PKB and the mitochondria: AKTing on apoptosis

Modulation of mitochondrial apoptosis by PI3K inhibitors

Most anticancer therapies exert their action by triggering programmed cell death (apoptosis) in cancer cells. The mitochondrial pathway of apoptosis is initiated by mitochondrial outer membrane permeabilization, leading to the release of apoptogenic factors such as cytochrome c or Smac from the mitochondrial intermembrane space into the cytosol. Mitochondrial outer membrane permeabilization is tightly controlled, for example by pro- and anti-apoptotic proteins of the Bcl-2 family. Recent evidence indicates that inhibition of the PI3K/Akt/mTOR pathway by small-molecule PI3K inhibitors primes cancer cells to mitochondrial apoptosis by tipping the balance towards pro-apoptotic Bcl-2 proteins, resulting in increased mitochondrial outer membrane permeabilization. Thus, mitochondrial apoptotic events play an important role in PI3K inhibitor-mediated sensitization for apoptosis.

Mesenchymal stem cells secrete multiple cytokines that promote angiogenesis and have contrasting effects on chemotaxis and apoptosis

We have previously shown that mesenchymal stem cells (MSC) improve function upon integration in ischemic myocardium. We examined whether specific cytokines and growth factors produced by MSCs are able to affect angiogenesis, cellular migration and apoptosis. Conditioned media (CM) was prepared by culturing MSC for 48 hours. CM displayed significantly elevated levels of VEGF, Monocyte Chemoattractant Protein-1 (MCP-1), macrophage inflammatory protein-1α (MIP-1α), MIP-1β and monokine induced by IFN-γ (MIG) compared to control media. MSC contained RNA for these factors as detected by RT-PCR. CM was able to induce angiogenesis in canine vascular endothelial cells. MCP-1 and MIP-1α increased cell migration of MSC while VEGF reduced it. H9c2 cells treated with CM under hypoxic conditions for 24 hours displayed a 16% reduction in caspase-3 activity compared to controls. PI 3-kinase γ inhibitor had no effect on controls but reversed the effect of CM on caspase-3 activity. MCP-1 alone mimicked the protective effect of CM while the PI 3-Kγ inhibitor did not reverse the effect of MCP-1. CM reduced phospho-BAD (Ser112) and phospho-Akt (Ser473) while increasing phospho-Akt (Thr308). MCP-1 reduced the level of phospho-Akt (Ser473) while having no effect on the other two; the PI 3-Kγ inhibitor did not alter the MCP-1 effect. ERK 1/2 phosphorylation was reduced in CM treated H9c2 cells, and inhibition of ERK 1/2 reduced the phosphorylation of Akt (Ser473), Akt (Thr308) and Bad (Ser112). In conclusion, MSC synthesize and secrete multiple paracrine factors that are able to affect MSC migration, promote angiogenesis and reduce apoptosis. While both MCP-1 and PI3-kinase are involved in the protective effect, they are independent of each other. It is likely that multiple pro-survival factors in addition to MCP-1 are secreted by MSC which act on divergent intracellular signaling pathways.

Specific roles of Akt iso forms in apoptosis and axon growth regulation in neurons

Akt is a member of the AGC kinase family and consists of three isoforms. As one of the major regulators of the class I PI3 kinase pathway, it has a key role in the control of cell metabolism, growth, and survival. Although it has been extensively studied in the nervous system, we have only a faint knowledge of the specific role of each isoform in differentiated neurons. Here, we have used both cortical and hippocampal neuronal cultures to analyse their function. We characterized the expression and function of Akt isoforms, and some of their substrates along different stages of neuronal development using a specific shRNA approach to elucidate the involvement of each isoform in neuron viability, axon development, and cell signalling. Our results suggest that three Akt isoforms show substantial compensation in many processes. However, the disruption of Akt2 and Akt3 significantly reduced neuron viability and axon length. These changes correlated with a tendency to increase in active caspase 3 and a decrease in the phosphorylation of some elements of the mTORC1 pathway. Indeed, the decrease of Akt2 and more evident the inhibition of Akt3 reduced the expression and phosphorylation of S6. All these data indicate that Akt2 and Akt3 specifically regulate some aspects of apoptosis and cell growth in cultured neurons and may contribute to the understanding of mechanisms of neuron death and pathologies that show deregulated growth.

Signaling pathways mediating the neuroprotective effects of sex steroids and SERMs in Parkinson's disease

Studies with the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson's disease have shown the ability of 17β-estradiol to protect the nigrostriatal dopaminergic system. This paper reviews the signaling pathways mediating the neuroprotective effect of 17β-estradiol against MPTP-induced toxicity. The mechanisms of 17β-estradiol action implicate activation of signaling pathways such as the phosphatidylinositol-3 kinase/Akt and the mitogen-activated protein kinase pathways. 17β-estradiol signaling is complex and integrates multiple interactions with signaling molecules that act to potentiate a protective effect. 17β-estradiol signaling is mediated via estrogen receptors, including GPER1, but others receptors, such as the IGF-1 receptor, are implicated in the neuroprotective effect. Glial and neuronal crosstalk is a critical factor in the maintenance of dopamine neuronal survival and in the neuroprotective action of 17β-estradiol. Compounds that stimulate GPER1 such as selective estrogen receptor modulators and phytoestrogens show neuroprotective activity and are alternatives to 17β-estradiol.

Receptor-specific mechanisms regulate phosphorylation of AKT at Ser473: role of RICTOR in β1 integrin-mediated cell survival

A tight control over AKT/PKB activation is essential for cells, and they realise this in part by regulating the phosphorylation of Ser473 in the “hydrophobic motif” of the AKT carboxy-terminal region. The RICTOR-mTOR complex (TORC2) is a major kinase for AKT Ser473 phosphorylation after stimulation by several growth factors, in a reaction proposed to require p21-activated kinase (PAK) as a scaffold. However, other kinases may catalyse this reaction in stimuli-specific manners. Here we characterised the requirement of RICTOR, ILK, and PAK for AKT Ser473 phosphorylation downstream of selected family members of integrins, G protein-coupled receptors, and tyrosine-kinase receptors and analysed the importance of this phosphorylation site for adhesion-mediated survival. siRNA-mediated knockdown in HeLa and MCF7 cells showed that RICTOR-mTOR was required for phosphorylation of AKT Ser473, and for efficient phosphorylation of the downstream AKT targets FOXO1 Thr24 and BAD Ser136, in response to β1 integrin-stimulation. ILK and PAK1/2 were dispensable for these reactions. RICTOR knockdown increased the number of apoptotic MCF7 cells on β1 integrin ligands up to 2-fold after 24 h in serum-free conditions. β1 integrin-stimulation induced phosphorylation of both AKT1 and AKT2 but markedly preferred AKT2. RICTOR-mTOR was required also for LPA-induced AKT Ser473 phosphorylation in MCF7 cells, but, interestingly, not in HeLa cells. PAK was needed for the AKT Ser473 phosphorylation in response to LPA and PDGF, but not to EGF. These results demonstrate that different receptors utilise different enzyme complexes to phosphorylate AKT at Ser473, and that AKT Ser473 phosphorylation significantly contributes to β1 integrin-mediated anchorage-dependent survival of cells.

Protein Kinase Signaling at the Crossroads of Myocyte Life and Death in Ischemic Heart Disease

Myocardial ischemia results in death of cardiac myocytes via tightly-regulated and interconnected signaling pathways. Protein kinases play crucial roles in this regulation and are highly amenable to therapeutic intervention, making targeted inhibition an attractive strategy for ischemic heart disease. Recent studies have uncovered numerous kinases that participate in the cardiomyocyte response to ischemic injury, thus potentiating the development of new therapeutics. Moreover, many kinase signaling pathways converge at the mitochondria, a key participant in both cardiomyocyte physiology and the pathogenesis of ischemic heart disease. Herein we highlight kinase pathways regulating three major drivers of cell death: mitochondrial permeability transition pore opening (mPTP), programmed necrosis and Ca²⁺ overload-induced mitochondrial dysfunction. Inhibition of each of these kinase pathways has been proposed as a means to limit cardiomyocyte death from ischemia/reperfusion (I/R) injury.

Ampelopsin inhibits H₂O₂-induced apoptosis by ERK and Akt signaling pathways and up-regulation of heme oxygenase-1

Oxidative stress plays an important role in neurodegenerative disorders. Ampelopsin, a flavonoid abundant in Rattan tea (Ampelopsis grossedentata), is a potent antioxidant and its neuroprotective effect against H₂O₂-induced apoptosis in PC12 cells is investigated here for the first time. It was found that treatment of cells with ampelopsin for 1 h significantly reduced the loss of vitality, LDH release and apoptosis and inhibited the formation of reactive oxygen species (ROS). Ampelopsin was able to prevent the activation of p38 induced by H₂O₂. In addition, up-regulation of heme oxygenase-1 (HO-1) expression by ampelopsin was shown to be both dose- and time-dependent. Mechanically, HO-1 expression induced by ampelopsin was found to be due to activation of the ERK and Akt signaling pathways, because it was almost completely blocked by the specific inhibitors of ERK and Akt. These results suggest that ampelopsin increases cellular antioxidant defense through activation of the ERK and Akt signaling pathways, which induces HO-1 expression and thereby protects PC12 cells from H₂O₂-induced apoptosis.

AKT signaling pathway activated by HIN-1 methylation in non-small cell lung cancer

The purpose of this study is to determine the epigenetic changes and function of High in Normal-1 (HIN-1) in non-small cell lung cancer (NSCLC). HIN-1 expression was examined by semiquantitative RT-PCR before and after 5-aza-2'-deoxycytidine (5-aza) treatment in NSCLC cell lines. Promoter methylation status of HIN-1 was tested by methylation-specific PCR (MSP). Effect of forced expression of HIN-1 on different key molecules of AKT signaling pathway was tested by Western Blot analysis in H157 and H23 cell lines. Promoter methylations are inversely correlated with expression of HIN-1 in eight (H23, H157, 95D, H1299, H358, H1752, H460, A549) of ten NSCLC cell lines and re-expression was observed by 5-aza treatment. We then tested promoter methylation of HIN-1 in primary NSCLC tissues. Methylation was detected in 73 out of 152 (48%) NSCLC cases. Forced expression of HIN-1 in NSCLC cell lines inhibited colony formation and induce apoptosis. Furthermore, overexpression of HIN-1 reduces the expression of phosphorated-AKT (p-AKT), c-myc, Bcl-2 and cyclinD1 while Bax was increased. Our data suggest that HIN-1 is a potential tumor suppressor gene in NSCLC, silenced by promoter hypermethylation and negatively regulate AKT signaling pathway.

Protein kinases and phosphatases in the control of cell fate

Protein phosphorylation controls many aspects of cell fate and is often deregulated in pathological conditions. Several recent findings have provided an intriguing insight into the spatial regulation of protein phosphorylation across different subcellular compartments and how this can be finely orchestrated by specific kinases and phosphatases. In this review, the focus will be placed on (i) the phosphoinositide 3-kinase (PI3K) pathway, specifically on the kinases Akt and mTOR and on the phosphatases PP2a and PTEN, and on (ii) the PKC family of serine/threonine kinases. We will look at general aspects of cell physiology controlled by these kinases and phosphatases, highlighting the signalling pathways that drive cell division, proliferation, and apoptosis.

High cell surface death receptor expression determines type I versus type II signaling

Previous studies have suggested that there are two signaling pathways leading from ligation of the Fas receptor to induction of apoptosis. Type I signaling involves Fas ligand-induced recruitment of large amounts of FADD (FAS-associated death domain protein) and procaspase 8, leading to direct activation of caspase 3, whereas type II signaling involves Bid-mediated mitochondrial perturbation to amplify a more modest death receptor-initiated signal. The biochemical basis for this dichotomy has previously been unclear. Here we show that type I cells have a longer half-life for Fas message and express higher amounts of cell surface Fas, explaining the increased recruitment of FADD and subsequent signaling. Moreover, we demonstrate that cells with type II Fas signaling (Jurkat or HCT-15) can signal through a type I pathway upon forced receptor overexpression and that shRNA-mediated Fas down-regulation converts cells with type I signaling (A498) to type II signaling. Importantly, the same cells can exhibit type I signaling for Fas and type II signaling for TRAIL (TNF-α-related apoptosis-inducing ligand), indicating that the choice of signaling pathway is related to the specific receptor, not some other cellular feature. Additional experiments revealed that up-regulation of cell surface death receptor 5 levels by treatment with 7-ethyl-10-hydroxy-camptothecin converted TRAIL signaling in HCT116 cells from type II to type I. Collectively, these results suggest that the type I/type II dichotomy reflects differences in cell surface death receptor expression.

Susceptibility to simvastatin-induced toxicity is partly determined by mitochondrial respiration and phosphorylation state of Akt

Statins are widely used to prevent cardiovascular diseases. They are well-tolerated, with side-effects mainly seen in skeletal muscle. How these side-effects are caused is unknown. We compared isolated primary mouse skeletal muscle myocytes, C2C12 myotubes and liver HepG2 cells to detect differences that could uncover why statins are toxic in skeletal muscle but less so in the liver. 10μM simvastatin caused a decrease in mitochondrial respiration in the primary mouse myocytes and C2C12 myotubes, but had no effect in the HepG2 cells. Mitochondrial integrity is maintained by multiple signaling pathways. One of these pathways, Igf-1/Akt signaling, is also heavily implicated in causing statin-induced toxicity by upregulating atrogin-1. We found that phosphorylated Akt was reduced in C2C12 myotubes but not in HepG2 cells. HepG2 mitochondrial respiration became susceptible to simvastatin-treatment after Akt inhibition, and mitochondrial respiration was rescued in Igf-1-treated C2C12 myotubes. These results suggest that disruption of Igf-1/Akt signaling is a causative factor in simvastatin-induced mitochondrial dysfunction in C2C12 myotubes, whereas HepG2 cells are protected by maintaining Igf-1/Akt signaling. We conclude that phosphorylation of Akt is a key indicator of susceptibility to statin-induced toxicity. How statins can disrupt Igf-1/Akt signaling is unknown. Statins reduce geranylgeranylation of small GTPases, such as Rap1. Previous studies implicate Rap1 as a link between cAMP/Epac and Igf-1/Akt signaling. Transient transfection of constitutively active Rap1 into C2C12 myotubes led to a partial rescue of simvastatin-induced inhibition of mitochondrial respiration, providing a novel link between signaling and respiration.

Integrin signaling, cell survival, and anoikis: distinctions, differences, and differentiation

Cell survival and apoptosis implicate an increasing complexity of players and signaling pathways which regulate not only the decision-making process of surviving (or dying), but as well the execution of cell death proper. The same complex nature applies to anoikis, a form of caspase-dependent apoptosis that is largely regulated by integrin-mediated, cell-extracellular matrix interactions. Not surprisingly, the regulation of cell survival, apoptosis, and anoikis furthermore implicates additional mechanistic distinctions according to the specific tissue, cell type, and species. Incidentally, studies in recent years have unearthed yet another layer of complexity in the regulation of these cell processes, namely, the implication of cell differentiation state-specific mechanisms. Further analyses of such differentiation state-distinct mechanisms, either under normal or physiopathological contexts, should increase our understanding of diseases which implicate a deregulation of integrin function, cell survival, and anoikis.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

A requirement for the p85 PI3K adapter protein BCAP in the protection of macrophages from apoptosis induced by endoplasmic reticulum stress

Macrophages are innate immune cells that play key roles in regulation of the immune response and in tissue injury and repair. In response to specific innate immune stimuli, macrophages may exhibit signs of endoplasmic reticulum (ER) stress and progress to apoptosis. Factors that regulate macrophage survival under these conditions are poorly understood. In this study, we identified B cell adapter protein (BCAP), a p85 PI3K-binding adapter protein, in promoting survival in response to the combined challenge of LPS and ER stress. BCAP was unique among nine PI3K adapter proteins in being induced >10-fold in response to LPS. LPS-stimulated macrophages incubated with thapsigargin, a sarcoplasmic/endoplasmic reticulum calcium ATPase inhibitor that induces ER stress, underwent caspase-3 activation and apoptosis. Macrophages from BCAP(-/-) mice exhibited increased apoptosis in response to these stimuli. BCAP-deficient macrophages demonstrated decreased activation of Akt, but not ERK, and, unlike BCAP-deficient B cells, expressed normal amounts of the NF-κB subunits, c-Rel and RelA. Retroviral transduction of BCAP-deficient macrophages with wild-type BCAP, but not a Y4F BCAP mutant defective in binding the SH2 domain of p85 PI3K, reversed the proapoptotic phenotype observed in BCAP-deficient macrophages. We conclude that BCAP is a nonredundant PI3K adapter protein in macrophages that is required for maximal cell survival in response to ER stress. We suggest that as macrophages engage their pathogenic targets, innate immune receptors trigger increased expression of BCAP, which endows them with the capacity to withstand further challenges from ongoing cellular insults, such as ER stress.

Experimental therapy of ovarian cancer with synthetic makaluvamine analog: in vitro and in vivo anticancer activity and molecular mechanisms of action

The present study was designed to determine the biological effects of novel marine alkaloid analog 7-(4-fluorobenzylamino)-1,3,4,8-tetrahydropyrrolo[4,3,2-de]quinolin-8(1H)-one (FBA-TPQ) on human ovarian cancer cells for its anti-tumor potential and the underlying mechanisms as a novel chemotherapeutic agent. Human ovarian cancer cells (A2780 and OVCAR-3), and Immortalized non-tumorigenic human Ovarian Surface Epithelial cells (IOSE-144), were exposed to FBA-TPQ for initial cytotoxicity evaluation (via MTS assay kit, Promega). The detailed in-vitro (cell level) and in-vivo (animal model) studies on the antitumor effects and possible underlying mechanisms of action of the compounds were then performed. FBA-TPQ exerted potent cytotoxicity against human ovarian cancer A2780 and OVCAR-3 cells as an effective inhibitor of cell growth and proliferation, while exerting lesser effects on non-tumorigenic IOSE-144 cells. Further study in the more sensitive OVCAR-3 cell line showed that it could potently induce cell apoptosis (Annexin V-FITC assay), G2/M cell cycle arrest (PI staining analysis) and also dose-dependently inhibit OVCAR-3 xenograft tumors' growth on female athymic nude mice (BALB/c, nu/nu). Mechanistic studies (both in vitro and in vivo) revealed that FBA-TPQ might exert its activity through Reactive Oxygen Species (ROS)-associated activation of the death receptor, p53-MDM2, and PI3K-Akt pathways in OVCAR-3 cells, which is in accordance with in vitro microarray (Human genome microarrays, Agilent) data analysis (GEO accession number: GSE25317). In conclusion, FBA-TPQ exhibits significant anticancer activity against ovarian cancer cells, with minimal toxicity to non-tumorigenic human IOSE-144 cells, indicating that it may be a potential therapeutic agent for ovarian cancer.

Benzothiophene Selective Estrogen Receptor Modulators Provide Neuroprotection by a novel GPR30-dependent Mechanism

The clinical benzothiophene SERM (BT-SERM), raloxifene, was compared with estrogens in protection of primary rat neurons against oxygen-glucose deprivation (OGD). Structure-activity relationships for neuroprotection were determined for a family of BT-SERMs displaying a spectrum of ERα and ERβ binding affinity and agonist/antagonist activity, leading to discovery of a neuroprotective pharmacophore, present in the clinically relevant SERMS, raloxifene and desmethylarzoxifene (DMA), for which submicromolar potency was observed for neuroprotection. BT-SERM neuroprotection did not correlate with binding to ER nor classical ER activity, however, both the neuroprotective SERMs and estrogens were shown, using pharmacological probes, to activate the same kinase signaling cascades. The antiestrogen ICI 182,780 inhibited the actions of estrogens, but not those of BT-SERMs, whereas antagonism of the G-protein coupled receptor, GPR30, was effective for both SERMs and estrogens. Since SERMs have antioxidant activity, ER-independent mechanisms were studied using the classical phenolic antioxidants, BHT and Trolox, and the Nrf2-dependent cytoprotective electrophile, sulforaphane. However, neuroprotection by these agents was not sensitive to GPR30 antagonism. Collectively, these data indicate that the activity of neuroprotective BT-SERMs is GPR30-dependent and ER-independent and not mediated by antioxidant effects. Comparison of novel BT-SERM derivatives and analogs identified a neuroprotective pharmacophore of potential use in design of novel neuroprotective agents with a spectrum of ER activity.

Phosphatidylserine is a critical modulator for Akt activation

Akt activation relies on the binding of Akt to phosphatidylinositol-3,4,5-trisphosphate (PIP(3)) in the membrane. Here, we demonstrate that Akt activation requires not only PIP(3) but also membrane phosphatidylserine (PS). The extent of insulin-like growth factor-induced Akt activation and downstream signaling as well as cell survival under serum starvation conditions positively correlates with plasma membrane PS levels in living cells. PS promotes Akt-PIP(3) binding, participates in PIP(3)-induced Akt interdomain conformational changes for T308 phosphorylation, and causes an open conformation that allows for S473 phosphorylation by mTORC2. PS interacts with specific residues in the pleckstrin homology (PH) and regulatory (RD) domains of Akt. Disruption of PS-Akt interaction by mutation impairs Akt signaling and increases susceptibility to cell death. These data identify a critical function of PS for Akt activation and cell survival, particularly in conditions with limited PIP(3) availability. The novel molecular interaction mechanism for Akt activation suggests potential new targets for controlling Akt-dependent cell survival and proliferation.

The kinase SGK1 in the endoderm and mesoderm promotes ectodermal survival by down-regulating components of the death-inducing signaling complex

A balance between cell survival and apoptosis is essential for animal development. Although proper development involves multiple interactions between germ layers, little is known about the intercellular and intertissue signaling pathways that promote cell survival in neighboring or distant germ layers. We found that serum- and glucocorticoid-inducible kinase 1 (SGK1) promoted ectodermal cell survival during early Xenopus embryogenesis through a non-cell-autonomous mechanism. Dorsal depletion of SGK1 in Xenopus embryos resulted in shortened axes and reduced head structures with defective eyes, and ventral depletion led to defective tail morphologies. Although the gene encoding SGK1 was mainly expressed in the endoderm and dorsal mesoderm, knockdown of SGK1 caused excessive apoptosis in the ectoderm. SGK1-depleted ectodermal explants showed little or no apoptosis, suggesting non-cell-autonomous effects of SGK1 on ectodermal cells. Microarray analysis revealed that SGK1 knockdown increased the expression of genes encoding FADD (Fas-associated death domain protein) and caspase-10, components of the death-inducing signaling complex (DISC). Inhibition of DISC function suppressed excessive apoptosis in SGK1-knockdown embryos. SGK1 acted through the transcription factor nuclear factor κB (NF-κB) to stimulate production of bone morphogenetic protein 7 (BMP7), and overexpression of BMP7 in SGK1-knockdown embryos reduced the abundance of DISC components. We show that phosphoinositide 3-kinase (PI3K) functioned upstream of SGK1, thus revealing an endodermal and mesodermal pathway from PI3K to SGK1 to NF-κB that produces BMP7, which promotes ectodermal survival by decreasing DISC function.

The α-isoform of class II phosphoinositide 3-kinase is necessary for the activation of ERK but not Akt/PKB

Phosphoinositide 3-kinases (PI3Ks) are key enzymes that activate intracellular signaling molecules when a number of different growth factors bind to cell surface receptors. PI3Ks are divided into three classes (I, II, III), and enzymes of each class have different tissue specificities and physiological functions. The α-isoform (PI3K-C2α) of class II PI3Ks is considered ubiquitous and preferentially activated by insulin. Our previous study showed that suppression of PI3K-C2α leads to apoptotic cell death. The aim of this study is to determine whether depletion of PI3K-C2α affects ERK or PKB/Akt activity following stimulation with serum and insulin growth factors in Chinese hamster ovary cells expressing human insulin receptors (CHO-IR) and human HepG2 liver cells. Different antisense oligonucleotides (ODNs), which were designed based on the sequence of the C2 domain of the human PI3K-C2α gene, were transfected into cells to inhibit PI3K-C2α expression. Insulin- or serum-induced stimulation of ERK was significantly suppressed by depletion of PI3K-C2α, whereas phosphorylation of IRS-1 and the stimulation of PKB/Akt by insulin were not affected. The number of apoptotic cells was also increased by depletion of PI3K-C2α protein levels. Taken together, our data indicate that PI3K-C2α may be a crucial factor in the stimulation of ERK activity in response to serum or insulin, whereas it is less important for the stimulation of PKB/Akt activity in response to insulin.

Protein kinase networks regulating glucocorticoid-induced apoptosis of hematopoietic cancer cells: fundamental aspects and practical considerations

Glucocorticoids (GCs) are integral components in the treatment protocols of acute lymphoblastic leukemia, multiple myeloma, and non-Hodgkin lymphoma owing to their ability to induce apoptosis of these malignant cells. Resistance to GC therapy is associated with poor prognosis. Although they have been used in clinics for decades, the signal transduction pathways involved in GC-induced apoptosis have only partly been resolved. Accumulating evidence shows that this cell death process is mediated by a communication between nuclear GR affecting gene transcription of pro-apoptotic genes such as Bim, mitochondrial GR affecting the physiology of the mitochondria, and the protein kinase glycogen synthase kinase-3 (GSK3), which interacts with Bim following exposure to GCs. Prevention of Bim up-regulation, mitochondrial GR translocation, and/or GSK3 activation are common causes leading to GC therapy failure. Various protein kinases positively regulating the pro-survival Src-PI3K-Akt-mTOR and Raf-Ras-MEK-ERK signal cascades have been shown to be activated in malignant leukemic cells and antagonize GC-induced apoptosis by inhibiting GSK3 activation and Bim expression. Targeting these protein kinases has proven effective in sensitizing GR-positive malignant lymphoid cells to GC-induced apoptosis. Thus, intervening with the pro-survival kinase network in GC-resistant cells should be a good means of improving GC therapy of hematopoietic malignancies.

Cardioprotective properties of Crataegus oxycantha extract against ischemia-reperfusion injury

The aim of the study was to investigate the cardioprotective effect and mechanism of Crataegus oxycantha (COC) extract, a well-known natural antioxidant-based cardiotonic, against ischemia/reperfusion (I/R) injury. Electron paramagnetic resonance studies showed that COC extract was capable of scavenging superoxide, hydroxyl, and peroxyl radicals, in vitro. The cardioprotective efficacy of the extract was studied in a crystalloid perfused heart model of I/R injury. Hearts were subjected to 30min of global ischemia followed by 45min of reperfusion. During reperfusion, COC extract was infused at a dose rate of 1mg/ml/min for 10min. Hearts treated with COC extract showed a significant recovery in cardiac contractile function, reduction in infarct size, and decrease in creatine kinase and lactate dehydrogenase activities. The expressions of xanthine oxidase and NADPH oxidase were significantly reduced in the treated group. A significant upregulation of the anti-apoptotic proteins Bcl-2 and Hsp70 with simultaneous downregulation of the pro-apoptotic proteins cytochrome c and cleaved caspase-3 was observed. The molecular signaling cascade including phospho-Akt (ser-473) and HIF-1alpha that lead to the activation or suppression of apoptotic pathway also showed a significant protective role in the treatment group. No significant change in phospho-p38 levels was observed. The results suggested that the COC extract may reduce the oxidative stress in the reperfused myocardium, and play a significant role in the inhibition of apoptotic pathways leading to cardioprotection.

Mixed lineage kinase-3 stabilizes and functionally cooperates with TRIBBLES-3 to compromise mitochondrial integrity in cytokine-induced death of pancreatic beta cells

Mixed lineage kinases (MLKs) have been implicated in cytokine signaling as well as in cell death pathways. Our studies show that MLK3 is activated in leukocyte-infiltrated islets of non-obese diabetic mice and that MLK3 activation compromises mitochondrial integrity and induces apoptosis of beta cells. Using an ex vivo model of islet-splenocyte co-culture, we show that MLK3 mediates its effects via the pseudokinase TRB3, a mammalian homolog of Drosophila Tribbles. TRB3 expression strongly coincided with conformational change and mitochondrial translocation of BAX. Mechanistically, MLK3 directly interacted with and stabilized TRB3, resulting in inhibition of Akt, a strong suppressor of BAX translocation and mitochondrial membrane permeabilization. Accordingly, attenuation of MLK3 or TRB3 expression each prevented cytokine-induced BAX conformational change and attenuated the progression to apoptosis. We conclude that MLKs compromise mitochondrial integrity and suppress cellular survival mechanisms via TRB3-dependent inhibition of Akt.

Lipoxin A4 impairment of apoptotic signaling in macrophages: implication of the PI3K/Akt and the ERK/Nrf-2 defense pathways

Lipoxin A(4) (LXA(4)) is an endogenous lipid mediator that requires transcellular metabolic traffic for its synthesis. The targets of LXA(4) on neutrophils are well described, contributing to attenuation of inflammation. However, effects of lipoxins on macrophage are less known, particularly the action of LXA(4) on the regulation of apoptosis of these cells. Our data show that pretreatment of human or murine macrophages with LXA(4) at the concentrations prevailing in the course of resolution of inflammation (nanomolar range) significantly inhibits the apoptosis induced by staurosporine, etoposide and S-nitrosoglutathione or by more pathophysiological stimuli, such as LPS/IFNgamma challenge. The release of mitochondrial mediators of apoptosis and the activation of caspases was abrogated in the presence of LXA(4). In addition to this, the synthesis of reactive oxygen species induced by staurosporine was attenuated and antiapoptotic proteins of the Bcl-2 family accumulated in the presence of lipoxin. Analysis of the targets of LXA(4) identified an early activation of the PI3K/Akt and ERK/Nrf-2 pathways, which was required for the observation of the antiapoptotic effects of LXA(4). These data suggest that the LXA(4), released after the recruitment of neutrophils to sites of inflammation, exerts a protective effect on macrophage viability that might contribute to a better resolution of inflammation.

NSAIDs, Mitochondria and Calcium Signaling: Special Focus on Aspirin/Salicylates

Aspirin (acetylsalicylic acid) is a well-known nonsteroidal anti-inflammatory drug (NSAID) that has long been used as an anti-pyretic and analgesic drug. Recently, much attention has been paid to the chemopreventive and apoptosis-inducing effects of NSAIDs in cancer cells. These effects have been thought to be primarily attributed to the inhibition of cyclooxygenase activity and prostaglandin synthesis. However, recent studies have demonstrated unequivocally that certain NSAIDs, including aspirin and its metabolite salicylic acid, exert their anti-inflammatory and chemopreventive effects independently of cyclooxygenase activity and prostaglandin synthesis inhibition. It is becoming increasingly evident that two potential common targets of NSAIDs are mitochondria and the Ca²⁺ signaling pathway. In this review, we provide an overview of the current knowledge regarding the roles of mitochondria and Ca²⁺ in the apoptosis-inducing effects as well as some side effects of aspirin, salicylates and other NSAIDs, and introducing the emerging role of L-type Ca²⁺ channels, a new Ca²⁺ entry pathway in non-excitable cells that is up-regulated in human cancer cells.

Vascular endothelial growth factor increases neurogenesis after traumatic brain injury

Activation of endogenous stem cells has been proposed as a novel form of therapy in a variety of neurologic disorders including traumatic brain injury (TBI). Vascular endothelial growth factor (VEGF) is expressed in the brain after TBI and serves as a potent activator of angiogenesis and neurogenesis. In this study, we infused exogenous VEGF into the lateral ventricles of mice for 7 days after TBI using mini-osmotic pumps to evaluate the effects on recovery and functional outcome. The results of our study show that VEGF significantly increases the number of proliferating cells in the subventricular zone and in the perilesion cortex. Fate analysis showed that most newborn cells differentiated into astrocytes and oligodendroglia and only a few cells differentiated into neurons. Functional outcome was significantly better in mice treated with VEGF compared with vehicle-treated animals after TBI. Injury size was significantly smaller at 90 days after TBI in VEGF-treated animals, suggesting additional neuroprotective effects of VEGF. In conclusion, VEGF significantly augments neurogenesis and angiogenesis and reduces lesion volumes after TBI. These changes are associated with significant improvement in recovery rates and functional outcome.

Selective blockade of protein kinase B protects the rat and human myocardium against ischaemic injury

Protein kinase B (PKB/Akt) plays a critical role in cell survival but the investigation of its involvement has been limited by the lack of specific pharmacological agents. In this study, using novel PKB inhibitors (VIII and XI), we investigated the role of PKB in cardioprotection of the rat and human myocardium, the location of PKB in relation to mitoK(ATP) channels and p38 mitogen-activated protein kinase (p38 MAPK), and whether the manipulation of PKB can overcome the unresponsiveness to protection of the diabetic myocardium. Myocardial slices from rat left ventricle and from the right atrial appendage of patients undergoing elective cardiac surgery were subjected to 90 min ischaemia/120 min reoxygenation at 37 degrees C. Tissue injury was assessed by creatine kinase (CK) released and determination of cell necrosis and apoptosis. The results showed that blockade of PKB activity caused significant reduction of CK release and cell death, a benefit that was as potent as ischaemic preconditioning and could be reproduced by blockade of phosphatidylinositol 3-kinase (PI-3K) with wortmannin and LY 294002. The protection was time dependent with maximal benefit seen when PKB and PI-3K were inhibited before ischaemia or during both ischaemia and reoxygenation. In addition, it was revealed that PKB is located downstream of mitoK(ATP) channels but upstream of p38 MAPK. PKB inhibition induced a similar degree of protection in the human and rat myocardium and, importantly, it reversed the unresponsiveness to protection of the diabetic myocardium. In conclusion, inhibition of PKB plays a critical role in protection of the mammalian myocardium and may represent a clinical target for the reduction of ischaemic injury.

Phosphoinositide 3-kinase signaling in the vertebrate retina

The phosphoinositide (PI) cycle, discovered over 50 years ago by Mabel and Lowell Hokin, describes a series of biochemical reactions that occur on the inner leaflet of the plasma membrane of cells in response to receptor activation by extracellular stimuli. Studies from our laboratory have shown that the retina and rod outer segments (ROSs) have active PI metabolism. Biochemical studies revealed that the ROSs contain the enzymes necessary for phosphorylation of phosphoinositides. We showed that light stimulates various components of the PI cycle in the vertebrate ROS, including diacylglycerol kinase, PI synthetase, phosphatidylinositol phosphate kinase, phospholipase C, and phosphoinositide 3-kinase (PI3K). This article describes recent studies on the PI3K-generated PI lipid second messengers in the control and regulation of PI-binding proteins in the vertebrate retina.

Identification of a novel proapoptotic function of resveratrol in fat cells: SIRT1-independent sensitization to TRAIL-induced apoptosis

The phytochemical resveratrol has recently gained attention for its protection against metabolic disease and for extension of life span, which have been linked to its metabolic effects and SIRT1 activation in fat cells. However, little is known about the effect of resveratrol on fat cell apoptosis. Here, we identify a novel, SIRT1-independent mechanism by which resveratrol regulates fat cell numbers. We demonstrate for the first time that resveratrol enhances TNF-related apoptosis-inducing ligand (TRAIL)- or CD95-induced apoptosis of human preadipocytes in a highly synergistic manner (EC(50) at 72 h: resveratrol, >300 microM; TRAIL, >100 ng/ml; combination: 30 microM resveratrol and 10 ng/ml TRAIL, combination index 0.4). Similar results in primary human preadipocytes prepared from subcutaneous white adipose tissue and mature human adipocytes underline the relevance to human physiology. Mechanistic studies reveal that resveratrol inhibits PI3K-driven phosphorylation of Akt, leading to increased Bax activation, loss of mitochondrial membrane potential, cytochrome c release, and caspase-dependent apoptosis. The synergistic interaction of resveratrol and TRAIL depends on the intrinsic apoptosis pathway and caspases, since Bcl-2 overexpression and the caspase inhibitor zVAD.fmk inhibit apoptosis, whereas knockdown of SIRT1 by RNA interference has no effect. The discovery of this novel activity of resveratrol significantly advances the knowledge of fat tissue regulation by resveratrol and has important implications for its use in metabolic and age-related diseases.

Serine/threonine kinase akt activation regulates the activity of retinal serine/threonine phosphatases, PHLPP and PHLPPL

In our previous studies, we have shown that insulin receptor (IR) activation leads to the activation of phosphoinositide 3-kinase (PI3K) and Akt activation in rod photoreceptors. This pathway is functionally important for photoreceptor survival as deletion of IR and one of the isoforms of Akt (Akt2) resulted in stress-induced photoreceptor degeneration. However, the molecular mechanism of this degeneration is not known. Akt signaling is known to be regulated by the serine/threonine phosphatases, PH domain and leucine-rich repeat protein phosphatases (PHLPP) and PHLPP-like (PHLPPL). In this study, we characterized these two phosphatases in the retina and examined the role of IR, PI3K, and Akt signaling on the activity of PHLPP and PHLPPL. Most of the studies published on PHLPP and PHLPPL are directed toward Akt dephosphorylation; however, there are no studies available to date on how the enzyme activities of these phosphatases are regulated. We made a novel finding in this study that both PHLPP and PHLPPL activities were significantly decreased in the presence of insulin ex vivo. The insulin-induced decrease of phosphatase activities were PI3K-dependent as pre-treatment of ex vivo retinal cultures with LY294002 significantly reversed the insulin-induced inhibition. It has been shown previously that PHLPP and PHLPPL regulate the dephosphorylation of Akt isoforms, and our results demonstrate for the first time that retinal PHLPP and PHLPPL activities are under the control of the IR-activated PI3K/Akt pathway.

Cannabinoid receptor ligands as potential anticancer agents — high hopes for new therapies?

Objectives

The endocannabinoid system is an endogenous lipid signalling network comprising arachidonic-acid-derived ligands, cannabinoid (CB) receptors, transporters and endocannabinoid degrading enzymes. The CB1 receptor is predominantly expressed in neurons but is also co-expressed with the CB2 receptor in peripheral tissues. In recent years, CB receptor ligands, including Δ9-tetrahydrocannabinol, have been proposed as potential anticancer agents.

Key findings

This review critically discusses the pharmacology of CB receptor activation as a novel therapeutic anticancer strategy in terms of ligand selectivity, tissue specificity and potency. Intriguingly, antitumour effects mediated by cannabinoids are not confined to inhibition of cancer cell proliferation; cannabinoids also reduce angiogenesis, cell migration and metastasis, inhibit carcinogenesis and attenuate inflammatory processes. In the last decade several new selective CB1 and CB2 receptor agents have been described, but most studies in the area of cancer research have used non-selective CB ligands. Moreover, many of these ligands exert prominent CB receptor-independent pharmacological effects, such as activation of the G-protein-coupled receptor GPR55, peroxisome proliferator-activated receptor gamma and the transient receptor potential vanilloid channels.

Summary

The role of the endocannabinoid system in tumourigenesis is still poorly understood and the molecular mechanisms of cannabinoid anticancer action need to be elucidated. The development of CB2-selective anticancer agents could be advantageous in light of the unwanted central effects exerted by CB1 receptor ligands. Probably the most interesting question is whether cannabinoids could be useful in chemoprevention or in combination with established chemotherapeutic agents.

Lyn-mediated mitochondrial tyrosine phosphorylation is required to preserve mitochondrial integrity in early liver regeneration

Functional alterations in mitochondria such as overproduction of ROS (reactive oxygen species) and overloading of calcium, with subsequent change in the membrane potential, are traditionally regarded as pro-apoptotic conditions. Although such events occur in the early phases of LR (liver regeneration) after two-thirds PH (partial hepatectomy), hepatocytes do not undergo apoptosis but continue to proliferate until the mass of the liver is restored. The aim of the present study was to establish whether tyrosine phosphorylation, an emerging mechanism of regulation of mitochondrial function, participates in the response to liver injury following PH and is involved in contrasting mitochondrial pro-apoptotic signalling. Mitochondrial tyrosine phosphorylation, negligible in the quiescent liver, was detected in the early phases of LR with a trend similar to the events heralding mitochondrial apoptosis and was attributed to the tyrosine kinase Lyn, a member of the Src family. Lyn was shown to accumulate in an active form in the mitochondrial intermembrane space, where it was found to be associated with a multiprotein complex. Our results highlight a role for tyrosine phosphorylation in accompanying, and ultimately counteracting, mitochondrial events otherwise leading to apoptosis, hence conveying information required to preserve the mitochondrial integrity during LR.

Beneficial effects of PTP1B deficiency on brown adipocyte differentiation and protection against apoptosis induced by pro- and anti-inflammatory stimuli

Insulin is an inducer of brown fat adipogenesis through the activation of a signalling network that involves positive/negative modulators. Given the importance of brown adipose tissue (BAT) for basal thermogenic energy expenditure, we investigated the role of PTP1B in the acquisition of terminal differentiated phenotype and in the apoptotic responses of brown adipocytes. Immortalized brown preadipocytes lacking (PTP1B(-/-)) or expressing (PTP1B(+/+)) PTP1B have been generated. PTP1B deficiency accelerated a full program of brown adipogenesis including induction of transcription factors, coactivators, adipogenic markers and signalling molecules. Fully differentiated PTP1B(-/-) brown adipocytes were resistant to tumor necrosis factor (TNFalpha)-induced apoptosis as these cells were protected against caspase-8 activation, FLIP degradation, Bid cleavage and caspase-3 activation compared to wild-type controls. These events were recovered by PTP1B rescue. Survival signalling including phosphorylation of IRS-1 and Akt/PKB and BclxL expression were decreased in TNFalpha-treated PTP1B(-/-) cells but not in the wild-type. Similarly, PTP1B(-/-) brown adipocytes were protected against resveratrol-induced apoptosis. Phosphorylation of Akt/PKB and Foxo1 phosphorylation/acetylation decreased exclusively in resveratrol-treated wild-type cells, leading to nuclear localization of Foxo1 and up-regulation of Bim. Thus, PTP1B inhibition could be of benefit against obesity by counteracting TNFalpha-induced brown fat atrophy, and combined with resveratrol might improve low-grade inflammation.

Evidence that phosphatidylinositol 3-kinase is involved in sperm-induced tyrosine kinase signaling in Xenopus egg fertilization

BACKGROUND

Studies have examined the function of PI 3-kinase in the early developmental processes that operate in oocytes or early embryos of various species. However, the roles of egg-associated PI 3-kinase and Akt, especially in signal transduction at fertilization, are not well understood.

RESULTS

Here we show that in Xenopus eggs, a potent inhibitor of phosphatidylinositol 3-kinase (PI 3-kinase), LY294002 inhibits sperm-induced activation of the tyrosine kinase Src and a transient increase in the intracellular concentration of Ca2+ at fertilization. LY294002 also inhibits sperm-induced dephosphorylation of mitogen-activated protein kinase, breakdown of cyclin B2 and Mos, and first embryonic cleavage, all of which are events of Ca2+-dependent egg activation. In fertilized eggs, an 85-kDa subunit of PI 3-kinase (p85) undergoes a transient translocation to the low-density, detergent-insoluble membranes (membrane microdomains) where Src tyrosine kinase signaling is operating. However, the tyrosine phosphorylation of p85 in fertilized eggs is not as evident as that in H2O2-activated eggs, arguing against the possibility that PI 3-kinase is activated by Src phosphorylation. Nevertheless, sperm-induced activation of PI 3-kinase has been demonstrated by the finding that Akt, a serine/threonine-specific protein kinase, is phosphorylated at threonine-308. The threonine-phosphorylated Akt also localizes to the membrane microdomains of fertilized eggs. Application of bp(V), an inhibitor of PTEN that dephosphorylates PIP3, the enzymatic product of PI 3-kinase, promotes parthenogenetic activation of Xenopus eggs. In vitro kinase assays demonstrate that PIP3 activates Src in a dose-dependent manner.

CONCLUSIONS

These results suggest that PI 3-kinase is involved in sperm-induced egg activation via production of PIP3 that would act as a positive regulator of the Src signaling pathway in Xenopus fertilization.

Inhibition of PI3K-Akt signaling blocks exercise-mediated enhancement of adult neurogenesis and synaptic plasticity in the dentate gyrus

Background

Physical exercise has been shown to increase adult neurogenesis in the dentate gyrus and enhances synaptic plasticity. The antiapoptotic kinase, Akt has also been shown to be phosphorylated following voluntary exercise; however, it remains unknown whether the PI3K-Akt signaling pathway is involved in exercise-induced neurogenesis and the associated facilitation of synaptic plasticity in the dentate gyrus.

Methodology/Principal Findings

To gain insight into the potential role of this signaling pathway in exercise-induced neurogenesis and LTP in the dentate gyrus rats were infused with the PI3K inhibitor, LY294002 or vehicle control solution (icv) via osmotic minipumps and exercised in a running wheel for 10 days. Newborn cells in the dentate gyrus were date-labelled with BrdU on the last 3 days of exercise. Then, they were either returned to the home cage for 2 weeks to assess exercise-induced LTP and neurogenesis in the dentate gyrus, or were killed on the last day of exercise to assess proliferation and activation of the PI3K-Akt cascade using western blotting.

Conclusions/Significance

Exercise increases cell proliferation and promotes survival of adult-born neurons in the dentate gyrus. Immediately after exercise, we found that Akt and three downstream targets, BAD, GSK3β and FOXO1 were activated. LY294002 blocked exercise-induced phosphorylation of Akt and downstream target proteins. This had no effect on exercise-induced cell proliferation, but it abolished most of the beneficial effect of exercise on the survival of newly generated dentate gyrus neurons and prevented exercise-induced increase in dentate gyrus LTP. These results suggest that activation of the PI3 kinase-Akt signaling pathway plays a significant role via an antiapoptotic function in promoting survival of newly formed granule cells generated during exercise and the associated increase in synaptic plasticity in the dentate gyrus.

L-type Ca2+ channels: a new player in the regulation of Ca2+ signaling, cell activation and cell survival in immune cells

Ca(2+) is a highly versatile intracellular second messenger in many cell types, and regulates many complicated cellular processes, including cell activation, proliferation and apoptosis. Influx of Ca(2+) from the extracellular fluid is required for sustained elevation of the cytosolic Ca(2+) concentration and full activation of Ca(2+)-dependent processes. It is widely accepted that Ca(2+) release-activated Ca(2+) channels are the major routes of Ca(2+) influx in electrically non-excitable cells, including hematopoietic cells, whereas voltage-gated Ca(2+) channels such as L-type Ca(2+) channels (LTCCs) serve as the principal routes of Ca(2+) entry into electrically excitable cells such as neurons and myocytes. However, recent pharmacological and molecular genetic studies have revealed the existence of functional LTCCs and/or LTCC-like channels in a variety of immune cells including mast cells. In this article, we review recent advances in our understanding of Ca(2+) signaling in immune cells with a special interest in mast cells. We highlight roles for LTCCs in antigen receptor-mediated mast cell activation and survival.

Apoptosis and autophagy: Regulation of caspase-9 by phosphorylation

Cell death by the process of apoptosis plays important roles in development, tissue homeostasis, diseases and drug responses. The cysteine aspartyl protease caspase-9 plays a central role in the mitochondrial or intrinsic apoptotic pathway that is engaged in response to many apoptotic stimuli. Caspase-9 is activated in a large multimeric complex, the apoptosome, which is formed with apoptotic peptidase activating factor 1 (Apaf-1) in response to the release of cytochrome c from mitochondria. Once activated, caspase-9 cleaves and activates the effector caspases 3 and 7 to bring about apoptosis. This pathway is tightly regulated at multiple steps, including apoptosome formation and caspase-9 activation. Recent work has shown that caspase-9 is the direct target for regulatory phosphorylation by multiple protein kinases activated in response to extracellular growth/survival factors, osmotic stress or during mitosis. Here, we review these advances and discuss the possible roles of caspase-9 phosphorylation in the regulation of apoptosis during development and in pathological states, including cancer.

Interleukin-10 provides direct trophic support to neurons

Interleukin (IL)-10, a prototypical anti-inflammatory cytokine, has been shown to provide beneficial effects in neuronal injury in vivo but the full range of actions has not been established. In order to understand the neuronal mechanisms underlying IL-10-mediated neuroprotection, we examined the effect of IL-10 on primary neurons in culture. We found that IL-10 exerted a direct trophic influence on spinal cord neurons, and that activation of the neuronal IL-10 receptor provided trophic support and survival cues to overcome the neurotoxic effects of glutamate in vitro. IL-10 treatment resulted in activation of janus-associated kinases/signal transducers and transcription factors and phosphatidylinositol 3-kinase-AKT pathways in neurons to enhance expression of Bcl-2 and Bcl-x(L); under stress conditions IL-10 blocks cytochrome c release and caspase cleavage. IL-10 activation of the canonical nuclear factor kappaB pathway enhanced translocation of p50 and p65 and enhanced their binding to kappaB DNA sequences, with p50 playing a more prominent role in neuronal survival. These data indicate that in addition to known anti-inflammatory effects through astroglia in other inflammatory cells, IL-10 has direct neuronal effects with important implications for development and neuroprotection.

Prostaglandin E(2) induces fibroblast apoptosis by modulating multiple survival pathways

Although the lipid mediator prostaglandin E(2) (PGE(2)) exerts antifibrotic effects by inhibiting multiple fibroblast functions, its ability to regulate fibroblast survival is unknown. Here, we examined the effects of this prostanoid on apoptosis and apoptosis pathways in normal and fibrotic lung fibroblasts. As compared to medium alone, 24 h of treatment with PGE(2) increased apoptosis of normal lung fibroblasts in a dose-dependent manner (EC(50) approximately 50 nM), as measured by annexin V staining, caspase 3 activity, cleavage of poly-ADP-ribose polymerase, and single-stranded DNA levels. PGE(2) also potentiated apoptosis elicited by Fas ligand plus cycloheximide. These proapoptotic actions were dependent on signaling through the EP2/EP4 receptors and by downstream activation of both caspases 8 and 9. Silencing and gene deletion of PTEN demonstrated that the effects of PGE(2) involved decreased activity of the prosurvival molecule Akt. PGE(2) also down-regulated expression of survivin, an inhibitor of apoptosis, and increased expression of Fas. Fibroblasts from patients with pulmonary fibrosis exhibited resistance to the apoptotic effects of PGE(2). These findings show for the first time that, in contrast to its effects on many other cell types, PGE(2) promotes apoptosis in lung fibroblasts through diverse pathways. They provide another dimension by which PGE(2) may inhibit, and perhaps even reverse, fibrogenesis in patients with interstitial lung disease.

Mitochondrial integrity: preservation through Akt/Pim-1 kinase signaling in the cardiomyocyte

The central role of mitochondria as mediators of cell survival is indisputable and gathering increasing attention as a focal point for interventional strategies to mitigate apoptotic cell death in the wake of cardiomyopathic injury. A legacy of signal transduction studies has proven that mitochondrial integrity can be enhanced by kinases involved in cell survival. Among the many survival signaling cascades under investigation, the wide-ranging impact of Akt upon mitochondrial biology is well known. However, despite years of investigation, emerging research continues to reveal new mechanisms governing the protective effects of Akt signaling in the context of cardiomyocyte mitochondria. This review focuses on two emerging pathways that mediate preservation of mitochondrial function downstream of Akt: hexokinase and Pim-1 kinase.