The activation of protein kinase B by H2O2 or heat shock is mediated by phosphoinositide 3-kinase and not by mitogen-activated protein kinase-activated protein kinase-2

The Role of Mitochondrial and Redox Alterations in the Skeletal Myopathy Associated with Chronic Kidney Disease

Significance: An estimated 700 million people globally suffer from chronic kidney disease (CKD). In addition to increasing cardiovascular disease risk, CKD is a catabolic disease that results in a loss of muscle mass and function, which are strongly associated with mortality and a reduced quality of life. Despite the importance of muscle health and function, there are no treatments available to prevent or attenuate the myopathy associated with CKD. Recent Advances: Recent studies have begun to unravel the changes in mitochondrial and redox homeostasis within skeletal muscle during CKD. Impairments in mitochondrial metabolism, characterized by reduced oxidative phosphorylation, are found in both rodents and patients with CKD. Associated with aberrant mitochondrial function, clinical and preclinical findings have documented signs of oxidative stress, although the molecular source and species are ill-defined. Critical Issues: First, we review the pathobiology of CKD and its associated myopathy, and we review muscle cell bioenergetics and redox biology. Second, we discuss evidence from clinical and preclinical studies that have implicated the involvement of mitochondrial and redox alterations in CKD-associated myopathy and review the underlying mechanisms reported. Third, we discuss gaps in knowledge related to mitochondrial and redox alterations on muscle health and function in CKD. Future Directions: Despite what has been learned, effective treatments to improve muscle health in CKD remain elusive. Further studies are needed to uncover the complex mitochondrial and redox alterations, including post-transcriptional protein alterations, in patients with CKD and how these changes interact with known or unknown catabolic pathways contributing to poor muscle health and function. Antioxid. Redox Signal. 38, 318-337.

A RAC-alpha serine/threonine-protein kinase (CgAKT1) involved in the synthesis of CgIFNLP in oyster Crassostrea gigas

The RAC-alpha serine/threonine-protein kinase (AKT) is one of the most important protein kinases involved in many biological processes in eukaryotes. In the present study, a novel AKT homologue named CgAKT1 was identified from the Pacific oyster Crassostrea gigas. The open reading frame (ORF) of CgAKT1 cDNA was of 1482 bp encoding a peptide with 493 amino acid residues. There were classical domains in the predicted CgAKT1 protein, including an N-terminal pleckstrin homology domain, a central catalytic domain and a C-terminal hydrophobic domain. The mRNA transcripts of CgAKT1 were detected in all the examined tissues of C. gigas with higher level in gills (8.24-fold of that in mantle, p < 0.05) and haemocytes (3.62-fold of that in mantle, p < 0.05). After poly (I:C) stimulation, the mRNA expression of CgAKT1 decreased significantly in haemocytes from 3 h (0.44-fold of that in the control group, p < 0.001) to 24 h (0.20-fold of that in the control group, p < 0.001), and then increased significantly at 48 h (3.65-fold of that in the control group, p < 0.05). The expression level of CgAKT1 mRNA increased significantly at 6 h after rCgIFNLP stimulation, which was 3.60-fold of that in the control group (p < 0.001). The Alexa Fluor 488 positive signals of CgAKT1 protein were found to be distributed in the cytoplasm and cell membrane of haemocytes, while those in the cytoplasm became weaker after poly (I:C) stimulation. In CgAKT1-RNAi oysters, the mRNA expression of cyclic GMP-AMP synthase (CgcGAS) and TANK-binding kinase 1 (CgTBK1) did not change significantly, but the mRNA expression level of stimulator of interferon gene (CgSTING), interferon regulatory factor-1 (CgIRF-1), interferon regulatory factor-8 (CgIRF-8) and IFN-like protein (CgIFNLP) increased significantly, which was 1.40-fold, 1.53-fold, 1.72-fold and 1.99-fold of that in EGFP-RNAi oysters (p < 0.05), respectively. In CgIFNLP-RNAi oysters, the transcripts of CgAKT1 decreased significantly compared to those in EGFP-RNAi oysters (0.16-fold, p < 0.01). Moreover, the expression of p-CgTBK1, CgSTING and CgIFNLP at the protein level in the oysters treated with p-AKT1 activator (SC-79) was significantly suppressed after poly (I:C) stimulation. After the transfection of CgAKT1, the expression of p-cGAS protein in HEK293T cells increased significantly, while the cyclic GMP-AMP in the cells and the interferon (IFN-β) in the cell culture fluid decreased significantly compared with that in the control group. These results indicated that CgAKT1 might play a negative role in antiviral immunity of oyster by regulating the synthesis of CgIFNLP.

The Heat Shock Connection: Skeletal Muscle Hypertrophy and Atrophy

Skeletal muscle is an integral tissue system that plays a crucial role in the physical function of all vertebrates and is a key target for maintaining or improving health and performance across the lifespan. Based largely on cellular and animal models, there is some evidence that various forms of heat stress with or without resistance exercise may enhance skeletal muscle growth or reduce its loss. It is not clear whether these stimuli are similarly effective in humans or meaningful in comparison to exercise alone across various heating methodologies. Furthermore, the magnitude by which heat stress may influence whole body thermoregulatory responses and the connection to skeletal muscle adaptation remains ambiguous. Finally, the underlying mechanisms, which may include interaction between relevant heat shock proteins and intracellular hypertrophy and atrophy related factors, remain unclear. In this narrative mini-review we examine the relevant literature regarding heat stress alone or in combination with resistance exercise emphasizing skeletal muscle hypertrophy and atrophy across cellular and animal models, as well as human investigations. Additionally, we present working mechanistic theories for heat shock protein mediated signaling effects regarding hypertrophy and atrophy related signaling processes. Importantly, continued research is necessary to determine the practical effects and mechanisms of heat stress with and without resistance exercise on skeletal muscle function via growth and maintenance.

Alpha-Enolase Protects Hepatocyte Against Heat Stress Through Focal Adhesion Kinase-Mediated Phosphatidylinositol 3-Kinase/Akt Pathway

Accumulating pieces of evidence showed that α-enolase (ENO1) is a multifunctional protein that plays a crucial role in a variety of pathophysiological processes. In our previous study, differential expression of ENO1 was observed in different heat-tolerance duck breeds. Here, we examined in vitro expression level of ENO1 in hepatocytes against heat stress. The mechanisms of ENO1 on cell glycolysis, growth, and its potential regulatory pathways were also analyzed. The results showed that ENO1 expression in messenger RNA and protein levels were both greatly increased in heat-treated cells compared with non-treated cells. ENO1-overexpressed cells significantly elevated cell viability and glycolysis levels. It was further shown that stably upregulated ENO1 activated focal adhesion kinase-phosphatidylinositol 3-kinase/Akt and its downstream signals. In addition, the interaction between ENO1 and 70-kDa heat shock protein was detected using co-immunoprecipitation. Our research suggests that ENO1 may interact with 70-kDa heat shock protein to protect hepatocyte against heat stress through focal adhesion kinase-mediated phosphatidylinositol 3-kinase/Akt pathway.

Chlorpyrifos induces cell proliferation in MCF-7 and MDA-MB-231 cells, through cholinergic and Wnt/β-catenin signaling disruption, AChE-R upregulation and oxidative stress generation after single and repeated treatment

Chlorpyrifos (CPF) biocide, is associated with breast cancer. The processes underlying this association have not been elucidated to date. CPF increases MCF-7 and MDA-MB-231 cell proliferation after acute and long-term treatment, partially through KIAA1363 overexpression and aryl-hydrocarbon receptor activation but also through estrogen receptor-alpha activation after 24 h exposure in MCF-7 cells, suggesting other mechanisms may be involved. CPF induces reactive oxygen species (ROS) generation, acetylcholine accumulation, and overexpression of acetylcholinesterase-R/S (AChE-R/S) variants, while it also alters the Wnt/β-catenin pathway, both in vitro and in vivo, in processes different from cancer. These latter mechanisms are also linked to cell proliferation and could mediate this effect induced by CPF. Our results show that CPF (0.01-100 μM), following one-day and fourteen-days treatment, respectively, induced ROS generation and lipid peroxidation, and acetylcholine accumulation due to AChE inhibition, Wnt/β-catenin up- or downregulation depending on the CPF treatment concentration, and AChE-R and AChE-S overexpression, with the latter being mediated through GSK-3β activity alteration. Finally, CPF promoted cell division through ACh and ROS accumulation, AChE-R overexpression, and Wnt/β-catenin signaling disruption. Our results provide novel information on the effect of CPF on human breast cancer cell lines that may help to explain its involvement in breast cancer.

Modulation of Heat-Shock Proteins Mediates Chicken Cell Survival against Thermal Stress

Heat stress is one of the most challenging environmental stresses affecting domestic animal production, particularly commercial poultry, subsequently causing severe yearly economic losses. Heat stress, a major source of oxidative stress, stimulates mitochondrial oxidative stress and cell dysfunction, leading to cell damage and apoptosis. Cell survival under stress conditions needs urgent response mechanisms and the consequent effective reinitiation of cell functions following stress mitigation. Exposure of cells to heat-stress conditions induces molecules that are ready for mediating cell death and survival signals, and for supporting the cell's tolerance and/or recovery from damage. Heat-shock proteins (HSPs) confer cell protection against heat stress via different mechanisms, including developing thermotolerance, modulating apoptotic and antiapoptotic signaling pathways, and regulating cellular redox conditions. These functions mainly depend on the capacity of HSPs to work as molecular chaperones and to inhibit the aggregation of non-native and misfolded proteins. This review sheds light on the key factors in heat-shock responses for protection against cell damage induced by heat stress in chicken.

Anthrax lethal factor cleaves regulatory subunits of phosphoinositide-3 kinase to contribute to toxin lethality

Anthrax lethal toxin (LT), produced by Bacillus anthracis, comprises a receptor-binding moiety, protective antigen and the lethal factor (LF) protease^1,2. Although LF is known to cleave mitogen-activated protein kinase kinases (MEKs/MKKs) and some variants of the NLRP1 inflammasome sensor, targeting of these pathways does not explain the lethality of anthrax toxin^1,2. Here we report that the regulatory subunits of phosphoinositide-3 kinase (PI3K)-p85α (PIK3R1) and p85β (PIK3R2)^3,4-are substrates of LF. Cleavage of these proteins in a proline-rich region between their N-terminal Src homology and Bcr homology domains disrupts homodimer formation and impacts PI3K signalling. Mice carrying a mutated p85α that cannot be cleaved by LF show a greater resistance to anthrax toxin challenge. The LF(W271A) mutant cleaves p85α with lower efficiency and is non-toxic to mice but can regain lethality when combined with PI3K pathway inhibitors. We provide evidence that LF targets two signalling pathways that are essential for growth and metabolism and that the disabling of both pathways is likely necessary for lethal anthrax infection.

Ubiquitin ligase CHIP functions as an oncogene and activates the AKT signaling pathway in prostate cancer

Carboxyl terminus of Hsc-70-interacting protein (CHIP) is an E3 ubiquitin ligase that induces the ubiquitination and degradation of numerous tumor-associated proteins and serves as a suppressor or promoter in tumor progression. To date, the molecular mechanism of CHIP in prostate cancer remains unknown. Therefore, the present study investigated the biological function of CHIP in prostate cancer cells and obtained evidence that CHIP expression is upregulated in prostate cancer tissues. The CHIP vector was introduced into DU145 cancer cells and the cell biological behaviour was examined through a series of experiments, including cell growth, cell apoptosis and migration and invasion assays. The results indicated that the overexpression of CHIP in DU145 prostatic cancer cells promoted cell proliferation through activation of the protein kinase B (AKT) signaling pathway, which subsequently increased cyclin D1 protein levels and decreased p21 and p27 protein levels. The overexpression of CHIP significantly increased the migration and invasion of the DU145 cells, which is possible due to activation of the AKT signaling pathway and upregulation of vimentin. The expression level of CHIP was observed to be increased in human prostate cancer tissues compared with the adjacent normal tissue. Furthermore, the CHIP expression level exhibited a positively association with the Gleason score of the patents. These findings indicate that CHIP functions as an oncogene in prostate cancer.

Treadmill exercise activates PI3K/Akt signaling pathway leading to GSK-3β inhibition in the social isolated rat pups

Social isolation is known to precipitate depression-like symptoms in rodents and has emerged as a dependable paradigm to screen the behavioral and neurobiological changes observed in humans. In the present study, the undying mechanisms of treadmill exercise on social isolation-induced depression was evaluated. The rat pups in the social isolation groups were housed individually. The social isolation procedures started on the postnatal day 14. The rat pups in the exercise groups were forced to run on treadmill for 30 min once a day from postnatal day 21 to postnatal day 34. The expression of phosphoinositide 3 kinase (PI3K), tyrosine kinase B (Akt), and glycogen synthase kinase 3β (GSK-3β) in the hippocampus were determined by using western blot analysis. The ratio phosphorylated PI3K (p-PI3K)/PI3K and phosphorylated Akt (p-Akt)/Akt were decreased and the ratio of phosphorylated-GSK-3 (p-GSK-3β)/GSK-3β was increased by social isolation. Treadmill exercise increased the ratio p-PI3K/PI3K and p-Akt/Akt and suppressed the ratio of p-GSK-3β/GSK-3β in the hippocampus of social isolated rat pups. Treadmill exercise activates PI3K/Akt signaling pathway leading to GSK-3β inhibition in social isolated rats. These results suggested that treadmill exercise may improve depressive symptoms via activation of PI3K/Akt signaling pathway.

GSK3 and its interactions with the PI3K/AKT/mTOR signalling network

Glycogen Synthase Kinase-3 (GSK3 or GSK-3) is a promiscuous protein kinase and its phosphorylation of its diverse substrates has major influences on many areas of physiology and pathology, including cellular metabolism, lineage commitment and neuroscience. GSK3 was one of the first identified substrates of the heavily studied oncogenic kinase AKT, phosphorylation by which inhibits GSK3 activity via the formation of an autoinhibitory pseudosubstrate sequence. This has led to investigation of the role of GSK3 inhibition as a key component of the cellular responses to growth factors and insulin, which stimulate the class I PI 3-Kinases and in turn AKT activity and GSK3 phosphorylation. GSK3 has been shown to phosphorylate several upstream and downstream components of the PI3K/AKT/mTOR signalling network, including AKT itself, RICTOR, TSC1 and 2, PTEN and IRS1 and 2, with the potential to apply feedback control within the network. However, it has been clear for some time that functionally distinct, insulated pools of GSK3 exist which are regulated independently, so that for some GSK3 substrates such as β-catenin, phosphorylation by GSK3 is not controlled by input from PI3K and AKT. Instead, as almost all GSK3 substrates require a priming phosphorylated residue to be 4 amino acids C-terminal to the Ser/Thr phosphorylated by GSK3, the predominant form of regulation of the activity of GSK3 often appears to be through control over these priming events, specific to individual substrates. Therefore, a major role of GSK3 can be viewed as an amplifier of the electrostatic effects on protein function which are caused by these priming phosphorylation events. Here we discuss these different aspects to GSK3 regulation and function, and the functions of GSK3 as it integrates with signalling through the PI3K-AKT-mTOR signalling axis.

Dynamic Phosphorylation of Apoptosis Signal Regulating Kinase 1 (ASK1) in Response to Oxidative and Electrophilic Stress

Apoptosis signal-regulating kinase 1 (ASK1) is a critical cellular stress sensor that senses diverse reactive chemotypes and integrates these chemical signals into a single biological pathway response. It is unknown whether ASK1 senses all stressors in the same way or if unique stress-specific mechanisms detect distinct chemotypes. In order to answer this question, we treated ASK1-expressing cells with two distinct stress activators, H2O2 and 4-hydroxy-2-nonenal (HNE), and monitored the phosphorylation state of ASK1. Phosphorylation is an important regulator for the activity of ASK1, and we hypothesized that these two chemically distinct molecules may produce differences in the phosphorylation state of ASK1. Shotgun mass spectrometry and manual validation identified 12 distinct ASK1 phosphosites. Targeted parallel reaction monitoring assays were used to track the phosphorylation dynamics of each confirmed site in response to treatment. Eleven phosphosites exhibited dynamic response to one or both treatments. Six of these sites were identified in both H2O2- and HNE-treated cells, and four of these exhibited a consistent response between the two molecules. The results confirm that different chemotypes produce distinct phosphorylation patterns in concert with activation of a common MAPK pathway.

Heat Stress-Induced PI3K/mTORC2-Dependent AKT Signaling Is a Central Mediator of Hepatocellular Carcinoma Survival to Thermal Ablation Induced Heat Stress

Thermal ablative therapies are important treatment options in the multidisciplinary care of patients with hepatocellular carcinoma (HCC), but lesions larger than 2–3 cm are plagued with high local recurrence rates and overall survival of these patients remains poor. Currently no adjuvant therapies exist to prevent local HCC recurrence in patients undergoing thermal ablation. The molecular mechanisms mediating HCC resistance to thermal ablation induced heat stress and local recurrence remain unclear. Here we demonstrate that the HCC cells with a poor prognostic hepatic stem cell subtype (Subtype HS) are more resistant to heat stress than HCC cells with a better prognostic hepatocyte subtype (Subtype HC). Moreover, sublethal heat stress rapidly induces phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) dependent-protein kinase B (AKT) survival signaling in HCC cells in vitro and at the tumor ablation margin in vivo. Conversely, inhibition of PI3K/mTOR complex 2 (mTORC2)-dependent AKT phosphorylation or direct inhibition of AKT function both enhance HCC cell killing and decrease HCC cell survival to sublethal heat stress in both poor and better prognostic HCC subtypes while mTOR complex 1 (mTORC1)-inhibition has no impact. Finally, we showed that AKT isoforms 1, 2 and 3 are differentially upregulated in primary human HCCs and that overexpression of AKT correlates with worse tumor biology and pathologic features (AKT3) and prognosis (AKT1). Together these findings define a novel molecular mechanism whereby heat stress induces PI3K/mTORC2-dependent AKT survival signaling in HCC cells and provide a mechanistic rationale for adjuvant AKT inhibition in combination with thermal ablation as a strategy to enhance HCC cell killing and prevent local recurrence, particularly at the ablation margin.

Inhibition of mTOR promotes hyperthermia sensitivity in SMMC-7721 human hepatocellular carcinoma cell line

The mammalian target of rapamycin (mTOR) is a critical mediator of the phosphoinositide 3-kinase/protein kinase B/mTOR signaling pathway, and mTOR activity is induced following heat shock. Thermotherapy is used to treat hepatocellular carcinoma (HCC). However, the role of mTOR in modulating thermosensitivity in HCC has yet to be elucidated. In the present study, the antisense plasmid pEGFP-C1-mTOR was transfected into SMMC-7721 cells, and the expression levels of mTOR were analyzed by reverse transcription-polymerase chain reaction and western blot analysis. The thermal responses of the transfected cells were also examined. The results revealed that SMMC-7721 cells were sensitive to heat treatment, and cell viability was significantly inhibited following hyperthermia treatment (P<0.01). The mRNA and protein expression levels of mTOR decreased post-transfection. Cell proliferation, colony-forming ability and motility were all significantly decreased following hyperthermia treatment in the transfected cells. Flow cytometry analysis demonstrated that apoptosis was significantly increased following treatment (P<0.01). The number of cells in S phase was increased, and the cell cycle was arrested in S phase. In conclusion, inhibition of mTOR increased the thermosensitivity of SMMC-7721 cells by increasing cellular apoptosis and inducing S phase arrest.

Musclin is an activity-stimulated myokine that enhances physical endurance

Exercise remains the most effective way to promote physical and metabolic wellbeing, but molecular mechanisms underlying exercise tolerance and its plasticity are only partially understood. In this study we identify musclin-a peptide with high homology to natriuretic peptides (NP)-as an exercise-responsive myokine that acts to enhance exercise capacity in mice. We use human primary myoblast culture and in vivo murine models to establish that the activity-related production of musclin is driven by Ca(2+)-dependent activation of Akt1 and the release of musclin-encoding gene (Ostn) transcription from forkhead box O1 transcription factor inhibition. Disruption of Ostn and elimination of musclin secretion in mice results in reduced exercise tolerance that can be rescued by treatment with recombinant musclin. Reduced exercise capacity in mice with disrupted musclin signaling is associated with a trend toward lower levels of plasma atrial NP (ANP) and significantly smaller levels of cyclic guanosine monophosphate (cGMP) and peroxisome proliferator-activated receptor gamma coactivator 1-α in skeletal muscles after exposure to exercise. Furthermore, in agreement with the established musclin ability to interact with NP clearance receptors, but not with NP guanyl cyclase-coupled signaling receptors, we demonstrate that musclin enhances cGMP production in cultured myoblasts only when applied together with ANP. Elimination of the activity-related musclin-dependent boost of ANP/cGMP signaling results in significantly lower maximum aerobic capacity, mitochondrial protein content, respiratory complex protein expression, and succinate dehydrogenase activity in skeletal muscles. Together, these data indicate that musclin enhances physical endurance by promoting mitochondrial biogenesis.

ChAkt1 involvement in orchestrating the immune and heat shock responses in Crassostrea hongkongensis: Molecular cloning and functional characterization

G-protein-coupled receptors (GPCRs) are the largest class of cell-surface receptors and play crucial roles in virtually every organ system. As one of the major downstream effectors of GPCRs, Akt can acquire information from the receptors and coordinate intracellular responses for many signaling pathways, through which the serine/threonine kinase masters numerous aspects of biological processes, such as cell survival, growth, proliferation, migration, angiogenesis, and metabolism. In the present study, we have characterized the first Akt1 ortholog in mollusks using the Hong Kong oyster, Crassostrea hongkongensis (designed ChAkt1). The full-length cDNA is 2223 bp and encodes a putative protein of 493 amino acids that contains an amino-terminal pleckstin homology (PH) domain, a central catalytic domain, and a carboxy-terminal regulatory domain. Quantitative real-time PCR analysis showed that ChAkt1 mRNA is broadly expressed in various tissues and during different stages of the oyster's embryonic and larval development. Upon exposure to two stressors (microbial infection and heat shock), the expression level of ChAkt1 mRNA increases significantly. Furthermore, ChAkt1 is located in the cytoplasm in HEK293T cells, where the over-expression of ChAkt1 regulates the transcriptional activities of NF-κB and p53 reporter genes. Taken together, our results indicate that ChAkt1 most likely plays a central role in response to various stimuli in oysters and has a particular response to microbial pathogens and high temperature.

Mitogen-activated protein kinase-activated protein kinase 2 mediates resistance to hydrogen peroxide-induced oxidative stress in human hepatobiliary cancer cells

The development and progression of liver cancer are characterized by increased levels of reactive oxygen species (ROS). ROS-induced oxidative stress impairs cell proliferation and ultimately leads to cell death. Although liver cancer cells are especially resistant to oxidative stress, mechanisms of such resistance remain understudied. We identified the MAPK-activated protein kinase 2 (MK2)/heat shock protein 27 (Hsp27) signaling pathway mediating defenses against oxidative stress. In addition to MK2 and Hsp27 overexpression in primary liver tumors compared to adjacent nontumorous tissues, the MK2/Hsp27 pathway is activated by hydrogen peroxide-induced oxidative stress in hepatobiliary cancer cells. MK2 inactivation or inhibition of MK2 or Hsp27 expression increases caspase-3 and PARP cleavage and DNA breaks and therefore cell death. Interestingly, MK2/Hsp27 inhibition decreases antioxidant defenses such as heme oxygenase 1 through downregulation of the transcription factor nuclear factor erythroid-derived 2-like 2. Moreover, MK2/Hsp27 inhibition decreases both phosphorylation of epidermal growth factor receptor (EGFR) and expression of its ligand, heparin-binding EGF-like growth factor. A new identified partner of MK2, the scaffold PDZ protein EBP50, could facilitate these effects through MK2/Hsp27 pathway regulation. These findings demonstrate that the MK2/Hsp27 pathway actively participates in resistance to oxidative stress and may contribute to liver cancer progression.

Inhibition of PI3K Signalling Selectively Affects Medulloblastoma Cancer Stem Cells

Medulloblastoma is the most common malignant brain tumor of childhood. Although survival has slowly increased in the past years, the prognosis of these patients remains unfavourable. In this context, it has been recently shown that the intracellular signaling pathways activated during embryonic cerebellar development are deregulated in MDB. One of the most important is PI3K/AKT/mTOR, implicated in cell proliferation, survival, growth, and protein synthesis. Moreover, a fraction of MDB cells has been shown to posses stemlike features, to express typical neuronal precursor markers (Nestin and CD133), and to be maintained by the hypoxic cerebellar microenvironment. This subpopulation of MDB cells is considered to be responsible for treatment resistance and recurrence. In this study, we evaluated the effects of PI3K/AKT pathway inhibition on primary cultures of MDB and particularly on the cancer stem cell (CSC) population (CD133⁺). PI3K inhibition was able to counteract MDB cell growth and to promote differentiation of stemlike MDB cells. Moreover, PI3K/AKT pathway suppression induced dramatic cell death through activation of the mitochondrial proapoptotic cascade. Finally, analysis on the stem cells fraction revealed that the MDB CSC population is more sensitive to PI3K targeting compared to the whole cancerous population and its nonstem cell counterpart.

TORC2 mediates the heat stress response in Drosophila by promoting the formation of stress granules

The kinase TOR is found in two complexes, TORC1, which is involved in growth control, and TORC2, whose roles are less well defined. Here, we asked whether TORC2 has a role in sustaining cellular stress. We show that TORC2 inhibition in Drosophila melanogaster leads to a reduced tolerance to heat stress, whereas sensitivity to other stresses is not affected. Accordingly, we show that upon heat stress, both in the animal and Drosophila cultured S2 cells, TORC2 is activated and is required for maintaining the level of its known target, Akt1 (also known as PKB). We show that the phosphorylation of the stress-activated protein kinases is not modulated by TORC2 nor is the heat-induced upregulation of heat-shock proteins. Instead, we show, both in vivo and in cultured cells, that TORC2 is required for the assembly of heat-induced cytoprotective ribonucleoprotein particles, the pro-survival stress granules. These granules are formed in response to protein translation inhibition imposed by heat stress that appears to be less efficient in the absence of TORC2 function. We propose that TORC2 mediates heat resistance in Drosophila by promoting the cell autonomous formation of stress granules.

Regulation of eNOS enzyme activity by posttranslational modification

The regulation of endothelial NO synthase (eNOS) employs multiple different cellular control mechanisms impinging on level and activity of the enzyme. This review aims at summarizing the current knowledge on the posttranslational modifications of eNOS, including acylation, nitrosylation, phosphorylation, acetylation, glycosylation and glutathionylation. Sites, mediators and impact on enzyme localization and activity of the single modifications will be discussed. Moreover, interdependence, cooperativity and competition between the different posttranslational modifications will be elaborated with special emphasis on the susceptibility of eNOS to metabolic cues.

Helium preconditioning protects mouse liver against ischemia and reperfusion injury through the PI3K/Akt pathway

BACKGROUND & AIMS

Hepatic ischemia and reperfusion (I/R) injury is a major complication of liver transplantation, hepatic resection and trauma. Helium preconditioning (HPC) exerts protection against ischemic stress. We investigated potential beneficial effects of HPC on I/R-induced liver injury and investigated mechanisms underlying HPC-induced protection.

METHODS

We employed a model of segmental warm hepatic I/R on BALB/c mice. Serum ALT was measured and livers were analysed by histology, RT-PCR and western blot. HPC was induced by inhalation of a 70% helium/30% oxygen mixture for three 5-min periods, interspersed with three 5-min washout periods by room air. We tested which component of HPC (the helium/air mixture inhalation, the air room gap, or the interaction between these two factors) is protective.

RESULTS

We found that HPC caused a significant increase in Akt phosphorylation in hepatocytes. The HPC-induced Akt phosphorylation resulted in decreased hepatocellular injury and improved survival rate of the treated animals. PI3K inhibitors abolished HPC induced effects. HPC-induced Akt phosphorylation affected expression of its downstream molecules. The effects of HPC on the PI3K/Akt pathway were attenuated by adenosine A2A receptor blockade, but could be re-established by PTEN inhibition. We demonstrated that the interaction of helium/air breathing and air gaps is responsible for the observed effects of HPC.

CONCLUSIONS

HPC may be a promising strategy leading to a decrease in I/R induced liver injury in clinical settings. Additionally, the PI3K/Akt pathway plays an essential role in the protective effects of HPC in hepatic I/R injury.

Gene silencing mediated by endogenous microRNAs under heat stress conditions in mammalian cells

Heat shock, sudden change in temperature, triggers various responses in cells for protecting the cells from such a severe circumstance. Here we investigated gene silencing mediated by endogenous microRNAs (miRNAs) in mammalian cells exposed to a mild hyperthermia, by means of miRNA activity assay using a luciferase reporter gene as well as miRNA expression analysis using a DNA microarray. Our findings indicated that the gene silencing activities involving miRNAs were enhanced without increasing in their expression levels under heat-stress conditions. Additionally, the gene silencing activity appeared to be independent of the cytoprotective action involving heat shock proteins that are immediately activated in heat-shocked cells and that function as molecular chaperons for restoring heat-denatured proteins to normal proteins. Our current findings suggested the possibility that gene silencing involving endogenous miRNAs might play a subsidiary role in heat-shocked cells for an aggressive inhibition of the expression of heat-denatured proteins.

Stem cells, redox signaling, and stem cell aging

SIGNIFICANCE

Functional stem cell decline has been postulated to result in loss of maintenance of tissue homeostasis leading to organismal decline and diseases of aging.

RECENT ADVANCES

Recent findings implicate redox metabolism in the control of stem cell pool and stem cell aging. Although reactive oxygen species (ROS) are better known for their damaging properties to DNA, proteins and lipids, recent findings suggest that ROS may also be an integral physiological mediator of cellular signaling in primary cells.

CRITICAL ISSUES

Here we review recent published work on major signaling pathways and transcription factors that are regulated by ROS and mediate ROS regulation of stem cell fate. We will specifically focus on how alterations in this regulation may be implicated in disease and particularly in diseases of stem cell aging. In general, based on the work described here we propose a model in which ROS function as stem cell rheostat.

FUTURE DIRECTIONS

Future work in elucidating how ROS control stem cell cycling, apoptotic machinery, and lineage determination should shed light on mechanisms whereby ROS may control stem cell aging.

Long-term exposure of 3T3 fibroblast cells to endocrine disruptors alters sensitivity to oxidative injury

When Swiss 3T3 fibroblasts were exposed to bisphenol A (BPA) or nonylphenol (NP) within a range of 0.1-100 nM for 30-45 days, increased resistance to oxidative injury was found. Western blot analysis indicated concomitant increased expression of bcl-2 protein and reduced histone methylation levels in cells after BPA or NP exposure. Using a heterologous expression system, both chemicals could stimulate G protein-coupled receptor 30 (GPR30), a transmembrane estrogen receptor predominantly expressed in 3T3 cells, at lower concentrations, which gave increased survival. Taken together, these results suggest that BPA or NP exposure might cause alterations in cellular activity against oxidative stress, possibly through GPR30.

Hydrogen peroxide sensing, signaling and regulation of transcription factors

The regulatory mechanisms by which hydrogen peroxide (H₂O₂) modulates the activity of transcription factors in bacteria (OxyR and PerR), lower eukaryotes (Yap1, Maf1, Hsf1 and Msn2/4) and mammalian cells (AP-1, NRF2, CREB, HSF1, HIF-1, TP53, NF-κB, NOTCH, SP1 and SCREB-1) are reviewed. The complexity of regulatory networks increases throughout the phylogenetic tree, reaching a high level of complexity in mammalians. Multiple H₂O₂ sensors and pathways are triggered converging in the regulation of transcription factors at several levels: (1) synthesis of the transcription factor by upregulating transcription or increasing both mRNA stability and translation; (ii) stability of the transcription factor by decreasing its association with the ubiquitin E3 ligase complex or by inhibiting this complex; (iii) cytoplasm–nuclear traffic by exposing/masking nuclear localization signals, or by releasing the transcription factor from partners or from membrane anchors; and (iv) DNA binding and nuclear transactivation by modulating transcription factor affinity towards DNA, co-activators or repressors, and by targeting specific regions of chromatin to activate individual genes. We also discuss how H₂O₂ biological specificity results from diverse thiol protein sensors, with different reactivity of their sulfhydryl groups towards H₂O₂, being activated by different concentrations and times of exposure to H₂O₂. The specific regulation of local H₂O₂ concentrations is also crucial and results from H₂O₂ localized production and removal controlled by signals. Finally, we formulate equations to extract from typical experiments quantitative data concerning H₂O₂ reactivity with sensor molecules. Rate constants of 140 M⁻¹ s⁻¹ and ≥1.3 × 10³ M⁻¹ s⁻¹ were estimated, respectively, for the reaction of H₂O₂ with KEAP1 and with an unknown target that mediates NRF2 protein synthesis. In conclusion, the multitude of H₂O₂ targets and mechanisms provides an opportunity for highly specific effects on gene regulation that depend on the cell type and on signals received from the cellular microenvironment.

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Complexity of redox regulation increases along the phylogenetic tree.

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Complex regulatory networks allow for a high degree of H₂O₂ biological plasticity.

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H₂O₂ modulates gene expression at all steps from transcription to protein synthesis.

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Fast response (s) is mediated by sensors with high H₂O₂ reactivity.

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Low reactivity H₂O₂ sensors may mediate slow (h) or localized H₂O₂ responses.

The emerging role of mTOR signalling in antibacterial immunity

Mammalian target of rapamycin (mTOR) is a central regulator of cellular metabolic homeostasis that is highly conserved in evolution. Recent evidence has revealed the existence of a complex interplay between mTOR signalling and immunity. We review here the emerging role of mTOR signalling in the regulation of Toll-like receptor-dependent innate responses and in the activation of T cells and antigen-presenting cells. We also highlight the importance of amino-acid starvation-driven mTOR inhibition in the control of autophagy and intracellular bacterial clearance.

Bidirectional regulation of NF-κB by reactive oxygen species: a role of unfolded protein response

Nuclear factor-κB (NF-κB) is a transcription factor that plays a crucial role in coordinating innate and adaptive immunity, inflammation, and apoptotic cell death. NF-κB is activated by various inflammatory stimuli including peptide factors and infectious microbes. It is also known as a redox-sensitive transcription factor activated by reactive oxygen species (ROS). Over the past decades, various investigators focused on the role of ROS in the activation of NF-κB by cytokines and lipopolysaccharides. However, recent studies also suggested that ROS have the potential to repress NF-κB activity. Currently, it is not well addressed how ROS regulate activity of NF-κB in a bidirectional fashion. In this paper, we summarize evidence for positive and negative regulation of NF-κB by ROS, possible redox-sensitive targets for NF-κB signaling, and mechanisms underlying biphasic and bidirectional influences of ROS on NF-κB, especially focusing on a role of ROS-mediated induction of endoplasmic reticulum stress.

Vasopressin activates Akt/mTOR pathway in smooth muscle cells cultured in high glucose concentration

Mammalian target of rapamycin (mTOR) complex is a key regulator of autophagy, cell growth and proliferation. Here, we studied the effects of arginine vasopressin (AVP) on mTOR activation in vascular smooth muscle cells cultured in high glucose concentration. AVP induced the mTOR phosphorylation in A-10 cells grown in high glucose, in contrast to cells cultured in normal glucose; wherein, only basal phosphorylation was observed. The AVP-induced mTOR phosphorylation was inhibited by a PI3K inhibitor. Moreover, the AVP-induced mTOR activation inhibited autophagy and increased thymidine incorporation in cells grown in high glucose. This increase was abolished by rapamycin which inhibits the mTORC1 complex formation. Our results suggest that AVP stimulates mTOR phosphorylation by activating the PI3K/Akt signaling pathway and, subsequently, inhibits autophagy and raises cell proliferation in A-10 cells maintained in high glucose concentration.

Role of oxidative and nitrosative stress in autogenous bone grafts to the mandible using guided bone regeneration and a deproteinized bovine bone material

The aim of this study was to evaluate the role of oxidative and nitrosative stress in autogenous bone grafts to the mandible based on immunohistochemical analysis.

MATERIAL AND METHODS

Using a well-established sheep model autogenous bone grafts were harvested form the iliac bone. A combination of a Collagen Membrane (CM) and Deproteinized Bovine Bone Material (DBBM) was used to cover the bone graft (Experiment 2). This modification was compared with simple onlay bone grafts (Experiment 1). Immunohistochemically, the expression of specific stable degradation products of oxidative and nitrosative stress was compared between the two experimental groups.

RESULTS

Specific markers for oxidative and nitrosative stress showed statistically significant differences in expression in the different experimental groups. The influence of oxidative and nitrosative stress on osteoblasts (OB), osteoclasts (OC), and osteocytes (OCy) was analysed. Experiment 2 showed increased expression of markers in OB and decreased expression in OC.

CONCLUSIONS

Taking the result of this study and reports from the literature into consideration grafts in Experiment 2 showed less resorption and atrophy, higher activity of OB and inhibition of OC, and less expression of Reactive Oxygen and Nitrogen Species (RONS) as markers of oxidative stress within the graft. These data illustrate the improved remodelling processes in grafts using CM and DBBM.

Cross talk between the Akt and p38α pathways in macrophages downstream of Toll-like receptor signaling

The stimulation of Toll-like receptors (TLRs) on macrophages by pathogen-associated molecular patterns (PAMPs) results in the activation of intracellular signaling pathways that are required for initiating a host immune response. Both phosphatidylinositol 3-kinase (PI3K)-Akt and p38 mitogen-activated protein kinase (MAPK) signaling pathways are activated rapidly in response to TLR activation and are required to coordinate effective host responses to pathogen invasion. In this study, we analyzed the role of the p38-dependent kinases MK2/3 in the activation of Akt and show that lipopolysaccharide (LPS)-induced phosphorylation of Akt on Thr308 and Ser473 requires p38α and MK2/3. In cells treated with p38 inhibitors or an MK2/3 inhibitor, phosphorylation of Akt on Ser473 and Thr308 is reduced and Akt activity is inhibited. Furthermore, BMDMs deficient in MK2/3 display greatly reduced phosphorylation of Ser473 and Thr308 following TLR stimulation. However, MK2/3 do not directly phosphorylate Akt in macrophages but act upstream of PDK1 and mTORC2 to regulate Akt phosphorylation. Akt is recruited to phosphatidylinositol 3,4,5-trisphosphate (PIP3) in the membrane, where it is activated by PDK1 and mTORC2. Analysis of lipid levels in MK2/3-deficient bone marrow-derived macrophages (BMDMs) revealed a role for MK2/3 in regulating Akt activity by affecting availability of PIP3 at the membrane. These data describe a novel role for p38α-MK2/3 in regulating TLR-induced Akt activation in macrophages.

Redox regulation of protein kinases

Protein kinases represent one of the largest families of genes found in eukaryotes. Kinases mediate distinct cellular processes ranging from proliferation, differentiation, survival, and apoptosis. Ligand-mediated activation of receptor kinases can lead to the production of endogenous hydrogen peroxide (H₂O₂) by membrane-bound NADPH oxidases. In turn, H₂O₂ can be utilized as a secondary messenger in signal transduction pathways. This review presents an overview of the molecular mechanisms involved in redox regulation of protein kinases and its effects on signaling cascades. In the first half, we will focus primarily on receptor tyrosine kinases (RTKs), whereas the latter will concentrate on downstream non-receptor kinases involved in relaying stimulant response. Select examples from the literature are used to highlight the functional role of H₂O₂ regarding kinase activity, as well as the components involved in H₂O₂ production and regulation during cellular signaling. In addition, studies demonstrating direct modulation of protein kinases by H₂O₂ through cysteine oxidation will be emphasized. Identification of these redox-sensitive residues may help uncover signaling mechanisms conserved within kinase subfamilies. In some cases, these residues can even be exploited as targets for the development of new therapeutics. Continued efforts in this field will further basic understanding of kinase redox regulation, and delineate the mechanisms involved in physiological and pathological H₂O₂ responses.

Heat stress activates the Akt/mTOR signalling pathway in rat skeletal muscle

AIM

It is well known that various stimuli, such as mechanical stress and nutrients, induce muscle hypertrophy thorough the Akt/mTOR signalling pathway, which is a key mediator of protein synthesis and hypertrophy in skeletal muscle. It was recently reported that heat stress also induces an increase in muscle weight and muscle protein content. In addition, heat stress enhances Akt/mTOR signalling after one bout of resistance exercise. However, it remains unclear whether increased temperature itself stimulates the Akt/mTOR signalling pathway.

METHODS

Forty-two male Wistar rats (279.5 ± 1.2 g) were divided into a control group (CON) or one of five thermal stress groups at 37, 38, 39, 40 or 41 °C (n = 7 each group). After overnight fasting, both legs were immersed in different temperatures of hot water for 30 min under sodium pentobarbital anaesthesia. The soleus and plantaris muscles were immediately removed from both legs after the thermal stress.

RESULTS

The phosphorylation of mTOR or 4E-BP1 and heat shock protein (HSP) expression levels were similar among groups in both the soleus and plantaris muscles. However, Akt and p70S6K phosphorylation significantly increased at 41 °C in the soleus and plantaris muscles. Moreover, we observed a temperature-dependent increase in Akt and p70S6K phosphorylation in both muscles.

CONCLUSION

Our data indicate that the altered temperature increased phosphorylation in a temperature-dependent manner in rat skeletal muscle and may itself be a key stimulator of Akt/mTOR signalling.

Suppression of inflammatory responses during myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis is regulated by AKT3 signaling

AKT3, a member of the serine/threonine kinase AKT family, is involved in a variety of biologic processes. AKT3 is expressed in immune cells and is the major AKT isoform in the CNS representing 30% of the total AKT expressed in spinal cord, and 50% in the brain. Myelin-oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE) is a mouse model in which lymphocytes and monocytes enter the CNS, resulting in inflammation, demyelination, and axonal injury. We hypothesized that during EAE, deletion of AKT3 would negatively affect the CNS of AKT3(-/-) mice, making them more susceptible to CNS damage. During acute EAE, AKT3(-/-)mice were more severely affected than wild type (WT) mice. Evaluation of spinal cords showed that during acute and chronic disease, AKT3(-/-) spinal cords had more demyelination compared with WT spinal cords. Quantitative RT-PCR determined higher levels of IL-2, IL-17, and IFN-γ mRNA in spinal cords from AKT3(-/-) mice than WT. Experiments using bone marrow chimeras demonstrated that AKT3(-/-) mice receiving AKT3-deficient bone marrow cells had elevated clinical scores relative to control WT mice reconstituted with WT cells, indicating that altered function of both CNS cells and bone marrow-derived immune cells contributed to the phenotype. Immunohistochemical analysis revealed decreased numbers of Foxp3(+) regulatory T cells in the spinal cord of AKT3(-/-) mice compared with WT mice, whereas in vitro suppression assays showed that AKT3-deficient Th cells were less susceptible to regulatory T cell-mediated suppression than their WT counterparts. These results indicate that AKT3 signaling contributes to the protection of mice against EAE.

Early transformative changes in normal ovarian surface epithelium induced by oxidative stress require Akt upregulation, DNA damage and epithelial-stromal interaction

Ovarian cancer is the deadliest gynecological malignancy due to detection of cancer at a late stage when the disease has metastasized. One likely progenitor cell type of ovarian cancer is the ovarian surface epithelium (OSE), which proliferates rapidly in the presence of inflammatory cytokines and oxidative stress following ovulation. To determine whether oxidative stress induces DNA damage leading to spontaneous transformative changes in normal OSE, an immortalized mouse OSE cell line (MOSE cells) or normal mouse ovarian organoids were treated with hydrogen peroxide (H2O2) and loss of contact inhibition was assessed by soft agar assay. In response to H2O2, OSE cells grown in 3D exhibited growth in soft agar but MOSE cells grown on 2D plastic did not, indicating a critical role for epithelial-stromal interactions in neoplastic initiation. Loss of contact inhibition in response to H2O2 correlated with an increase in proliferation, DNA damage and upregulation of the oncogene Akt1. Use of a reactive oxygen species scavenger or Akt inhibitor blocked H2O2-induced proliferation and growth in soft agar. Although parental MOSE cells did not undergo transformation by H2O2, MOSE cells stably overexpressing constitutively active myristoylated Akt or knockdown of phosphatase and tensin homolog (PTEN) exhibited loss of contact inhibition and increased proliferation. This study indicates that normal OSE undergo transformative changes induced by oxidative stress and that this process requires Akt upregulation and activation. A 3D model that retains tissue architecture is critical for studying this process and may lead to development of new intervention strategies directed at early stages of ovarian cancer.

Cigarette smoke extract stimulates epithelial-mesenchymal transition through Src activation

Epithelial-mesenchymal transition (EMT) is implicated in the pathogenesis of lung fibrosis and cancer metastasis, two conditions associated with cigarette smoke (CS). CS has been reported to promote the EMT process. CS is the major cause of lung cancer and nearly half of lung cancer patients are active smokers. Nonetheless, the mechanism whereby CS induces EMT remains largely unknown. In this study we investigated the induction of EMT by CS and explored the underlying mechanisms in the human non-small-cell lung carcinoma (H358) cell line. We demonstrate that exposure to an extract of CS (CSE) decreases E-cadherin and increases N-cadherin and vimentin, markers of EMT, in H358 cells cultured in RPMI 1640 medium with 1% fetal bovine serum. Pretreatment with N-acetylcysteine (NAC), a potent antioxidant and precursor of glutathione, abrogated changes in these EMT markers. In addition, CSE activated Src kinase (shown as increased phosphorylation of Src at Tyr418), and the Src kinase inhibitor PP2 inhibited CS-stimulated EMT changes, suggesting that Src is critical in CSE-stimulated EMT induction. Furthermore, NAC treatment abrogated CSE-stimulated Src activation. However, co-incubation with catalase had no effect on CSE-mediated Src activation. Finally, acrolein, an unsaturated aldehyde present in CSE, caused Src activation. Taken together, these data suggest that CSE initiates EMT through Src, which is activated by CS through redox modification.

Heat shock protein 72 inhibits c-Jun N-terminal kinase 3 signaling pathway via Akt1 during cerebral ischemia

Although recent researches show that Heat Shock Protein 72 (HSP72) plays an important role in neuronal survival, little knowledge is known about the precise mechanisms during cerebral ischemia/reperfusion (I/R). Our present study investigated the neuroprotective mechanisms of HSP72 against ischemic brain injury induced by cerebral I/R. Mild heat shock pretreatment was employed to induce the overexpression of HSP72 by immersing rats into the water bath at 42°C for 20 min before cerebral I/R. HSP72 antisense oligodeoxynucleotides (ODNs) were used to inhibit HSP72 expression by intracerebroventricular infusion once per day for 3 days before cerebral I/R animal model was induced by four-vessel occlusion for 15 min transient ischemia and then reperfused for various time in Sprague-Dawley rats. Immunoprecipitation and immunoblotting were used to detect the expression of the related proteins. HE-staining and TUNEL-staining were carried out to examine the neuronal death of hippocampal CA1 region. Results showed that mild heat shock could increase the phosphorylation of protein kinase B (Akt), inhibit the assembly of MLK3-MKK7-JNK3 signaling module, diminish the phosphorylation of JNK3 and c-Jun, and decrease the activation of caspase-3. Furthermore, mild heat shock could significantly protect neurons against cerebral I/R. Whereas, all of the aforementioned effects of mild heat shock were reversed by HSP72 antisense ODNs. In summary, our results imply that Akt1 activation is involved in the neuroprotection of HSP72 against ischemic brain injury via suppressing JNK3 signaling pathway and provide a new experimental foundation for stroke therapy.

Identification of Akt interaction protein PHF20/TZP that transcriptionally regulates p53

Akt regulates a diverse array of cellular functions, including cell survival, proliferation, differentiation, and metabolism. Although a number of molecules have been identified as upstream regulators and downstream targets of Akt, the mechanisms by which Akt regulates these cellular processes remain elusive. Here, we demonstrate that a novel transcription factor, PHF20/TZP (referring to Tudor and zinc finger domain containing protein), binds to Akt and induces p53 expression at the transcription level. Knockdown of PHF20 significantly reduces p53. PHF20 inhibits cell growth, DNA synthesis, and cell survival. Akt phosphorylates PHF20 at Ser(291) in vitro and in vivo, which results in its translocation from the nucleus to the cytoplasm and attenuation of PHF20 function. These data indicate that PHF20 is a substrate of Akt and plays a role in Akt cell survival/growth signaling.

Therapeutic strategies for head and neck cancer based on p53 status

Squamous cell carcinomas of the head and neck (HNSCC) are one of the most common types of cancers worldwide, and despite advances in treatment, they still represent a clinical challenge. Inactivation of one or more components in the p53 signaling pathway is an extremely common event in human neoplasia, including HNSCC. The loss of p53 function is responsible for increased aggressiveness in cancers, while tumor chemoresistance and radioresistance can depend on deleted p53 expression, or on the expression of mutated-p53 proteins. Thus, consideration and manipulation of the p53 status during HNSCC cancer therapy should be considered. This review discusses the p53 signaling pathways activated by various cellular stresses, including exposure to cancer therapies. The recognition of the p53 status in cancer cells is a significant factor and could provide valuable assistance during the selection of an effective therapeutic approach.

LPS induced inflammatory responses in human peripheral blood mononuclear cells is mediated through NOX4 and Giα dependent PI-3kinase signalling

COPD is a disease of innate immunity and bacterial infections are a dominant cause of exacerbations in the later stages resulting in poor health and high mortality. The pathogen-associated molecular pattern (PAMP) lipopolysaccharide (LPS) is sensed by immune cells through activation of the toll-like receptor 4 (TLR4). This leads to the activation of NADPH oxidase (NOX) and NF-κB which together drive COPD inflammation. In this study we show in human PBMCs that LPS stimulated proinflammatory cytokine release (CXCL8 and IL6) was inhibited by approximately 50% by the broad specificity phosphatidylinositol 3-kinase (PI3K) inhibitor, wortmannin. Our results also demonstrate that activation of PI3K following LPS stimulation is mediated by a NOX4 dependent mechanism releasing endogenous H2O2, as the NOX4 inhibitor apocynin blocked LPS induced AKT phosphorylation. Moreover, LPS-induced PI3K activation was inhibited by the anti-oxidant N-acetylcysteine in a concentration dependent manner (IC50 ~100 μM). In addition, our data demonstrated that inhibition of small G proteins, by pre-treatment with pertussis toxin, inhibited LPS-induced AKT phosphorylation. Furthermore, the G-protein inhibitors pertussis toxin and mastoparan both inhibited LPS-induced CXCL8 and IL-6 release by approximately 50%. Together, these data indicate there is a mechanism in human PBMCs where TLR4 activation by LPS leads to ROS generation through NOX4 and activation of the PI3K pathway. This effect is apparently mediated through small G proteins facilitating the release of pro-inflammatory cytokines.

Tyr740 and Tyr751 residues of platelet-derived growth factor beta receptor are responsible for the redox regulation of phosphatase and tensin homolog in the cells stimulated with platelet-derived growth factor

Exposure of cells to hydrogen peroxide or platelet-derived growth factor (PDGF) induced Akt phosphorylation and oxidation of phosphatase and tensin homolog (PTEN). The Cys124 and Cys71 residues of PTEN were critical for the formation of a disulfide bond and the intermediate glutathionylation in the process of reduction of the disulfide bond. To determine which specific tyrosine residues of the PDGF beta receptor (PDGFβR) is involved in PDGF-induced PTEN oxidation and Akt phosphorylation, we investigated a kinase activity-deficient mutant and PDGFβR mutants where the tyrosine residues in the binding site for phosphoinositide 3-kinase (PI3K), GTPase-activating protein of Ras, Src homology 2 domain containing protein-tyrosine phosphatase-2, and phospholipase C-1 were replaced by Phe. Both PTEN oxidation and Akt phosphorylation did not occur in response to PDGF in the kinase-deficient mutant and in the PDGFβR mutant with a mutation in the PI3K binding site (Tyr740 and Tyr751). Thus, the kinase activity and the constituent Tyr740 and Tyr751 residues of PDGFβR in the cells stimulated with PDGF are responsible for the oxidation of PTEN and the Akt phosphorylation.

Ankrd2/ARPP is a novel Akt2 specific substrate and regulates myogenic differentiation upon cellular exposure to H(2)O(2)

A proteomic-based search for novel substrates of Akt was undertaken in C₂C₁₂ murine muscle cells. Our data demonstrate that Akt isoform 2 phosphorylates Ankrd2 at Serine 99 in response to H₂O₂ stimuli, regulating muscle differentiation rate.

Activation of Akt-mediated signaling pathways is crucial for survival, differentiation, and regeneration of muscle cells. A proteomic-based search for novel substrates of Akt was therefore undertaken in C₂C₁₂ murine muscle cells exploiting protein characterization databases in combination with an anti–phospho-Akt substrate antibody. A Scansite database search predicted Ankrd2 (Ankyrin repeat domain protein 2, also known as ARPP) as a novel substrate of Akt. In vitro and in vivo studies confirmed that Akt phosphorylates Ankrd2 at Ser-99. Moreover, by kinase assay with recombinant Akt1 and Akt2, as well as by single-isoform silencing, we demonstrated that Ankrd2 is a specific substrate of Akt2. Ankrd2 is typically found in skeletal muscle cells, where it mediates the transcriptional response to stress conditions. In an attempt to investigate the physiological implications of Ankrd2 phosphorylation by Akt2, we found that oxidative stress induced by H₂O₂ triggers this phosphorylation. Moreover, the forced expression of a phosphorylation-defective mutant form of Ankrd2 in C₂C₁₂ myoblasts promoted a faster differentiation program, implicating Akt-dependent phosphorylation at Ser-99 in the negative regulation of myogenesis in response to stress conditions.

Signaling and Damaging Functions of Free Radicals in Aging-Free Radical Theory, Hormesis, and TOR

Harman's Free Radical Theory of Aging has been considered as a major theory of aging for more than 50 years. In 1956 Dr. Harman proposed that the accumulation of free radicals with the age causes the damage of biomolecules by these reactive species and the development of pathological disorders resulting in cell senescence and organismal aging. His hypothesis was supported by numerous experimental studies demonstrated an increase in free radical levels in cells and living organisms with aging. In subsequent years important discoveries of new physiological free radicals superoxide and nitric oxide have been made that led to understanding of other important functions of free radicals. It has been shown that superoxide and nitric oxide together with their diamagnetic reaction products hydrogen peroxide and peroxynitrite (all are now named reactive oxygen and nitrogen species, ROS and RNS) function as signaling species in many physiological enzymatic/gene processes. Furthermore, the disturbance of ROS and RNS physiological signaling can be an origin of various pathologies and aging. These discoveries demanded to widen original free radical theory of aging and to consider the damaging ROS signaling as an important, maybe major route to cell senescence and organismal aging. However, some experimental findings such as the extension of lifespan by calorie restriction of yeast, flies, worms, and mice, and favorable effects of physical exercises stimulated criticism of free radical theory because the expansion of lifespan accompanied in some cases by increasing oxidative stress. On these grounds such theories as Hormesis and Target of rapamycin (mTOR) theories refute the role of ROS and oxidative stress in aging. Accordingly, a major purpose of this review to show that ROS signaling is probably the most important enzyme/gene pathway responsible for the development of cell senescence and organismal aging and that ROS signaling might be considered as further development of free radical theory of aging. In spite of apparent contradictions the Hormesis or TOR theories are also describing processes of aging development regulated by ROS signaling.

Functional characterization of a haplotype in the AKT1 gene associated with glucose homeostasis and metabolic syndrome

A small 12-kb haplotype upstream of the AKT1 gene has been found to be associated with insulin resistance phenotypes. We sought to define the functional consequences of the three component polymorphic loci (rs1130214, rs10141867, rs33925946) on AKT1 and the upstream ZBTB42 gene. 5' RACE analysis of AKT1 transcripts in human skeletal muscle biopsies showed the predominant promoter to be 2.5 kb upstream of exon 2, and distinct from those promoters previously reported in rat. We then studied the effect of each of the three haplotype polymorphisms in transcriptional reporter assays in muscle, bone, and fat cell culture models, and found that each modulated enhancer and repressor activity are in a cell-specific and differentiation-specific manner. Our results in promoter assays are consistent with the human phenotype data; we found an anabolic effect on muscle and bone with increased mRNA expression of AKT1, and catabolic effect on fat with decreased expression. To test the hypothesis that rs10141867 affects transcription levels of the novel zinc finger protein ZBTB42 in vivo, we developed the allele-specific expression assay using Taqman technology to test for allelic differences within heterozygotes. The allele containing the derived polymorphism (haplotype H2) showed a 1.75-fold increase in expression in human skeletal muscle. Our data show a particularly complex effect of the component polymorphisms of a single haplotype on cells and tissues, suggesting that the coordination of different tissue-specific effects may have driven selection for the H2 haplotype. In light of the recent abundance of SNP association studies, our approach can serve as a method for exploring the biological function of polymorphisms that show significant genotype/phenotype associations.

Erythropoietin increases expression and function of vascular copper- and zinc-containing superoxide dismutase

Previous studies have shown that treatment with erythropoietin (EPO) exerts vascular protective effects. The exact mechanisms responsible for these effects are not completely understood. In the present study, we hypothesized that EPO stimulates expression and activity of copper- and zinc-containing superoxide dismutase (SOD1), thus protecting vascular tissue from oxidative stress induced by excessive concentrations of superoxide anions. EPO treatment of wild-type mice for 2 weeks (1000 U/kg, SC, biweekly) significantly increased aortic expression of SOD1. This effect resulted in a significant reduction of superoxide anion concentrations in aorta of treated mice. The ability of EPO to reduce vascular production of superoxide anions was abolished in SOD1-deficient mice. In a mouse model of wire-induced injury of the common carotid artery, treatment of wild-type mice with EPO prevented pathological remodeling, whereas the vascular effect of EPO was absent in SOD1-deficient mice. Our findings demonstrate that treatment with EPO increases vascular expression of SOD1. This effect appears to be an important molecular mechanism underlying vascular protection by EPO.

Redox regulation of tumor necrosis factor signaling

Tumor necrosis factor-alpha (TNF) is a key cytokine that has been shown to play important physiologic (e.g., inflammation) and pathophysiologic (e.g., various liver pathologies) roles. In liver and other tissues, TNF treatment results in the simultaneous activation of an apoptotic pathway (i.e., TRADD, RIP, JNK) and a survival pathway mediated by NF-kappaB transcription of survival genes (i.e., GADD45beta, Mn-SOD, cFLIP). The cellular response (e.g., proliferation versus apoptosis) to TNF is determined by the balance between the apoptotic signaling pathway and the NF-kappaB survival pathway stimulated by TNF. Reactive oxygen species (ROS) are important modulators of signaling pathways and can regulate both apoptotic signaling and NF-kappaB transcription triggered by TNF. ROS are important in mediating the sustained activation of JNK, to help mediate apoptosis after TNF treatment. In some cells, ROS are second messengers that mediate apoptosis after TNF stimulation. Conversely, ROS can cause redox modifications that inhibit NF-kappaB activation, which can lead to cell death triggered by TNF. Consequently, the redox status of cells can determine the biologic response that TNF will induce in cells. In many liver pathologies, ROS generated extrinsically (e.g., inflammation) or intrinsically (i.e., drugs, toxins) may act in concert with TNF to promote hepatocyte death and liver injury through redox inhibition of NF-kappaB.