The life of a cell: apoptosis regulation by the PI3K/PKB pathway. Biochem J. 2008;415:333-344. [PMID: 18842113 DOI: 10.1042/BJ20081056]

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.

Targeting nonclassical oncogenes for therapy in T-ALL

Constitutive phosphoinositide 3-kinase (PI3K)/Akt activation is common in T cell acute lymphoblastic leukemia (T-ALL). Although four distinct class I PI3K isoforms (α, β, γ, δ) could participate in T-ALL pathogenesis, none has been implicated in this process. We report that in the absence of PTEN phosphatase tumor suppressor function, PI3Kγ or PI3Kδ alone can support leukemogenesis, whereas inactivation of both isoforms suppressed tumor formation. The reliance of PTEN null T-ALL on the combined activities of PI3Kγ/δ was further demonstrated by the ability of a dual inhibitor to reduce disease burden and prolong survival in mice as well as prevent proliferation and promote activation of proapoptotic pathways in human tumors. These results support combined inhibition of PI3Kγ/δ as therapy for T-ALL.

CaMKII-γ mediates phosphorylation of BAD at Ser170 to regulate cytokine-dependent survival and proliferation

Phosphorylation of the BH3 (Bcl-2 homology domain 3)-only protein BAD (Bcl-2/Bcl-X(L)-antagonist, causing cell death) can either directly disrupt its association with the pro-survival proteins Bcl-X(L) and/or Bcl-2, or cause association of BAD with 14-3-3 proteins. In the present study, we further characterize phosphorylation of BAD at Ser170, a unique site with unclear function. We provide further evidence that mutation of Ser170 to a phospho-mimetic aspartic acid residue (S170D) can have a profound inhibitory effect on the pro-apoptosis function of BAD. Furthermore, mutated BAD with an alanine substitution inhibited cell proliferation, slowing progression specifically through S-phase. We identify the kinase responsible for phosphorylation at this site as CaMKII-γ (γ isoform of Ca2+/calmodulin-dependent kinase II), but not the other three isoforms of CaMKII, revealing an extraordinary specificity among these closely related kinases. Furthermore, cytokine treatment increased BAD-Ser170-directed CaMKII-γ activity and phosphorylation of CaMKII-γ at an activating site, and CaMKII activity directed to the BAD-Ser170 site was elevated during S-phase. Treating cells with a selective inhibitor of CaMKII caused apoptosis in cells expressing BAD, but not in cells expressing the BAD-S170D mutant. The present study provides support for BAD-Ser170 phosphorylation playing a key role not only in regulating BAD's pro-apoptotic activity, but also in cell proliferation.

Thymoquinone-induced platelet apoptosis

Thymoquinone (TQ) is a nutrient with anticarcinogenic activity that stimulates suicidal death of tumor cells. Moreover, TQ triggers suicidal death of erythrocytes or eryptosis, an effect at least partially due to increase in cytosolic Ca(2+) activity and ceramide formation. The present experiments explored whether TQ influences apoptosis of blood platelets. Cell membrane scrambling was determined utilizing Annexin V binding to phosphatidylserine exposing platelets, cytosolic Ca(2+) activity utilizing Fluo 3-AM fluorescence, caspase activity utilizing immunofluorescence and Western blotting of active caspase-3 and inactive procaspase-3, mitochondrial potential utilizing DiOC(6) fluorescence and ceramide by FACS analysis of ceramide-binding antibodies. A 30 min exposure to TQ (≥5 µM) was followed by Annexin V binding, paralleled by caspase activation, increase of cytosolic Ca(2+) activity, mitochondrial depolarization, and ceramide formation. P-selectin exposure and integrin α(IIb) β(3) activation did not increase in response to TQ. Nominal absence of extracellular Ca(2+) blunted but did not fully abolish the TQ-induced activation of caspase-3. The effects of TQ on platelets are significantly abolished with phosphoinositide-3 kinase (PI3K) inhibitor wortmannin and G-protein coupled receptor (GPCR) inhibitor pertussis toxin treatment prior to TQ stimulation. In conclusion, TQ triggers suicidal death of blood platelets in a PI3K-dependent manner, possibly through a GPCR family receptor; an effect paralleled by increase of cytosolic Ca(2+) activity, ceramide formation, mitochondrial depolarization, and caspase-3 activation.

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.

ATP acts as a survival signal and prevents the mineralization of aortic valve

Calcific aortic valve disease (CAVD) is a disorder related to progressive mineralization of valvular tissue that is a leading cause of heart disease. Thus far, there is no medical treatment to prevent the mineralization of aortic valves. It is generally thought that pathologic mineralization is linked to apoptosis of vascular cells. However, the role of apoptosis during mineralization as well as the survival signals for valvular interstitial cells (VICs), the main cellular component of aortic valves, remains to be identified. Here, through several lines of evidence, we show that bioavailability of extracellular ATP is a signal which determines survival or apoptosis of VICs and, in doing so, plays a major role in the development of CAVD. Specifically, in CAVD and in VIC cultures undergoing mineralization, we found a high level of the ectonucleotidase ENPP1. In addition, a genetic polymorphism in the intron 9 of the ENPP1 gene was associated with CAVD in a case-control cohort as well as with mRNA expression levels of ENPP1 in aortic valves. A high level of ENPP1 in CAVD promoted apoptosis-mediated mineralization of VICs by depleting the extracellular pool of ATP. We then documented that release of ATP by VICs promoted cell survival via the P2Y(2) receptor and the PI3K/Akt signaling pathway. Hence, our results show that level of ENPP1 modulates extracellular concentration of ATP, which is an important survival signal for VICs. These findings may help to develop novel pharmacological treatment for CAVD.

Microarray analysis of Akt PH domain binding employing synthetic biotinylated analogs of all seven phosphoinositide headgroup isomers

Signaling lipids control many of the most important biological pathways, typically by recruiting cognate protein binding targets to cell surfaces, thereby regulating both their function and subcellular localization. A critical family of signaling lipids is that of the phosphatidylinositol polyphosphates (PIP(n)s), which is composed of seven isomers that vary based on phosphorylation pattern. A key protein that is activated upon PIP(n) binding is Akt, which then plays important roles in regulating the cell cycle, and is thus aberrant in disease. Characterization of protein-PIP(n) binding interactions is hindered by the complexity of the membrane environment and of the PIP(n) structures. Herein, we describe two rapid assays of use for characterizing protein-PIP(n) binding interactions. First, a microplate-based binding assay was devised to characterize the binding of effectors to immobilized synthetic PIP(n) headgroup-biotin conjugates corresponding to all seven isomers. The assay was implemented for simultaneous analysis of Akt-PH domain, indicating PI(3,4,5)P(3) and PI(3,4)P(2) as the primary ligands. In addition, density-dependant studies indicated that the amount of ligand immobilized on the surface affected the amplitude of protein binding, but not the affinity, for Akt-PH. Since the PIP(n) ligand motifs used in this analysis lack the membrane environment and glycerolipid backbone, yet still exhibit high-affinity protein binding, these results narrow down the structural requirements for Akt recognition. Additionally, binding detection was also achieved through microarray analysis via the robotic pin printing of ligands onto glass slides in a miniaturized format. Here, fluorescence-based detection provided sensitive detection of binding using minimal amounts of materials. Due to their high-throughput and versatile attributes, these assays provide invaluable tools for probing and perturbing protein-membrane binding interactions.

[The study of PI3K/AKT pathway in lung cancer metastasis and drug resistance]

磷脂酰肌醇-3-激酶/丝苏氨酸蛋白激酶（phosphatidyl-inositol 3-kinase/serine-threonine kinase, PI3K/ AKT）信号通路是细胞内重要信号转导通路之一，通过影响下游多种效应分子的活化状态，在细胞内发挥抑制凋亡、促进增殖的关键作用，与人类多种肿瘤的发生发展密切相关。研究表明PI3K/AKT信号通路在恶性肿瘤细胞的增殖、血管新生和转移及对放化疗的拮抗中都起着重要作用。对PI3K/AKT信号通路的深入研究有望找到肿瘤预防和药物治疗的新靶点。本文简要介绍了PI3K/AKT信号通路的组成与功能调节，并着重阐述了其在肺癌转移和耐药中的作用。

Phosphatidylinositol 3,4,5-trisphosphate activity probes for the labeling and proteomic characterization of protein binding partners

Phosphatidylinositol polyphosphate lipids, such as phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P₃], regulate critical biological processes, many of which are aberrant in disease. These lipids often act as site-specific ligands in interactions that enforce membrane association of protein binding partners. Herein, we describe the development of bifunctional activity probes corresponding to the headgroup of PI(3,4,5)P₃ that are effective for identifying and characterizing protein binding partners from complex samples, namely cancer cell extracts. These probes contain both a photoaffinity tag for covalent labeling of target proteins and a secondary handle for subsequent detection or manipulation of labeled proteins. Probes bearing different secondary tags were exploited, either by direct attachment of a fluorescent dye for optical detection or by using an alkyne that can be derivatized after protein labeling via click chemistry. First, we describe the design and modular synthetic strategy used to generate multiple probes with different reporter tags of use for characterizing probe-labeled proteins. Next, we report initial labeling studies using purified protein, the PH domain of Akt, in which probes were found to label this target, as judged by in-gel detection. Furthermore, protein labeling was abrogated by controls including competition with an unlabeled PI(3,4,5)P₃ headgroup analogue as well as through protein denaturation, indicating specific labeling. In addition, probes featuring linkers of different lengths between the PI(3,4,5)P₃ headgroup and photoaffinity tag led to variations in protein labeling, indicating that a shorter linker was more effective in this case. Finally, proteomic labeling studies were performed using cell extracts; labeled proteins were observed by in-gel detection and characterized using postlabeling with biotin, affinity chromatography, and identification via tandem mass spectrometry. These studies yielded a total of 265 proteins, including both known and novel candidate PI(3,4,5)P₃-binding proteins.

Dual mTORC1/mTORC2 inhibition diminishes Akt activation and induces Puma-dependent apoptosis in lymphoid malignancies

The mammalian target of rapamycin (mTOR) plays crucial roles in proliferative and antiapoptotic signaling in lymphoid malignancies. Rapamycin analogs, which are allosteric mTOR complex 1 (mTORC1) inhibitors, are active in mantle cell lymphoma and other lymphoid neoplasms, but responses are usually partial and short-lived. In the present study we compared the effects of rapamycin with the dual mTORC1/mTORC2 inhibitor OSI-027 in cell lines and clinical samples representing divers lymphoid malignancies. In contrast to rapamycin, OSI-027 markedly diminished proliferation and induced apoptosis in a variety of lymphoid cell lines and clinical samples, including specimens of B-cell acute lymphocytic leukemia (ALL), mantle cell lymphoma, marginal zone lymphoma and Sezary syndrome. Additional analysis demonstrated that OSI-027-induced apoptosis depended on transcriptional activation of the PUMA and BIM genes. Overexpression of Bcl-2, which neutralizes Puma and Bim, or loss of procaspase 9 diminished OSI-027-induced apoptosis in vitro. Moreover, OSI-027 inhibited phosphorylation of mTORC1 and mTORC2 substrates, up-regulated Puma, and induced regressions in Jeko xenografts. Collectively, these results not only identify a pathway that is critical for the cytotoxicity of dual mTORC1/mTORC2 inhibitors, but also suggest that simultaneously targeting mTORC1 and mTORC2 might be an effective anti-lymphoma strategy in vivo.

RAS Interaction with PI3K: More Than Just Another Effector Pathway

RAS PROTEINS ARE SMALL GTPASES KNOWN FOR THEIR INVOLVEMENT IN ONCOGENESIS: around 25% of human tumors present mutations in a member of this family. RAS operates in a complex signaling network with multiple activators and effectors, which allows them to regulate many cellular functions such as cell proliferation, differentiation, apoptosis, and senescence. Phosphatidylinositol 3-kinase (PI3K) is one of the main effector pathways of RAS, regulating cell growth, cell cycle entry, cell survival, cytoskeleton reorganization, and metabolism. However, it is the involvement of this pathway in human tumors that has attracted most attention. PI3K has proven to be necessary for RAS-induced transformation in vitro, and more importantly, mice with mutations in the PI3K catalytic subunit p110α that block its ability to interact with RAS are highly resistant to endogenous oncogenic KRAS-induced lung tumorigenesis and HRAS-induced skin carcinogenesis. These animals also have a delayed development of the lymphatic vasculature. Many PI3K inhibitors have been developed that are now in clinical trials. However, it is a complex pathway with many feedback loops, and interactions with other pathways make the results of its inhibition hard to predict. Combined therapy with another RAS-regulated pathway such as RAF/MEK/ERK may be the most effective way to treat cancer, at least in animal models mimicking the human disease. In this review, we will summarize current knowledge about how RAS regulates one of its best-known effectors, PI3K.

Phosphoinositide phosphatase SHIP-1 regulates apoptosis induced by edelfosine, Fas ligation and DNA damage in mouse lymphoma cells

S49 mouse lymphoma cells undergo apoptosis in response to the ALP (alkyl-lysophospholipid) edelfosine (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine), FasL (Fas ligand) and DNA damage. S49 cells made resistant to ALP (S49AR) are defective in sphingomyelin synthesis and ALP uptake, and also have acquired resistance to FasL and DNA damage. However, these cells can be re-sensitized following prolonged culturing in the absence of ALP. The resistant cells show sustained ERK (extracellular-signal-regulated kinase)/Akt activity, consistent with enhanced survival signalling. In search of a common mediator of the observed cross-resistance, we found that S49AR cells lacked the PtdIns(3,4,5)P3 phosphatase SHIP-1 [SH2 (Src homology 2)-domain-containing inositol phosphatase 1], a known regulator of the Akt survival pathway. Re-sensitization of the S49AR cells restored SHIP-1 expression as well as phosphoinositide and sphingomyelin levels. Knockdown of SHIP-1 mimicked the S49AR phenotype in terms of apoptosis cross-resistance, sphingomyelin deficiency and altered phosphoinositide levels. Collectively, the results of the present study suggest that SHIP-1 collaborates with sphingomyelin synthase to regulate lymphoma cell death irrespective of the nature of the apoptotic stimulus.

Role of protein kinase C and epidermal growth factor receptor signalling in growth stimulation by neurotensin in colon carcinoma cells

Background

Neurotensin has been found to promote colon carcinogenesis in rats and mice, and proliferation of human colon carcinoma cell lines, but the mechanisms involved are not clear. We have examined signalling pathways activated by neurotensin in colorectal and pancreatic carcinoma cells.

Methods

Colon carcinoma cell lines HCT116 and HT29 and pancreatic adenocarcinoma cell line Panc-1 were cultured and stimulated with neurotensin or epidermal growth factor (EGF). DNA synthesis was determined by incorporation of radiolabelled thymidine into DNA. Levels and phosphorylation of proteins in signalling pathways were assessed by Western blotting.

Results

Neurotensin stimulated the phosphorylation of both extracellular signal-regulated kinase (ERK) and Akt in all three cell lines, but apparently did so through different pathways. In Panc-1 cells, neurotensin-induced phosphorylation of ERK, but not Akt, was dependent on protein kinase C (PKC), whereas an inhibitor of the β-isoform of phosphoinositide 3-kinase (PI3K), TGX221, abolished neurotensin-induced Akt phosphorylation in these cells, and there was no evidence of EGF receptor (EGFR) transactivation. In HT29 cells, in contrast, the EGFR tyrosine kinase inhibitor gefitinib blocked neurotensin-stimulated phosphorylation of both ERK and Akt, indicating transactivation of EGFR, independently of PKC. In HCT116 cells, neurotensin induced both a PKC-dependent phosphorylation of ERK and a metalloproteinase-mediated transactivation of EGFR that was associated with a gefitinib-sensitive phosphorylation of the downstream adaptor protein Shc. The activation of Akt was also inhibited by gefitinib, but only partly, suggesting a mechanism in addition to EGFR transactivation. Inhibition of PKC blocked neurotensin-induced DNA synthesis in HCT116 cells.

Conclusions

While acting predominantly through PKC in Panc-1 cells and via EGFR transactivation in HT29 cells, neurotensin used both these pathways in HCT116 cells. In these cells, neurotensin-induced activation of ERK and stimulation of DNA synthesis was PKC-dependent, whereas activation of the PI3K/Akt pathway was mediated by stimulation of metalloproteinases and subsequent transactivation of the EGFR. Thus, the data show that the signalling mechanisms mediating the effects of neurotensin involve multiple pathways and are cell-dependent.

Akt as a victim, villain and potential hero in Parkinson's disease pathophysiology and treatment

There are two major purposes of this essay. The first is to summarize existing evidence that irrespective of the initiating causes, neuron death and degeneration in Parkinson's disease (PD) are due to the common feature of failure of signaling by Akt, a kinase involved in neuron survival and maintenance of synaptic contacts. The second is to consider possible means by which such a failure of Akt signaling might be benignly prevented or reversed in neurons affected by PD, so as to treat PD symptoms, block disease progression, and potentially, promote recovery.

Role of extracellular matrix renal tubulo-interstitial nephritis antigen (TINag) in cell survival utilizing integrin (alpha)vbeta3/focal adhesion kinase (FAK)/phosphatidylinositol 3-kinase (PI3K)/protein kinase B-serine/threonine kinase (AKT) signaling pathway

Tubulo-interstitial nephritis antigen (TINag) is an extracellular matrix protein expressed in tubular basement membranes. Combined mutations in TINag and nephrocystin-1 genes lead to nephronophthisis with reduced cell survival. Because certain extracellular matrix proteins are known to modulate cell survival, studies were initiated in Lewis rats lacking TINag to assess if they are more susceptible to cisplatin-induced injury. Cisplatin induced a higher degree of tubular cell damage and apoptosis in regions where TINag is expressed in a parental Wistar strain. This was accompanied by an accentuated increase in serum creatinine and Kim-1 RNA and renal expression of Bax, p53, and its nuclear accumulation, mtDNA fragmentation, and a decrease of Bcl-2. Cisplatin induced fulminant apoptosis of HK-2 cells with increased caspase3/7 activity, mtDNA fragmentation, and a reduced cell survival. These effects were partially reversed in cells maintained on TINag substratum. Far Western/solid phase assays established TINag binding with integrin αvβ3 comparable with vitronectin. Transfection of cells with αv-siRNA accentuated cisplatin-induced apoptosis, aberrant translocation of cytochrome c and Bax, and reduced cell survival. The αv-siRNA decreased expression of integrin-recruited focal adhesion kinase (FAK) and p-FAK, while increasing the expression of p53 and p-p53. Similarly, p-AKT was reduced although ILK was unaffected. Inhibition of PI3K had similar adverse cellular effects. These effects were ameliorated in cells on TINag substratum. In vivo, a higher degree of decrease in the expression of p-FAK and pAKT was observed in Lewis rats following cisplatin treatment. These in vivo and in vitro studies demonstrate an essential role of TINag in cellular survival to maintain proper tubular homeostasis utilizing integrin αvβ3 and downstream effectors.

Expression and cellular distribution of vascular endothelial growth factor-C system in cortical tubers of the tuberous sclerosis complex

Cortical tubers are malformations of cortical development in patients with tuberous sclerosis complex (TSC), and highly associated with pediatric intractable epilepsy. Recent evidence has shown that signaling mediated through vascular endothelial growth factor-C (VEGF-C) and its receptors, VEGFR-2 and VEGFR-3, has direct effects on both neurons and glial cells. To understand the potential role of VEGF-C system in the pathogenesis of cortical tubers, we investigated the expression patterns of VEGF-C signaling in cortical tubers compared with age-matched normal control cortex (CTX). We found that VEGF-C, VEGFR-2 and VEGFR-3 were clearly upregulated in tubers at both the mRNA and protein levels, compared with CTX. The in situ hybridization and immunostaining results demonstrated that VEGF-C, VEGFR-2 and VEGFR-3 were highly expressed in dysplastic neurons (DNs), giant cells (GCs) and reactive astrocytes within tubers. Most DNs/GCs expressing VEGF-C and its receptors co-labeled with neuronal rather than astrocytic markers, suggesting a neuronal lineage. In addition, protein levels of Akt-1, p-Bad and ERK1/2, the important downstream factors of the VEGF-C pathway, were significantly increased in cortical tubers, indicating involvement of VEGF-C-dependent prosurvival signaling in cortical tubers. Taken together, our results suggest a putative role for the VEGF-C signaling pathway in the pathogenesis of cortical tubers.

Involvement of the glycogen synthase kinase-3 signaling pathway in TBI pathology and neurocognitive outcome

BACKGROUND

Traumatic brain injury (TBI) sets in motion cascades of biochemical changes that result in delayed cell death and altered neuronal architecture. Studies have demonstrated that inhibition of glycogen synthase kinase-3 (GSK-3) effectively reduces apoptosis following a number of stimuli. The Wnt family of proteins, and growth factors are two major factors that regulate GSK-3 activity. In the absence of stimuli, GSK-3 is constitutively active and is complexed with Axin, adenomatous polyposis coli (APC), and casein kinase Iα (CK1α) and phosphorylates ß-Catenin leading to its degradation. Binding of Wnt to Frizzled receptors causes the translocation of GSK-3 to the plasma membrane, where it phosphorylates and inactivates the Frizzled co-receptor lipoprotein-related protein 6 (LRP6). Furthermore, the translocation of GSK-3 reduces ß-Catenin phosphorylation and degradation, leading to ß-Catenin accumulation and gene expression. Growth factors activate Akt, which in turn inhibits GSK-3 activity by direct phosphorylation, leading to a reduction in apoptosis.

METHODOLOGY/PRINCIPAL FINDINGS

Using a rodent model, we found that TBI caused a rapid, but transient, increase in LRP6 phosphorylation that is followed by a modest decrease in ß-Catenin phosphorylation. Phospho-GSK-3β immunoreactivity was found to increase three days post injury, a time point at which increased Akt activity following TBI has been observed. Lithium influences several neurochemical cascades, including inhibiting GSK-3. When the efficacy of daily lithium was assessed, reduced hippocampal neuronal cell loss and learning and memory improvements were observed. These influences were partially mimicked by administration of the GSK-3-selective inhibitor SB-216763, as this drug resulted in improved motor function, but only a modest improvement in memory retention and no overt neuroprotection.

CONCLUSION/SIGNIFICANCE

Taken together, our findings suggest that selective inhibition of GSK-3 may offer partial cognitive improvement. As a broad spectrum inhibitor of GSK-3, lithium offers neuroprotection and robust cognitive improvement, supporting its clinical testing as a treatment for TBI.

Dendritic cell-epithelium interplay is a determinant factor for corneal epithelial wound repair

The functions of intraepithelial dendritic cells (DCs) are critical for mucosal innate and adaptive immunity, but little is known about the role of tissue-specific DCs in epithelial homeostasis and tissue repair. By using the epithelial debridement wound model and CD11c-diphtheria toxin receptor mice that express a CD11c promoter-driven diphtheria toxin receptor, we showed that DCs migrate along with the epithelial sheet to cover the wound and that local depletion of DCs resulted in a significant delay in epithelial wound closure. In response to wounding, migratory epithelia produce CXCL10, thymic stromal lymphopoietin, and IL-1β and its antagonist soluble IL-1 receptor antagonist (sIL-1Ra); depletion of corneal DCs reversed their elevated expressions to a different extent, suggesting a DC-mediated positive feedback loop in epithelial gene expression. Furthermore, both CXCL10 and thymic stromal lymphopoietin were localized in migratory epithelia, suggesting that epithelial cells play a key role in DC infiltration and activation in injured corneas. On the other hand, DC depletion resulted in suppressed epithelial AKT activation, increased cell apoptosis, and decreased polymorphonuclear leukocyte infiltration in the healing cornea. These results indicate that DCs and epithelium form a functional entity at mucosal surfaces for maintaining corneal homeostasis and for tissue repair.

Acquired radioresistance of cancer and the AKT/GSK3β/cyclin D1 overexpression cycle

Fractionated radiotherapy (RT) is widely used in cancer therapy for its advantages in the preservation of normal tissues. However, repopulation of surviving tumor cells during fractionated RT limits the efficacy of RT. In fact, repopulating tumors often acquire radioresistance and this is the major cause of failure of RT. We have recently demonstrated that human tumor cells acquire radioresistance when exposed to fractionated radiation (FR) of X-rays every 12 hours for 1 month. The acquired radioresistance was associated with overexpression of cyclin D1, a result of a series of molecular changes; constitutive activation of DNA-PK and AKT with concomitant down-regulation of glycogen synthase kinase-3β (GSK3β) which results in suppression of cyclin D1 proteolysis. Aberrant cyclin D1 overexpression in S-phase induced DNA double strand breaks which activated DNA-PK and established the vicious cycle of cycling D1 overexpression. This overexpression of cyclin D1 is responsible for the radioresistance phenotype of long-term FR cells, since this phenotype was completely abrogated by treatment of FR cells by the API-2, an AKT inhibitor or by a Cdk4 inhibitor. Thus, targeting the AKT/GSK3β/cyclin D1/Cdk4 pathway can be an efficient modality to suppress acquired radioresistance of tumor cells. In this article, I overview the newly discovered molecular mechanisms underlying acquired radioresistance of tumor cells induced by FR, and propose a strategy for eradication of tumors using fractionated RT by overcoming tumor radioresistance.

Oncogenic YAP promotes radioresistance and genomic instability in medulloblastoma through IGF2-mediated Akt activation

Radiation therapy remains the standard of care for many cancers, including the malignant pediatric brain tumor medulloblastoma. Radiation leads to long-term side effects, while radio-resistance contributes to tumor recurrence. Radio-resistant medulloblastoma cells occupy the peri-vascular niche. They express Yes-associated protein (YAP), a Sonic hedgehog (Shh) target markedly elevated in Shh-driven medulloblastomas. Here we report that YAP accelerates tumor growth and confers radio-resistance, promoting ongoing proliferation after radiation. YAP activity enables cells to enter mitosis with un-repaired DNA through driving IGF2 expression and Akt activation, resulting in ATM/Chk2 inactivation and abrogation of cell cycle checkpoints. Our results establish a central role for YAP in counteracting radiation-based therapies and driving genomic instability, and indicate the YAP/IGF2/Akt axis as a therapeutic target in medulloblastoma.

The E-box binding factors Max/Mnt, MITF, and USF1 act coordinately with FoxO to regulate expression of proapoptotic and cell cycle control genes by phosphatidylinositol 3-kinase/Akt/glycogen synthase kinase 3 signaling

Phosphatidylinositol (PI) 3-kinase/Akt signaling plays a critical role in cell proliferation and survival, partly by regulation of FoxO transcription factors. Previous work using global expression profiling indicated that inhibition of PI 3-kinase in proliferating cells led to induction of genes that promote cell cycle arrest and apoptosis. The upstream regulatory regions of these genes had binding sites not only for FoxO, but also for Myc/Max transcription factors. In the present study, we have addressed the role of Myc family members and related E-box-binding proteins in the regulation of these genes. Chromatin immunoprecipitations and RNA interference indicated that transcription was repressed by Max-Mnt-Sin3a-histone deacetylase complexes in proliferating cells. Inhibition of PI 3-kinase led to a loss of Max/Mnt binding and transcriptional induction by MITF and USF1, as well as FoxO. Both MITF and USF1 were activated by glycogen synthase kinase (GSK) 3, with GSK3 phosphorylation sites on USF1 identified as the previously described activating site threonine 153 as well as serine 186. siRNA against MITF as well as against FoxO3a protected cells from apoptosis following PI 3-kinase inhibition. These results define a novel E-box-regulated network that functions coordinately with FoxO to regulate transcription of apoptotic and cell cycle regulatory genes downstream of PI 3-kinase/Akt/GSK3 signaling.

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.

Cell cycle arrest and apoptosis induced by methyl 3,5-dicaffeoyl quinate in human colon cancer cells: Involvement of the PI3K/Akt and MAP kinase pathways

Methyl 3,5-dicaffeoyl quinate (MDQ) is a flavonoid glucoside found in several plants that scavenges 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radicals and peroxynitrite, and inhibits the formation of cholesteryl ester hydroperoxide during the copper ion-induced oxidation of blood plasma in rats. In this study, MDQ inhibited proliferation and induced apoptosis in HT-29 cells in a dose-dependent manner as detected by 1-(4,5-dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), trypan blue exclusion, and flow cytometric assays. Western blot analysis showed that apoptosis was dependent on caspase-3 activity. PARP cleavage and the cytosolic release of cytochrome c from mitochondria increased significantly. In addition, these events were accompanied by a collapse in the mitochondrial membrane potential and a decreased Bcl-2/Bax ratio. Furthermore, the MDQ-induced G(0)/G(1) arrest was correlated with an increase in p27 and a decrease in cyclin D1 and p53. MDQ also inhibited the phosphorylation of PI3K/Akt and ERK; significantly reduced NF-κB; and in general displayed a significant anti-proliferative effect via a cell cycle arrest and apoptotic induction in HT-29 cells. These results suggest that MDQ has therapeutic potential against human colon carcinoma.

Insulin and the heart

The main role of insulin in the heart under physiological conditions is obviously the regulation of substrate utilization. Indeed, insulin promotes glucose uptake and its utilization via glycolysis. Insulin, promoting glucose as the main cardiac energy substrate, reduces myocardial O(2) consumption and increases cardiac efficiency. Moreover, insulin seems to augment cardiomyocyte contraction, while it affects favorably myocardial relaxation, increases ribosomal biogenesis and protein synthesis, stimulates vascular endothelial growth factor (VEGF) and thereby angiogenesis, suppresses apoptosis, promotes cell survival and finally ameliorates both myocardial microcirculation and coronary artery resistance, leading to increased blood perfusion of myocardium. Thus, insulin acts directly on heart muscle, and this action is mediated principally through PKB/Akt signal pathway. Under pathological conditions, such as type 2 diabetes, myocardial ischaemia, and cardiac hypertrophy, insulin signal transduction pathways and action are clearly modified. In this review we summarize the evidence that the heart is an important target of insulin action and that elimination of these actions is important in disease states.

Gq protein-induced apoptosis is mediated by AKT kinase inhibition that leads to protein kinase C-induced c-Jun N-terminal kinase activation

G(q) protein-coupled receptors (G(q)PCRs) regulate various cellular processes, including mainly proliferation and differentiation. In a previous study we found that in prostate cancer cells, the G(q)PCR of gonadotropin-releasing hormone (GnRH) induces apoptosis by reducing the PKC-dependent AKT activity and elevating JNK phosphorylation. Because it was thought that G(q)PCRs mainly induce activation of AKT, we first undertook to examine how general this phenomenon is. In a screen of 21 cell lines we found that PKC activation results in the reduction of AKT activity, which correlates nicely with JNK activation and in some cases with apoptosis. To understand further the signaling pathways involved in this stimulation, we studied in detail SVOG-4O and αT3-1 cells. We found that prostaglandin F2α and GnRH agonist (GnRH-a) indeed induce significant Gα(q)- and PKC-dependent apoptosis in these cells. This is mediated by two signaling branches downstream of PKC, which converge at the level of MLK3 upstream of JNK. One branch consists of c-Src activation of the JNK cascade, and the second involves reduction of AKT activity that alleviates its inhibitory effect on MLK3 to allow the flow of the c-Src signal to JNK. At the MAPKK level, we found that the signal is transmitted by MKK7 and not MKK4. Our results present a general mechanism that mediates a G(q)PCR-induced, death receptor-independent, apoptosis in physiological, as well as cancer-related systems.

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.

Sporamin induce apoptosis in human tongue carcinoma cells by down-regulating Akt/GSK-3 signaling

We investigated the effects of sporamin, the major soluble protein with a kunitz-type trypsin inhibitory activity in the root tuber of the sweet potato, on cell proliferation, apoptosis, Akt/GSK-3 signaling and its related genes to provide more insights in the mechanism behind the inhibitory effects of sporamin in a human tongue cancer line Tca8113. In this study, sporamin inhibited cell proliferation and induced apoptosis in Tca8113 cells in a concentration-dependent and time-dependent manner. Consistently, Bax was up-regulated and Bcl-2 was down-regulated in sporamin-treated cells. Furthermore, Akt/GSK-3 signaling was down-regulated in sporamin-treated cells. Consistently, the phosphorylated Bad was significantly declined in sporamin-treated Tca8113 cells. These results suggest the antiproliferative effects of sporamin in Tca8113 cells might result partly from induction of apoptosis by down-regulating Akt/GSK-3 pathway.

Molecular mechanisms of liver regeneration and protection for treatment of liver dysfunction and diseases

Liver regeneration is a necessary process that most liver damage depends on for recovery. Regeneration is achieved by a complex interactive network consisting of liver cells (hepatocytes, Kupffer cells, sinusoidal endothelial cells, hepatic stellate cells, and stem cells) and extrahepatic organs (thyroid gland, adrenal gland, pancreas, duodenum, and autonomous nervous system). The restoration of liver volume depends on hepatocyte proliferation, which includes initiation, proliferation, and termination phases. Hepatocytes are "primed" mainly by Kupffer cells via cytokines (IL-6 and TNF-alpha) and then "proliferation" and "cell growth" of hepatocytes are induced by the stimulations of cytokines and growth factors (HGF and TGF-alpha). Liver regeneration is achieved by cell proliferation and cell growth, where the IL-6/STAT3 and PI3-K/PDK1/Akt pathways play pivotal roles, respectively. IL-6/STAT3 pathway regulates hepatocyte proliferation via cyclin D1/p21 and protects against cell death by upregulating FLIP, Bcl-2, Bcl-xL, Ref1, and MnSOD. PI3-K/PDK1/Akt is known to be responsible for regulation of cell size via its downstream molecules such as mTOR in addition to being known for its survival, anti-apoptotic and anti-oxidative properties. Although the molecular mechanisms of liver regeneration have been actively studied, the mechanisms of liver regeneration must be elucidated and leveraged for the sufficient treatment of liver diseases.

Ephexin4 and EphA2 mediate resistance to anoikis through RhoG and phosphatidylinositol 3-kinase

Disruption of cell-extracellular matrix interaction causes epithelial cells to undergo apoptosis called anoikis, and resistance to anoikis has been suggested to be a critical step for cancer cells to metastasize. EphA2 is frequently overexpressed in a variety of human cancers, and recent studies have found that overexpression of EphA2 contributes to malignant cellular behavior, including resistance to anoikis, in several different types of cancer cells. Here we show that Ephexin4, a guanine nucleotide exchange factor for the small GTPase RhoG that interacts with EphA2, plays an important role in the regulation of anoikis. Knockdown of Ephexin4 promoted anoikis in HeLa cells, and experiments using a knockdown-rescue approach showed that activation of RhoG, phosphatidylinositol 3-kinase (PI3K), and Akt was required for the Ephexin4-mediated suppression of anoikis. Indeed, Ephexin4 knockdown caused a decrease in RhoG activity and Akt phosphorylation in HeLa cells cultured in suspension. In addition, Ephexin4 was involved in the EphA2-mediated suppression of anoikis. Taken together, these results suggest that Ephexin4 mediates resistance to anoikis through activation of RhoG and PI3K downstream of EphA2.

Control of host cell phosphorylation by legionella pneumophila

Phosphorylation is one of the most frequent modifications in intracellular signaling and is implicated in many processes ranging from transcriptional control to signal transduction in innate immunity. Many pathogens modulate host cell phosphorylation pathways to promote growth and establish an infectious disease. The intracellular pathogen Legionella pneumophila targets and exploits the host phosphorylation system throughout the infection cycle as part of its strategy to establish an environment beneficial for replication. Key to this manipulation is the L. pneumophila Icm/Dot type IV secretion system, which translocates bacterial proteins into the host cytosol that can act directly on phosphorylation cascades. This review will focus on the different stages of L. pneumophila infection, in which host kinases and phosphatases contribute to infection of the host cell and promote intracellular survival of the pathogen. This includes the involvement of phosphatidylinositol 3-kinases during phagocytosis as well as the role of phosphoinositide metabolism during the establishment of the replication vacuole. Furthermore, L. pneumophila infection modulates the NF-κB and mitogen-activated protein kinase pathways, two signaling pathways that are central to the host innate immune response and involved in regulation of host cell survival. Therefore, L. pneumophila infection manipulates host cell signal transduction by phosphorylation at multiple levels.

Lonely death dance of human pluripotent stem cells: ROCKing between metastable cell states

Two kinds of human pluripotent cells, human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), promise new avenues for medical innovation. These human cells share many similarities with mouse counterparts, including pluripotency, and they exhibit several unique properties. This review examines the diversity of mammalian pluripotent cells from a perspective of metastable pluripotency states. An intriguing phenomenon unique to human pluripotent stem cells is dissociation-induced apoptosis, which has been a technical problem for various cellular manipulations. The discovery that this apoptosis is suppressed by ROCK inhibitors brought revolutionary change to this troublesome situation. We discuss possible links of the metastable pluripotent state to ROCK-dependent human embryonic stem cell apoptosis and summarize recent progress in molecular understandings of this phenomenon.

Early gene expression changes in the retinal ganglion cell layer of a rat glaucoma model

PURPOSE

To identify patterns of early gene expression changes in the retinal ganglion cell layer (GCL) of a rodent model of chronic glaucoma.

METHODS

Prolonged elevation of intraocular pressure (IOP) was produced in rats by episcleral vein injection of hypertonic saline (N = 30). GCLs isolated by laser capture microdissection were grouped by grading of the nerve injury (<25% axon degeneration for early injury; >25% for advanced injury). Gene expression was determined by cDNA microarray of independent GCL RNA samples. Quantitative PCR (qPCR) was used to further examine the expression of selected genes.

RESULTS

By array analysis, 533 GCL genes (225 up, 308 down) were significantly regulated in early injury. Compared to only one major upregulated gene class of metabolism regulation, more were downregulated, including mitochondria, ribosome, proteasome, energy pathways, protein synthesis, protein folding, and synaptic transmission. qPCR confirmed an early upregulation of Atf3. With advanced injury, 1790 GCL genes were significantly regulated (997 up, 793 down). Altered gene categories included upregulated protein synthesis, immune response, and cell apoptosis and downregulated dendrite morphogenesis and axon extension. Of all the early changed genes, 50% were not present in advanced injury. These uniquely affected genes were mainly associated with upregulated transcription regulation and downregulated protein synthesis.

CONCLUSIONS

Early GCL gene responses to pressure-induced injury are characterized by an upregulation of Atf3 and extensive downregulation in genes associated with cellular metabolism and neuronal functions. Most likely, these changes represent those specific to RGCs and are thus potentially important for enhancing RGC survival in glaucoma.

Melatonin and vitamin D3 synergistically down-regulate Akt and MDM2 leading to TGFβ-1-dependent growth inhibition of breast cancer cells

Melatonin and vitamin D3 inhibit breast cancer cell growth and induce apoptosis, but they have never been combined as a breast cancer treatment. Therefore, we investigated whether their association could lead to an enhanced anticancer activity. In MCF-7 breast cancer cells, melatonin together with vitamin D3, induced a synergistic proliferative inhibition, with an almost complete cell growth arrest at 144 hr. Cell growth blockade is associated to an activation of the TGFβ-1 pathway, leading to increased TGFβ-1, Smad4 and phosphorylated-Smad3 levels. Concomitantly, melatonin and D3, alone or in combination, caused a significant reduction in Akt phosphorylation and MDM2 values, with a consequent increase of p53/MDM2 ratio. These effects were completely suppressed by adding a monoclonal anti-TGFβ-1 antibody to the culture medium. Taken together, these results indicate that cytostatic effects triggered by melatonin and D3 are likely related to a complex TGFβ-1-dependent mechanism, involving down-regulation of both MDM2 and Akt-phosphorylation.

Apoptotic cell signaling in cancer progression and therapy

Apoptosis is a tightly regulated cell suicide program that plays an essential role in the development and maintenance of tissue homeostasis by eliminating unnecessary or harmful cells. Impairment of this native defense mechanism promotes aberrant cellular proliferation and the accumulation of genetic defects, ultimately resulting in tumorigenesis, and frequently confers drug resistance to cancer cells. The regulation of apoptosis at several levels is essential to maintain the delicate balance between cellular survival and death signaling that is required to prevent disease. Complex networks of signaling pathways act to promote or inhibit apoptosis in response to various cues. Apoptosis can be triggered by signals from within the cell, such as genotoxic stress, or by extrinsic signals, such as the binding of ligands to cell surface death receptors. Various upstream signaling pathways can modulate apoptosis by converging on, and thereby altering the activity of, common central control points within the apoptotic signaling pathways, which involve the BCL-2 family proteins, inhibitor of apoptosis (IAP) proteins, and FLICE-inhibitory protein (c-FLIP). This review highlights the role of these fundamental regulators of apoptosis in the context of both normal apoptotic signaling mechanisms and dysregulated apoptotic pathways that can render cancer cells resistant to cell death. In addition, therapeutic strategies aimed at modulating the activity of BCL-2 family proteins, IAPs, and c-FLIP for the targeted induction of apoptosis are briefly discussed.

On the role of phosphatidylinositol 3-kinase, protein kinase b/Akt, and glycogen synthase kinase-3β in photodynamic injury of crayfish neurons and glial cells

Photodynamic treatment that causes intense oxidative stress and cell death is currently used in neurooncology. However, along with tumor cells, it may damage healthy neurons and glia. To study the involvement of signaling processes in photodynamic injury or protection of neurons and glia, we used crayfish mechanoreceptor consisting of a single neuron surrounded by glial cells. It was photosensitized with alumophthalocyanine Photosens. Application of specific inhibitors showed that phosphatidylinositol 3-kinase did not participate in photoinduced death of neurons and glia. Akt was involved in photoinduced necrosis but not in apoptosis of neurons and glia. Glycogen synthase kinase-3β participated in photoinduced apoptosis of glial cells and in necrosis of neurons. Therefore, phosphatidylinositol 3-kinase/protein kinase Akt/glycogen synthase kinase-3β pathway was not involved as a whole in photodynamic injury of crayfish neurons and glia but its components, Akt and glycogen synthase kinase-3β, independently and cell specifically regulated death of neurons and glial cells. According to these data, necrosis in this system was a controlled but not a non-regulated cell death mode. The obtained results may be used for the search of pharmacological agents selectively modulating death and survival of normal neurons and glial cells during photodynamic therapy of brain tumors.

The androgen receptor induces integrin α6β1 to promote prostate tumor cell survival via NF-κB and Bcl-xL Independently of PI3K signaling

Recent studies indicate that androgen receptor (AR) signaling is critical for prostate cancer cell survival, even in castration-resistant disease wherein AR continues to function independently of exogenous androgens. Integrin-mediated adhesion to the extracellular matrix is also important for prostate cell survival. AR-positive prostate cancer cells express primarily integrin α6β1 and adhere to a laminin-rich matrix. In this study, we show that active nuclear-localized AR protects prostate cancer cells from death induced by phosphoinositide 3-kinase (PI3K) inhibition when cells adhere to laminin. Resistance to PI3K inhibition is mediated directly by an AR-dependent increase in integrin α6β1 mRNA transcription and protein expression. Subsequent signaling by integrin α6β1 in AR-expressing cells increased NF-κB activation and Bcl-xL expression. Blocking AR, integrin α6, NF-κB, or Bcl-xL concurrent with inhibition of PI3K was sufficient and necessary to trigger death of laminin-adherent AR-expressing cells. Taken together, these results define a novel integrin-dependent survival pathway in prostate cancer cells that is regulated by AR, independent of and parallel to the PI3K pathway. Our findings suggest that combined targeting of both the AR/α6β1 and PI3K pathways may effectively trigger prostate cancer cell death, enhancing the potential therapeutic value of PI3K inhibitors being evaluated in this setting.

Host cellular signaling induced by influenza virus

A wide range of host cellular signal transduction pathways can be stimulated by influenza virus infection. Some of these signal transduction pathways induce the host cell's innate immune response against influenza virus, while others are essential for efficient influenza virus replication. This review examines the cellular signaling induced by influenza virus infection in host cells, including host pattern recognition receptor (PRR)-related signaling, protein kinase C (PKC), Raf/MEK/ERK and phosphatidy-linositol-3-kinase (PI3K)/Akt signaling, and the corresponding effects on the host cell and/or virus, such as recognition of virus by the host cell, viral absorption and entry, viral ribonucleoprotein (vRNP) export, translation control of cellular and viral proteins, and virus-induced cell apoptosis. Research into influenza virus-induced cell signaling promotes a clearer understanding of influenza virus-host interactions and assists in the identification of novel antiviral targets and antiviral strategies.

Widespread effects of nicotinic acid on gene expression in insulin-sensitive tissues: implications for unwanted effects of nicotinic acid treatment

Nicotinic acid (NA; or niacin) has been used as a hypolipidemic agent for more than 4 decades. However, the mechanisms underlying the effects of NA treatment (wanted and unwanted) are still poorly understood. In the present study, we discovered that NA infusion in rats resulted in dephosphorylation (ie, activation) of the forkhead transcription factor FOXO1 in insulin-sensitive tissues such as skeletal and cardiac muscles, liver, and adipose tissue. These NA effects were opposite to the effects of insulin to increase FOXO1 phosphorylation. To test whether NA alters gene expression in these tissues, rats were infused for 7 hours with NA (30 μmol/h) and/or insulin (5 mU/[kg min]); and gene expression was evaluated using a microarray analysis. Nicotinic acid had widespread effects on gene expression in all of the tissues studied, and the number of genes affected by NA greatly exceeded that of genes affected by insulin. A systematic (or strategic) analysis of the microarray data revealed that there were numerous genes whose expression was regulated inversely by insulin and NA in correlation with FOXO1 phosphorylation, representing potential FOXO1 target genes. We also identified a group of genes whose expression was altered by NA exclusively in adipose tissue, presumably because of stimulation of the NA receptor in this tissue. Finally, there were genes whose expression was altered by both NA and insulin, likely via lowering plasma free fatty acid levels, including lipoprotein lipase and adenosine triphosphate-binding cassette A1, which play a major role in the regulation of circulating lipids. Thus, our data suggest that NA alters gene expression in insulin-sensitive tissues by various mechanisms. Some of the NA-induced changes in gene expression are discussed as potential mechanisms underlying wanted and unwanted effects of NA treatment.

F-spondin regulates neuronal survival through activation of disabled-1 in the chicken ciliary ganglion

The extracellular membrane-associated protein F-spondin has been implicated in cell-matrix and cell-cell adhesion and plays an important role in axonal pathfinding. We report here that F-spondin is expressed in non-neuronal cells in the embryonic chicken ciliary ganglion (CG) and robustly promotes survival of cultured CG neurons. Using deletion constructs of F-spondin we found that the amino-terminal Reelin/Spondin domain cooperates with thrombospondin type 1 repeat (TSR) 6, a functional TGFβ-activation domain. In ovo treatment with blocking antibodies raised against the Reelin/Spondin domain or the TSR-domains caused increased apoptosis of CG neurons during the phase of programmed cell death and loss of about 30% of the neurons compared to controls. The Reelin/Spondin domain receptor - APP and its downstream signalling molecule disabled-1 are expressed in CG neurons. F-spondin induced rapid phosphorylation of disabled-1. Moreover, both blocking the central APP domain and interference with disabled-1 signalling disrupted the survival promoting effect of F-spondin. Taken together, our data suggest that F-spondin can promote neuron survival by a mechanism involving the Reelin/Spondin and the TSR domains.

Nox4 NADPH oxidase-derived reactive oxygen species, via endogenous carbon monoxide, promote survival of brain endothelial cells during TNF-α-induced apoptosis

We investigated the role of reactive oxygen species (ROS) in promoting cell survival during oxidative stress induced by the inflammatory mediator tumor necrosis factor-α (TNF-α) in cerebral microvascular endothelial cells (CMVEC) from newborn piglets. Nox4 is the major isoform of NADPH oxidase responsible for TNF-α-induced oxidative stress and apoptosis in CMVEC. We present novel data that Nox4 NADPH oxidase-derived ROS also initiate a cell survival mechanism by increasing production of a gaseous antioxidant mediator carbon monoxide (CO) by constitutive heme oxygenase-2 (HO-2). TNF-α rapidly enhanced endogenous CO production in a superoxide- and NADPH oxidase-dependent manner in CMVEC with innate, but not with small interfering RNA (siRNA)-downregulated Nox4 activity. CORM-A1, a CO-releasing compound, inhibited Nox4-mediated ROS production and enhanced cell survival in TNF-α-challenged CMVEC. The ROS-induced CO-mediated survival mechanism requires functional interactions between the protein kinase B/Akt and extracellular signal-related kinase (ERK)/p38 MAPK signaling pathways activated by TNF-α. In Akt siRNA-transfected CMVEC and in cells with pharmacologically inhibited Akt, Erk1/2, and p38 mitogen-activated protein kinase (MAPK) activities, CORM-A1 was no longer capable of blocking Nox4 activation and apoptosis caused by TNF-α. Overall, Nox4 NADPH oxidase-derived ROS initiate both death and survival pathways in TNF-α-challenged CMVEC. The ROS-dependent cell survival pathway is mediated by an endogenous antioxidant CO, which inhibits Nox4 activation via a mechanism that includes Akt, ERK1/2, and p38 MAPK signaling pathways. The ability of CO to inhibit TNF-α-induced ERK1/2 and p38 MAPK activities in an Akt-dependent manner appears to be the key element in ROS-dependent survival of endothelial cells during TNF-α-mediated brain inflammatory disease.

The JAK3-selective inhibitor PF-956980 reverses the resistance to cytotoxic agents induced by interleukin-4 treatment of chronic lymphocytic leukemia cells: potential for reversal of cytoprotection by the microenvironment

Extensive evidence suggests that the malignant cells of chronic lymphocytic leukemia (CLL) patients are in close contact with activated T lymphocytes, which secrete a range of cytoprotective cytokines including interleukin-4 (IL-4). IL-4 induced the rapid phosphorylation and activation of the signal transducer and activator of transcription 6 transcription factor in CLL cells in vitro. Longer incubation with IL-4 resulted in up-regulation of the antiapoptotic proteins, Mcl-1 and Bcl-XL. All of these events were blocked by the JAK3-selective inhibitor, PF-956980. A dye reduction cytotoxicity assay showed that IL-4 induced resistance to the cytotoxic drugs fludarabine and chlorambucil and to the novel p53-elevating agent nutlin 3. IL-4–induced drug resistance was reversed by PF-956980. These conclusions were confirmed by independent assays for apoptosis induction (annexin V binding, cleavage of poly[ADP-ribose] polymerase, and morphologic analysis). Coculture with bone marrow stromal cells in the presence of supernatants derived from activated T-lymphocyte cultures also protected CLL cells from apoptosis induction by chlorambucil. Protection by these combined signals was reversed by PF-956980. The data here provide a preclinical rationale for the possible therapeutic use of PF-956980 in conjunction with conventional cytotoxic drugs to achieve more extensive killing of CLL cells by overcoming antiapoptotic signaling by the microenvironment.

Serum and glucocorticoid-inducible kinase 1 (SGK1) is necessary for vascular remodeling during angiogenesis

The unquestionable importance of the cardiovascular system for pre- and postnatal life has prompted dissection of the molecular mechanisms underlying its development. Serum and glucocorticoid-inducible kinase 1 (SGK1) is a serine/threonine kinase lying downstream of the phosphoinositide 3 (PI3) kinase pathway, whose embryonic function remains unknown. Here, we show that disruption of Sgk1 in the mouse C57BL/6J genetic background leads to embryonic lethality at embryonic day 10.5-11.5 due to severe embryonic and extraembryonic angiogenic defects and to impaired myocardial trabeculation. Absence of SGK1 results in increased apoptosis of endothelial cells, and of vascular smooth muscle cells highlighting a prosurvival role for SGK1 during angiogenesis. Sgk1 null embryos also display reduced expression levels of Notch signaling genes and decreased expression of the arterial markers Efnb2 and Nrp1. These findings uncover a novel and essential function for SGK1 in cardiovascular development contributing to a better understanding of mammalian angiogenesis.