Protein kinase C, but not tyrosine kinases or Ras, plays a critical role in angiotensin II-induced activation of Raf-1 kinase and extracellular signal-regulated protein kinases in cardiac myocytes

Unraveling the interplay between RAS/RAF/MEK/ERK signaling pathway and autophagy in cancer: From molecular mechanisms to targeted therapy

RAS/RAF/MEK/ERK signaling pathway is one of the most important pathways of Mitogen-activated protein kinases (MAPK), which widely participate in regulating cell proliferation, differentiation, apoptosis and signaling transduction. Autophagy is an essential mechanism that maintains cellular homeostasis by degrading aged and damaged organelles. Recently, some studies revealed RAS/RAF/MEK/ERK signaling pathway is closely related to autophagy regulation and has a dual effect in tumor cells. However, the specific mechanism by which RAS/RAF/MEK/ERK signaling pathway participates in autophagy regulation is not fully understood. This article provides a comprehensive review of the research progress with regard to the RAS/RAF/MEK/ERK signaling pathway and autophagy, as well as their interplay in cancer therapy. The impact of small molecule inhibitors that target the RAS/RAF/MEK/ERK signaling pathway on autophagy is discussed in this study. The advantages and limitations of the clinical combination of these small molecule inhibitors with autophagy inhibitors are also explored. The findings from this study may provide additional perspectives for future cancer treatment strategies.

Between Inflammation and Autophagy: The Role of Leptin-Adiponectin Axis in Cardiac Remodeling

Cardiac remodeling is the process by which the heart adapts to stressful stimuli, such as hypertension and ischemia/reperfusion; it ultimately leads to heart failure upon long-term exposure. Autophagy, a cellular catabolic process that was originally considered as a mechanism of cell death in response to detrimental stimuli, is thought to be one of the main mechanisms that controls cardiac remodeling and induces heart failure. Dysregulation of the adipokines leptin and adiponectin, which plays essential roles in lipid and glucose metabolism, and in the pathophysiology of the neuroendocrine and cardiovascular systems, has been shown to affect the autophagic response in the heart and to contribute to accelerate cardiac remodeling. The obesity-associated protein leptin is a pro-inflammatory, tumor-promoting adipocytokine whose elevated levels in obesity are associated with acute cardiovascular events, and obesity-related hypertension. Adiponectin exerts anti-inflammatory and anti-tumor effects, and its reduced levels in obesity correlate with the pathogenesis of obesity-associated cardiovascular diseases. Leptin- and adiponectin-induced changes in autophagic flux have been linked to cardiac remodeling and heart failure. In this review, we describe the different molecular mechanisms of hyperleptinemia- and hypoadiponectinemia-mediated pathogenesis of cardiac remodeling and the involvement of autophagy in this process. A better understanding of the roles of leptin, adiponectin, and autophagy in cardiac functions and remodeling, and the exact signal transduction pathways by which they contribute to cardiac diseases may well lead to discovery of new therapeutic agents for the treatment of cardiovascular remodeling.

Precision medicine for heart failure based on molecular mechanisms: The 2019 ISHR Research Achievement Award Lecture

Heart failure is a leading cause of death, and the number of patients with heart failure continues to increase worldwide. To realize precision medicine for heart failure, its underlying molecular mechanisms must be elucidated. In this review summarizing the "The Research Achievement Award Lecture" of the 2019 XXIII ISHR World Congress held in Beijing, China, we would like to introduce our approaches for investigating the molecular mechanisms of cardiac hypertrophy, development, and failure, as well as discuss future perspectives.

Association of Regulatory Genetic Variants for Protein Kinase Cα with Mortality and Drug Efficacy in Patients with Heart Failure

PURPOSE

Protein kinase C alpha (gene: PRKCA) is a key regulator of cardiac contractility. Two genetic variants have recently been discovered to regulate PRKCA expression in failing human heart tissue (rs9909004 [T → C] and rs9303504 [C → G]). The association of those variants with clinical outcomes in patients with heart failure (HF), and their interaction with HF drug efficacy, is unknown.

METHODS

Patients with HF in a prospective registry starting in 2007 were genotyped by whole genome array (n = 951). The primary outcome was all-cause mortality. Cox proportional hazards models adjusted for established clinical risk factors and genomic ancestry tested the independent association of rs9909004 or rs9303504 and the variant interactions with cornerstone HF pharmacotherapies (beta-blockers or angiotensin-converting enzyme inhibitors/angiotensin receptor blockers) in additive genetic models.

RESULTS

The minor allele of rs9909004, but not of rs9303504, was independently associated with a decreased risk for all-cause mortality: adjusted HR = 0.81 (95% CI = 0.67-0.98), p = 0.032. The variants did not significantly interact with mortality benefit associated with cornerstone HF pharmacotherapies (p > 0.1 for all).

CONCLUSIONS

A recently discovered cardiac-specific regulatory variant for PRKCA (rs9909004) was independently associated with a decreased risk for all-cause mortality in patients with HF. The variant did not interact with mortality benefit associated with cornerstone HF pharmacotherapies.

Hypertrophy of human embryonic stem cell-derived cardiomyocytes supported by positive feedback between Ca2+ and diacylglycerol signals

Human embryonic stem cell-derived cardiomyocytes develop pronounced hypertrophy in response to angiotensin-2, endothelin-1, and a selected mix of three fatty acids. All three of these responses are accompanied by increases in both basal cytoplasmic Ca2+ and diacylglycerol, quantified with the Ca2+ sensor Fluo-4 and a FRET-based diacylglycerol sensor expressed in these cardiomyocytes. The heart glycoside, ouabain (30 nM), and a recently developed inhibitor of diacylglycerol lipases, DO34 (1 μM), cause similar hypertrophy responses, and both responses are accompanied by equivalent increases of basal Ca2+ and diacylglycerol. These results together suggest that basal Ca2+ and diacylglycerol form a positive feedback signaling loop that promotes execution of cardiac growth programs in these human myocytes. Given that basal Ca2+ in myocytes depends strongly on the Na+ gradient, we also tested whether nanomolar ouabain concentrations might stimulate Na+/K+ pumps, as described by others, and thereby prevent hypertrophy. However, stimulatory effects of nanomolar ouabain (1.5 nM) were not verified on Na+/K+ pump currents in stem cell-derived myocytes, nor did nanomolar ouabain block hypertrophy induced by endothelin-1. Thus, low-dose ouabain is not a "protective" intervention under the conditions of these experiments in this human myocyte model. To summarize, the major aim of this study has been to characterize the progression of hypertrophy in human embryonic stem cell-derived cardiac myocytes in dependence on diacylglycerol and Na+ gradient changes, developing a case that positive feedback coupling between these mechanisms plays an important role in the initiation of hypertrophy programs.

Protein phosphatase 5 regulates titin phosphorylation and function at a sarcomere-associated mechanosensor complex in cardiomyocytes

Serine/threonine protein phosphatase 5 (PP5) is ubiquitously expressed in eukaryotic cells; however, its function in cardiomyocytes is unknown. Under basal conditions, PP5 is autoinhibited, but enzymatic activity rises upon binding of specific factors, such as the chaperone Hsp90. Here we show that PP5 binds and dephosphorylates the elastic N2B-unique sequence (N2Bus) of titin in cardiomyocytes. Using various binding and phosphorylation tests, cell-culture manipulation, and transgenic mouse hearts, we demonstrate that PP5 associates with N2Bus in vitro and in sarcomeres and is antagonistic to several protein kinases, which phosphorylate N2Bus and lower titin-based passive tension. PP5 is pathologically elevated and likely contributes to hypo-phosphorylation of N2Bus in failing human hearts. Furthermore, Hsp90-activated PP5 interacts with components of a sarcomeric, N2Bus-associated, mechanosensor complex, and blocks mitogen-activated protein-kinase signaling in this complex. Our work establishes PP5 as a compartmentalized, well-controlled phosphatase in cardiomyocytes, which regulates titin properties and kinase signaling at the myofilaments.

Protein phosphatase 5 (PP5) is expressed in many cell types but its role in cardiomyocytes is unknown. Here the authors show that PP5 binds and dephosphorylates elastic titin in cardiac sarcomeres, and that PP5 is increased in heart failure, reducing cardiomyocyte compliance.

Angiotensin II-triggered kinase signaling cascade in the central nervous system

Recent studies have projected the renin-angiotensin system as a central component of the physiological and pathological processes of assorted neurological disorders. Its primary effector hormone, angiotensin II (Ang II), not only mediates the physiological effects of vasoconstriction and blood pressure regulation in cardiovascular disease but is also implicated in a much wider range of neuronal activities and diseases, including Alzheimer's disease, neuronal injury, and cognitive disorders. Ang II produces different actions by acting on its two subtypes of receptors (AT1 and AT2); however, the well-known physiological actions of Ang II are mainly mediated through AT1 receptors. Moreover, recent studies also suggest the important functional role of AT2 receptor in the brain. Ang II acts on AT1 receptors and conducts its functions via MAP kinases (ERK1/2, JNK, and p38MAPK), glycogen synthase kinase, Rho/ROCK kinase, receptor tyrosine kinases (PDGF and EGFR), and nonreceptor tyrosine kinases (Src, Pyk2, and JAK/STAT). AT1R-mediated NADPH oxidase activation also leads to the generation of reactive oxygen species, widely implicated in neuroinflammation. These signaling cascades lead to glutamate excitotoxicity, apoptosis, cerebral infarction, astrocyte proliferation, nociception, neuroinflammation, and progression of other neurological disorders. The present review focuses on the Ang II-triggered signal transduction pathways in central nervous system.

The PLC/PKC/Ras/MEK/Kv channel pathway is involved in uncarboxylated osteocalcin-regulated insulin secretion in rats

Uncarboxylated osteocalcin, a bone matrix protein, has been proposed to regulate glucose metabolism by increasing insulin secretion, improving insulin sensitivity and stimulating β cell proliferation. Our previous study also indicated that uncarboxylated osteocalcin stimulates insulin secretion by inhibiting voltage-gated potassium (K_V) channels. The goal of this study is to further investigate the underlying mechanisms for the regulation of Kv channels and insulin secretion by uncarboxylated osteocalcin. Insulin secretion and Kv channel currents were examined by radioimmunoassay and patch-clamp technique, respectively. Calcium imaging system was applied to measure intracellular Ca²⁺ concentration ([Ca²⁺]_i). The protein levels were detected by western blot. The results showed that uncarboxylated osteocalcin potentiated insulin secretion, inhibited Kv channels and increased [Ca²⁺]_i compared to control. These effects were suppressed by phospholipase-C (PLC)/protein kinase C (PKC)/Ras/MAPK-ERK kinase (MEK) signaling pathway, indicating that this signaling pathway plays an important role in uncarboxylated osteocalcin-regulated insulinotropic effect. In addition, the results also showed that adenylyl cyclase (AC) did not influence the effect of uncarboxylated osteocalcin on insulin secretion and Kv channels, suggesting that AC is not involved in uncarboxylated osteocalcin-stimulated insulin secretion. These findings provide new insight into the mechanism of uncarboxylated osteocalcin-regulated insulin secretion.

Dominant negative Ras attenuates pathological ventricular remodeling in pressure overload cardiac hypertrophy

The importance of the oncogene Ras in cardiac hypertrophy is well appreciated. The hypertrophic effects of the constitutively active mutant Ras-Val12 are revealed by clinical syndromes due to the Ras mutations and experimental studies. We examined the possible anti-hypertrophic effect of Ras inhibition in vitro using rat neonatal cardiomyocytes (NRCM) and in vivo in the setting of pressure-overload left ventricular (LV) hypertrophy (POH) in rats. Ras functions were modulated via adenovirus directed gene transfer of active mutant Ras-Val12 or dominant negative mutant N17-DN-Ras (DN-Ras). Ras-Val12 expression in vitro activates NFAT resulting in pro-hypertrophic and cardio-toxic effects on NRCM beating and Z-line organization. In contrast, the DN-Ras was antihypertrophic on NRCM, inhibited NFAT and exerted cardio-protective effects attested by preserved NRCM beating and Z line structure. Additional experiments with silencing H-Ras gene strategy corroborated the antihypertrophic effects of siRNA-H-Ras on NRCM. In vivo, with the POH model, both Ras mutants were associated with similar hypertrophy two weeks after simultaneous induction of POH and Ras-mutant gene transfer. However, LV diameters were higher and LV fractional shortening lower in the Ras-Val12 group compared to control and DN-Ras. Moreover, DN-Ras reduced the cross-sectional area of cardiomyocytes in vivo, and decreased the expression of markers of pathologic cardiac hypertrophy. In isolated adult cardiomyocytes after 2 weeks of POH and Ras-mutant gene transfer, DN-Ras improved sarcomere shortening and calcium transients compared to Ras-Val12. Overall, DN-Ras promotes a more physiological form of hypertrophy, suggesting an interesting therapeutic target for pathological cardiac hypertrophy.

Pleiotropic Effects of Angiotensin II Receptor Signaling in Cardiovascular Homeostasis and Aging

Most of the pathophysiological actions of angiotensin II (Ang II) are mediated through the Ang II type 1 (AT1) receptor, a member of the seven-transmembrane G protein-coupled receptor family. Essentially, AT1 receptor signaling is beneficial for organismal survival and procreation, because it is crucial for normal organ development, and blood pressure and electrolyte homeostasis. On the other hand, AT1 receptor signaling has detrimental effects, such as promoting various aging-related diseases that include cardiovascular diseases, diabetes, chronic kidney disease, dementia, osteoporosis, and cancer. Pharmacological or genetic blockade of AT1 receptor signaling in rodents has been shown to prevent the progression of aging-related phenotypes and promote longevity. In this way, AT1 receptor signaling exerts antagonistic and pleiotropic effects according to the ages and pathophysiological conditions. Here we review the pleiotropic effects of AT1 receptor signaling in cardiovascular homeostasis and aging.

Src is required for mechanical stretch-induced cardiomyocyte hypertrophy through angiotensin II type 1 receptor-dependent β-arrestin2 pathways

Angiotensin II (AngII) type 1 receptor (AT1-R) can be activated by mechanical stress (MS) without the involvement of AngII during the development of cardiomyocyte hypertrophy, in which G protein-independent pathways are critically involved. Although β-arrestin2-biased signaling has been speculated, little is known about how AT1-R/β-arrestin2 leads to ERK1/2 activation. Here, we present a novel mechanism by which Src kinase mediates AT1-R/β-arrestin2-dependent ERK1/2 phosphorylation in response to MS. Differing from stimulation by AngII, MS-triggered ERK1/2 phosphorylation is neither suppressed by overexpression of RGS4 (the negative regulator of the G-protein coupling signal) nor by inhibition of Gαq downstream protein kinase C (PKC) with GF109203X. The release of inositol 1,4,5-triphosphate (IP₃) is increased by AngII but not by MS. These results collectively suggest that MS-induced ERK1/2 activation through AT1-R might be independent of G-protein coupling. Moreover, either knockdown of β-arrestin2 or overexpression of a dominant negative mutant of β-arrestin2 prevents MS-induced activation of ERK1/2. We further identifies a relationship between Src, a non-receptor tyrosine kinase and β-arrestin2 using analyses of co-immunoprecipitation and immunofluorescence after MS stimulation. Furthermore, MS-, but not AngII-induced ERK1/2 phosphorylation is attenuated by Src inhibition, which also significantly improves pressure overload-induced cardiac hypertrophy and dysfunction in mice lacking AngII. Finally, MS-induced Src activation and hypertrophic response are abolished by candesartan but not by valsartan whereas AngII-induced responses can be abrogated by both blockers. Our results suggest that Src plays a critical role in MS-induced cardiomyocyte hypertrophy through β-arrestin2-associated angiotensin II type 1 receptor signaling.

Non-canonical signalling and roles of the vasoactive peptides angiotensins and kinins

GPCRs (G-protein-coupled receptors) are among the most important targets for drug discovery due to their ubiquitous expression and participation in cellular events under both healthy and disease conditions. These receptors can be activated by a plethora of ligands, such as ions, odorants, small ligands and peptides, including angiotensins and kinins, which are vasoactive peptides that are classically involved in the pathophysiology of cardiovascular events. These peptides and their corresponding GPCRs have been reported to play roles in other systems and under pathophysiological conditions, such as cancer, central nervous system disorders, metabolic dysfunction and bone resorption. More recently, new mechanisms have been described for the functional regulation of GPCRs, including the transactivation of other signal transduction receptors and the activation of G-protein-independent pathways. The existence of such alternative mechanisms for signal transduction and the discovery of agonists that can preferentially trigger one signalling pathway over other pathways (called biased agonists) have opened new perspectives for the discovery and development of drugs with a higher specificity of action and, therefore, fewer side effects. The present review summarizes the current knowledge on the non-canonical signalling and roles of angiotensins and kinins.

Reactive oxygen species activation of MAPK pathway results in VEGF upregulation as an undesired irradiation response

BACKGROUND

Radioresistance limits the effectiveness of radiotherapy in head and neck squamous cell carcinoma. We previously demonstrated post-radiogenic mitogen-activated protein kinase (MAPK) pathway activation and vascular endothelial growth factor (VEGF) release resulting in reduced tumor cell response. Here, we examined the association of this mechanism with the induction of reactive oxygen species (ROS) under irradiation (IR).

METHODS

Intracellular ROS after IR were measured. We modeled radiation-induced ROS by exposure of two SCC lines to H2 O2 and evaluated the impact of irradiation and ROS on ERK phosphorylation by Western blot, immunohistochemistry, and ELISA.

RESULTS

We found elevated pERK levels after treatment with IR and H2 O2 , which could be distinctly suppressed by U0126. Immunohistochemistry and ELISA revealed increased intracellular VEGF levels after H2 O2 application.

CONCLUSIONS

Our data show that irradiation-induced ROS activate the MAPK pathway and release of VEGF. As VEGF is known to be released after cellular distress resulting in cytoprotection, the described mechanism is potentially of importance for therapy success.

Mitogen-Activated Protein (MAP) Kinase Scaffolding Proteins: A Recount

The mitogen-activated protein kinase (MAPK) pathway is the canonical signaling pathway for many receptor tyrosine kinases, such as the Epidermal Growth Factor Receptor. Downstream of the receptors, this pathway involves the activation of a kinase cascade that culminates in a transcriptional response and affects processes, such as cell migration and adhesion. In addition, the strength and duration of the upstream signal also influence the mode of the cellular response that is switched on. Thus, the same components can in principle coordinate opposite responses, such as proliferation and differentiation. In recent years, it has become evident that MAPK signaling is regulated and fine-tuned by proteins that can bind to several MAPK signaling proteins simultaneously and, thereby, affect their function. These so-called MAPK scaffolding proteins are, thus, important coordinators of the signaling response in cells. In this review, we summarize the recent advances in the research on MAPK/extracellular signal-regulated kinase (ERK) pathway scaffolders. We will not only review the well-known members of the family, such as kinase suppressor of Ras (KSR), but also put a special focus on the function of the recently identified or less studied scaffolders, such as fibroblast growth factor receptor substrate 2, flotillin-1 and mitogen-activated protein kinase organizer 1.

PIKE mediates EGFR proliferative signaling in squamous cell carcinoma cells

One of the key drivers for squamous cell carcinoma (SCC) proliferation is activation of the epidermal growth factor receptor (EGFR), a known proto-oncogene. However, the mechanism of EGFR-dependent SCC proliferation remains unclear. Our previous studies indicate that epidermal growth factor (EGF)-induced SCC cell proliferation requires the SH3 domain of phospholipase C-γ1 (PLC-γ1), but not its catalytic activity. The SH3 domain of PLC-γ1 is known to activate the short form of nuclear phosphatidylinositol 3-kinase enhancer (PIKE) that enhances the activity of nuclear class Ia phosphatidylinositol 3-kinase (PI3K) required for proliferation. However, PIKE has been described for more than a decade to be present exclusively in neuronal cells. In the present study, we found that PIKE was highly expressed in malignant human keratinocytes (SCC4 and SCC12B2) but had low expression in normal human keratinocytes. Immunohistochemical analysis showed strong nuclear staining of PIKE in human epidermal and tongue SCC specimens but little staining in the adjacent non-cancerous epithelium. Treatment of SCC4 cells with EGF-induced translocation of PLC-γ1 to the nucleus and binding of PLC-γ1 to the nuclear PIKE. Knockdown of PLC-γ1 or PIKE blocked EGF-induced activation of class Ia PI3K and protein kinase C-ζ and phosphorylation of nucleolin in the nucleus as well as EGF-induced SCC cell proliferation. However, inhibition of the catalytic activity of PLC-γ1 had little effect. These data suggest that PIKE has a critical role in EGF-induced SCC cell proliferation and may function as a proto-oncogene in SCC.

Protective Role of the ACE2/Ang-(1-9) Axis in Cardiovascular Remodeling

Despite reduction in cardiovascular (CV) events and end-organ damage with the current pharmacologic strategies, CV disease remains the primary cause of death in the world. Pharmacological therapies based on the renin angiotensin system (RAS) blockade are used extensively for the treatment of hypertension, heart failure, and CV remodeling but in spite of their success the prevalence of end-organ damage and residual risk remain still high. Novel approaches must be discovered for a more effective treatment of residual CV remodeling and risk. The ACE2/Ang-(1–9) axis is a new and important target to counterbalance the vasoconstrictive/proliferative RAS axis. Ang-(1–9) is hydrolyzed slower than Ang-(1–7) and is able to bind the Ang II type 2 receptor. We review here the current experimental evidence suggesting that activation of the ACE2/Ang-(1–9) axis protects the heart and vessels (and possibly the kidney) from adverse cardiovascular remodeling in hypertension as well as in heart failure.

Flotillin-1/reggie-2 protein plays dual role in activation of receptor-tyrosine kinase/mitogen-activated protein kinase signaling

Our previous work has shown that the membrane microdomain-associated flotillin proteins are potentially involved in epidermal growth factor (EGF) receptor signaling. Here we show that knockdown of flotillin-1/reggie-2 results in reduced EGF-induced phosphorylation of specific tyrosines in the EGF receptor (EGFR) and in inefficient activation of the downstream mitogen-activated protein (MAP) kinase and Akt signaling. Although flotillin-1 has been implicated in endocytosis, its depletion affects neither the endocytosis nor the ubiquitination of the EGFR. However, EGF-induced clustering of EGFR at the cell surface is altered in cells lacking flotillin-1. Furthermore, we show that flotillins form molecular complexes with EGFR in an EGF/EGFR kinase-independent manner. However, knockdown of flotillin-1 appears to affect the activation of the downstream MAP kinase signaling more directly. We here show that flotillin-1 forms a complex with CRAF, MEK1, ERK, and KSR1 (kinase suppressor of RAS) and that flotillin-1 knockdown leads to a direct inactivation of ERK1/2. Thus, flotillin-1 plays a direct role during both the early phase (activation of the receptor) and late (activation of MAP kinases) phase of growth factor signaling. Our results here unveil a novel role for flotillin-1 as a scaffolding factor in the regulation of classical MAP kinase signaling. Furthermore, our results imply that other receptor-tyrosine kinases may also rely on flotillin-1 upon activation, thus suggesting a general role for flotillin-1 as a novel factor in receptor-tyrosine kinase/MAP kinase signaling.

Mitogen-activated protein kinases in mammalian oxidative stress responses

All aerobic organisms are exposed to oxidative stress during their lifetime and are required to respond appropriately for maintenance of their survival and homeostasis. Sustained exposure to oxidative stress has devastating effects in organisms, and, not surprisingly, oxidative stress has been implicated in numerous human diseases. Therefore, an understanding of how mammals respond to oxidative stress is crucial both biologically and clinically. Intracellular signaling pathways, which are activated in response to excessive oxygen radicals, play essential roles in overcoming oxidative stress. The mitogen-activated protein kinase (MAPK) signaling pathways are involved in diverse physiological processes, and are critical for induction of oxidative stress responses. In this review, we will discuss the physiological roles of MAPKs in oxidative stress, the upstream signaling pathways leading to MAPK activation, their regulation, and the MAPK downstream substrates, with a focus on mammalian systems.

The effect of adrenalectomy on the cardiac response to subacute fetal anemia

The mechanisms that stimulate fetal heart growth during anemia are unknown. To examine the hypothesis that adrenal hormones contribute to this process, we determined the effects of adrenalectomy (Adx) on heart growth and the activation of cardiac mitogen-activated protein kinases (MAPKs) in the presence and absence of fetal anemia. To identify mechanisms contributing to the initiation of cardiac growth, the duration of anemia was limited to a period shorter than that previously described to result in increased cardiac mass. Four groups of fetal sheep were studied (Adx-Anemic, Adx-Control, Intact-Anemic, Intact-Control). Anemia was created by daily controlled hemorrhage for 5 days; hearts were collected for analysis at 133 d gestation (term 145 d). Cardiomyocyte morphometry, immunohistochemistry for Ki-67 (proliferation marker), and Western blotting for protein levels of MAPKs and proliferating cell nuclear antigen (PCNA) were performed. Blood pressure, heart rate, heart weight-to-body weight ratio, and cardiomyocyte length and width remained similar among groups throughout the study. PCNA levels in the Adx-Anemic group were twice as high as in any other group (both ventricles, p < 0.05). Levels of phosphorylated extracellular signal-regulated kinase (ERK) were ~60% higher in the Intact-Anemic and Adx-Anemic groups, compared with the Intact-Control and Adx-Control groups (p < 0.02). These results suggest that adrenal hormones may attenuate fetal cardiomyocyte proliferation in response to anemia (as evidenced by the increased PCNA in Adx-Anemic fetuses) and that phosphorylation of myocardial ERK results from fetal anemia, irrespective of the status of the fetal adrenal gland.

Redox control of GTPases: from molecular mechanisms to functional significance in health and disease

Small GTPases, including the proto-oncoprotein Ras and Rho GTPases, are involved in various cellular signaling events. Some of these small GTPases are redox sensitive, including Ras, Rho, Ran, Dexras1, and Rhes GTPases. Thus, the redox-mediated regulation of these GTPases often determines the course of their cellular signaling cascades. This article takes into consideration the application of Marcus theory to potential redox-based molecular mechanisms in the regulation of these redox-sensitive GTPases and the relevance of such mechanisms to a specific redox-sensitive motif. The discussion also takes into account various diseases, including cancers, heart, and neuronal disorders, that are often linked with the dysregulation of the redox signaling cascades associated with these redox-sensitive GTPases.

Angiotensin II increases mRNA levels of all TGF-beta isoforms in quiescent and activated rat hepatic stellate cells

AII (angiotensin II) is a vasoactive peptide that plays an important role in the development of liver fibrosis mainly by regulating profibrotic cytokine expression such as TGF-beta (transforming growth factor-beta). Activated HSCs (hepatic stellate cells) are the major cell type responsible for ECM (extracellular matrix) deposition during liver fibrosis and are also a target for AII and TGF-beta actions. Here, we studied the effect of AII on the mRNA levels of TGF-beta isoforms in primary cultures of rat HSCs. Both quiescent and activated HSCs were stimulated with AII for different time periods, and mRNA levels of TGF-beta1, TGF-beta2 and TGF-beta3 isoforms were evaluated using RNaseI protection assay. The mRNA levels of all TGF-beta isoforms, particularly TGF-beta2and TGF-beta3, were increased after AII treatment in activated HSCs. In addition, activated HSCs were able to produce active TGF-beta protein after AII treatment. The mRNA expression of TGF-beta isoforms induced by AII required both ERK1/2 and Nox (NADPH oxidase) activation but not PKC (protein kinase C) participation. ERK1/2 activation induced by AII occurs via AT1 receptors, but independently of either PKC and Nox activation or EGFR (epidermal growth factor receptor) transactivation. Interestingly, AII has a similar effect on TGF-beta expression in quiescent HSCs, although it has a smaller but significant effect on ERK1/2 activation in these cells.

Angiotensin1-9 antagonises pro-hypertrophic signalling in cardiomyocytes via the angiotensin type 2 receptor

The renin–angiotensin system (RAS) regulates blood pressure mainly via the actions of angiotensin (Ang)II, generated via angiotensin converting enzyme (ACE). The ACE homologue ACE2 metabolises AngII to Ang1-7, decreasing AngII and increasing Ang1-7, which counteracts AngII activity via the Mas receptor. However, ACE2 also converts AngI to Ang1-9, a poorly characterised peptide which can be further converted to Ang1-7 via ACE. Ang1-9 stimulates bradykinin release in endothelium and has antihypertrophic actions in the heart, attributed to its being a competitive inhibitor of ACE, leading to decreased AngII, rather than increased Ang1-7. To date no direct receptor-mediated effects of Ang1-9 have been described. To further understand the role of Ang1-9 in RAS function we assessed its action in cardiomyocyte hypertrophy in rat neonatal H9c2 and primary adult rabbit left ventricular cardiomyocytes, compared to Ang1-7. Cardiomyocyte hypertrophy was stimulated with AngII or vasopressin, significantly increasing cell size by approximately 1.2-fold (P < 0.05) as well as stimulating expression of the hypertrophy gene markers atrial natriuretic peptide, brain natriuretic peptide, β-myosin heavy chain and myosin light chain (2- to 5-fold, P < 0.05). Both Ang1-9 and Ang1-7 were able to block hypertrophy induced by either agonist (control, 186.4 μm; AngII, 232.8 μm; AngII+Ang1-7, 198.3 μm; AngII+Ang1-9, 195.9 μm; P < 0.05). The effects of Ang1-9 were not inhibited by captopril, supporting previous evidence that Ang1-9 acts independently of Ang1-7. Next, we investigated receptor signalling via angiotensin type 1 and type 2 receptors (AT1R, AT2R) and Mas. The AT1R antagonist losartan blocked AngII-induced, but not vasopressin-induced, hypertrophy. Losartan did not block the antihypertrophic effects of Ang1-9, or Ang1-7 on vasopressin-stimulated cardiomyocytes. The Mas antagonist A779 efficiently blocked the antihypertrophic effects of Ang1-7, without affecting Ang1-9. Furthermore, Ang1-7 activity was also inhibited in the presence of the bradykinin type 2 receptor antagonist HOE140, without affecting Ang1-9. Moreover, we observed that the AT2R antagonist PD123,319 abolished the antihypertrophic effects of Ang1-9, without affecting Ang1-7, suggesting Ang1-9 signals via the AT2R. Radioligand binding assays demonstrated that Ang1-9 was able to bind the AT2R (pKi = 6.28 ± 0.1). In summary, we ascribe a direct biological role for Ang1-9 acting via the AT2R. This has implications for RAS function and identifying new therapeutic targets in cardiovascular disease.

ERK is integral to the IFN-γ-mediated activation of STAT1, the expression of key genes implicated in atherosclerosis, and the uptake of modified lipoproteins by human macrophages

The proinflammatory cytokine IFN-gamma is a master regulator of atherosclerosis and mediates its cellular actions mainly through STAT1. Unfortunately, the impact of other IFN-gamma inducible pathways on STAT1 activation and the regulation of downstream responses associated with atherosclerosis in human macrophages are poorly understood and were therefore investigated. In this study, we demonstrate that the IFN-gamma-mediated phosphorylation of STAT1 on Ser(727), crucial for its maximal activity, was attenuated in human macrophages by pharmacological inhibition of ERK. In these cells, IFN-gamma induced changes in the expression of several key genes implicated in atherosclerosis, such as MCP-1, through an ERK-dependent mechanism. Additionally, the IFN-gamma-induced activity of STAT1-responsive promoters was attenuated by transfection of dominant-negative forms of ERK and other key components of this pathway. Furthermore, the IFN-gamma-induced uptake of acetylated and oxidized low-density lipoprotein by human macrophages was attenuated by pharmacological inhibition or RNA interference-mediated knockdown of ERK. These studies suggest a critical role for ERK signaling in the IFN-gamma-mediated changes in macrophage cholesterol homeostasis and gene expression during atherosclerosis.

Alterations of cardiac ERK1/2 expression and activity due to volume overload were attenuated by the blockade of RAS

The activities and protein content of extracellular signal-regulated kinase (ERK)1/2 in the heart were measured in rats at 4 and 16 weeks after volume overload due to aortocaval shunt. Protein content of phosphorylated ERK1/2 was increased at both 4 and 16 weeks, whereas protein content of total ERK1/2 was increased only at 16 weeks of inducing volume overload. The ERK1/2 activities, estimated as phospho-Elk-1 content, were also increased at 4 and 16 weeks of inducing volume overload. The increased phosphorylated ERK1/2 and E-26-like (Elk)-1 protein content in 16 weeks failing hearts was much greater than that in 4 weeks hypertrophied hearts. These changes in phosphorylated ERK1/2 and Elk-1 protein content in both 4 and 16 weeks volume overloaded animals were attenuated by treatment with enalapril and/or losartan. The results indicate that activation of ERK1/2 may be involved in the development of cardiac hypertrophy and heart failure due to volume overload, and these changes are partially prevented by blockade of the renin-angiotensin system (RAS).

Inhibition of the renin-angiotensin system and target organ protection

The renin-angiotensin system (RAS) is involved in the pathological mechanisms of target organ damage, as well as in the induction of hypertension. RAS inhibition by angiotensin converting enzyme (ACE) inhibitors and angiotensin (Ang) II receptor blockers can prevent tissue damage by inhibition of Ang II type 1 receptor signaling. A beneficial effect of RAS inhibition on the heart, vasculature and kidney in cardiovascular disease has been reported. However, RAS inhibition can also prevent fibroproliferative diseases and damage of other tissues, such as brain, adipose tissue and muscle, because local RAS has an important role in tissue damage compared with circulating RAS. Moreover, other players, such as Ang II type 2 receptor signaling, aldosterone and ACE2 have been highlighted. Furthermore, there has also been a focus on the emerging concept of regulation of RAS, such as receptor-interacting proteins and receptor modifications, in the new discovery of therapeutic agents for tissue protection. The RAS has a pivotal role in various target organ damage, with complicated mechanisms; therefore, blockade of RAS may be therapeutically effective in preventing organ damage, as well as in having an antihypertensive effect.

Olmesartan improves left ventricular function in pressure-overload hypertrophied rat heart by blocking angiotensin II receptor with synergic effects of upregulation of angiotensin converting enzyme 2

It is not clear how the blocking effect of angiotensin II receptors by olmesartan affects the functional recovery of pressure-overload hypertrophied heart. Hypertrophied heart was created by abdominal aortic banding above the celiac artery in Wistar rats at the age of eight weeks. Hypertrophied heart was excised and studied at 10 and 16 weeks after the operation (HT groups). For the last four weeks before the experiment, olmesartan (0.2 mg/kg per day) was administered subcutaneously by osmotic minipumps (Olm groups). Left ventricular function was measured by Langendorff perfusion. The levels of mRNA for angiotensin-converting enzyme (ACE), ACE2 and extracellular signal-regulated kinases (ERKs) in myocardium were analyzed by RT-PCR. Left ventricular systolic (+d P/dtmax, left ventricular systolic pressure) and diastolic functions (-d P/dtmax, tau) were impaired in HT groups, while in Olm groups they were significantly improved. The left ventricle to body weight (LV/BW) ratio increased significantly in HT groups, but in Olm groups the LV/BW ratio decreased significantly in comparison with HT groups. The ACE2 mRNA level was significantly higher in Olm groups as compared with HT groups. Plasma angiotensin II and the ERK mRNA level in HT groups increased significantly, but decreased in Olm groups in comparison with HT groups significantly. Olmesartan improved left ventricular function and hypertrophy through the increase of the ACE2 mRNA and decrease of both angiotensin II and ERK mRNA in pressure-overload rat heart.

Role of oxidative stress in pancreatic inflammation

Reactive oxygen and reactive nitrogen species (ROS/RNS) have been implicated in the pathogenesis of acute and chronic pancreatitis. Clinical and basic science studies have indicated that ROS/RNS formation processes are intimately linked to the development of the inflammatory disorders. The detrimental effects of highly reactive ROS/RNS are mediated by their direct actions on biomolecules (lipids, proteins, and nucleic acids) and activation of proinflammatory signal cascades, which subsequently lead to activation of immune responses. The present article summarizes the possible sources of ROS/RNS formation and the detailed signaling cascades implicated in the pathogenesis of pancreatic inflammation, as observed in acute and chronic pancreatitis. A therapeutic ROS/RNS-scavenging strategy has been advocated for decades; however, clinical studies examining such approaches have been inconsistent in their results. Emerging evidence indicates that pancreatitis-inducing ROS/RNS generation may be attenuated by targeting ROS/RNS-generating enzymes and upstream mediators.

Chronic inhibition of the Na+/H+ - exchanger causes regression of hypertrophy, heart failure, and ionic and electrophysiological remodelling

BACKGROUND AND PURPOSE

Increased activity of the Na+/H+ -exchanger (NHE-1) in heart failure underlies raised [Na+]i causing disturbances of calcium handling. Inhibition of NHE-1, initiated at the onset of pressure/volume overload, prevents development of hypertrophy, heart failure and remodelling. We hypothesized that chronic inhibition of NHE-1, initiated at a later stage, would induce regression of hypertrophy, heart failure, and ionic and electrophysiological remodelling.

EXPERIMENTAL APPROACH

Development of heart failure in rabbits was monitored electrocardiographically and echocardiographically, after one or three months. Cardiac myocytes were also isolated. One group of animals were treated with cariporide (inhibitor of NHE-1) in the diet after one month. Cytoplasmic calcium, sodium and action potentials were measured with fluorescent markers and sarcoplasmic reticulum calcium content by rapid cooling. Calcium after-transients were elicited after rapid pacing. Sodium channel current (INa) was measured using patch-clamp techniques.

KEY RESULTS

Hypertrophy and heart failure developed after one month and progressed during the next two months. After one month, dietary treatment with cariporide was initiated. Two months of treatment reduced hypertrophy and heart failure, duration of action potential QT-interval and QRS, and restored sodium and calcium handling and the incidence of calcium after-transients. In cardiac myocytes, parameters of INa were not changed by cariporide.

CONCLUSION AND IMPLICATIONS

In rabbit hearts with hypertrophy and signs of heart failure one month after induction of pressure/volume overload, two months of dietary treatment with the NHE-1 inhibitor cariporide caused regression of hypertrophy, heart failure and ionic and electrophysiological remodelling.

Roles of the Raf/MEK/ERK pathway in cell growth, malignant transformation and drug resistance

Growth factors and mitogens use the Ras/Raf/MEK/ERK signaling cascade to transmit signals from their receptors to regulate gene expression and prevent apoptosis. Some components of these pathways are mutated or aberrantly expressed in human cancer (e.g., Ras, B-Raf). Mutations also occur at genes encoding upstream receptors (e.g., EGFR and Flt-3) and chimeric chromosomal translocations (e.g., BCR-ABL) which transmit their signals through these cascades. Even in the absence of obvious genetic mutations, this pathway has been reported to be activated in over 50% of acute myelogenous leukemia and acute lymphocytic leukemia and is also frequently activated in other cancer types (e.g., breast and prostate cancers). Importantly, this increased expression is associated with a poor prognosis. The Ras/Raf/MEK/ERK and Ras/PI3K/PTEN/Akt pathways interact with each other to regulate growth and in some cases tumorigenesis. For example, in some cells, PTEN mutation may contribute to suppression of the Raf/MEK/ERK cascade due to the ability of activated Akt to phosphorylate and inactivate different Rafs. Although both of these pathways are commonly thought to have anti-apoptotic and drug resistance effects on cells, they display different cell lineage specific effects. For example, Raf/MEK/ERK is usually associated with proliferation and drug resistance of hematopoietic cells, while activation of the Raf/MEK/ERK cascade is suppressed in some prostate cancer cell lines which have mutations at PTEN and express high levels of activated Akt. Furthermore the Ras/Raf/MEK/ERK and Ras/PI3K/PTEN/Akt pathways also interact with the p53 pathway. Some of these interactions can result in controlling the activity and subcellular localization of Bim, Bak, Bax, Puma and Noxa. Raf/MEK/ERK may promote cell cycle arrest in prostate cells and this may be regulated by p53 as restoration of wild-type p53 in p53 deficient prostate cancer cells results in their enhanced sensitivity to chemotherapeutic drugs and increased expression of Raf/MEK/ERK pathway. Thus in advanced prostate cancer, it may be advantageous to induce Raf/MEK/ERK expression to promote cell cycle arrest, while in hematopoietic cancers it may be beneficial to inhibit Raf/MEK/ERK induced proliferation and drug resistance. Thus the Raf/MEK/ERK pathway has different effects on growth, prevention of apoptosis, cell cycle arrest and induction of drug resistance in cells of various lineages which may be due to the presence of functional p53 and PTEN and the expression of lineage specific factors.

[Insulin and angiotensin II signaling pathways cross-talk: implications with the association between diabetes mellitus, arterial hypertension and cardiovascular disease]

Insulin (Ins) and angiotensin II (AII) play pivotal roles in the control of two vital and closely related systems: the metabolic and the circulatory, respectively. A failure in the proper action of each of these hormones results, to a variable degree, in the development of two highly prevalent and commonly overlapping diseases--diabetes mellitus (DM) and hypertension (AH). In recent years, a series of studies has revealed a tight connection between the signal transduction pathways that mediate Ins and AII actions in target tissues. This molecular cross-talk occurs at multiple levels and plays an important role in phenomena that range from the action of anti-hypertensive drugs to cardiac hypertrophy and energy acquisition by the heart. At the extracellular level, the angiotensin-converting enzyme controls AII synthesis but also interferes with Ins signaling through the proper regulation of AII and the accumulation of bradykinin. At an early intracellular level, AII, acting through JAK-2/IRS-1/PI3-kinase, JNK and ERK, may induce the serine phosphorylation and inhibition of key elements of the Ins-signaling pathway. Finally, by inducing the expression of the regulatory protein SOCS-3, AII may impose a late control on the Ins signal. This review will focus on the main advances obtained in this field and will discuss the implications of this molecular cross-talk in the common clinical association between DM and AH.

Ras triggers acidosis-induced activation of the extracellular-signal-regulated kinase pathway in cardiac myocytes

In cardiac myocytes, sustained (3 min) intracellular acidosis activates the ERK1/2 (extracellular-signal-regulated kinase 1/2) pathway and, through this pathway, increases sarcolemmal NHE (Na+/H+ exchanger) activity [Haworth, McCann, Snabaitis, Roberts and Avkiran (2003) J. Biol. Chem. 278, 31676-31684]. In the present study, we aimed to determine the time-dependence, pH-dependence and upstream signalling mechanisms of acidosis-induced ERK1/2 activation in ARVM (adult rat ventricular myocytes). Cultured ARVM were subjected to intracellular acidosis for up to 20 min by exposure to NH4Cl, followed by washout with a bicarbonate-free Tyrode solution containing the NHE1 inhibitor cariporide. After the desired duration of intracellular acidosis, the phosphorylation status of ERK1/2 and its downstream effector p90(RSK) (90 kDa ribosomal S6 kinase) were determined by Western blotting. This revealed a time-dependent transient phosphorylation of both ERK1/2 and p90(RSK) by intracellular acidosis (intracellular pH approximately 6.6), with maximum activation occurring at 3 min and a return to basal levels by 20 min. When the degree of intracellular acidosis was varied from approximately 6.8 to approximately 6.5, maximum ERK1/2 phosphorylation was observed at an intracellular pH of 6.64. Inhibition of MEK1/2 [MAPK (mitogen-activated protein kinase)/ERK kinase 1/2) by pre-treatment of ARVM with U0126 or adenoviral expression of dominant-negative D208A-MEK1 protein prevented the phosphorylation of ERK1/2 by sustained intracellular acidosis, as did inhibition of Raf-1 with GW 5074 or ZM 336372. Interference with Ras signalling by the adenoviral expression of dominant-negative N17-Ras protein or with FPT III (farnesyl protein transferase inhibitor III) also prevented acidosis-induced ERK1/2 phosphorylation, whereas inhibiting G-protein signalling [by adenoviral expression of RGS4 or Lsc, the RGS domain of p115 RhoGEF (guanine nucleotide-exchange factor)] or protein kinase C (with bisindolylmaleimide I) had no effect. Our data show that, in ARVM, sustained intracellular acidosis activates ERK1/2 through proximal activation of the classical Ras/Raf/MEK pathway.

Heme oxygenase-1 gene transfer inhibits angiotensin II-mediated rat cardiac myocyte apoptosis but not hypertrophy

Cardiac myocyte apoptosis underlies the pathophysiology of cardiomyopathy, and plays a critical role in the transition from myocardial hypertrophy to heart failure. Angiotensin II (Ang II) induces cardiac myocyte apoptosis and hypertrophy which contribute to heart failure possibly through enhanced oxidative stress; however, the mechanisms underlying the activation of both pathways and their interactions remain unclear. In the present study, we have investigated whether overexpression of the antioxidant protein heme oxygenase-1 (HO-1) protects against apoptosis and hypertrophy in cultured rat cardiac myocytes treated with Ang II. Our findings demonstrate that Ang II (100 nM, 24 h) alone upregulates HO-1 expression and induces both myocyte hypertrophy and apoptosis, assessed by measuring terminal deoxynucleotidyltransferase dUTP nick-end labelling (TUNEL) staining, caspase-3 activity and mitochondrial membrane potential. Ang II elicited apoptosis was augmented in the presence of tin protoporphyrin, an inhibitor of HO activity, while HO-1 gene transfer to myocytes attenuated Ang II-mediated apoptosis but not hypertrophy. Adenoviral overexpression of HO-1 was accompanied by a significant increase in Ang II induced phosphorylation of Akt, however, Ang II-mediated p38 mitogen activated protein kinase (MAPK) phosphorylation was attenuated. Inhibition of phosphotidylinositol-3-kinase enhanced myocyte apoptosis elicited by Ang II, however, p38MAPK inhibition had no effect, suggesting that overexpression of HO-1 protects myocytes via augmented Akt activation and not through modulation of p38MAPK activation. Our findings identify the signalling pathways by which HO-1 gene transfer protects against apoptosis and suggest that overexpression of HO-1 in cardiomyopathies may delay the transition from myocyte hypertrophy to heart failure.

Role of Ras in ethanol modulation of angiotensin II activated p42/p44 MAP kinase in rat hepatocytes

Angiotensin II plays a role in both liver cell proliferation and liver injury but the effects of ethanol on angiotensin II signaling in liver are not clearly understood. We have investigated the role of Ras in ethanol modulation of p42/p44 mitogen-activated protein kinase (MAPK) stimulated by angiotensin II (Ang II) in primary cultures of rat hepatocytes. Hepatocytes were incubated with ethanol (100 mM) for 24 h, then stimulated with Ang II (100 nM). The level of p42/p44 MAPK phosphorylation was measured by Western blot analysis and Ras activation was assessed by specific binding of Ras-GTP (activated form) to a GST-RBD fusion protein containing Ras-binding domain (RBD) of Raf-1. Ethanol potentiated p42/p44 MAPK activation by Ang II, whereas ethanol alone did not significantly affect phosphorylation of p42/p44 MAPK. Ang II increased Ras activity by about 2 fold. Ethanol exposure increased Ang II stimulated Ras activity by an additional about 2 fold. Ethanol alone elicited a small increase in basal Ras activity. Pretreatment with manumycin A (10 microM), a Ras farnesylation inhibitor, partially blocked both Ang II-activated and ethanol-potentiated MAPK activities. These data provided the first evidence that ethanol potentiation of Ang II stimulated p42/p44 MAPK is mediated, in part, by Ras in hepatocytes.

Reactive oxygen species-induced activation of the MAP kinase signaling pathways

An abundance of scientific literature exists demonstrating that oxidative stress influences the MAPK signaling pathways. This review summarizes these findings for the ERK, JNK, p38, and BMK1 pathways. For each of these different MAPK signaling pathways, the following is reviewed: the proteins involved in the signaling pathways, how oxidative stress can activate cellular signaling via these pathways, the types of oxidative stress that are known to induce activation of the different pathways, and the specific cell types in which oxidants induce MAPK responses. In addition, the functional outcome of oxidative stress-induced activation of these pathways is discussed. The purpose of this review is to provide the reader with an overall understanding and appreciation of oxidative stress-induced MAPK signaling.

Constitutively active alpha subunits of G(q/11) and G(12/13) families inhibit activation of the pro-survival Akt signaling cascade

Accumulating evidence indicates that G protein signaling plays an active role in the regulation of cell survival. Our previous study demonstrated the regulatory effects of G(i/o) proteins in nerve growth factor-induced activation of pro-survival Akt kinase. In the present study we explored the role of various members of the G(s), G(q/11) and G(12/13) subfamilies in the regulation of Akt in cultured mammalian cells. In human embryonic kidney 293 cells transiently expressing constitutively active mutants of G alpha11, G alpha14, G alpha16, G alpha12, or G alpha13 (G alpha11QL, G alpha14QL, G alpha16QL, G alpha12QL and G alpha13QL, respectively), basal phosphorylation of Akt was attenuated, as revealed by western blotting analysis using a phosphospecific anti-Akt immunoglobulin. In contrast, basal Akt phosphorylation was unaffected by the overexpression of a constitutively active G alpha(s) mutant (G alpha(s)QL). Additional experiments showed that G alpha11QL, G alpha14QL, G alpha16QL, G alpha12QL and G alpha13QL, but not G alpha(s)QL, attenuated phosphorylation of the Akt-regulated translation regulator tuberin. Moreover, they were able to inhibit the epidermal growth factor-induced Akt activation and tuberin phosphorylation. The inhibitory mechanism of Gq family members was independent of phospholipase Cbeta activation and calcium signaling because G alpha11QL, G alpha14QL and G alpha16QL remained capable of inhibiting epidermal growth factor-induced Akt activation in cells pretreated with U73122 and the intracellular calcium chelator, BAPTA/AM. Finally, overexpression of the dominant negative mutant of RhoA blocked G alpha12QL- and G alpha13QL-mediated inhibition, suggesting that activated G alpha12 and G alpha13 inhibit Akt signaling via RhoA. Collectively, this study demonstrated the inhibitory effect of activated G alpha11, G alpha14, G alpha16, G alpha12 and G alpha13 on pro-survival Akt signaling.

FGF-2 protects small cell lung cancer cells from apoptosis through a complex involving PKCepsilon, B-Raf and S6K2

Patients with small cell lung cancer (SCLC) die because of chemoresistance. Fibroblast growth factor-2 (FGF-2) increases the expression of antiapoptotic proteins, XIAP and Bcl-X(L), and triggers chemoresistance in SCLC cells. Here we show that these effects are mediated through the formation of a specific multiprotein complex comprising B-Raf, PKCepsilon and S6K2. S6K1, Raf-1 and other PKC isoforms do not form similar complexes. RNAi-mediated downregulation of B-Raf, PKCepsilon or S6K2 abolishes FGF-2-mediated survival. In contrast, overexpression of PKCepsilon increases XIAP and Bcl-X(L) levels and chemoresistance in SCLC cells. In a tetracycline-inducible system, increased S6K2 kinase activity triggers upregulation of XIAP, Bcl-X(L) and prosurvival effects. However, increased S6K1 kinase activity has no such effect. Thus, S6K2 but not S6K1 mediates prosurvival/chemoresistance signalling.

The multi-faceted cross-talk between the insulin and angiotensin II signaling systems

Insulin and angiotensin II are hormones that play pivotal roles in the control of two vital and closely related systems, the metabolic and the circulatory systems, respectively. A failure in the proper action of each of these hormones results, to a variable degree, in the development of two highly prevalent and commonly overlapping diseases-diabetes mellitus and hypertension. In recent years, a series of studies has revealed a tight connection between the signal transduction pathways that mediate insulin and angiotensin II actions in target tissues. This molecular cross-talk occurs at multiple levels and plays an important role in phenomena that range from the action of anti-hypertensive drugs to cardiac hypertrophy and energy acquisition by the heart. At the extracellular level, the angiotensin-converting enzyme controls angiotensin II synthesis but also interferes with insulin signaling through the proper regulation of angiotensin II and through the accumulation of bradykinin. At an early intracellular level, angiotensin II, acting through JAK-2/IRS-1/PI3-kinase, JNK and ERK, may induce the serine phosphorylation and inhibition of key elements of the insulin-signaling pathway. Finally, by inducing the expression of the regulatory protein SOCS-3, angiotensin II may impose a late control on the insulin signal. This review will focus on the main advances obtained in this field and will discuss the implications of this molecular cross-talk in the common clinical association between diabetes mellitus and hypertension.

Deletion of angiotensin-converting enzyme 2 accelerates pressure overload-induced cardiac dysfunction by increasing local angiotensin II

Angiotensin-converting enzyme 2 (ACE2) is a carboxypeptidase that cleaves angiotensin II to angiotensin 1-7. Recently, it was reported that mice lacking ACE2 (ACE2(-/y) mice) exhibited reduced cardiac contractility. Because mechanical pressure overload activates the cardiac renin-angiotensin system, we used ACE2(-/y) mice to analyze the role of ACE2 in the response to pressure overload. Twelve-week-old ACE2(-/y) mice and wild-type (WT) mice received transverse aortic constriction (TAC) or sham operation. Sham-operated ACE2(-/y) mice exhibited normal cardiac function and had morphologically normal hearts. In response to TAC, ACE2(-/y) mice developed cardiac hypertrophy and dilatation. Furthermore, their hearts displayed decreased cardiac contractility and increased fetal cardiac gene induction, compared with WT mice. In response to chronic pressure overload, ACE2(-/y) mice developed pulmonary congestion and increased incidence of cardiac death compared with WT mice. On a biochemical level, cardiac angiotensin II concentration and activity of mitogen-activated protein (MAP) kinases were markedly increased in ACE2(-/y) mice in response to TAC. Administration of candesartan, an AT1 subtype angiotensin receptor blocker, attenuated the hypertrophic response and suppressed the activation of MAP kinases in ACE2(-/y) mice. Activation of MAP kinases in response to angiotensin II was greater in cardiomyocytes isolated from ACE2(-/y) mice than in those isolated from WT mice. ACE2 plays an important role in dampening the hypertrophic response to pressure overload mediated by angiotensin II. Disruption of this regulatory function may accelerate cardiac hypertrophy and shorten the transition period from compensated hypertrophy to cardiac failure.