Cellular stresses differentially activate c-Jun N-terminal protein kinases and extracellular signal-regulated protein kinases in cultured ventricular myocytes

Reversible covalent c-Jun N-terminal kinase inhibitors targeting a specific cysteine by precision-guided Michael-acceptor warheads

There has been a surge of interest in covalent inhibitors for protein kinases in recent years. Despite success in oncology, the off-target reactivity of these molecules is still hampering the use of covalent warhead-based strategies. Herein, we disclose the development of precision-guided warheads to mitigate the off-target challenge. These reversible warheads have a complex and cyclic structure with optional chirality center and tailored steric and electronic properties. To validate our proof-of-concept, we modified acrylamide-based covalent inhibitors of c-Jun N-terminal kinases (JNKs). We show that the cyclic warheads have high resilience against off-target thiols. Additionally, the binding affinity, residence time, and even JNK isoform specificity can be fine-tuned by adjusting the substitution pattern or using divergent and orthogonal synthetic elaboration of the warhead. Taken together, the cyclic warheads presented in this study will be a useful tool for medicinal chemists for the deliberate design of safer and functionally fine-tuned covalent inhibitors.

The endocrinological component and signaling pathways associated to cardiac hypertrophy

Although myocardial growth corresponds to an adaptive response to maintain cardiac contractile function, the cardiac hypertrophy is a condition that occurs in many cardiovascular diseases and typically precedes the onset of heart failure. Different endocrine factors such as thyroid hormones, insulin, insulin-like growth factor 1 (IGF-1), angiotensin II (Ang II), endothelin (ET-1), catecholamines, estrogen, among others represent important stimuli to cardiomyocyte hypertrophy. Thus, numerous endocrine disorders manifested as changes in the local environment or multiple organ systems are especially important in the context of progression from cardiac hypertrophy to heart failure. Based on that information, this review summarizes experimental findings regarding the influence of such hormones upon signalling pathways associated with cardiac hypertrophy. Understanding mechanisms through which hormones differentially regulate cardiac hypertrophy could open ways to obtain therapeutic approaches that contribute to prevent or delay the onset of heart failure related to endocrine diseases.

JNK signaling pathway regulates sorbitol-induced Tau proteolysis and apoptosis in SH-SY5Y cells by targeting caspase-3

Growing evidence suggests that Diabetes Mellitus increases the risk of developing Alzheimer's disease. It is well known that hyperglycemia, a key feature of Diabetes Mellitus, may induce plasma osmolarity disturbances. Both hyperglycemia and hyperosmolarity promote the altered post-translational regulation of microtubule-associated protein Tau. Interestingly, abnormal hyperphosphorylation and cleavage of Tau have been proven to lead to the genesis of filamentous structures referred to as neurofibrillary tangles, the main pathological hallmark of Alzheimer's disease. We have previously described that hyperosmotic stress induced by sorbitol promotes Tau proteolysis and apoptosis in SH-SY5Y cells via caspase-3 activation. In order to gain insights into the regulatory mechanisms of such processes, in this work we explored the intracellular signaling pathways that regulate these events. We found that sorbitol treatment significantly enhanced the activation of conventional families of MAPK in SH-SY5Y cells. Tau proteolysis was completely prevented by JNK inhibition but not affected by either ERK1/2 or p38 MAPK blockade. Moreover, inhibition of JNK, but not ERK1/2 or p38 MAPK, efficiently prevented sorbitol-induced apoptosis and caspase-3 activation. In summary, we provide evidence that JNK signaling pathway is an upstream regulator of hyperosmotic stress-induced Tau cleavage and apoptosis in SH-SY5Y through the control of caspase-3 activation.

c-Jun N-terminal kinase activity is required for efficient respiratory syncytial virus production

Respiratory syncytial virus (RSV) is a major cause of respiratory infections in infants and the elderly, leading to more deaths than influenza each year worldwide. With no RSV antiviral or efficacious vaccine currently available, improved understanding of the host-RSV interaction is urgently required. Here we examine the contribution to RSV infection of the host stress-regulated c-Jun N-terminal kinase (JNK), for the first time. Peak JNK1/2 phosphoactivation is observed at ∼24 h post-infection, correlating with the time of virus assembly. The release of infectious RSV virions from infected cells was significantly reduced by either JNK1/2 siRNA knockdown or treatment with the JNK-specific inhibitor, JNK-IN-VIII. High resolution microscopy confirmed RSV accumulation in the host cell cytoplasm. The results implicate JNK1/2 as a key host factor for RSV virus production, raising the possibility of agents targeting JNK activity as potential anti-RSV therapeutics.

Crosstalk between mitogen-activated protein kinases and mitochondria in cardiac diseases: therapeutic perspectives

Cardiovascular diseases cause more mortality and morbidity worldwide than any other diseases. Although many intracellular signaling pathways influence cardiac physiology and pathology, the mitogen-activated protein kinase (MAPK) family has garnered significant attention because of its vast implications in signaling and crosstalk with other signaling networks. The extensively studied MAPKs ERK1/2, p38, JNK, and ERK5, demonstrate unique intracellular signaling mechanisms, responding to a myriad of mitogens and stressors and influencing the signaling of cardiac development, metabolism, performance, and pathogenesis. Definitive relationships between MAPK signaling and cardiac dysfunction remain elusive, despite 30 years of extensive clinical studies and basic research of various animal/cell models, severities of stress, and types of stimuli. Still, several studies have proven the importance of MAPK crosstalk with mitochondria, powerhouses of the cell that provide over 80% of ATP for normal cardiomyocyte function and play a crucial role in cell death. Although many questions remain unanswered, there exists enough evidence to consider the possibility of targeting MAPK-mitochondria interactions in the prevention and treatment of heart disease. The goal of this review is to integrate previous studies into a discussion of MAPKs and MAPK-mitochondria signaling in cardiac diseases, such as myocardial infarction (ischemia), hypertrophy and heart failure. A comprehensive understanding of relevant molecular mechanisms, as well as challenges for studies in this area, will facilitate the development of new pharmacological agents and genetic manipulations for therapy of cardiovascular diseases.

Endothelin-1-dependent signaling pathways in the myocardium

Endothelin-1 (ET-1) is a locally acting vasoactive peptide that also has profound effects on the contractile properties and growth of the cardiac myocyte. Binding of ET-1 to its transmembrane heptahelical receptors activates G proteins of the G(q) and G(i) classes. Activation of G(q) stimulates hydrolysis of phosphatidylinositol-4,5-bisphosphate, and the diacylglycerol thus formed stimulates protein kinase C. Subsequently, the protein kinase Raf is activated and this leads to activation of the extracellular signal-regulated protein kinase (ERK) subfamily of mitogen-activated protein kinases. Activation of G(i) counteracts β-adrenoceptor-mediated increases in cAMP concentrations. We have attempted to rationalize the established physiological consequences of ET-1 agonism in the cardiac myocyte (that is, on contraction and growth) in terms of activation of these signaling pathways.

Adenovirus-mediated overexpression of cardiac troponin I-interacting kinase promotes cardiomyocyte hypertrophy

1. Cardiac troponin I-interacting kinase (TNNI3K) is a novel cardiac-specific kinase gene. Quantitative real-time reverse transcription polymerase chain reaction analysis showed a significant increase in TNNI3K mRNA expression in hypertrophic cardiomyocytes induced by endothelin-1 (ET-1). The aim of the present study was to investigate the effects of TNNI3K on neonate rat cardiomyocyte hypertrophy induced by ET-1. 2. Adenoviruses were amplified in 293A cells. To determine a reasonable adenovirus infection dose cardiomyocytes were infected with an adenovirus carrying human TNNI3K (Ad-TNNI3K) at varying multiplicity of infection (MOI) and the expression of TNNI3K was analysed by western blot. 3. Cardiomyocytes were infected with either a control adenovirus carrying green fluorescent protein (Ad-GFP) or Ad-TNNI3K. Compared with Ad-GFP, the Ad-TNNI3K induced an increase in sarcomere organization, cell surface area, (3) H-leucine incorporation and β-MHC re-expression. This type of hypertrophic phenomenon is similar to that observed in Ad-GFP-infected hypertrophic cardiomyocytes induced by ET-1. To determine the functional role of TNNI3K in ET-1-induced hypertrophic cardiomyocytes, the cells were infected with Ad-GFP or Ad-TNNI3K. Ad-TNNI3K induced an increase in sarcomere organization, cell surface area and (3) H-leucine incorporation compared with Ad-GFP. 4. These results suggest that TNNI3K overexpression induces cardiomyocytes hypertrophy and accelerates hypertrophy in hypertrophic cardiomyocytes. Therefore, TNNI3K might be an interesting target for the clinical treatment of hypertrophy.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Monophosphothreonyl extracellular signal-regulated kinases 1 and 2 (ERK1/2) are formed endogenously in intact cardiac myocytes and are enzymically active

ERK1 and ERK2 (ERK1/2) are central to the regulation of cell division, growth and survival. They are activated by phosphorylation of the Thr- and the Tyr- residues in their Thr-Glu-Tyr activation loops. The dogma is that dually-phosphorylated ERK1/2 constitute the principal activities in intact cells. We previously showed that, in neonatal rat cardiac myocytes, endothelin-1 and phorbol 12-myristate 13-acetate (PMA) powerfully and rapidly (maximal at ~ 5 min) activate ERK1/2. Here, we show that dually-phosphorylated ERK1/2 rapidly (< 2 min) appear in the nucleus following stimulation with endothelin-1. We characterized the active ERK1/2 species in myocytes exposed to endothelin-1 or PMA using MonoQ FPLC. Unexpectedly, two peaks of ERK1 and two peaks of ERK2 activity were resolved using in vitro kinase assays. One of each of these represented the dually-phosphorylated species. The other two represented activities for ERK1 or ERK2 which were phosphorylated solely on the Thr- residue. Monophosphothreonyl ERK1/2 represented maximally ~ 30% of total ERK1/2 activity after stimulation with endothelin-1 or PMA, and their k_cat values were estimated to be minimally ~ 30% of the dually-phosphorylated species. Appearance of monophosphothreonyl ERK1/2 was rapid but delayed in comparison with dually-phosphorylated ERK1/2. Of 10 agonists studied, endothelin-1 and PMA were most effective in terms of ERK1/2 activation and in stimulating the appearance of monophosphothreonyl and dually-phosphorylated ERK1/2. Thus, enzymically active monophosphothreonyl ERK1/2 are formed endogenously following activation of the ERK1/2 cascade and we suggest that monophosphothreonyl ERK1/2 arise by protein tyrosine phosphatase-mediated dephosphorylation of dually-phosphorylated ERK1/2.

ERK1/2 signaling dominates over RhoA signaling in regulating early changes in RNA expression induced by endothelin-1 in neonatal rat cardiomyocytes

Background

Cardiomyocyte hypertrophy is associated with changes in gene expression. Extracellular signal-regulated kinases 1/2 (ERK1/2) and RhoA [activated by hypertrophic agonists (e.g. endothelin-1)] regulate gene expression and are implicated in the response, but their relative significance in regulating the cardiomyocyte transcriptome is unknown. Our aim was to establish the significance of ERK1/2 and/or RhoA in the early cardiomyocyte transcriptomic response to endothelin-1.

Methods/Principal Findings

Cardiomyocytes were exposed to endothelin-1 (1 h) with/without PD184352 (to inhibit ERK1/2) or C3 transferase (C3T, to inhibit RhoA). RNA expression was analyzed using microarrays and qPCR. ERK1/2 signaling positively regulated ∼65% of the early gene expression response to ET-1 with a small (∼2%) negative effect, whereas RhoA signaling positively regulated ∼10% of the early gene expression response to ET-1 with a greater (∼14%) negative contribution. Of RNAs non-responsive to endothelin-1, 66 or 448 were regulated by PD184352 or C3T, respectively, indicating that RhoA had a more significant effect on baseline RNA expression. mRNAs upregulated by endothelin-1 encoded a number of receptor ligands (e.g. Ereg, Areg, Hbegf) and transcription factors (e.g. Abra/Srf) that potentially propagate the response.

Conclusions/Significance

ERK1/2 dominates over RhoA in the early transcriptomic response to endothelin-1. RhoA plays a major role in maintaining baseline RNA expression but, with upregulation of Abra/Srf by endothelin-1, RhoA may regulate changes in RNA expression over longer times. Our data identify ERK1/2 as a more significant node than RhoA in regulating the early stages of cardiomyocyte hypertrophy.

Modulation of interleukin signalling and gene expression in cardiac myocytes by endothelin-1

The related inflammatory cytokines, interleukin- (IL-) 1beta and IL-33, are both implicated in the response of the heart to injury. They also activate mitogen-activated protein kinases (MAPKs) in cardiac myocytes. The hypertrophic Gq protein-coupled receptor agonist endothelin-1 is a potentially cardioprotective peptide and may modulate the inflammatory response. Endothelin-1 also stimulates (MAPKs) in cardiac myocytes and promotes rapid changes in expression of mRNAs encoding intercellular and intracellular signalling components including receptors for IL-33 (ST2) and phosphoprotein phosphatases. Prior exposure to endothelin-1 may specifically modulate the response to IL-33 and, more globally, influence MAPK activation by different stimuli. Neonatal rat ventricular myocytes were exposed to IL-1beta or IL-33 with or without pre-exposure to endothelin-1 (5h) and MAPK activation assessed. IL-33 activated ERK1/2, JNKs and p38-MAPK, but to a lesser degree than IL-1beta. Endothelin-1 increased expression of soluble IL-33 receptors (sST2 receptors) which may prevent binding of IL-33 to the cell-surface receptors. However, pretreatment with endothelin-1 only inhibited activation of p38-MAPK by IL-33 with no significant influence on ERK1/2 and a small increase in activation of JNKs. Inhibition of p38-MAPK signalling following pretreatment with endothelin-1 was also detected with IL-1beta, H(2)O(2) or tumour necrosis factor alpha (TNFalpha) indicating an effect intrinsic to the signalling pathway. Endothelin-1 pretreatment suppressed the increase in expression of IL-6 mRNA induced by IL-1beta and decreased the duration of expression of TNFalpha mRNA. Coupled with the general decrease in p38-MAPK signalling, we conclude that endothelin-1 attenuates the cardiac myocyte inflammatory response, potentially to confer cardioprotection.

The effect of the JNK inhibitor, JIP peptide, on human T lymphocyte proliferation and cytokine production

Although JNK is a potential target for treating chronic inflammatory diseases, its role in T lymphocyte function remains controversial. To overcome some of the previous limitations in addressing this issue we have used the recently described transactivator of transcription-JNK-interacting protein (TAT-JIP) peptide, a specific inhibitor that was derived from the minimal JNK-binding region of the scaffold protein, JNK-interacting protein 1 (JIP-1), coupled to the short cell-permeable HIV TAT sequence. Pretreatment of purified human T lymphocytes with the TAT-JIP peptide inhibited the phosphorylation of endogenous jun activated by PHA-PMA. This was associated with a corresponding inhibition of lymphoproliferation, and of IL-2, IFN-gamma, lymphotoxin, and IL-10 cytokine production. Similar results were also found using mouse splenic T cells. Examination of the specificity of TAT-JIP revealed that although the peptide was more selective than the pharmacological inhibitor, SP600125, it also inhibited cyclin-dependent kinase 2, p70 ribosomal protein S6 kinase, and serum and glucocorticoid-regulated kinase activity. Nevertheless, these data demonstrate for the first time the ability of the TAT-JIP peptide to inhibit the JNK pathway and the phosphorylation of jun in intact cells, thereby preventing the activation of the transcription factor, AP-1, and the production of Th1 and Th2 cytokines. Thus JNK could potentially be a target for the development of drugs for the treatment of autoimmune inflammatory diseases.

Herpes simplex virus type 1 ICP27 induces p38 mitogen-activated protein kinase signaling and apoptosis in HeLa cells

The herpes simplex virus type 1 (HSV-1) protein ICP27 has been implicated in a variety of functions important for viral replication including host shutoff, viral gene expression, activation of mitogen-activated protein kinases p38 and Jun N-terminal protein kinase (JNK), and apoptosis inhibition. In the present study we sought to examine the functions of ICP27 in the absence of viral infection by creating stable HeLa cell lines that inducibly express ICP27. Here, we characterize two such cell lines and show that ICP27 expression is associated with a cellular growth defect. The observed defect is caused at least in part by the induction of apoptosis as indicated by caspase-3 activation, annexin V staining, and characteristic changes in cellular morphology. In an effort to identify the function of ICP27 responsible for inducing apoptosis, we show that ICP27 expression is sufficient to activate p38 signaling to a level that is similar to that observed during wild-type HSV-1 infection. However, ICP27 expression alone is unable to lead to a strong activation of JNK signaling. Using chemical inhibitors, we show that the ICP27-mediated activation of p38 signaling is responsible for the observed induction of apoptosis in the induced cell lines. Our findings suggest that during viral infection, ICP27 activates p38 and JNK signaling pathways via two distinct mechanisms. ICP27 directly activates p38 signaling, leading to stimulation of the host cell apoptotic pathways. In contrast, robust activation of JNK signaling by ICP27 requires one or more delayed early or late viral gene products and may be associated with the inhibition of apoptosis.

SB203580, a pharmacological inhibitor of p38 MAP kinase transduction pathway activates ERK and JNK MAP kinases in primary cultures of human hepatocytes

Mitogen-activated protein kinases (MAPKs) were extensively studied in cancer-derived cell lines; however, studies in non-transformed human cells are scarce. In the current paper, we studied the effect of SB203580, a pharmacological inhibitor of p38 MAPK, on activation and inhibition of p38 MAPK transduction partway in primary human hepatocytes (in vitro model of differentiated cells) in comparison with several tumor cell lines (proliferating non-differentiated in vitro model). In addition, we analyzed the effect of SB203580 on extracellular-regulated protein kinase (ERK) and c-jun-N-terminal kinase (JNK) pathways both in primary human hepatocytes and tumor cell lines employing primary antibodies detecting phosphorylated kinases. We show that SB203580 activates ERK and JNK in primary cultures of human hepatocytes. The levels of ERK-P(Thr202/Tyr204), JNK-P(Thr183/Tyr185) and c-Jun-P(Ser63/73), a target down-stream protein of JNK, were increased by SB203580. In contrast, SB203580 activated ERK but not JNK in HepG2, HL-60, Saos-2 and HaCaT human cancer cell lines. We tested, whether the effects of SB203580 are due to metabolism. Using liquid chromatography/mass spectrometry, we found one minor metabolite in human liver microsomes but not in HepG2 cells. These data imply that biotransformation could be responsible for the effects of SB203580 in human hepatocytes. This study is the first report on the effects of MAPK activators (sorbitol, anisomycin, EGF) and MAPK inhibitors in primary human hepatocytes. We observed differential effects of these compounds in primary human hepatocytes and in cancer cells, implying the cell-type specificity and the essential differences between the role and function of MAPKs in normal and cancer cells.

Temporal regulation of expression of immediate early and second phase transcripts by endothelin-1 in cardiomyocytes

BACKGROUND

Endothelin-1 stimulates Gq protein-coupled receptors to promote proliferation in dividing cells or hypertrophy in terminally differentiated cardiomyocytes. In cardiomyocytes, endothelin-1 rapidly (within minutes) stimulates protein kinase signaling, including extracellular-signal regulated kinases 1/2 (ERK1/2; though not ERK5), with phenotypic/physiological changes developing from approximately 12 h. Hypertrophy is associated with changes in mRNA/protein expression, presumably consequent to protein kinase signaling, but the connections between early, transient signaling events and developed hypertrophy are unknown.

RESULTS

Using microarrays, we defined the early transcriptional responses of neonatal rat cardiomyocytes to endothelin-1 over 4 h, differentiating between immediate early gene (IEG) and second phase RNAs with cycloheximide. IEGs exhibited differential temporal and transient regulation, with expression of second phase RNAs within 1 h. Of transcripts upregulated at 30 minutes encoding established proteins, 28 were inhibited >50% by U0126 (which inhibits ERK1/2/5 signaling), with 9 inhibited 25-50%. Expression of only four transcripts was not inhibited. At 1 h, most RNAs (approximately 67%) were equally changed in total and polysomal RNA with approximately 17% of transcripts increased to a greater extent in polysomes. Thus, changes in expression of most protein-coding RNAs should be reflected in protein synthesis. However, approximately 16% of transcripts were essentially excluded from the polysomes, including some protein-coding mRNAs, presumably inefficiently translated.

CONCLUSION

The phasic, temporal regulation of early transcriptional responses induced by endothelin-1 in cardiomyocytes indicates that, even in terminally differentiated cells, signals are propagated beyond the primary signaling pathways through transcriptional networks leading to phenotypic changes (that is, hypertrophy). Furthermore, ERK1/2 signaling plays a major role in this response.

A Chemical Screen Identifies Anisomycin as an Anoikis Sensitizer That Functions by Decreasing FLIP Protein Synthesis

Malignant epithelial cells with metastatic potential resist apoptosis that normally occurs upon loss of anchorage from the extracellular matrix, a process termed "anoikis." Resistance to anoikis enables malignant cells to survive in an anchorage-independent manner, which leads to the formation of distant metastases. To understand the regulation of anoikis, we designed, automated, and conducted a high-throughput chemical screen for anoikis sensitizers. PPC-1 anoikis-resistant prostate cancer cells were seeded in hydrogel-coated ultralow binding plates for suspension conditions and standard tissue culture plates to promote adhesion. After seeding, cells were treated with aliquots from a library of previously characterized small molecules, and viability was assessed using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt, assay. From this chemical screen, we identified anisomycin that induced apoptosis in suspension conditions, but was not toxic to these cells grown under adherent conditions. Anisomycin sensitized cells to anoikis by decreasing levels of the caspase-8 inhibitor FLIP and subsequently activating the death receptor pathway of caspase activation. Although anisomycin activated c-Jun-NH(2)-kinase and p38, these kinases were not functionally important for the effect of anisomycin on anoikis and FLIP. Rather, anisomycin decreased FLIP and sensitized cells to anoikis by inhibiting its protein synthesis. Finally, we showed that anisomycin decreased distal tumor formation in a mouse model of prostate cancer metastases. Thus, a novel chemical screen identified anisomycin as an anoikis sensitizer that acts by decreasing FLIP protein synthesis. Our results suggest that FLIP is a suppressor of anoikis and inhibiting FLIP protein synthesis may be a useful antimetastatic strategy.

Signaling pathways mediating cardiac myocyte gene expression in physiological and stress responses

The contractile cells in the heart (the cardiac myocytes) are terminally differentiated. In response to pathophysiological stresses, cardiac myocytes undergo hypertrophic growth or apoptosis, responses associated with the development of cardiac pathologies. There has been much effort expended in gaining an understanding of the stimuli which promote these responses, and in identifying the intracellular signaling pathways which are activated and potentially involved. These signaling pathways presumably modulate gene and protein expression to elicit the end-stage response. For the regulation of gene expression, the signal may traverse the cytoplasm to modulate nuclear-localized transcription factors as occurs with the mitogen-activated protein kinase or protein kinase B/Akt cascades. Alternatively, the signal may promote translocation of transcription factors from the cytoplasm to the nucleus as is seen with the calcineurin/NFAT and JAK/STAT systems. We present an overview of the principal signaling pathways implicated in the regulation of gene expression in cardiac myocyte pathophysiology, and summarize the current understanding of these pathways, the transcription factors they regulate and the changes in gene expression associated with the development of cardiac pathologies. Finally, we discuss how intracellular signaling and gene expression may be integrated to elicit the overall change in cellular phenotype.

Ageing to arrhythmias: conundrums of connections in the ageing heart

The proportion of the population that is elderly continues to increase, leading to an increasing need to address problems chiefly associated with old age. Progressive ageing of the heart is associated with an increasing incidence of arrhythmias and disorders of the normal origin of the heartbeat, the sinoatrial node. This intrinsic pacemaker of the heart has an increasing tendency with age to lose its dominant role in pacing the heart, and regulation of heart rate becomes erratic. This 'sick sinus syndrome' is associated with fainting, palpitations, shortness of breath and sudden death. Current treatment of this condition is by implantation of an artificial pacemaker, an intervention increasingly required with age. The current evidence suggests that the normal heartbeat fails due to changes in the expression of critical proteins that ensure the correct production and conduction of the cardiac action potential. Depletion of a protein directly responsible for providing electrical connections between the cells of the heart, connexin 43, appears to leave the normal cardiac pacemaker disconnected and unable to drive the heart. This process may be associated with age-dependent changes in stress-related signalling. Simple interventions such as exercise could impact on the processes hypothesized to be involved and may offer a means to preserve the stability of the electrical activity of the heart into old age without pharmacological manipulation.

Physiological effects of ultrasound mist on fibroblasts

BACKGROUND

Chronic wounds present an increasing challenge in healthcare and consume a substantial portion of healthcare cost. Although new treatments have been developed, treatment success has not been improved greatly. Ultrasound has long been employed in medicine. Its unique ability to deliver energy makes it an ideal candidate as a wound care modality. We proposed that ultrasound would differentially affect intracellular signaling pathways and, with the ability to assess this effect using a noncontact form of ultrasound, were provided with a means to test this proposal.

METHODS

The cellular morphology, mitogenic activities, expression of keratinocyte growth factor (KGF) and transforming growth factor beta-1 (TGF-beta1), and activation of extracellular regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways of dermal fibroblasts were studied after ultrasound treatment. Untreated and scrape-wounded fibroblasts were utilized as controls.

RESULTS

There was no difference in morphology observed, except for vacuolization in ultrasound-treated fibroblasts. Mitogenic activities were similar between ultrasound-treated and scrape-wounded fibroblasts. Ultrasound-treated fibroblasts exhibited a much earlier increase in KGF expression, ERK activation, and JNK activation. The ERK/JNK ratio was increased markedly in ultrasound-treated fibroblasts.

CONCLUSION

We conclude that ultrasound induces cellular responses that may be beneficial to wound healing.

Using hyperosmolar stress to measure biologic and stress-activated protein kinase responses in preimplantation embryos

We used hyperosmolar stress to test blastocysts for their biologic and enzymatic responses to culture stress. Embryos mount dose- and time-dependent responses to hyperosmolar stress. Biological responses included slowed cavitation and cell accumulation and increased apoptosis at increasing doses. These responses were preceded by stress-activated protein kinase (SAPK) phosphorylation and nuclear translocation consistent with its causal role. For cavitation and new cell cycle initiation, 200 mM sorbitol caused stasis. Above 200 mM, sorbitol was ultimately lethal and below 200 mM, its embryos had milder effects. Phosphorylated SAPK was induced rapidly in embryos at 0.5 h in a dose-dependent manner from 0 to 600 mM sorbitol. Higher hyperosmolarity caused a biphasic peak of phosphorylated SAPK, but there was no return to baseline through 3 h. At 24 h, a dose-dependent response persisted that was linear from 0 to 200 mM sorbitol. Hyperosmolar stress rapidly induced, within 0.5 h, phosphorylated, nuclear c-Jun and decreased phosphorylated, nuclear c-Myc in a SAPK-dependent manner. The data suggest that SAPK is induced and functions on down-stream effector molecules in a temporal and quantitative manner consistent with its function in the embryonic homeostatic response to stress. The remarkable resistance of embryos to high concentrations of sorbitol suggests that part of its homeostatic response is different from that of somatic cells.

A biochemical approach to wound healing through the use of modalities

Wound healing is a complex pathway that is energy dependent. Nonhealing wounds frequently require the use of physical modalities to achieve healing. There is much debate over which treatment modality to use, with varying clinical results in the literature. This review paper describes a common biochemical pathway that helps the clinician understand, at a molecular level, how the transference of energy to a wound can result in positive clinical results. The mechanisms of action for ultraviolet light, electrical stimulation, and ultrasound are reviewed along with a proposed biochemical roadmap. An emphasis on protein biochemistry is supported with an extensive review of the literature.

Differential requirement of MKK4 and MKK7 in JNK activation by distinct scaffold proteins

Different scaffold proteins play distinct roles in various signaling pathways by recruiting different downstream molecules. Here, using MKK4(-/-) and MKK4(-/-)/7(-/-) murine embryonic fibroblast cells, we examined differential employment of MKK4 and MKK7 by scaffold proteins Axin, Dvl, and Epstein-Barr virus latent membrane protein-1 (LMP-1) in mediating JNK activation. We present evidence that Axin depends mainly on MKK7 for activation of JNK, while Dvl depends almost equally on MKK4 and MKK7 for JNK activation, In contrast, LMP-1-induced JNK activation is primarily dependent on MKK4. Our results demonstrate that Axin, Dvl, and LMP-1 differentially utilize MKK4 and MKK7 for JNK activation.

Oxidative stress and growth-regulating intracellular signaling pathways in cardiac myocytes

The toxic effects of oxidative stress on cells (including cardiac myocytes, the contractile cells of the heart) are well known. However, an increasing body of evidence has suggested that increased production of reactive oxygen species (ROS) promotes cardiac myocyte growth. Thus, ROS may be 'second messenger' molecules in their own right, and growth-promoting neurohumoral agonists might exert their effects by stimulating production of ROS. The authors review the principal growth-promoting intracellular signaling pathways that are activated by ROS in cardiac myocytes, namely the mitogen-activated protein kinase cascades (extracellular signal-regulated kinases 1/2, c-Jun N-terminal kinases, and p38-mitogen-activated protein kinases) and the phosphoinositide 3-kinase/protein kinase B (Akt) pathway. Possible mechanisms are discussed by which these pathways are activated by ROS, including the oxidation of active site cysteinyl residues of protein and lipid phosphatases with their consequent inactivation, the potential involvement of protein kinase C or the apoptosis signal-regulating kinase 1, and the current models for the activation of the guanine nucleotide binding protein Ras.

Using U0126 to dissect the role of the extracellular signal-regulated kinase 1/2 (ERK1/2) cascade in the regulation of gene expression by endothelin-1 in cardiac myocytes

The hypertrophic agonist endothelin-1 rapidly but transiently activates the extracellular signal-regulated kinase 1/2 (ERK1/2) cascade (and other signalling pathways) in cardiac myocytes, but the events linking this to hypertrophy are not understood. Using Affymetrix rat U34A microarrays, we identified the short-term (2-4 h) changes in gene expression induced in neonatal myocytes by endothelin-1 alone or in combination with the ERK1/2 cascade inhibitor, U0126. Expression of 15 genes was significantly changed by U0126 alone, and expression of an additional 78 genes was significantly changed by endothelin-1. Of the genes upregulated by U0126, four are classically induced through the aryl hydrocarbon receptor (AhR) by dioxins suggesting that U0126 activates the xenobiotic response element in cardiac myocytes potentially independently of effects on ERK1/2 signalling. The 78 genes showing altered expression with endothelin-1 formed five clusters: (i) three clusters showing upregulation by endothelin-1 according to time course (4 h > 2 h; 2 h > 4 h; 2 h approximately 4 h) with at least partial inhibition by U0126; (ii) a cluster of 11 genes upregulated by endothelin-1 but unaffected by U0126 suggesting regulation through signalling pathways other than ERK1/2; (iii) a cluster of six genes downregulated by endothelin-1 with attenuation by U0126. Thus, U0126 apparently activates the AhR in cardiac myocytes (which must be taken into account in protracted studies), but careful analysis allows identification of genes potentially regulated acutely via the ERK1/2 cascade. Our data suggest that the majority of changes in gene expression induced by endothelin-1 are mediated by the ERK1/2 cascade.

Induction of a ribotoxic stress response that stimulates stress-activated protein kinases by 13-deoxytedanolide, an antitumor marine macrolide

13-Deoxytedanolide is a structurally unique macrolide with strong antitumor activity isolated from a marine sponge. Recently, we showed that 13-deoxytedanolide bound to the large subunit of the yeast ribosome and inhibited polypeptide elongation in vitro, but the mechanism by which it exerts antitumor activity is still unknown. Here we show that 13-deoxytedanolide strongly induces plasminogen activator inhibitor 1 (PAI-1) promoter-derived gene expression. 13-Deoxytedanolide, unlike TGF-beta, did not cause apparent nuclear translocation of Smad2/3, but it relocalized the temperature-sensitive mutant of mouse p53 (p53Val153) from the cytoplasm to the nucleus at a nonpermissive temperature, suggesting that 13-deoxytedanolide inhibits protein synthesis. Indeed, the drug inhibited in vivo protein synthesis at low nanomolar concentrations and strongly activated stress-activated protein kinases such as p38 mitogen-activated protein kinase and Jun NH2-terminal protein kinase (JNK). Anisomycin, a well-known inducer of ribotoxic stress that activates both p38 and JNK, also activated PAI-1 gene expression, while other protein synthesis inhibitors that do not activate the kinases failed to do so. PAI-1 gene expression by 13-deoxytedanolide and anisomycin was blocked by SB202190, a specific inhibitor of p38, and SP600125, an inhibitor of both p38 and JNK. 13-Deoxytedanolide and anisomycin caused activation of apoptosis signal-regulating kinase 1, MKK3/MKK6, and SEK1/MKK4, the regulatory kinases upstream of p38 and JNK. These results suggest that 13-deoxytedanolide, like anisomycin, triggers a ribotoxic stress response that activates stress-activated protein kinase cascades, thereby inducing PAI-1 gene expression and apoptosis.

Hypoxic stress suppresses RNA polymerase III recruitment and tRNA gene transcription in cardiomyocytes

RNA polymerase (pol) III transcription decreases when primary cultures of rat neonatal cardiomyocytes are exposed to low oxygen tension. Previous studies in fibroblasts have shown that the pol III-specific transcription factor IIIB (TFIIIB) is bound and regulated by the proto-oncogene product c-Myc, the mitogen-activated protein kinase ERK and the retinoblastoma tumour suppressor protein, RB. The principal function of TFIIIB is to recruit pol III to its cognate gene template, an activity that is known to be inhibited by RB and stimulated by ERK. We demonstrate by chromatin immunoprecipitation (ChIP) that c-Myc also stimulates pol III recruitment by TFIIIB. However, hypoxic conditions cause TFIIIB dissociation from c-Myc and ERK, at the same time as increasing its interaction with RB. Consistent with this, ChIP assays indicate that the occupancy of tRNA genes by pol III is significantly reduced, whereas promoter binding by TFIIIB is undiminished. The data suggest that hypoxia can inhibit pol III transcription by altering the interactions between TFIIIB and its regulators and thus compromising its ability to recruit the polymerase. These effects are independent of cell cycle changes.

Inhibition of p38 mitogen-activated protein kinase attenuates interleukin-1beta-induced thermal hyperalgesia and inducible nitric oxide synthase expression in the spinal cord

We have reported recently that intrathecal (i.t.) injection of interleukin-1beta (IL-1beta), at a dose of 100 ng, induces inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production in the spinal cord and results in thermal hyperalgesia in rats. This study further examines the role of mitogen-activated protein kinase (MAPK) in i.t. IL-1beta-mediated iNOS-NO cascade in spinal nociceptive signal transduction. All rats were implanted with an i.t. catheter either with or without an additional microdialysis probe. Paw withdrawal latency to radiant heat is used to assess thermal hyperalgesia. The iNOS and MAPK protein expression in the spinal cord dorsal horn were examined by western blot. The [NO] in CSF dialysates were also measured. Intrathecal IL-1beta leads to a time-dependent up-regulation of phosphorylated p38 (p-p38) MAPK protein expression in the spinal cord 30-240 min following IL-1beta injection (i.t.). However, neither the phosphorylated extracellular signal-regulated kinase (p-ERK) nor phosphorylated c-Jun NH2-terminal kinase (p-JNK) was affected. The total amount of p38, ERK, and JNK MAPK proteins were not affected following IL-1beta injection. Intrathecal administration of either selective p38 MAPK, or JNK, or ERK inhibitor alone did not affect the thermal nociceptive threshold or iNOS protein expression in the spinal cord. However, pretreatment with a p38 MAPK inhibitor significantly reduced the IL-1beta-induced p-p38 MAPK expression by 38-49%, and nearly completely blocked the subsequent iNOS expression (reduction by 86.6%), NO production, and thermal hyperalgesia. In contrast, both ERK and JNK inhibitor pretreatments only partially (approximately 50%) inhibited the IL-1beta-induced iNOS expression in the spinal cord. Our results suggest that p38 MAPK plays a pivotal role in i.t. IL-1beta-induced spinal sensitization and nociceptive signal transduction.

Disruption of two putative nuclear localization sequences is required for cytosolic localization of mitogen-activated protein kinase phosphatase-2

MAP kinase phosphatase-2 (MKP-2) is a member of a family of dual specificity phosphatases (DSPs) that function in both the cytosol and nucleus to inactivate the MAP kinases. The mechanism that controls the subcellular distribution of these proteins is currently unclear. In this study, we have used site-directed mutagenesis to remove two novel nuclear localization sequences, NLS-1 and -2, either alone or in combination (DNLS). Loss of NLS-1 or NLS-2 alone did not alter the nuclear targeting of MKP-2 but mutation of both resulted in MKP-2 being retained within the cytosol. Furthermore, whilst expression of WT-MKP-2, NLS-1 or NLS-2 reduced both sorbitol- or UV-stimulated nuclear c-Jun N-terminal kinase (JNK) activity in HEK293 cells, this effect was absent in cells expressing DNLS-MKP-2. Similarly, transient transfection of WT-MKP-2, NLS-1 or NLS-2, but not DNLS-MKP-2 was able to substantially reduce agonist-stimulated ANF reporter activity in rat cardiac myocytes. Taken together, these results indicate that whilst both novel NLS participate in the nuclear localization of MKP-2, the expression of either sequence is sufficient to retain nuclear targeting.

Inhibition of protein synthesis and activation of stress-activated protein kinases by onnamide A and theopederin B, antitumor marine natural products

During the course of screening for the agents that activate transforming growth factor-beta (TGF-beta) signaling cascade, onnamide A and theopederin B, heterocyclic compounds related to mycalamides from a marine sponge, were found to induce plasminogen activator inhibitor-1 (PAI-1) promoter-derived gene expression in Mv1Lu cells. The maximum induction of the PAI-1 promoter by onnamide A and theopederin B was observed at the concentrations of 50 nM and 2 nM, respectively. These compounds strongly inhibited protein synthesis at the 50% inhibitory concentrations of 30 nM for onnamide A and 1.9 nM for theopederin B, and induced activation of p38 mitogen-activated protein kinase and c-Jun NH2-terminal protein kinase (JNK). Anisomycin, a well-known inducer of ribotoxic stress that inhibits protein synthesis and activates both p38 kinase and JNK, also activated PAI-1 gene expression. Furthermore, PAI-1 expression by onnamide A, theopederin B, and anisomycin was inhibited by SB202190 and SP600125, specific inhibitors of stress-activated protein kinases. Onnamide A and theopederin B were cytotoxic to a variety of cell lines and strongly induced apoptosis in HeLa cells within 24 h, which was accompanied by the sustained activation of p38 kinase and JNK. These results suggest that onnamide A and theopedirin B trigger a ribotoxic stress-like response, thereby inducing p38 kinase and JNK activation, the kinase-dependent PAI-1 gene expression, and apoptosis.

Effects of aging on pressure-induced MAPK activation in the rat aorta

With increasing age, the cardiovascular system experiences substantial alterations in cellular morphology and function. Whilst the factors regulating these changes are unknown, the mitogen-activated protein kinase (MAPK) pathways have emerged as critical components for mediating numerous cellular responses including control of cell growth, differentiation and adaptation. Here we compare the expression, basal activation and the ability of increased pressure to activate the MAPK pathways in adult (6-month-old), aged (30-month-old) and very aged (36-month-old) Fischer 344xBrown Norway F1 hybrid rats. Histochemical analysis demonstrated an age-related increase in tunica media thickness of approximately 11 and 21% in aortae from aged and very aged animals, respectively. Western blot analysis of the MAPK family extracellular signal-regulated kinase (ERK 1/2), p38, and c-Jun NH2 -terminal kinase (JNK) MAPKs showed differential expression and activation among these proteins with age. Expression of ERK 1/2, p38, and JNK were unchanged, slightly increased (10+/-17.5%) or significantly increased (72.3+/-27%), respectively, in very aged aortae. In contrast, basal activation levels of these proteins were reduced (-26.2+/-7.4%), markedly increased (97.0+/-16.8%), and slightly increased (14.4+/-4.5%), respectively, in very aged compared with 6-month rat aortae. An acute increase of aortic intraluminal pressure (200 mmHg) indicated that ERK 1/2 regulation differed from p38 or JNK. Pressure loading-induced phosphorylation of ERK1/2 was unchanged or increased with aging while p38 and JNK phosphorylation was attenuated (P<0.01). These observations confirm previous conclusions that MAPK proteins are regulated mechanically and expand these studies to suggest that MAPK expression and the control of activation are changed with aging.

Attenuation of acute lung injury in mice by oxymatrine is associated with inhibition of phosphorylated p38 mitogen-activated protein kinase

Oxymatrine is one of the alkaloids extracted from Chinese herb Sophora japonica (Sophora flavescens Ait.) with activities of anti-inflammation, inhibiting immune reaction, antivirus, protecting hepatocytes and antihepatic fibrosis. However, the effect of oxymatrine on acute lung injury (ALI) has not been known yet. In this study, the effect of oxymatrine on ALI was investigated using an oleic acid-induced ALI mouse model. Morphological findings showed that the oleic acid group demonstrated a marked lung injury represented by prominent atelectasis, intraalveolar and interstitial patchy hemorrhage, edema, thickened alveolar septum, formation of hyaline membranes and the existence of inflammatory cells in alveolar spaces. While in the oxymatrine/dexamethasone group, these changes were less severe and in the vicinity of the control group. Furthermore, pretreatment with oxymatrine significantly alleviated oleic acid-induced lung injury accompanied by reduction of lung index and wet-to-dry weight ratio, decreases in serum TNF-alpha level and inhibition of phosphorylated p38 MAPK. These findings suggest that oxymatrine has a beneficial effect on acute lung injury induced by oleic acid in mice and may inhibit the production of proinflammatory cytokine, TNF-alpha, by means of the inhibition of p38 MAPK.

Despite minimal hemodynamic alterations endotoxemia modulates NOS and p38-MAPK phosphorylation via metalloendopeptidases

In the present study, we hypothesized that endotoxemia produces metalloendopeptidase (MEPD)-dependent generation of endothelin-1 (ET-1) and alters NOS expression correlating with p38-mitogen-activated protein kinase (MAPK) phosphorylation in thoracic aorta. Male Sprague-Dawley rats (350-400 g) were subjected to two groups randomly; sham-treated (N = 10) and lipopolysaccharide (LPS)-treated (N = 10) (E. coli LPS 2 mg/kg bolus + 2 mg/kg infusion for 30 min). The animals in each group were further subdivided into vehicle and MEPD inhibitor phosphoramidon (1 mg/kg bolus, PHOS)-treated groups. LPS produces a significant decrease in mean arterial pressure (MAP) at 2 h post endotoxemia that was blocked by PHOS. PHOS attenuated LPS-induced increase in tumor necrosis factor-alpha (TNF-alpha) concentration at 2- and 24 h post-LPS administration. LPS significantly elevated plasma concentrations of ET-1 at 2- and 24 h post endotoxemia. An upregulated preproET-1 expression following both LPS and MEPD inhibition was observed in thoracic aorta at 2 h post treatment. PHOS effectively blocked conversion of preproET-1 to ET-1 in thoracic aorta locally at 24 h post treatment in endotoxic rats. PHOS inhibited LPS-induced upregulation of inducible NOS (iNOS), downregulation of endothelial NOS (eNOS) and elevation of NO byproducts (NOx) in thoracic aorta. PHOS also blocked LPS-induced upregulated p38-MAPK phosphorylation in thoracic aorta at 24 h post endotoxemia. The data revealed that LPS induces MEPD-sensitive inflammatory response syndrome (SIRS) at 2- and 24 h post endotoxemia. We concluded that inhibition of MEPD not only decreases the levels of ET-1 but also simultaneously downregulates protein expression of iNOS and phosphorylated p38-MAPK while increasing eNOS in thoracic aorta during SIRS in endotoxemia. We suggest that MEPD-dependent ET-1 and NO mechanisms may be involved in endotoxemia-induced altered p38-MAPK phosphorylation.

Mitogen-activated protein kinases and selected downstream targets display organ-specific responses in the hibernating ground squirrel

The responses of mitogen-activated protein kinase (MAPK) family members, including the extracellular signal-regulated kinases (ERKs), the c-jun NH2-terminal kinases (JNKs) and p38MAPK, during mammalian hibernation were analyzed in five organs of Richardson's ground squirrels, Spermophilus richardsonii. Each kinase subfamily responded differently in torpor and each showed organ-specific patterns of response. ERK1/2 activities increased significantly in muscle and brain during hibernation but decreased in kidney and liver. JNK activity rose in four organs (except brain) during hibernation whereas active, phosphorylated p38MAPK increased only in muscle and heart. Activities of ERK-activated kinases also responded to hibernation: MAPKAPK-1 rose in muscle and brain, MAPKAPK-2 decreased in liver and kidney but rose in the other three organs, and p70S6K kinase activity decreased kidney and heart. Transcription factors, c-Jun and CREB, also showed organ-specific responses during torpor. The data suggest key roles for MAPKs in the regulation of the known organ-specific changes in gene expression and protein phosphorylation that define the hibernation phenotype.

Inhibition of p38 mitogen-activated protein kinase may decrease intestinal epithelial cell apoptosis and improve intestinal epithelial barrier function after ischemia- reperfusion injury

AIM: To investigate the role of p38 mitogen-activated protein kinase in rat small intestine after ischemia-reperfusion (I/R) insult and the relationship between activation of p38 MAPK and apoptotic cell death of intestine.

METHODS: Ninety Wistar rats were divided randomly into three groups, namely sham-operated group (C), I/R vehicle group (R) and SB203580 pre-treated group (S). In groups R and S, the superior mesenteric artery (SMA) was separated and occluded for 45 min, then released for reperfusion for 0.25, 0.5, 1, 2, 6, 12 and 24 h. In group C, SMA was separated without occlusion. Plasma D-lactate levels were examined and histological changes were observed under a light microscope. The activity of p38 MAPK was determined by Western immunoblotting and apoptotic cells were detected by the terminal deoxynucleotidyl transferase (TdT)-mediated dUDP-biotin nick end labeling (TUNEL).

RESULTS: Intestinal ischemia followed by reperfusion activated p38 MAPK, and the maximal level of activation (7.3-fold vs sham-operated group) was reached 30 min after I/R. Treatment with SB 203580, a p38 MAPK inhibitor, reduced intestinal apoptosis (26.72±3.39% vs 62.50±3.08% in I/R vehicle, P<0.01) and decreased plasma D-lactate level (0.78±0.15 mmol/L in I/R vehicle vs 0.42±0.17 mmol/L in SB-treated group) and improved post-ischemic intestinal histological damage.

CONCLUSION: p38 MAPK plays a crucial role in the signal transduction pathway mediating post-ischemic intestinal apoptosis, and inhibition of p38 MAPK may attenuate ischemia-reperfusion injury.

Gene expression profiling identifies activating transcription factor 3 as a novel contributor to the proapoptotic effect of curcumin

The antitumor effect of curcumin (diferuloylmethane) is well established. However, there have been no unbiased studies to identify novel molecular targets of this compound. We therefore undertook a gene expression profiling study to identify novel targets of curcumin. A cDNA array comprised of 12,625 probes was used to compare total RNA extracted from curcumin-treated and untreated MDA-1986 cells for differential gene expression. We identified 202 up-regulated mRNAs and 505 transcripts decreased ≥2-fold. The proapoptotic activating transcription factor 3 (ATF3) was induced &gt;4-fold. Two negative regulators of growth control [antagonizer of myc transcriptional activity (Mad) and p27kip1] were induced 68- and 3-fold, respectively. Additionally, two dual-activity phosphatases (CL 100 and MKP-5), which inactivate the c-jun-NH2-kinases, showed augmented expression, coinciding with reduced expression of the upstream activators of c-jun-NH2-kinase (MEKK and MKK4). Of the repressed genes, the expression of Frizzled-1 (Wnt receptor) was most strongly attenuated (8-fold). Additionally, two genes implicated in growth control (K-sam, encoding the keratinocyte growth factor receptor, and HER3) as well as the E2F-5 transcription factor, which regulates genes controlling cell proliferation, also showed down-regulated expression. Considering its role in apoptosis, we determined the contribution of ATF3 to the antitumor effect of curcumin. Curcumin-treated MDA-1986 cells showed a rapid, dose-dependent increase in ATF3/mRNA protein. Moreover, expression of an exogenous ATF3 cDNA synergized with curcumin in inducing apoptosis. Thus, we have identified several putative, novel molecular targets of curcumin and showed that one, (ATF3) contributes to the proapoptotic effects of this compound.

A functional comparison of the venom of three Australian jellyfish—Chironex fleckeri, Chiropsalmus sp., and Carybdea xaymacana—on cytosolic Ca2+, haemolysis and Artemia sp. lethality

Cnidarian venoms produce a wide spectrum of envenoming syndromes in humans ranging from minor local irritation to death. Here, the effects of Chironex fleckeri, Chiropsalmus sp., and Carybdea xaymacana venoms on ventricular myocyte cytosolic Ca2+, haemolysis and Artemia sp. lethality are compared for the first time. All three venoms caused a large, irreversible elevation of cytosolic Ca2+ in myocytes as measured using the Ca2+ sensitive fluorescent probe Indo-1. The L-type Ca2+ channel antagonist verapamil had no effect on Ca2+ influx whilst La3+, a non-specific channel and pore blocker, inhibited the effect. Haemolytic activity was observed for all venoms, with C. xaymacana venom displaying the greatest activity. These activities are consistent with the presence of a pore-forming toxin existing in the venoms which has been demonstrated by transmission electron microscopy in the case of C. fleckeri. The venom of C. fleckeri was found to be more lethal against Artemia sp. than the venom of the other species, consistent with the order of known human toxicities. This suggests that the observed lytic effects may not underlie the lethal effects of the venom, and raises the question of how such potent activities are dealt with by envenomed humans.

Regulation of gene and protein expression in cardiac myocyte hypertrophy and apoptosis

Considerable efforts have been expended in elucidating the inter-cellular and intra-cellular signaling pathways which elicit cardiac myocyte hypertrophy or apoptosis, and in identifying the changes which are associated with the end-stage of the response. The challenge now is to link the two. Although some of the signaling effects will be the acute modulation of existing protein function, long-term effects which bring about and maintain the hypertrophic state or which culminate in cell death are mediated at the level of gene and protein expression. With the advances in micro-array technology and genome sequencing, it is now possible to obtain a picture of the global gene expression profile in myocytes or in whole heart which dictates the proteins which could be made. This is not the final picture since additional regulation at the level of translation modulates the relative proportions of each protein that can be made from the transcriptome. Even here, further regulation of protein stability and turnover means that ultimately it is still necessary to examine the proteome to determine what may cause the functional changes in a cell. Thus, in order to gain a full picture of events which regulate the response and gain some insight into possible points of intervention for therapy, it is necessary to examine gene expression, mRNA translation and protein expression in concert.

Reverse two-hybrid screening identifies residues of JNK required for interaction with the kinase interaction motif of JNK-interacting protein-1

The development of specific inhibitors for the c-Jun N-terminal kinase (JNK) family of mitogen-activated protein kinases (MAPKs) has been a recent research focus because of the association of JNK with cell death in conditions such as stroke and neurodegeneration. We have demonstrated previously the presence of critical inhibitory residues within an 11-mer peptide (TI-JIP) based on the sequence of JNK-interacting protein-1 (JIP-1). However, the corresponding region of JNK bound by this JIP-1-based peptide was unknown. To identify this region, we used a novel reverse two-hybrid approach with TI-JIP as bait. We screened a library of JNK1 mutants that had been generated by random PCR mutagenesis and found three mutants of JNK1 that failed to interact with TI-JIP. The mutations in JNK1 were L131R, R309W, and Y320H. Of these mutated residues, Leu-131 and Tyr-320 were located on a common face of the JNK protein close to other residues implicated previously in the interactions of MAPKs with substrates, phosphatases, and scaffolds. To test whether these JNK1 mutants were thus affected in their regulation, we evaluated their activation in mammalian cells in response to hyperosmolarity or cotransfection with a constitutively active upstream kinase or their direct phosphorylation by either MAPK kinase (MKK)4 or MKK7. In each situation, all three JNK mutants were not activated or phosphorylated to the same level as wild-type JNK. Therefore, the results of our unbiased reverse two-hybrid screening approach have identified residues of JNK responsible for binding JIP-1-based peptides as well as MKK4 or MKK7.

Phosphorylation of the mitochondrial protein Sab by stress-activated protein kinase 3

Mitogen-activated protein kinases (MAPKs) transduce extracellular signals into responses such as growth, differentiation, and death through their phosphorylation of specific substrate proteins. Early studies showed the consensus sequence (Pro/X)-X-(Ser/Thr)-Pro to be phosphorylated by MAPKs. Docking domains such as the "kinase interaction motif" (KIM) also appear to be crucial for efficient substrate phosphorylation. Here, we show that stress-activated protein kinase-3 (SAPK3), a p38 MAPK subfamily member, localizes to the mitochondria. Activated SAPK3 phosphorylates the mitochondrial protein Sab, an in vitro substrate of c-Jun N-terminal kinase (JNK). Sab phosphorylation by SAPK3 was dependent on the most N-terminal KIM (KIM1) of Sab and occurred primarily on Ser321. This appeared to be dependent on the position of Ser321 within Sab and the sequence immediately surrounding it. Our results suggest that SAPK3 and JNK may share a common target at the mitochondria and provide new insights into the substrate recognition by SAPK3.

The critical features and the mechanism of inhibition of a kinase interaction motif-based peptide inhibitor of JNK

We previously reported that a small peptide based on amino acids 143-153 of the c-Jun N-terminal kinase (JNK)-binding domain of JIP-1 functioned as an in vitro inhibitor of JNK activity. This peptide (TI-JIP: RP-KRPTTLNLF) resembles the kinase-interaction motif (KIM = (K/R)(2-3)X(1-6)(L/I)X(L/I)), which is common to upstream activators, downstream substrates, phosphatases, and scaffold proteins present in MAPK cascades. In this study, we characterized the mechanism of JNK inhibition by this peptide and further investigated the biochemical features of this peptide resulting in potent JNK inhibition. We also tested various KIM-based peptides for their ability to inhibit JNK activity. TI-JIP was found to be competitive with respect to the phosphoacceptor substrate c-Jun (K(I) = 0.39 +/- 0.08 microm), and exhibit mixed (non-competitive) inhibition with respect to ATP. All seven substitutions of Pro-5 we tested significantly reduced the JNK inhibition, as did altering the Pro-5 to Leu-8 spacing. When we independently tested eight substitutions of either Thr-6 or Thr-7, only one substitution in each position was well tolerated. Furthermore, peptides based on the KIMs from other proteins were significantly less potent JNK inhibitors than TI-JIP, including a peptide from the JNK interactor Sab that contained all critical inhibitory residues present in TI-JIP. Therefore, despite having previously identified Arg-4, Pro-5, Leu-8, and Leu-10 in TI-JIP as independently critical for mediating JNK inhibition, we find their presence in other 11-mer peptides is not sufficient for JNK inhibition. TI-JIP is therefore a unique KIM-based inhibitor of JNK activity.

Protein kinase C-dependent activation of P44/42 mitogen-activated protein kinase and heat shock protein 70 in signal transduction during hepatocyte ischemic preconditioning

AIM: To investigate the significance of protein kinase C (PKC), P44/42 mitogen-activated protein kinase (MAPKs) and heat shock protein (HSP)70 signal transduction during hepatocyte ischemic preconditioning.

METHODS: In this study we used an in vitro ischemic preconditioning (IP) model for hepatocytes and an in vivo model for rat liver to investigate the significance of protein kinase C (PKC), P44/42 mitogen-activated protein kinase (P44/42 MAPKs) and heat shock protein 70 (HSP70) signal transduction in IP. Through a normal liver cell hypoxic preconditioning (HP) model in which cultured normal liver cells were subjected to 3 cycles of 5 min of incubation under hypoxic conditions followed by 5 min of reoxygenation and subsequently exposed to hypoxia and reoxygenation for 6 h and 9 h respectively. PKC inhibitor, activator and MEK inhibitor were utilized to analyze the phosphorylation of PKC, the expression of P44/42 MAPKs and HSP70. Viability and cellular ultrastructure were also observed. By using rat liver as an in vivo model of liver preconditioning (3 cycles of 10-min occlusion and 10-min reperfusion), in vivo phosphorylation of PKC and P44/42MAPKs, HSP70 expression were further analyzed. AST/ALT concentration, cellular structure and ultrastruture were also observed. All the data were statistically analyzed.

RESULTS: Similar results were obtained in both in vivo and in vitro IP models. Compared with the control without IP (or HP), the phosphorylation of PKC and P44/42 MAPKs and the expression of HSP70 were obviously increased in IP (or HP) treated model in which cytoprotection could be found. The effects of preconditioning were mimicked by stimulating PKC with 4β phorobol-12-myristate13-acetate (PMA). Conversely, inhibiting PKC with chelerythrine abolished the protection given by preconditioning. PD98059, inhibitor of MEK (the upstream kinase of P44/42MAPKs), also reverted the cytoprotection exerted by preconditioning.

CONCLUSION: The results demonstrate that preconditioning induces a rapid activation of P44/42MAPKs and PKC activation plays a pivotal role in the activation of P44/42 MAPKs pathway that participates in the preservation of liver cells. HSP expression is regulated by signals in PKC dependent P44/ 42 MAPKs pathway.

Obligatory role for endogenous endothelin in mediating the hypertrophic effects of phenylephrine and angiotensin II in neonatal rat ventricular myocytes: evidence for two distinct mechanisms for endothelin regulation

Various Gq protein-coupled receptor agonists such as the alpha1 adrenoceptor agonist phenylephrine, angiotensin II, and endothelin-1 are potent hypertrophic factors. There is evidence of potential cross talk between these agents, particularly in terms of endothelin-1 as playing a central role in mediating the actions of other hypertrophic factors. Using cultured rat neonatal ventricular myocytes, we assessed the potential cross talk between these factors and sought to examine the potential underlying mechanisms. Twenty-four-hour exposure to either agent produced significant hypertrophy as determined by cell size and molecular markers. Although the hypertrophic effects of phenylephrine and angiotensin II were expectedly prevented by alpha1 and AT1 receptor antagonists, respectively, these effects were also blocked by the ETA receptor antagonist BQ123 [cyclo(D-Asp-Pro-D-Val-Leu-D-Trp)] but not by the ETB antagonist BQ788 (N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyltryptophanyl-D-norleucine). Both phenylephrine and angiotensin II significantly increased protein expression of both endothelin receptor subtypes. Both phenylephrine and angiotensin II produced significant activation of p38 as well as extracellular signal-regulated protein kinase and c-Jun NH2-terminal kinase, although this was unaffected by endothelin receptor blockade. Further studies revealed that the effects of phenylephrine and angiotensin II were mediated by stimulated endothelin-1 production occurring via two separate mechanisms: angiotensin II by increasing the levels of the endothelin-1 precursor prepro endothelin-1 and phenylephrine by upregulating endothelin-converting enzyme 1. Our results indicate that the endothelin-1 system plays an obligatory role in the hypertrophic response to both phenylephrine and angiotensin II in cultured myocytes through a mechanism independent of mitogenactivated protein kinase activation.

Endothelin-1–Induced Cardiac Hypertrophy Is Inhibited by Activation of Peroxisome Proliferator–Activated Receptor-α Partly Via Blockade of c-Jun NH2-Terminal Kinase Pathway

BACKGROUND

Peroxisome proliferator-activated receptor-alpha (PPAR-alpha) is a lipid-activated nuclear receptor that negatively regulates the vascular inflammatory gene response by interacting with transcription factors, nuclear factor-kappaB, and AP-1. However, the roles of PPAR-alpha activators in endothelin (ET)-1-induced cardiac hypertrophy are not yet known.

METHODS AND RESULTS

First, in cultured neonatal rat cardiomyocytes, a PPAR-alpha activator, fenofibrate (10 micromol/L), and PPAR-alpha overexpression markedly inhibited the ET-1-induced increase in protein synthesis. Second, fenofibrate markedly inhibited ET-1-induced increase in c-Jun gene expression and phosphorylation of c-Jun and JNK. These results suggest that this PPAR-alpha activator interferes with the formation and activation of AP-1 protein induced by ET-1 in cardiomyocytes. Third, fenofibrate significantly inhibited the increase of ET-1 mRNA level by ET-1, which was also confirmed by luciferase assay. Electrophoretic mobility shift assay revealed that fenofibrate significantly decreased the ET-1-stimulated or phorbol 12-myristate 13-acetate-stimulated AP-1 DNA binding activity, and the nuclear extract probe complex was supershifted by anti-c-Jun antibody. Fourth, 24 hours after aortic banding (AB) operation, fenofibrate treatment significantly inhibited left ventricular hypertrophy and hypertrophy-related gene expression pattern (ET-1, brain natriuretic peptide, and beta-myosin heavy chain mRNA) in AB rats.

CONCLUSIONS

These results suggest that PPAR-alpha activation interferes with the signaling pathway of ET-1-induced cardiac hypertrophy through negative regulation of AP-1 binding activity, partly via inhibition of the JNK pathway in cultured cardiomyocytes. We also revealed that fenofibrate treatment inhibited left ventricle hypertrophy and phenotypic changes in cardiac gene expression in AB rats in vivo.

Bax, reactive oxygen, and cytochrome c release in neuronal apoptosis

Half of all neurons produced during embryogenesis undergo apoptotic death shortly before birth or soon thereafter. Two cell culture models have been used extensively to investigate the cellular and molecular mechanisms underlying apoptosis during neuronal development: (a) sympathetic neurons deprived of their required neurotrophic factor, nerve growth factor, and (b) cerebellar granule neurons deprived of serum in low-potassium medium. A dramatic increase in mitochondrial-derived reactive oxygen species (ROS) occurs during the apoptotic death of both of these cell types. These ROS lie downstream from the proapoptotic protein, Bax. Bax normally resides in the cytoplasm, but translocates to the outer mitochondrial membrane during apoptosis. Once associated with mitochondria, Bax causes release of apoptogenic factors from the mitochondria into the cytoplasm, thus inducing or augmenting the apoptotic cascade. Although there is much controversy about the exact mechanism by which Bax causes release of these factors, recent evidence suggests that the Bax-induced ROS are critical for this release to occur in both sympathetic and cerebellar granule neurons. Because Bax is critical for the apoptotic death of many other types of neurons, it is likely that increased ROS is important for the death of these cells as well.

Hydrogen sulfide induces serum-independent cell cycle entry in nontransformed rat intestinal epithelial cells

Hydrogen sulfide (H2S), produced by commensal sulfate-reducing bacteria, is an environmental insult that potentially contributes to chronic intestinal epithelial disorders. We tested the hypothesis that exposure of nontransformed intestinal epithelial cells (IEC-18) to the reducing agent sodium hydrogen sulfide (NaHS) activates molecular pathways that underlie epithelial hyperplasia, a phenotype common to both ulcerative colitis (UC) and colorectal cancer. Exposure of IEC-18 cells to NaHS rapidly increased the NADPH/NADP ratio, reduced the intracellular redox environment, and inhibited mitochondrial respiratory activity. The addition of 0.2-5 mM NaHS for 4 h increased the IEC-18 proliferative cell fraction (P<0.05), as evidenced by analysis of the cell cycle and proliferating cell nuclear antigen expression, while apoptosis occurred only at the highest concentration of NaHS. Thirty minutes of NaHS exposure increased (P<0.05) c-Jun mRNA concentrations, consistent with the observed activation of mitogen activated protein kinases (MAPK). Microarray analysis confirmed an increase (P<0.05) in MAPK-mediated proliferative activity, likely reflecting the reduced redox environment of NaHS-treated cells. These data identify functional pathways by which H2S may initiate epithelial dysregulation and thereby contribute to UC or colorectal cancer. Thus, it becomes crucial to understand how genetic background may affect epithelial responsiveness to this bacterial-derived environmental insult.