Activation of protein kinase B induced by H(2)O(2) and heat shock through distinct mechanisms dependent and independent of phosphatidylinositol 3-kinase

Targeting Akt in cancer for precision therapy

Biomarkers-guided precision therapeutics has revolutionized the clinical development and administration of molecular-targeted anticancer agents. Tailored precision cancer therapy exhibits better response rate compared to unselective treatment. Protein kinases have critical roles in cell signaling, metabolism, proliferation, survival and migration. Aberrant activation of protein kinases is critical for tumor growth and progression. Hence, protein kinases are key targets for molecular targeted cancer therapy. The serine/threonine kinase Akt is frequently activated in various types of cancer. Activation of Akt promotes tumor progression and drug resistance. Since the first Akt inhibitor was reported in 2000, many Akt inhibitors have been developed and evaluated in either early or late stage of clinical trials, which take advantage of liquid biopsy and genomic or molecular profiling to realize personalized cancer therapy. Two inhibitors, capivasertib and ipatasertib, are being tested in phase III clinical trials for cancer therapy. Here, we highlight recent progress of Akt signaling pathway, review the up-to-date data from clinical studies of Akt inhibitors and discuss the potential biomarkers that may help personalized treatment of cancer with Akt inhibitors. In addition, we also discuss how Akt may confer the vulnerability of cancer cells to some kinds of anticancer agents.

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.

The role of phosphatidylinositol-3-OH-kinase (PI3-kinase) and respiratory burst enzymes in the [omim][BF4]-mediated toxic mode of action in mussel hemocytes

The present study investigates the role of phosphatidylinositol-3-OH-kinase (PI3-kinase) and respiratory burst enzymes, NADPH oxidase and NO synthase, in the 1-methyl-3-octylimidazolium tetrafluoroborate ([omim][BF₄])-mediated toxic mode of action in mussel hemocytes. Specifically, cell viability (using the neutral red uptake assay) was primarily tested in hemocytes treated with different concentrations of [omim][BF₄] (0.1-10 mg L^-1) and thereafter [omim][BF₄]-mediated oxidative (in terms of superoxide anions/O₂^- and nitric oxide/NO generation, as well as the enhancement of lipid peroxidation by-products, in terms of malondialdehyde/MDA) and genotoxic (in terms of DNA damage) effects were determined in hemocytes treated with 1 mg L^-1 [omim][BF₄]. Moreover, in order to investigate, even indirectly and non-entirely specific, the role of PI3-kinase, NADPH oxidase and NO synthase, the [omim][BF₄]-mediated effects were also investigated in hemocytes pre-incubated with wortmannin (50 nM), diphenyleneiodonium chloride (DPI 10 μM) and N^G-nitro-_l-arginine methyl ester (l-NAME 10 μM), respectively. The results showed that [omim][BF₄] ability to enhance O₂^-, NO, MDA and DNA damage, via its interaction with cellular membranes, was significantly attenuated in the presence of each inhibitor in almost all cases. The current findings revealed for the first time that certain signaling molecules, such as PI3-kinase, as well as respiratory burst enzymes activation, such as NADPH oxidase and NO synthase, could merely attribute to the [omim][BF₄]-mediated mode of action, thus enriching our knowledge for the molecular mechanisms of ILs toxicity.

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.

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.

The role of AKT/mTOR pathway in stress response to UV-irradiation: implication in skin carcinogenesis by regulation of apoptosis, autophagy and senescence

Induction of DNA damage by UVB and UVA radiation may generate mutations and genomic instability leading to carcinogenesis. Therefore, skin cells being repeatedly exposed to ultraviolet (UV) light have acquired multilayered protective mechanisms to avoid malignant transformation. Besides extensive DNA repair mechanisms, the damaged skin cells can be eliminated by induction of apoptosis, which is mediated through the action of tumor suppressor p53. In order to prevent the excessive loss of skin cells and to maintain the skin barrier function, apoptotic pathways are counteracted by anti-apoptotic signaling including the AKT/mTOR pathway. However, AKT/mTOR not only prevents cell death, but is also active in cell cycle transition and hyper-proliferation, thereby also counteracting p53. In turn, AKT/mTOR is tuned down by the negative regulators being controlled by the p53. This inhibition of AKT/mTOR, in combination with transactivation of damage-regulated autophagy modulators, guides the p53-mediated elimination of damaged cellular components by autophagic clearance. Alternatively, p53 irreversibly blocks cell cycle progression to prevent AKT/mTOR-driven proliferation, thereby inducing premature senescence. Conclusively, AKT/mTOR via an extensive cross talk with p53 influences the UV response in the skin with no black and white scenario deciding over death or survival.

(-)-Epigallocatechin-3-gallate induces apoptosis in human endometrial adenocarcinoma cells via ROS generation and p38 MAP kinase activation

(-)-Epigallocatechin-3-gallate (EGCG), the major polyphenol in green tea, has been shown to inhibit carcinogenesis of various tumor types. The aim of this study was to elucidate the antiproliferative potential of EGCG and its mechanism in human endometrial cancer cells (Ishikawa cells) and primary endometrial adenocarcinoma cells. The antiproliferative effect of EGCG was evaluated by cell viability assay. Apoptosis was measured by annexin/propidium iodide staining. Reactive oxygen species (ROS) generation was measured by using 2',7'-dichlorofluorescin diacetate dye. Expression of mitogen-activated protein kinases, proliferation and apoptotic markers were measured by immunoblot analysis. EGCG was found to inhibit proliferation in Ishikawa as well as in primary endometrial adenocarcinoma cells and effectively down-regulated the expression of proliferation markers, i.e., estrogen receptor α, progesterone receptor, proliferating cell nuclear antigen and cyclin D1. EGCG also decreased the activation of ERK and downstream transcription factors fos and jun. EGCG caused apoptotic cell death accompanied by up-regulation of proapoptotic Bax and down-regulation of antiapoptotic protein Bcl2. EGCG induced the cleavage of caspase-3 and poly(ADP-ribose) polymerase, the hallmark of apoptosis. EGCG significantly induced the ROS generation as well as p38 activation in Ishikawa cells, which appeared to be a critical mediator in EGCG-induced apoptosis. The apoptotic effect of EGCG and the p38 activation were blocked by pretreatment of cells with the ROS scavenger N-acetylcysteine. EGCG reduced the glutathione levels, which might be responsible for enhanced ROS generation causing oxidative stress in endometrial cancer cells. Taken together, these results suggest that EGCG inhibits cellular proliferation via inhibiting ERK activation and inducing apoptosis via ROS generation and p38 activation in endometrial carcinoma cells.

Evidence for phosphatidylinositol-3-OH-kinase (PI3-kinase) involvement in Cd-mediated oxidative effects on hemocytes of mussels

This study investigated phosphatidylinositol-3-OH-kinase (PI3-kinase) involvement in the induction of cadmium-mediated oxidative effects on hemocytes of mussel Mytilus galloprovincialis. PI3-kinase was investigated with the use of wortmannin, a specific covalent inhibitor of PI3-kinase. Moreover, phorbol-myristate acetate (PMA), a well-known protein kinase C (PKC)-mediated NADPH oxidase and nitric oxide (NO) synthase stimulator, was also used for elucidating PI3-kinase involvement during the respiratory burst process in challenge hemocytes. According to the results, cells pre-treated with non-toxic concentrations of wortmannin (1 and/or 50 nM, as revealed by neutral red retention assay) for 15 min, showed a significant attenuation of cadmium ability (at concentration of 50 μM) to promote cell death, superoxide anion (O(2)(-)) production, NO generation and lipid peroxidation (in terms of malondialdehyde equivalents). On the other hand, wortmannin-treated cells showed a significant attenuation of PMA ability to induce NO generation but not O(2)(-) production. These findings reveal that PI3-kinase could lead to a PKC-independent induction of NO synthase activity in cells faced with pro-oxidants, such as cadmium, while its activation could be fundamental for the regulation of NAPDH oxidase activity, probably through a PKC-dependent signaling pathway.

BBR induces apoptosis in HepG2 cell through an Akt-ASK1-ROS-p38MAPKs-linked cascade

Berberine (BBR) has indicated significant antimicrobial activity against a variety of organisms including bacteria, viruses, and fungi. The mechanism by which BBR initiates apoptosis remains poorly understood. In the present study, we demonstrated that BBR exhibited significant cytotoxicity in human hepatoma HepG2 cells. Herein, we investigated cytotoxicity mechanism of BBR in HepG2 cells. The results showed that the induction of apoptosis in HepG2 cells by BBR was characterized by DNA fragmentation, an increased percentage of annexin V, and the activation of caspase-3. The expressions of Bcl-2 protein and pro-caspase-3 were reduced by BBR in HepG2 cells. However, Bax protein was increased in the cells. BBR-induced apoptosis was preceded by increased generation of reactive oxygen species (ROS). NAC treatment, a scavenger of ROS, reversed BBR-induced apoptosis effects via inhibition of Bax activation and Bcl-2 inactivation. BBR-induced, dose-dependent induction of apoptosis was accompanied by sustained phosphorylation of MAP Kinases (JNK and p38 MAPK), ASK1, Akt, and p53. Furthermore, SB203580, p38 inhibitor, reduced the apoptotic effect of BBR, and blocks the generation of ROS and NO as well as activation of Bax. We found that the treatment of HepG2 cells with BBR triggers generation of ROS through Akt phosphorylation, resulting in dissociation of the ASK1-mediated activation of JNK and p38 pathways.

The role of signalling molecules on actin glutathionylation and protein carbonylation induced by cadmium in haemocytes of mussel Mytilus galloprovincialis (Lmk)

This study investigated the role of Na(+)/H(+) exchanger (NHE) and signalling molecules, such as cAMP, PKC, PI 3-kinase, and immune defence enzymes, NADPH oxidase and nitric oxide synthase, in the induction of protein glutathionylation and carbonylation in cadmium-treated haemocytes of mussel Mytilus galloprovincialis. Glutathionylation was detected by western blot analysis and showed actin as its main target. A significant increase of both actin glutathionylation and protein carbonylation, were observed in haemocytes exposed to micromolar concentration of cadmium chloride (5 micromol l(-1)). Cadmium seems to cause actin polymerization that may lead to its increased glutathionylation, probably to protect it from cadmium-induced oxidative stress. It is therefore possible that polymerization of actin plays a signalling role in the induction of both glutathionylation and carbonylation processes. NHE seems to play a regulatory role in the induction of oxidative damage and actin glutathionylation, since its inhibition by 2 micromol l(-1) cariporide, significantly diminished cadmium effects in each case. Similarly, attenuation of cadmium effects were observed in cells pre-treated with either 11 micromol l(-1) GF-109203X, a potent inhibitor of PKC, 50 nmol l(-1) wortmannin, an inhibitor of PI 3-kinase, 0.01 mmol l(-1) forskolin, an adenylyl cyclase activator, 10 micromol l(-1) DPI, a NADPH oxidase inhibitor, or 10 micromol l(-1) L-NAME, a nitric oxide synthase inhibitor, suggesting a possible role of PKC, PI 3-kinase and cAMP, as well as NADPH oxidase and nitric oxide synthase in the enhancement of cadmium effects on both actin glutathionylation and protein carbonylation.

Identification of novel pharmacological targets to minimize excitotoxic retinal damage

Excitotoxic neuronal death is a common feature of neurodegenerative and ischemic diseases of the central nervous system (CNS) and of a variety of ocular diseases, including glaucoma. Glaucoma, one of the leading causes of blindness in the world, is characterized by a progressive degeneration of retinal ganglion cells (RGCs) and their axons and is often associated with elevated intraocular pressure (IOP). Retinal ischemia/reperfusion induced by experimental elevation of IOP leads to damage and loss of RGCs. Under these conditions, structural, functional, and biochemical changes implicate the accumulation of extracellular glutamate and activation of the excitotoxic cascade. Beside the activation of associated pathways, death of RGCs is accompanied by impaired endogenous defenses, such as the PI3K/Akt prosurvival pathway. Original neurochemical and pharmacological evidence are discussed here to strengthen the role for excitotoxicity in RGCs death occurring in experimental, angle closure, glaucoma in conjunction with the discovery of novel molecular targets to potentiate endogenous prosurvival defenses in the glaucomatous retina.

Dissociation between the translocation and the activation of Akt in fMLP-stimulated human neutrophils--effect of prostaglandin E2

PGE(2) and other cAMP-elevating agents are known to down-regulate most functions stimulated by fMLP in human polymorphonuclear neutrophils. We reported previously that the inhibitory potential of PGE(2) resides in its capacity to suppress fMLP-stimulated PI-3Kgamma activation via the PGE(2) receptor EP(2) and hence, to decrease phosphatidylinositol 3,4,5-triphosphate [PI(3,4,5)P(3)] formation. Akt activity is stimulated by fMLP through phosphorylation on threonine 308 (Thr308) and serine 473 (Ser473) by 3-phosphoinositide-dependent kinase 1 (PDK1) and MAPK-AP kinase (APK)-APK-2 (MAPKAPK-2), respectively, in a PI-3K-dependent manner. Despite the suppression of fMLP-induced PI-3Kgamma activation observed in the presence of PGE(2), we show that Akt is fully phosphorylated on Thr308 and Ser473. However, fMLP-induced Akt translocation is decreased markedly in this context. PGE(2) does not affect the phosphorylation of MAPKAPK-2 but decreases the translocation of PDK1 induced by fMLP. Other cAMP-elevating agents such as adenosine (Ado) similarly block the fMLP-induced PI-3Kgamma activation process but do not inhibit Akt phosphorylation. However, Akt activity stimulated by fMLP is down-regulated slightly by agonists that elevate cAMP levels. Whereas protein kinase A is not involved in the maintenance of Akt phosphorylation, it is required for the inhibition of Akt translocation by PGE(2). Moreover, inhibition of fMLP-stimulated PI-3Kdelta activity by the selective inhibitor IC87114 only partially affects the late phase of Akt phosphorylation in the presence of PGE(2). Taken together, these results suggest that cAMP-elevating agents, such as PGE(2) or Ado, are able to induce an alternative mechanism of Akt activation by fMLP in which the translocation of Akt to PI(3,4,5)P(3)-enriched membranes is not required prior to its phosphorylation.

Mechanisms of cell death in oxidative stress

Reactive oxygen or nitrogen species (ROS/RNS) generated endogenously or in response to environmental stress have long been implicated in tissue injury in the context of a variety of disease states. ROS/RNS can cause cell death by nonphysiological (necrotic) or regulated pathways (apoptotic). The mechanisms by which ROS/RNS cause or regulate apoptosis typically include receptor activation, caspase activation, Bcl-2 family proteins, and mitochondrial dysfunction. Various protein kinase activities, including mitogen-activated protein kinases, protein kinases-B/C, inhibitor-of-I-kappaB kinases, and their corresponding phosphatases modulate the apoptotic program depending on cellular context. Recently, lipid-derived mediators have emerged as potential intermediates in the apoptosis pathway triggered by oxidants. Cell death mechanisms have been studied across a broad spectrum of models of oxidative stress, including H2O2, nitric oxide and derivatives, endotoxin-induced inflammation, photodynamic therapy, ultraviolet-A and ionizing radiations, and cigarette smoke. Additionally ROS generated in the lung and other organs as the result of high oxygen therapy or ischemia/reperfusion can stimulate cell death pathways associated with tissue damage. Cells have evolved numerous survival pathways to counter proapoptotic stimuli, which include activation of stress-related protein responses. Among these, the heme oxygenase-1/carbon monoxide system has emerged as a major intracellular antiapoptotic mechanism.

An analog of a dipeptide-like structure of FK506 increases glial cell line-derived neurotrophic factor expression through cAMP response element-binding protein activated by heat shock protein 90/Akt signaling pathway

Glial cell line-derived neurotrophic factor (GDNF) is an important neurotrophic factor that has therapeutic implications for neurodegenerative disorders. We previously showed that leucine-isoleucine (Leu-Ile), an analog of a dipeptide-like structure of FK506 (tacrolimus), induces GDNF expression both in vivo and in vitro. In this investigation, we sought to clarify the cellular mechanisms underlying the GDNF-inducing effect of this dipeptide. Leu-Ile transport was investigated using fluorescein isothiocyanate-Leu-Ile in cultured neurons, and the results showed the transmembrane mobility of this dipeptide. By liquid chromatography-mass spectrometry and quartz crystal microbalance assay, we identified heat shock cognate protein 70 as a protein binding specifically to Leu-Ile, and molecular modeling showed that the ATPase domain is the predicted binding site. Leu-Ile stimulated Akt phosphorylation, which was attenuated significantly by heat shock protein 90 (Hsp90) inhibitor geldanamycin (GA). Moreover, enhanced interaction between phosphorylated Akt and Hsp90 was detected by immunoprecipitation. Leu-Ile elicited an increase in cAMP response element binding protein (CREB) phosphorylation, which was inhibited by GA, indicating that CREB is a downstream target of Hsp90/Akt signaling. Leu-Ile elevated the levels of GDNF mRNA and protein expression, whereas inhibition of CREB blocked such effects. Leu-Ile promoted the binding activity of phosphorylated CREB with cAMP response element. These findings show that CREB plays a key role in transcriptional regulation of GDNF expression induced by Leu-Ile. In conclusion, Leu-Ile activates Hsp90/Akt/CREB signaling, which contributes to the upregulation of GDNF expression. It may represent a novel lead compound for the treatment of dopaminergic neurons or motoneuron diseases.

Akt is activated via insulin/IGF-1 receptor in rat retina with episcleral vein cauterization

The Akt serine/threonine kinase mediates pro-survival signalings in retina and was reported to be activated in a response to some retinal and optic nerve injuries. Human and experimental glaucoma induce apoptosis of retinal ganglion cells (RGCs). The purpose of this study is to test whether episcleral vein cauterization (EVC) to chronically elevate intraocular pressures (IOPs) in rats increase apoptosis of RGCs and affect activation of Akt and its upstream insulin-like growth factor (IGF)-1 receptor/Insulin receptor. Three episcleral veins in left eyes of Sprague-Dawley rats were cauterized to elevate IOPs. Up to 6 months, IOPs were monitored and the retina was dissected at several time points. The numbers of terminal dUTP nick end labeling (TUNEL)-positive cells and those of RGCs labeled with fluorogold were counted in flat-mounted retina. Immunohistochemistry and immunoblotting were performed to identify cells expressing phosphorylated Akt and to quantify the phospho- to total ratios of Akt and IGF-1 receptor/insulin receptor. EVC significantly elevated IOPs up to 2 months, increased TUNEL-positive cells in an IOP-dependent fashion, and reduced 34.5% of RGCs at 6 months (P<0.001) compared with contralateral retinas. Phosphorylated Akt was specifically expressed in RGCs until 1 month after cauterization. Akt (P=0.036) and IGF-1 receptor/Insulin receptor (P=0.003) were transiently phosphorylated at 3 days. Intrinsic activation of the IGF-1 receptor/Insulin receptor to Akt pathway may occur in RGCs in retina with EVC.

Seasonal, tissue-specific regulation of Akt/protein kinase B and glycogen synthase in hibernators

Yellow-bellied marmots ( Marmota flaviventris) exhibit a circannual cycle of hyperphagia and nutrient storage in the summer followed by hibernation in the winter. This annual cycle of body mass gain and loss is primarily due to large-scale accumulation of lipid in the summer, which is then mobilized and oxidized for energy during winter. The rapid and predictable change in body mass makes these animals ideal for studies investigating the molecular basis for body weight regulation. In the study described herein, we monitored seasonal changes in the protein levels and activity of a central regulator of anabolic metabolism, the serine-threonine kinase Akt-protein kinase B (Akt/PKB), during the months accompanying maximal weight gain and entry into hibernation (June-November). Interestingly, under fasting conditions, Akt/PKB demonstrated a tissue-specific seasonal activation. Specifically, although Akt/PKB levels did not change, the activity of Akt/PKB (isoforms 1/α and 2/β) in white adipose tissue (WAT) increased significantly in July. Moreover, glycogen synthase, which lies downstream of Akt/PKB on a linear pathway linking the enzyme to the stimulation of glycogen synthesis, demonstrated a similar pattern of seasonal activation. By contrast, Akt/PKB activity in skeletal muscle peaked much later (i.e., September). These data suggest the existence of a novel, tissue-specific mechanism regulating Akt/PKB activation during periods of marked anabolism.

A positive role of phosphatidylinositol 3-kinase in aging phenotype expression in cultured human diploid fibroblasts

In order to detect the role that phosphatidylinositol 3-kinase (PI3K) plays in the aging of human diploid fibroblasts, we analyzed cellular inositol phospholipids and expression of PI3Ks. In aged cells a decrease in phosphatidylinositol 3,4-bisphosphate (PI3,4P(2)) was notable, while phosphatidylinositol 3-phosphate (PI3P) and phosphatidylinositol 4,5-bisphosphate (PI4,5P(2)) decreased slightly. On the other hand, the messages of PI3K IIalpha, Vps34, and p110delta decreased and that of PI3K IIbeta increased during aging. These changes might relate to the aging phenomena, with the PI3K subspecies functioning differentially. Consistently, a PI3K inhibitor LY294002 greatly suppressed enlargement and flattening of cell body and nucleus as well as cell proliferation, both phenotypes being typical of aged cells. An oxidative stress, pulse exposure to hydrogen peroxide (H(2)O(2)), induced these senescent cell-like phenotypes, which LY294002 was also able to abolish. Upon examining three different cell systems (HL-60, N1E-115, and PC-12 cells) we found clear parallelism in a cellular event between the dependence on a PI3K activity and the sensitivity to H(2)O(2). On the analogy of these relationships, we could hypothesize that expression of an aging phenotype such as the morphogenesis is positively promoted by some PI3K subspecies, if such a phenotype as cell cycling is negatively affected by attenuation of another PI3K function in the course of cellular aging.

Caspase activation is accelerated by the inhibition of arsenite-induced, membrane rafts-dependent Akt activation

Renewed interest in arsenic has been shown recently due to its dual nature of being a potent toxin and a drug for treatment of acute promyelocytic leukemia (APL) because of its ability to trigger caspase activation. Here, we found that sodium arsenite (NaAsO(2)) also triggers the signal for activation of Akt and downstream glycogen synthase 3beta (GSK3beta). Such Akt/GSK3beta activation was abrogated completely by wortmannin, an inhibitor of PI-3 kinase, and greatly by pertussis toxin, a G-protein inhibitor. Arsenite-induced Akt phosphorylation also was inhibited by sequestrating membrane cholesterol with beta cyclodextrin. Reducing reagents/reactive oxygen species (ROS) scavengers reduced arsenite-induced Akt phosphorylation and beta cyclodextrin reduced arsenite-mediated ROS production, suggesting that arsenite-induced G-protein/Akt/GSK3beta pathway is membrane raft dependent and redox linked. We also found that a combination of a low concentration (1 microM) of arsenite and wortmannin triggers the signal for caspase activation, whereas neither of these elements alone did so. These results suggested that selective blockade of the arsenite-provoked PI-3 kinase/Akt pathway can promote the arsenite-triggered pathway for caspase activation, and this may open a new study area for wider applications of arsenic as a drug for treating various kinds of leukemia.

Expression of the serum- and glucocorticoid-inducible protein kinase, Sgk, is a cell survival response to multiple types of environmental stress stimuli in mammary epithelial cells

The effects of multiple stress stimuli on the cellular utilization of the serum- and glucocorticoid-inducible protein kinase (Sgk) were examined in NMuMg mammary epithelial cells exposed to hyperosmotic stress induced by the organic osmolyte sorbitol, heat shock, ultraviolet irradiation, oxidative stress induced by hydrogen peroxide, or to dexamethasone, a synthetic glucocorticoid that represents a general class of physiological stress hormones. Each of the stress stimuli induced Sgk protein expression with differences in the kinetics and duration of induction and in subcellular localization. The environmental stresses, but not dexamethasone, stimulated Sgk expression through a p38/MAPK-dependent pathway. In each case, a hyperphosphorylated active Sgk protein was produced under conditions in which Akt, the close homolog of Sgk, remained in its non-phosphorylated state. Ectopic expression of wild type Sgk or of the T256D/S422D mutant Sgk that mimics phosphorylation conferred protection against stress-induced cell death in NMuMg cells. In contrast, expression of the T256A/S422A Sgk phosphorylation site mutant has no effect on cell survival. Sgk is known to phosphorylate and negatively regulate pro-apoptotic forkhead transcription factor FKHRL1. The environmental stress stimuli that induce Sgk, but not dexamethasone, strongly inhibited the nuclear transcriptional activity and increased the cytoplasmic retention of FKHRL1. Also, the conditional IPTG inducible expression of wild type Sgk, but not of the kinase dead T256A mutant Sgk, protected Con8 mammary epithelial tumor cells from serum starvation-induced apoptosis. Taken together, our study establishes that induction of enzymatically active Sgk functions as a key cell survival component in response to different environmental stress stimuli.

Induction of heat shock proteins (HSPs) by sodium arsenite in cultured astrocytes and reduction of hydrogen peroxide-induced cell death

Induction of heat shock proteins (HSPs) protects cells from oxidative injury. Here Hsp72, Hsp27 and heme oxygenase-1 (HO-1) were induced in cultured rat astrocytes, and protection against oxidative stress was investigated. Astrocytes were treated with sodium arsenite (20-50 micro m) for 1 h, which was non-toxic to cells, 24 h later they were exposed to 400 micro m H2O2 for 1 h, and cell death was evaluated at different time points. Arsenite triggered strong induction of HSPs, which was prevented by 1 micro g/mL cycloheximide (CXH). H2O2 caused cell loss and increased cell death with features of apoptosis, i.e. TdT-mediated dUTP nick-end labelling (TUNEL) reaction and caspase-3 activation. These features were abrogated by pre-treatment with arsenite, which prevented cell loss and significantly reduced the number of dead cells. The protective effect of arsenite was not detected in the presence of CHX. Pre-treatment with arsenite increased protein kinase B (Akt) and extracellular signal regulated kinase 1/2 (ERK1/2) phosphorylation after H2O2. However, while Akt phosphorylation was prevented by CHX, Erk1/2 phosphorylation was further enhanced by CHX. The results show that transient arsenite pre-treatment induces Hsp72, HO-1 and, to a lesser extent, Hsp27; it reduces H2O2-induced astrocyte death; and it causes selective activation of Akt following H2O2. It is suggested that HSP expression at the time of H2O2 exposure protects astrocytes from oxidative injury and apoptotic cell death by means of pro-survival Akt.

PKB binding proteins. Getting in on the Akt

Protein kinase B (PKB) has emerged as the focal point for many signal transduction pathways, regulating multiple cellular processes such as glucose metabolism, transcription, apoptosis, cell proliferation, angiogenesis, and cell motility. In addition to acting as a kinase toward many substrates involved in these processes, PKB forms complexes with other proteins that are not substrates, but rather act as modulators of PKB activity and function. In this review, we discuss the implications of these data in understanding the multitude of functions predicted for PKB in cells.

Inhibition of JNK by cellular stress- and tumor necrosis factor alpha-induced AKT2 through activation of the NF kappa B pathway in human epithelial Cells

Previous studies have demonstrated that AKT1 and AKT3 are activated by heat shock and oxidative stress via both phosphatidylinositol 3-kinase-dependent and -independent pathways. However, the activation and role of AKT2 in the stress response have not been fully elucidated. In this study, we show that AKT2 in epithelial cells is activated by UV-C irradiation, heat shock, and hyperosmolarity as well as by tumor necrosis factor alpha (TNFalpha) through a phosphatidylinositol 3-kinase-dependent pathway. The activation of AKT2 inhibits UV- and TNF alpha-induced c-Jun N-terminal kinase (JNK) and p38 activities that have been shown to be required for stress- and TNF alpha-induced programmed cell death. Moreover, AKT2 interacts with and phosphorylates I kappa B kinase alpha. The phosphorylation of I kappa B kinase alpha and activation of NF kappa B mediates AKT2 inhibition of JNK but not p38. Furthermore, phosphatidylinositol 3-kinase inhibitor or dominant negative AKT2 significantly enhances UV- and TNF alpha-induced apoptosis, whereas expression of constitutively active AKT2 inhibits programmed cell death in response to UV and TNFalpha -induced apoptosis by inhibition of stress kinases and provide the first evidence that AKT inhibits stress kinase JNK through activation of the NF kappa B pathway.

Apoptosis in murine hepatoma hepa 1c1c7 wild-type, C12, and C4 cells mediated by bilirubin

Elevated serum and tissue bilirubin concentrations that occur in pathological conditions such as cholestasis, jaundice, and other liver diseases are known to stimulate cytotoxic responses. In preliminary studies, we noted that bilirubin seemed to cause apoptosis in murine hepatoma Hepa 1c1c7 wild-type (WT) cells. Consequently, we investigated apoptosis caused by bilirubin in WT, mutant C12 [aryl hydrocarbon receptor (AHR)-deficient], and C4 (AHR nuclear translocator-deficient) Hepa 1c1c7 cells. Three independent measures of apoptosis were used to quantify the effects of exogenous bilirubin (0, 1, 10, 25, 50, or 100 microM). Caspase-3 activity and cytochrome c release from mitochondria increased at 3 h post-treatment, before increased caspase-8 activity at 6 h, and nuclear condensation by 24 h after treatment with bilirubin. No differences in whole-cell lipid peroxidation were observed between the cell types; however, intracellular reactive oxygen species (ROS) production was greater in WT cells than C12 or C4 cells 3 h after bilirubin exposure. Pretreatment of cells for 1 h with 1 or 10 microM alpha-naphthoflavone, an AHR antagonist, before bilirubin exposure resulted in decreased caspase-3 activity at 6 h and nuclear condensation at 24 h in WT cells. These results indicate that bilirubin, a potential AHR ligand, causes apoptosis in murine Hepa 1c1c7 WT cells by a mechanism(s) partially involving the AHR, disruption of membrane integrity, and increased intracellular ROS production.

GeneBlocs are powerful tools to study and delineate signal transduction processes that regulate cell growth and transformation

The study of signal transduction processes using antisense oligonucleotides is often complicated by low intracellular stability of the antisense reagents or by nonspecific effects that cause toxicity. Here, we introduce a new class of antisense molecules, so-called GeneBlocs, which are characterized by improved stability, high target RNA specificity, and low toxicity. GeneBlocs allow for efficient downregulation of mRNA expression at nanomolar concentrations, and they do not interfere with cell proliferation. We demonstrate these beneficial properties using a positive readout system. GeneBloc-mediated inhibition of tumor suppressor PTEN (phosphatase and tension homologue detected on chromosome 10) expression leads to hyperactivation of the phosphatidylinositol (PI) 3-kinase pathway, thereby mimicking the loss of PTEN function and its early consequences observed in mammalian cancer cells. Specifically, cells treated with PTEN GeneBlocs show functional activation of Akt, a downstream effector of PI 3-kinase signaling, and exhibit enhanced proliferation when seeded on a basement membrane matrix. In addition, GeneBlocs targeting the catalytic subunit of PI 3-kinase, p110, specifically inhibit signal transduction of endogenous or recombinant PI 3-kinase. This demonstrates that GeneBlocs are powerful tools to analyze and to modulate signal transduction processes and, therefore, represent alternative reagents for the validation of gene function.

Phospholipase C-gamma1 is required for cell survival in oxidative stress by protein kinase C

Phospholipase C-gamma1 (PLC-gamma1) activation has been reported to enhance cell survival during the cellular response to oxidative stress. We studied the role of protein kinase C (PKC) pathways in mediating PLC-gamma1 survival signalling in oxidative stress by using mouse embryonic fibroblasts genetically deficient in PLC-gamma1 (Plcg1(-/-)) and its wild type (Plcg1(+/+)). PLC-gamma1 was activated by H(2)O(2) treatment in a dose- and time-dependent manner. Activation of PKC was also markedly increased in both cell lines treated with H(2)O(2) (1-5 mM), but with low doses (50-200 microM), PKC activation was considerably decreased in Plcg1(-/-) cells. After treatment with H(2)O(2), PKC-dependent phosphorylation of Bcl-2 and cell viability of Plcg1(-/-) cells decreased dramatically and caspase-3-like activity increased significantly compared with that of the wild-type cells. Furthermore, pretreatment of Plcg1(+/+) cells with PKC-specific inhibitor decreased levels of PKC-dependent Bcl-2 phosphorylation, enhanced caspase-3 activity and their sensitivity to H(2)O(2). On the contrary, treatment of Plcg1(-/-) cells with PKC-specific activator increased the Bcl-2 phosphorylation, decreased caspase-3 activity and improved their survival. These results suggest that PLC-gamma1 mediates survival signalling in oxidative-stress response by PKC-dependent phosphorylation of Bcl-2 and inhibition of caspase-3.

Glycogen synthase kinase-3beta, mood stabilizers, and neuroprotection

Glycogen synthase kinase-3beta (GSK-3beta) is a central component in many critical intracellular signaling mechanisms. These include the phosphatidylinositol 3-kinase/Akt cell survival pathway, which inhibits GSK-3beta activity. GSK-3beta itself inhibits the activation of several transcription factors, which are important cell survival factors, such as heat shock factor 1. These factors likely contribute to the recent revelation that GSK-3beta is a pro-apoptotic enzyme. Recently, lithium has been identified as a selective and direct inhibitor of GSK-3beta. Based on these findings, we have proposed that part of the neuroprotectant properties of lithium is due to its ability to inhibit GSK-3beta, and thus block the facilitation of apoptosis produced by GSK-3beta. Since several anticonvulsants recently have been shown to be effective mood stabilizers, we examined if these agents are capable of protecting cells from GSK-3beta-facilitated apoptosis. In addition to lithium, both valproic acid and lamotrigine, but not carbamazepine, provided protection from GSK-3beta-facilitated apoptosis in human neuroblastoma SH-SY5Y cells. These results demonstrate that several drugs therapeutic for bipolar disorder can provide neuroprotection by inhibiting the pro-apoptotic effects of GSK-3beta, providing new evidence that dysregulation of GSK-3beta may contribute to the pathophysiology of bipolar disorder.

Stimulation of protein kinase B and p70 S6 kinase by the histamine H1 receptor in DDT1MF-2 smooth muscle cells

1. Previous studies have shown that the histamine H(1) receptor activates p42/p44 mitogen-activated protein kinases (MAPK) in DDT(1)MF-2 smooth muscle cells via a phosphatidylinositol 3-kinase (PI-3K)-dependent pathway. In this study the effect of histamine H(1) receptor stimulation on protein kinase B (PKB) and p70 S6 kinase, both of which are downstream targets of PI-3K, has been investigated. Increases in PKB and p70 S6 kinase activation were monitored by Western blotting using phospho-specific PKB (Ser(473)) and p70 S6 kinase (Thr(421)/Ser(424)) antibodies. 2. Histamine stimulated time and concentration-dependent increases in the phosphorylation of PKB and p70 S6 kinase in DDT(1)MF-2 cells. Both responses were completely inhibited by the histamine H(1) receptor antagonist mepyramine and following pre-treatment with pertussis toxin, to block G(i)/G(o) protein dependent pathways. 3. The PI-3K inhibitors wortmannin (IC(50) 5.9+/-0.5 nM) and LY 294002 (IC(50) 6.9+/-0.8 microM) attenuated the increase in PKB phosphorylation induced by histamine (100 microM) in a concentration-dependent manner. 4. Histamine-induced increases in p70 S6 kinase phosphorylation were partially sensitive to rapamycin (20 nM; 68% inhibition) but completely blocked by wortmannin (100 nM), LY 294002 (30 microM) and the MAPK kinase inhibitor PD 98059 (50 microM). 5. In summary, these data demonstrate that the histamine H(1) receptor stimulates PKB and p70 S6 kinase phosphorylation in DDT(1)MF-2 smooth muscle cells. However, functional studies revealed that histamine does not stimulate DDT(1)MF-2 cell proliferation or attenuate staurosporine-induced caspase-3 activity. The challenge for future research will be to link the stimulation of these kinase pathways with the physiological and pathophysiological roles of the histamine H(1) receptor.

Akt phosphorylates and negatively regulates apoptosis signal-regulating kinase 1

The Akt family of serine/threonine-directed kinases promotes cellular survival in part by phosphorylating and inhibiting death-inducing proteins. Here we describe a novel functional interaction between Akt and apoptosis signal-regulating kinase 1 (ASK1), a mitogen-activated protein kinase kinase kinase. Akt decreased ASK1 kinase activity stimulated by both oxidative stress and overexpression in 293 cells by phosphorylating a consensus Akt site at serine 83 of ASK1. Activation of the phosphoinositide 3-kinase (PI3-K)/Akt pathway also inhibited the serum deprivation-induced activity of endogenous ASK1 in L929 cells. An association between Akt and ASK1 was detected in cells by coimmunoprecipitation. Phosphorylation by Akt inhibited ASK1-mediated c-Jun N-terminal kinase and activating transcription factor 2 activities in intact cells. Finally, activation of the PI3-K/Akt pathway reduced apoptosis induced by ASK1 in a manner dependent on phosphorylation of serine 83 of ASK1. These results provide the first direct link between Akt and the family of stress-activated kinases.

Akt/protein kinase B isoforms are differentially regulated by epidermal growth factor stimulation

Overexpression of epidermal growth factor receptor (EGFR) in certain cancers is well established. There is growing evidence that epidermal growth factor (EGF) activates Akt/protein kinase B (PKB) in a phosphoinositide 3-OH kinase (PI3K)-dependent manner, but it is not yet clear which Akt isoforms are involved in this signal transduction pathway. We investigated the functional regulation of three Akt isoforms, Akt1/PKBalpha, Akt2/PKBbeta, and Akt3/PKBgamma, in esophageal cancer cells where EGFR is frequently overexpressed. Upon EGF simulation, phosphorylation of Akt1 at the Ser-473 residue was remarkably induced. This result was corroborated by in vitro Akt kinase assays using glycogen synthase kinase 3beta as the substrate. PI3K inhibitors, wortmannin or LY294002, significantly blocked the Akt kinase activity induced by EGF. Akt2 activity was evaluated by electrophoretic mobility shift assays. Robust activation of Akt2 by EGF was observed in some cell lines in a PI3K-dependent manner. EGF-induced Akt3 activation was demonstrated by Ser-472 phosphorylation of Akt3 but in a restrictive fashion. In aggregate, EGF-mediated activation of Akt isoforms is overlapping and distinctive. The mechanism by which EGFR recruits the PI3K/Akt pathway was in part differentially regulated at the level of Ras but independent of heterodimerization of EGFR with either ErbB2 or ErbB3 based upon functional dissection of pathways in esophageal cancer cell lines.

Syk is required for the activation of Akt survival pathway in B cells exposed to oxidative stress

Syk has been demonstrated to play a crucial role in oxidative stress signaling in B cells. Here we report that Syk is required for the activation of the phosphatidylinositol (PI) 3-kinase-Akt survival pathway in B cells exposed to oxidative stress. Phosphorylation and activation of the serine-threonine kinase Akt were markedly increased in B cells treated with H(2)O(2). In Syk-deficient DT40 cells treated with low doses of H(2)O(2) (10-100 microm), Akt activation was considerably reduced. Pretreatment with wortmannin, a PI 3-kinase-specific inhibitor, completely blocked the Syk-dependent Akt activation. Following stimulation by low doses of H(2)O(2), a significant increase in PI 3-kinase activity was found in wild-type but not in Syk-deficient cells. These findings suggest that PI 3-kinase mediates Syk-dependent Akt activation pathway. Furthermore, viability of Syk-deficient cells, after exposure to H(2)O(2), was dramatically decreased and caspase-9 activity was greatly increased compared with that of the wild-type cells. These results suggest that Syk is essential for the Akt survival pathway in B cells and enhances cellular resistance to oxidative stress-induced apoptosis.

Akt-dependent cytokine production in mast cells

Cross-linking of FcepsilonRI induces the activation of three protein tyrosine kinases, Lyn, Syk, and Bruton's tyrosine kinase (Btk), leading to the secretion of a panel of proinflammatory mediators from mast cells. This study showed phosphorylation at Ser-473 and enzymatic activation of Akt/protein kinase B, the crucial survival kinase, upon FcepsilonRI stimulation in mouse mast cells. Phosphorylation of Akt is regulated positively by Btk and Syk and negatively by Lyn. Akt in turn can regulate positively the transcriptional activity of interleukin (IL)-2 and tumor necrosis factor (TNF)-alpha promoters. Transcription from the nuclear factor kappaB (NF-kappaB), nuclear factor of activated T cells (NF-AT), and activator protein 1 (AP-1) sites within these promoters is under the control of Akt activity. Accordingly, the signaling pathway involving IkappaB-alpha, a cytoplasmic protein that binds NF-kappaB and inhibits its nuclear translocation, appears to be regulated by Akt in mast cells. Catalytic activity of glycogen synthase kinase (GSK)-3beta, a serine/threonine kinase that phosphorylates NF-AT and promotes its nuclear export, seems to be inhibited by Akt. Importantly, Akt regulates the production and secretion of IL-2 and TNF-alpha in FcepsilonRI-stimulated mast cells. Altogether, these results revealed a novel function of Akt in transcriptional activation of cytokine genes via NF-kappaB, NF-AT, and AP-1 that contributes to the production of cytokines.

Activation of protein kinase B by the A(1)-adenosine receptor in DDT(1)MF-2 cells

In this study the effect of insulin and A(1)-adenosine receptor stimulation on protein kinase B (PKB) activation has been investigated in the hamster vas deferens smooth muscle cell line DDT(1)MF-2. Increases in PKB phosphorylation were determined by Western blotting using an antibody that detects PKB phosphorylation at Ser(473). Insulin, a recognized activator of PKB, stimulated a concentration-dependent increase in PKB phosphorylation in DDT(1)MF-2 cells (EC(50) 5+/-1 pM). The selective A(1)-adenosine receptor agonist N(6)-cyclopentyladenosine (CPA) stimulated time and concentration-dependent increases in PKB phosphorylation in DDT(1)MF-2 cells (EC(50) 1.3+/-0.5 nM). CPA-mediated increases in PKB phosphorylation were antagonized by the A(1)-adenosine receptor selective antagonist 1,3-dipropylcyclopentylxanthine (DPCPX) yielding an apparent K(D) value of 2.3 nM. Pre-treatment of DDT(1)MF-2 cells with pertussis toxin (PTX, 100 ng ml(-1) for 16 h), to block G(i)/G(o)-dependent pathways, abolished CPA (1 microM) induced phosphorylation of PKB. In contrast, responses to insulin (100 nM) were resistant to PTX pre-treatment. The phosphatidylinositol 3-kinase (PI-3K) inhibitors wortmannin (IC(50) 10.3+/-0.6 nM) and LY 294002 (IC(50) 10.3+/-1.2 microM) attenuated the phosphorylation of PKB elicited by CPA (1 microM) in a concentration-dependent manner. Wortmannin (30 nM) and LY 294002 (30 microM) also blocked responses to insulin (100 nM). Removal of extracellular Ca(2+) and chelation of intracellular Ca(2+) with BAPTA had no significant effect on CPA-induced PKB phosphorylation. Similarly, pretreatment (30 min) with inhibitors of protein kinase C (Ro 31-8220; 10 microM), tyrosine kinase (genistein; 100 microM), mitogen-activated protein (MAP) kinase kinase (PD 98059; 50 microM) and p38 MAPK (SB 203580; 20 microM) had no significant effect on CPA-induced PKB phosphorylation. In conclusion, these data demonstrate that A(1)-adenosine receptor stimulation in DDT(1)MF-2 cells increases PKB phosphorylation through a PTX and PI-3K-sensitive pathway.

Evidence that 3'-phosphorylated polyphosphoinositides are generated at the nuclear surface: use of immunostaining technique with monoclonal antibodies specific for PI 3,4-P(2)

Phosphatidylinositol (PI) 3,4-P(2) is a phosphoinositide that has been shown to be important for signal transduction in growth factor stimulation. We have produced monoclonal antibodies specific for PI 3,4-P(2), which were able to detect PI 3,4-P(2) generated in 293T cells treated with H(2)O(2), or in MKN45/BD110 cells expressing activated PI 3-kinase in immunostaining. Prolonged treatment with 0.05% Tween 20 resulted in detection of staining not only at the plasma membrane, but also at the nuclear surface, indicating that 3'-phosphorylated phosphoinositides can be generated and function in the nucleus.