Thromboxane A(2) receptor mediated activation of the mitogen activated protein kinase cascades in human uterine smooth muscle cells

Antiplatelet Effect of Daphnetin Is Regulated by cPLA2-Mediated Thromboxane A2 Generation in Mice

Coumarin derivatives have been recognized for their antithrombotic, anti-inflammatory, and antioxidant properties, and daphnetin is one of the natural coumarin derivatives isolated from Daphne Koreana Nakai. Although the pharmacological value of daphnetin is well documented in diverse biological activities, its antithrombotic effect has not been studied to date. Here, we characterized the role and underlying mechanism of daphnetin in the regulation of platelet activation using murine platelets. In order to check the effect of daphnetin on platelet function, we first measured the effect of daphnetin on platelet aggregation and secretion. Collagen-induced platelet aggregation and dense granule secretion were partially inhibited by daphnetin. Interestingly, 2-MeSADP-induced secondary waves of aggregation and secretion were completely inhibited by daphnetin. It is known that 2-MeSADP-induced secretion and the resultant secondary wave of aggregation are mediated by the positive feedback effect of thromboxane A₂ (TxA₂) generation, suggesting the important role of daphnetin on TxA₂ generation in platelets. Consistently, daphnetin did not affect the 2-MeSADP-induced platelet aggregation in aspirinated platelets where the contribution of TxA₂ generation was blocked. Additionally, platelet aggregation and secretion induced by a low concentration of thrombin, which is affected by the positive feedback effect of TxA₂ generation, were partially inhibited in the presence of daphnetin. Importantly, 2-MeSADP- and thrombin-induced TxA₂ generation was significantly inhibited in the presence of daphnetin, confirming the role of daphnetin on TxA₂ generation. Finally, daphnetin significantly inhibited 2-MeSADP-induced cytosolic phospholipase A₂ (cPLA₂) and ERK phosphorylation in non-aspirinated platelets. Only cPLA₂ phosphorylation, not ERK phosphorylation, was significantly inhibited by daphnetin in aspirinated platelets. In conclusion, daphnetin plays a critical role in platelet function by inhibiting TxA₂ generation through the regulation of cPLA₂ phosphorylation.

Seratrodast, a thromboxane A2 receptor antagonist, inhibits neuronal ferroptosis by promoting GPX4 expression and suppressing JNK phosphorylation

More than 30 % of individuals with epilepsy are refractory to currently available drugs, highlighting the urgent need to develop novel candidate drugs. Accumulating evidence implicates the key role of ferroptosis in the pathophysiology of epileptic seizuresand its potential as a new drug target. Drug repurposing is a promising strategy for the rapid generation of new candidate drugs from the market drugs with new therapeutic indications, such as the best-selling drug thalidomide. Herein, we reported the discovery of Seratrodast, a market drug of thromboxane A2 receptor antagonist as a new ferroptosis inhibitor (IC₅₀: 4.5 μmol·L^-1). Seratrodast could reduce lipid ROS production, regulate the system x_c^-/glutathione (GSH)/glutathione peroxidase 4 (GPX4) axis, and inhibit JNK phosphorylation and p53 expression. In addition, Seratrodast elevated GPX4 expression and decreased JNK phosphorylation in pentylenetetrazole-induced seizures in mice. Seratrodast increased the latency of seizures and reduced seizure duration in pentylenetetrazole-induced seizures. Our results suggest Seratrodast might be either a ferroptosis inhibitor or a novel lead compound for further optimization of novel drug discovery.

Characterization and modulation of brain lipids content of rainbow trout fed with 100% plant based diet rich in omega-3 long chain polyunsaturated fatty acids DHA and EPA

Brain functions are known to be mainly modulated by adequate dietary intake. Inadequate intake as can be an excess or significant deficiency affect cognitive processes, behavior, neuroendocrine functions and synaptic plasticity with protective or harmful effects on neuronal physiology. Lipids, in particular, ω-6 and ω-3 long chain polyunsaturated fatty acids (LC-PUFAs) play structural roles and govern the different functions of the brain. Hence, the goal of this study was to characterize the whole brain fatty acid composition (precursors, enzymatic and non-enzymatic oxidation metabolites) of fish model of rainbow trout fed with three experimental plant-based diet containing distinct levels of eicosapentaenoic acid (EPA, 20:5 ω-3) and docosahexaenoic acid (DHA, 22:6 ω-3) (0% for low, 15.7% for medium and 33.4% for high, total fatty acid content) during nine weeks. Trout fed with the diet devoid of DHA and EPA showed reduced brain content of total ω-3 LC-PUFAs, with diminution of EPA and DHA. Selected enzymatic (cyclooxygenases and lipoxygenases) oxidation metabolites of arachidonic acid (AA, 20:4 ω-6) decrease in medium and high ω-3 LC-PUFAs diets. On the contrary, total selected enzymatic oxidation metabolites of DHA and EPA increased in high ω-3 LC-PUFAs diet. Total selected non-enzymatic oxidation metabolites of DHA (not detected for EPA) increased in medium and high ω-3 LC-PUFAs diets. In conclusion, this work revealed for the first time in fish model the presence of some selected enzymatic and non-enzymatic oxidation metabolites in brain and the modulation of brain lipid content by dietary DHA and EPA levels.

Differential expression of the TPα and TPβ isoforms of the human T Prostanoid receptor during chronic inflammation of the prostate: Role for FOXP1 in the transcriptional regulation of TPβ during monocyte-macrophage differentiation

Inflammation is linked to prostate cancer (PCa) and to other diseases of the prostate. The prostanoid thromboxane (TX)A₂ is a pro-inflammatory mediator implicated in several prostatic diseases, including PCa. TXA₂ signals through the TPα and TPβ isoforms of the T Prostanoid receptor (TP) which exhibit several functional differences and transcriptionally regulated by distinct promoters Prm1 and Prm3, respectively, within the TBXA2R gene. This study examined the expression of TPα and TPβ in inflammatory infiltrates within human prostate tissue. Strikingly, TPβ expression was detected in 94% of infiltrates, including in B- and T-lymphocytes and macrophages. In contrast, TPα was more variably expressed and, where present, expression was mainly confined to macrophages. To gain molecular insight into these findings, expression of TPα and TPβ was evaluated as a function of monocyte-to-macrophage differentiation in THP-1 cells. Expression of both TPα and TPβ was upregulated following phorbol-12-myristate-13-acetate (PMA)-induced differentiation of monocytic THP-1 to their macrophage lineage. Furthermore, FOXP1, an essential transcriptional regulator down-regulated during monocyte-to-macrophage differentiation, was identified as a key trans-acting factor regulating TPβ expression through Prm3 in THP-1 cells. Knockdown of FOXP1 increased TPβ, but not TPα, expression in THP-1 cells, while genetic reporter and chromatin immunoprecipitation (ChIP) analyses established that FOXP1 exerts its repressive effect on TPβ through binding to four cis-elements within Prm3. Collectively, FOXP1 functions as a transcriptional repressor of TPβ in monocytes. This repression is lifted in differentiated macrophages, allowing for upregulation of TPβ expression and possibly accounting for the prominent expression of TPβ in prostate tissue-resident macrophages.

Heteromerization fingerprints between bradykinin B2 and thromboxane TP receptors in native cells

Bradykinin (BK) and thromboxane-A2 (TX-A2) are two vasoactive mediators that modulate vascular tone and inflammation via binding to their cognate "class A" G-protein coupled receptors (GPCRs), BK-B2 receptors (B2R) and TX-prostanoid receptors (TP), respectively. Both BK and TX-A2 lead to ERK1/2-mediated vascular smooth muscle cell (VSMC) proliferation and/or hypertrophy. While each of B2R and TP could form functional dimers with various GPCRs, the likelihood that B2R-TP heteromerization could contribute to their co-regulation has never been investigated. The main objective of this study was to investigate the mode of B2R and TP interaction in VSMC, and its possible impact on downstream signaling. Our findings revealed synergistically activated ERK1/2 following co-stimulation of rat VSMC with a subthreshold dose of BK and effective doses of the TP stable agonist, IBOP, possibly involving biased agonist signaling. Single detection of each of B2R and TP in VSMC, using in-situ proximity ligation assay (PLA), provided evidence of the constitutive expression of nuclear and extranuclear B2R and TP. Moreover, inspection of B2R-TP PLA signals in VSMC revealed agonist-modulated nuclear and extranuclear proximity between B2R and TP, whose quantification varied substantially following single versus dual agonist stimulations. B2R-TP interaction was further verified by the findings of co-immunoprecipitation (co-IP) analysis of VSMC lysates. To our knowledge, this is the first study that provides evidence supporting the existence of B2R-TP heteromerization fingerprints in primary cultured VSMC.

The prostaglandin H2 analog U-46619 improves the differentiation efficiency of human induced pluripotent stem cells into endothelial cells by activating both p38MAPK and ERK1/2 signaling pathways

BACKGROUND

We have shown that the differentiation of human-induced pluripotent stem cells (hiPSCs) into endothelial cells (ECs) is more efficient when performed with a 3-dimensional (3D) scaffold of biomaterial than in monolayers. The current study aims to further increase hiPSC-EC differentiation efficiency by deciphering the signaling pathways in 3D scaffolds.

METHODS AND RESULTS

We modified our 3D protocol by using U-46619 to upregulate both p38 mitogen-activated protein kinase (p38MAPK) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, which increased the differentiation efficiency (as measured by CD31 expression) to as high as 89% in two established hiPSC lines. The differentiated cells expressed arteriovenous, but not lymphatic, markers; formed tubular structures and EC lumen in vitro; had significantly shorter population-doubling times than monolayer-differentiated hiPSC-ECs; and restored perfusion and vascularity in a murine hind limb ischemia model. The differentiation efficiency was also > 85% in three hiPSC lines that had been derived from patients with diseases or disease symptoms that have been linked to endothelial dysfunction.

CONCLUSIONS

These observations demonstrate that activating both p38MAPK and ERK1/2 signaling pathways with U-46619 improves the efficiency of arteriovenous hiPSC-EC differentiation and produces cells with greater proliferative capacity.

Expression of the TPα and TPβ isoforms of the thromboxane prostanoid receptor (TP) in prostate cancer: clinical significance and diagnostic potential

The prostanoid thromboxane (TX) A₂ plays a central role in haemostasis and is increasingly implicated in cancer progression. TXA₂ signals through two T Prostanoid receptor (TP) isoforms termed TPα and TPβ, with both encoded by the TBXA2R gene. Despite exhibiting several functional and regulatory differences, the role of the individual TP isoforms in neoplastic diseases is largely unknown.

This study evaluated expression of the TPα and TPβ isoforms in tumour microarrays of the benign prostate and different pathological (Gleason) grades of prostate cancer (PCa). Expression of TPβ was significantly increased in PCa relative to benign tissue and strongly correlated with increasing Gleason grade. Furthermore, higher TPβ expression was associated with increased risk of biochemical recurrence (BCR) and significantly shorter disease-free survival time in patients post-surgery. While TPα was more variably expressed than TPβ in PCa, increased/high TPα expression within the tumour also trended toward increased BCR and shorter disease-free survival time. Comparative genomic CpG DNA methylation analysis revealed substantial differences in the extent of methylation of the promoter regions of the TBXA2R that specifically regulate expression of TPα and TPβ, respectively, both in benign prostate and in clinically-derived tissue representative of precursor lesions and progressive stages of PCa. Collectively, TPα and TPβ expression is differentially regulated both in the benign and tumourigenic prostate, and coincides with clinical pathology and altered CpG methylation of the TBXA2R gene. Analysis of TPβ, or a combination of TPα/TPβ, expression levels may have significant clinical potential as a diagnostic biomarker and predictor of PCa disease recurrence.

Regulated expression of the TPβ isoform of the human T prostanoid receptor by the tumour suppressors FOXP1 and NKX3.1: Implications for the role of thromboxane in prostate cancer

The prostanoid thromboxane (TX)A₂ signals through the TPα and TPβ isoforms of T Prostanoid receptor (TP) that are transcriptionally regulated by distinct promoters termed Prm1 and Prm3, respectively, within the TBXA2R gene. We recently demonstrated that expression of TPα and TPβ is increased in PCa, differentially correlating with Gleason grade and with altered CpG methylation of the individual Prm1/Prm3 regions within the TBXA2R. The current study sought to localise the sites of CpG methylation within Prm1 and Prm3, and to identify the main transcription factors regulating TPβ expression through Prm3 in the prostate adenocarcinoma PC-3 and LNCaP cell lines. Bisulfite sequencing revealed extensive differences in the pattern and status of CpG methylation of the individual Prm1 and Prm3 regions that regulate TPα and TPβ expression, respectively, within the TBXA2R. More specifically, Prm1 is predominantly hypomethylated while Prm3 is hypermethylated across its entire sequence in PC-3 and LNCaP cells. Furthermore, the tumour suppressors FOXP1 and NKX3.1, strongly implicated in PCa development, were identified as key transcription factors regulating TPβ expression through Prm3 in both PCa cell lines. Specific siRNA-disruption of FOXP1 and NKX3.1 each coincided with up-regulated TPβ protein and mRNA expression, while genetic-reporter and chromatin immunoprecipitation (ChIP) analyses confirmed that both FOXP1 and NKX3.1 bind to cis‑elements within Prm3 to transcriptionally repress TPβ in the PCa lines. Collectively these data identify Prm3/TPβ as a bona fide target of FOXP1 and NKX3.1 regulation, providing a mechanistic basis, at least in part, for the highly significant upregulation of TPβ expression in PCa.

Reciprocal regulation of β2-adrenoceptor-activated cAMP response-element binding protein signalling by arrestin2 and arrestin3

Activation of Gs coupled receptors (e.g. β₂-adrenoreceptor (β₂AR)) expressed within the uterine muscle layer (myometrium), promotes intracellular cAMP generation, inducing muscle relaxation through short-term inhibition of contractile proteins, and longer-term modulation of cellular phenotype to promote quiescence. In the myometrium cAMP-driven modulation of cell phenotype is facilitated by CREB activity, however despite the importance of CREB signalling in the promotion of myometrial quiescence during pregnancy, little is currently known regarding the molecular mechanisms involved. Thus, we have characterised β-adrenoceptor-stimulated CREB signalling in the immortalised ULTR human myometrial cell line. The non-selective β-adrenoceptor agonist isoprenaline induced time- and concentration-dependent CREB phosphorylation, which was abolished by the β₂AR selective antagonist ICI118,551. β₂AR-stimulated CREB phosphorylation was mediated through a short-term PKA-dependent phase, and longer-term Src/p38 MAPK-dependent/PKA-independent phase. Since in model cells, arrestin2 can facilitate β₂AR-mediated Src/p38 recruitment, we examined whether CREB signalling was activated through a similar process in myometrial cells. Depletion of arrestin2 attenuated p38 phosphorylation, whilst arrestin3 depletion enhanced and prolonged isoprenaline-stimulated p38 signals, which was reversed following inhibition of Src. Knockdown of arrestin2 led to enhanced short-term (up to 10min), and attenuated longer-term (>10min) isoprenaline-stimulated CREB phosphorylation. Contrastingly, removal of arrestin3 enhanced and prolonged isoprenaline-stimulated CREB phosphorylation, whilst depletion of both arrestins abolished CREB signals at time points >5min. In summary, we have delineated the molecular mechanisms coupling β₂AR activity to CREB signalling in ULTR myometrial cells, revealing a biphasic activation process encompassing short-term PKA-dependent, and prolonged Src/arrestin2/p38-dependent components. Indeed, our data highlight a novel arrestin-mediated modulation of CREB signalling, suggesting a reciprocal relationship between arrestin2 and arrestin3, wherein recruitment of arrestin3 restricts the ability of β₂AR to activate prolonged CREB phosphorylation by precluding recruitment of an arrestin2/Src/p38 complex.

Physiological role of reactive oxygen species as promoters of natural defenses

It has been 60 yr since the discovery of reactive oxygen species (ROS) in biology and the beginning of the scientific community's attempt to understand the impact of the unpaired electron of ROS molecules in biological pathways, which was eventually noted to be toxic. Several studies have shown that the presence of ROS is essential in triggering or acting as a secondary factor for numerous pathologies, including metabolic and genetic diseases; however, it was demonstrated that chronic treatment with antioxidants failed to show efficacy and positive effects in the prevention of diseases or health complications that result from oxidative stress. On the contrary, such treatment has been shown to sometimes even worsen the disease. Because of the permanent presence of ROS in organisms, elaborate mechanisms to adapt with these reactive molecules and to use them without necessarily blocking or preventing their actions have been studied. There is now a large body of evidence that shows that living organisms have conformed to the presence of ROS and, in retrospect, have adapted to the bioactive molecules that are generated by ROS on proteins, lipids, and DNA. In addition, ROS have undergone a shift from being molecules that invoked oxidative damage in regulating signaling pathways that impinged on normal physiological and redox responses. Working in this direction, this review unlocks a new conception about the involvement of cellular oxidants in the maintenance of redox homeostasis in redox regulation of normal physiological functions, and an explanation for its essential role in numerous pathophysiological states is noted.-Roy, J., Galano, J.-M., Durand, T., Le Guennec, J.-Y., Lee, J. C.-Y. Physiological role of reactive oxygen species as promoters of natural defenses.

Regulation of protein kinase C-related kinase (PRK) signalling by the TPα and TPβ isoforms of the human thromboxane A2 receptor: Implications for thromboxane- and androgen- dependent neoplastic and epigenetic responses in prostate cancer

The prostanoid thromboxane (TX) A₂ and its T Prostanoid receptor (the TP) are increasingly implicated in prostate cancer (PCa). Mechanistically, we recently discovered that both TPα and TPβ form functional signalling complexes with members of the protein kinase C-related kinase (PRK) family, AGC- kinases essential for the epigenetic regulation of androgen receptor (AR)-dependent transcription and promising therapeutic targets for treatment of castrate-resistant prostate cancer (CRPC). Critically, similar to androgens, activation of the PRKs through the TXA₂/TP signalling axis induces phosphorylation of histone H3 at Thr11 (H3Thr11), a marker of androgen-induced chromatin remodelling and transcriptional activation, raising the possibility that TXA₂-TP signalling can mimic and/or enhance AR-induced cellular changes even in the absence of circulating androgens such as in CRPC. Hence the aim of the current study was to investigate whether TXA₂/TP-induced PRK activation can mimic and/or enhance AR-mediated cellular responses in the model androgen-responsive prostate adenocarcinoma LNCaP cell line. We reveal that TXA₂/TP signalling can act as a neoplastic- and epigenetic-regulator, promoting and enhancing both AR-associated chromatin remodelling (H3Thr11 phosphorylation, WDR5 recruitment and acetylation of histone H4 at lysine 16) and AR-mediated transcriptional activation (e.g of the KLK3/prostate-specific antigen and TMPRSS2 genes) through mechanisms involving TPα/TPβ mediated-PRK1 and PRK2, but not PRK3, signalling complexes. Overall, these data demonstrate that TPα/TPβ can act as neoplastic and epigenetic regulators by mimicking and/or enhancing the actions of androgens within the prostate and provides further mechanistic insights into the role of the TXA₂/TP signalling axis in PCa, including potentially in CRPC.

Protein kinase C-related kinase 1 and 2 play an essential role in thromboxane-mediated neoplastic responses in prostate cancer

The prostanoid thromboxane (TX) A₂ is increasingly implicated in neoplastic progression, including prostate cancer (PCa). Mechanistically, we recently identified protein kinase C-related kinase (PRK) 1 as a functional interactant of both the TPα and TPβ isoforms of the human T prostanoid receptor (TP). The interaction with PRK1 was not only essential for TPα/TPβ-induced PCa cell migration but also enabled the TXA₂-TP axis to induce phosphorylation of histone H3 at Thr11 (H3Thr11), an epigenetic marker both essential for and previously exclusively associated with androgen-induced chromatin remodelling and transcriptional activation. PRK1 is a member of a subfamily of three structurally related kinases comprising PRK1/PKNα, PRK2/PKNγ and PRK3/PKNβ that are widely yet differentially implicated in various cancers. Hence, focusing on the setting of prostate cancer, this study investigated whether TPα and/or TPβ might also complex with PRK2 and PRK3 to regulate their activity and neoplastic responses. While TPα and TPβ were found in immune complexes with PRK1, PRK2 and PRK3 to regulate their activation and signalling, they do so differentially and in a TP agonist-regulated manner dependent on the T-loop activation status of the PRKs but independent of their kinase activity. Furthermore, TXA₂-mediated neoplastic responses in prostate adenocarcinoma PC-3 cells, including histone H3Thr11 phosphorylation, was found to occur through a PRK1- and PRK2-, but not PRK3-, dependent mechanism. Collectively, these data suggest that TXA₂ acts as both a neoplastic and epigenetic regulator and provides a mechanistic explanation, at least in part, for the prophylactic benefits of Aspirin in reducing the risk of certain cancers.

Thromboxane A2 stimulates neurite outgrowth in cerebral cortical neurons via mitogen activated protein kinase signaling

Thromboxane A2 (TXA2) is a central prostanoid in the cardiovascular system and is a crucial mediator of vascular homeostasis and platelet aggregation. In this study, we report a novel role for TXA2 in neurite outgrowth. TXA2 receptor is expressed in rat cortical neurons, and treatment with the TXA2 agonist U-46619 promotes neurite outgrowth in a concentration-dependent manner. We investigated the molecular mechanism underlying U-46619-induced neurite outgrowth in cortical neurons. Blockade of the phosphorylation of mitogen activated protein kinase (MAPK) prevents U-46619-mediated neurite outgrowth. These data indicates that TXA2 functions as a positive regulator of neurite outgrowth via a mechanism dependent on MAPKs in cortical neurons.

Effect of cyclooxygenase (COX)-2 inhibition on mouse renal interstitial fibrosis

Unilateral ureteral obstruction (UUO) is a well-established model for the study of interstitial fibrosis in the kidney. In this study, we investigated the effects of a COX-2 inhibitor, meloxicam, on UUO-induced renal interstitial fibrosis in mice. Serum creatinine, blood urea nitrogen and urinary glucose were significantly increased by UUO. However, all of these changes were attenuated by meloxicam (1 mg/kg/day). Masson׳s trichrome staining showed that interstitial fibrosis was significantly increased by UUO, but that meloxicam also significantly diminished the area of UUO-induced fibrosis. Heat shock protein (HSP) 47 protein, a collagen-specific molecular chaperone essential for the biosynthesis of collagen molecules, and type IV collagen mRNA were increased in kidneys of UUO mice. Meloxicam reduced the expression of both HSP47 protein and type IV collagen mRNA. The phosphorylation of extracellular regulated kinase (ERK) and c-jun-N-terminal kinase (JNK) was increased by UUO, but these changes were inhibited by meloxicam. Collectively, these results suggest that COX-2 may be involved in the expression of HSP47 and type IV collagen through the phosphorylation of ERK and JNK, accelerating renal interstitial fibrosis.

Biochemical assay of G protein-coupled receptor oligomerization: adenosine A1 and thromboxane A2 receptors form the novel functional hetero-oligomer

G protein-coupled receptors (GPCRs) are classified into a family of seven transmembrane receptors. Receptor oligomerization may be the key to the expression and function of these receptors, for example, ligand binding, desensitization, membrane trafficking, and signaling. The accumulation of evidence that GPCRs form an oligomerization with a functional alternation may change the strategy for the discovery of novel drugs targeting GPCRs. Identification of the oligomer is essential to elucidate GPCR oligomerization. GPCR oligomerizations have been demonstrated using various biochemical approaches, which include the coimmunoprecipitation method, fluorescence resonance energy transfer assay, and bioluminescence RET assay. Thus, various assays are useful for the study of GPCR oligomerization, and we should choose the best method to match the purpose. We previously targeted adenosine A1 and thromboxane A2 (TP) receptors to form a functionally novel hetero-oligomer, since both receptors function in the same cells. This chapter describes the methods used to detect GPCR oligomerization and alterations in the signaling pathways, principally according to our findings on oligomerization between adenosine A1 and TPα receptors.

Transcriptional regulation of the human thromboxane A2 receptor gene by Wilms' tumor (WT)1 and hypermethylated in cancer (HIC) 1 in prostate and breast cancers

The prostanoid thromboxane (TX) A(2) plays a central role in hemostasis and is increasingly implicated in neoplastic disease, including prostate and breast cancers. In humans, TXA(2) signals through the TPα and TPβ isoforms of the T prostanoid receptor, two structurally related receptors transcriptionally regulated by distinct promoters, Prm1 and Prm3, respectively, within the TP gene. Focusing on TPα, the current study investigated its expression and transcriptional regulation through Prm1 in prostate and breast cancers. Expression of TPα correlated with increasing prostate and breast tissue tumor grade while the TXA(2) mimetic U46619 promoted both proliferation and migration of the respective prostate (PC3) and breast (MCF-7 and MDA-MD-231) derived-carcinoma cell lines. Through 5' deletional and genetic reporter analyses, several functional upstream repressor regions (URRs) were identified within Prm1 in PC3, MCF-7 and MDA-MB-231 cells while site-directed mutagenesis identified the tumor suppressors Wilms' tumor (WT)1 and hypermethylated in cancer (HIC) 1 as the trans-acting factors regulating those repressor regions. Chromatin immunoprecipitation (ChIP) studies confirmed that WT1 binds in vivo to multiple GC-enriched WT1 cis-elements within the URRs of Prm1 in PC3, MCF-7 and MDA-MB-231 cells. Furthermore, ChIP analyses established that HIC1 binds in vivo to the HIC1((b))cis-element within Prm1 in PC3 and MCF-7 cells but not in the MDA-MB-231 carcinoma line. Collectively, these data establish that WT1 and HIC1, both tumor suppressors implicated in prostate and breast cancers, transcriptionally repress TPα expression and thereby provide a strong genetic basis for understanding the role of TXA2 in the progression of certain human cancers.

Inverse agonism of SQ 29,548 and Ramatroban on Thromboxane A2 receptor

G protein-coupled receptors (GPCRs) show some level of basal activity even in the absence of an agonist, a phenomenon referred to as constitutive activity. Such constitutive activity in GPCRs is known to have important pathophysiological roles in human disease. The thromboxane A2 receptor (TP) is a GPCR that promotes thrombosis in response to binding of the prostanoid, thromboxane A2. TP dysfunction is widely implicated in pathophysiological conditions such as bleeding disorders, hypertension and cardiovascular disease. Recently, we reported the characterization of a few constitutively active mutants (CAMs) in TP, including a genetic variant A160T. Using these CAMs as reporters, we now test the inverse agonist properties of known antagonists of TP, SQ 29,548, Ramatroban, L-670596 and Diclofenac, in HEK293T cells. Interestingly, SQ 29,548 reduced the basal activity of both, WT-TP and the CAMs while Ramatroban was able to reduce the basal activity of only the CAMs. Diclofenac and L-670596 showed no statistically significant reduction in basal activity of WT-TP or CAMs. To investigate the role of these compounds on human platelet function, we tested their effects on human megakaryocyte based system for platelet activation. Both SQ 29,548 and Ramatroban reduced the platelet hyperactivity of the A160T genetic variant. Taken together, our results suggest that SQ 29,548 and Ramatroban are inverse agonists for TP, whereas, L-670596 and Diclofenac are neutral antagonists. Our findings have important therapeutic applications in the treatment of TP mediated pathophysiological conditions.

Signaling pathways involved in isoprostane-mediated fibrogenic effects in rat hepatic stellate cells

Despite evidence supporting a potential role for F2-isoprostanes (F2-IsoP's) in liver fibrosis, their signaling mechanisms are poorly understood. We have previously provided evidence that F2-IsoP's stimulate hepatic stellate cell (HSC) proliferation and collagen hyperproduction by activation of a modified form of isoprostane receptor homologous to the classic thromboxane receptor (TP). In this paper, we examined which signal transduction pathways are set into motion by F2-IsoP's to exert their fibrogenic effects. HSCs were isolated from rat liver, cultured to their activated myofibroblast-like phenotype, and then treated with the isoprostane 15-F2t-isoprostane (15-F2t-IsoP). Inositol trisphosphate (IP3) and adenosine 3',5'-cyclic monophosphate (cAMP) levels were determined using commercial kits. Mitogen-activated protein kinase (MAPK) and cyclin D1 expression was assessed by Western blotting. Cell proliferation and collagen synthesis were determined by measuring [(3)H]thymidine and [(3)H]proline incorporation, respectively. 15-F2t-IsoP elicited an activation of extracellular-signal-regulated kinase (ERK), p38 MAPK, and c-Jun NH2-terminal kinase (JNK), which are known to be also regulated by G-protein-coupled receptors. Preincubation with specific ERK (PD98059), p38 (SB203580), or JNK (SP600125) inhibitors prevented 15-F2t-IsoP-induced cell proliferation and collagen synthesis. 15-F2t-IsoP decreased cAMP levels within 30 min, suggesting binding to the TPβ isoform and activation of Giα protein. Also, 15-F2t-IsoP increased IP3 levels within a few minutes, suggesting that the Gq protein pathway is also involved. In conclusion, the fibrogenic effects of F2-IsoP's in HSCs are mediated by downstream activation of MAPKs, through TP binding that couples via both Gqα and Giα proteins. Targeting TP receptor, or its downstream pathways, may contribute to preventing oxidative damage in liver fibrosis.

Functional variants in the thromboxane A2 receptor gene are associated with lung function in childhood-onset asthma

BACKGROUND

The thromboxane A2 receptor (TBXA2R) gene is associated with asthma, but no functional genetic variations are known to associate with the disease or its related phenotypes.

OBJECTIVE

To investigate the association of TBXA2R polymorphisms with asthma susceptibility and related phenotypes and to identify functionally relevant polymorphisms.

METHODS

We performed comprehensive sequencing of the TBXA2R gene in 48 Japanese control subjects and found a set of variants (SNP1 G>T rs2238634, SNP2 T>G rs2238633, SNP3 C>T rs2238632 and SNP4 G>A rs2238631) in intron 1 in linkage disequilibrium with c.795 T>C rs1131882, which was previously reported to be associated with asthma and related phenotypes. To investigate the effect of four common haplotypes (H1, H2, H3 and H4) on transcriptional activity, we performed a luciferase assay in primary bronchial smooth muscle cells (BSMCs) and human airway epithelial cells (BEAS-2B). We also studied the haplotype association with lung function, TBXA2R mRNA levels, and eosinophil fraction/count in peripheral blood in childhood-onset asthma patients and/or controls.

RESULTS

H2 and H4, containing minor alleles of SNP2 and SNP3, had significantly higher transcriptional activities than H1 consisting of major alleles (P < 0.001 in BSMCs and BEAS-2B). Homozygotes for redefined haplotype h2 corresponding to minor alleles of SNP2 and SNP3 were associated with lower lung function in childhood-onset asthma patients compared to other zygotes (baseline Forced expiratory volume in one second (FEV1)/ Forced vital capacity (FVC) and Forced expiratory flow between 25% and 75% of the FVC (%FEF(25-75%)): P = 0.00201 and 0.0128, respectively, and post-bronchodilator FEV1/FVC and %FEF(25-75%): P = 0.00224 and 0.0393 respectively). Haplotype h2 was also associated with higher mRNA levels in control peripheral blood cells and higher blood eosinophil fractions and counts in female controls.

CONCLUSIONS AND CLINICAL RELEVANCE

Genetic variants were identified in the TBXA2R gene that influenced transcriptional activity and were associated with asthma-related phenotypes. Thromboxane pathways may therefore play important roles in airway inflammation and remodelling in asthma patients.

Oxidative stress and increased formation of vasoconstricting F2-isoprostanes in patients with reversible cerebral vasoconstriction syndrome

The pathophysiology of reversible cerebral vasoconstriction syndrome (RCVS) is unknown. Oxidative stress is detrimental to endothelial function and vascular reactivity. We hypothesized that the oxidative stress marker 8-iso-prostaglandin F2α, which is also a potent vasoconstrictor, might contribute to the pathogenesis of RCVS. Recruited participants included 103RCVS patients, 53 patients with primary headache with acute severe attacks, and 54 healthy controls. Subjects recruited prior to 2009 were discovery cohort, whereas those after 2009, replication cohort. Urine samples were obtained from all patients at registration and from 79 patients with RCVS again at remission stage. Urine 8-iso-prostaglandin F2α was analyzed by liquid chromatography-tandem mass spectrometry. Patients with RCVS received magnetic resonance angiography and transcranial color-coded sonography. In RCVS patients, the urine 8-iso-prostaglandin F2α level was higher than that in the other groups in discovery, replication, and combined cohorts (RCVS, 0.29±0.18; primary headache with acute severe attacks, 0.21±0.19; control, 0.18±0.09ng/mg creatinine; P<0.001), and it was positively correlated with the flow velocities of major intracranial arteries, especially within the first week of disease onset (middle cerebral artery, Spearman's correlation coefficient [rs]=0.580, P=0.002; anterior cerebral artery, rs=0.472, P=0.042; posterior cerebral artery, rs=0.457, P=0.022; basilar artery, rs= 0.530, P=0.002). The 8-iso-prostaglandin F2α level decreased from the ictalto remission stage in RCVS patients (0.31±0.21 vs 0.16±0.10ng/mg creatinine, P<0.001). 8-Iso-prostaglandin F2α was higher in patients with RCVS and correlated with the severity of vasoconstrictions. Further studies are required to explore its potential pathogenic role.

Isoprostanes and neuroprostanes: total synthesis, biological activity and biomarkers of oxidative stress in humans

Isoprostanes (IsoPs) and neuroprostanes (NeuroPs) are formed in vivo by a free radical non-enzymatic mechanism involving peroxidation of arachidonic acid (AA, C20:4 n-6) and docosahexaenoic acid (DHA, C22:6 n-3) respectively. This review summarises our research in the total synthesis of these lipid metabolites, as well as their biological activities and their utility as biomarkers of oxidative stress in humans.

The p90 ribosomal S6 kinase (RSK) is a mediator of smooth muscle contractility

In the canonical model of smooth muscle (SM) contraction, the contractile force is generated by phosphorylation of the myosin regulatory light chain (RLC₂₀) by the myosin light chain kinase (MLCK). Moreover, phosphorylation of the myosin targeting subunit (MYPT1) of the RLC₂₀ phosphatase (MLCP) by the RhoA-dependent ROCK kinase, inhibits the phosphatase activity and consequently inhibits dephosphorylation of RLC₂₀ with concomitant increase in contractile force, at constant intracellular [Ca²⁺]. This pathway is referred to as Ca²⁺-sensitization. There is, however, emerging evidence suggesting that additional Ser/Thr kinases may contribute to the regulatory pathways in SM. Here, we report data implicating the p90 ribosomal S6 kinase (RSK) in SM contractility. During both Ca²⁺- and agonist (U46619) induced SM contraction, RSK inhibition by the highly selective compound BI-D1870 (which has no effect on MLCK or ROCK) resulted in significant suppression of contractile force. Furthermore, phosphorylation levels of RLC₂₀ and MYPT1 were both significantly decreased. Experiments involving the irreversible MLCP inhibitor microcystin-LR, in the absence of Ca²⁺, revealed that the decrease in phosphorylation levels of RLC₂₀ upon RSK inhibition are not due solely to the increase in the phosphatase activity, but reflect direct or indirect phosphorylation of RLC₂₀ by RSK. Finally, we show that agonist (U46619) stimulation of SM leads to activation of extracellular signal-regulated kinases ERK1/2 and PDK1, consistent with a canonical activation cascade for RSK. Thus, we demonstrate a novel and important physiological function of the p90 ribosomal S6 kinase, which to date has been typically associated with the regulation of gene expression.

Influence of cigarette smoking on synthesis of eicosanoids, isoprostanes and lipoxygenase metabolites in apical periodontitis

Arachidonic acid (AA) is metabolized to eicosanoids and isoprostanes (IPs) via different pathways. The presence of granuloma in apical periodontitis (AP) is linked with inflammation and the synthesis of metabolites of AA.

OBJECTIVE

We investigated the conversion rate of (14)C labelled arachidonic acid ((14)C-AA), the lipoxygenases (LOX) products and the endogenous synthesis of eicosanoids and IPs in extracted granuloma. Furthermore, we assessed if there are markers for bone destruction and the influence of cigarette smoking.

PATIENTS AND METHODS

In 46 patients with symptoms and corresponding radiological signs of AP, teeth were extracted including the periapical granuloma. The endogenous synthesis of eicosanoids and IPs, the conversion rate of (14)C-AA and LOX products in extracted granuloma were analyzed.

RESULTS

We found that smoking increases significantly the synthesis of IPs and LOX-metabolites in granuloma. Furthermore, smoking may have contributed to significant differences in qualitative and quantitative profile of eicosanoids, IPs and the conversion rate of (14)C-AA independent of the size of the granuloma.

CONCLUSIONS

Our data demonstrate that in smokers with granuloma due to AP products of lipid peroxidation as 8-iso-PGF(2α) and products of the LOX-pathway are increased at the expense of cyclooxygenase products. The size of granuloma did not influence the amount of synthesized eicosanoids, IPs or LOX-metabolites out of (14)C-AA whereas cigarette smoking was a significantly influencing and modifiable risk factor.

Hetero-oligomerization between adenosine A₁ and thromboxane A₂ receptors and cellular signal transduction on stimulation with high and low concentrations of agonists for both receptors

Growing evidence indicates that G protein-coupled receptors can form homo- and hetero-oligomers to diversify signal transduction. However, the molecular mechanisms and physiological significance of G protein-coupled receptor-oligomers are not fully understood. Both ADOR1 (adenosine A(1) receptor) and TBXA2R (thromboxane A(2) receptor α; TPα receptor), members of the G protein-coupled receptor family, act on astrocytes and renal mesangial cells, suggesting certain functional correlations. In this study, we explored the possibility that adenosine A(1) and TPα receptors form hetero-oligomers with novel pharmacological profiles. We showed that these receptors hetero-oligomerize by conducting coimmunoprecipitation and bioluminescence resonance energy transfer (BRET(2)) assays in adenosine A(1) receptor and TPα receptor-cotransfected HEK293T cells. Furthermore, coexpression of the receptors affected signal transduction including the accumulation of cyclic AMP and phosphorylation of extracellular signal-regulated kinase-1 and -2 was significantly increased by high and low concentrations of adenosine A(1) receptor agonist and TPα agonists, respectively. Our study provides evidence of hetero-oligomerization between adenosine A(1) and TPα receptors for the first time, and suggests that this oligomerization affects signal transduction responding to different concentrations of receptor agonists.

Enhanced airway smooth muscle cell thromboxane receptor signaling via activation of JNK MAPK and extracellular calcium influx

Thromboxane is a key inflammatory mediator and potent airway constrictor. It acts on thromboxane A(2) (TP) receptors and contributes to airway inflammation and airway hyperresponsiveness that is the characteristic feature of asthma. The present study was designed to study TP receptor signaling in airway smooth muscle cells by using an organ culture model and a set of selective pharmacological inhibitors for mitogen-activated protein kinase (MAPK) and calcium signal pathways. Western-blot, immunohistochemistry, myograph and a selective TP receptor agonist U46619 were used for examining TP receptor signal proteins and function. Organ culture of rat bronchial segments for up to 48 h induces a time-dependently increased airway contractile response to U46619. This indicates that organ culture increases TP receptor signaling in the airway smooth muscle cells. The enhanced bronchial contraction was attenuated by the inhibition of c-Jun N-terminal kinase (JNK) MAPK activity, chelation of extracellular calcium and calcium channel blocker nifedipine, suggesting that JNK MAPK activity and elevated intracellular calcium level are required for the TP receptor signaling. In conclusion, airway smooth muscle cell TP receptor signaling occurs via JNK MAPK activity and the elevation of extracellular calcium influx, which may provide knowledge for understanding the signaling pathway responsible for the modulation of TP receptor mediated airway hyperresponsiveness to thromboxane.

4-Methylnitrosamino-1-3-pyridyl-1-butanone (NNK) promotes lung cancer cell survival by stimulating thromboxane A2 and its receptor

The role of thromboxane A(2) (TxA(2)) in smoking-associated lung cancer is poorly understood. This study was conducted to study the role of TxA(2) in smoking carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-promoted cell survival and growth in human lung cancer cells. We found that NNK increased TxA(2) synthase (TxAS) expression and thromboxane B(2) (TxB(2)) generation in cultured lung cancer cells, the result of which was supported by the increased level of TxAS in lung cancer tissues of smokers. Both TxAS-specific inhibitor furegrelate and TxA(2) receptor antagonist SQ29548 completely blocked NNK-mediated cell survival and growth via inducting apoptosis. TxA(2) receptor agonist U46619 reconstituted a near-full survival and growth response to NNK when TxAS was inhibited, affirming the role of TxA(2) receptor in NNK-mediated cell survival and growth. Suppression of cyclic adenosine monophosphate response element binding protein (CREB) activity by its small interference RNA blocked the effect of NNK. Phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase (ERK) also had a positive role. Altogether, our results have revealed that NNK stimulates TxA(2) synthesis and activates its receptor in lung cancer cells. The increased TxA(2) may then activate CREB through PI3K/Akt and extracellular ERK pathways, thereby contributing to the NNK-promoted survival and growth of lung cancer cells.

Thromboxane prostanoid receptor stimulation induces shedding of the transmembrane chemokine CX3CL1 yet enhances CX3CL1-dependent leukocyte adhesion

In atherosclerosis, chemokines recruit circulating mononuclear leukocytes to the vascular wall. A key factor is CX3CL1, a chemokine with soluble and transmembrane species that acts as both a chemoattractant and an adhesion molecule. Thromboxane A2 and its receptor, TP, are also critical to atherogenesis by promoting vascular inflammation and consequent leukocyte recruitment. We examined the effects of TP stimulation on processing and function of CX3CL1, using CX3CL1-expressing human ECV-304 cells and primary human vascular endothelial cells. TP agonists promoted rapid shedding of cell surface CX3CL1, which was inhibited by pharmacological inhibitors or specific small interfering RNA targeting tumor necrosis factor-α-converting enzyme (TACE). Because it reduced cell surface CX3CL1, we predicted that TP stimulation would inhibit adhesion of leukocytes expressing the CX3CL1 cognate receptor but, paradoxically, saw enhanced adhesion. We questioned whether the enhanced ability of the remaining membrane-associated CX3CL1 to bind targets was caused by changes in its lateral mobility. Using fluorescence recovery after photobleaching, we found that plasmalemmal CX3CL1 was initially tethered but ultimately mobilized by TP agonists. TP stimulation provoked clustering of transmembrane CX3CL1 at sites of contact with adherent leukocytes. These data demonstrate that TP stimulation induces two distinct effects: a rapid cleavage of surface CX3CL1, thereby releasing the soluble chemoattractant, plus mobilization of the remaining transmembrane CX3CL1 to enhance the avidity of interactions with adherent leukocytes. The dual effect of TP allows CX3CL1 to recruit leukocytes to sites of vascular inflammation while enhancing their adhesion once recruited.

Activation of thromboxane A(2) receptors induces orphan nuclear receptor Nurr1 expression and stimulates cell proliferation in human lung cancer cells

Previous studies implicate that activation of thromboxane A(2) receptor (TP) induced cell proliferation and transformation in several cell lines. We report here that the activation of TP by its agonist, [1S-[1alpha, 2alpha (Z), 3beta (1E, 3S*), 4alpha]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo [2.2.1] hept-2-yl]-5-heptenoic acid (I-BOP), induced Nurr1 expression and stimulated proliferation of human lung cancer cells. Nurr1, an orphan nuclear receptor in the nuclear receptor subfamily 4A subfamily, has been implicated in cell proliferation, differentiation and apoptosis. I-BOP markedly induced Nurr1 messenger RNA and protein levels as compared with other subfamily members, Nur77 and Nor-1. The signaling pathways of I-BOP-induced Nurr1 expression were examined by using various inhibitors of signaling molecules. The induction of Nurr1 expression by I-BOP appeared to be mediated through protein kinase A (PKA)/cAMP response element binding (CREB), protein kinase C and mitogen-activated protein kinase/extracellular signal-regulated kinase pathways and not related to epidermal growth factor receptor and prostaglandin E(2) pathways. Transcriptional activation of Nurr1 gene by I-BOP was further investigated at the promoter level in H157 cells. 5'-Deletion analysis, site-directed mutagenesis and luciferase reporter assay demonstrated that Nurr1 expression was induced by I-BOP in a PKA/CREB-dependent manner. Further studies have revealed that Nurr1 may mediate cyclin D1 expression and I-BOP-induced cell proliferation in H157 cells since small interfering RNA of Nurr1 blocked I-BOP-induced cyclin D1 expression and cell proliferation and also decreased cell growth rate. These results provide strong evidence that Nurr1 plays a significant role in cell proliferation and may mediate TP agonist-induced proliferation in lung cancer cells.

Characterization of anandamide-stimulated cannabinoid receptor signaling in human ULTR myometrial smooth muscle cells

Accumulating evidence highlights the importance of the endocannabinoid anandamide (AEA) as a key mediator in reproductive physiology. Current data suggest potential roles for AEA in gametogenesis, fertilization, and parturition. AEA exerts its actions through two G protein-coupled receptors, termed cannabinoid receptor 1 (CB1), and 2 (CB2), and the ligand-gated transient receptor potential vanilloid receptor type 1 (TRPV1) ion channel. At present, the cellular mechanism(s) and consequences of AEA signaling in reproductive tissues, especially the myometrium, are poorly understood. Here, we examine the expression of CB1, CB2, and TRPV1 in the human myometrial smooth muscle cell-line (ULTR) and characterize intracellular signaling after stimulation with AEA. Radioligand binding analysis revealed a total CB receptor expression of 76 +/- 24 fmol/mg protein, with both quantitative PCR and competition binding studies indicating a negligible CB2 component. AEA caused Galpha(i/o)-dependent inhibition of adenylate cyclase to reduce intracellular cAMP levels. In addition, AEA caused a 2.5- to 3.5-fold increase in ERK activation, which was ablated by inhibition of Galpha(i/o), phosphoinositide-3-kinase and Src-kinase activities, but not by inhibition of Ca(2+)/calmodulin-dependent protein kinase or protein kinase C activities. TRPV1 channel activation with capsaicin failed to activate ERK. Consistent with these findings, the selective agonists, arachidonyl-2-chloroethylamide (CB1) and L759656 (CB2), and selective antagonists AM251 (CB1) and JTE907 (CB2), provided pharmacological evidence that the ERK signaling pathway is activated through endogenously expressed CB1. These findings provide an insight into myometrial AEA signaling, highlighting a potential role for endocannabinoids in the regulation of gene expression in myometrial smooth muscle cells.

Differential regulation of RhoA-mediated signaling by the TPalpha and TPbeta isoforms of the human thromboxane A2 receptor: independent modulation of TPalpha signaling by prostacyclin and nitric oxide

In humans, thromboxane (TX) A₂ signals through the TPα and TPβ isoforms of the TXA₂ receptor that exhibit common and distinct roles. For example, Gq/phospholipase (PL)Cβ signaling by TPα is directly inhibited by the vasodilators prostacyclin and nitric oxide (NO) whereas that signaling by TPβ is unaffected. Herein, we investigated whether TPα and/or TPβ regulate G₁₂/Rho activation and whether that signaling might be differentially regulated by prostacyclin and/or NO. Both TPα and TPβ independently regulated RhoA activation and signaling in clonal cells over-expressing TPα or TPβ and in primary human aortic smooth muscle cells (1° AoSMCs). While RhoA-signaling by TPα was directly impaired by prostacyclin and NO through protein kinase (PK)A- and PKG-dependent phosphorylation, respectively, signaling by TPβ was not directly affected by either agent. Collectively, while TPα and TPβ contribute to RhoA activation, our findings support the hypothesis that TPα is involved in the dynamic regulation of haemostasis and vascular tone, such as in response to prostacyclin and NO. Conversely, the role of TPβ in such processes remains unsolved. Data herein provide essential new insights into the physiologic roles of TPα and TPβ and, through studies in AoSMCs, reveal an additional mode of regulation of VSM contractile responses by TXA₂.

Thromboxane receptor activates the AMP-activated protein kinase in vascular smooth muscle cells via hydrogen peroxide

Thromboxane A2 receptor (TPr) stimulation induces cellular hypertrophy in vascular smooth muscle cells (VSMCs); however, regulation of VSMC hypertrophy remains poorly understood. Here we show that TPr stimulation activates AMP-activated kinase (AMPK), which in turn limits TPr-induced protein synthesis in VSMCs. Exposure of cultured VSMCs to either TPr agonists, IBOP and U46619, or exogenous hydrogen peroxide (H2O2) caused time- and dose-dependent AMPK activation, as evidenced by increased phosphorylation of both AMPK-Thr172 and acetyl-coenzyme A carboxylase-Ser79, a downstream enzyme of AMPK, whereas SQ29548, a selective TPr antagonist, significantly attenuated TPr-enhanced AMPK activation. In parallel, both IBOP and U46619 significantly increased the production of reactive oxygen species such as H2O2. Furthermore, adenoviral overexpression of catalase (an H2O2 scavenger) abolished, whereas superoxide dismutase (which catalyzes H2O2 formation) enhanced, IBOP-induced AMPK activation, suggesting that TPr-activated AMPK was mediated by H2O2. Consistently, exposure of VSMCs to either TPr agonists or exogenous H2O2 dose-dependently increased the phosphorylation of LKB1 (at serines 428 and 307), an AMPK kinase, as well as coimmunoprecipitation of AMPK with LKB1. In addition, direct mutagenesis of either Ser428 or Ser307 of LKB1 into alanine, like the kinase-dead LKB1 mutant, abolished both TPr-stimulated AMPK activation and coimmunoprecipitation. Finally, genetic inhibition of AMPK significantly accentuated IBOP-enhanced protein synthesis, whereas adenoviral overexpression of constitutively active AMPK abolished IBOP-enhance protein synthesis in VSMCs. We conclude that TPr stimulation triggers reactive oxygen species-mediated LKB1-dependent AMPK activation, which in return inhibits cellular protein synthesis in VSMCs.

Thromboxane A2: physiology/pathophysiology, cellular signal transduction and pharmacology

Thromboxane A(2) (TXA(2)), an unstable arachidonic acid metabolite, elicits diverse physiological/pathophysiological actions, including platelet aggregation and smooth muscle contraction. TXA(2) has been shown to be involved in allergies, modulation of acquired immunity, atherogenesis, neovascularization, and metastasis of cancer cells. The TXA(2) receptor (TP) communicates mainly with G(q) and G(13), resulting in phospholipase C activation and RhoGEF activation, respectively. In addition, TP couples with G(11), G(12), G(13), G(14), G(15), G(16), G(i), G(s) and G(h). TP is widely distributed in the body, and is expressed at high levels in thymus and spleen. The second extracellular loop of TP is an important ligand-binding site, and Asp(193) is a key amino acid. There are two alternatively spliced isoforms of TP, TPalpha and TPbeta, which differ only in their C-terminals. TPalpha and TPbeta communicate with different G proteins, and undergo hetero-dimerization, resulting in changes in intracellular traffic and receptor protein conformations. TP cross-talks with receptor tyrosine kinases, such as EGF receptor, to induce cell proliferation and differentiation. TP is glycosylated in the N-terminal region for recruitment to plasma membranes. Furthermore, TP conformation is changed by coupling to G proteins, showing several states of agonist binding. Finally, several drugs modify TP-mediated events; these include cyclooxygenase inhibitors, TXA(2) synthase inhibitors and TP antagonists. Some flavonoids of natural origin also have TP receptor antagonistic activity. Recent advances in TP research have clarified TXA(2)-mediated events in detail, and further study will supply more beneficial information about TXA(2) pathophysiology.

Activation of Thromboxane Receptor Upregulates Interleukin (IL)-1β–Induced VCAM-1 Expression Through JNK Signaling

Objective— Activation of thromboxane receptors (TPr) is implicated in atherosclerosis and inflammation. This study examined how activation of TPr modulates IL-1β–induced vascular cell adhesion molecule (VCAM)-1 expression in aortic vascular smooth muscle cells (VSMCs).

Methods and Results— In VSMCs, activation of TPr with U46619, a stable thromboxane A 2 mimetic, alone did not induce VCAM-1 expression, but enhanced that caused by IL-1β. The enhancement of VCAM-1 expression caused by U46619 occurred at the transcriptional level and was inhibited either by SP600125, a c-Jun N-terminal kinase (JNK) inhibitor, or by overexpression of a dominant-negative JNK1, but not by SB203580, a p38 mitogen-activated protein kinase inhibitor. The activation of JNK by U46619 resulted in enhanced phosphorylation and nuclear translocation of c-Jun associated with an enhanced activation of activator protein (AP)-1, which were abolished by SQ29548, a TPr antagonist, or the JNK inhibitor. Treatment of the cells with U46619 alone did not induce NF-κB activation. Furthermore, U46619 enhanced IL-1β–induced THP-1 monocyte binding to VSMCs, which was inhibited by SQ29548 or SP600125.

Conclusion— This study demonstrates that activation of TPr upregulates IL-1β–induced VCAM-1 expression by enhancing the activation of JNK pathway that leads to enhanced AP-1 activation.

Activation of extracellular signal-regulated kinase by 12-hydroxyheptadecatrienoic acid in prostate cancer PC3 cells

Both 12-hydroxyheptadecatrienoic acid (12-HHT) and thromboxane A2 (TXA2) are products derived from prostaglandin H2 (PGH2) catalyzed by thromboxane synthase. Whether or not they exhibit similar actions remains to be determined. While TXA2-induced activation of extracellular signal-regulated kinases (ERKs) has been extensively studied, 12-HHT-induced activation of ERKs has not been explored. We reported for the first time that 12-HHT induced activation of ERKs in human prostate cancer cell line, PC3. We also compared the mechanisms of 12-HHT- and I-BOP-, a TXA2 mimetic, mediated ERK activation in PC3 cells. The activation of ERKs induced by either agent was shown to involve protein kinase C (PKC)-, protein kinase A (PKA)-, Src kinase and phosphoinositide-3 kinase (PI-3K)-dependent mechanisms in addition to the transactivation of the EGF receptor (EGFR) and the involvement of matrix metalloproteinases (MMPs) based on the sensitivity of the activation to their respective inhibitors. JNK/SAPK and p38 MAPK pathways were responsive to I-BOP but not to 12-HHT stimulation. Both 12-HHT- and I-BOP-induced activations of ERKs were also examined in other human prostate cancer cells, human lung cancer cells, and human lung fibroblast. I-BOP appeared to induce activation of ERKs in most cell lines, whereas 12-HHT induced activation of ERKs only in lung fibroblast in addition to PC3 cells. It appears that TPs are more generally expressed and the potential 12-HHT receptor (s) is expressed in limited specific cell types. Our results suggest that increased expression of thromboxane synthase as seen in prostate tumor may stimulate tumorigenesis as a consequence of concurrent increased synthesis of two fatty acids capable of activating ERKs.

Activation of thromboxane receptor alpha induces expression of cyclooxygenase-2 through multiple signaling pathways in A549 human lung adenocarcinoma cells

Human lung adenocarcinoma A549 cells stably transfected with TPalpha (A549-TPalpha) were used to study agonist I-BOP-induced expression of cyclooxygenase-2 (COX-2) and the related mechanisms of induced expression. I-BOP, a TP agonist, induced a time- and dose-dependent expression of COX-2 in A549-TPalpha cells. The signaling pathways of I-BOP-induced COX-2 expression were elucidated by using various inhibitors of the signaling molecules. The effects of these inhibitors were assessed at protein level, enzyme activity and promoter activity of COX-2. Within MAPK family, both ERK and p38 MAPK but not JNK/SAPK pathways were involved in the induction. Other pathways such as JAK/Stat3 pathway and beta-catenin/TCF/LEF pathway also participated in the induction. The activation of key signaling molecules, ERK, p38 MAPK, CREB and NF-kappaB, involved in the COX-2 transcription was further studied at the phosphorylation step. Activation of ERK and p38 MAPK appeared to be mediated primarily by transactivation of EGFR, whereas activation of CREB and NF-kappaB was mediated by PKA, PKC and ERK. The role of CREB and NF-kappaB in I-BOP-induced COX-2 expression was further explored at the promoter level. Studies on promoter fragments and mutation of responsive motifs indicated that CRE and NF-kappaB sites are critical for the COX-2 induction. Distal NF-kappaB site is essential for the basal induction of the COX-2 transcription, whereas CRE and proximal NF-kappaB sites are important for the induced transcription. These results indicate that I-BOP-induced COX-2 expression through multiple signaling pathways.

Homologous desensitization of signalling by the alpha (alpha) isoform of the human thromboxane A2 receptor: a specific role for nitric oxide signalling

Thromboxane (TX) A₂ plays a central role in hemostasis, regulating platelet activation status and vascular tone. We have recently established that the TPβ isoform of the human TXA₂ receptor (TP) undergoes rapid, agonist-induced homologous desensitization of signalling largely through a G protein-coupled receptor kinase (GRK) 2/3-dependent mechanism with a lesser role for protein kinase (PK) C. Herein, we investigated the mechanism of desensitization of signalling by the TPα isoform. TPα undergoes profound agonist-induced desensitization of signalling (intracellular calcium mobilization and inositol 1,4,5 trisphosphate generation) in response to the TXA₂ mimetic U46619 but, unlike that of TPβ, this is independent of GRKs. Similar to TPβ, TPα undergoes partial agonist-induced desensitization that occurs through a GF 109203X-sensitive, PKC mechanism where Ser¹⁴⁵ within intracellular domain (IC)₂ represents the key phospho-target. TPα also undergoes more profound sustained PKC- and PKG-dependent desensitization where Thr³³⁷ and Ser³³¹, respectively, within its unique C-tail domain were identified as the phospho-targets. Desensitization was impaired by the nitric oxide synthase (NOS), soluble guanylyl cyclase (sGC) and PKG inhibitors l-NAME, LY 83583 and KT5823, respectively, indicating that homologous desensitization of TPα involves nitric oxide generation and signalling. Consistent with this, U46619 led to rapid phosphorylation/activation of endogenous eNOS. Collectively, data herein suggest a mechanism whereby agonist-induced PKC phosphorylation of Ser¹⁴⁵ partially and transiently impairs TPα signalling while PKG- and PKC-phosphorylation at both Ser³³¹ and Thr³³⁷, respectively, within its C-tail domain profoundly desensitizes TPα, effectively terminating its signalling. Hence, in addition to the agonist-mediated PKC feedback mechanism, U46619-activation of the NOS/sGC/PKG pathway plays a significant role in inducing homologous desensitization of TPα.

Distinct effects of z-335, a new thromboxane A2 receptor antagonist, on rabbit platelets and aortic smooth muscle

The effect of a novel thromboxane A2 receptor (TP) antagonist, (+/-)-sodium[2-(4-chlorophenylsulfonylaminomethyl)- indan-5-yl]acetate monohydrate (Z-335), on the U46619-induced responses was compared between rabbit platelets and aorta. Z-335 inhibited platelet shape change induced by U46619 with higher efficacy than SQ29548, a common TP antagonist. The U46619-induced platelet aggregation was inhibited by Z-335 in a noncompetitive manner, while it was competitively inhibited by SQ29548. Z-335 inhibited U46619-induced vasoconstriction of rabbit aorta with higher efficacy than SQ29548. The pA2 value of Z-335 in aortic vasoconstriction was significantly higher than in platelet shape change. The competitive binding study showed the higher pKi value of Z-335 against [3H]-SQ29548 binding in rabbit aortic smooth muscle cells than in platelets. These data suggest that Z-335 has useful characteristics of TP antagonism.

Cell signaling pathways to αB-crystallin following stresses of the cytoskeleton

Small heat shock proteins (sHSPs) act as chaperone, but also in protecting the different cytoskeletal components. Recent results suggest that alphaB-crystallin, a member of sHSPs family, might regulate actin filament dynamics, stabilize them in a phosphorylation dependent manner, and protect the integrity of intermediate filaments (IF) against extracellular stress. We demonstrate that vinblastin and cytochalasin D, which respectively disorganize microtubules and actin microfilaments, trigger the activation of the p38/MAPKAP2 kinase pathway and lead to the specific alphaB-crystallin phosphorylation at serine 59. Upstream of p38, we found that RhoK, PKC and PKA are selectively involved in the activation of p38 and phosphorylation of alphaB-crystallin, depending on the cytoskeletal network disorganized. Moreover, we demonstrate that chronic perturbations of IF network result in the same activation of p38 MAPK and alphaB-crystallin phosphorylation, as with severe disorganization of other cytoskeletal networks. Finally, we also show that Ser 59 phosphorylated alphaB-crystallin colocalizes with cytoskeletal components. Thus, disturbance of cytoskeleton leads by converging signaling pathways to the phosphorylation of alphaB-crystallin, which probably acts as a protective effector of the cytoskeleton.

Cardiovascular pharmacology and physiology of the isoprostanes

F(2)-isoprostanes are a complex family of compounds produced from arachidonic acid via a free radical-catalyzed mechanism. Their quantification as a pathophysiological biomarker provides a unique opportunity to investigate lipid peroxidation in vascular diseases. Their measurement also provides an interesting biomarker for the rational dose selection of antioxidants in vascular diseases where oxidative stress might be involved. In addition to their use as biomarkers, some isoprostanes possess a biological activity. The 15-series F(2)- and E(2)-isoprostanes mediate vasoconstriction in different vascular beds and species. In addition, 15-F(2t)-IsoP induces smooth muscle cells mitogenesis and monocyte adhesion to endothelial cells. The data available supports but does not prove the hypothesis that isoprostanes are involved in vascular physiology and pathogenesis.

Homologous desensitization of signalling by the beta (β) isoform of the human thromboxane A2 receptor

Thromboxane (TX) A(2) is a potent stimulator of platelet activation/aggregation and smooth muscle contraction and contributes to a variety of pathologies within the vasculature. In this study, we investigated the mechanism whereby the cellular responses to TXA(2) mediated through the TPbeta isoform of the human TXA(2) receptor (TP) are dynamically regulated by examining the mechanism of agonist-induced desensitization of intracellular signalling and second messenger generation by TPbeta. It was established that TPbeta is subject to profound agonist-induced homologous desensitization of signalling (intracellular calcium mobilization and inositol 1,3,5 trisphosphate generation) in response to stimulation with the TXA(2) mimetic U46619 and this occurs through two key mechanisms: TPbeta undergoes partial agonist-induced desensitization that occurs through a GF 109203X-sensitive, protein kinase (PK)C mechanism whereby Ser(145) within intracellular domain (IC)(2) has been identified as the key phospho-target. In addition, TPbeta also undergoes more profound and sustained agonist-induced desensitization involving G protein-coupled receptor kinase (GRK)2/3-phosphorylation of both Ser(239) and Ser(357) within its IC(3) and carboxyl-terminal C-tail domains, respectively. Inhibition of phosphorylation of either Ser(239) or Ser(357), through site directed mutagenesis, impaired desensitization while mutation of both Ser(239) and Ser(357) almost completely abolished desensitization of signalling, GRK phosphorylation and beta-arrestin association, thereby blocking TPbeta internalization. These data suggest a model whereby agonist-induced PKC phosphorylation of Ser(145) partially impairs. TPbeta signalling while GRK2/3 phosphorylation at both Ser(239) and Ser(357) within its IC(3) and C-tail domains, respectively, sterically inhibits G-protein coupling, profoundly desensitizing signalling, and promotes beta-arrestin association and, in turn, facilitates TPbeta internalization. Thromboxane (TX) A(2) is a potent stimulator of platelet aggregation and smooth muscle contraction and contributes to a variety of vascular pathologies. Herein the mechanism whereby the cellular responses to TXA(2) mediated through the TPbeta isoform of the human TXA(2) receptor (TP) are dynamically regulated was investigated by examining the mechanism of its agonist-induced desensitization of intracellular signalling and second messenger generation. TPbeta is subject to profound agonist-induced homologous desensitization of signalling (intracellular calcium mobilization and inositol 1,3,5 trisphosphate generation) in response to stimulation with the TXA(2) mimetic U46619 and this occurs through two key mechanisms: TPbeta undergoes partial agonist-induced desensitization that occurs through a GF 109203X-sensitive, protein kinase (PK)C mechanism whereby Ser(145) within intracellular domain (IC)(2) was identified as the key phospho-target. In addition, TPbeta also undergoes more profound and sustained agonist-induced desensitization involving G protein-coupled receptor kinase (GRK)2/3-phosphorylation of both Ser(239) and Ser(357) within its IC(3) and carboxyl-terminal C-tail domains, respectively. Inhibition of phosphorylation of either Ser(239) or Ser(357), through site directed mutagenesis, impaired desensitization while mutation of both Ser(239) and Ser(357) almost completely abolished desensitization of signalling, GRK phosphorylation and beta-arrestin association, thereby blocking TPbeta internalization. These data suggest a model whereby agonist-induced PKC phosphorylation of Ser(145) partially impairs TPbeta signalling while GRK2/3 phosphorylation at both Ser(239) and Ser(357) within its IC(3) and C-tail domains, respectively, sterically inhibits G-protein coupling, profoundly desensitizing signalling, and promotes beta-arrestin association and, in turn, facilitates TPbeta internalization.

Synthetic peroxisome proliferator-activated receptor γ agonists rosiglitazone and troglitazone suppress transcription by promoter 3 of the human thromboxane A2 receptor gene in human erythroleukemia cells

The human thromboxane (TX)A2 receptor (TP) gene encodes two TP isoforms, TPalpha and TPbeta, that are regulated by distinct promoters designated promoter Prm1 and Prm3, respectively. Previous studies established that 15d-Delta12,14-prostaglandin J2 (15d-PGJ2) selectively inhibits Prm3 activity and TPbeta expression through a peroxisome proliferator-activated receptor (PPAR)gamma mechanism without affecting Prm1 activity or TPalpha expression in human megakaryocytic erythroleukemia (HEL) 92.1.7 cells. Herein, we investigated the effect of synthetic thiazolidinedione (TZD) PPARgamma ligands rosiglitazone and troglitazone on TP gene expression in HEL cells. Like 15d-PGJ2, both TZDs suppressed Prm3 activity, TPbeta mRNA expression and TP-mediated calcium mobilization without affecting Prm1 or TPalpha mRNA expression. However, unlike 15d-PGJ2, both TZDs mediated their PPARgamma-dependent effects through trans-repression of an activator protein-1 (AP-1) element, a site previously found to be critical for basal Prm3 activity. These data provide further evidence for the role of PPARgamma in regulating the human TP gene; they highlight further differences in TPalpha and TPbeta expression/regulation and point to essential differences between natural and synthetic PPARgamma agonists in mediating those effects.

Glycogen synthase kinase-3 phosphorylation, T-cell factor signaling activation, and cell morphology change following stimulation of thromboxane receptor alpha

Previous reports showed that activation of the thromboxane receptor (TP) induced some types of cells to proliferate. We report here that TPalpha activates beta-catenin/T-cell factor (Tcf)/lymphoid enhancer factor (Lef) pathway through phosphorylation of glycogen synthase kinase (GSK)-3. TP agonist [1S-alpha,2alpha(Z),3beta(1E,3S),4alpha]]-7-[3-[3-hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid (I-BOP) induced both alpha and beta forms of GSK-3 phosphorylation in human embryonic kidney (HEK)293 cells stably overexpressing TPalpha (HEK293-TPalpha). N-[2-(4-Bromocinnamylamino)ethyl]-5-isoquinoline (H89), a protein kinase A (PKA) inhibitor, totally blocked the phosphorylation of GSK-3, whereas wortmannin, a phosphatidylinositol 3-kinase (PI-3 kinase) inhibitor, partially attenuated it, suggesting that PKA as well as PI-3 kinase/Akt pathway were involved in TP-induced phosphorylation of GSK-3. I-BOP consistently stimulated an approximately 8-fold increase over basal Tcf/Lef reporter gene activity in HEK293-TPalpha cells. Furthermore, I-BOP-induced Tcf/Lef reporter gene activity was totally inhibited by H89 and partially inhibited by wortmannin. I-BOP also induced overexpression of Tcf/Lef downstream target gene cyclin D1. Blockade of the beta-catenin expression by small interfering RNA approach attenuated I-BOP-induced expression of cyclin D1, indicating that the induction was mediated by beta-catenin/Tcf/Lef pathway. Finally, I-BOP resulted in the morphology change, such as cell rounding and aggregation, in HEK293-TPalpha cells after 1-h incubation. However, HEK293-TPalpha cells were not able to revert back to normal shape even 24 h after the removal of the agonist, suggesting that the prolonged activation of the Tcf/Lef promoter induced downstream gene expression leading to cell permanent morphology change that was related to cell transformation. Together, our results showed for the first time TP agonist-induced phosphorylation of GSK-3 and activation of Tcf/Lef signaling leading to cell proliferation and transformation.

Associations of plasma 8-isoprostane levels with the presence and extent of coronary stenosis in patients with coronary artery disease

Oxidative stress may play a role in the development of atherosclerosis. The purpose of the present study was to explore the relationship between 8-isoprostaglandin F(2alpha) (8-iso-PGF(2alpha)) levels and the presence of coronary artery disease (CAD) and to also clarify whether 8-iso-PGF(2alpha) might add independently to measures of CAD extent. The study group consisted of 241 consecutive patients who were undergoing coronary angiography for suspected CAD. 8-iso-PGF(2alpha) levels were recorded for all participants. The analysis revealed a significant difference in 8-iso-PGF(2alpha) levels in patients with and without hypertension (P<0.001), in patients with diabetes relative to nondiabetic patients (P<0.05), and in males respect to females (P<0.001). A significant positive correlation was found between age and 8-iso-PGF(2alpha) levels (P<0.001). 8-iso-PGF(2alpha) levels correlated with the number of cardiovascular risk factors (P<0.001). 8-iso-PGF(2alpha) levels were higher in the CAD(+) respect to the CAD(-) groups (337.7+/-80.2 and 263.8+/-74.2 pg/ml and P<0.001). A stepwise elevation in the 8-iso-PGF(2alpha) levels was found depending on the number of affected vessels (P<0.001). The 8-iso-PGF(2alpha) levels showed a significant positive correlation with the numbers of >50 and >25% stenotic segments (P<0.001) and the extent score of coronary stenosis (P<0.001). The multivariate logistic regression analysis indicated 8-iso-PGF(2alpha) as an independent factor associated with CAD (odds ratio, 2.47 and P=0.001). The results suggested that 8-iso-PGF(2alpha) is associated with the presence of CAD in patients undergoing coronary angiography and is also related to the extent of coronary stenosis in Chinese population.

14-3-3zeta interacts with human thromboxane receptors and is involved in the agonist-induced activation of the extracellular-signal-regulated kinase

Thromboxane receptor (TP) signaling results in a broad range of cellular responses including kinase activation and subsequent nuclear signaling events involved in cell transformation, proliferation, and cell survival. Proteins that may participate in the early signaling following receptor activation remain to be identified. We found that 14-3-3zeta is a novel protein interacting with TP intracellular loop 3 (i3) by yeast two-hybrid system. This interaction was further confirmed by GST pull-down and co-immunoprecipitation methods. Site-directed mutagenesis studies indicated that Pro-236 of the TP-i3 was involved in the binding to the 14-3-3zeta. Co-immunoprecipitation studies in the same cell lysate by TP antibody showed that TP binds not only with the 14-3-3zeta but also with the Raf-1. Our data also demonstrated that TP receptor activation induced by agonist rapidly recruited 14-3-3zeta and Raf-1 to form a complex with the TP on the plasma membrane. The significance of assembling this protein complex was examined by TP agonist-induced extracellular-signal-regulated kinase (ERK) phosphorylation in intact cells. TP agonist, I-BOP, induced ERK phosphorylation in HEK 293 cells expressing wild type TPalpha but significantly lower in those expressing TPalpha-P236V mutant. Attenuation of the expression of 14-3-3zeta by 14-3-3zeta siRNA decreased I-BOP-induced ERK phosphorylation indicating the involvement of the 14-3-3zeta in the signal transduction process. These results suggest that 14-3-3zeta may serve as a scaffold protein to form a protein complex consisting of TP, 14-3-3zeta, and Raf-1, and that this protein complex may be involved in the activation of ERK pathway following TP receptor activation.

Different Pathways for Activation of Extracellular Signal-Regulated Kinase through Thromboxane A2 Receptor Isoforms

Thromboxane A2 receptor (TP) consists of two alternatively spliced isoforms, TPalpha and TPbeta, which differ in their cytoplasmic tails. In the present study, we examined the difference in signal transduction of TPalpha and TPbeta, using stably expressing cells of TPalpha and TPbeta. The cells expressing TPalpha (TPalpha-SC2) and TPbeta (TPbeta-SC15) were selected based on the similar binding sites of [3H]-SQ29548, a TP antagonist. U46619, a TP agonist, elicited phosphoinositide hydrolysis in TPalpha-SC2 and TPbeta-SC15 cells with a similar concentration-dependency. U46619 also caused the phosphorylation of extracellular signal-regulated kinase (ERK1/2) in both TPalpha-SC2 and TPbeta-SC15 cells. While the peak of the phosphorylation of ERK1/2 was observed 5 min after addition of U46619 in TPalpha-SC2 cells, the long lasting phosphorylation up to 60 min was in TPbeta-SC15 cells. U46619-induced phosphorylation of ERK1/2 at 5 min was inhibited by pertussis toxin in both cells, suggesting that G(i) is involved in the phosphorylation mediated via both TP isoforms. Interfering G(12/13) activity by overexpression of p115-RGS reduced U46619-induced ERK1/2 phosphorylation in TPbeta-SC15 cells, but not in TPalpha-SC2 cells. H89, an inhibitor of protein kinase A (PKA), reduced U46619-induced ERK1/2 phosphorylation in TPalpha-SC2 cells, but not in TPbeta-SC15 cells. These results indicate that G(i) may be involved in TP-mediated ERK1/2 phosphorylation in both isoforms. In addition, H89-sensitive kinase and G(12/13) may be involved in TP-mediated ERK1/2 phosphorylation in TPalpha and TPbeta, respectively.

Thromboxane A2 promotes interleukin-6 biosynthesis mediated by an activation of cyclic AMP-response element-binding protein in 1321N1 human astrocytoma cells

1321N1 human astrocytoma cells express thromboxane A2 (TXA2) receptors (TP). However, physiological consequences of TXA2 signaling in glial cells remain unclear. Herein, we show that TXA2 promotes interleukin-6 (IL-6) biosynthesis in glial cells. A TP agonist, 9,11-dideoxy-9alpha,11alpha-methanoepoxy-prosta-5Z,13E-dien-1-oic acid (U46619), enhanced IL-6 production in both 1321N1 cells and cultured mouse astrocytes. It has been shown that IL-6 gene expression is regulated by various transcription factors. Among them, we found a significant increase in cyclic AMP-response element-binding protein (CREB) activity with its phosphorylation at Ser133 by U46619 in 1321N1 cells. Although U46619 increased IL-6 promoter activity, a mutation at cyclic AMP-response element (CRE) on the promoter clearly suppressed the effect, suggesting that CRE is involved in U46619-induced IL-6 expression. Furthermore, both CREB and IL-6 promoter activities were suppressed by SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole], a p38 mitogen-activated protein kinase (MAPK) inhibitor, and H89 [N-[2-(4-bromocinnamylamino)-ethyl]-5-isoquinoline], a protein kinase A (PKA) inhibitor, indicating involvements of p38 MAPK and PKA in CREB activation and IL-6 expression. To determine which G-proteins are implicated in the U46619-induced IL-6 synthesis, the interfering mutants of Galpha(q), Galpha12, or Galpha13 by were overexpressed in 1321N1 cells adenoviral approach. It is noteworthy that the Galpha(q) or Galpha13 mutant blocked the IL-6 production by U46619. The constitutively active mutant of Galpha(q), Galpha12, or Galpha13 enhanced IL-6 production, indicating that Galpha(q) and Galpha13 were involved in U46619-induced IL-6 production. In conclusion, TXA2 enhances the IL-6 biosynthesis via the PKA p38 MAPK/CREB pathway in 1321N1 cells. IL-6 induction depends on Galpha(q) and Galpha13 as well. This is the first report showing TP-mediated IL-6 production in glial cells.

Les isoprostanes, biomarqueurs de peroxydation lipidique chez l'homme. Partie 3 : biomarqueurs et médiateurs en physiologie et pathologie vasculaire

The 15-series F(2)-isoprostanes mediate vasoconstriction in different vascular beds and species. This contraction is mediated by the thromboxane receptors stimulation, and may be modulated by the endothelium. Furthermore, 15-F(2t)-IsoP induces smooth muscle cells mitogenesis and monocyte adhesion to endothelial cells. Some 15-series E(2)-isoprostanes are more potent than F(2)-isoprostanes. In clinical studies, 15-F(2t)-IsoP levels are increased in vascular disorders involving atherosclerosis, ischemia-reperfusion and inflammation. F(2)-isoprostane levels correlate to the severity of heart failure and pulmonary hypertension, raising the potential prognostic interest of these biomarkers. Whether the effects observed in vitro are observed consistently in vivo at physiological concentrations and whether these effects contribute to pathological states in vivo is still debated.