ANG II-induced cell proliferation is dually mediated by c-Src/Yes/Fyn-regulated ERK1/2 activation in the cytoplasm and PKCζ-controlled ERK1/2 activity within the nucleus

c-Src Inhibition Improves Cardiovascular Function but not Remodeling or Fibrosis in Angiotensin II–Induced Hypertension

c-Src plays an important role in angiotensin II (Ang II) signaling. Whether this member of the Src family kinases is involved in the development of Ang II–induced hypertension and associated cardiovascular damage in vivo remains unknown. Here, we studied Ang II–infused (400 ng/kg/min) mice in which c-Src was partially deleted ( c-Src +/− ) and in wild-type (WT, c-Src +/+ ) mice treated with a c-Src inhibitor (CGP077675; 25 mg/kg/d). Ang II increased blood pressure and induced endothelial dysfunction in WT mice, responses that were ameliorated in c-Src +/− and CGP077675-treated mice. Vascular wall thickness and cross-sectional area were similarly increased by Ang II in WT and c-Src +/− mice. CGP077675 further increased cross-sectional area in hypertensive mice. Cardiac dysfunction (ejection fraction and fractional shortening) in Ang II–infused WT mice was normalized in c-Src +/− mice. Increased oxidative stress (plasma thiobarbituric acid–reactive substances, hydrogen peroxide, and vascular superoxide generation) in Ang II–infused WT mice was attenuated in c-Src–deficient and CGP077675-treated mice. Hyperactivation of vascular c-Src, ERK1/2 (extracellular signal–regulated kinase 1/2), and JNK (c-Jun N-terminal kinase) in hypertensive mice was normalized in CGP077675-treated and c-Src +/− mice. Vascular fibronectin was increased by Ang II in all groups and further augmented by CGP077675. Cardiac fibrosis and inflammation induced by Ang II were amplified in c-Src +/− and CGP-treated mice. Our data indicate that although c-Src downregulation attenuates development of hypertension, improves endothelial and cardiac function, reduces oxidative stress, and normalizes vascular signaling, it has little beneficial effect on fibrosis. These findings suggest a divergent role for c-Src in Ang II–dependent hypertension, where c-Src may be more important in regulating redox-sensitive cardiac and vascular function than fibrosis and remodeling.

The role of β-arrestin2-dependent signaling in thoracic aortic aneurysm formation in a murine model of Marfan syndrome

Ang II type 1a receptor (AT1aR)-mediated activation of MAPKs contributes to thoracic aortic aneurysm (TAA) development in Marfan syndrome (MFS). β-Arrestin2 (βarr2) is known to mediate AT1aR-dependent MAPK activation, as well as proproliferative and profibrotic signaling in aortic vascular smooth muscle cells. Therefore, we investigated whether βarr2-dependent signaling contributes to TAA formation in MFS. We used a murine model of MFS [fibrillin (Fbn)(C1039G/+)] to generate an MFS murine model in combination with genetic βarr2 deletion (Fbn(C1039G/+)/βarr2(-/-)). Fbn(C1039G/+)/βarr2(-/-) mice displayed delayed aortic root dilation compared with Fbn(C1039G/+) mice. The mRNA and protein expression of several mediators of TAA formation, including matrix metalloproteinase (MMP)-2 and -9, was reduced in the aorta of Fbn(C1039G/+)/βarr2(-/-) mice relative to Fbn(C1039G/+) mice. Activation of ERK1/2 was also decreased in the aortas of Fbn(C1039G/+)/βarr2(-/-) mice compared with Fbn(C1039G/+) animals. Small interfering RNA targeting βarr2 inhibited angiotensin-stimulated expression of proaneurysmal signaling mediators in primary aortic root smooth muscle cells. Angiotensin-stimulated expression of the proaneurysmal signaling mediators MMP-2 and -9 was inhibited by blockade of ERK1/2 or the EGF receptor, whereas blockade of the transforming growth factor-β receptor had no effect. These results suggest that βarr2 contributes to TAA formation in MFS by regulating ERK1/2-dependent expression of proaneurysmal genes and proteins downstream of the AT1aR. Importantly, this demonstration of the unique signaling mechanism by which βarr2 contributes to aneurysm formation identifies multiple novel, potential therapeutic targets in MFS.

The Nox1/4 Dual Inhibitor GKT137831 or Nox4 Knockdown Inhibits Angiotensin-II-Induced Adult Mouse Cardiac Fibroblast Proliferation and Migration. AT1 Physically Associates With Nox4

Both oxidative stress and inflammation contribute to chronic hypertension-induced myocardial fibrosis and adverse cardiac remodeling. Here we investigated whether angiotensin (Ang)-II-induced fibroblast proliferation and migration are NADPH oxidase (Nox) 4/ROS and IL-18 dependent. Our results show that the potent induction of mouse cardiac fibroblast (CF) proliferation and migration by Ang-II is markedly attenuated by Nox4 knockdown and the Nox inhibitor DPI. Further, Nox4 knockdown and DPI pre-treatment attenuated Ang-II-induced IL-18, IL-18Rα and collagen expression, and MMP9 and LOX activation. While neutralization of IL-18 blunted Ang-II-induced CF proliferation and migration, knockdown of MMP9 attenuated CF migration. The antioxidant NAC and the cell-permeable SOD mimetics Tempol, MnTBAP, and MnTMPyP attenuated oxidative stress and inhibited CF proliferation and migration. The Nox1/Nox4 dual inhibitor GKT137831 also blunted Ang-II-induced H2 O2 production and CF proliferation and migration. Further, AT1 bound Nox4, and Ang-II enhanced their physical association. Notably, GKT137831 attenuated the AT1/Nox4 interaction. These results indicate that Ang-II induces CF proliferation and migration in part via Nox4/ROS-dependent IL-18 induction and MMP9 activation, and may involve AT1/Nox4 physical association. Thus, either (i) neutralizing IL-18, (ii) blocking AT1/Nox4 interaction or (iii) use of the Nox1/Nox4 inhibitor GKT137831 may have therapeutic potential in chronic hypertension-induced adverse cardiac remodeling.

Sinodielide A exerts thermosensitizing effects and induces apoptosis and G2/M cell cycle arrest in DU145 human prostate cancer cells via the Ras/Raf/MAPK and PI3K/Akt signaling pathways

Sinodielide A (SA) is a naturally occurring guaianolide, which is isolated from the root of Sinodielsia yunnanensis. This root, commonly found in Yunnan province, is used in traditional Chinese medicine as an antipyretic, analgesic and diaphoretic agent. A number of studies have reported that agents isolated from a species of Umbelliferae (Apiaceae) have antitumor activities. We previously reported, using combined treatments with this medicinal herb and hyperthermia at various temperatures, an enhanced cytotoxicity in the human prostate cancer androgen‑independent cell lines, PC3 and DU145, and analyzed the related mechanisms. In the present study, we investigated the effects of treatment with SA prior to hyperthermia on the thermosensitivity of DU145 cells, and the mechanisms related to the induction of apoptosis and G(2)/M cell cycle arrest via the activation of extracellular-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) signaling pathways, as well as the phosphoinositide 3-kinase (PI3K)/Akt signaling pathways. Cells were exposed to hyperthermia alone (40-44˚C) or hyperthermia in combination with SA. Lethal damage to cells treated with mild hyperthermia (40 or 42˚C) for up to 6 h was slight; however, hyperthermia in combination with SA synergistically enhanced thermosensivity. Lethal damage to cells treated with acute hyperthermia (43 or 44˚C) was more severe, but these effects were also enhanced and were more significant by the combined treatment with SA. The kinetics of apoptosis induction and cell cycle distribution were analyzed by flow cytometry. In addition, the levels of ERK1/2, JNK and Akt were determined by western blot analysis. The incidence of apoptotic cells after treatment with SA (20.0 µM) at 37˚C for 4 h, hyperthermia (44˚C) alone for 30 min, and the combination in sequence were examined. The sub-G1 division (%) in the diagram obtained by flow cytometry was applied to that assay. The percentage of apoptotic cells (10.53±5.02%) was higher at 48 h as compared to 0, 12 and 24 h after treatment. The distribution of DU145 cells in the G2/M cell cycle phase was markedly increased after 24 h of heating at 44˚C and after the combined treatment with heating and SA. The phosphorylation of ERK1/2 was reduced following treatment with heating and SA, while the levels of phosphorylated JNK (p-JNK) were markedly increased immediately after heating at 44˚C and when heating was combined with SA. By contrast, the levels of phosphorylated Akt (p-Akt) were immediately increased only after heating at 44˚C. Thus, we concluded that SA exerts its thermosensitizing effects on DU145 cells by inhibiting the activation of the MAPK/ERK1/2 and PI3K/Akt signaling pathways.

Novel signaling mechanisms of intracellular angiotensin II-induced NHE3 expression and activation in mouse proximal tubule cells

Expression of a cytosolic cyan fluorescent fusion protein of angiotensin II (ECFP/ANG II) in proximal tubules increases blood pressure in rodents. To determine cellular signaling pathways responsible for this response, we expressed ECFP/ANG II in transport-competent mouse proximal convoluted tubule cells (mPCT) from wild-type (WT) and type 1a ANG II receptor-deficient (AT(1a)-KO) mice and measured its effects on intracellular ANG II levels, surrogates of Na/H exchanger 3 (NHE3)-dependent Na(+) absorption, as well as MAP kinases and NF-κB signaling. In WT mPCT cells, ECFP/ANG II expression doubled ANG II levels, increased NHE3 expression and membrane phospho-NHE3 proteins threefold and intracellular Na(+) concentration by 65%. These responses were associated with threefold increases in phospho-ERK 1/2 and phospho-p38 MAPK, fivefold increases in p65 subunit of NF-κB, and threefold increases in phospho-IKKα/β (Ser 176/180) proteins. These signaling responses to ECFP/ANG II were inhibited by losartan (AT(1) blocker), PD123319 (AT(2) blocker), U0126 (MEK1/MEK2 inhibitor), and RO 106-9920 (NF-κB inhibitor). In mPCT cells of AT(1a)-KO mice, ECFP/ANG II also increased the levels of NHE3, p-ERK1/2, and p65 proteins above their controls, but considerably less so than in WT cells. In WT mice, selective expression of ECFP/ANG II in vivo in proximal tubules significantly increased blood pressure and indices of sodium reabsorption, in particular levels of phosphorylated NHE3 protein in the membrane fraction and proton gradient-stimulated (22)Na(+) uptake by proximal tubules. We conclude that intracellular ANG II may induce NHE3 expression and activation in mPCTs via AT(1a)- and AT(2) receptor-mediated activation of MAP kinases ERK 1/2 and NF-κB signaling pathways.

Effect of heparin-derived oligosaccharide on vascular smooth muscle cell proliferation

In this study, the effect of heparin-derived oligosaccharide on bovine vascular smooth muscle cell (VSMC) proliferation and signal transduction mechanism was investigated. Extracellular-signal-regulated kinase (ERK) 1/2 has been implicated in the regulation of various cellular functions including proliferation, and we sought to define a functional role for ERK 1/2 in an established proliferation model in order to find a possible mechanism for inhibition of VSMC proliferation by heparin-derived oligosaccharide. The VSMC proliferation model was developed by platelet-derived growth factor (PDGF), and the level of ERK 1/2 protein and messenger RNA was determined by reverse transcriptase-polymerase chain reaction, Western blotting, and immunocytochemical methods. Flow cytometry analysis indicated that heparin-derived oligosaccharide blocked PDGF-induced cell cycle progression by arresting cells in the G0/G1 phase. The results imply that heparin-derived oligosaccharide inhibits VSMC proliferation by moderating the gene and the phosphorylation levels of ERK 1/2, eventually blocking G1/S transition, may be one of the mechanisms for inhibition of VSMC proliferation by heparin-derived oligosaccharide.

Protein kinase C (PKC)ζ-mediated Gαq stimulation of ERK5 protein pathway in cardiomyocytes and cardiac fibroblasts

Gq-coupled G protein-coupled receptors (GPCRs) mediate the actions of a variety of messengers that are key regulators of cardiovascular function. Enhanced Gα(q)-mediated signaling plays an important role in cardiac hypertrophy and in the transition to heart failure. We have recently described that Gα(q) acts as an adaptor protein that facilitates PKCζ-mediated activation of ERK5 in epithelial cells. Because the ERK5 cascade is known to be involved in cardiac hypertrophy, we have investigated the potential relevance of this pathway in cardiovascular Gq-dependent signaling using both cultured cardiac cell types and chronic administration of angiotensin II in mice. We find that PKCζ is required for the activation of the ERK5 pathway by Gq-coupled GPCR in neonatal and adult murine cardiomyocyte cultures and in cardiac fibroblasts. Stimulation of ERK5 by angiotensin II is blocked upon pharmacological inhibition or siRNA-mediated silencing of PKCζ in primary cultures of cardiac cells and in neonatal cardiomyocytes isolated from PKCζ-deficient mice. Moreover, upon chronic challenge with angiotensin II, these mice fail to promote the changes in the ERK5 pathway, in gene expression patterns, and in hypertrophic markers observed in wild-type animals. Taken together, our results show that PKCζ is essential for Gq-dependent ERK5 activation in cardiomyocytes and cardiac fibroblasts and indicate a key cardiac physiological role for the Gα(q)/PKCζ/ERK5 signaling axis.

AT₂receptors recruit c-Src, SHP-1 and FAK upon activation by Ang II in PND15 rat hindbrain

The functional role of AT(2) receptors is unclear and it activates unconventional signaling pathways, which in general do not involve a classical activation of a G-protein. In the present study, we aimed to investigate the transduction mechanism of AT(2) Ang II receptors in PND15 rat hindbrain membrane preparations, which represents a physiological developmental condition. To determine whether Ang II AT(2) receptors induced association to SHP-1 in rat hindbrain, co-immunoprecipitation assays were performed. Stimulation of Ang II AT(2) receptors induced both a transient tyr-phosphorylation and activation of SHP-1. The possible participation of c-Src in Ang II-mediated SHP-1 activation, we demonstrated by recruitment of c-Src in immunocomplexes obtained with anti AT(2) or anti-SHP-1 antibodies. The association of SHP-1 to c-Src was inhibited by PD123319 and the c-Src inhibitor PP2. Similarly, SHP-1 activity determined in AT(2)-immunocomplexes was inhibited by PD123319 and the c-Src inhibitor PP2. Following stimulation with Ang II, AT(2) receptors recruit c-Src, which was responsible for SHP-1 tyr-phosphorylation and activation. Since AT(2) receptors are involved in neuron migration, we tested the presence of FAK in immunocomplexes. Surprisingly, AT(2)-immunocomplexes contained mainly the 85kDa fragment of FAK. Besides, p125FAK associated to SHP-1. In summary, we demonstrated the presence of an active signal transduction mechanism in PND15 rat hindbrain, a developmental stage critical for cerebellar development. In this model, we showed a complex containing AT(2)/SHP-1/c-Src/p85FAK, suggesting a potential role of Ang II AT(2) receptors in cerebellar development and neuronal differentiation.

Multiplex analysis of Src family kinase signaling by microbead suspension arrays

There is renewed interest in the Src family of protein tyrosine kinases (SFKs) as a result of their potential utility as molecular targets for cancer therapy. This protein family consists of 9 nonreceptor tyrosine kinases that, although implicated in a diverse array of cellular functions, possess a similar modular structure. Here we describe a simple and efficient multiplex microbead immunoassay (MMIA), based on Luminex xMAP technology, which allows for the simultaneous detection of 8 phosphorylated SFKs in a single assay. Microbead sets identifiable by unique fluorescence were individually coated with antibodies specific for an individual SFK member. Detection of phosphorylated SFKs was accomplished using a secondary antibody directed against phosphotyrosine. The assay requires < or = 10 microg of cell lysate or nanogram amounts of purified SFK. The use of a generic secondary antibody allows for the expansion of the assay to include any other tyrosine kinase for which a specific antibody exists. Using either mammalian cell lines or purified, recombinant kinases as the SFK source, we demonstrate the utility of the assay by evaluating the phosphorylation status of SFK members following several in vitro manipulations designed to modulate the phosphotyrosine content of the kinases. These results show that the SFK multiplex assay is a robust tool to investigate the function of SFKs in basic and potentially in clinical research.

High-salt diet during pregnancy and angiotensin-related cardiac changes

OBJECTIVES

High-salt intake has been demonstrated in link to hypertension, and cardiovascular diseases could be programmed in fetal origins. We determined the influence of high-salt diet during pregnancy on the development of the heart.

METHODS

Fetal cardiac structures, cell cycle, renin-angiotensin system (RAS), and epigenetic alternations in the heart following maternal high salt intake during pregnancy were examined.

RESULTS

Following exposure to high salt, disorganized myofibrillae and mitochondria cristae loss were found in the fetus, S-phase for cardiac cells was enhanced, plasma angiotensin II decreased, and cardiac angiotensin II increased in the fetus. Angiotensin II-increased S-phase in the fetal cardiac cells was primarily via AT1 receptor mechanisms. AT2 receptor mRNA and protein in the fetal heart were not affected, whereas AT1 receptor protein, AT1a, and AT1b mRNA were increased. DNA methylation was found at the CpG sites that were related to AT1b receptors in the fetal heart. Cardiac AT1 receptor protein in the adult offspring was also higher following exposure to prenatal high salt.

CONCLUSION

The results suggest a relationship between high-salt diet in pregnancy and developmental changes of the cardiac cells and renin-angiotensin system.

Src tyrosine kinase regulates angiotensin II-induced protein kinase Czeta activation and proliferation in vascular smooth muscle cells

Protein kinase Czeta (PKCzeta) isoform plays a critical role in angiotensin II (AngII)-elicited extracellular signal-regulated kinase 1/2 (ERK1/2) activation and proliferation in vascular smooth muscle cells (VSMCs). However, the exact signal transduction mechanism by which AngII activates PKCzeta has not been clarified. In this study, we investigated the role of Src in PKCzeta activation and VSMCs proliferation induced by AngII. AngII-induced rapid activation of PKCzeta, which was associated with its phosphorylation and nuclear translocation. AngII not only induced Src activation but also promoted the physical association between Src and PKCzeta, which was abolished by Src inhibition with PP2. Src inhibition also abrogated AngII-stimulated PKCzeta activation, ERK1/2 phosphorylation and VSMCs proliferation. In conclusion, Src kinase plays an important role in AngII-elicited PKCzeta activation and the subsequent downstream signaling including ERK1/2 activation and VSMCs proliferation.

G alpha(q) acts as an adaptor protein in protein kinase C zeta (PKCzeta)-mediated ERK5 activation by G protein-coupled receptors (GPCR)

G(q)-coupled G protein-coupled receptors (GPCR) mediate the actions of a variety of messengers that are key regulators of different cellular functions. These receptors can regulate a highly interconnected network of biochemical routes that control the activity of several members of the mitogen-activated protein kinase (MAPK) family. The ERK5 MAPK has been shown to be activated by G(q)-coupled GPCR via unknown mechanisms. We find that the atypical protein kinase C (PKCzeta), previously reported to interact with the ERK5 activator MEK5 and to be involved in epidermal growth factor-mediated ERK5 stimulation, plays a crucial role in the activation of the ERK5 pathway by G(q)-coupled GPCR. Stimulation of ERK5 by G(q)-coupled GPCR is abolished upon pharmacological inhibition of PKCzeta as well as in embryonic fibroblasts obtained from PKCzeta-deficient mice. Both PKCzeta and MEK5 associate to G alpha(q) upon activation of GPCR, thus forming a ternary complex that seems essential for the activation of ERK5. These data put forward a novel function of G alpha(q) as a scaffold protein involved in the modulation of the ERK5 cascade by GPCR that could be relevant in G(q)-mediated physiological functions.

ALK1-Fc inhibits multiple mediators of angiogenesis and suppresses tumor growth

Activin receptor-like kinase-1 (ALK1) is a type I, endothelial cell-specific member of the transforming growth factor-beta superfamily of receptors known to play an essential role in modulating angiogenesis and vessel maintenance. In the present study, we sought to examine the angiogenic and tumorigenic effects mediated upon the inhibition of ALK1 signaling using a soluble chimeric protein (ALK1-Fc). Of 29 transforming growth factor-beta-related ligands screened by surface plasmon resonance, only bone morphogenetic protein (BMP9) and BMP10 displayed high-affinity binding to ALK1-Fc. In cell-based assays, ALK1-Fc inhibited BMP9-mediated Id-1 expression in human umbilical vein endothelial cells and inhibited cord formation by these cells on a Matrigel substrate. In a chick chorioallantoic membrane assay, ALK1-Fc reduced vascular endothelial growth factor-, fibroblast growth factor-, and BMP10-mediated vessel formation. The growth of B16 melanoma explants was also inhibited significantly by ALK1-Fc in this assay. Finally, ALK1-Fc treatment reduced tumor burden in mice receiving orthotopic grafts of MCF7 mammary adenocarcinoma cells. These data show the efficacy of chimeric ALK1-Fc proteins in mitigating vessel formation and support the view that ALK1-Fc is a powerful antiangiogenic agent capable of blocking vascularization.

Role of IRS-4 in PI3-K activation by insulin in HepG2 cells, modulation by Angiotensin II

Insulin receptor substrate-4 (IRS-4) has a limited tissue expression and its modulation by tyr-phosphorylation is still controversial. We evaluated the participation of IRS-4 in the cross-talk between Angiotensin II (Ang II) and Insulin (Ins) receptors in HepG2 cells. Ins (10(-7)M) induced tyr-phosphorylation of IRS-4 (maximal at 5 min), an effect potentiated by Ang II AT(1) receptors. Phosphatydilinositol-3 kinase (PI3-K) inhibitors Wortmanin or LY294002 reduced Ang II effect on tyr-phosphorylation of IRS-4 to a level comparable to that of Ins alone. Physical association between IRS-4 substrate and PI3-K was demonstrated by co-immunoprecipitation. Recruitment of PI3-K by IRS-4 was induced by Ins (10(-7)M, 5 min) not by Ang II (10(-7)M) and this was inhibited by Wortmanin and LY294002. Ang II did not modify either the association or activation of PI3-K in immunocomplexes. The present data provide novel evidence of IRS-4 phosphorylation mediated by Ins, an effect modulated by Ang II. We report also Ins-induced PI3-K activation mediated by IRS-4. Our findings suggest a role for IRS-4 as a docking protein in the Ins signaling pathway that involves PI3-K association and activation. The present data suggest a possible participation of IRS-4 in cell proliferation Ins-induced.

Alterations of nAChRs and ERK1/2 in the brains of rats with chronic fluorosis and their connections with the decreased capacity of learning and memory

In order to reveal the mechanism of the decreased ability of learning and memory induced by chronic fluorosis, nicotinic acetylcholine receptors (nAChRs) and the pathway of extracellular signal regulated protein kinase (ERK1/2) were investigated by using the rats fed with different concentrations of sodium fluoride for 6 months. Spatial learning and memory of the rats were evaluated by Morris Water Maze test. The expressions of nAChRs, ERK1/2 and mitogen-induced extracellular kinase (MEK1/2) at protein and mRNA levels were detected by Western blotting and real-time PCR, respectively. The results showed that as compared with controls, the learning and memory capacity in the rats with fluorosis was decreased. The protein expressions of alpha7 and alpha4 nAChR subunits in rat brains with fluorosis were decreased by 35% and 33%, whereas the corresponding receptor subunit mRNAs did not exhibit any changes. The increases of phospho- and total-ERK1/2 as well as phospho-MEK1/2 at the protein levels were found in the brains of rats with fluorosis as compared to controls, and no difference of ERK1/2 mRNA was found. In addition, the activation rate of phospho-ERK1/2 was decreased in the brains affected with fluorosis. The modifications of nAChRs and ERK1/2 pathway might be connected with the molecular mechanisms in the decreased capacity of learning and memory of the rats with fluorosis.

Activation of MEK 1/2 and p42/44 MAPK by angiotensin II in hepatocyte nucleus and their potentiation by ethanol

Hepato-subcellular effect of angiotensin II (Ang II) and ethanol on the p42/44 mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK 1/2) was investigated in the nucleus of rat hepatocytes. Hepatocytes were treated with ethanol (100 mM) for 24h and stimulated with Ang II (100 nM, 5 min). The levels of p42/44 MAPK and MEK 1/2 were monitored in the nuclear fraction using antibodies. Ang II itself caused significant accumulation of phosphorylated p42/44 MAPK (phospho-p42/44 MAPK) in the nucleus without any significant translocation of p42/44 MAPK protein thereby suggesting activation of p42/44 MAPK in the nucleus. Ang II caused marked accumulation of phosphorylated MEK 1/2 (phospho-MEK 1/2) in the nucleus without any significant accumulation of MEK 1/2 protein. Ratio of phospho-MEK 1/2 to MEK 1/2 protein in the nucleus after Ang II treatment was 2.4 times greater than control suggesting phosphorylation of MEK 1/2 inside the nucleus. Ethanol had no effect on the protein level or the activation of p42/44 MAPK in the nucleus. Ethanol treatment potentiated nuclear activation of p42/44 MAPK by Ang II but not translocation of p42/44 MAPK protein. This was accompanied by potentiation of Ang II-stimulated accumulation of phospho-MEK 1/2 in the nucleus by ethanol. MEK 1/2 inhibitor, U-0126 inhibited Ang II response and its potentiation by ethanol. These results suggest that Ang II-mediated accumulation of phospho-p42/44 MAPK in the hepatocyte nucleus involves MEK 1/2-dependent activation and this effect is potentiated by ethanol.

Role of the renin-angiotensin system in prostate cancer

Prostate cancer is highly prevalent in Western society, and its early stages can be controlled by androgen ablation therapy. However, the cancer eventually regresses to an androgen-independent state for which there is no effective treatment. The renin-angiotensin system (RAS), in particular the octapeptide angiotensin II, is now recognised to have important effects on growth factor signalling and cell growth in addition to its well known actions on blood pressure, fluid homeostasis and electrolyte balance. All components of the RAS have been recently identified in the prostate, consistent with the expression of a local RAS system in this tissue. This review focuses on the role of the RAS in the prostate, and the possibility that this pathway may be a potential therapeutic target for the treatment of prostate cancer and other prostatic diseases.

Independent beta-arrestin2 and Gq/protein kinase Czeta pathways for ERK stimulated by angiotensin type 1A receptors in vascular smooth muscle cells converge on transactivation of the epidermal growth factor receptor

Recent studies in receptor-transfected cell lines have demonstrated that extracellular signal-regulated kinase (ERK) activation by angiotensin type 1A receptor and other G protein-coupled receptors can be mediated by both G protein-dependent and β-arrestin-dependent mechanisms. However, few studies have explored these mechanisms in primary cultured cells expressing endogenous levels of receptors. Accordingly, here we utilized the β-arrestin biased agonist for the angiotensin type 1A receptor, SII-angiotensin (SII), and RNA interference techniques to investigate angiotensin II (ANG)-activated β-arrestin-mediated mitogenic signaling pathways in rat vascular smooth muscle cells. Both ANG and SII induced DNA synthesis via the ERK activation cascade. Even though SII cannot induce calcium influx (G protein activation) after receptor stimulation, it does cause ERK activation, although less robustly than ANG. Activation by both ligands is diminished by depletion of β-arrestin2 by small interfering RNA, although the effect is more complete with SII. ERK activation at early time points but not later time points is strongly inhibited by those protein kinase C inhibitors that can block protein kinase Cζ. Moreover, ANG- and SII-mediated ERK activation require transactivation of the epidermal growth factor receptor via metalloprotease 2/9 and Src kinase. β-Arrestin2 facilitates ANG and SII stimulation of Src-mediated phosphorylation of Tyr-845 on the EGFR, a known site for Src phosphorylation. These studies delineate a convergent mechanism by which G protein-dependent and β-arrestin-dependent pathways can independently mediate ERK-dependent transactivation of the EGFR in vascular smooth muscle cells thus controlling cellular proliferative responses.

Involvement of c-Src tyrosine kinase in SHP-1 phosphatase activation by Ang II AT2 receptors in rat fetal tissues

Angiotensin II (Ang II) AT(2) receptors are abundantly expressed in rat fetal tissues where they probably contribute to development. In the present study we examine the effects of Ang II type 2 receptor stimulation on SHP-1 activation. Ang II (10(-7) M) elicits a rapid and transient tyrosine phosphorylation of SHP-1, maximal at 1 min, in a dose-dependent form, blocked by the AT(2) antagonist, PD123319. SHP-1 phosphorylation is followed in time by tyrosine dephosphorylation of different proteins, suggesting a sequence of events. Ang II induces association of SHP-1 to AT(2) receptors as shown by co-immunoprecipitation, Western blot and binding assays. SHP-1 activity was determined in immunocomplexes obtained with either anti-AT(2) or anti-SHP-1 antibodies, after Ang II stimulation (1 min), in correlation with the maximal level of SHP-1 phosphorylation. Interestingly, following receptor stimulation (1 min) c-Src was associated to AT(2) or SHP-1 immunocomplexes. Preincubation with the c-Src inhibitor PP2 inhibited SHP-1 activation and c-Src association, thus confirming the participation of c-Src in this pathway. We demonstrated here for the first time the involvement of c-Src in SHP-1 activation via AT(2) receptors present in an ex vivo model expressing both receptor subtypes. In this model, AT(2) receptors are not constitutively associated to SHP-1 and SHP-1 is not constitutively activated. Thus, we clearly establish that SHP-1 activation, mediated by the AT(2) subtype, involves c-Src and precedes protein tyrosine dephosphorylation, in rat fetal membranes.

Characterization of Fyn signaling on the age-dependent immuno-modulation on traumatic rats

Traumatic stress is well characterized to develop immuno-depression in our previous report. Here, we provide evidence that adult and aged rats showed similar decrease in lymphocyte proliferation and natural killer (NK) cell activity. However, compared with beginning recovering from traumatic stress after 3 day and fully recovered by 7 day in adult rats, aged rats begin the recovery phage later than 3 day and do not fully recovered by 7 day. In parallel, Fyn expression in cerebral cortex was augmented with the highest level at 3 day of trauma in both age groups of rats, although aged rats exhibited lower level than the younger cohorts. Immune consequences were consequently modified by intracerebroventricular (i.c.v.) injection of Fyn antibody or recombinant adenovirus expressing active Fyn. Finally, the increase in Fyn expression was converged on ERK1/2 (extracellular signal regulated kinase 1/2) activation. Taken together, the data indicated that immunological processes in response to traumatic stress was age dependent, Fyn-ERK1/2 signal pathway was required to convey the recovery signals.

Intracellular ANG II directly induces in vitro transcription of TGF-beta1, MCP-1, and NHE-3 mRNAs in isolated rat renal cortical nuclei via activation of nuclear AT1a receptors

The present study tested the hypothesis that intracellular ANG II directly induces transcriptional effects by stimulating AT(1a) receptors in the nucleus of rat renal cortical cells. Intact nuclei were freshly isolated from the rat renal cortex, and transcriptional responses to ANG II were studied using in vitro RNA transcription assays and semiquantitative RT-PCR. High-power phase-contrast micrographs showed that isolated nuclei were encircled by an intact nuclear envelope and stained strongly by the DNA marker 4',6-diamidino-2-phenylindole, but not by the membrane or endosomal markers. Fluorescein isothiocyanate-labeled ANG II and [(125)I]Val(5)-ANG II binding confirmed the presence of ANG II receptors in the nuclei with a predominance of AT(1) receptors. RT-PCR showed that AT(1a) mRNA expression was threefold greater than AT(1b) receptor mRNAs in these nuclei. In freshly isolated nuclei, ANG II increased in vitro [alpha-(32)P]CTP incorporation in a concentration-dependent manner, and the effect was confirmed by autoradiography and RNA electrophoresis. ANG II markedly increased in vitro transcription of mRNAs for transforming growth factor-beta1 by 143% (P < 0.01), macrophage chemoattractant protein-1 by 89% (P < 0.01), and the sodium and hydrogen exchanger-3 by 110% (P < 0.01). These transcriptional effects of ANG II on the nuclei were completely blocked by the AT(1) receptor antagonist losartan (P < 0.01). By contrast, ANG II had no effects on transcription of angiotensinogen and glyceraldehyde-3-phosphate dehydrogenase mRNAs. Because these transcriptional effects of ANG II in isolated nuclei were induced by ANG II in the absence of cell surface receptor-mediated signaling and completely blocked by losartan, we concluded that ANG II may directly stimulate nuclear AT(1a) receptors to induce transcriptional responses that are associated with tubular epithelial sodium transport, cellular growth and hypertrophy, and proinflammatory cytokines.

Angiotensin II-induced extracellular signal-regulated kinase 1/2 activation is mediated by protein kinase Cdelta and intracellular calcium in adult rat cardiac fibroblasts

Angiotensin II (Ang II)-induced proliferation of cardiac fibroblasts is a major contributing factor to the pathogenesis of cardiac fibrosis. Ang II activates extracellular signal-regulated kinase (ERK) 1/2 to induce cardiac fibroblast proliferation, but the signaling pathways leading to ERK 1/2 activation have not been elucidated in these cells. The goal of the current study was to identify the intracellular mediators of Ang II-induced ERK 1/2 activation in adult rat cardiac fibroblasts. We determined that 100 nmol/L of Ang II-induced ERK 1/2 phosphorylation is inhibited by simultaneous chelation of cytosolic calcium and downregulation of protein kinase C (PKC) by phorbol ester or by the specific PKCdelta inhibitor rottlerin, as well as PKCdelta small interfering RNA, but not by inhibition of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate, phorbol ester, rottlerin, or PKCdelta small interfering RNA alone. We also found that Ang II does not transactivate the epidermal growth factor receptor in adult cardiac fibroblasts, because pretreatment with 1 mumol/L of AG 1478 did not significantly inhibit [(3)H]-thymidine incorporation or ERK 1/2 activation. In addition, immunoprecipitation of the epidermal growth factor receptor demonstrated no significant Ang II-induced phosphorylation of tyrosine residues. Inhibition of phosphatidylinositide 3-kinase, PKCzeta, and src tyrosine kinase had no effect on Ang II-induced ERK 1/2 activation. Collectively, these data demonstrate that Ang II does not transactivate the epidermal growth factor receptor in adult rat cardiac fibroblasts to activate ERK 1/2, a common pathway described in vascular smooth muscle and other cell types, but rather occurs via activation of distinct parallel signaling pathways mechanistically controlled by intracellular Ca(2+) and PKCdelta.

The effect of angiotensin II and IV on ERK1/2 and CREB signalling in cultured rat astroglial cells

Angiotensin peptides produced by the brain renin-angiotensin system have established roles in cognition, but there is no mechanistic basis of angiotensin effects on memory. Astroglial cells present throughout the whole brain, synthesize all the components of the renin-angiotensin system and express angiotensin receptors; therefore our aim was to assess changes in intracellular signalling pathways related to memory formation, particularly the activation of CREB and ERK1/2 in astroglial cells grown in the presence of angiotensin peptides. Cultured rat astroglial cells were treated for 24 h with 10 microM angiotensin II and/or 10 microM angiotensin IV in the presence or absence of 100 microM losartan (AT1-receptor antagonist) or 100 microM PD123319 (AT2-receptor antagonist). Both angiotensin peptides alone were without effect on culture protein levels and cell viability and did not induce oxidative stress, but both peptides together slightly elevated cell growth rates and increased damaged, apoptotic cell numbers. This effect was most probably mediated by the AT1 receptor. Angiotensin II but not angiotensin IV increased intracellular calcium via activation of AT1 receptor. Angiotensin IV but not angiotensin II increased extracellular-regulated protein kinases 1 and 2 (ERK1/2) by 65% and T202, T204 phosphorylated ERK1/2 levels by 36%; this effect was blocked in part by both losartan and PD123319. Angiotensin II but not angiotensin IV increased cyclic AMP-responsive element binding protein (CREB) expression by almost 100% and elevated Ser 133-phosphorylated CREB levels by 56%. These effects were also inhibited in part by both losartan and PD123319. Our results indicate that CREB activation in cultured rat glial cells is mediated mostly by angiotensin II. Angiotensin IV appears to affect the ERK1/2 pathway.

Role of Protein Kinase Cζ and Its Adaptor Protein p62 in Voltage-Gated Potassium Channel Modulation in Pulmonary Arteries

Voltage-gated potassium (K(V)) channels play an essential role in regulating pulmonary artery function, and they underpin the phenomenon of hypoxic pulmonary vasoconstriction. Pulmonary hypertension is characterized by inappropriate vasoconstriction, vascular remodeling, and dysfunctional K(V) channels. In the current study, we aimed to elucidate the role of PKCzeta and its adaptor protein p62 in the modulation of K(V) channels. We report that the thromboxane A(2) analog 9,11-dideoxy-11alpha,9alpha-epoxymethano-prostaglandin F(2alpha) methyl acetate (U46619) inhibited K(V) currents in isolated mice pulmonary artery myocytes and the K(V) current carried by human cloned K(V)1.5 channels expressed in Ltk(-) cells. Using protein kinase C (PKC)zeta(-/-) and p62(-/-) mice, we demonstrate that these two proteins are involved in the K(V) channel inhibition. PKCzeta coimmunoprecipitated with K(V)1.5, and this interaction was markedly reduced in p62(-/-) mice. Pulmonary arteries from PKCzeta(-/-) mice also showed a diminished [Ca(2+)](i) and contractile response, whereas genetic inactivation of p62(-/-) resulted in an absent [Ca(2+)](i) response, but it preserved contractile response to U46619. These data demonstrate that PKCzeta and its adaptor protein p62 play a key role in the modulation of K(V) channel function in pulmonary arteries. These observations identify PKCzeta and/or p62 as potential therapeutic targets for the treatment of pulmonary hypertension.

Gene expression fingerprinting for human hereditary hemorrhagic telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) or Osler-Weber-Rendu syndrome is an autosomal dominant vascular disorder characterized by telangiectases and internal arteriovenous malformations. It is caused by mutations in elements of the transforming growth factor-beta (TGF-beta) receptor complex: endoglin, a co-receptor, responsible for HHT1, or ALK1 (activin receptor-like kinase 1), a type I receptor leading to HHT2. Recently, we have established cultures of HHT endothelial cells, primary targets of the disease. These cells showed deficient TGF-beta signaling and angiogenesis, representing a useful human model to study the molecular mechanism of this disease. To understand the pathogenic mechanism underlying HHT, we have used total RNA probes to compare HHT versus non-HHT cells by expression microarrays. This work represents a systematic study to identify target genes affected in HHT cells. Given the similarity of symptoms in HHT1 and HHT2, special interest has been put on the identification of common targets for both HHT types. As a result, 277 downregulated and 63 upregulated genes were identified in HHT versus control cells. These genes are involved in biological processes relevant to the HHT pathology, such as angiogenesis, cytoskeleton, cell migration, proliferation and NO synthesis. The type of misregulated genes found in HHT endothelial cells lead us to propose a model of HHT pathogenesis, opening new perspectives to understand this disorder. Moreover, as the disease is originated by mutations in proteins of the TGF-beta receptor complex, these results may be useful to find out targets of the TGF-beta pathway in endothelium.

ERK1/2 regulates ANG II-dependent cell proliferation via cytoplasmic activation of RSK2 and nuclear activation of elk1

In a concurrently submitted article, we show that ANG II-induced ERK1/2 activation is mediated by both c-Src/Yes/Fyn and heterotrimeric G protein/PKCζ-dependent signaling. Furthermore, we show that heterotrimeric G protein/PKCζ-activated ERK1/2 is destined for the nucleus while ERK1/2 activated by c-Src/Yes/Fyn-dependent signaling remains in the cytoplasm. Interestingly, both mechanisms of activation are required for maximum ANG II-induced cell proliferation. In this study, we sought to determine the mechanisms by which ERK1/2 facilitate cell proliferation via these distinct nuclear and cytoplasmic events, using cells that were lacking either c-Src/Yes/Fyn or heterotrimeric G protein/PKCζ-dependent ERK1/2 activation. A loss of c-Src/Yes/Fyn blocked ANG II-dependent RSK2 activation, RSK2 nuclear translocation, serum-response factor (SRF) phosphorylation, a portion of c-fos transcriptional activity and c-Fos phosphorylation. Blocking ANG II-induced heterotrimeric G protein/PKCζ activity resulted in a loss of ERK1/2 nuclear translocation, elk1 phosphorylation, and the remaining portion of c-fos transcriptional activity not dependent on c-Src/Yes/Fyn. Inhibition of RSK with the potent and selective inhibitor, SL0101, attenuated ANG II-induced cell proliferation, and, in combination with a PKCζ pseudosubstrate, completely attenuated cell proliferation. Thus we conclude that ERK1/2 mediate ANG II-dependent cell proliferation via distinct cytoplasmic and nuclear signaling events, which are in turn governed by c-Src/Yes/Fyn and heterotrimeric G protein/PKCζ-dependent signaling, respectively.