Angiotensin II-induced transcriptional activation of the cyclin D1 gene is mediated by Egr-1 in CHO-AT(1A) cells

Trinity of inflammation, innate immune cells and cross-talk of signalling pathways in tumour microenvironment

Unresolved inflammation is a pathological consequence of persistent inflammatory stimulus and perturbation in regulatory mechanisms. It increases the risk of tumour development and orchestrates all stages of tumorigenesis in selected organs. In certain cancers, inflammatory processes create the appropriate conditions for neoplastic transformation. While in other types, oncogenic changes pave the way for an inflammatory microenvironment that leads to tumour development. Of interest, hallmarks of tumour-promoting and cancer-associated inflammation are striking similar, sharing a complex network of stromal (fibroblasts and vascular cells) and inflammatory immune cells that collectively form the tumour microenvironment (TME). The cross-talks of signalling pathways initially developed to support homeostasis, change their role, and promote atypical proliferation, survival, angiogenesis, and subversion of adaptive immunity in TME. These transcriptional and regulatory pathways invariably contribute to cancer-promoting inflammation in chronic inflammatory disorders and foster "smouldering" inflammation in the microenvironment of various tumour types. Besides identifying common target sites of numerous cancer types, signalling programs and their cross-talks governing immune cells' plasticity and functional diversity can be used to develop new fate-mapping and lineage-tracing mechanisms. Here, we review the vital molecular mechanisms and pathways that establish the connection between inflammation and tumour development, progression, and metastasis. We also discussed the cross-talks between signalling pathways and devised strategies focusing on these interaction mechanisms to harness synthetic lethal drug combinations for targeted cancer therapy.

Agomelatine prevents angiotensin II-induced endothelial and mononuclear cell adhesion

Agomelatine is a non-selective melatonin receptor agonist and an atypical antidepressant with anti-inflammatory, neuroprotective, and cardioprotective effects. The renin-angiotensin system modulates blood pressure and vascular homeostasis. Angiotensin II (Ang II) and its receptor Ang II type I receptor (AT₁R) are recognized as contributors to the pathogenesis of cardiovascular and cardiometabolic diseases, including diabetes, obesity, and atherosclerosis. The recruitment and attachment of monocytes to the vascular endothelium is a major event in the early stages of atherosclerosis and other cardiovascular diseases. In the present study, we demonstrate that agomelatine reduced Ang II-induced expression of AT₁R while significantly inhibiting the attachment of monocytes to endothelial cells induced by Ang II and mediated by ICAM-1 and VCAM-1. Additionally, Ang II inhibited the expression of the chemokines CXCL1, MCP-1, and CCL5, which are critical in the process of immune cell recruitment and invasion. Agomelatine also suppressed the expression of TNF-α, IL-8, and IL-12, which are proinflammatory cytokines that promote endothelial dysfunction and atherogenesis. Importantly, we demonstrate that the inhibitory effect of agomelatine against the expression of adhesion molecules is mediated through the downregulation of Egr-1 signaling. Together, our findings provide evidence of a novel mechanism of agomelatine that may be practicable in the treatment and prevention of cardiovascular diseases.

EGR-1 plays a protective role in AMPK inhibitor compound C-induced apoptosis through ROS-induced ERK activation in skin cancer cells

Skin cancer is caused by abnormal proliferation, gene regulation and mutation of epidermis cells. Compound C is commonly used as an inhibitor of AMP-activated protein kinase (AMPK), which serves as an energy sensor in cells. Recently, compound C has been reported to induce apoptotic and autophagic death in various skin cancer cell lines via an AMPK-independent pathway. However, the signaling pathways activated in compound C-treated cancer cells remain unclear. The present oligodeoxynucleotide-based microarray screening assay showed that the mRNA expression of the zinc-finger transcription factor early growth response-1 (EGR-1), which helps regulate cell cycle progression and cell survival, was significantly upregulated in compound C-treated skin cancer cells. Compound C was demonstrated to induce EGR-1 mRNA and protein expression in a time and dose-dependent manner. Confocal imaging showed that compound C-induced EGR-1 protein expression was localized in the nucleus. Compound C was demonstrated to activate extracellular signal-regulated kinase (ERK) phosphorylation. Inhibition of this compound C-induced ERK phosphorylation downregulated the mRNA and protein expression of EGR-1. In addition, removal of compound C-induced reactive oxygen species (ROS) not only decreased ERK phosphorylation, but also inhibited compound C-induced EGR-1 expression. A functional assay showed that knock down of EGR-1 expression in cancer cells decreased the survival rate while also increasing caspase-3 activity and apoptotic marker expression after compound C treatment. However, no difference in autophagy marker light chain 3-II protein expression was observed between compound C-treated control cells and EGR-1-knockdown cells. Thus, it was concluded that that EGR-1 may antagonize compound C-induced apoptosis but not compound C-induced autophagy through the ROS-mediated ERK activation pathway.

DNA Methylation-Reprogrammed Ang II (Angiotensin II) Type 1 Receptor-Early Growth Response Gene 1-Protein Kinase C ε Axis Underlies Vascular Hypercontractility in Antenatal Hypoxic Offspring

As the most common clinical stress during mid and late pregnancy, antenatal hypoxia has profound adverse effects on individual's vascular health later in life, but the underlying mechanisms are still not understood. The purpose of this study was to reveal the mechanisms of the acquired vascular dysfunction in offspring imposed by antenatal hypoxia. Pregnant rats were housed in a normoxic or hypoxic (10.5% oxygen) chamber from gestation day 10 to 21. Male offspring were euthanized at gestational day 21 (fetus) or postnatal 16 weeks old (adult offspring). Mesenteric arteries were collected for examining Ang II (angiotensin II)-mediated vascular contractility, gene expression, and promoter methylation. Antenatal hypoxia increased vascular sensitivity to Ang II, which was resulted by an upregulated AT1R (angiotensin II type 1 receptor). The increased AT1R was correlated with a hypomethylation-mediated activated transcription of Agtr1a (alpha subtype of AT1R). In addition, we presented evidences that there was an AT1R-Egr1 (early growth response gene 1)-PKCε (ε isoform of protein kinase C) axis in vasculature; AT1R could modulate PKCε expression via upregulating Egr1; Egr1 mediated transcription activation of PKCε via Egr1 binding sites in PKCε gene promoter. Overall, antenatal hypoxia activated AT1R-Egr1-PKCε axis in vasculature, eventually predisposed offspring to vascular hypercontractility. This is the first description that antenatal hypoxia resulted in vascular adverse outcomes in postnatal offspring, was strongly associated with reprogrammed gene expression via a DNA methylation-mediated epigenetic mechanism, advancing understanding toward the influence of adverse antenatal factors in early life on long-term vascular health.

Promising Anti-atherosclerotic Effect of Berberine: Evidence from In Vitro, In Vivo, and Clinical Studies

Elevated levels of plasma cholesterol, impaired vascular wall, and presence of inflammatory macrophages are important atherogenic risk factors contributing to atherosclerotic plaque formation and progression. The interventions modulating these risk factors have been found to protect against atherosclerosis development and to decrease atherosclerosis-related cardiovascular disorders. Nutritional approaches involving supplements followed by improving dietary habits and lifestyle have become growingly attractive and acceptable methods used to control atherosclerosis risk factors, mainly high levels of plasma cholesterol. There are a large number of studies that show berberine, a plant bioactive compound, could ameliorate atherosclerosis-related risk factors. In the present literature review, we put together this studies and provide integrated evidence that exhibits berberine has the potential atheroprotective effect through reducing increased levels of plasma cholesterol, particularly low-density lipoprotein (LDL) cholesterol (LDL-C) via LDL receptor (LDLR)-dependent and LDL receptor-independent mechanisms, inhibiting migration and inflammatory activity of macrophages, improving the functionality of endothelial cells via anti-oxidant activities, and suppressing proliferation of vascular smooth muscle cells. In conclusion, berberine can exert inhibitory effects on the atherosclerotic plaque development mainly through LDL-lowering activity and suppressing atherogenic functions of mentioned cells. As the second achievement of this review, among the signaling pathways through which berberine regulates intracellular processes, AMP-activated protein kinase (AMPK) has a central and critical role, showing that enhancing activity of AMPK pathway can be considered as a promising therapeutic approach for atherosclerosis treatment.

Telmisartan attenuates N-nitrosodiethylamine-induced hepatocellular carcinoma in mice by modulating the NF-κB-TAK1-ERK1/2 axis in the context of PPARγ agonistic activity

Hepatocellular carcinoma (HCC) is characterized by bad prognosis and is the second most common reason for cancer-linked mortality. Treatment with sorafenib (SRF) alone increases patient survival by only a few months. A causal link has been determined between angiotensin II (Ang-II) and HCC. However, the mechanisms underlying the tumorigenic effects of Ang-II remain to be elucidated. N-Nitrosodiethylamine was utilized to examine the effects of telmisartan (TEL) (15 mg/kg), SRF (30 mg/kg), and a combination of these two agents on HCC mice. Downregulation of NF-кBP65 mRNA expression and inhibition of the phosphorylation-induced activation of both ERK1/2 and NF-кB P65 were implicated in the anti-tumor effects of TEL and SRF. Consequent regression of malignant changes and improvements in liver function associated with reduced levels of AFP, TNF-α, and TGF-β1 were also confirmed. Anti-proliferative, anti-metastatic, and anti-angiogenic effects of treatment were indicated by reduced hepatic cyclin D1 mRNA expression, reduced MMP-2 levels, and reduced VEGF levels, respectively. TEL, but not SRF, demonstrated agonistic activity for PPARγ receptors, as evidenced by increased PPARγ DNA binding activity, upregulation of CD36, and HO-1 mRNA expression followed by increased liver antioxidant capacity. Both TEL and SRF inhibited TAK1 phosphorylation-induced activation, indicating that TAK1 might act as a central mediator in the interaction between ERK1/2 and NF-кB. TEL, by modulating the ERK1/2, TAK1, and NF-кB signaling axis in the context of PPARγ agonistic activity, exerted anti-tumor effects and increased tumor sensitivity to SRF. Therefore, TEL is an encouraging agent for further clinical trials regarding the management of HCC.

Role of Thrombospondin-1 in Mechanotransduction and Development of Thoracic Aortic Aneurysm in Mouse and Humans

RATIONALE

Abnormal mechanosensing of smooth muscle cells (SMCs) resulting from the defective elastin-contractile units has been suggested to drive the formation of thoracic aortic aneurysms; however, the precise molecular mechanism has not been elucidated.

OBJECTIVE

The aim of this study was to identify the crucial mediator(s) involved in abnormal mechanosensing and propagation of biochemical signals during the aneurysm formation and to establish a basis for a novel therapeutic strategy.

METHODS AND RESULTS

We used a mouse model of postnatal ascending aortic aneurysms ( Fbln4SMKO; termed SMKO [SMC-specific knockout]), in which deletion of Fbln4 (fibulin-4) leads to disruption of the elastin-contractile units caused by a loss of elastic lamina-SMC connections. In this mouse, upregulation of Egr1 (early growth response 1) and angiotensin-converting enzyme leads to activation of Ang II (angiotensin II) signaling. Here, we showed that the matricellular protein, Thbs1 (thrombospondin-1), was highly upregulated in SMKO ascending aortas and in human thoracic aortic aneurysms. Thbs1 was induced by mechanical stretch and Ang II in SMCs, for which Egr1 was required, and reduction of Fbln4 sensitized the cells to these stimuli and led to higher expression of Egr1 and Thbs1. Deletion of Thbs1 in SMKO mice prevented the aneurysm formation in ≈80% of DKO (SMKO;Thbs1 knockout) animals and suppressed Ssh1 (slingshot-1) and cofilin dephosphorylation, leading to the formation of normal actin filaments. Furthermore, elastic lamina-SMC connections were restored in DKO aortas, and mechanical testing showed that structural and material properties of DKO aortas were markedly improved.

CONCLUSIONS

Thbs1 is a critical component of mechanotransduction, as well as a modulator of elastic fiber organization. Maladaptive upregulation of Thbs1 results in disruption of elastin-contractile units and dysregulation of actin cytoskeletal remodeling, contributing to the development of ascending aortic aneurysms in vivo. Thbs1 may serve as a potential therapeutic target for treating thoracic aortic aneurysms.

Perindopril, fosinopril and losartan inhibited the progression of diethylnitrosamine-induced hepatocellular carcinoma in mice via the inactivation of nuclear transcription factor kappa-B

Hepatocellular carcinoma (HCC) is a major global health problem. Therapeutic interventions of HCC are still limited because of its complicated molecular pathogenesis. Many reports showed that renin-angiotensin system (RAS) contributes to the development of different types of malignancies. Therefore, the present study aimed to examine the effect of RAS inhibition using perindopril (1 mg/kg), fosinopril (2 mg/kg), or losartan (10 mg/kg) on diethylnitrosamine-induced HCC compared to sorafenib (30 mg/kg). The administration of RAS inhibitors resulted in improved liver function and histologic picture with a reduction in AFP levels. These effects found to be mediated through inactivation of NFкB pathway by the inhibition of NFĸB p65 phosphorylation at the Ser536 residue and inhibition of the phosphorylation-induced degradation of NFĸBia. Consequently, expression levels of cyclin D1 mRNA were significantly lowered. In addition, NFкB-induced TNF-α and TGF-β1 levels were reduced leading to lower levels of MMP-2 and VEGF. We concluded that RAS inhibition either through inhibiting the ACE or the blockade of AT1R has the same therapeutic benefit and that the tissue affinity of the ACEIs has no impact on its anti-tumor activity. These results suggest that ACEIs and ARBs can serve as promising candidates for further clinical trials in the management of HCC.

Binding and inhibition of the ternary complex factor Elk-4/Sap1 by the adapter protein Dok-4

The adapter protein Dok-4 (downstream of kinase-4) has been reported as both an activator and inhibitor of Erk and Elk-1, but lack of knowledge about the identity of its partner molecules has precluded any mechanistic insight into these seemingly conflicting properties. We report that Dok-4 interacts with the transactivation domain of Elk-4 through an atypical phosphotyrosine-binding domain-mediated interaction. Dok-4 possesses a nuclear export signal and can relocalize Elk-4 from nucleus to cytosol, whereas Elk-4 possesses two nuclear localization signals that restrict interaction with Dok-4. The Elk-4 protein, unlike Elk-1, is highly unstable in the presence of Dok-4, through both an interaction-dependent mechanism and a pleckstrin homology domain-dependent but interaction-independent mechanism. This is reversed by proteasome inhibition, depletion of endogenous Dok-4 or lysine-to-arginine mutation of putative Elk-4 ubiquitination sites. Finally, Elk-4 transactivation is potently inhibited by Dok-4 overexpression but enhanced by Dok-4 knockdown in MDCK renal tubular cells, which correlates with increased basal and EGF-induced expression of Egr-1, Fos and cylcinD1 mRNA, and cell proliferation despite reduced Erk activation. Thus, Dok-4 can target Elk-4 activity through multiple mechanisms, including binding of the transactivation domain, nuclear exclusion and protein destabilization, without a requirement for inhibition of Erk.

Erythropoietin Regulation by Angiotensin II

The renin-angiotensin system (RAS) is a key regulator of blood pressure and blood volume homeostasis. The RAS is primarily comprised of the precursor protein angiotensinogen and the two proteases, renin and angiotensin-converting enzyme (ACE). Angiotensin I (Ang I) is derived from angiotensinogen by renin, but appears to have no biological activity. In contrast, angiotensin II (Ang II) that has a variety of biological functions in the cells is converted from Ang I through removal of two-C-terminal residues by ACE. The physiological effects of Ang II are due to Ang II signaling through specific receptor binding, resulting in muscle contraction leading to increased blood pressure and volume. To modulate RAS, three classes of drugs have been developed: (1) renin inhibitors to prevent angiotensinogen conversion to Ang I, (2) ACE inhibitors, to prevent Ang I processing to Ang II and (3) angiotensin receptor blockers, to inhibit Ang II signaling through its receptor. Studies using the RAS inhibitors and Ang II demonstrated that RAS signaling mediates actions of Ang II in the regulation of proliferation and differentiation of specific hematopoietic cell types, especially in the red blood cell lineage. Accumulating evidence indicates that RAS regulates EPO, an essential mediator of red cell production, for human anemia and erythropoiesis in vivo and in vitro. The regulation of EPO expression by Ang II may be responsible for maintaining red blood cell homeostasis. This review highlights the biological roles of RAS for blood cell and EPO homeostasis through Ang II signaling. The molecular mechanism for Ang II-induced EPO production of the cell or tissue type-specific expression is discussed.

BRG1 interacts with GLI2 and binds Mef2c gene in a hedgehog signalling dependent manner during in vitro cardiomyogenesis

Background

The Hedgehog (HH) signalling pathway regulates cardiomyogenesis in vivo and in differentiating P19 embryonal carcinoma (EC) cells, a mouse embryonic stem (mES) cell model. To further assess the transcriptional role of HH signalling during cardiomyogenesis in stem cells, we studied the effects of overexpressing GLI2, a primary transducer of the HH signalling pathway, in mES cells.

Results

Stable GLI2 overexpression resulted in an enhancement of cardiac progenitor-enriched genes, Mef2c, Nkx2-5, and Tbx5 during mES cell differentiation. In contrast, pharmacological blockade of the HH pathway in mES cells resulted in lower expression of these genes. Mass spectrometric analysis identified the chromatin remodelling factor BRG1 as a protein which co-immunoprecipitates with GLI2 in differentiating mES cells. We then determined that BRG1 is recruited to a GLI2-specific Mef2c gene element in a HH signalling-dependent manner during cardiomyogenesis in P19 EC cells, a mES cell model.

Conclusions

Thus, we propose a mechanism where HH/GLI2 regulates the expression of Mef2c by recruiting BRG1 to the Mef2c gene, most probably via chromatin remodelling, to ultimately regulate in vitro cardiomyogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-016-0127-8) contains supplementary material, which is available to authorized users.

Cyclooxygenase-2 promotes tumor growth and suppresses tumor immunity

Cyclooxygenase-2 (COX-2), an inducible form of the enzyme that catalyzes the first step in the synthesis of prostanoids, is associated with inflammatory diseases and carcinogenesis, which is suspected to promote angiogenesis and tissue invasion of tumors and resistance to apoptosis. Meanwhile, COX-2 contributes to immune evasion and resistance to cancer immunotherapy, which plays a crucial role in the innate and adaptive immune response. The activity of COX-2-PGE2-EP signal pathway can suppress Dendritic cells (DCs), natural killer (NK), T cells, type-1 immunity excluding type-2 immunity which promote tumor immune evasion. COX-2 and the prostaglandin cascade play important roles in the "inflammogenesis of cancer". In addition, COX-inhibitors can inhibit tumor immune evasion. Therefore, we can exert the COX-inhibitors to facilitate the patients to benefit from addition of COX-inhibitors to standard cytotoxic therapy.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

Regulation of mice liver regeneration by early growth response-1 through the GGPPS/RAS/MAPK pathway

BACKGROUND & AIMS

Liver regeneration (LR) consists of a series of complicated processes in which several transcription factors play important roles. Among them, the early growth response 1 gene (EGR-1) is rapidly induced in response to liver resection. Previous studies have shown that EGR-1-/- mice exhibit delayed hepatocellular mitotic progression after partial hepatectomy (PH). The mechanism underlying the EGR-1 regulated LR is still unknown. Our aim is to elucidate the underlying mechanism.

METHODS

Mice infected with adenoviral vectors expressing GFP, EGR-1 or dominant negative EGR-1 (dnEGR-1) were subjected to 2/3 PH. The serum starvation recovery cell model was chosen to mimic the regeneration process for the in vitro studies. Cell proliferation and signaling pathways downstream of geranylgeranyl diphosphate synthase (GGPPS) were examined in the regenerating liver and serum starvation recovery cell model.

RESULTS

Loss of function of EGR-1 significantly inhibited liver recovery and the expression of cyclin D1, cyclin E, and proliferating cell nuclear antigen (PCNA). The expression of GGPPS and the activity of the downstream RAS/MAPK pathway were inhibited in dnEGR-1-infected liver, which was consistent with the serum-induced cell model. In addition, loss of function of EGR-1 aggravated liver damage with increased serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels.

CONCLUSIONS

EGR-1-induced GGPPS plays a vital role in the LR after PH through the RAS/MAPK signaling.

Angiotensin II increases fibronectin and collagen I through the β-catenin-dependent signaling in mouse collecting duct cells

The contribution of angiotensin II (ANG II) to renal and tubular fibrosis has been widely reported. Recent studies have shown that collecting duct cells can undergo mesenchymal transition suggesting that collecting duct cells are involved in interstitial fibrosis. The Wnt/β-catenin signaling pathway plays an essential role in development, organogenesis, and tissue homeostasis; however, the dysregulation of this pathway has been linked to fibrosis. In this study, we investigated whether AT1 receptor activation induces the expression of fibronectin and collagen I via the β-catenin pathway in mouse collecting duct cell line M-1. ANG II (10(-7) M) treatment in M-1 cells increased mRNA, protein levels of fibronectin and collagen I, the β-catenin target genes (cyclin D1 and c-myc), and the myofibroblast phenotype. These effects were prevented by candesartan, an AT1 receptor blocker. Inhibition of the β-catenin degradation with pyrvinium pamoate (pyr; 10(-9) M) prevented the ANG II-induced expression of fibronectin, collagen I, and β-catenin target genes. ANG II treatment promoted the accumulation of β-catenin protein in a time-dependent manner. Because phosphorylation of glycogen synthase kinase-3β (GSK-3β) inhibits β-catenin degradation, we further evaluated the effects of ANG II and ANG II plus pyr on p-ser9-GSK-3β levels. ANG II-dependent upregulation of β-catenin protein levels was correlated with GSK-3β phosphorylation. These effects were prevented by pyr. Our data indicate that in M-1 collecting duct cells, the β-catenin pathway mediates the stimulation of fibronectin and collagen I in response to AT1 receptor activation.

Characterization of the PLCB1 promoter and regulation by early growth response transcription factor EGR-1

The Gαq/-Gα11-PLCβ1 pathway is important for intracellular signalling and associated with pathological conditions, such as cardiac hypertrophy. The GNAQ and GNA11 promoters (encoding for Gαq and Gα11) have already been characterized and are both regulated by the transcription factor early growth response 1 (Egr-1). In contrast, the PLCB1 promoter (encoding for the direct downstream effector PLCβ1) has neither been cloned nor characterized. Therefore, the purpose of this study was to 1) characterize the PLCB1 promoter, and 2) assess its potential regulation by Egr-1. By means of 5'- Rapid Amplification of 5'-cDNA ends analysis in human heart tissue we found an initiation of transcription from multiple starting points, the main transcription starting point being located at nt-235 relative to the translation start point. The PLCB1 promoter was cloned and deletion constructs were generated. Luciferase assays were performed in three different cell lines and regulatory regions were identified between nt-595/nt-313 (Hek293: P=0.013; HASMC: P=0.019; H9c2: P=0.005). In electrophoretic mobility shift assays one specific Egr-1 binding site was identified at nt-451/-419 and PLCB1 promoter activity was increased more than 5-fold (Hek293: P=0.0008) and 1,6- fold (H9c2: P=0.0499) following overexpression of Egr-1. Thus, the PLCB1 promoter was characterized for the first time and a specific interaction with the transcription factor Egr-1 was shown. Our data provide a potential molecular mechanism relating to pathophysiological conditions such as cardiac hypertrophy where activation by Egr-1 of Gαq/Gα11-PLCβ1 plays an important role.

Mechanism of erythropoietin regulation by angiotensin II

Erythropoietin (EPO) is the primary regulator of red blood cell development. Although hypoxic regulation of EPO has been extensively studied, the mechanism(s) for basal regulation of EPO are not well understood. In vivo studies in healthy human volunteers and animal models indicated that angiotensin II (Ang II) and angiotensin converting enzyme inhibitors regulated blood EPO levels. In the current study, we found that Ang II induced EPO expression in situ in murine kidney slices and in 786-O kidney cells in culture as determined by reverse transcription polymerase chain reaction. We further investigated the signaling mechanism of Ang II regulation of EPO in 786-O cells. Pharmacological inhibitors of Ang II type 1 receptor (AT1R) and extracellular signal-regulated kinase 1/2 (ERK1/2) suppressed Ang II transcriptional activation of EPO. Inhibitors of AT2R or Src homology 2 domain-containing tyrosine phosphatase had no effect. Coimmunoprecipiation experiments demonstrated that p21Ras was constitutively bound to the AT1R; this association was increased by Ang II but was reduced by the AT1R inhibitor telmisartan. Transmembrane domain (TM) 2 of AT1R is important for G protein-dependent ERK1/2 activation, and mutant D74E in TM2 blocked Ang II activation of ERK1/2. Ang II signaling induced the nuclear translocation of the Egr-1 transcription factor, and overexpression of dominant-negative Egr-1 blocked EPO promoter activation by Ang II. These data identify a novel pathway for basal regulation of EPO via AT1R-mediated Egr-1 activation by p21Ras-mitogen-activated protein kinase/ERK kinase-ERK1/2. Our current data suggest that Ang II, in addition to regulating blood volume and pressure, may be a master regulator of erythropoiesis.

Cavin-3 dictates the balance between ERK and Akt signaling

Cavin-3 is a tumor suppressor protein of unknown function. Using both in vivo and in vitro approaches, we show that cavin-3 dictates the balance between ERK and Akt signaling. Loss of cavin-3 increases Akt signaling at the expense of ERK, while gain of cavin-3 increases ERK signaling at the expense Akt. Cavin-3 facilitates signal transduction to ERK by anchoring caveolae to the membrane skeleton of the plasma membrane via myosin-1c. Caveolae are lipid raft specializations that contain an ERK activation module and loss of the cavin-3 linkage reduces the abundance of caveolae, thereby separating this ERK activation module from signaling receptors. Loss of cavin-3 promotes Akt signaling through suppression of EGR1 and PTEN. The in vitro consequences of the loss of cavin-3 include induction of Warburg metabolism (aerobic glycolysis), accelerated cell proliferation, and resistance to apoptosis. The in vivo consequences of cavin-3 knockout are increased lactate production and cachexia. DOI:http://dx.doi.org/10.7554/eLife.00905.001.

Mechanisms of RAS/β-catenin interactions

Signaling through the WNT/β-catenin and the RAS (rat sarcoma)/MAPK (mitogen-activated protein kinase) pathways plays a key role in the regulation of various physiological cellular processes including proliferation, differentiation, and cell death. Aberrant mutational activation of these signaling pathways is closely linked to the development of cancer in many organs, in humans as well as in laboratory animals. Over the past years, more and more evidence for a close linkage of the two oncogenic signaling cascades has accumulated. Using different experimental approaches, model systems, and experimental conditions, a variety of molecular mechanisms have been identified by which signal transduction through WNT/β-catenin and RAS interact, either in a synergistic or an antagonistic manner. Mechanisms of interaction comprise an upstream crosstalk at the level of pathway-activating ligands and their receptors, interrelations of cytosolic kinases involved in either pathways, as well as interaction in the nucleus related to the joint regulation of target gene transcription. Here, we present a comprehensive review of the current knowledge on the interaction of RAS/MAPK- and WNT/β-catenin-driven signal transduction in mammalian cells.

PKCδ-dependent activation of ERK1/2 leads to upregulation of the human NHE2 transcriptional activity in intestinal epithelial cell line C2BBe1

The apical Na+/H+ exchanger (NHE) isoform NHE2 is involved in transepithelial Na+ absorption in the intestine. Our earlier studies have shown that mitogenic agent phorbol 12-myristate 13-acetate (PMA) induces the expression of NHE2 through activation of transcription factor early growth response-1 (Egr-1) and its interactions with the NHE2 promoter. However, the signaling pathways involved in transcriptional stimulation of NHE2 in response to PMA in the intestinal epithelial cells are not known. Chemical inhibitors and genetic approaches were used to investigate the signaling pathways responsible for the stimulation of NHE2 expression by PMA via Egr-1 induction. We show that, in response to PMA, PKCδ, a member of novel PKC isozymes, and MEK-ERK1/2 pathway of mitogen-activated protein kinases stimulate the NHE2 expression in C2BBe1 intestinal epithelial cells. PMA rapidly and transiently induced activation of PKCδ. Small inhibitory RNA-mediated knockdown of PKCδ blocked the stimulatory effect of PMA on the NHE2 promoter activity. In addition, blockade of PKCδ by rottlerin, a PKCδ-specific inhibitor, and ERK1/2 by U0126, a MEK-ERK inhibitor, abrogated PMA-induced Egr-1 expression. Immunofluorescence studies revealed that inhibition of ERK1/2 activation prevents translocation of PMA-induced Egr-1 into the nucleus. Consistent with these data, PMA-induced Egr-1 interaction with the NHE2 promoter region was prevented in nuclear extracts from U0126-pretreated cells. In conclusion, our data provide the first evidence that the stimulatory effect of PMA on NHE2 expression is mediated through the initial activation of PKCδ, subsequent PKCδ-dependent activation of MEK-ERK1/2 signaling pathway, and stimulation of Egr-1 expression. Furthermore, we show that transcription factor Egr-1 acts as an intermediate effector molecule that links the upstream signaling cues to the long-term stimulation of NHE2 expression by PMA in C2BBe1 cells.

GPER mediates the Egr-1 expression induced by 17β-estradiol and 4-hydroxitamoxifen in breast and endometrial cancer cells

Early growth response-1 (Egr-1) is an immediate early gene involved in relevant biological events including the proliferation of diverse types of cell tumors. In a microarray analysis performed in breast cancer cells, 17β-estradiol (E2) and the estrogen receptor antagonist 4-hydroxitamoxifen (OHT) up-regulated Egr-1 through the G protein-coupled receptor named GPR30/GPER. Hence, in this study, we aimed to provide evidence regarding the ability of E2, OHT and the selective GPER ligand G-1 to regulate Egr-1 expression and function through the GPER/EGFR/ERK transduction pathway in both Ishikawa (endometrial) and SkBr3 (breast) cancer cells. Interestingly, we demonstrate that Egr-1 is involved in the transcription of genes regulating cell proliferation like CTGF and cyclin D1 and required for the proliferative effects induced by E2, OHT, and G-1 in both Ishikawa and SkBr3 cells. In addition, we show that GPER mediates the expression of Egr-1 also in carcinoma-associated fibroblasts (CAFs). Our data suggest that Egr-1 may represent an important mediator of the biological effects induced by E2 and OHT through GPER/EGFR/ERK signaling in breast and endometrial cancer cells. The results obtained in CAFs provide further evidence regarding the potential role exerted by the GPER-dependent Egr-1 up-regulation in tumor development and progression. Therefore, Egr-1 may be included among the bio-markers of estrogen and antiestrogen actions and may be considered as a further therapeutic target in both breast and endometrial tumors.

Immediate-early transcriptional response to angiotensin II in human adrenocortical cells

Angiotensin II binds to the angiotensin II receptors type 1 (AT1 receptors) in adrenocortical cells and triggers an intracellular signaling cascade leading to changes in the gene expression pattern. Here, we show that stimulation with angiotensin II induces the expression of biologically active early growth response (Egr)-1, a zinc finger transcription factor, in human H295R adrenocortical cells. Expression of a dominant-negative mutant of the ternary complex factor Elk-1, a key transcriptional regulator of serum response element-driven gene transcription, prevented Egr-1 expression in angiotensin II-stimulated H295R cells, indicating that Ets-like protein-1 (Elk-1) or related ternary complex factors connect the intracellular signaling cascade elicited by activation of AT1 receptors with transcription of the Egr-1 gene. These data were corroborated by the fact that angiotensin II stimulation increased the transcription activation potential of Elk-1. In addition, activator protein-1 transcriptional activity was significantly elevated in angiotensin II-treated H295R cells. Expression of c-Jun and c-Fos was increased as well as the transcription activation potential of c-Fos. Expression of a dominant-negative mutant of Elk-1 reduced c-Fos expression in angiotensin II-stimulated adrenocortical cells, suggesting that the serum response element within the c-Fos promoter functions as an angiotensin II-response element. Expression of a dominant-negative mutant of c-Jun reduced activator protein-1 activity in angiotensin II-stimulated adrenocortical cells and reduced the up-regulation of c-Jun after angiotensin II stimulation. Thus, c-Jun regulates its own expression in adrenocortical cells. Together, the data show that angiotensin II stimulation activates the transcription factors Egr-1, Elk-1, c-Jun, and c-Fos in adrenocortical cells, leading to stimulus-dependent changes in the gene expression pattern.

Early growth response (EGR)-1 is required for timely cell-cycle entry and progression in hepatocytes after acute carbon tetrachloride exposure in mice

Cell-cycle induction in hepatocytes protects from prolonged tissue damage after toxic liver injury. Early growth response (Egr)-1(-/-) mice exhibit increased liver injury after carbon tetrachloride (CCl(4)) exposure and reduced TNF-α production. Because TNF-α is required for prompt cell-cycle induction after liver injury, here, we tested the hypothesis that Egr-1 is required for timely hepatocyte entry into the cell cycle after CCl(4)-induced liver injury. Acute liver injury was induced by a single injection of CCl(4). Assays were employed to assess indices of the cell cycle in liver after CCl(4) exposure. Bromodeoxyuridine incorporation peaked in wild-type mice at 48 h after CCl(4) but was reduced by 80% in Egr-1(-/-) mice. Proliferating-cell nuclear-antigen immunohistochemistry revealed blocks in cell-cycle entry and progression to DNA synthesis in Egr-1-deficient mice 48 h after CCl(4). Cyclin D, important for G0/G1 progression, was reduced at baseline and 36 h after CCl(4). Cyclin E1, required for G1/S-phase transition, was reduced in Egr-1(-/-) mice 24 and 48 h after CCl(4) exposure and was associated with reduced phosphorylation of the retinoblastoma protein. Proliferation in Egr-1(-/-) mice was delayed, rather than blocked, because indices of cell-cycle progression were restored 72 h after CCl(4) exposure. We concluded that Egr-1 was required for prompt cell-cycle entry (G0- to G1-phase) and G1/S-phase transition after toxic liver injury. These data support the hypothesis that Egr-1 provides hepatoprotection in the CCl(4)-injured liver, attributable, in part, to timely cell-cycle induction and progression.

Transcriptional regulation of the Na⁺/H⁺ exchanger NHE3 by chronic exposure to angiotensin II in renal epithelial cells

Angiotensin II (Ang II) exerts an acute bimodal effect on proximal tubule NHE3: while low doses stimulate the exchanger, high doses inhibit it. In the present study, we have investigated the chronic effects of Ang II on NHE3 expression and transcriptional regulation. Treatment of a tubular epithelial cell line, OKP, with Ang II 10(-11)M significantly increased NHE protein expression and mRNA levels, without evidence of bimodal effect. No change in mRNA half-life was detected, but transient transfection studies showed a significant increase in NHE3 promoter activity. Binding sites for Sp1/Egr-1 and AP2 transcription factors of the NHE3 proximal promoter were mutated and we observed that the Sp1/Egr-1 binding site integrity is necessary for Ang II stimulatory effects. Inhibition of cytochrome P450, PI3K, PKA and MAPK pathways prevented the Ang II stimulatory effect on the NHE3 promoter activity. Taking all the results together, our data reveal that chronic Ang II treatment exerts a stimulatory effect on NHE3 expression and promoter activity. The Ang II up-regulation of the NHE3 promoter activity appears to involve the Sp1/Egr-1 binding site and the interplay of several intracellular signaling pathways.

Role of JNK/ATF-2 pathway in inhibition of thrombospondin-1 (TSP-1) expression and apoptosis mediated by doxorubicin and camptothecin in FTC-133 cells

Our previous studies have shown that camptothecin and doxorubicin triggered ceramide accumulation via de novo synthesis pathway. De novo ceramide generation was responsible for the drug-induced apoptosis through a caspase-3-dependent pathway and a decrease of thrombospondin-1 expression in human thyroid carcinoma FTC-133 cells. Here, we demonstrate that Jun N-terminal kinases play a critical role in camptothecin- and doxorubicin-induced down-regulation of thrombospondin-1 expression: i) de novo ceramide synthesis pathway activates Jun N-terminal kinase 1/2 resulting in activating transcription factor 2 phosphorylation; ii) cell treatment by SP600125, a Jun N-terminal kinase specific inhibitor, strongly reduced activating transcription factor 2 phosphorylation and completely abolished camptothecin and doxorubicin effects; and iii) activating transcription factor 2 expression silencing greatly attenuated camptothecin- and doxorubicin-induced down-regulation of thrombospondin-1 expression and apoptosis. The set of our data established that camptothecin- and doxorubicin-induced activation of Jun N-terminal kinase/activating transcription factor 2 pathway via de novo ceramide synthesis down-regulates thrombospondin-1 expression and apoptosis in human thyroid carcinoma FTC-133 cells. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

The elements of human cyclin D1 promoter and regulation involved

Cyclin D1 is a cell cycle machine, a sensor of extracellular signals and plays an important role in G1-S phase progression. The human cyclin D1 promoter contains multiple transcription factor binding sites such as AP-1, NF-қB, E2F, Oct-1, and so on. The extracellular signals functions through the signal transduction pathways converging at the binding sites to active or inhibit the promoter activity and regulate the cell cycle progression. Different signal transduction pathways regulate the promoter at different time to get the correct cell cycle switch. Disorder regulation or special extracellular stimuli can result in cell cycle out of control through the promoter activity regulation. Epigenetic modifications such as DNA methylation and histone acetylation may involved in cyclin D1 transcriptional regulation.

Cyclo-oxygenase 2 up-regulates the effect of multidrug resistance

COX-2 (cyclo-oxygenase 2), an inducible form of the enzyme that catalyses the first step in the synthesis of prostanoids, is associated with inflammatory diseases and carcinogenesis, which is suspected to promote angiogenesis and tissue invasion of tumours and resistance to apoptosis. COX-2 is also involved in drug resistance and poor prognosis of many neoplastic diseases or cancers. The activation of the COX-2/PGE2 (prostaglandin E2)/prostaglandin E receptor signal pathway can up-regulate the expression of all three ABC (ATP-binding-cassette) transporters, MDR1/P-gp (multidrug resistance/P-glycoprotein), MRP1 (multidrug-resistance protein 1) and BCRP (breast-cancer-resistance protein), which encode efflux pumps, playing important roles in the development of multidrug resistance. In addition, COX inhibitors inhibit the expression of MDR1/P-gp, MRP1 and BCRP and enhance the cytotoxicity of anticancer drugs. Therefore we can use the COX inhibitors to potentialize the effects of chemotherapeutic agents and reverse multidrug resistance to facilitate the patient who may benefit from addition of COX inhibitors to standard cytotoxic therapy.

Egr-1 is involved in the inhibitory effect of leptin on PPARgamma expression in hepatic stellate cell in vitro

AIMS

Hepatic stellate cell (HSC) activation is a key step in the hepatic fibrogenic process. Increasing evidence demonstrates the pro-fibrogenic action of leptin in rodent liver. Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a potential molecular target for inhibition of HSC activation. Our previous study suggested that leptin markedly down-regulated PPARgamma gene expression in HSCs. The aim of this study is to explore the molecular mechanisms underlying the inhibitory effect of leptin on PPARgamma expression in rat HSCs in vitro.

MAIN METHODS

The effects of leptin on the expression and trans-activation activity of early growth response-1 (Egr-1) are examined by using real-time PCR, Western blotting analysis, transient transfection, and electrophoretic mobility shift assay. The role of Egr-1 in PPARgamma gene expression is demonstrated by co-transfection approach, Western blotting analysis and real-time PCR.

KEY FINDINGS

We document that leptin increases Egr-1 expression at protein and mRNA levels, and significantly stimulates Egr-1 trans-activation activity. Moreover, leptin induces the expression and activity of Egr-1 through activation of extracellular signal-regulated kinase (ERK) or phosphatidylinositol 3-kinase/AKT signaling (PI-3K/AKT) pathway. Further investigation reveals that Egr-1 exerts a clear inhibitory effect on the promoter activity and expression of PPARgamma gene and demonstrates that Egr-1 increases the expression of HSC activation markers and promotes HSC growth. Taken together, these findings suggest that Egr-1 is involved in the inhibitory effect of leptin on PPARgamma expression in rat HSCs in vitro.

SIGNIFICANCE

Our results provide novel insights into the mechanisms of leptin-induced inhibition of PPARgamma expression in HSCs in vitro.

Angiotensin II regulation of adrenocortical gene transcription

Angiotensin II (Ang II) is the key peptide hormone in the renin-angiotensin-aldosterone system (RAAS). Its ability to regulate levels of circulating aldosterone relies on actions on adrenal glomerulosa cells. Many of the Ang II effects on glomerulosa cells involve a precisely coordinated regulation of signaling cascades and gene expression. The development of genome-wide gene arrays has allowed the definition of transcriptome-wide effects of Ang II in adrenocortical cells. Analysis of the Ang II gene targets reveals broad effects on cellular gene expression, particularly the rapid induction of numerous transcription factors that may regulate long-term steroid metabolism and cell growth/proliferation. Herein we discuss the Ang II-induced genes in adrenocortical cells and review the progress in defining the role of these genes in zona glomerulosa function.

Mycophenolic acid inhibits the autocrine PDGF-B synthesis and PDGF-BB-induced mRNA expression of Egr-1 in rat mesangial cells

BACKGROUND

Uncontrolled mesangial cell (MC) proliferation within the context of glomerular disease contributes to the development of glomerulosclerosis. Mesangial autocrine growth factor stimulation has been described as a pathogenic factor. We investigated the effects of mycophenolic acid (MPA), the active metabolite of the immunosuppressant mycophenolate mofetil (MMF), on proliferation factors of cultured rat MCs. MPA was tested on the expression of platelet-derived growth factor-B (PDGF-B) and its receptor beta (PDGFR-beta), the immediate early gene (IEG) c-fos and the early growth response gene-1 (Egr-1), and AP-1 activation.

METHODS

Growth-arrested rat MCs were stimulated with 10% fetal calf serum (FCS) or 10-25 ng/ml platelet-derived growth factor-BB (PDGF-BB) in the presence or absence of MPA (0.019-10 microM) with or without guanosine (100 microM). MC proliferation was quantified by 5-bromo-2'-deoxyuridine (BrdU) incorporation and direct cell counting. Cytotoxicity of MPA was evaluated using the MTT and LDH tests. Protein expression of PDGF-B and its receptor PDGFR-beta was quantified by western blot analysis. The effect of MPA on gene expression of PDGF-B, Egr-1 and c-fos was determined by the reverse transcriptase-polymerase chain reaction (RT-PCR). AP-1 activation was analysed by an electrophoretic mobility shift assay (EMSA).

RESULTS

Exposure of MCs to MPA caused a concentration-dependent inhibition of FCS-induced cell proliferation (cell number increase) with an IC50 of 0.44 +/- 0.03 microM and DNA synthesis with an IC50 of 0.52 +/- 0.02 microM without cell cytotoxicity in the therapeutic range. MPA decreased the PDGF-B protein expression and mRNA self-induction of PDGF-B but did not alter the protein expression of PDGFR-beta. MPA strongly inhibited the PDGF-BB-induced mRNA expression of Egr-1 decreasing to 7.6 +/- 2.5% after 30 min (P <or= 0.001) and to 4.7 +/- 3.1% after 1 h (P <or= 0.05), both being compared to the maximal expression induced by PDGF-BB. PDGF-BB-induced c-fos expression under MPA was unchanged after 30 min and decreased to 57 +/- 26% after 1 h (n.s.). MPA treatment did not affect PDGF-BB-induced AP-1 activity determined after 1 h and 2 h. The inhibitory MPA effect on PDGF-BB-induced PDGF-B expression was not significantly restored by guanosine (56 +/- 18% versus 32 +/- 17% after 2 h, n.s.), and MPA inhibition of PDGF-BB-induced Egr-1 expression was not reversed by exogenous guanosine.

CONCLUSIONS

Treatment of cultured MCs with MPA inhibits MC proliferation correlating with a downregulation of the PDGF-B gene and protein expression and a suppression of Egr-1 mRNA expression. Since exogenous guanosine was not able to reverse the inhibitory MPA effect on PDGF-B and Egr-1 expression, we conclude that the antiproliferative effect of MPA on MCs may not solely depend on dGTP depletion but on a specific interference with the autocrine PDGF-B synthesis and Egr-1 expression of MCs.

Propranolol promotes Egr1 gene expression in cardiomyocytes via beta-adrenoceptors

Recent research has revealed that propranolol, a beta-adrenoceptor antagonist, causes extracellular signal-regulated kinase (ERK) cascade activation, nuclear translocation of phospho-ERK and increased transcriptional activity in cultured cell lines. Given the importance of beta-adrenoceptor antagonists in the treatment of heart failure, we evaluated the capability of propranolol of promoting the ERK-dependent gene expression at the cardiomyocyte level. To this end, the gene expression of the early growth response factor 1 (Egr1), a well-recognized indicator of nuclear extracellular signal-regulated kinase 1/2 (ERK1/2) activation, was assessed by quantitative real-time RT-PCR in vivo as well as in vitro experiments. Propranolol, administered at the dose of 10 mg/kg/day in C57BL/6 mice, caused a approximately 19-fold increase of Egr1 mRNA expression in left ventricular myocardium along with a approximately 2.1-fold increase of Egr1 protein expression. Isoproterenol, a nonselective beta-adrenoceptor agonist, also increased Egr1 mRNA and protein expression but to a lesser degree. Remarkably, isoproterenol administration was associated with the development of cardiac hypertrophy, whereas propranolol-treated mice showed a completely normal cardiac morphology. The effect of propranolol on Egr1 mRNA expression was abrogated in mice lacking beta(1)- and beta(2)-adrenoceptors indicating that propranolol increases Egr1 mRNA expression in a beta-adrenoceptor-dependent manner. The role of beta-adrenoceptors was further confirmed by showing that propranolol was able to increase Egr1 mRNA and protein levels in cultured neonatal cardiomyocytes. Collectively, these results indicate that propranolol promotes Egr1 gene expression in cardiomyocytes via beta-adrenoceptors with a mechanism which is independent of its ability to antagonize the effects of catecholamines. It is also suggested that cardiomyocyte growth and Egr1 gene overexpression are not obligate processes.

Mitogenic signaling pathways induced by G protein-coupled receptors

G protein-coupled receptor (GPCR) agonists, including neurotransmitters, hormones, chemokines, and bioactive lipids, act as potent cellular growth factors and have been implicated in a variety of normal and abnormal processes, including development, inflammation, and malignant transformation. Typically, the binding of an agonistic ligand to its cognate GPCR triggers the activation of multiple signal transduction pathways that act in a synergistic and combinatorial fashion to relay the mitogenic signal to the nucleus and promote cell proliferation. A rapid increase in the activity of phospholipases C, D, and A2 leading to the synthesis of lipid-derived second messengers, Ca2+ fluxes and subsequent activation of protein phosphorylation cascades, including PKC/PKD, Raf/MEK/ERK, and Akt/mTOR/p70S6K is an important early response to mitogenic GPCR agonists. The EGF receptor (EGFR) tyrosine kinase has emerged as a transducer in the signaling by GPCRs, a process termed transactivation. GPCR signal transduction also induces striking morphological changes and rapid tyrosine phosphorylation of multiple cellular proteins, including the non-receptor tyrosine kinases Src, focal adhesion kinase (FAK), and the adaptor proteins CAS and paxillin. The pathways stimulated by GPCRs are extensively interconnected by synergistic and antagonistic crosstalks that play a critical role in signal transmission, integration, and dissemination. The purpose of this article is to review recent advances in defining the pathways that play a role in transducing mitogenic responses induced by GPCR agonists.

Vasopressin receptor subtype 2 activation increases cell proliferation in the renal medulla of AQP1 null mice

Aquaporin (AQP) 1 null mice have a defect in the renal concentrating gradient because of their inability to generate a hyperosmotic medullary interstitium. To determine the effect of vasopressin on renal medullary gene expression, in the absence of high local osmolarity, we infused 1-deamino-8-d-arginine vasopressin (dDAVP), a V(2) receptor (V(2)R)-specific agonist, in AQP1 null mice for 7 days. cDNA microarray analysis was performed on the renal medullary tissue, and 5,140 genes of the possible 12,000 genes on the array were included in the analysis. In the renal medulla of AQP1 null mice, 245 transcripts were identified as increased by dDAVP infusion and 200 transcripts as decreased (1.5-fold or more). Quantitative real-time PCR measurements confirmed the increases seen for cyclin D1, early growth response gene 1, and activating transcription factor 3, genes associated with changes in cell cycle/growth. Changes in mRNA expression were correlated with changes in protein expression by semiquantitative immunoblotting; cyclin D1 and ATF3 were increased significantly in abundance following dDAVP infusion in the renal medulla of AQP1 null mice (161 and 461%, respectively). A significant increase in proliferation of medullary collecting ducts cells, following V(2)R activation, was identified by proliferating cell nuclear antigen immunohistochemistry; colocalization studies with AQP2 indicated that the increase in proliferation was primarily observed in principal cells of the inner medullary collecting duct (IMCD). V(2)R activation, via dDAVP, increased AQP2 and AQP3 protein abundance in the cortical collecting ducts of AQP1 null mice. However, V(2)R activation did not increase AQP2 protein abundance in the IMCD of AQP1 null mice.

ARA54 is involved in transcriptional regulation of the cyclin D1 gene in human cancer cells

Cyclin D1 is one of the major enhancers of cell cycle progression and its expression is regulated in several growth stimulatory signaling pathways. ARA54 is an androgen receptor (AR) co-activator that enhances AR-dependent transcriptional activation. Although expression of ARA54 mRNA is observed in a variety of human tissues at low levels, the AR- or androgen-independent function of ARA54 in those tissues remains unclear. In this study, we identified a novel role for ARA54 in the regulation of cyclin D1 expression in the absence of AR stimulation in human cancer cells. Depletion of endogenous ARA54 by small interfering RNA decreased both the protein and mRNA levels of cyclin D1. These changes did not result from a reduction in the half-life of either the protein or the mRNA, but from suppression of cyclin D1 gene transcription. In T98G cells, depletion of ARA54 increased the population of cells in G(1) phase, but reduced the population of cells in S phase, leading to a significant increase in the G(1)/S ratio and impaired cell growth. Furthermore, the amount of ARA54 mRNA appeared to positively correlate with cyclin D1 mRNA levels in specimens of clinical colon carcinomas, indicating that ARA54 is not only involved in the regulation of cyclin D1 expression in cultured cell lines but also in clinical cancer specimens. These results suggest that ARA54 might participate in enhancing cell cycle progression and cell proliferation via induction of cyclin D1.

Activating Transcription Factor-1-mediated Hepatocyte Growth Factor-induced Down-regulation of Thrombospondin-1 Expression Leads to Thyroid Cancer Cell Invasion

Hepatocyte growth factor (HGF) plays a major role in the pathogenesis of a variety of human epithelial tumors including papillary carcinoma of the thyroid. Previous reports demonstrated that HGF, acting through the Met receptor, repressed thrombospondin-1 (TSP-1) expression. To study the mechanisms by which HGF down-regulated TSP-1 expression, we transiently transfected a panel of deleted human TSP-1 promoter reporter plasmids into papillary thyroid carcinoma cells. We identified a region between -1210 and -1123 bp relative to the transcription start site that is responsive to HGF treatment and harbors a cAMP-responsive element (CRE) at position -1199 (TGACGTCC). Overexpression of various members of the CRE-binding protein family identified activating transcription factor-1 (ATF-1) as the transcription factor responsible for HGF-induced repression of TSP-1 promoter activity. This inhibition was associated with a concomitant increase in the abundance of nuclear ATF-1 protein. Gel shift and antibody supershift studies indicated that ATF-1 was involved in DNA binding to the TSP-1-CRE site. Finally, we utilized small hairpin RNA to target ATF-1 and showed that these small interfering RNA constructs significantly inhibited ATF-1 expression at both the RNA and the protein level. ATF-1 knockdown prevented HGF-induced down-regulation of TSP-1 promoter activity and protein expression and also reduced HGF-dependent tumor cell invasion. Taken together, our results indicate that HGF-induced down-regulation of TSP-1 expression is mediated by the interaction of ATF-1 with the CRE binding site in the TSP-1 promoter and that this transcription factor plays a crucial role for tumor invasiveness in papillary carcinoma of the thyroid triggered by HGF.

Reactive oxygen species, cell growth, cell cycle progression and vascular remodeling in hypertension

Reactive oxygen species (ROS) include superoxide, hygrogen peroxide and hydroxyl radical. Under physiological conditions, all vascular cell types produce ROS in a controlled and regulated fashion, mainly through nonphagocyte NADPH oxidase. An imbalance between pro-oxidants and antioxidants results in oxidative stress. ROS are important intracellular signaling molecules. There is growing evidence that increased oxidative stress and associated oxidative damage are mediators of vascular injury in hypertension, as well as in other cardiovascular diseases. Oxidative stress causes vascular injury by reducing nitric oxide bioavailability, altering endothelial function and vascular contraction/dilation, promoting vascular smooth muscle cell proliferation and hypertrophy, and increasing extracellular matrix deposition and inflammation. The present review focuses on the regulatory role of ROS on cell growth and cell cycle progression and discusses implications of these events in vascular remodeling in hypertension.

Identification of a putative nuclear localization sequence within ANG II AT(1A) receptor associated with nuclear activation

Angiotensin II (ANG II) type 1 (AT(1)) receptors, similar to other G protein-coupled receptors, undergo desensitization and internalization, and potentially nuclear localization, subsequent to agonist interaction. Evidence suggests that the carboxy-terminal tail may be involved in receptor nuclear localization. In the present study, we examined the carboxy-terminal tail of the receptor for specific regions responsible for the nuclear translocation phenomenon and resultant nuclear activation. Human embryonic kidney cells stably expressing either a wild-type AT(1A) receptor-green fluorescent protein (AT(1A)R/GFP) construct or a site-directed mutation of a putative nuclear localization sequence (NLS) [K307Q]AT(1A)R/GFP (KQ/AT(1A)R/GFP), were examined for differences in receptor nuclear trafficking and nuclear activation. Receptor expression, intracellular signaling, and ANG II-induced internalization of the wild-type/GFP construct and of the KQ/AT(1A)R/GFP mutant was similar. Laser scanning confocal microscopy showed that in cells expressing the AT(1A)R/GFP, trafficking of the receptor to the nuclear area and colocalization with lamin B occurred within 30 min of ANG II (100 nM) stimulation, whereas the KQ/AT(1A)R/GFP mutant failed to demonstrate nuclear localization. Immunoblotting of nuclear lysates with an anti-GFP antibody confirmed these observations. Nuclear localization of the wild-type receptor correlated with increase transcription for both EGR-1 and PTGS-2 genes while the nuclear-deficient KQ/AT(1A)R/GFP mutant demonstrated increases for only the EGR-1 gene. These results suggest that a NLS (KKFKKY; aa307-312) is located within the cytoplasmic tail of the AT(1A) receptor and that nuclear localization of the receptor corresponds with specific activation of transcription for the COX-2 gene PTGS-2.

Upregulation of rat Ccnd1 gene by exendin-4 in pancreatic beta cell line INS-1: interaction of early growth response-1 with cis-regulatory element

AIMS/HYPOTHESIS

The aim of this study was to investigate the effect of exendin-4 on the expression of cyclin D1 gene (Ccnd1), which is critical in regulating the progression of the cell cycle in INS-1 cells.

MATERIALS AND METHODS

INS-1 cells were stimulated with exendin-4 (10 nmol/l). Transient transfection and luciferase reporter assays were performed to measure promoter activities of rat Ccnd1. Electrophoretic mobility shift and chromatin immunoprecipitation assays were used to examine the binding of transcription factors to sites responsive to exendin-4 in vitro and in vivo, respectively.

RESULTS

Exendin-4 increased both Ccnd1 mRNA and its protein levels in a time-dependent manner. The region from -174 to +130 of the promoter was found to contain cis-regulatory elements responsible for exendin-4-mediated gene induction. Early growth response-1 (EGR1) protein was bound to the region from -153 to -134, which includes the putative EGR1 binding site (5'-CACCCCCGC-3'). Moreover, exendin-4 recruited EGR1 protein to the promoter in vivo.

CONCLUSIONS/INTERPRETATION

These findings suggest that exendin-4 activates Ccnd1 transcription through induction of EGR1 binding to a cis-regulatory element between -153 and -134 on the rat Ccnd1 promoter. These results provide an important indication that exendin-4 is a growth factor regulating beta cell proliferation.

Regulation of the neuronal proteasome by Zif268 (Egr1)

Most forms of neuronal plasticity are associated with induction of the transcription factor Zif268 (Egr1/Krox24/NGF-IA). In a genome-wide scan, we obtained evidence for potential modulation of proteasome subunit and regulatory genes by Zif268 in neurons, a finding of significance considering emerging evidence that the proteasome modulates synaptic function. Bioinformatic analysis indicated that the candidate proteasome Zif268 target genes had a rich concentration of putative Zif268 binding sites immediately upstream of the transcriptional start sites. Regulation of the mRNAs encoding the psmb9 (Lmp2) and psme2 (PA28beta) proteasome subunits, along with the proteasome-regulatory kinase serum/glucocorticoid-regulated kinase (SGK) and the proteasome-associated antigen peptide transporter subunit 1 (Tap1), was confirmed after transfection of a neuronal cell line with Zif268. Conversely, these mRNAs were upregulated in cerebral cortex tissue from Zif268 knock-out mice relative to controls, confirming that Zif268 suppresses their expression in the CNS. Transfected Zif268 reduced the activity of psmb9, SGK, and Tap1 promoter-reporter constructs. Altered psmb9, SGK, and Tap1 mRNA levels were also observed in an in vivo model of neuronal plasticity involving Zif268 induction: the effect of haloperidol administration on striatal gene expression. Consistent with these effects on proteasome gene expression, increased Zif268 expression suppressed proteasome activity, whereas Zif268 knock-out mice exhibited elevated cortical proteasome activity. Our findings reveal that Zif268 regulates the expression of proteasome and related genes in neuronal cells and provide new evidence that altered expression of proteasome activity after Zif268 induction may be a key component of long-lasting CNS plasticity.

Regulation of Na+/H+ exchanger-NHE3 by angiotensin-II in OKP cells

Previous studies have shown that circulating Angiotensin II (A-II) increases renal Na+ reabsorption via elevated Na+/H+ exchanger isoform 3 (NHE3) activity. We hypothesized that prolonged exposure to A-II leads to an increased expression of renal NHE3 by a transcriptionally mediated mechanism. To test this hypothesis, we utilized the proximal tubule-like OKP cell line to evaluate the effects of 16-h treatment with A-II on NHE3 activity and gene expression. A-II significantly stimulated NHE3-mediated, S-3226-sensitive Na+/H+ exchange. Inhibition of transcription with actinomycin D abolished the stimulatory effect of A-II on NHE3-mediated pH recovery in acid-loaded OKP cells. This prolonged exposure to A-II was also found to elevate endogenous NHE3 mRNA (by 40%)-an effect also abolished by inhibition of gene transcription. To evaluate the molecular mechanism by which A-II regulates NHE3 expression, the activity of NHE3 promoter driven reporter gene was analyzed in transient transfection assays. In transfected OKP cells, rat NHE3 promoter activity was significantly stimulated by A-II treatment, and preliminary mapping indicated that the A-II responsive element(s) is present between 149 and 548 bp upstream of the transcription initiation site in the NHE3 gene promoter. We conclude that a transcriptional mechanism is at least partially responsible for the chronic effects of A-II treatment on renal NHE3 activity.

Berberine suppresses MEK/ERK-dependent Egr-1 signaling pathway and inhibits vascular smooth muscle cell regrowth after in vitro mechanical injury

Vascular smooth muscle cell (SMC) proliferation plays an important role in the pathogenesis of atherosclerosis and post-angioplasty restenosis. Berberine is a well-known component of the Chinese herb medicine Huanglian (Coptis chinensis), and is capable of inhibiting SMC contraction and proliferation, yet the exact mechanism is unknown. We therefore investigated the effect of berberine on SMC growth after mechanic injury in vitro. DNA synthesis and cell proliferation assay were performed to show that berberine inhibited serum-stimulated rat aortic SMC growth in a concentration-dependent manner. Mechanical injury with sterile pipette tip stimulated the regrowth of SMCs. Treatment with berberine prevented the regrowth and migration of SMCs into the denuded trauma zone. Western blot analysis showed that activation of the MEK1/2 (mitogen-activated protein kinase kinase 1/2), extracellular signal-regulated kinase (ERK), and up-regulation of early growth response gene (Egr-1), c-Fos and Cyclin D1 were observed sequentially after mechanic injury in vitro. Semi-quantitative reverse-transcription PCR assay further confirmed the increase of Egr-1, c-Fos, platelet-derived growth factor (PDGF) and Cyclin D1 expression in a transcriptional level. However, berberine significantly attenuated MEK/ERK activation and downstream target (Egr-1, c-Fos, Cyclin D1 and PDGF-A) expression after mechanic injury in vitro. Our study showed that berberine blocked injury-induced SMC regrowth by inactivation of ERK/Egr-1 signaling pathway thereby preventing early signaling induced by injury in vitro. The anti-proliferative properties of berberine may be useful in treating disorders due to inappropriate SMC growth.

Cyclin D1 activation through ATF-2 in Reg-induced pancreatic beta-cell regeneration

Regenerating gene product (Reg) is induced in pancreatic beta-cells and acts as an autocrine/paracrine growth factor for regeneration via a cell surface Reg receptor. However, the manner by which Reg induces beta-cell regeneration was unknown. In the present study, we found that Reg increased phospho-ATF-2, which binds to -57 to -52 of the cyclin D1 gene to activate the promoter. The Reg/ATF-2-induced cyclin D1 promoter activation was attenuated by PI(3)K inhibitors such as LY294002 and wortmannin. In Reg knockout mouse islets, the levels of phospho-ATF-2, cyclin D1, and phospho-Rb were greatly decreased. These results indicate that the Reg-Reg receptor system stimulates the PI(3)K/ATF-2/cyclin D1 signaling pathway to induce beta-cell regeneration.

Bombesin regulates cyclin D1 expression through the early growth response protein Egr-1 in prostate cancer cells

Our previous studies indicate that the activation of mitogen-activated protein kinase (MAPK) pathway is involved in bombesin-induced cell proliferation in prostate cancer cells. Cyclin D1 is a critical regulator involved in cell cycle progression through the G1 phase into the S phase, thereby contributing to cell proliferation. Mostly, mitogen-stimulated expression of cyclin D1 is attributed to the extracellular signal-regulated kinase (ERK) activation. Here, we found that bombesin induced human cyclin D1 expression on both mRNA and protein levels in DU-145 prostate cancer cells. Mutational analyses showed that bombesin-enhanced cyclin D1 transcription required the binding of nuclear proteins to the -143 to -105 region of the human cyclin D1 promoter, which contains binding sites for transcription factors Sp-1 and early growth response protein (Egr-1). Do novo protein synthesis was requisite for bombesin-induced cyclin D1 expression. Further studies showed Egr-1 was induced upon bombesin stimulation. The induction of Egr-1 expression and its binding to the cyclin D1 promoter were essential for bombesin-enhanced cyclin D1 transcription. Inhibition of MAPK pathway with either the MEK1 inhibitor PD98059 or a dominant-negative Ras mutant, RasN17, abolished bombesin-induced cyclin D1 activation. Taken together, bombesin-induced cyclin D1 expression in prostate cancer cells is mediated by Egr-1 activation and the interaction of Egr-1 with the Egr-1/Sp1 motif of the cyclin D1 promoter through the activation of MAPK pathway. These findings represent a novel mechanism of bombesin-dependent stimulation of mitogenesis by regulating directly the cell cycle in prostate cancer.

Receptor-specific Ubiquitination of β-Arrestin Directs Assembly and Targeting of Seven-transmembrane Receptor Signalosomes

Angiotensin II type 1a (AT1a), vasopressin V2, and neurokinin 1 (NK1) receptors are seven-transmembrane receptors (7TMRs) that bind and co-internalize with the multifunctional adaptor protein, beta-arrestin. These receptors also lead to robust and persistent activation of extracellular-signal regulated kinase 1/2 (ERK1/2) localized on endosomes. Recently, the co-trafficking of receptor-beta-arrestin complexes to endosomes was demonstrated to require stable beta-arrestin ubiquitination (Shenoy, S. K., and Lefkowitz, R. J. (2003) J. Biol. Chem. 278, 14498-14506). We now report that lysines at positions 11 and 12 in beta-arrestin2 are specific and required sites for its AngII-mediated sustained ubiquitination. Thus, upon AngII stimulation the mutant beta-arrestin2(K11,12R) is only transiently ubiquitinated, does not form stable endocytic complexes with the AT1aR, and is impaired in scaffolding-activated ERK1/2. Fusion of a ubiquitin moiety in-frame to beta-arrestin2(K11,12R) restores AngII-mediated trafficking and signaling. Wild type beta-arrestin2 and beta-arrestin2(K11R,K12R)-Ub, but not beta-arrestin2(K11R,K12R), prevent nuclear translocation of pERK. These findings imply that sustained beta-arrestin ubiquitination not only directs co-trafficking of receptor-beta-arrestin complexes but also orchestrates the targeting of "7TMR signalosomes" to microcompartments within the cell. Surprisingly, binding of beta-arrestin2(K11R,K12R) to V2R and NK1R is indistinguishable from that of wild type beta-arrestin2. Moreover, ubiquitination patterns and ERK scaffolding of beta-arrestin2(K11,12R) are unimpaired with respect to V2R stimulation. In contrast, a quintuple lysine mutant (beta-arrestin2(K18R,K107R,K108R,K207R,K296R)) is impaired in endosomal trafficking in response to V2R but not AT1aR stimulation. Our findings delineate a novel regulatory mechanism for 7TMR signaling, dictated by the ubiquitination of beta-arrestin on specific lysines that become accessible for modification due to the specific receptor-bound conformational states of beta-arrestin2.

Exploring the characteristics of sequence elements in proximal promoters of human genes

Central to reconstruction of cis-regulatory networks is identification and classification of naturally occurring transcription factor-binding sites according to the genes that they control. We have examined salient characteristics of 9-mers that occur in various orders and combinations in the proximal promoters of human genes. In evaluations of a dataset derived with respect to experimentally defined transcription initiation sites, in some cases we observed a clear correspondence of highly ranked 9-mers with protein-binding sites in genomic DNA. Evaluations of the larger dataset, derived with respect to the 5' end of human ESTs, revealed that a subset of the highly ranked 9-mers corresponded to sites for several known transcription factor families (including CREB, ETS, EGR-1, SP1, KLF, MAZ, HIF-1, and STATs) that play important roles in the regulation of vertebrate genes. We identified several highly ranked CpG-containing 9-mers, defining sites for interactions with the CREB and ETS families of proteins, and identified potential target genes for these proteins. The results of the studies imply that the CpG-containing transcription factor-binding sites regulate the expression of genes with important roles in pathways leading to cell-type-specific gene expression and pathways controlled by the complex networks of signaling systems.

Stretch-inducible Expression of the Angiogenic Factor CCN1 in Vascular Smooth Muscle Cells Is Mediated by Egr-1

CCN1 is an angiogenic factor that promotes cell adhesion, proliferation, and differentiation. CCN1-deficient mice suffer embryonic death because of vascular defects, demonstrating that CCN1 is required for vessel development. Because mechanical stretch may act as a trigger for vessel development, we investigated the impact of mechanical stretch on the regulatory mechanism of CCN1 expression. Mechanical stretch rapidly enhances CCN1 expression and release in vascular smooth muscle cells (VSMC) in vitro and CCN1 expression in murine aortic segments in vivo. Transfection experiments of VSMC with deletion constructs of the CCN1 promoter revealed the regulatory region responsible for the stretch-induced CCN1 expression in the approximately 200-bp promoter region upstream of the TATA-box containing potential binding sites for early growth response-1 (Egr-1), nuclear factor of activated T-cells and cAMP response element binding protein. Decoy oligonucleotides to Egr-1, but not to nuclear factor of activated T-cells or cAMP response element binding protein, abolished the stretch-induced transcription of CCN1. In addition, mutagenesis of the Egr-1 binding site within the CCN1 promoter completely blunted the stretch-induced activation of the promoter. Furthermore, mechanical stretch induced the expression and DNA-binding activity of Egr-1 in VSMC as demonstrated by Western blot and electromobility shift assay. Moreover, a pressure overload-dependent de novo synthesis of Egr-1 was observed after aortic banding. These findings indicate that mechanical stretch leads to enhanced expression of CCN1 via the mechanosensitive transcription factor Egr-1, suggesting a central role for mechanical stretch in the regulation of CCN1-dependent pro-angiogenic potency.

Modulation of cyclin D1 and early growth response factor-1 gene expression in interleukin-1beta-treated rat smooth muscle cells by n-6 and n-3 polyunsaturated fatty acids

The proliferation of smooth muscle cells (SMC) is a key event in the development of atherosclerosis. In addition to growth factors or cytokines, we have shown previously that n-3 polyunsaturated fatty acids (PUFAs) act in opposition to n-6 PUFAs by modulating various steps of the inflammatory process. We have investigated the molecular mechanisms by which the incorporation of the n-6 PUFA, arachidonic acid, increases the proliferation of rat SMC treated with interleukin-1beta, while the n-3 PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), elicit no mitogenic response. Incorporation of EPA or DHA into SMC, which are then activated by interleukin-1beta to mimic inflammation, decreases promoter activity of the cyclin D1 gene and phosphorylation of the retinoblastoma protein. Together, our data demonstrate that n-3 effects are dependent on the Ras/Raf-1/extracellular signal regulated kinase (ERK)/mitogen-activated protein kinase pathway, and that down-regulation of the cyclin D1 promoter activity is mediated by the specific binding of the early growth response factor-1. Finally, we have shown that the incorporation of EPA and DHA also increased the concentration of caveolin-1 and caveolin-3 in caveolae, which correlated with n-3 PUFA inhibition of SMC proliferation through the mitogen-activated protein kinase pathway. We provide evidence indicating that, in contrast to n-6 PUFAs, n-3 PUFAs exert antiproliferative effects on SMC through the mitogen-activated protein kinase/ERK pathway.