Co-induction of cell death and survival pathways by phosphoinositide 3-kinase

Polymyxin-Induced Metabolic Perturbations in Human Lung Epithelial Cells

Inhaled polymyxins are associated with toxicity in human lung epithelial cells that involves multiple apoptotic pathways. However, the mechanism of polymyxin-induced pulmonary toxicity remains unclear. This study aims to investigate polymyxin-induced metabolomic perturbations in human lung epithelial A549 cells. A549 cells were treated with 0.5 or 1.0 mM polymyxin B or colistin for 1, 4, and 24 h. Cellular metabolites were analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and significantly perturbed metabolites (log₂ fold change [log₂FC] ≥ 1; false-discovery rate [FDR] ≤ 0.2) and key pathways were identified relative to untreated control samples. At 1 and 4 h, very few significant changes in metabolites were observed relative to the untreated control cells. At 24 h, taurine (log₂FC = -1.34 ± 0.64) and hypotaurine (log₂FC = -1.20 ± 0.27) were significantly decreased by 1.0 mM polymyxin B. The reduced form of glutathione (GSH) was significantly depleted by 1.0 mM polymyxin B at 24 h (log₂FC = -1.80 ± 0.42). Conversely, oxidized glutathione (GSSG) was significantly increased by 1.0 mM both polymyxin B (log₂FC = 1.38 ± 0.13 at 4 h and 2.09 ± 0.20 at 24 h) and colistin (log₂FC = 1.33 ± 0.24 at 24 h). l-Carnitine was significantly decreased by 1.0 mM of both polymyxins at 24 h, as were several key metabolites involved in biosynthesis and degradation of choline and ethanolamine (log₂FC ≤ -1); several phosphatidylserines were also increased (log₂FC ≥ 1). Polymyxins perturbed key metabolic pathways that maintain cellular redox balance, mitochondrial β-oxidation, and membrane lipid biogenesis. These mechanistic findings may assist in developing new pharmacokinetic/pharmacodynamic strategies to attenuate the pulmonary toxicities of inhaled polymyxins and in the discovery of new-generation polymyxins.

Ras-Mediated Activation of NF-κB and DNA Damage Response in Carcinogenesis

Cancer is a multi-step process during which cells acquire mutations that eventually lead to uncontrolled cell growth and division and evasion of programmed cell death. The oncogenes such as Ras and c-Myc may be responsible in all three major stages of cancer i.e., early, intermediate, and late. The NF-κB has been shown to control the expression of genes linked with tumor pathways such as chronic inflammation, tumor cell survival, anti-apoptosis, proliferation, invasion, and angiogenesis. In the last few decades, various biomarker pathways have been identified that play a critical role in carcinogenesis such as Ras, NF-κB and DNA damage.

Atrial Natriuretic Peptide: A Potential Early Therapy for the Prevention of Multiple Organ Dysfunction Syndrome Following Severe Trauma

Trauma remains a tremendous medical burden partly because of increased expenditure for the management of multiple organ dysfunction syndrome (MODS) developed during hospital stay. The intestinal barrier injury continues to be a second insult resulting in MODS which currently lacks efficient strategies for prevention. Recent studies have uncovered multi-organ protective benefits of atrial natriuretic peptide (ANP) in cardiovascular disease. However, the role of ANP in the prevention of MODS following severe trauma has not been understood. In our laboratory study, 1-h infusion of exogenous ANP during hemorrhagic shock following severe trauma induced high-level expression of endogenous serum ANP after 24 h, this effect was related to the improved level of functional biomarkers in multiple organs. Such phenomenon has not been found in other laboratories. A thorough literature review consequently was performed to uncover the potential mechanisms, to appraise therapy safety, and to propose uncertainties. In severe trauma, short-term exogenous ANP therapy during hemorrhagic shock may promote sustained endogenous expression of ANP from intestinal epithelium through activating a positive feedback loop mechanism involving phospholipase C-γ1 and reactive oxygen species crosstalk. This feedback loop may prevent MODS through multiple signaling pathways. Administration of ANP during hemorrhagic shock is thought to be safe. Further studies are required to confirm our proposed mechanisms and to investigate the dose, duration, and timing of ANP therapy in severe trauma.

Involvement of SULF2 in y-irradiation-induced invasion and resistance of cancer cells by inducing IL-6 expression

Cancer cells that survive radiotherapy often display enhanced invasiveness and resistance to death stimuli. Previous findings have suggested that ionizing radiation (IR) induces such undesirable effects by stimulating the STAT3/Bcl-XL pathway. To identify novel cellular components that mediate these actions of IR, we irradiated lung cancer cells with sublethal doses of y-rays and screened for the induction of IR-responsive genes by microarray analysis. The genes encoding 2 extracellular proteins, SULF2 and IL-6, were found to be upregulated, and these results were confirmed by polymerase chain reactions and western blot analyses. Because the IR-mediated induction of SULF2 was a novel finding, we also confirmed the phenomenon in vivo using xenograft tumors in mice. Analyses of signaling processes revealed that IR induced SULF2 expression via p53, which then promoted IL-6 expression by stabilizing β-catenin, followed by stimulation of the STAT3/Bcl-XL pathway. Consistently, both SULF2 and IL-6 mediated IR-induced invasion and resistance to death stimuli. To investigate whether SULF2 contributes to IR-induced tumor metastasis, we irradiated tumors in mice with sublethal doses of IR. This treatment promoted the entry of tumor cells into the blood stream (intravasation), which was abolished by downregulating SULF2 expression in tumor cells. These results demonstrated that SULF2 can mediate the detrimental effects of IR in vivo. Therefore, SULF2 may be potentially used as a therapeutic and diagnostic target to predict and overcome the malignant effects of IR, particularly in tumors expressing p53 wild-type.

Insulin-like growth factor-I-stimulated Akt phosphorylation and oligodendrocyte progenitor cell survival require cholesterol-enriched membranes

Previously we showed that insulin-like growth factor-I (IGF-I) promotes sustained phosphorylation of Akt in oligodendrocyte progenitor cells (OPCs) and that Akt phosphorylation is required for survival of these cells. The direct mechanisms, however, by which IGF-I promotes Akt phosphorylation are currently undefined. Recently, cholesterol-enriched membranes (CEMs) have been implicated in regulation of growth factor-mediated activation of the PI3K/Akt pathway and survival of mature oligodendrocytes; however, less is know about their role in OPC survival. In the present study, we investigate the role of CEMs in IGF-I-mediated Akt phosphorylation and OPC survival. We report that acute disruption of membrane cholesterol with methyl-beta-cyclodextrin results in altered OPC morphology and inhibition of IGF-I-mediated Akt phosphorylation. We also report that long-term inhibition of cholesterol biosynthesis with 25-hydroxycholesterol blocks IGF-I stimulated Akt phosphorylation and cell survival. Moreover, we show that the PI3K regulatory subunit, p85, Akt, and the IGF-IR are sequestered within cholesterol-enriched fractions in steady-state stimulation of the IGF-IR and that phosphorylated Akt and IGF-IR are present in cholesterol-enriched fractions with IGF-I stimulation. Together, the results of these studies support a role for CEMs or "lipid rafts" in IGF-I-mediated Akt phosphorylation and provide a better understanding of the mechanisms by which IGF-I promotes OPC survival.

Peroxiredoxin 6 promotes lung cancer cell invasion by inducing urokinase-type plasminogen activator via p38 kinase, phosphoinositide 3-kinase, and Akt

The peroxiredoxin family of peroxidase has six mammalian members (Prx 1-6). Considering their frequent up-regulation in cancer cells, Prxs may contribute to cancer cells' survival in face of oxidative stress. Here, we show that Prx 6 promotes the invasiveness of lung cancer cells, accompanied by an increase in the activity of phosphoinositide 3-kinase (PI3K), the phosphorylation of p38 kinase and Akt, and the protein levels of uPA. Functional studies reveal that these components support Prx 6-induced invasion in the sequence p38 kinase/PI3K, Akt, and uPA. The findings provide a new understanding of the action of Prx 6 in cancer.

BH4 peptide derived from Bcl-xL and Bax-inhibitor peptide suppresses apoptotic mitochondrial changes in heat stressed bovine oocytes

Mitochondria play an important role in the integration and transmission of cell death signals mediated by the Bcl-2 family proteins. Experiments were conducted to determine whether the anti-apoptotic peptides BH4 domain of Bcl-xL (TAT-BH4) and Bax inhibitor peptide (BIP) suppresses heat stress (HS) injury in oocytes by reduction of apoptotic-like events. Cumulus-oocyte complexes (COCs) were matured at 39 degrees C (control) or 41 degrees C (HS) for 21 hr then placed in maturation medium containing 0 or 100 microM BIP in water and 0 or 1 microM TAT-BH4 in dimethyl sulfoxide (DMSO), or a combination of both peptides (BIP + BH4). Peptide effects on embryo development, DNA fragmentation, mitochondrial membrane potential (Delta(Psi)m), and mitochondrial DNA (mtDNA) copy number were measured. All groups were fertilized and cultured in vitro at 39 degrees C for 8 days. Compared to control, HS-treated oocytes induced a decrease in embryo development (P < 0.05), increase in proportion of TUNEL-positive chromatin in oocytes and blastocysts (P < 0.05), and loss of oocyte Delta(Psi)m (P < 0.001). In the presence of BIP or BIP + BH4, development of HS-treated oocytes into blastocysts was increased (P < 0.05). Conversely, COCs matured with TAT-BH4 at 41 degrees C showed reduced embryonic development (P < 0.05). Exposure of HS-treated to each or both peptides resulted in a reduction of TUNEL frequency in oocytes and blastocysts cells derived from these oocytes (P < 0.05). The loss of Delta(Psi)m in HS-treated oocytes was not restored by exposure to BIP + BH4 and there was no effect in mtDNA copy number. In conclusion, the present results show that HS-induced apoptosis in bovine oocytes involves Bax and BH4 domain-dependent pathways.

Amplification of the gamma-irradiation-induced cell death pathway by reactive oxygen species in human U937 cells

Given the critical involvement of reactive oxygen species (ROS) in cell death, their hierarchical status in the cell pathway has been analyzed by many investigators. However, it has been shown that ROS can act either upstream or downstream of various death mediators depending on experimental settings. To investigate whether the contrasting relationships may exist in a single model system, human U937 cells were irradiated with lethal doses of gamma-rays. This resulted in a promotion of mitochondrial ROS production, which was found to be induced via sequential actions of c-Jun N-terminal kinase (JNK), Bax, and caspase-3. Interestingly, the induced ROS, in turn, re-activated JNK, Bax, and caspase-3 in the same model system. Consistently, the blockade of Bax action by RNA interference or Bcl-2 overexpression abolished the activation of JNK induced after, but not before, the production of ROS. Bcl-2 overexpression also blocked the translocation of Bax from the cytosol to the mitochondria only after the induction of ROS. Functional analyses revealed that the initial ROS-independent activations of JNK, Bax, and caspase-3 are not sufficient for cell death, and thus, should be re-activated by ROS in order to kill the cells. These findings suggest that ROS do not simply mediate the lethal action of gamma-irradiation, but actually amplify it by forming a feedback loop between a downstream effector caspase and the upstream initiation signals leading to the activation of JNK. This role for ROS appears to allow Bcl-2 to block the signaling events, which are initially induced upstream.

Role of insulin receptor and balance in insulin receptor isoforms A and B in regulation of apoptosis in simian virus 40-immortalized neonatal hepatocytes

We have investigated the unique role of the insulin receptor (IR) and the balance of its isoforms A and B in the regulation of apoptosis in simian virus 40 (SV40)-immortalized neonatal hepatocytes. Immortalized hepatocytes lacking (HIR KO) or expressing the entire IR (HIR LoxP), and cells expressing either IRA (HIR RecA) or IRB (HIR RecB) have been generated. IR deficiency in hepatocytes increases sensitivity to the withdrawal of growth factors, because these cells display an increase in reactive oxygen species, a decrease in Bcl-x(L), a rapid accumulation of nuclear Foxo1, and up-regulation of Bim. These events resulted in acceleration of caspase-3 activation, DNA laddering, and cell death. The single expression of either IRA or IRB produced a stronger apoptotic phenotype. In these cells, protein complexes containing IRA or IRB and Fas/Fas-associating protein with death domain activated caspase-8, and, ultimately, caspase-3. In hepatocytes expressing IRA, Bid cleavage and cytochrome C release were increased whereas direct activation of caspase-3 by caspase-8 and a more rapid apoptotic process occurred in hepatocytes expressing IRB. Conversely, coexpression of IRA and IRB in IR-deficient hepatocytes rescued from apoptosis. Our results suggest that balance alteration of IRA and IRB may serve as a ligand-independent apoptotic trigger in hepatocytes, which may regulate liver development.

The role of PKCzeta in amikacin-induced apoptosis in the cochlea: prevention by aspirin

Aminoglycoside antibiotics are ototoxic, inducing irreversible sensorineural hearing loss mediated by oxidative and excitotoxic stresses. The NF-kappaB pathway is involved in the response to aminoglycoside damage in the cochlea. However, the molecular mechanisms of this ototoxicity remain unclear. We investigated the expression of PKCzeta, a key regulator of NF-kappaB activation, in response to aminoglycoside treatment. Amikacin induced PKCzeta cleavage and nuclear translocation. These events were concomitant with chromatin condensation and paralleled the decrease in NF-kappaB (p65) levels in the nucleus. Amikacin also induced the nuclear translocation of apoptotic inducing factor (AIF). Prior treatment with aspirin prevented PKCzeta cleavage and nuclear translocation. Thus, aspirin counteracts the early effects of amikacin, thereby protecting hair cells and spiral ganglion neurons. These results demonstrate that PKCzeta acts as sentinel connecting specific survival pathways to mediate cellular responses to amikacin ototoxicity.

Inhibition of phosphatidylinositol 3-kinase causes cell death in rat osteoblasts through inactivation of Akt

Previous evidences indicated that phosphatidylinositol 3-kinase (PI3-kinase) is an important regulatory molecule that is involved in the cell growth and survival, and inhibition of the PI3-kinase activity enhances apoptotic cell death. However, the relationship between PI3-kinase activity and osteoblasts, capable of new bone formation, remained unknown. In the present study, pharmacological inhibitor of PI3-kinase LY294002 was used to observe the role of the PI3-kinase in the growth of rat osteoblasts. To identify its molecular mechanism, Western blots analysis and immunocytochemistry were applied to examine changes of Akt phosphorylation and its distribution. Our data showed that inhibition of PI3-kinase activity significantly triggered the decrease of cell growth, cell apoptosis and loss of mitochondrial membrane potential (Deltapsi(m)). Osteoblastic dysfunction stimulated by LY294002 was accompanied by inactivation of Akt and its redistribution. In all these results demonstrated that inhibition of PI3-kinase induced apoptotic cell death, which was mediated by inactivation of Akt pathway in rat osteoblasts.

C-Phycocyanin inhibits 2-acetylaminofluorene-induced expression of MDR1 in mouse macrophage cells: ROS mediated pathway determined via combination of experimental and In silico analysis

We studied the effects of C-Phycocyanin (C-PC), a biliprotein from Spirulina platensis on the 2-acetylaminofluorene (2-AAF)-induced expression of MDR1, encoded by the multidrug resistance (MDR1) gene, in mouse macrophage cell line (RAW 264.7). Our experimental and In silico studies revealed a significant inhibition of 2-AAF-induced expression of MDR1 protein in C-PC treated mouse macrophage cell line. MDR1 induction by 2-AAF was dependent on ROS (reactive oxygen species)-Akt (protein kinase B)-NF-kappaB (Nuclear factor kappa B) signaling pathway. Generation of ROS, phosphorylation of Akt and corresponding nuclear translocation of NF-kappaB, the events that play a major role in the induction of MDR1 expression, were decreased significantly in C-PC treated cells. NADPH oxidase inhibitor, DPI (Diphenyl iodide), and pharmacological inhibitor of Akt, Akt inhibitor IV, also showed a reduction in MDR1 expression, although not to the same extent as C-PC mediated inhibition of MDR1 expression. To further understand the mechanism, we created a computational model of the detailed ROS-Akt-NF-kappaB pathway. C-PC was modeled purely as a ROS scavenger and this representation matched the experimental trends accurately. Also the ROS levels determined through In silico investigation showed that C-PC was more effective in reduction of MDR1 expression than inhibitors of NADPH oxidase and Akt. Our experimental and In silico studies collectively suggest that 2-AAF induces MDR1 by ROS dependent pathway and C-PC is a potential negative regulator of MDR1 expression. This down regulation of MDR1 expression, induced by xenobiotics such as 2-AAF, suggests C-PC's usefulness in overcoming the drug resistance in cellular systems.

Link between Mitochondria and NADPH Oxidase 1 Isozyme for the Sustained Production of Reactive Oxygen Species and Cell Death

Although mitochondria and the Nox family of NADPH oxidase are major sources of reactive oxygen species (ROS) induced by external stimuli, there is limited information on their functional relationship. This study has shown that serum withdrawal promotes the production of ROS in human 293T cells by stimulating both the mitochondria and Nox1. An analysis of their relationship revealed that the mitochondria respond to serum withdrawal within a few minutes, and the ROS produced by the mitochondria trigger Nox1 action by stimulating phosphoinositide 3-kinase (PI3K) and Rac1. Activation of the PI3K/Rac1/Nox1 pathway was evident 4-8 h after but not earlier than serum withdrawal initiation, and this time lag was found to be required for an additional activator of the pathway, Lyn, to be expressed. Functional analysis suggested that, although the mitochondria contribute to the early (0-4 h) accumulation of ROS, the maintenance of the induced ROS levels to the later (4-8 h) phase required the action of the PI3K/Rac1/Nox1 pathway. Serum withdrawal-treated cells eventually lost their viability, which was reversed by blocking either the mitochondria-dependent induction of ROS using rotenone or KCN or the PI3K/Rac1/Nox1 pathway using the dominant negative mutants or small interfering RNAs. This suggests that mitochondrial ROS are essential but not enough to promote cell death, which requires the sustained accumulation of ROS by the subsequent action of Nox1. Overall, this study shows a signaling link between the mitochondria and Nox1, which is crucial for the sustained accumulation of ROS and cell death in serum withdrawal-induced signaling.