Intracellular signaling of angiotensin II-induced p70 S6 kinase phosphorylation at Ser(411) in vascular smooth muscle cells. Possible requirement of epidermal growth factor receptor, Ras, extracellular signal-regulated kinase, and Akt

Tonic ErbB signaling underlies TGFβ-induced activation of ERK and is required for lens cell epithelial to myofibroblast transition

Fibrosis is a major, but incompletely understood, component of many diseases. The most common vision-disrupting complication of cataract surgery involves differentiation of residual lens cells into myofibroblasts. In serum-free primary cultures of lens epithelial cells (DCDMLs), inhibitors of either ERK or of ErbB signaling prevent TGFβ from upregulating both early (fibronectin) and late (αSMA) markers of myofibroblast differentiation. TGFβ stimulates ERK in DCDMLs within 1.5 h. Kinase inhibitors of ErbBs, but not of several other growth factor receptors in lens cells, reduce phospho ERK to below basal levels in the absence or presence of TGFβ. This effect is attributable to constitutive ErbB activity playing a major role in regulating the basal levels pERK. Additional studies support a model in which TGFβ-generated reactive oxygen species serve to indirectly amplify ERK signaling downstream of tonically active ErbBs to mediate myofibroblast differentiation. ERK activity is in turn essential for expression of ErbB1 and ErbB2, major inducers of ERK signaling. By mechanistically linking TGFβ, ErbB, and ERK signaling to myofibroblast differentiation, our data elucidate a new role for ErbBs in fibrosis and reveal a novel mode by which TGFβ directs lens cell fate.

Aldosterone: Renal Action and Physiological Effects

Aldosterone exerts profound effects on renal and cardiovascular physiology. In the kidney, aldosterone acts to preserve electrolyte and acid-base balance in response to changes in dietary sodium (Na+ ) or potassium (K+ ) intake. These physiological actions, principally through activation of mineralocorticoid receptors (MRs), have important effects particularly in patients with renal and cardiovascular disease as demonstrated by multiple clinical trials. Multiple factors, be they genetic, humoral, dietary, or otherwise, can play a role in influencing the rate of aldosterone synthesis and secretion from the adrenal cortex. Normally, aldosterone secretion and action respond to dietary Na+ intake. In the kidney, the distal nephron and collecting duct are the main targets of aldosterone and MR action, which stimulates Na+ absorption in part via the epithelial Na+ channel (ENaC), the principal channel responsible for the fine-tuning of Na+ balance. Our understanding of the regulatory factors that allow aldosterone, via multiple signaling pathways, to function properly clearly implicates this hormone as central to many pathophysiological effects that become dysfunctional in disease states. Numerous pathologies that affect blood pressure (BP), electrolyte balance, and overall cardiovascular health are due to abnormal secretion of aldosterone, mutations in MR, ENaC, or effectors and modulators of their action. Study of the mechanisms of these pathologies has allowed researchers and clinicians to create novel dietary and pharmacological targets to improve human health. This article covers the regulation of aldosterone synthesis and secretion, receptors, effector molecules, and signaling pathways that modulate its action in the kidney. We also consider the role of aldosterone in disease and the benefit of mineralocorticoid antagonists. © 2023 American Physiological Society. Compr Physiol 13:4409-4491, 2023.

An Insight on Multicentric Signaling of Angiotensin II in Cardiovascular system: A Recent Update

The multifaceted nature of the renin-angiotensin system (RAS) makes it versatile due to its involvement in pathogenesis of the cardiovascular disease. Angiotensin II (Ang II), a multifaceted member of RAS family is known to have various potential effects. The knowledge of this peptide has immensely ameliorated after meticulous research for decades. Several studies have evidenced angiotensin I receptor (AT1 R) to mediate the majority Ang II-regulated functions in the system. Functional crosstalk between AT1 R mediated signal transduction cascades and other signaling pathways has been recognized. The review will provide an up-to-date information and recent discoveries involved in Ang II receptor signal transduction and their functional significance in the cardiovascular system for potential translation in therapeutics. Moreover, the review also focuses on the role of stem cell-based therapies in the cardiovascular system.

Cell signaling model for arterial mechanobiology

Arterial growth and remodeling at the tissue level is driven by mechanobiological processes at cellular and sub-cellular levels. Although it is widely accepted that cells seek to promote tissue homeostasis in response to biochemical and biomechanical cues—such as increased wall stress in hypertension—the ways by which these cues translate into tissue maintenance, adaptation, or maladaptation are far from understood. In this paper, we present a logic-based computational model for cell signaling within the arterial wall, aiming to predict changes in extracellular matrix turnover and cell phenotype in response to pressure-induced wall stress, flow-induced wall shear stress, and exogenous sources of angiotensin II, with particular interest in mouse models of hypertension. We simulate a number of experiments from the literature at both the cell and tissue level, involving single or combined inputs, and achieve high qualitative agreement in most cases. Additionally, we demonstrate the utility of this modeling approach for simulating alterations (in this case knockdowns) of individual nodes within the signaling network. Continued modeling of cellular signaling will enable improved mechanistic understanding of arterial growth and remodeling in health and disease, and will be crucial when considering potential pharmacological interventions.

Biological soft tissues are characterized by continuous production and removal of material, which endows them with a remarkable ability to adapt to changes in their biochemical and biomechanical environments. For arteries, mechanical stimuli result primarily from changes in blood pressure or flow, and biochemical changes are induced by multiple factors, including pharmacological intervention. In order to understand how arterial properties are maintained in health, or how they adapt or fail to adapt in disease, we must understand better how these diverse stimuli affect material turnover. Extracellular matrix is tightly regulated by mechano-sensing and mechano-regulation, and therefore cell signaling, thus we present a computational model of relevant signaling pathways within the vascular wall, with the aim of predicting changes in wall composition and function in response to three main inputs: pressure-induced wall stress, flow-induced wall shear stress, and exogenous angiotensin II. We obtain qualitative agreement with a range of experimental studies from the literature, and provide illustrative examples demonstrating how such models can be used to further our understanding of arterial remodeling.

ULK1 Phosphorylates and Regulates Mineralocorticoid Receptor

Mineralocorticoid receptor (MR) signaling regulates both renal Na-Cl reabsorption and K⁺ excretion. We previously demonstrated that phosphorylation of S843 in the MR ligand-binding domain in renal intercalated cells is involved in the balance of these activities by regulating ligand binding and signaling. However, the kinase that phosphorylates MR^S843 is unknown. Using a high-throughput screen assay of 197 kinases, we found that ULK1 is the principal kinase that is responsible for the phosphorylation of MR^S843. The results were confirmed by in vitro kinase assay, mass spectrometry, and siRNA knockdown experiments. Notably, phosphorylation at MR^S843 was markedly reduced in ULK1/2 double knockout mouse embryonic fibroblasts. Upstream, we show that ULK1 activity is inhibited by phosphorylation induced by angiotensin II via mTOR in cell culture and in vivo. These findings implicate mTOR and ULK1 as regulators of MR activity in intercalated cells, a pathway that is critical for maintaining electrolyte homeostasis.

A Rare Case of an Abdominal Aneurysm in a Patient with Lymphangioleiomyomatosis: A Case Report

INTRODUCTION

Lymphangioleiomyomatosis (LAM) is a multisystemic disorder characterized by the proliferation, metastasis, and infiltration of smooth muscle cells in the lung and other tissues. Although LAM is rarely seen in men, it is usually detected in women during the third decade of life. Renal microaneurysms have been reported in patients with LAM, but abdominal aneurysms have not. We describe a patient with a diagnosis of LAM who had an unusual aneurysm in the inferior pancreaticoduodenal artery.

CASE PRESENTATION

A 47-year-old Ecuadorian woman self-referred for a routine visit to her family physician. She had a history of allergy to nonsteroidal anti-inflammatory drugs, pneumothorax, bilateral pleurodesis, and LAM since 2007. For her annual follow-up, an ultrasonogram was recommended. The abdominal ultrasonographic report described "a mass with blood flow in the midabdomen." An abdominal computed tomography angiogram was performed and revealed a 2.6-cm aneurysm of the inferior pancreaticoduodenal artery. After diagnosis of arterial aneurysm, she underwent transcatheter arterial embolization and stent placement. She is currently healthy and carries out her activities normally.

DISCUSSION

Lymphangioleiomyomatosis is a rare lung disease of unknown etiology. Extrapulmonary manifestations include abdominal aneurysm. This type of lesion should be added to a search for aneurysms in all patients with LAM.

Role of Pendrin in the Pathophysiology of Aldosterone-Induced Hypertension

The recent advances in genetics and molecular biology have resulted in the characterization of key components that critically regulate renal NaCl transport and blood pressure. Pendrin is a Cl-/HCO3- exchanger that is highly expressed in thyroid, inner ear, and kidney. In the kidney, it is selectively present at the apical membrane in non-α intercalated cells of the connecting tubules and cortical collecting duct. Besides its role in acid/base homeostasis, accumulating studies using various genetically modified animals have provided compelling evidence that pendrin regulates extracellular fluid volume and electrolyte balance at the downstream of aldosterone signaling. We have shown that angiotensin II and aldosterone cooperatively control pendrin abundance partly through mammalian target of rapamycin signaling and mineralocorticoid receptor dephosphorylation, which is necessary for the kidney to prevent extracellular fluid loss and electrolyte disturbances under physiologic perturbations. In line with the experimental observations, several clinical data indicated that the impaired pendrin function can cause fluid and electrolyte abnormalities in humans. The purpose of this review is to provide an update on the recent progress regarding the role of pendrin in fluid and electrolyte homeostasis, as well as in the pathophysiology of hypertension associated with mineralocorticoid receptor signaling.

Electrolyte transport in the renal collecting duct and its regulation by the renin-angiotensin-aldosterone system

Distal nephron of the kidney plays key roles in fluid volume and electrolyte homeostasis by tightly regulating reabsorption and excretion of Na⁺, K⁺, and Cl^- Studies to date demonstrate the detailed electrolyte transport mechanisms in principal cells of the cortical collecting duct, and their regulation by renin-angiotensin-aldosterone system (RAAS). In recent years, however, accumulating data indicate that intercalated cells, another cell type that is present in the cortical collecting duct, also play active roles in the regulation of blood pressure. Notably, pendrin in β-intercalated cells not only controls acid/base homeostasis, but is also one of the key components controlling salt and K⁺ transport in distal nephron. We have recently shown that pendrin is regulated by the co-ordinated action of angiotensin II (AngII) and aldosterone, and at the downstream of AngII, mammalian target of rapamycin (mTOR) signaling regulates pendrin through inhibiting the kinase unc51-like-kinase 1 and promoting dephosphorylation of mineralocorticoid receptor (MR). In this review, we summarize recent advances in the current knowledge on the salt transport mechanisms in the cortical collecting duct, and their regulation by the RAAS.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Integrative gene ontology and network analysis of coronary artery disease associated genes suggests potential role of ErbB pathway gene EGFR

Coronary artery disease (CAD) is a major cause of mortality in India, more importantly the young Indians. Combinatorial and integrative approaches to evaluate pathways and genes to gain an improved understanding and potential biomarkers for risk assessment are required. Therefore, 608 genes from the CADgene database version 2.0, classified into 12 functional classes representing the atherosclerotic disease process, were analyzed. Homology analysis of the unique list of gene ontologies (GO) from each functional class gave 8 GO terms represented in 11 and 10 functional classes. Using disease ontology analysis 80 genes belonging to 8 GO terms, using FunDO suggested that 29 of them were identified to be associated with CAD. Extended network analysis of these genes using STRING version 9.1 gave 328 nodes and 4,525 interactions of which the top 5% had a node degree of ≥75 associated with pathways including the ErbB signaling pathway with epidermal growth factor receptor (EGFR) gene as the central hub. Evaluation of EFGR protein levels in age and gender-matched 342 CAD patients vs. 342 control subjects demonstrated significant differences [controls=149.76±2.47 pg/ml and CAD patients stratified into stable angina (SA)=161.65±3.40 pg/ml and myocardial infarction (MI)=171.51±4.26 pg/ml]. Logistic regression analysis suggested that increased EGFR levels exhibit 3-fold higher risk of CAD [odds ratio (OR) 3.51, 95% confidence interval [CI] 1.96–6.28, P≤0.001], upon adjustment for hypertension, diabetes and smoking. A unit increase in EGFR levels increased the risk by 2-fold for SA (OR 2.58, 95% CI 1.25–5.33, P=0.01) and 3.8-fold for MI (OR 3.82, 95% CI 1.94–7.52, P≤0.001) following adjustment. Thus, the use of ontology mapping and network analysis in an integrative manner aids in the prioritization of biomarkers of complex disease.

Decreased activation of placental mTOR family members is associated with the induction of intrauterine growth restriction by secondhand smoke in the mouse

Cigarette smoke is known to be a risk for the development of intrauterine growth restriction (IUGR). Our objective was to assess the effects of secondhand smoke (SHS) during pregnancy and to what extent it regulates the activation of mTOR family members and murine trophoblast invasion. Mice were treated to SHS for 4 days. Placental and fetal weights were recorded at the time of necropsy. Immunohistochemistry was used to determine the level of placental trophoblast invasion. Western blots were utilized to assess the activation of caspase 3, XIAP, mTOR, p70 and 4EBP1 in treated and control placental lysates. As compared to controls, treated animals showed: (1) decreased placental (1.4-fold) and fetal (2.3-fold) weights (p < 0.05); (2) decreased trophoblast invasion; (3) significantly decreased active caspase 3 (1.3-fold; p < 0.02) and increased active XIAP (3.6-fold; p < 0.05) in the placenta; and (4) a significant decrease in the activation of placental mTOR (2.1-fold; p < 0.05), p70 (1.9-fold; p < 0.05) and 4EBP1 (1.3-fold; p < 0.05). Confirmatory in vitro experiments revealed decreased trophoblast invasion when SW71 cells were treated with 0.5 or 1.0 % cigarette smoke extract (CSE). Similar to primary smoking, SHS may induce IUGR via decreased activation of the mTOR family of proteins in the placenta. Increased activation of the placental XIAP protein could be a survival mechanism for abnormal trophoblast cells during SHS exposure. Further, CSE reduced trophoblast invasion, suggesting a direct causative effect of smoke on susceptible trophoblast cells involved in IUGR progression. These results provide important insight into the physiological consequences of SHS exposure and smoke-mediated placental disease.

mTORC1 Signaling Contributes to Drinking But Not Blood Pressure Responses to Brain Angiotensin II

Mechanistic target of rapamycin complex 1 (mTORC1) is a molecular node that couples extracellular cues to a wide range of cellular events controlling various physiological processes. Here, we identified mTORC1 signaling as a critical mediator of angiotensin II (Ang II) action in the brain. In neuronal GT1-7 cells, we show that Ang II stimulates neuronal mTORC1 signaling in an Ang II type 1 receptor-dependent manner. In mice, a single intracerebroventricular (ICV) injection or chronic sc infusion of Ang II activated mTORC1 signaling in the subfornical organ, a critical brain region in cardiovascular control and fluid balance. Moreover, transgenic sRA mice with brain-specific overproduction of Ang II displayed increased mTORC1 signaling in the subfornical organ. To test the functional role of brain mTORC1 in mediating the action of Ang II, we examined the consequence of mTORC1 inhibition with rapamycin on Ang II-induced increase in water intake and arterial pressure. ICV pretreatment with rapamycin blocked ICV Ang II-mediated increases in the frequency, duration, and amount of water intake but did not interfere with the pressor response evoked by Ang II. In addition, ICV delivery of rapamycin significantly reduced polydipsia, but not hypertension, of sRA mice. These results demonstrate that mTORC1 is a novel downstream pathway of Ang II type 1 receptor signaling in the brain and selectively mediates the effect of Ang II on drinking behavior.

G Protein-Coupled Receptor Signaling in Stem Cells and Cancer

G protein-coupled receptors (GPCRs) are a large superfamily of cell-surface signaling proteins that bind extracellular ligands and transduce signals into cells via heterotrimeric G proteins. GPCRs are highly tractable drug targets. Aberrant expression of GPCRs and G proteins has been observed in various cancers and their importance in cancer stem cells has begun to be appreciated. We have recently reported essential roles for G protein-coupled receptor 84 (GPR84) and G protein subunit Gαq in the maintenance of cancer stem cells in acute myeloid leukemia. This review will discuss how GPCRs and G proteins regulate stem cells with a focus on cancer stem cells, as well as their implications for the development of novel targeted cancer therapies.

Roles of Caveolin-1 in Angiotensin II-Induced Hypertrophy and Inward Remodeling of Cerebral Pial Arterioles

Angiotensin II (Ang II) is a major determinant of inward remodeling and hypertrophy in pial arterioles that may have an important role in stroke during chronic hypertension. Previously, we found that epidermal growth factor receptor is critical in Ang II-mediated hypertrophy that may involve caveolin-1 (Cav-1). In this study, we examined the effects of Cav-1 and matrix metalloproteinase-9 (MMP9) on Ang II-mediated structural changes in pial arterioles. Cav-1-deficient (Cav-1(-/-)), MMP9-deficient (MMP9(-/-)), and wild-type mice were infused with either Ang II (1000 ng/kg per minute) or saline via osmotic minipumps for 28 days (n=6-8 per group). Systolic arterial pressure was measured by a tail-cuff method. Pressure and diameter of pial arterioles were measured through an open cranial window in anesthetized mice. Cross-sectional area of the wall was determined histologically in pressurized fixed pial arterioles. Expression of Cav-1, MMP9, phosphorylated epidermal growth factor receptor, and Akt was determined by Western blotting and immunohistochemistry. Deficiency of Cav-1 or MMP9 did not affect Ang II-induced hypertension. Ang II increased the expression of Cav-1, phosphorylated epidermal growth factor receptor, and Akt in wild-type mice, which was attenuated in Cav-1(-/-) mice. Ang II-induced hypertrophy, inward remodeling, and increased MMP9 expression in pial arterioles were prevented in Cav-1(-/-) mice. Ang II-mediated increases in MMP9 expression and inward remodeling, but not hypertrophy, were prevented in MMP9(-/-) mice. In conclusion, Cav-1 is essential in Ang II-mediated inward remodeling and hypertrophy in pial arterioles. Cav-1-induced MMP9 is exclusively involved in inward remodeling, not hypertrophy. Further studies are needed to determine the role of Akt in Ang II-mediated hypertrophy.

Alpha1a-Adrenoceptor Genetic Variant Triggers Vascular Smooth Muscle Cell Hyperproliferation and Agonist Induced Hypertrophy via EGFR Transactivation Pathway

α_1a Adrenergic receptors (α_1aARs) are the predominant AR subtype in human vascular smooth muscle cells (SMCs). α_1aARs in resistance vessels are crucial in the control of blood pressure, yet the impact of naturally occurring human α_1aAR genetic variants in cardiovascular disorders remains poorly understood. To this end, we present novel findings demonstrating that 3D cultures of vascular SMCs expressing human α_1aAR-247R (247R) genetic variant demonstrate significantly increased SMC contractility compared with cells expressing the α_1aAR-WT (WT) receptor. Stable expression of 247R genetic variant also triggers MMP/EGFR-transactivation dependent serum- and agonist-independent (constitutive) hyperproliferation and agonist-dependent hypertrophy of SMCs. Agonist stimulation reduces contractility Using pathway-specific inhibitors we determined that the observed hyperproliferation of 247R-expressing cells is triggered via β-arrestin1/Src/MMP-2/EGFR/ERK-dependent mechanism. MMP-2-specific siRNA inhibited 247R-triggered hyperproliferation indicating MMP-2 involvement in 247R-triggered hyperproliferation in SMCs. β-arrestin1-specific shRNA also inhibited 247R-triggered hyperproliferation but did not affect hypertrophy in 247R-expressing SMCs, indicating that agonist-dependent hypertrophy is independent of β-arrestin1. Our data reveal that in different cardiovascular cells the same human receptor genetic variant can activate alternative modulators of the same signaling pathway. Thus, our findings in SMCs demonstrate that depending on the type of cells expressing the same receptor (or receptor variant), different target-specific inhibitors could be used to modulate aberrant hyperproliferative or hypertrophic pathways in order to restore normal phenotype.

p70 S6-kinase mediates the cooperation between Akt1 and Mek1 pathways in fibroblast-mediated extracellular matrix remodeling

Previous studies have demonstrated both synergistic and opposing effects of Akt and Mek1/2 in various cell functions and disease states. Furthermore, Akt has been reported to inhibit and activate cRaf/Mek pathway, suggesting that their mutual interaction and cooperation may be cell type, stimuli and/or context specific. While PI3-kinase/Akt and cRaf/Mek pathways have been implicated in the regulation of extracellular matrix (ECM) remodeling, mutual interactions between these two pathways and their specific contributions to the events leading to ECM synthesis and assembly is not clear. We investigated the specific role of Akt1 and Mek1 in ECM synthesis and assembly by NIH 3T3 fibroblasts and how these effects were reconciled to mediate overall ECM remodeling. Our study identified that cooperation between Akt1 and Mek1 is necessary to mediate ECM synthesis. Whereas Akt1 activation resulted in Mek1 activation as evidenced by increased ERK1/2 phosphorylation, Mek1 inhibition using U0126 or DN-Mek1 resulted in enhanced Akt1 phosphorylation. Interestingly, both Akt1 and Mek1 activities were needed for the synthesis and assembly of ECM. The effect of Akt1 and Mek1 on ECM synthesis was reconciled through the activation of p70 S6-kinase via phosphorylation at T421/S424 and S411, respectively. Furthermore, Akt1 and Mek1 cooperated in mediating ECM assembly via activation of integrin β1. Together, we show for the first time that Akt1 and Mek1 pathways cooperate in the regulation of ECM remodeling by the fibroblasts.

Lack of efficacy of mTOR inhibitors and ACE pathway inhibitors as antifibrotic agents in evolving and established fibrosis in Mdr2⁻/⁻ mice

BACKGROUND & AIMS

Mammalian target of rapamycin and angiotensin-converting enzyme inhibition has been shown to have antifibrotic activity in models of liver fibrosis. The aim of our study was to determine the efficacy of rapamycin, everolimus, irbesartan and captopril, alone and in combination, as antifibrotic agents in the Mdr2(-/-) model of cholestasis both in early injury and established disease.

METHODS

Mdr2(-/-) mice were treated for 4 weeks with vehicle, rapamycin (1 mg/kg) or everolimus (5 mg/kg) every second day or with captopril (30 mg/kg/day), irbesartan (10 mg/kg/day) or vehicle. Further groups of 3-week-old Mdr2(-/-) mice were treated with rapamycin and irbesartan in combination (1 mg/kg/day and 10 mg/kg/day) or with rapamycin (2 mg/kg/day) for 4 weeks. Liver injury and fibrosis were compared between treated and untreated animals.

RESULTS

There were no significant improvements in liver injury, histology, hepatic hydroxyproline or profibrogenic gene expression following treatment with rapamycin, everolimus, captopril or irbesartan at any time point studied. Likewise, there were no improvements in liver histology or profibrogenic gene expression following combination therapy or high-dose rapamycin treatment.

CONCLUSIONS

The antifibrotic effects of rapamycin, everolimus, captopril and irbesartan seen in other models of fibrosis were not replicated in the Mdr2(-/-) model in this study. This highlights the clear need to test specific antifibrotic agents in a number of different animal models. We believe this animal model is ideal to study usefulness of antifibrotic agents in cholestatic liver disease because of the similarity in genetics and hepatic histopathology to human cholestatic liver disease.

Koschei the immortal and anti-aging drugs

In Slavic folklore, Koschei the Immortal was bony, thin and lean. Was his condition caused by severe calorie restriction (CR)? CR deactivates the target of rapamycin pathway and slows down aging. But the life-extending effect of severe CR is limited by starvation. What if Koschei's anti-aging formula included rapamycin? And was rapamycin (or another rapalog) combined with commonly available drugs such as metformin, aspirin, propranolol, angiotensin II receptor blockers and angiotensin-converting enzyme inhibitors.

Control of vascular smooth muscle function by Src-family kinases and reactive oxygen species in health and disease

Reactive oxygen species (ROS) are now recognised as second messenger molecules that regulate cellular function by reversibly oxidising specific amino acid residues of key target proteins. Amongst these are the Src-family kinases (SrcFKs), a multi-functional group of non-receptor tyrosine kinases highly expressed in vascular smooth muscle (VSM). In this review we examine the evidence supporting a role for ROS-induced SrcFK activity in normal VSM contractile function and in vascular remodelling in cardiovascular disease. VSM contractile responses to G-protein-coupled receptor stimulation, as well as hypoxia in pulmonary artery, are shown to be dependent on both ROS and SrcFK activity. Specific phosphorylation targets are identified amongst those that alter intracellular Ca(2+) concentration, including transient receptor potential channels, voltage-gated Ca(2+) channels and various types of K(+) channels, as well as amongst those that regulate actin cytoskeleton dynamics and myosin phosphatase activity, including focal adhesion kinase, protein tyrosine kinase-2, Janus kinase, other focal adhesion-associated proteins, and Rho guanine nucleotide exchange factors. We also examine a growing weight of evidence in favour of a key role for SrcFKs in multiple pro-proliferative and anti-apoptotic signalling pathways relating to oxidative stress and vascular remodelling, with a particular focus on pulmonary hypertension, including growth-factor receptor transactivation and downstream signalling, hypoxia-inducible factors, positive feedback between SrcFK and STAT3 signalling and positive feedback between SrcFK and NADPH oxidase dependent ROS production. We also discuss evidence for and against the potential therapeutic targeting of SrcFKs in the treatment of pulmonary hypertension.

p70 S6 kinase and actin dynamics: A perspective

p70 S6 kinase (p70^S6K), a member of the AGC serine/threonine kinase family, was initially identified as a key player, together with its downstream effector S6, in the regulation of cellular growth and survival. The p70^S6K protein has emerged in recent years as a multifunctional protein which also regulates the actin cytoskeleton and thus plays a role in cell migration. This new function is through two important activities of p70^S6K, namely actin cross-linking and Rac1 and Cdc42 activation. The testis is critically dependent on an intricate balance of fundamental cellular processes such as adhesion, migration, and differentiation. It is increasingly evident that Rho GTPases and actin binding proteins play fundamental roles in regulating spermatogenesis within the testis. In this review, we will discuss current findings of p70^S6K in the control of actin cytoskeleton dynamics. In addition, the potential role of p70^S6K in spermatogenesis and testicular function will be highlighted.

Placenta growth factor induces invasion and activates p70 during rapamycin treatment in trophoblast cells

PROBLEM

Aberrant trophoblast invasion has been associated with human intrauterine growth restriction (IUGR) and preeclampsia (PE). Our objective was to determine placenta growth factor (PlGF)-mediated regulation of cell invasion in trophoblast cells with reduced mammalian target of Rapamycin (mTOR) signaling.

METHOD OF STUDY

First trimester SW 71 trophoblast cells were subjected to invasion assays with the following conditions: 10% FBS, 10% FBS with Rapamycin, and 10% FBS with Rapamycin and PlGF. mTOR siRNA was also done in these cells. Western blots were performed on cell lysates with antibodies against phospho- and total mTOR, 70-kDa ribosomal protein kinase I (p70), 4EBP1, extracellular regulated kinase (ERK), and phosphatidylinositol-3 kinase (AKT).

RESULTS

Compared to controls, trophoblast cells showed: (i) a 33% decrease in invasion following Rapamycin treatment, (ii) protection from decreased invasion following Rapamycin and PlGF treatment, (iii) a 31% decrease in mTOR phosphorylation with Rapamycin, (iv) increased phosphorylation of p70 (43%) with Rapamycin and PlGF, and (v) a 76% decrease in invasion following mTOR depletion.

CONCLUSION

We conclude that first trimester trophoblast invasion is functionally decreased when phosphorylation of mTOR is prevented and this decrease is recovered with the addition of PlGF. Mechanistically, this recovery involves the phosphorylation of p70 independent of mTOR.

Role of mTOR downstream effector signaling molecules in Francisella tularensis internalization by murine macrophages

Francisella tularensis is an infectious, gram-negative, intracellular microorganism, and the cause of tularemia. Invasion of host cells by intracellular pathogens like Francisella is initiated by their interaction with different host cell membrane receptors and the rapid phosphorylation of different downstream signaling molecules. PI3K and Syk have been shown to be involved in F. tularensis host cell entry, and both of these signaling molecules are associated with the master regulator serine/threonine kinase mTOR; yet the involvement of mTOR in F. tularensis invasion of host cells has not been assessed. Here, we report that infection of macrophages with F. tularensis triggers the phosphorylation of mTOR downstream effector molecules, and that signaling via TLR2 is necessary for these events. Inhibition of mTOR or of PI3K, ERK, or p38, but not Akt signaling, downregulates the levels of phosphorylation of mTOR downstream targets, and significantly reduces the number of F. tularensis cells invading macrophages. Moreover, while phosphorylation of mTOR downstream effectors occurs via the PI3K pathway, it also involves PLCγ1 and Ca(2+) signaling. Furthermore, abrogation of PLC or Ca(2+) signaling revealed their important role in the ability of F. tularensis to invade host cells. Together, these findings suggest that F. tularensis invasion of primary macrophages utilize a myriad of host signaling pathways to ensure effective cell entry.

Role of adipokines signaling in the modulation of T cells function

The field that links immunity and metabolism is rapidly expanding. Apparently non-immunological disorders such as obesity and type 2 diabetes have been linked to immune dysregulation, suggesting that metabolic alterations can be induced by or be consequence of an altered self-immune tolerance. In this context, adipose tissue produces and releases a variety of pro-inflammatory and anti-inflammatory factors, termed "adipokines," which can be considered as the bridge between obesity-related exogenous factors, such as nutrition and lifestyle, and the molecular events leading to metabolic syndrome, inflammatory, and/or autoimmune conditions. In obesity, increased production of most adipokines impacts on multiple functions such as appetite and energy balance, modulation of immune responses, insulin sensitivity, angiogenesis, blood pressure, lipid metabolism, and so on. This report aims to discuss some of the recent topics of adipocytokine research and their related signaling pathways, that may be of particular importance as could lead to effective therapeutic strategies for obesity-associated diseases.

Redox signaling in pathophysiology of hypertension

Reactive oxygen species (ROS) are products of normal cellular metabolism and derive from various sources in different cellular compartments. Oxidative stress resultant from imbalance between ROS generation and antioxidant defense mechanisms is important in pathogenesis of cardiovascular diseases, such as hypertension, heart failure, atherosclerosis, diabetes, and cardiac hypertrophy. In this review we focus on hypertension and address sources of cellular ROS generation, mechanisms involved in regulation of radical homeostasis, superoxide dismutase isoforms in pathophysiology of hypertension; as well as radical intracellular signaling and phosphorylation processes in proteins of the affected cardiovascular tissues. Finally, we discuss the transcriptional factors involved in redox-sensitive gene transcription and antioxidant response, as well as their roles in hypertension.

Common drugs and treatments for cancer and age-related diseases: revitalizing answers to NCI's provocative questions

In 2011, The National Cancer Institute (NCI) has announced 24 provocative questions on cancer. Some of these questions have been already answered in “NCI's provocative questions on cancer: some answers to ignite discussion” (published in Oncotarget, 2011, 2: 1352.) The questions included “Why do many cancer cells die when suddenly deprived of a protein encoded by an oncogene?” “Can we extend patient survival by using approaches that keep tumors static?” “Why are some disseminated cancers cured by chemotherapy alone?” “Can we develop methods to rapidly test interventions for cancer treatment or prevention?” “Can we use our knowledge of aging to enhance prevention or treatment of cancer?” “What is the mechanism by which some drugs commonly and chronically used for other indications protect against cancer?” “How does obesity contribute to cancer risk?” I devoted a single subchapter to each the answer. As expected, the provocative questions were very diverse and numerous. Now I choose and combine, as a single problem, only three last questions, all related to common mechanisms and treatment of age-related diseases including obesity and cancer. Can we use common existing drugs for cancer prevention and treatment? Can we use some targeted “cancer-selective” agents for other diseases and … aging itself.

Inhibition of C2C12 myotube atrophy by a novel HSP70 inducer, celastrol, via activation of Akt1 and ERK1/2 pathways

Celastrol (CEL) is known as a potent inducer of heat shock protein (HSP) in non-muscle cells and exhibits cytoprotective function and inhibitory effects on proteasome and glucocorticoid receptor activities. To investigate an anti-atrophic effect of CEL on skeletal muscle cells, C2C12 myotubes were treated with 150 μM dexamethasone (DEX) for 24h and 1.5 μM CEL was added for the last 6h during the 24h DEX treatment. Compared to the control, the myotube diameter was reduced by a factor of 0.30 by DEX, but CEL treatment almost abrogated the DEX-induced atrophy. CEL treatment also increased expression of HSP72 and phosphorylation of heat shock transcription factor 1 (p-HSF1) 11-fold and 3.4-fold, respectively, as well as accumulation of p-HSF1 in the nucleus. Furthermore, CEL treatment elevated activities of Akt1, p70/S6K and ERK1/2 2.0- to 4.4-fold whereas DEX had no effect on these signaling activities. Inhibition of Akt1 and ERK1/2 pathways by specific inhibitors confirmed CEL-induced anti-atrophic effect. Moreover, DEX-mediated downregulation of FoxO3 phosphorylation and upregulation of MuRF1 expression and proteasome activity were abrogated by CEL treatment. These results demonstrate a novel anti-atrophic function of CEL in muscle cells via both activation of protein anabolic signals and suppression of catabolic signaling activities.

NCI's provocative questions on cancer: some answers to ignite discussion

National Cancer Institute has announced 24 provocative questions on cancer. Here I try to answer some of them by linking the dots of existing knowledge.

Exploiting p70 S6 kinase as a target for ovarian cancer

INTRODUCTION

The p70 S6 kinase (p70(S6K)) is frequently active in ovarian and a wide range of cancer types, and it has a crucial role in several processes considered hallmarks of cancer. Therefore, blocking p70(S6K) expression or activity may present a promising strategy for anticancer treatment.

AREAS COVERED

The current understanding of the molecular mechanisms that govern p70(S6K) regulation as well as its tumorigenic effects, which are involved in the initiation and progression in ovarian cancer, in particular the emerging new role of p70(S6K) in cell migration, which is a prerequisite of tumor metastasis. The p70(S6K) cellular substrates and/or interacting proteins. The current state of drugs that target this kinase, either alone or in combination with other targeted agents.

EXPERT OPINION

Targeting p70(S6K) through the use of small-molecule inhibitors, microRNAs and natural compounds may represent a beneficial new avenue for cancer therapy and opens new areas of investigation in p70(S6K) biology.

Constitutive stimulation of vascular smooth muscle cells by angiotensin II derived from an adenovirus encoding a furin-cleavable fusion protein

BACKGROUND

To fill the gap between acute and chronic stimulation methods of angiotensin II (Ang II) and obtain relevant signaling information, we have made an adenovirus vector encoding a furin-cleavable Ang II fusion protein.

METHODS

Vascular smooth muscle cells (VSMCs) were infected with adenovirus to evaluate Ang II production. Also, expression of early growth response-1 (Egr-1) and hypertrophic responses were examined in VSMCs.

RESULTS

Acute stimulation of VSMCs with synthetic Ang II showed the peptide had a half-life of less than 1 h. Infection of VSMCs with Ang II adenovirus showed a time-dependent production of Ang II as early as 2 days and up to 7 days postinfection. The Ang II adenovirus induced VSMC hypertrophy, stimulated Egr-1 expression, and suppressed Ang II type 1 receptor mRNA expression. Chronic Ang II infusion in mice for 2 weeks markedly enhanced Egr-1 immunostaining in carotid artery compared with the control saline infusion.

CONCLUSION

Application of the Ang II adenovirus vector to cultured cells will be useful to elucidate molecular and signaling mechanisms of cardiovascular diseases associated with enhanced Ang II production.

Activation of mTOR/p70S6 kinase by ANG II inhibits insulin-stimulated endothelial nitric oxide synthase and vasodilation

Elevated tissue levels of angiotensin II (ANG II) are associated with impairment of insulin actions in metabolic and cardiovascular tissues. ANG II-stimulated activation of mammalian target of rapamycin (mTOR)/p70 S6 kinase (p70S6K) in cardiovascular tissues is implicated in cardiac hypertrophy and vascular remodeling. However, the role of ANG II-stimulated mTOR/p70S6K in vascular endothelium is poorly understood. In the present study, we observed that ANG II stimulated p70S6K in bovine aortic endothelial cells. ANG II increased phosphorylation of insulin receptor substrate-1 (IRS-1) at Ser(636/639) and inhibited the insulin-stimulated phosphorylation of endothelial nitric oxide synthase (eNOS). An inhibitor of mTOR, rapamycin, attenuated the ANG II-stimulated phosphorylation of p70S6K and phosphorylation of IRS-1 (Ser(636/639)) and blocked the ability of ANG II to impair insulin-stimulated phosphorylation of eNOS, nitric oxide production, and mesenteric-arteriole vasodilation. Moreover, point mutations of IRS-1 at Ser(636/639) to Ala prevented the ANG II-mediated inhibition of insulin signaling. From these results, we conclude that activation of mTOR/p70S6K by ANG II in vascular endothelium may contribute to impairment of insulin-stimulated vasodilation through phosphorylation of IRS-1 at Ser(636/639). This ANG II-mediated impairment of vascular actions of insulin may help explain the role of ANG II as a link between insulin resistance and hypertension.

α1-Adrenoceptor-mediated contraction of rat aorta is partly mediated via transactivation of the epidermal growth factor receptor

BACKGROUND AND PURPOSE

High level of plasma catecholamines is a risk factor for vascular diseases such as hypertension and atherosclerosis. Catecholamines induce hypertrophy of vascular smooth muscle through α(1) -adrenoceptors, which in cell culture involves the transactivation of epidermal growth factor receptor (EGFR). We hypothesized that EGFR transactivation was also involved in contractions of rat aorta mediated by α(1) -adrenoceptors.

EXPERIMENTAL APPROACH

Thoracic aorta was isolated from 12-14 week old male Wistar rats. In vitro aortic contractile responses to cumulative doses of phenylephrine were characterized in the absence and presence of the EGFR kinase inhibitors, AG1478 and DAPH, in intact and endothelium-denuded rings. Involvement of signal transduction pathways was investigated by using heparin and inhibitors of Src, matrix metalloproteinase (MMP), extracellular signal-regulated kinase (ERK)1/2 and phosphatidyl inositol 3-kinase (PI3K). Phosphorylation of EGFR and ERK1/2 was measured after short-term phenylephrine or EGF stimulation in aorta segments in the presence of AG1478 and the PI3K inhibitor, wortmannin.

KEY RESULTS

AG1478 and DAPH concentration dependently attenuated phenylephrine-induced contractile responses in intact or endothelium-denuded aortic rings. Inhibition of PI3K (wortmannin and LY294002) but not heparin or inhibitors of Src or MMP, prevented the effect of AG1478 on the responses to phenylephrine. Phenylephrine induced phosphorylation of EGFR, which was partially blocked by AG1478. Phenylephrine also increased phosphorylation of ERK1/2, time-dependently and was blocked by AG1478 and wortmannin.

CONCLUSIONS AND IMPLICATIONS

Contractions of rat thoracic aorta mediated by α(1) -adrenoceptors involved transactivation of EGFR, mediated via a PI3K and ERK1/2 dependent pathway.

Cigarette smoke extract upregulates heme oxygenase-1 via PKC/NADPH oxidase/ROS/PDGFR/PI3K/Akt pathway in mouse brain endothelial cells

BACKGROUND

In the brain, the inducible form of heme oxygenase (HO-1) has been recently demonstrated to exacerbate early brain injury produced by intracerebral hemorrhagic stroke which incident rate has been correlated with cigarette smoking previously. Interestingly, cigarette smoke (CS) or chemicals present in CS have been shown to induce HO-1 expression in various cell types, including cerebral endothelial cells. However, the mechanisms underlying CS modulating HO-1 protein expression are not completely understood in the brain vessels.

OBJECTIVE

The aim of the present study was to investigate the mechanisms underlying CS modulating HO-1 protein expression in cerebral endothelial cells.

METHODS

Cultured cerebral endothelial cells (bEnd.3) were used to investigate whether a particulate phase of cigarette smoke extract (PPCSE) regulates HO-1 expression and to investigate the molecular mechanisms involved in HO-1 expression in bEnd.3 cells.

RESULTS

We demonstrated that PPCSE (30 μg/ml) significantly induced HO-1 protein expression and its enzymatic activity in bEnd.3 cells determined by western blotting and bilirubin formation, respectively. PPCSE-induced HO-1 expression was mediated through phosphatidylcholine phospholipase C (PC-PLC), PKCδ, and PI3K/Akt which were observed by pretreatment with their respective pharmacological inhibitors or transfection with dominant negative mutants of PKCδ and Akt. ROS scavenger (N-acetyl-L-cysteine, NAC) blocked the PPCSE-induced ROS generation and HO-1 expression. Pretreatment with selective inhibitors of PKCδ (rottlerin) and NADPH oxidase [diphenyleneiodonium chloride (DPI) and apocynin (APO)] attenuated the PPCSE-induced NADPH oxidase activity, ROS generation, and HO-1 expression. In addition, we found that PPCSE induced PI3K/Akt activation via NADPH oxidase/ROS-dependent PDGFR phosphorylation.

CONCLUSIONS

Taken together, these results suggested that PPCSE-induced HO-1 expression is mediated by a PC-PLC/PKCδ/NADPH oxidase-dependent PDGFR/PI3K/Akt pathway in bEnd.3 cells.

3,4-Di-O-Caffeoylquinic Acid Inhibits Angiotensin-II-Induced Vascular Smooth Muscle Cell Proliferation and Migration by Downregulating the JNK and PI3K/Akt Signaling Pathways

We previously reported 3,4-di-O-caffeoylquinic acid (CQC) protected vascular endothelial cells against oxidative stress and restored impaired endothelium-dependent vasodilatation. Here, we further investigated its anti-atherosclerotic effect against angiotensin II (Ang II) evoked proliferation and migration of cultured rat vascular smooth muscle cells (rVSMC). The results showed CQC (1–20 μM) clearly inhibited Ang-II-stimulated BrdU incorporation and cell migration of rVSMC in a concentration-dependent manner but without significant cytotoxicity. Western blot analysis revealed Ang II increased the phosphorylation levels of Akt and mitogen-activated protein kinases (MAPKs;p38, ERK1/2 and JNK) in rVSMC. In the presence of phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin and three individual MAPK inhibitors SB203580, PD98059 and SP600125, both Ang-II-induced cell proliferation and migration were significantly attenuated, although to differing extents, suggesting the PI3K and MAPK signal pathways all participated in regulating rVSMC proliferation and migration. Also, the CQC pretreatment markedly suppressed Ang-II-induced phosphorylation of Akt and JNK rather than ERK1/2, although it failed to affect p38 phosphorylation. In conclusion, our data demonstrate CQC may act by down-regulating Akt, JNK and part of the ERK1/2 pathways to inhibit Ang-II-induced rVSMC proliferation and migration. The anti-atherosclerotic effect of CQC is achieved either by endothelial cells protection or by VSMC proliferation/migration inhibition, suggesting this compound may be useful in preventing vascular diseases.

Caveolin-1 negatively regulates a metalloprotease-dependent epidermal growth factor receptor transactivation by angiotensin II

A metalloprotease, ADAM17, mediates the generation of mature ligands for the epidermal growth factor receptor (EGFR). This is the key signaling step by which angiotensin II (AngII) induces EGFR transactivation leading to hypertrophy and migration of vascular smooth muscle cells (VSMCs). However, the regulatory mechanism of ADAM17 activity remains largely unclear. Here we hypothesized that caveolin-1 (Cav1), the major structural protein of a caveolae, a membrane microdomain, is involved in the regulation of ADAM17. In cultured VSMCs, infection of adenovirus encoding Cav1 markedly inhibited AngII-induced EGFR ligand shedding, EGFR transactivation, ERK activation, hypertrophy and migration, but not intracellular Ca(2+) elevation. Methyl-β-cyclodextrin and filipin, reagents that disrupt raft structure, both stimulated an EGFR ligand shedding and EGFR transactivation in VSMCs. In addition, non-detergent sucrose gradient membrane fractionations revealed that ADAM17 cofractionated with Cav1 in lipid rafts. These results suggest that lipid rafts and perhaps caveolae provide a negative regulatory environment for EGFR transactivation linked to vascular remodeling induced by AngII. These novel findings may provide important information to target cardiovascular diseases under the enhanced renin angiotensin system.

TNF-alpha induces matrix metalloproteinase-9 expression in A549 cells: role of TNFR1/TRAF2/PKCalpha-dependent signaling pathways

Matrix metalloproteinases (MMPs), in particular MMP-9, have been shown to be induced by cytokines, including TNF-alpha and contributes to airway inflammation. However, the mechanisms underlying TNF-alpha-induced MMP-9 expression in human A549 cells remain unclear. Here, we report that TNF-alpha-induced MMP-9 gene expression was mediated through the TNFR1/TRAF2/PKCalpha-dependent signaling pathways in A549 cells, determined by zymographic, RT-PCR, and Western blotting analyses. TNF-alpha-induced MMP-9 expression was reduced by pretreatment with a TNFR Ab. Furthermore, TNF-alpha-induced TNFR1 and TRAF2 complex formation was revealed by immunoprecipitation using an anti-TNFR1 Ab followed by Western blot analysis against an anti-TRAF2 or anti-TNFR1 Ab. In addition, TNF-alpha-induced MMP-9 expression was also reduced by pretreatment with the inhibitor of PKCalpha (Gö6983), c-Src (PP1), EGFR (AG1478), or PI3K (LY294002) or transfection with siRNAs of PKCalpha, Src, EGFR, Akt, p65, p300, and c-Jun. On the other hand, TNF-alpha stimulated the phosphorylation of c-Src, EGFR, Akt, JNK1/2, and c-Jun, which were inhibited by pretreatment with Gö6983. We also showed that TNF-alpha induced Akt translocation and the formation of an Akt/p65/p300 complex. Pretreatment with the inhibitor of JNK1/2 (SP600125) but not the inhibitor of MEK1/2 (U0126), p38 MAPK (SB202190), or PI3K (LY294002), markedly inhibited TNF-alpha-induced c-Jun mRNA levels. Taken together, these data suggest that in A549 cells, TNF-alpha induces MMP-9 expression via the TNFR1/TRAF2/PKCalpha-dependent JNK1/2/c-Jun and c-Src/EGFR/PI3K/Akt pathways.

Placental mammalian target of rapamycin and related signaling pathways in an ovine model of intrauterine growth restriction

OBJECTIVE

Both phosphorylated (p) mammalian target of rapamycin (mTOR) and protein S6 kinase 1 (p70S6K) are known to regulate protein synthesis and are affected during intrauterine growth restriction (IUGR). We studied the mTOR pathway during hyperthermia (HT)-induced IUGR in sheep.

STUDY DESIGN

Beginning at 40 days gestational age, 4 ewes were exposed to HT for 55 days and 4 were exposed for 80 days to induce IUGR. Western blot analyses were performed for mTOR, p70S6K, 4E-binding protein 1, extracellularly regulated kinase (ERK), and AKT.

RESULTS

HT animals showed: smaller fetuses and placentas near term; reduced placental weight at midgestation; increased p-mTOR, p-ERK, and p-AKT; decreased p70S6K in the near-term cotyledons; decreased p- p70S6K; and increased p-ERK in the caruncles (maternal) near term.

CONCLUSION

Near-term IUGR ovine cotyledons showed up-regulation of p-mTOR, whereas p70S6K was decreased. This suggests that the changes in placental mTOR signaling proteins could be driven by the fetal stress observed near term in this model of IUGR.

p21-activated kinase 1 participates in vascular remodeling in vitro and in vivo

Vascular smooth muscle cell hypertrophy, proliferation, or migration occurs in hypertension, atherosclerosis, and restenosis after angioplasty, leading to pathophysiological vascular remodeling. Angiotensin II and platelet-derived growth factor are well-known participants of vascular remodeling and activate a myriad of downstream protein kinases, including p21-activated protein kinase (PAK1). PAK1, an effector kinase of small GTPases, phosphorylates several substrates to regulate cytoskeletal reorganization. However, the exact role of PAK1 activation in vascular remodeling remains to be elucidated. Here, we have hypothesized that PAK1 is a critical target of intervention for the prevention of vascular remodeling. Adenoviral expression of dominant-negative PAK1 inhibited angiotensin II-stimulated vascular smooth muscle cell migration. It also inhibited vascular smooth muscle cell proliferation induced by platelet-derived growth factor. PAK1 was activated in neointima of the carotid artery after balloon injury in the rat. Moreover, marked inhibition of the neointima hyperplasia was observed in a dominant-negative PAK1 adenovirus-treated carotid artery after the balloon injury. Taken together, these results suggest that PAK1 is involved in both angiotensin II and platelet-derived growth factor-mediated vascular smooth muscle cell remodeling, and inactivation of PAK1 in vivo could be effective in preventing pathophysiological vascular remodeling.

GPCR signalling to the translation machinery

G protein-coupled receptors (GPCRs) are involved in most physiological processes, many of them being engaged in fully differentiated cells. These receptors couple to transducers of their own, primarily G proteins and beta-arrestins, which launch intracellular signalling cascades. Some of these signalling events regulate the translational machinery to fine-tune general cell metabolism or to alter protein expression pattern. Though extensively documented for tyrosine kinase receptors, translational regulation by GPCRs is still poorly appreciated. The objective of this review paper is to address the following questions: i) is there a "GPCR signature" impacting on the translational machinery, and ultimately on the type of mRNA translated? ii) are the regulatory networks involved similar as those utilized by tyrosine kinase receptors? In particular, we will discuss the specific features of translational control mediated by GPCRs and highlight the intrinsic properties of GPCRs these mechanisms could rely on.

Angiotensin-induced EGF receptor transactivation inhibits insulin signaling in C9 hepatic cells

To investigate the potential interactions between the angiotensin II (Ang II) and insulin signaling systems, regulation of IRS-1 phosphorylation and insulin-induced Akt activation by Ang II were examined in clone 9 (C9) hepatocytes. In these cells, Ang II specifically inhibited activation of insulin-induced Akt Thr(308) and its immediate downstream substrate GSK-3alpha/beta in a time-dependent fashion, with approximately 70% reduction at 15 min. These inhibitory actions were associated with increased IRS-1 phosphorylation of Ser(636)/Ser(639) that was prevented by selective blockade of EGFR tyrosine kinase activity with AG1478. Previous studies have shown that insulin-induced phosphorylation of IRS-1 on Ser(636)/Ser(639) is mediated mainly by the PI3K/mTOR/S6K-1 sequence. Studies with specific inhibitors of PI3K (wortmannin) and mTOR (rapamycin) revealed that Ang II stimulates IRS-1 phosphorylation of Ser(636)/Ser(639) via the PI3K/mTOR/S6K-1 pathway. Both inhibitors blocked the effect of Ang II on insulin-induced activation of Akt. Studies using the specific MEK inhibitor, PD98059, revealed that ERK1/2 activation also mediates Ang II-induced S6K-1 and IRS-1 phosphorylation, and the impairment of Akt Thr(308) and GSK-3alpha/beta phosphorylation. Further studies with selective inhibitors showed that PI3K activation was upstream of ERK, suggesting a new mechanism for Ang II-induced impairment of insulin signaling. These findings indicate that Ang II has a significant role in the development of insulin resistance by a mechanism that involves EGFR transactivation and the PI3K/ERK1/2/mTOR-S6K-1 pathway.

Cigarette smoke extract induces COX-2 expression via a PKCalpha/c-Src/EGFR, PDGFR/PI3K/Akt/NF-kappaB pathway and p300 in tracheal smooth muscle cells

Exposure to cigarette smoke extract (CSE) leads to airway or lung inflammation, which may be mediated through cyclooxygenase-2 (COX-2) expression and its product prostaglandin E2 (PGE2) synthesis. The aim of this study was to investigate the molecular mechanisms underlying CSE-induced COX-2 expression in human tracheal smooth muscle cells (HTSMCs). Here, we describe that COX-2 induction is dependent on PKCalpha/c-Src/EGFR, PDGFR/PI3K/Akt/NF-kappaB signaling in HTSMCs. CSE stimulated the phosphorylation of c-Src, EGFR, PDGFR, and Akt, which were inhibited by pretreatment with the inhibitor of PKCalpha (Gö6976 or Gö6983), c-Src (PP1), EGFR (AG1478), PDGFR (AG1296), or PI3K (LY294002). Moreover, CSE induced a significant increase in COX-2 expression, which was reduced by pretreatment with these inhibitors or transfection with siRNA of PKCalpha, Src, or Akt. Furthermore, CSE-stimulated NF-kappaB p65 phosphorylation and translocation were also attenuated by pretreatment with Gö6976, PP1, AG1478, AG1296, or LY294002. CSE-induced COX-2 expression was also mediated through the recruitment of p300 associated with NF-kappaB in HTSMCs, revealed by coimmunoprecipitation and Western blot analysis. In addition, pretreatment with the inhibitors of NF-kappaB (helenalin) and p300 (garcinol) or transfection with p65 siRNA and p300 siRNA markedly inhibited CSE-regulated COX-2 expression. However, CSE-induced PGE2 generation was reduced by pretreatment with the inhibitor of COX-2 (NS-398). These results demonstrated that in HTSMCs, CSE-induced COX-2-dependent PGE2 generation was mediated through PKCalpha/c-Src/EGFR, PDGFR/PI3K/Akt leading to the recruitment of p300 with NF-kappaB complex.

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.

Leptin signaling: A key pathway in immune responses

Leptin is a hormone whose central role is to regulate endocrine functions and to control energy expenditure. After the discovery that leptin can also have pro-inflammatory effects, several studies have tried to address - at the molecular level - the pathways involved in leptin-induced modulation of the immune functions in normal and pathologic conditions. The signaling events influenced by leptin after its binding to the leptin receptor have been under scrutiny in the past few years, and considerable experimental work has elucidated the consequences of leptin effects on immune cells. This review examines the biochemistry, function and regulation of leptin signaling in view of possible intervention on this molecule for a better management and therapy of immune-mediated diseases.

Endothelial nitric oxide synthase inhibits G12/13 and rho-kinase activated by the angiotensin II type-1 receptor: implication in vascular migration

BACKGROUND

Although, endothelial nitric oxide (NO) synthase (eNOS) is believed to antagonize vascular remodeling induced by the angiotensin II (AngII) type-1 receptor, the exact signaling mechanism remains unclear.

METHODS AND RESULTS

By expressing eNOS to vascular smooth muscle cells (VSMCs) via adenovirus, we investigated a signal transduction mechanism of the eNOS gene transfer in preventing vascular remodeling induced by AngII. We found marked inhibition of AngII-induced Rho/Rho-kinase activation and subsequent VSMC migration by eNOS gene transfer whereas G(q)-dependent transactivation of the epidermal growth factor receptor by AngII remains intact. This could be explained by the specific inhibition of G(12/13) activation by eNOS-mediated G(12/13) phosphorylation.

CONCLUSIONS

The eNOS/NO cascade specifically targets the Rho/Rho-kinase system via inhibition of G(12/13) to prevent vascular migration induced by AngII, representing a novel signal cross-talk in cardiovascular protection by NO.

Impaired insulin-mediated vasorelaxation in diabetic Goto-Kakizaki rats is caused by impaired Akt phosphorylation

Insulin resistance associated with Type 2 diabetes contributes to impaired vasorelaxation. Previously, we showed the phosphorylation of myosin-bound phosphatase substrate MYPT1, a marker of the vascular smooth muscle cell (VSMC) contraction, was negatively regulated by Akt (protein kinase B) phosphorylation in response to insulin stimulation. In this study we examined the role of Akt phosphorylation on impaired insulin-induced vasodilation in the Goto-Kakizaki (GK) rat model of Type 2 diabetes. GK VSMCs had impaired basal and insulin-induced Akt phosphorylation as well as increases in basal MYPT1 phosphorylation, inducible nitric oxide synthase (iNOS) expression, and nitrite/nitrate production compared with Wistar-Kyoto controls. Both iNOS expression and the inhibition of angiotensin (ANG) II-induced MYPT1 phosphorylation were resistant to the effects of insulin in diabetic GK VSMC. We also measured the isometric tension of intact and denuded GK aorta using a myograph and observed significantly impaired insulin-induced vasodilation. Adenovirus-mediated overexpression of constitutively active Akt in GK VSMC led to significantly improved insulin sensitivity in terms of counteracting ANG II-induced contractile signaling via MYPT1, myosin light chain dephosphorylation, and reduced iNOS expression, S-nitrosylation and survivin expression. We demonstrated for the first time the presence of Akt-independent iNOS expression in the GK diabetic model and that the defective insulin-induced vasodilation observed in the diabetic vasculature can be restored by the overexpression of active Akt, which advocates a novel therapeutic strategy for treating diabetes.

Nerve growth factor inhibits Na+/H+ exchange and formula absorption through parallel phosphatidylinositol 3-kinase-mTOR and ERK pathways in thick ascending limb

In the medullary thick ascending limb, inhibiting the basolateral NHE1 Na(+)/H(+) exchanger with nerve growth factor (NGF) induces actin cytoskeleton remodeling that secondarily inhibits apical NHE3 and transepithelial HCO(3)(-) absorption. The inhibition by NGF is mediated 50% through activation of extracellular signal-regulated kinase (ERK). Here we examined the signaling pathway responsible for the remainder of the NGF-induced inhibition. Inhibition of HCO(3)(-) absorption was reduced 45% by the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY294002 and 50% by rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR), a downstream effector of PI3K. The combination of a PI3K inhibitor plus rapamycin did not cause a further reduction in the inhibition by NGF. In contrast, the combination of a PI3K inhibitor plus the MEK/ERK inhibitor U0126 completely eliminated inhibition by NGF. Rapamycin decreased NGF-induced inhibition of basolateral NHE1 by 45%. NGF induced a 2-fold increase in phosphorylation of Akt, a PI3K target linked to mTOR activation, and a 2.2-fold increase in the activity of p70 S6 kinase, a downstream effector of mTOR. p70 S6 kinase activation was blocked by wortmannin and rapamycin, consistent with PI3K, mTOR, and p70 S6 kinase in a linear pathway. Rapamycin-sensitive inhibition of NHE1 by NGF was associated with an increased level of phosphorylated mTOR in the basolateral membrane domain. These findings indicate that NGF inhibits HCO(3)(-) absorption in the medullary thick ascending limb through the parallel activation of PI3K-mTOR and ERK signaling pathways, which converge to inhibit NHE1. The results identify a role for mTOR in the regulation of Na(+)/H(+) exchange activity and implicate NHE1 as a possible downstream effector contributing to mTOR's effects on cell growth, proliferation, survival, and tumorigenesis.

Central role of Gq in the hypertrophic signal transduction of angiotensin II in vascular smooth muscle cells

The angiotensin II (AngII) type 1 receptor (AT(1)) plays a critical role in hypertrophy of vascular smooth muscle cells (VSMCs). Although it is well known that G(q) is the major G protein activated by the AT(1) receptor, the requirement of G(q) for AngII-induced VSMC hypertrophy remains unclear. By using cultured VSMCs, this study examined the requirement of G(q) for the epidermal growth factor receptor (EGFR) pathway, the Rho-kinase (ROCK) pathway, and subsequent hypertrophy. AngII-induced intracellular Ca(2+) elevation was completely inhibited by a pharmacological G(q) inhibitor as well as by adenovirus encoding a G(q) inhibitory minigene. AngII (100nm)-induced EGFR transactivation was almost completely inhibited by these inhibitors, whereas these inhibitors only partially inhibited AngII (100nm)-induced phosphorylation of a ROCK substrate, myosin phosphatase target subunit-1. Stimulation of VSMCs with AngII resulted in an increase of cellular protein and cell volume but not in cell number. The G(q) inhibitors completely blocked these hypertrophic responses, whereas a G protein-independent AT(1) agonist did not stimulate these hypertrophic responses. In conclusion, G(q) appears to play a major role in the EGFR pathway, leading to vascular hypertrophy induced by AngII. Vascular G(q) seems to be a critical target of intervention against cardiovascular diseases associated with the enhanced renin-angiotensin system.

Lipid rafts and caveolae in signaling by growth factor receptors

Lipid rafts and caveolae are microdomains of the plasma membrane enriched in sphingolipids and cholesterol, and hence are less fluid than the remainder of the membrane. Caveolae have an invaginated structure, while lipid rafts are flat regions of the membrane. The two types of microdomains have different protein compositions (growth factor receptors and their downstream molecules) suggesting that lipid rafts and caveolae have a role in the regulation of signaling by these receptors. The purpose of this review is to discuss this model, and the implications that it might have regarding a potential role for lipid rafts and caveolae in human cancer. Particular attention will be paid to the epidermal growth factor receptor, for which the largest amount of information is available. It has been proposed that caveolins act as tumor suppressors. The role of lipid rafts is less clear, but they seem to be capable of acting as 'signaling platforms', in which signal initiation and propagation can occur efficiently.