binds to platelet-activating-factor receptor on human macrophages. Implications in atherosclerosis

Atherosclerosis as a chronic inflammatory disease resulting from the imbalance of the pro- and anti-inflammatory factors in the vessel wall. PAF and PAF-like oxidized phospholipids generated upon LDL oxidation in the intima of the arteries may interact with infiltrated monocytes/macrophages and lead to the alteration of gene expression patterns accompanied by an impaired production of chemokines, interleukins and proteolytic and lipolytic enzymes. The aim of this study was to evaluate the binding capacity of the major component of PAF-like oxidized phospholipids, namely the 1-palmitoyl-2-oxovaleroyl-sn-glycero-3-phosphorylcholine (POVPC) to PAF-receptor (PAF-R) on the surface of human monocytes/macrophages and to further characterize the gene expression induced by such binding. We show that, POVPC binds to cultured human macrophages via PAF-R and transduces the signals leading to the intracellular Ca(2+) fluxes and modifies the transcription levels of numerous pro-inflammatory and pro-atherogenic genes. Although a some similarity of the gene expression patterns was observed when macrophages were activated with POVPC versus PAF, we observed that only POVPC treatment induced a several-fold activation of IL-8 gene. In turn, only PAF activated PAF-R, matrix metalloproteinase-13 and 15-lipoxygenase mRNA accumulation. Thus, we suggest, that POVPC signals in mature macrophages only in part through the PAF-R, a part of its effects may involve other receptors.

Expression and activity of SRC regulate interleukin-8 expression in pancreatic adenocarcinoma cells: implications for angiogenesis

Interleukin-8 (IL-8) is an angiogenic factor that promotes growth of pancreatic tumors. The purpose of this study was to determine if c-Src, a protein tyrosine kinase frequently overexpressed in pancreatic cancer, regulated IL-8 expression and to elucidate the Src-mediated signaling pathways that contribute to angiogenesis in pancreatic adenocarcinoma cells. In a panel of pancreatic cancer cell lines, expression of total and activated Src correlated with IL-8 production. Furthermore, ectopic expression of activated Src in PANC-1 cells with low endogenous Src activity significantly increased IL-8 production (P < 0.005). In contrast, pharmacologic inhibition of endogenous c-Src kinase activity or small interfering RNA-mediated "knockdown" of c-Src expression in L3.6pl cells with high Src expression and activity caused significant decreases in IL-8 production (P < 0.005). Inhibition of c-Src activity resulted in decreased phosphorylation of Akt, p38, and extracellular signal-regulated kinase (Erk)-1/2. Significant (P < 0.005) dose-dependent decreases were observed in IL-8 expression by inhibiting Src-dependent signaling molecules Erk-1/2 and p38 but not phosphatidylinositol 3-kinase. To assess the relevance of Src inhibition to angiogenesis, in vivo gelfoam assays were done. Robust infiltration of vessels was observed in gelfoam saturated with conditioned medium from pancreatic carcinoma cells. This angiogenesis was nearly abrogated in gelfoams saturated with conditioned medium from cells treated with the Src family kinase inhibitor, PP2 (P < 0.001). Thus, c-Src regulates critical "downstream" signaling pathways that contribute to expression of IL-8 in human pancreatic tumor cells, suggesting c-Src may be a target for therapeutic intervention in pancreatic adenocarcinoma.

Interleukin-22, a member of the IL-10 subfamily, induces inflammatory responses in colonic subepithelial myofibroblasts

BACKGROUND & AIMS

Interleukin (IL)-22, a member of the IL-10 subfamily, is a recently identified T-cell-derived cytokine. We investigated IL-22 expression in the inflamed mucosa of patients with inflammatory bowel disease (IBD) and analyzed its biologic activities in human colonic subepithelial myofibroblasts (SEMFs).

METHODS

Mucosal IL-22 expression was evaluated by immunohistochemical procedures. The effects of IL-22 on colonic SEMFs were investigated by cDNA microarrays, Northern blots, enzyme-linked immunosorbent assay, and electrophoretic gel mobility shift assays (EMSAs).

RESULTS

IL-22 was not detectable in normal colonic mucosa. In IBD mucosa, IL-22 expression was detectable in CD4-positive T cells. IL-22-positive cells were increased in ulcerative colitis and even more so in Crohn's disease. IL-22 receptor expression colocalized with a marker of SEMFs. IL-22 did not modulate SEMF proliferation and collagen synthesis. cDNA microarray analyses demonstrated that, in colonic SEMFs, IL-22 increased the messenger RNA (mRNA) expression of inflammatory cytokines (IL-6, IL-8, IL-11, and leukemia inhibitory factor [LIF]), chemokines, and matrix metalloproteinases. IL-22 induced an activation of nuclear factor (NF)-kappaB and activating protein (AP)-1 within 1 hour, and a blockade of NF-kappaB and AP-1 activation markedly reduced IL-22 induction of IL-6, IL-8, IL-11, and LIF mRNA. MAP-kinase inhibitors (PD98059, U0216, and SB202190) significantly reduced IL-22 induction of cytokine secretion. The combination of either IL-17 plus IL-22 or IL-19 plus IL-22 additively up-regulated cytokine secretion.

CONCLUSIONS

IL-22 derived from activated T cells acts on SEMFs to elicit expression of proinflammatory cytokines and matrix-degrading molecules indicating proinflammatory/remodeling roles in IBD.