Regulation of angiotensin II-induced phosphorylation of STAT3 in vascular smooth muscle cells

Ca2+ Signaling and Src Functions in Tumor Cells

Signaling by calcium ion (Ca2+) plays a prominent role in cell physiology, and these mechanisms are frequently altered in tumor cells. In this review, we consider the interplay of Ca2+ signaling and the functions of the proto-oncogene non-receptor tyrosine kinase c-Src in tumor cells, and the viral oncogenic variant v-Src in transformed cells. Also, other members of the Src-family kinases are considered in this context. The role of Ca2+ in the cell is frequently mediated by Ca2+-binding proteins, where the Ca2+-sensor protein calmodulin (CaM) plays a prominent, essential role in many cellular signaling pathways. Thus, we cover the available information on the role and direct interaction of CaM with c-Src and v-Src in cancerous cells, the phosphorylation of CaM by v-Src/c-Src, and the actions of different CaM-regulated Ser/Thr-protein kinases and the CaM-dependent phosphatase calcineurin on v-Src/c-Src. Finally, we mention some clinical implications of these systems to identify mechanisms that could be targeted for the therapeutic treatment of human cancers.

JAK/STAT pathway: Extracellular signals, diseases, immunity, and therapeutic regimens

Janus kinase/signal transduction and transcription activation (JAK/STAT) pathways were originally thought to be intracellular signaling pathways that mediate cytokine signals in mammals. Existing studies show that the JAK/STAT pathway regulates the downstream signaling of numerous membrane proteins such as such as G-protein-associated receptors, integrins and so on. Mounting evidence shows that the JAK/STAT pathways play an important role in human disease pathology and pharmacological mechanism. The JAK/STAT pathways are related to aspects of all aspects of the immune system function, such as fighting infection, maintaining immune tolerance, strengthening barrier function, and cancer prevention, which are all important factors involved in immune response. In addition, the JAK/STAT pathways play an important role in extracellular mechanistic signaling and might be an important mediator of mechanistic signals that influence disease progression, immune environment. Therefore, it is important to understand the mechanism of the JAK/STAT pathways, which provides ideas for us to design more drugs targeting diseases based on the JAK/STAT pathway. In this review, we discuss the role of the JAK/STAT pathway in mechanistic signaling, disease progression, immune environment, and therapeutic targets.

Low-Dose Tacrolimus Promotes the Migration and Invasion and Nitric Oxide Production in the Human-Derived First Trimester Extravillous Trophoblast Cells In Vitro

Placentation is one of the most important determinants for a successful pregnancy, and this is dependent on the process of trophoblast migration and invasion. Progesterone receptors (PGR) are critical effectors of progesterone (P4) signaling that is required for trophoblast migration and invasion conducive to a successful gestation. In immune complicated pregnancies, evidence has shown that abnormal placentation occurs because of aberrant expression of PGR. Therapeutic intervention with tacrolimus (FK506) was able to restore PGR expression and improve pregnancy outcomes in immune-complicated gestations; however, the exact mode of action of tacrolimus in assisting placentation is not clear. Here, we attempt to uncover the mode of action of tacrolimus by examining its effects on trophoblast invasion and migration in the human-derived extravillous trophoblast (EVT) cell line, the HTR-8/SVneo cells. Using a variety of functional assays, we demonstrated that low-dose tacrolimus (10 ng/mL) was sufficient to significantly (p < 0.001) stimulate the migration and invasion of the HTR-8/SVneo cells, inducing their cytosolic/nuclear progesterone receptor expression and activation, and modulating their Nitric Oxide (NO) production. Moreover, tacrolimus abrogated the suppressive effect of the NOS inhibitor Nω- Nitro-L-Arginine Methyl Ester (L-NAME) on these vital processes critically involved in the establishment of human pregnancy. Collectively, our data suggest an immune-independent mode of action of tacrolimus in positively influencing placentation in complicated gestations, at least in part, through promoting the migration and invasion of the first trimester extravillous trophoblast cells by modulating their NO production and activating their cytosolic/nuclear progesterone-receptors. To our knowledge, this is the first report to show that the mode of action of tacrolimus as a monotherapy for implantation failure is plausibly PGR-dependent.

Copy number amplification of ENSA promotes the progression of triple-negative breast cancer via cholesterol biosynthesis

Copy number alterations (CNAs) are pivotal genetic events in triple-negative breast cancer (TNBC). Here, our integrated copy number and transcriptome analysis of 302 TNBC patients reveals that gene alpha-endosulfine (ENSA) exhibits recurrent amplification at the 1q21.3 region and is highly expressed in TNBC. ENSA promotes tumor growth and indicates poor patient survival in TNBC. Mechanistically, we identify ENSA as an essential regulator of cholesterol biosynthesis in TNBC that upregulates the expression of sterol regulatory element-binding transcription factor 2 (SREBP2), a pivotal transcription factor in cholesterol biosynthesis. We confirm that ENSA can increase the level of p-STAT3 (Tyr705) and activated STAT3 binds to the promoter of SREBP2 to promote its transcription. Furthermore, we reveal the efficacy of STAT3 inhibitor Stattic in TNBC with high ENSA expression. In conclusion, the amplification of ENSA at the 1q21.3 region promotes TNBC progression and indicates sensitivity to STAT3 inhibitors.

Copy number alterations are pivotal genetic events in triple-negative breast cancer. Here the authors show the amplification of ENSA at the 1q21.3 region promotes the progression of TNBC via up-regulation of cholesterol biosynthesis.

Sphingosine 1-phosphate receptor type 2 positively regulates interleukin (IL)-4/IL-13-induced STAT6 phosphorylation

Previous reports have demonstrated that sphingosine 1-phosphate receptor type 2 (S1P₂) is involved in the activation of signal transducer and activator of transcription (STAT) 6. Additionally, the major signaling pathway of S1P₂ is the Rho-Rho kinase pathway. In this study, we examined the role of S1P₂ in STAT6 activation in a macrophage (Mφ) model using THP-1 cells differentiated with phorbol 12-myristate 13-acetate (PMA). We established S1P₂^knockout THP-1 cells using the CRISPR-Cas9 gene editing system. The PMA-treated S1P₂^knockout THP-1 Mφs showed decreases in IL-4/IL-13-induced phosphorylation of Janus-activated kinase (JAK) 1, JAK2, and STAT6 as well as mRNA expression of the M2 marker ARG1 compared with wild-type THP-1 Mφs. Pretreatment of PMA-treated THP-1 Mφs with the S1P₂ antagonist JTE-013, the Rho inhibitor Rhosin or the Rho kinase inhibitor Y27632 inhibited the IL-4/IL-13-induced increase in STAT6 phosphorylation. The expressions of suppressor of cytokine signaling 3 in the S1P₂^knockout THP-1 Mφs were higher than those in wild-type THP-1 Mφs. In addition, the protein tyrosine phosphatase inhibitor vanadate enhanced IL-4-induced STAT6 phosphorylation in the S1P₂^knockout THP-1 Mφs, suggesting that S1P₂-Rho-Rho kinase inhibited the negative regulation of STAT6. These results suggest that the S1P₂-Rho-Rho kinase pathway is necessary for full activation of STAT6 by IL-4/IL-13 in Mφs.

The Role of JAK/STAT Molecular Pathway in Vascular Remodeling Associated with Pulmonary Hypertension

Pulmonary hypertension is defined as a group of diseases characterized by a progressive increase in pulmonary vascular resistance (PVR), which leads to right ventricular failure and premature death. There are multiple clinical manifestations that can be grouped into five different types. Pulmonary artery remodeling is a common feature in pulmonary hypertension (PH) characterized by endothelial dysfunction and smooth muscle pulmonary artery cell proliferation. The current treatments for PH are limited to vasodilatory agents that do not stop the progression of the disease. Therefore, there is a need for new agents that inhibit pulmonary artery remodeling targeting the main genetic, molecular, and cellular processes involved in PH. Chronic inflammation contributes to pulmonary artery remodeling and PH, among other vascular disorders, and many inflammatory mediators signal through the JAK/STAT pathway. Recent evidence indicates that the JAK/STAT pathway is overactivated in the pulmonary arteries of patients with PH of different types. In addition, different profibrotic cytokines such as IL-6, IL-13, and IL-11 and growth factors such as PDGF, VEGF, and TGFβ1 are activators of the JAK/STAT pathway and inducers of pulmonary remodeling, thus participating in the development of PH. The understanding of the participation and modulation of the JAK/STAT pathway in PH could be an attractive strategy for developing future treatments. There have been no studies to date focused on the JAK/STAT pathway and PH. In this review, we focus on the analysis of the expression and distribution of different JAK/STAT isoforms in the pulmonary arteries of patients with different types of PH. Furthermore, molecular canonical and noncanonical JAK/STAT pathway transactivation will be discussed in the context of vascular remodeling and PH. The consequences of JAK/STAT activation for endothelial cells and pulmonary artery smooth muscle cells’ proliferation, migration, senescence, and transformation into mesenchymal/myofibroblast cells will be described and discussed, together with different promising drugs targeting the JAK/STAT pathway in vitro and in vivo.

The pleiotropic role of transcription factor STAT3 in oncogenesis and its targeting through natural products for cancer prevention and therapy

Signal transducer and activator of transcription 3 (STAT3) is one of the crucial transcription factors, responsible for regulating cellular proliferation, cellular differentiation, migration, programmed cell death, inflammatory response, angiogenesis, and immune activation. In this review, we have discussed the classical regulation of STAT3 via diverse growth factors, cytokines, G-protein-coupled receptors, as well as toll-like receptors. We have also highlighted the potential role of noncoding RNAs in regulating STAT3 signaling. However, the deregulation of STAT3 signaling has been found to be associated with the initiation and progression of both solid and hematological malignancies. Additionally, hyperactivation of STAT3 signaling can maintain the cancer stem cell phenotype by modulating the tumor microenvironment, cellular metabolism, and immune responses to favor drug resistance and metastasis. Finally, we have also discussed several plausible ways to target oncogenic STAT3 signaling using various small molecules derived from natural products.

STAT3: a multifaceted oncoprotein

Signal transducer and activator of transcription (STAT) 3 is a key signalling protein engaged by a multitude of growth factors and cytokines to elicit diverse biological outcomes including cellular growth, differentiation, and survival. The complete loss of STAT3 is not compatible with life and even partial loss of function mutations lead to debilitating pathologies like hyper IgE syndrome. Conversely, augmented STAT3 activity has been reported in as many as 50% of all human tumours. The dogma of STAT3 activity posits that it is a tyrosine phosphorylated transcription factor which modulates the expression of hundreds of genes. However, the regulation and biological consequences of STAT3 activation are far more complex. In addition to tyrosine phosphorylation, STAT3 is decorated with a plethora of post-translational modifications which regulate STAT3's nuclear function in addition to its non-genomic activities. In addition to these emerging complexities in the biochemical regulation of STAT3 activity, recent studies reveal that STAT3 is either oncogenic or a tumour suppressor. This review will explore these complexities.

Linking energy sensing to suppression of JAK-STAT signalling: A potential route for repurposing AMPK activators?

Exaggerated Janus kinase-signal transducer and activator of transcription (JAK-STAT) signalling is key to the pathogenesis of pro-inflammatory disorders, such as rheumatoid arthritis and cardiovascular diseases. Mutational activation of JAKs is also responsible for several haematological malignancies, including myeloproliferative neoplasms and acute lymphoblastic leukaemia. Accumulating evidence links adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK), an energy sensor and regulator of organismal and cellular metabolism, with the suppression of immune and inflammatory processes. Recent studies have shown that activation of AMPK can limit JAK-STAT-dependent signalling pathways via several mechanisms. These novel findings support AMPK activation as a strategy for management of an array of disorders characterised by hyper-activation of the JAK-STAT pathway. This review discusses the pivotal role of JAK-STAT signalling in a range of disorders and how both established clinically used and novel AMPK activators might be used to treat these conditions.

The complex roles of STAT3 and STAT5 in maintaining redox balance: Lessons from STAT-mediated xCT expression in cancer cells

STAT3 and STAT5 mediate diverse cellular processes, transcriptionally regulating gene expression and interacting with cytoplasmic proteins. Their canonical activity is stimulated by cytokines/growth factors through JAK-STAT signaling. As targets of oncogenes with intrinsic tyrosine kinase activity, STAT3 and STAT5 become constitutively active in hematologic neoplasms and solid tumors, promoting cell proliferation and survival and modulating redox homeostasis. This review summarizes reactive oxygen species (ROS)-regulated STAT activation and how STATs influence ROS production. ROS-induced effects on post-translational modifications are presented, and STAT3/5-mediated regulation of xCT, a redox-sensitive target up-regulated in numerous cancers, is discussed with regard to transcriptional cross-talk.

STAT3 targeting by polyphenols: Novel therapeutic strategy for melanoma

Melanoma or malignant melanocytes appear with the low incidence rate, but very high mortality rate worldwide. Epidemiological studies suggest that polyphenolic compounds contribute for prevention or treatment of several cancers particularly melanoma. Such findings motivate to dig out novel therapeutic strategies against melanoma, including research toward the development of new chemotherapeutic and biologic agents that can target the tumor cells by different mechanisms. Recently, it has been found that signal transducer and activator of transcription 3 (STAT3) is activated in many cancer cases surprisingly. Different evidences supply the aspect that STAT3 activation plays a vital role in the metastasis, including proliferation of cells, survival, invasion, migration, and angiogenesis. This significant feature plays a vital role in various cellular processes, such as cell proliferation and survival. Here, we reviewed the mechanisms of the STAT3 pathway regulation and their role in promoting melanoma. Also, we have evaluated the emerging data on polyphenols (PPs) specifically their contribution in melanoma therapies with an emphasis on their regulatory/inhibitory actions in relation to STAT3 pathway and current progress in the development of phytochemical therapeutic techniques. An understanding of targeting STAT3 by PPs brings an opportunity to melanoma therapy. © 2016 BioFactors, 43(3):347-370, 2017.

Decreased STAT3 Phosphorylation Mediates Cell Swelling in Ammonia-Treated Astrocyte Cultures

Brain edema, due largely to astrocyte swelling, and the subsequent increase in intracranial pressure and brain herniation, are major complications of acute liver failure (ALF). Elevated level of brain ammonia has been strongly implicated in the development of astrocyte swelling associated with ALF. The means by which ammonia brings about astrocyte swelling, however, is incompletely understood. Recently, oxidative/nitrosative stress and associated signaling events, including activation of mitogen-activated protein kinases (MAPKs), as well as activation of the transcription factor, nuclear factor-kappaB (NF-κB), have been implicated in the mechanism of ammonia-induced astrocyte swelling. Since these signaling events are known to be regulated by the transcription factor, signal transducer and activator of transcription 3 (STAT3), we examined the state of STAT3 activation in ammonia-treated cultured astrocytes, and determined whether altered STAT3 activation and/or protein expression contribute to the ammonia-induced astrocyte swelling. STAT3 was found to be dephosphorylated (inactivated) at Tyrosine705 in ammonia-treated cultured astrocytes. Total STAT3 protein level was also reduced in ammonia-treated astrocytes. We also found a significant increase in protein tyrosine phosphatase receptor type-1 (PTPRT-1) protein expression in ammonia-treated cultured astrocytes, and that inhibition of PTPRT-1 enhanced the phosphorylation of STAT3 after ammonia treatment. Additionally, exposure of cultured astrocytes to inhibitors of protein tyrosine phosphatases diminished the ammonia-induced cell swelling, while cultured astrocytes over-expressing STAT3 showed a reduction in the astrocyte swelling induced by ammonia. Collectively, these studies strongly suggest that inactivation of STAT3 represents a critical event in the mechanism of the astrocyte swelling associated with acute liver failure.

Suspension survival mediated by PP2A-STAT3-Col XVII determines tumour initiation and metastasis in cancer stem cells

Targeting tumour-initiating cells (TICs) would lead to new therapies to cure cancer. We previously demonstrated that TICs have the capacity to survive under suspension conditions, while other cells undergo anoikis. Here we show that TICs exhibit increased phosphorylation levels of S727STAT3 because of PP2A inactivation. Collagen 17 gene expression is upregulated in a STAT3-dependent manner, which also stabilizes laminin 5 and engages cells to form hemidesmosome-like junctions in response. Blocking the PP2A-S727STAT3-collagen 17 pathway inhibits the suspension survival of TICs and their ability to form tumours in mice, while activation of the same pathway increases the suspension survival and tumour-initiation capacities of bulk cancer cells. The S727STAT3 phosphorylation levels correlate with collagen 17 expression in colon tumour samples, and correlate inversely with survival. Finally, this signalling axis enhances the ability of TIC to form tumours in mouse models of malignant lung cancer pleural effusion and spontaneous colon cancer metastasis.

Hyperglycemia and angiotensin II cooperate to enhance collagen I deposition by cardiac fibroblasts through a ROS-STAT3-dependent mechanism

Cardiac fibroblasts significantly contribute to diabetes-induced structural and functional changes in the myocardium. The objective of the present study was to determine the effects of high glucose (alone or supplemented with angiotensin II) in the activation of the JAK2/STAT3 pathway and its involvement in collagen I production by cardiac fibroblasts. We observed that the diabetic environment 1) enhanced tyrosine phosphorylation of JAK2 and STAT3; 2) induced nuclear localization of tyrosine phosphorylated STAT3 through a reactive oxygen species-mediated mechanism, with angiotensin II stimulation further enhancing STAT3 nuclear accumulation; and 3) stimulated collagen I production. The effects were inhibited by depletion of reactive oxygen species or silencing of STAT3 in high glucose alone or supplemented with exogenous angiotensin II. Combined, our data demonstrate that increased collagen I deposition in the setting of high glucose occurred through a reactive oxygen species- and STAT3-dependent mechanism. Our results reveal a novel role for STAT3 as a key signaling molecule of collagen I production in cardiac fibroblasts exposed to a diabetic environment.

STAT3 signaling in pulmonary arterial hypertension

Pulmonary artery hypertension (PAH) is a proliferative disorder associated with enhanced pulmonary artery smooth muscle cell proliferation and suppressed apoptosis. The sustainability of this phenotype requires the activation of pro-survival transcription factor like the signal transducers and activators of transcription-3 (STAT3). Using multidisciplinary and translational approaches, we and others have demonstrated that STAT3 activation in both human and experimental models of PAH accounts for the modulation of the expression of several proteins already known as implicated in PAH pathogenesis, as well as for signal transduction to other transcription factors. Furthermore, recent data demonstrated that STAT3 could be therapeutically targeted in different animal models and some molecules are actually in clinical trials for cancer or PAH treatment.

Transcription Factor STAT3 as a Novel Molecular Target for Cancer Prevention

Signal Transducers and Activators of Transcription (STATs) are a family of transcription factors that regulate cell proliferation, differentiation, apoptosis, immune and inflammatory responses, and angiogenesis. Cumulative evidence has established that STAT3 has a critical role in the development of multiple cancer types. Because it is constitutively activated during disease progression and metastasis in a variety of cancers, STAT3 has promise as a drug target for cancer therapeutics. Recently, STAT3 was found to have an important role in maintaining cancer stem cells in vitro and in mouse tumor models, suggesting STAT3 is integrally involved in tumor initiation, progression and maintenance. STAT3 has been traditionally considered as nontargetable or undruggable, and the lag in developing effective STAT3 inhibitors contributes to the current lack of FDA-approved STAT3 inhibitors. Recent advances in cancer biology and drug discovery efforts have shed light on targeting STAT3 globally and/or specifically for cancer therapy. In this review, we summarize current literature and discuss the potential importance of STAT3 as a novel target for cancer prevention and of STAT3 inhibitors as effective chemopreventive agents.

GSTpi protects against angiotensin II-induced proliferation and migration of vascular smooth muscle cells by preventing signal transducer and activator of transcription 3 activation

Angiotensin II (Ang II)-elicited excessive proliferation, hypertrophy and migration of vascular smooth muscle cells (VSMCs) are vital to the pathogenesis of atheroclerosis. Glutathione S-transferase pi (GSTpi) exists extensively in various kinds of cells and protects cells against different stresses. However, knowledge remains limited about what GSTpi acts in VSMCs. We investigated the effect of GSTpi on Ang II-induced VSMC proliferation, hypertrophy and migration and its latent mechanism. Overexpression and RNAi experiments demonstrated that GSTpi inhibited Ang II-induced proliferation, hypertrophy and migration of VSMCs and arrested progression of cell cycle from G0/G1 to S phase. Immunoprecipitation, mass spectrometry and confocal microscopy analyses showed that GSTpi directly associated with signal transducer and activator of transcription 3 (STAT3) to prevent Ang II-triggered binding of Src to STAT3 and thus suppressed Ang II-stimulated phosphorylation and nuclear translocation of STAT3, as well as cyclin D1 expression. In contrast, GSTpi didn't affect Ang II-activated extracellular signal-regulated kinase (ERK1/2). GSTpi acts as a negative regulator to prevent Ang II-triggered proliferative signaling in VSMCs, suggesting that it may protect vessels against the stresses associated with atherosclerosis formation.

Role of STAT3 in cancer metastasis and translational advances

Signal transducer and activator of transcription 3 (STAT3) is a latent cytoplasmic transcription factor, originally discovered as a transducer of signal from cell surface receptors to the nucleus. It is activated by tyrosine phosphorylation at position 705 leading to its dimerization, nuclear translocation, DNA binding, and activation of gene transcription. Under normal physiological conditions, STAT3 activation is tightly regulated. However, compelling evidence suggests that STAT3 is constitutively activated in many cancers and plays a pivotal role in tumor growth and metastasis. It regulates cellular proliferation, invasion, migration, and angiogenesis that are critical for cancer metastasis. In this paper, we first describe the mechanism of STAT3 regulation followed by how STAT3 is involved in cancer metastasis, then we summarize the various small molecule inhibitors that inhibit STAT3 signaling.

Signal transducer and activator of transcription 3 (STAT3) degradation by proteasome controls a developmental switch in neurotrophin dependence

Neonatal brains develop through a program that eliminates about half of the neurons. During this period, neurons depend on neurotrophins for their survival. Recently, we reported that, at the conclusion of the naturally occurring death period, neurons become neurotrophin-independent and, further, that this developmental switch is achieved by the emergence of a second survival pathway mediated by signal transducer and activator of transcription 3 (STAT3). Here I show that calcineurin plays a key role in controlling the developmental switch in mouse hippocampal neurons. Calcineurin promotes the degradation of STAT3 via the ubiquitin-proteasome pathway. Inhibition of calcineurin acutely increases total levels of STAT3 as well as its activated forms, resulting in decreased levels of the tumor suppressor p53 and its proapoptotic target, Bax. In vivo and in vitro, calcineurin regulates levels of STAT3 and neurotrophin dependence. TMF/ARA 160 (TATA element modulatory factor/androgen receptor co-activator 160), the key mediator of STAT3 ubiquitination, is required for calcineurin-dependent STAT3 degradation. Thus, these results show that the ubiquitin-proteasome pathway controls the critical developmental switch of neurotrophin dependence in the newborn hippocampus.

Selenate enhances STAT3 transcriptional activity in endothelial cells: differential actions of selenate and selenite on LIF cytokine signaling and cell viability

Sodium selenate may have utility in treating Alzheimer's disease and diabetes; however, its impact on the associated proinflammatory cytokine signaling of endothelial cells has not been investigated. We report that treatment of human microvascular endothelial cells with sodium selenate at a pharmacological dose (100 μM) enhanced tyrosine phosphorylation of nuclear STAT3 on Y705 in response to IL-6-type cytokine, leukemia inhibitory factor (LIF), indicative of enhanced STAT3 activity. Accordingly, STAT3 nuclear binding to DNA was increased, as well as LIF-induced gene expression of chemokine (C-C motif) ligand 2 (CCL2). CCL2 plays a key role in inflammatory processes associated with neuronal degenerative and vascular diseases. The enhancing action of selenate on LIF-induced STAT3 Y705 phosphorylation was replicated by vanadate and a specific inhibitor of protein tyrosine phosphatase, non-receptor type 1 (PTP1B). Moreover, we observed that selenite, the cellular reduction bioproduct of selenate but not selenate itself, inhibited enzymatic activity of human recombinant PTP1B. Our findings support the conclusion that in human microvascular endothelial cells selenate has a vanadate-like effect in inhibiting PTP1B and enhancing proinflammatory STAT3 activation. These findings raise the possibility that beneficial actions of supranutritional levels of selenate for treating Alzheimer's and diabetes may be offset by a proinflammatory action on endothelial cells.

Calyculin A reveals serine/threonine phosphatase protein phosphatase 1 as a regulatory nodal point in canonical signal transducer and activator of transcription 3 signaling of human microvascular endothelial cells

Vascular inflammation is initiated by stimuli acting on endothelial cells. A clinical feature of vascular inflammation is increased circulating interleukin 6 (IL-6) type cytokines such as leukemia inhibitory factor (LIF), but their role in vascular inflammation is not fully defined. IL-6 type cytokines activate transcription factor signal transducer and activator of transcription 3 (STAT3), which has a key role in inflammation and the innate immune response. Canonical STAT3 gene induction is due to phosphorylation of (1) Y705, leading to STAT3 dimerization and DNA binding and (2) S727, enhancing homodimerization and DNA binding by recruiting p300/CBP. We asked whether enhancing S727 STAT3 phosphorylation using the protein phosphatase 1 (PP1) inhibitor, calyculin A, would enhance LIF-induced gene expression in human microvascular endothelial cells (HMEC-1). Cotreatment with calyculin A and LIF markedly increased STAT3 S727 phosphorylation, without affecting the increase in the nuclear fraction of STAT3 phosphorylated on Y705. PP2A inhibitors, okadaic acid and fostriecin, did not enhance STAT3 S727 phosphorylation. Surprisingly, calyculin A eliminated LIF-induced gene expression: (1) calyculin A reduced binding of nuclear extracts to a STAT3 consensus site, thereby reducing the overall level of binding observed with LIF; and (2) calyculin A caused p300/CBP phosphorylation, thus resulting in reduced acetylation activity and degradation. Together, these findings reveal a pivotal role of a protein serine/threonine phosphatases that is likely PP1 in HMEC in controlling STAT3 transcriptional activity.

NADPH-oxidase-dependent reactive oxygen species mediate EGFR transactivation by FPRL1 in WKYMVm-stimulated human lung cancer cells

Cross talk between unrelated cell surface receptors, such as G-protein-coupled receptors (GPCR) and receptor tyrosine kinases (RTK), is a crucial signaling mechanism to expand the cellular communication network. We investigated the ability of the GPCR formyl peptide receptor-like 1 (FPRL1) to transactivate the RTK epidermal growth factor receptor (EGFR) in CaLu-6 cells. We observed that stimulation with WKYMVm, an FPRL1 agonist isolated by screening synthetic peptide libraries, induces EGFR tyrosine phosphorylation, p47(phox) phosphorylation, NADPH-oxidase-dependent superoxide generation, and c-Src kinase activity. As a result of EGFR transactivation, phosphotyrosine residues provide docking sites for recruitment and triggering of the STAT3 pathway. WKYMVm-induced EGFR transactivation is prevented by the FPRL1-selective antagonist WRWWWW, by pertussis toxin (PTX), and by the c-Src inhibitor PP2. The critical role of NADPH-oxidase-dependent superoxide generation in this cross-talk mechanism is corroborated by the finding that apocynin or a siRNA against p22(phox) prevents EGFR transactivation and c-Src kinase activity. In addition, WKYMVm promotes CaLu-6 cell growth, which is prevented by PTX and by WRWWWW. These results highlight the role of FPRL1 as a potential target of new drugs and suggest that targeting both FPRL1 and EGFR may yield superior therapeutic effects compared with targeting either receptor separately.

Jak2-Independent Activation of Stat3 by Intracellular Angiotensin II in Human Mesangial Cells

Ang II is shown to mediate the stimulatory effect of high glucose on TGF-b1 and extracellular matrix proteins in glomerular mesangial cells. Also inhibition of Ang II formation in cell media (extracellular) and lysates (intracellular) blocks high-glucose effects on TGF-b1 and matrix more effectively compared to inhibition of extracellular Ang II alone. To investigate whether intracellular Ang II can stimulate TGF-b1 and matrix independent of extracellular Ang II, cultured human mesangial cells were transfected with Ang II to increase intracellular Ang II levels and its effects on TGF-b1 and matrix proteins were determined. Prior to transfection, cells were treated with candesartan to block extracellular Ang II-induced responses via cell membrane AT1 receptors. Transfection of cells with Ang II resulted in increased levels of intracellular Ang II which was accompanied by increased production of TGF-b1, collagen IV, fibronectin, and cell proliferation as well. On further examination, intracellular Ang II was found to activate Stat3 transcription factor including increased Stat3 protein expression, tyrosine 705 phosphorylation, and DNA-binding activity. Treatment with AG-490, an inhibitor of Jak2, did not block intracellular Ang II-induced Stat3 phosphorylation at tyrosine 705 residue indicating a Jak2-independent mechanism used by intracellular Ang II for Stat3 phosphorylation. In contrast, extracellular Ang II-induced tyrosine 705 phosphorylation of Stat3 was inhibited by AG-490 confirming the presence of a Jak2-dependent pathway. These findings suggest that intracellular Ang II increases TGF-b1 and matrix in human mesangial cells and also activates Stat3 transcription factor without involvement of the extracellular Ang II signaling pathway.

Targeting of protein phosphatases PP2A and PP2B to the C-terminus of the L-type calcium channel Ca v1.2

The L-type Ca(2+) channel Ca(v)1.2 forms macromolecular signaling complexes that comprise the β(2) adrenergic receptor, trimeric G(s) protein, adenylyl cyclase, and cAMP-dependent protein kinase (PKA) for efficient signaling in heart and brain. The protein phosphatases PP2A and PP2B are part of this complex. PP2A counteracts increase in Ca(v)1.2 channel activity by PKA and other protein kinases, whereas PP2B can either augment or decrease Ca(v)1.2 currents in cardiomyocytes depending on the precise experimental conditions. We found that PP2A binds to two regions in the C-terminus of the central, pore-forming α(1) subunit of Ca(v)1.2: one region spans residues 1795-1818 and the other residues 1965-1971. PP2B binds immediately downstream of residue 1971. Injection of a peptide that contained residues 1965-1971 and displaced PP2A but not PP2B from endogenous Ca(v)1.2 increased basal and isoproterenol-stimulated L-type Ca(2+) currents in acutely isolated cardiomyocytes. Together with our biochemical data, these physiological results indicate that anchoring of PP2A at this site of Ca(v)1.2 in the heart negatively regulates cardiac L-type currents, likely by counterbalancing basal and stimulated phosphorylation that is mediated by PKA and possibly other kinases.

Multi-component signaling complexes of the delta-opioid receptor with STAT5B and G proteins

Besides mediating opioid responses in the nervous system and the peripheral tissues, opioid receptors are implicated in signaling mechanisms shared by cytokine receptors. Recent observations have shown that the Signal Transducer and Activator of Transcription 5A (STAT5A) interacts with the mu-opioid receptor (mu-OR) and is phosphorylated upon mu-OR stimulation (Mazarakou and Georgoussi, 2005). In the present study we demonstrate that another member of the STAT family, STAT5B, associates constitutively with the C-terminal tail of the delta-opioid receptor (delta-CT). [D-Ser(2), Leu(5), Thr(6)]-enkephalin-exposure of HEK293 cells, expressing stably the delta-opioid receptor (delta-OR), leads to receptor-dependent STAT5B tyrosine phosphorylation and transcriptional activation. This phosphorylation occurs in a G protein-dependent manner and is carried out by a c-Src kinase. Co-immunoprecipitation studies indicate that STAT5B forms pairs with selective Galpha and Gbetagamma subunits of G proteins and activated c-Src kinase in HEK293 cells. These interactions are formed either constitutively, or upon receptor stimulation. We also demonstrate that the delta-CT serves as a platform for the formation of a multi-component signaling complex (signalosome), consisting of STAT5B, c-Src and selective G protein members. We can thus conclude that STAT5B signaling can be modulated by its coupling with a specific subset of G protein subunits, revealing a novel signaling mechanism for the transcriptional regulation of STAT5B-dependent genes.

Deregulated NFATc1 activity transforms murine fibroblasts via an autocrine growth factor-mediated Stat3-dependent pathway

The nuclear factor of activated T cells (NFAT) family of transcription factors has recently been implicated with a role in tumorigenesis. Forced expression of a constitutively active NFATc1 mutant (caNFATc1) has been shown to transform immortalized murine fibroblasts in vitro, while constitutive activation of the NFAT-signaling pathway has been found in a number of human cancers, where it has been shown to contribute towards various aspects of the tumor phenotype. Here we have investigated the molecular mechanisms underlying the oncogenic potential of deregulated NFAT activity. We now show that ectopic expression of caNFATc1 in murine 3T3-L1 fibroblasts induces the secretion of an autocrine factor(s) that is sufficient to promote the transformed phenotype. We further demonstrate that this NFATc1-induced autocrine factor(s) specifically induces the tyrosine phosphorylation of the Stat3 transcription factor via a JAK kinase-dependent pathway. Interestingly, this effect of sustained NFAT signaling on the autocrine growth factor-mediated activation of Stat3 is not restricted to murine fibroblasts, but is also observed in the PANC-1 and MCF10A human cell lines. Most importantly, we find that the shRNA-mediated depletion of endogenous Stat3 significantly attenuates the ability of caNFATc1 to transform 3T3-L1 fibroblasts. Taken together, our results afford significant new insights into the molecular mechanisms underlying the oncogenic potential of deregulated NFATc1 activity by demonstrating that constitutive NFATc1 activity transforms cells via an autocrine factor-mediated pathway that is critically dependent upon the activity of the Stat3 transcription factor.

Signal transducer and activator of transcription-3, inflammation, and cancer: how intimate is the relationship?

Signal transducer and activator of transcription-3 (STAT-3) is one of six members of a family of transcription factors. It was discovered almost 15 years ago as an acute-phase response factor. This factor has now been associated with inflammation, cellular transformation, survival, proliferation, invasion, angiogenesis, and metastasis of cancer. Various types of carcinogens, radiation, viruses, growth factors, oncogenes, and inflammatory cytokines have been found to activate STAT-3. STAT-3 is constitutively active in most tumor cells but not in normal cells. Phosphorylation of STAT-3 at tyrosine 705 leads to its dimerization, nuclear translocation, DNA binding, and gene transcription. The phosphorylation of STAT-3 at serine 727 may regulate its activity negatively or positively. STAT-3 regulates the expression of genes that mediate survival (survivin, bcl-xl, mcl-1, cellular FLICE-like inhibitory protein), proliferation (c-fos, c-myc, cyclin D1), invasion (matrix metalloproteinase-2), and angiogenesis (vascular endothelial growth factor). STAT-3 activation has also been associated with both chemoresistance and radioresistance. STAT-3 mediates these effects through its collaboration with various other transcription factors, including nuclear factor-kappaB, hypoxia-inducible factor-1, and peroxisome proliferator activated receptor-gamma. Because of its critical role in tumorigenesis, inhibitors of this factor's activation are being sought for both prevention and therapy of cancer. This has led to identification of small peptides, oligonucleotides, and small molecules as potential STAT-3 inhibitors. Several of these small molecules are chemopreventive agents derived from plants. This review discusses the intimate relationship between STAT-3, inflammation, and cancer in more detail.

Signal transducer and activator of transcription-3, inflammation, and cancer: how intimate is the relationship?

Signal transducer and activator of transcription-3 (STAT-3) is one of six members of a family of transcription factors. It was discovered almost 15 years ago as an acute-phase response factor. This factor has now been associated with inflammation, cellular transformation, survival, proliferation, invasion, angiogenesis, and metastasis of cancer. Various types of carcinogens, radiation, viruses, growth factors, oncogenes, and inflammatory cytokines have been found to activate STAT-3. STAT-3 is constitutively active in most tumor cells but not in normal cells. Phosphorylation of STAT-3 at tyrosine 705 leads to its dimerization, nuclear translocation, DNA binding, and gene transcription. The phosphorylation of STAT-3 at serine 727 may regulate its activity negatively or positively. STAT-3 regulates the expression of genes that mediate survival (survivin, bcl-xl, mcl-1, cellular FLICE-like inhibitory protein), proliferation (c-fos, c-myc, cyclin D1), invasion (matrix metalloproteinase-2), and angiogenesis (vascular endothelial growth factor). STAT-3 activation has also been associated with both chemoresistance and radioresistance. STAT-3 mediates these effects through its collaboration with various other transcription factors, including nuclear factor-kappaB, hypoxia-inducible factor-1, and peroxisome proliferator activated receptor-gamma. Because of its critical role in tumorigenesis, inhibitors of this factor's activation are being sought for both prevention and therapy of cancer. This has led to identification of small peptides, oligonucleotides, and small molecules as potential STAT-3 inhibitors. Several of these small molecules are chemopreventive agents derived from plants. This review discusses the intimate relationship between STAT-3, inflammation, and cancer in more detail.

HDAC3 influences phosphorylation of STAT3 at serine 727 by interacting with PP2A

Signal transducer and activator of transcription 3 (STAT3), which mediates biological actions in many physiological processes, is activated by cytokines and growth factors, and has been reported to be involved in the pathogenesis of various human diseases. Here, we show that treatment of HeLa cells with a histone deacetylase (HDAC) inhibitor, trichostatin A, or small-interfering RNA (siRNA)-mediated repression of HDAC3, enhances phosphorylation of STAT3 at Ser727. Furthermore, dephosphorylation of STAT3 at Ser727 by protein phosphatase 2A (PP2A) was restored by treatment of cells with HDAC3 siRNA. We further found that formation of a complex between STAT3 and PP2A was enhanced in the presence of HDAC3. Importantly, small-interfering RNA-mediated repression of both HDAC3 and PP2A effectively enhanced leukemia inhibitory factor (LIF)-induced STAT3 activation. These results indicate that HDAC3 may act as a scaffold protein for PP2A to regulate the LIF/STAT3-mediated signaling pathway.

Ethanol inhibition of angiotensin II-stimulated Tyr705 and Ser727 STAT3 phosphorylation in cultured rat hepatocytes: relevance to activation of p42/44 mitogen-activated protein kinase

Angiotensin (Ang) II-stimulated phosphorylation of signal transducer and activator transcription (STAT) 3 in rat hepatocytes and the effects of ethanol on this activation were investigated. Angiotensin II (100 nM) stimulated Tyr705 and Ser727 phosphorylation of STAT3 and formation of sis-inducing factor complexes. In the presence of U-0126 (10microM), a p42/44 mitogen-activated protein kinase (MAPK) kinase inhibitor, Ang II further increased Tyr705 phosphorylation of STAT3 but completely abrogated Ser727 phosphorylation of STAT3. Inhibition of p42/44MAPK also increased STAT3 DNA-binding activity. Pretreatment with ethanol (100mM) for 24h resulted in decrease in Tyr705 phosphorylation of STAT3 by ethanol alone and inhibition of Tyr705 phosphorylation of STAT3 stimulated by Ang II. Although ethanol potentiates Ang II stimulated p42/44 MAPK activation in hepatocytes, ethanol inhibited Ser727 phosphorylation of STAT3 stimulated by Ang II. Angiotensin II-stimulated STAT3-binding activity was not significantly affected by ethanol treatment. These results suggest a negative regulation of Ang II-stimulated STAT3 tyrosine phosphorylation and STAT3-binding activity through p42/44 MAPK activation in hepatocytes. However, ethanol modulation of Ang II-stimulated STAT3 phosphorylation occurs by MAPK independent mechanisms. Ethanol potentiation of MAPK signaling without suppression of STAT3 function may modulate the course of alcoholic liver injury.

Alpha-1 adrenergic receptor transactivates signal transducer and activator of transcription-3 (Stat3) through activation of Src and epidermal growth factor receptor (EGFR) in hepatocytes

Hepatocytes express adrenergic receptors (ARs) that modulate several functions, including liver regeneration, hepatocyte proliferation, glycogenolysis, gluconeogenesis, synthesis of urea and fatty acid metabolism. Adrenergic hepatic function in adults is mainly under the control of alpha(1)-ARs; however, the mechanism through which they influence diverse processes remains incompletely understood. This study describes a novel alpha(1)-AR-mediated transactivation of signal transducer and activator of transcription-3 (Stat3) in primary and transformed hepatocytes. Treatment of primary rat hepatocytes with the alpha(1)-AR agonist, phenylephrine (PE), induced a rapid phosphorylation of Stat3. PE also increased Stat3 phosphorylation, DNA binding and transcription activity in transformed human hepatocellular carcinoma cells (Hep3B). The PE-induced Stat3 phosphorylation, DNA binding and reporter activity were completely blocked by the selective alpha(1)-AR antagonist, prazosin. In addition, transfection of Hep3B cells with human alpha(1B)-AR expression vector also enhanced Stat3 phosphorylation and reporter activity. Moreover, overexpression of RGS2, a protein inhibitor of G(q/11) signaling, blocked PE-induced Stat3 phosphorylation and reporter activity. The observations that PE induced the formation of c-Src-Stat3 binding complex and phosphorylation of epidermal growth factor receptor (EGFR) and that inhibiting Src and EGFR prevented PE-induced Stat3 activation indicate the involvement of Src and EGFR. Taken together, these observations demonstrate a novel alpha(1)-AR-mediated Stat3 activation that involves G(q/11), Src, and EGFR in hepatic cells.

Platelet-derived growth factor-induced stabilization of cyclooxygenase 2 mRNA in rat smooth muscle cells requires the c-Src family of protein-tyrosine kinases

Cyclooxygenases (COXs) are crucial rate-limiting enzymes required for the biosynthesis of prostaglandins. COX-2 is an inducible isoform of this enzyme, which is believed to play important roles in the development of atherosclerotic vascular disease. We found that COX-2 expression rapidly increases in response to various signaling events, including activation of the platelet-derived growth factor (PDGF) pathway. Activation of PDGF receptor (PDGFR) in rat aortic vascular smooth muscle cells leads to c-Src-dependent stabilization of COX-2 mRNA requiring an AU-rich region within the 3'-untranslated region of this transcript. This regulation correlates with tyrosine phosphorylation of the RNA-associated protein, CUG-binding protein 2 (CUGBP2), which appears to enhance its interaction with COX-2 mRNA. Site-directed mutagenesis of putative tyrosine phosphorylation sites in CUGBP2 identified tyrosine 39 as a c-Src target, and a CUGBP2 with a mutated tyrosine 39 displayed an attenuated ability to bind COX-2 mRNA. We further show that silencing of CUGBP2 with specific small interference RNAs significantly reduces PDGF-dependent induction of COX-2 at both mRNA and protein levels. Furthermore, forced expression of CUGBP2 or constitutively active c-Src leads to stabilization of co-expressed COX-2 mRNA. Finally, in vitro RNA decay assay demonstrates that CUGBP2 is functionally required for the stabilization of COX-2 mRNA. Therefore, our data suggest that tyrosine phosphorylation of CUGBP2 is an important underlying mechanism for the ability of PDGFR/c-Src signaling to control the stability of COX-2 mRNA.

Nuclear translocation of calcineurin Aβ but not calcineurin Aα by platelet-derived growth factor in rat aortic smooth muscle

Calcineurin regulates the proliferation of many cell types through activation of the nuclear factor of activated T cells (NFAT). Two main isoforms of the calcineurin catalytic subunit [calcineurin A (CnA)α and CnAβ] have been identified, although their expression and function are largely unknown in smooth muscle. Western blot analysis and confocal imaging were performed in freshly isolated and cultured rat aortic myocytes to identify these CnA isoforms and elucidate the effect of PDGF on their cellular distribution and interaction with NFAT isoforms. CnAα and CnAβ isoforms displayed differential cellular distribution, with CnAα being evenly distributed between the nucleus and cytosol and CnAβ being restricted to the cytosol. In contrast with the rat brain, we found no evidence for particulate/membrane localization of calcineurin. PDGF caused significant nuclear translocation of CnAβ and induced smooth muscle cell proliferation, with both effects being abrogated by the calcineurin inhibitor cyclosporin A, the novel NFAT inhibitors A-285222 and inhibitor of NFAT-calcineurin association-6, and the adenylyl cyclase activator forskolin. PDGF also caused cyclosporin A-sensitive translocation of NFATc3, with no apparent effect on either CnAα or NFATc1 distribution. Moreover, ∼87% of nuclear CnAβ was found to colocalize with NFATc3, consistent with the finding that CnAβ bound more avidly than CnAα to a glutathione S-transferase-NFATc3 fusion protein. Based on their differential distribution in aortic muscle, our results suggest that CnAα and CnAβ are likely to have different cellular functions. However, CnAβ appears to be specifically activated by PDGF, and we postulate that calcineurin-dependent nuclear translocation of NFATc3 is involved in smooth muscle proliferation induced by this mitogen.

Prostanoid- and interleukin-1-induced primary genes in cementoblastic cells

BACKGROUND

Cementum is a key component of a functional periodontal organ. However, regenerating lost cementum is difficult and often incomplete. Identifying molecular mediators of cementoblast differentiation and function should lead to better targeted treatment for periodontitis. Prostaglandins increase mineralization of murine cementoblastic OCCM cells and alveolar bone formation, whereas the cytokine interleukin-1 (IL-1) inhibits alveolar bone formation. We hypothesized that differentially induced primary genes in OCCM cells may mediate anabolic and catabolic responses. Our objective was to identify primary genes differentially induced by the synthetic prostanoid fluprostenol and IL-1 in cementoblastic cells.

METHODS

Confluent OCCM cells were pretreated with the protein synthesis inhibitor cycloheximide followed by fluprostenol or IL-1 for 1.5 hours. cDNA generated from each group was used for cDNA subtraction hybridization to identify differentially induced genes. Preferential gene induction was verified by Northern blot analysis.

RESULTS

Thirteen fluprostenol- and seven IL-1-regulated genes were identified. Among the fluprostenol-induced genes was mitogen-activated protein (MAP) kinase phosphatase 1 (MKP1), a negative regulator of MAP kinase signaling. To verify the cDNA subtraction hybridization results, OCCM cells were treated with fluprostenol or prostaglandin F2 (PGF2), and MKP1 mRNA levels were determined. The 0.001 to 1 microM fluprostenol and 0.01 to 1 microM PGF2 significantly induced MKP1 mRNA levels, which peaked at 1 hour of treatment and returned to baseline at 2 hours.

CONCLUSIONS

Fluprostenol enhanced, whereas IL-1 inhibited, OCCM mineralization. Using cDNA subtraction hybridization, we identified primary genes that correlate with the observed anabolic and catabolic responses. These findings further our understanding of cementoblast function and suggest that differentially induced genes may mediate cementum formation and resorption.

Modulation of Stat3 activation by the cytosolic phospholipase A2alpha and cyclooxygenase-2-controlled prostaglandin E2 signaling pathway

A variety of human cancers show constitutive activation of signal transducer and activator of transcription-3 (Stat3) and overexpression of cyclooxygenase-2 (COX-2). This study describes a novel cross-talk between the COX-2-controlled prostaglandin E(2) (PGE(2)) and Stat3 signaling pathways that coordinately regulate human cancer cell growth. COX-2-derived PGE(2) induces interleukin-6 production through activation of EP(4) receptor and subsequent phosphorylation of gp130/Stat3 in human cholangiocarcinoma cells. In parallel, activation of COX-2/PGE(2) signaling also enhances Stat3 phosphorylation and reporter activity through EP(1) receptor-induced activation of c-Src and EGFR in these cells. Moreover, the observations that EP(1) receptor is detected in the nucleus as well as in the Stat3.DNA binding complex and that activation of EP(1) receptor in the nuclei enhances Stat3 activation depicts a previously undescribed G protein-coupled receptor in the nucleus for Stat3 activation and tumor cell growth.

Arginine-Vasopressin Activates the JAK-STAT Pathway in Vascular Smooth Muscle Cells

JAK (Janus-activated kinase)-STAT (signal transducers and activators of transcription) signaling is a major signal transduction pathway in mammalian cells. Different growth factors and cytokines were reported as activators of the JAK-STAT pathway in various cell types. Interestingly, arginine-vasopressin (AVP) was never reported as an inducer of the JAK-STAT pathway. In the present study, we show for the first time that AVP stimulation of vascular smooth muscle cells (VSMCs) induces STAT3 tyrosine and serine phosphorylation, followed by nuclear translocation of the phosphorylated STAT3. In addition, we found that AVP induced JAK2 tyrosine phosphorylation. Taken together, these results demonstrate that AVP activates the JAK-STAT pathway in VSMCs. Furthermore, our results indicate that AVP-induced STAT3 tyrosine phosphorylation requires both JAK2 and c-Src tyrosine kinases. The present study also implicates that extracellular signal-regulated kinase (ERK1/2), which are serine/threonine kinases, are the mediators of STAT3 serine phosphorylation upon AVP stimulation. We further suggest that AVP-induced STAT3 serine phosphorylation negatively modulates AVP-induced STAT3 tyrosine phosphorylation. Finally, our results implicate a novel role for the JAK-STAT pathway, mediating AVP-induced VSMC hypertrophy.

STAT3-independent inhibition of lysophosphatidic acid-mediated upregulation of connective tissue growth factor (CTGF) by cucurbitacin I

Cucurbitacins are recognised as anti-tumour agents because of their interference with STAT3 signalling, but may also affect the integrity of the actin cytoskeleton. In the present study the effect of cucurbitacin I was investigated in fibroblasts. In these cells, cucurbitacin I interfered with lysophosphatidic acid (LPA) signalling. It inhibited tyrosine phosphorylation of focal adhesion proteins and induction of connective tissue growth factor (CTGF), a potent profibrotic protein. Inhibition of Src family kinases with PP2, but not the inactive analogue PP3, also interfered with LPA-mediated tyrosine phosphorylation and induction of CTGF. Jak2-STAT3 signalling seemed to be the connecting link, because CTGF induction was sensitive to AG490, an inhibitor of Jak2, and cucurbitacin I, an inhibitor of Jak2 and STAT3. However, LPA did not activate tyrosine phosphorylation of STAT3. Furthermore, cucurbitacin I was as effective in STAT3 knock out cells as in control cells. Therefore, the inhibitory effect of cucurbitacin I was not related to inhibition of STAT3. Immunocytochemical analysis of cucurbitacin I-treated cells revealed disassembly of F-actin fibres, reorganisation into F-actin patches and resolution of focal adhesions. The phenotypic changes resembled changes observed after treatment of the cells with cytochalasin D, which has been shown to interfere with CTGF induction. Concentrations of cucurbitacin I, which have been shown to target Jak2-STAT3 signalling, thus, profoundly affect the actin cytoskeleton and may therefore modulate cell morphology, migration, adherence and gene expression also in non-tumour cells.

Transcriptional activation of c-Fos by constitutively active Galpha(16)QL through a STAT1-dependent pathway

Hematopoietic restrictive Galpha(16) has long been known to stimulate phospholipase Cbeta (PLCbeta) and induce mitogen-activated protein kinase (MAPK) phosphorylation. Recently, we have demonstrated that Galpha(16) is capable of inducing the phosphorylation and transcriptional activation of transcription factors, such as signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappaB (NFkappaB). However, the downstream signaling regulation by Galpha(16) has not yet been documented. In the present study, we have determined the signaling mechanism by which constitutively active Galpha(16) mediates c-Fos transcriptional activation in human embryonic kidney (HEK) 293 cells. Overexpression of constitutively active Galpha(16), Galpha(16)QL, resulted in the stimulation of c-Fos transcriptional activation in HEK 293 cells. The participation of PLCbeta, c-Src/Janus kinase 2 (JAK2) and extracellular signal-regulated kinase (ERK) signaling pathways in Galpha(16)QL-induced c-Fos transcriptional activation was demonstrated by the use of their specific inhibitors. However, c-Jun N terminal kinase (JNK), p38 MAPK and phosphatidylinositol-3 kinase (PI3K) were not required. Interestingly, the dominant negative mutant of STAT1, but not STAT3, suppressed c-Fos transcriptional activation induced by Galpha(16)QL, implying that STAT1 was involved in this signaling mechanism. To further examine the role of STAT1 in the signaling pathway of Galpha(16), we demonstrated that Galpha(16)QL was able to induce STAT1 activation. Also, stimulation of adenosine A1 receptor-coupled Galpha(16) was shown to induce ERK and STAT1 phosphorylations in a concentration-dependent manner. Using selective inhibitors, PLCbeta, c-Src/JAK and ERK, but not JNK, p38 MAPK and PI3K, were shown to be involved in Galpha(16)QL-induced STAT1 activation. Collectively, our results demonstrate for the first time that stimulation of Galpha(16) can lead to STAT1-dependent c-Fos transcriptional activation via PLCbeta, c-Src/JAK and ERK pathways.

Key role of Src kinase in S100B-induced activation of the receptor for advanced glycation end products in vascular smooth muscle cells

The receptor for advanced glycation end products (RAGE) and its ligands have been implicated in the activation of oxidant stress and inflammatory pathways in vascular smooth muscle cells (VSMCs) leading to the initiation and augmentation of atherosclerosis. Here we report that non-receptor Src tyrosine kinase and the membrane protein caveolin-1 (Cav-1) play a key role in the activation of RAGE by S100B in VSMCs. S100B increased the activation of Src kinase and tyrosine phosphorylation of caveolin-1 in VSMCs. A RAGE-specific antibody blocked both these effects. An inhibitor of Src kinase, PP2, significantly blocked S100B-induced activation of Src kinase, mitogen-activated protein kinases, transcription factors NF-kappaB and STAT3, superoxide production, tyrosine phosphorylation of Cav-1, VSMC migration, and expression of the pro-inflammatory genes monocyte chemotactic protein-1 and interleukin-6. Cholesterol depletion also inhibited S100B-induced effects indicating the requirement for intact caveolae in RAGE-specific signaling. Nucleofection of either a Src dominant negative mutant, or a Cav-1 mutant lacking the scaffolding domain, or Cav-1 short hairpin RNA significantly reduced S100B-induced inflammatory gene expression in VSMCs. Furthermore, VSMCs derived from insulin-resistant and diabetic db/db mice displayed increased RAGE expression, Src activation, and migration compared with those from control db/+ mice. The RAGE antibody blocked enhanced migration in db/db cells. These studies demonstrate for the first time that, in VSMCs, Src kinase and Cav-1 play important roles in RAGE-mediated inflammatory gene expression and migration, key events associated with diabetic vascular complications.

STAT5A interacts with and is phosphorylated upon activation of the mu-opioid receptor

Signal Transducers and Activators of Transcription (STATs) are transcription factors shown to be activated by G protein-coupled receptors. In the present study, we demonstrate that acute morphine or [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]enkephalin (DAMGO) exposure of COS-7 cells transiently transfected with the micro-opioid receptor and STAT5A, leads to receptor-dependent tyrosine phosphorylation of STAT5A. Activation of HEK293 cells, stably expressing the micro-opioid receptor with micro-opioid agonists results in the transcriptional activation of a STAT-responsive reporter gene. Pertussis toxin has no effect on the level of STAT5A phosphorylation, while the Src inhibitor PP1 abolishes opioid-dependent STAT5A phosphorylation. All three opioid receptor subtypes -micro, delta and kappa- share the conserved motif YXXL (amino-acids 336-339 for the micro-opioid receptor), known to be critical for STAT5A/5B binding. Co-immunoprecipitation and pull-down experiments using a GST-carboxyl-terminal tail of the micro-opioid receptor and rat brain, or COS-7 cell cytosolic extracts, demonstrate the direct binding of STAT5A to this region. Mutation of the Y336 to alanine does not prevent STAT5A binding, whereas deletion of the entire putative STAT5A binding site YXXL abolishes STAT5A interaction to the carboxyl-terminal tail of the micro-opioid receptor. Collectively, our results demonstrate the association of STAT5A with the micro-opioid receptor and reveal novel signalling pathways in the regulation of transcription by the micro-opioid receptor.

The role of STAT-3 in the mediation of smooth muscle cell response to cyclic strain

Hemodynamic forces, including shear stress and cyclic strain, have been recognised as important modulators of vascular cell morphology and function. However, the mechanism by which vascular cells sense and transduce the extracellular mechanical signals into the cell nucleus has not yet been clarified. The purpose of our study was to assess the involvement of the signal transducer and activator of transcription-3 (STAT-3) in the signaling pathway mediating the response of vascular smooth muscle cells (SMC) to cyclic strain. Embryonic A7r5 SMC derived from thoracic aortas of DB1X rats were seeded on flexible collagen I-coated plates. Cells were subjected to 10% average strain at 60 cycles/min for various time periods. Activation of STAT-3, p38, extracellular signal-regulated kinase (ERK) 1/2 and Src was assessed by immunoblotting using phosphospecific antibodies. The interactions between STAT-3 phosphorylation and p38, ERK1/2, phosphatidylinositol-3 (PI3K), mammalian target of rapamycin (mTOR), Janus kinase (JAK) 2 and Src were evaluated by pretreating the cells with specific inhibitors including SB202190, PD98059, LY294002, wortmannin, rapamycin, AG490 and PP1. Serine phosphorylation of STAT-3 was increased by 2-fold after 15 min of cyclic strain, while tyrosine phosphorylation was increased by 2.3-fold after 60 min. Inhibition of ERK1/2 by PD98059 prevented serine phosphorylation of STAT-3, whereas inhibition of Src by PP1 prevented STAT-3 tyrosine phosphorylation. Pretreating the cells with SB202190, a specific inhibitor of p38, resulted in an increase in basal phosphorylation of ERK1/2 and a subsequent increase in basal serine phosphorylation of STAT-3. In conclusion, both serine and tyrosine phosphorylation of STAT-3 are involved in the signaling pathway mediating the effects of cyclic strain on vascular SMC. Serine phosphorylation of STAT-3 is mediated by ERK1/2, while tyrosine phosphorylation is mediated by Src. A negative feedback loop was also found between p38 and ERK1/2.

Prostacyclin receptor induces STAT1 and STAT3 phosphorylations in human erythroleukemia cells: a mechanism requiring PTX-insensitive G proteins, ERK and JNK

The ability of the human prostacyclin receptor (hIP) to regulate the activities of signal transducers and activators of transcription (STATs) has not yet been documented. In the present study, we have delineated the mechanism by which hIP induces STAT3 phosphorylations in human erythroleukemia (HEL) cells. Stimulation of endogenous hIP by its specific agonist, cicaprost, resulted in STAT3 Tyr705 and Ser727 phosphorylations in a time- and concentration-dependent manner. Cicaprost-induced STAT3 Tyr705 and Ser727 phosphorylations were resistant to pertussis toxin (PTX) treatment, suggesting that these responses were mediated through PTX-insensitive G proteins. In addition, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK), but not p38 MAPK, were shown to be phosphorylated by cicaprost in a time- and concentration-dependent manner via PTX-insensitive G proteins. The levels of the interaction between STAT3, ERK and JNK were enhanced by cicaprost treatment. The involvement of Raf-1, MEK1/2 and JNK in cicaprost-induced phosphorylations of STAT3 was illustrated by the use of their selective inhibitors. In contrast, p38 MAPK did not appear to be required. Similar observations were obtained with STAT1 upon stimulation by cicaprost. Taken together, these results demonstrate for the first time that hIP activation by cicaprost can lead to STAT1 and STAT3 phosphorylations via signaling pathways involving PTX-insensitive G proteins, ERK and JNK.

AT1R blockade reduces IFN-γ production in lymphocytes in vivo and in vitro

BACKGROUND

Type 1 angiotensin II (Ang II) receptor (AT(1)R) signaling induces proinflammatory responses. Recent studies suggest that T lymphocytes express AT(1)R; yet the effects of Ang II binding to AT(1)R on T cells are poorly understood. We examined the effect of AT(1)R blockade on release of the proinflammatory cytokine, interferon-gamma (IFN-gamma) by human lymphocytes in vivo and in vitro.

METHODS

We used an AT(1)R blocker losartan in a randomized clinical trial in kidney transplant recipients over a 12-month period [AT(1)R blocker (N= 11) and control (N= 10)]. Peripheral blood lymphocytes, isolated from both cohorts, were analyzed by enzyme-linked immunosorbent spot assays (ELISPOT) analyses and real-time reverse transcription-polymerase chain reaction (RT-PCR) to enumerate IFN-gamma producing T cells and IFN-gamma mRNA levels. The effects of AT(1)R blockade in vitro were assessed using human alloreactive T cells and an IFN-gamma producing human cytotoxic T-lymphocyte line. Alloreactive T cells were treated with losartan or candesartan and enzyme-linked immunosorbant assay (ELISA) was used to measure IFN-gamma protein release. The cytotoxic T-lymphocyte line also was AT(1)R blocker-treated prior to determining IFN-gamma producing cells by intracellular cytokine staining.

RESULTS

The AT(1)R blocker cohort had a significant decrease in IFN-gamma producing peripheral blood lymphocytes (P< or = 0.05 for each time point) and IFN-gamma mRNA levels (P= 0.01 vs. control patients). Losartan also decreased IFN-gamma production (P < 0.001) in purified alloreactive T cells in vitro as did candesartan. Moreover, Ang II amplified IFN-gamma generation (P < 0.05) in alloreactive T cells while AT(1)R blocker treatment inhibited Ang II's effect (P < 0.04). AT(1)R blocker treatment furthermore also inhibited IFN-gamma production in the cytotoxic T-lymphocyte line.

CONCLUSION

AT(1)R blockers may have a clinically relevant immunomodulatory role by blocking IFN-gamma production in T cells.

Signal transduction activator of transcription 5 (STAT5) dysfunction in autoimmune monocytes and macrophages

Autocrine granulocyte macrophage-colony stimulating factor (GM-CSF) sequentially activates intracellular components in monocyte/macrophage production of the pro-inflammatory and immunoregulatory prostanoid, prostaglandin E2 (PGE2). GM-CSF first induces STAT5 signaling protein phosphorylation, then prostaglandin synthase 2 (COX2/PGS2) gene expression, and finally IL-10 production, to downregulate the cascade. Without activation, monocytes of at-risk, type 1 diabetic (T1D), and autoimmune thyroid disease (AITD) humans, and macrophages of nonobese diabetic (NOD) mice have aberrantly high GM-CSF, PGS2, and PGE2 expression, but normal levels of IL-10. After GM-CSF stimulation, repressor STAT5A and B isoforms (80-77kDa) in autoimmune human and NOD monocytes and activator STAT5A (96-94kDa) and B (94-92kDa) isoforms in NOD macrophages stay persistently tyrosine phosphorylated. This STAT5 phosphorylation persisted despite treatment in vitro with IL-10, anti-GM-CSF antibody, or the JAK2/3 inhibitor, AG490. Phosphorylated STAT5 repressor isoforms in autoimmune monocytes had diminished DNA binding capacity on GAS sequences found in the PGS2 gene enhancer. In contrast, STAT5 activator isoforms in NOD macrophages retained their DNA binding capacity on these sites much longer than in healthy control strain macrophages. These findings suggest that STAT5 dysfunction may contribute to dysregulation of GM-CSF signaling and gene activation, including PGS2, in autoimmune monocytes and macrophages.

Expression and activation of STAT3 in chronic proliferative immune complex glomerulonephritis and the effect of fosinopril

BACKGROUND

Signal transducers and activators of transcription (STATs) are cytoplasmic proteins that are activated in response to stimulation from various cytokines. Among these, STAT3 is an important member that has been implicated in the inflammatory proliferation of cells. We hypothesized that STAT3 may be activated in kidneys of rats having modified chronic immune complex glomerulonephritis, and that angiotensin-converting enzyme (ACE) inhibition with fosinopril may prevent the activation of STAT3 and subsequent upregulation of tissue inhibitor of metalloproteinase-1 (TIMP-1), which are effects that may explain the therapeutic effects of fosinopril on nephritis.

METHODS

Fifty-one Wistar rats were randomly divided into three groups that included a control group, a model group and a fosinopril group. Bovine serum albumin (BSA) nephritis was induced by subcutaneous immunization and daily intraperitoneal (i.p.) administration of BSA. To accentuate the nephritis, we performed uni-nephrectomy and gave 100 microg of lipopolysaccharide (LPS) as an i.p. injection. Macrophage infiltration (ED-1) was assessed with immunohistochemistry. The expression and activation of STAT3 and the expression of TIMP-1, one of the STAT3 downstream genes, were observed in renal tissues of rats by means of immunohistochemistry, electrophoretic mobility shift assay (EMSA), western blot and northern blot. The relationships between STAT3 phosphorylation, 24 h urinary protein excretion and TIMP-1 expression were also analysed.

RESULTS

Northern blot showed that the mRNA expression of both STAT3 and TIMP-1 was significantly increased in kidneys from the model group, but significantly decreased in the fosinopril group (P<0.05). Western blot analysis revealed similar increases in the expression of STAT3, phospho-STAT3 (p-STAT3) and TIMP-1 in the model group. Analysis of immunohistochemistry showed that STAT3 and p-STAT3 were expressed in very few cells of normal rats, that expression was strong in model rats and that this increased expression was attenuated in the fosinopril group (P<0.05). The expression of p-STAT3 in glomeruli was positively correlated with 24 h proteinuria as well as with glomerular TIMP-1 expression. Double staining showed that some ED-1-positive cells also contained p-STAT3-positive staining.

CONCLUSIONS

The present study showed that STAT3 is expressed and activated in kidneys of rats with modified immune complex glomerulonephritis. These rats also had increased ED-1-positive cells, with some cells showing simultaneous expression of p-STAT3 and ED-1, which may contribute to glomerular inflammatory proliferation and extracellular matrix accumulation. Finally, fosinopril downregulated STAT3 activation and ED-1 influx, which are effects that may attenuate renal damage in this model.