3-(Hydroxymethyl)-bearing phosphatidylinositol ether lipid analogues and carbonate surrogates block PI3-K, Akt, and cancer cell growth

Synthesis of ether lipids: natural compounds and analogues

Ether lipids are compounds present in many living organisms including humans that feature an ether bond linkage at the sn-1 position of the glycerol. This class of lipids features singular structural roles and biological functions. Alkyl ether lipids and alkenyl ether lipids (also identified as plasmalogens) correspond to the two sub-classes of naturally occurring ether lipids. In 1979 the discovery of the structure of the platelet-activating factor (PAF) that belongs to the alkyl ether class of lipids increased the interest in these bioactive lipids and further promoted the synthesis of non-natural ether lipids that was initiated in the late 60's with the development of edelfosine (an anticancer drug). More recently, ohmline, a glyco glycero ether lipid that modulates selectively SK3 ion channels and reduces in vivo the occurrence of bone metastases, and other glyco glycero ether also identified as GAEL (glycosylated antitumor ether lipids) that exhibit promising anticancer properties renew the interest in this class of compounds. Indeed, ether lipid represent a new and promising class of compounds featuring the capacity to modulate selectively the activity of some membrane proteins or, for other compounds, feature antiproliferative properties via an original mechanism of action. The increasing interest in studying ether lipids for fundamental and applied researches invited to review the methodologies developed to prepare ether lipids. In this review we focus on the synthetic method used for the preparation of alkyl ether lipids either naturally occurring ether lipids (e.g., PAF) or synthetic derivatives that were developed to study their biological properties. The synthesis of neutral or charged ether lipids are reported with the aim to assemble in this review the most frequently used methodologies to prepare this specific class of compounds.

Role of PI3K-AKT-mTOR Pathway as a Pro-Survival Signaling and Resistance-Mediating Mechanism to Therapy of Prostate Cancer

Androgen deprivation therapy (ADT) and androgen receptor (AR)-targeted therapy are the gold standard options for treating prostate cancer (PCa). These are initially effective, as localized and the early stage of metastatic disease are androgen- and castration-sensitive. The tumor strongly relies on systemic/circulating androgens for activating AR signaling to stimulate growth and progression. However, after a certain point, the tumor will eventually develop a resistant stage, where ADT and AR antagonists are no longer effective. Mechanistically, it seems that the tumor becomes more aggressive through adaptive responses, relies more on alternative activated pathways, and is less dependent on AR signaling. This includes hyperactivation of PI3K-AKT-mTOR pathway, which is a central signal that regulates cell pro-survival/anti-apoptotic pathways, thus, compensating the blockade of AR signaling. The PI3K-AKT-mTOR pathway is well-documented for its crosstalk between genomic and non-genomic AR signaling, as well as other signaling cascades. Such a reciprocal feedback loop makes it more complicated to target individual factor/signaling for treating PCa. Here, we highlight the role of PI3K-AKT-mTOR signaling as a resistance mechanism for PCa therapy and illustrate the transition of prostate tumor from AR signaling-dependent to PI3K-AKT-mTOR pathway-dependent. Moreover, therapeutic strategies with inhibitors targeting the PI3K-AKT-mTOR signal used in clinic and ongoing clinical trials are discussed.

Anticancer Activity of Triazolo-Thiadiazole Derivatives and Inhibition of AKT1 and AKT2 Activation

The fusion of 1,2,4-triazole and 1,3,4-thiadiazole rings results in a class of heterocycles compounds with an extensive range of pharmacological properties. A series of 1,2,4-triazolo[3,4-b]-1,2,4-thiadiazoles was synthesized and tested for its enzyme inhibition potential and anticancer activity. The results show that 1,2,4-triazolo[3,4-b]-1,2,4-thiadiazoles display potent anticancer properties in vitro against a panel of cancer cells and in vivo efficacy in HT-29 human colon tumor xenograft in CB17 severe combined immunodeficient (SCID) mice. Preliminary mechanistic studies revealed that KA25 and KA39 exhibit time- and concentration-dependent inhibition of Akt Ser-473 phosphorylation. Molecular modeling experiments indicated that 1,2,4-triazolo[3,4-b]-1,2,4-thiadiazoles bind well to the ATP binding site in Akt1 and Akt2. The low acute toxicity combined with in vitro and in vivo anticancer activity render triazolo[3,4-b]thiadiazoles KA25, KA26, and KA39 promising cancer therapeutic agents.

Inositol Polyphosphate-Based Compounds as Inhibitors of Phosphoinositide 3-Kinase-Dependent Signaling

Signaling pathways regulated by the phosphoinositide 3-kinase (PI3K) enzymes have a well-established role in cancer development and progression. Over the past 30 years, the therapeutic potential of targeting this pathway has been well recognized, and this has led to the development of a multitude of drugs, some of which have progressed into clinical trials, with few of them currently approved for use in specific cancer settings. While many inhibitors compete with ATP, hence preventing the catalytic activity of the kinases directly, a deep understanding of the mechanisms of PI3K-dependent activation of its downstream effectors led to the development of additional strategies to prevent the initiation of this signaling pathway. This review summarizes previously published studies that led to the identification of inositol polyphosphates as promising parent molecules to design novel inhibitors of PI3K-dependent signals. We focus our attention on the inhibition of protein-membrane interactions mediated by binding of pleckstrin homology domains and phosphoinositides that we proposed 20 years ago as a novel therapeutic strategy.

Mechanisms of Androgen Receptor Agonist- and Antagonist-Mediated Cellular Senescence in Prostate Cancer

The androgen receptor (AR) plays a leading role in the control of prostate cancer (PCa) growth. Interestingly, structurally different AR antagonists with distinct mechanisms of antagonism induce cell senescence, a mechanism that inhibits cell cycle progression, and thus seems to be a key cellular response for the treatment of PCa. Surprisingly, while physiological levels of androgens promote growth, supraphysiological androgen levels (SAL) inhibit PCa growth in an AR-dependent manner by inducing cell senescence in cancer cells. Thus, oppositional acting ligands, AR antagonists, and agonists are able to induce cellular senescence in PCa cells, as shown in cell culture model as well as ex vivo in patient tumor samples. This suggests a dual AR-signaling dependent on androgen levels that leads to the paradox of the rational to keep the AR constantly inactivated in order to treat PCa. These observations however opened the option to treat PCa patients with AR antagonists and/or with androgens at supraphysiological levels. The latter is currently used in clinical trials in so-called bipolar androgen therapy (BAT). Notably, cellular senescence is induced by AR antagonists or agonist in both androgen-dependent and castration-resistant PCa (CRPC). Pathway analysis suggests a crosstalk between AR and the non-receptor tyrosine kinase Src-Akt/PKB and the PI3K-mTOR-autophagy signaling in mediating AR-induced cellular senescence in PCa. In this review, we summarize the current knowledge of therapeutic induction and intracellular pathways of AR-mediated cellular senescence.

NGL-3 in the regulation of brain development, Akt/GSK3b signaling, long-term depression, and locomotive and cognitive behaviors

Netrin-G ligand-3 (NGL-3) is a postsynaptic adhesion molecule known to directly interact with the excitatory postsynaptic scaffolding protein postsynaptic density-95 (PSD-95) and trans-synaptically with leukocyte common antigen-related (LAR) family receptor tyrosine phosphatases to regulate presynaptic differentiation. Although NGL-3 has been implicated in the regulation of excitatory synapse development by in vitro studies, whether it regulates synapse development or function, or any other features of brain development and function, is not known. Here, we report that mice lacking NGL-3 (Ngl3^−/− mice) show markedly suppressed normal brain development and postnatal survival and growth. A change of the genetic background of mice from pure to hybrid minimized these developmental effects but modestly suppressed N-methyl-D-aspartate (NMDA) receptor (NMDAR)-mediated synaptic transmission in the hippocampus without affecting synapse development, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor (AMPAR)-mediated basal transmission, and presynaptic release. Intriguingly, long-term depression (LTD) was near-completely abolished in Ngl3^−/− mice, and the Akt/glycogen synthase kinase 3β (GSK3β) signaling pathway, known to suppress LTD, was abnormally enhanced. In addition, pharmacological inhibition of Akt, but not activation of NMDARs, normalized the suppressed LTD in Ngl3^−/− mice, suggesting that Akt hyperactivity suppresses LTD. Ngl3^−/− mice displayed several behavioral abnormalities, including hyperactivity, anxiolytic-like behavior, impaired spatial memory, and enhanced seizure susceptibility. Among them, the hyperactivity was rapidly improved by pharmacological NMDAR activation. These results suggest that NGL-3 regulates brain development, Akt/GSK3β signaling, LTD, and locomotive and cognitive behaviors.

Metabolite profiling and in-vitro colon cancer protective activity of Cycas revoluta cone extract

The methanolic extract of Cycas revoluta cone (MECR) was analyzed by GC-MS and UHPLC for metabolite profiling and was evaluated for anti-colon cancer property by using in vitro assays like Cell Viability Assay, Colony Formation Assay, ROS Determination, Flowcytometry, DAPI staining assay, Tunel assay. GC-MS and HPLC analysis confirmed the presence of different phytochemicals in the extract of Cycas revoluta cone. In-vitro studies showed MECR extract showed significant anti-colon cancer activity by reducing proliferation and inducing apoptosis in colon cancer cell (HCT-8) line, but no such activity was seen in normal colon cell (CCD-18Co) line. The investigation confirms that MECR may be a promising candidate in colon cancer protection.

Analysis of correlation between HP infection and activation of PI3K/Akt pathway in mucosal tissues of gastric cancer and precancerous lesions

The aim of the study was to investigate the correlation between Helicobacter pylori (HP) infection and activation of the phosphatidylinositol-3-kinase/Akt (PI3K/Akt) pathway in mucosal tissues of gastric cancer and precancerous lesions. Patients with chronic atrophic gastritis (n=52) and gastric cancer (n=98) were treated in the Department of Gastroenterology at The Fifth People's Hospital of Chongqing from August 2011 to August 2016 were selected, and the biopsy tissue and serum specimens were collected. The HP infection was detected via enzyme-linked immunosorbent assay (ELISA), and the expression level of phosphorylated-Akt (p-Akt) was detected via immunohistochemistry (IHC). Moreover, in vivo experiments were performed to simulate HP infection in gastric cancer cells (MGC-803 and AGS), and the p-Akt protein level, PI3K activity and cell proliferative activity were detected. Finally, the changes in Akt protein level were detected by co-culture of gastric cancer cells via LY294002, a PI3K inhibitor, and HP. The positive rate of HP infection in patients with chronic atrophic gastritis was 84.6% (44/52), which was significantly higher than that in patients with gastric cancer [73.5% (72/98)] (p<0.05). The positive rate of HP infection in patients with early gastric cancer (86.4%) was significantly higher than that in patients with moderate-advanced gastric cancer (69.7%) (p<0.05). Results of IHC and western blot analysis revealed that the p-Akt expression level in HP-positive tissues was obviously higher than that in HP-negative tissues (p<0.05). In vitro cell experiments revealed that the PI3K activity was enhanced and the PI3K/Akt pathway was significantly activated after HP infection in tumor cells, thus promoting the proliferation of tumor cells (p<0.05) in a time-dependent manner. After LY294002 inhibited PI3K activity, Akt was not significantly activated by HP infection. Thus, HP activates the PI3K/Akt pathway in gastric cancer cells, thereby promoting tumor cell proliferation.

Heat shock protein 27 (HSPB1) suppresses the PDGF-BB-induced migration of osteoblasts

Heat shock protein 27 (HSP27/HSPB1), one of the small heat shock proteins, is constitutively expressed in various tissues. HSP27 and its phosphorylation state participate in the regulation of multiple physiological and pathophysiological cell functions. However, the exact roles of HSP27 in osteoblasts remain unclear. In the present study, we investigated the role of HSP27 in the platelet-derived growth factor‑BB (PDGF‑BB)‑stimulated migration of osteoblast-like MC3T3-E1 cells. PDGF-BB by itself barely upregulated the expression of HSP27 protein, but stimulated the phosphorylation of HSP27 in these cells. The PDGF-BB‑induced cell migration was significantly downregulated by HSP27 overexpression. The PDGF-BB-induced migrated cell numbers of the wild‑type HSP27-overexpressing cells and the phospho‑mimic HSP27-overexpressing (3D) cells were less than those of the unphosphorylatable HSP27-overexpressing (3A) cells. PD98059, an inhibitor of MEK1/2, SB203580, an inhibitor of p38 mitogen-activated protein kinase, and SP600125, an inhibitor of stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) reduced the PDGF-BB-induced migration of these cells, whereas Akt inhibitor or rapamycin, an inhibitor of upstream kinase of p70 S6 kinase (mTOR), barely affected the migration. However, the PDGF-BB-induced phosphorylation of p44/p42 MAPΚ, p38 MAPK and SAPK/JNK was not affected by HSP27 overexpression. There were no significant differences in the phosphorylation of p44/p42 MAPΚ, p38 MAP kinase or SAPK/JNK between the 3D cells and the 3A cells. These results strongly suggest that HSP27 functions as a negative regulator in the PDGF-BB-stimulated migration of osteoblasts, and the suppressive effect is amplified by the phosphorylation state of HSP27.

Intramolecular Cyclization of Carbonate and Thiocarbonate Derivatives of myo-Inositol in the Solid State: Implications for Acyl Group Transfer Reactions in Molecular Crystals

Racemic 4-O-phenoxycarbonyl and 4-O-phenoxythiocarbonyl derivatives of myo-inositol orthoformate undergo thermal intramolecular cyclization in the solid state to yield the corresponding 4,6-bridged carbonates and thiocarbonates, respectively. The thermal cyclization also occurs in the solution and molten states, but less efficiently, suggesting that these cyclization reactions are aided by molecular pre-organization, although not strictly topochemically controlled. Crystal structures of two carbonates and a thiocarbonate clearly revealed that the relative orientation of the electrophile and the nucleophile in the crystal lattice facilitates the intramolecular cyclization reaction and forbids the intermolecular reaction. The correlation observed between the chemical reactivity and the non-covalent interactions in the crystal of the reactants provides a way to estimate the chemical stability of analogous molecules in the solid state.

Regulation by heat shock protein 22 (HSPB8) of transforming growth factor-α-induced ovary cancer cell migration

Accumulating evidence suggests that heat shock proteins (HSPs) are implicated in progression of cancer. HSP22 (HSPB8), a small HSP, is recognized to be ubiquitously expressed in various tissues. However, the expression and the role of HSP22 in ovarian cancer remain to be clarified. In the present study, we investigated the involvement of HSP22 in transforming growth factor (TGF)-α-induced migration of ovarian cancer cells. The expression of HSP22 was detected in a serous ovarian cancer cell line, SKOV3.ip1. The migration was reduced by down-regulation of HSP22 expression. The TGF-α-induced migration was reduced by SB203580 (a p38 MAP kinase inhibitor), SP600125 (a SAPK/JNK inhibitor) and Y27632 (a Rho-kinase inhibitor). However, down-regulation of HSP22 had little effect on the TGF-α-induced phosphorylation of p38 MAP kinase, SAPK/JNK and MYPT, a target protein of Rho-kinase. The HSP22 expression was further analyzed in 20 resected specimens of human ovarian serous carcinoma. The expression of HSP22 was detected in all the twenty tissues (8.24-109.22 pg/mg protein), and the cases with highly expression of HSP22 showed a tendency to acquire the progressive ability. Our results strongly suggest that HSP22 acts as a positive regulator in TGF-α-induced migration of ovarian cancer cells, subsequently directing ovarian cancer toward progression.

Complex impacts of PI3K/AKT inhibitors to androgen receptor gene expression in prostate cancer cells

Background

Androgen deprivation therapy (ADT) is the first-line treatment to metastatic prostate cancer (PCa). However, sustained expression and function of the androgen receptor (AR) gene contribute to the progression of castration resistant prostate cancers (CRPC). Additionally, tumors can adapt the PI3K/AKT survival pathway to escape ADT. Co-targeting AR and PI3K/AKT signaling has been proposed to be a more effective therapeutic means for CRPC patients. Many clinical trials are ongoing to test whether PI3K/AKT inhibitors are beneficial to PCa patients. However whether these inhibitors have any impacts on the expressions of full length AR (AR-FL) and its splice variant (AR-V7) remains unclear.

Methods

Four human prostate cancer cell lines (LNCaP, LNCaP95, VCaP and 22Rv1) with different genetic backgrounds were treated with five PI3K/AKT inhibitors (LY294002, Wortmannin, BKM120, AKTi and AZD5363) and or AKT siRNA. AR and AR-V7 protein and mRNA levels were measured by immunoblotting and real-time PCR assays. AR gene transcription initiation, alternative RNA splicing and AR mRNA degradation rates were also determined.

Results

PI3K/AKT inhibitors had various impacts on AR protein expressions primarily through alterations of AR gene transcription initiation and RNA splicing. However, these effects remained unchanged in the presence RNA silencing of the AKT genes.

Conclusion

PI3K/AKT inhibitors have off-target effects on AR gene expression in prostate cancer cells, which shall be considered when applying these inhibitors to PCa patients, particularly patients under ADT treatment.

Down-regulation by resveratrol of basic fibroblast growth factor-stimulated osteoprotegerin synthesis through suppression of Akt in osteoblasts

It is firmly established that resveratrol, a natural food compound abundantly found in grape skins and red wine, has beneficial properties for human health. In the present study, we investigated the effect of basic fibroblast growth factor (FGF-2) on osteoprotegerin (OPG) synthesis in osteoblast-like MC3T3-E1 cells and whether resveratrol affects the OPG synthesis. FGF-2 stimulated both the OPG release and the expression of OPG mRNA. Resveratrol significantly suppressed the FGF-2-stimulated OPG release and the mRNA levels of OPG. SRT1720, an activator of SIRT1, reduced the FGF-2-induced OPG release and the OPG mRNA expression. PD98059, an inhibitor of upstream kinase activating p44/p42 mitogen-activated protein (MAP) kinase, had little effect on the FGF-2-stimulated OPG release. On the other hand, SB203580, an inhibitor of p38 MAP kinase, SP600125, an inhibitor of stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), and Akt inhibitor suppressed the OPG release induced by FGF-2. Resveratrol failed to affect the FGF-2-induced phosphorylation of p44/p42 MAP kinase, p38 MAP kinase or SAPK/JNK. The phosphorylation of Akt induced by FGF-2 was significantly suppressed by resveratrol or SRT1720. These findings strongly suggest that resveratrol down-regulates FGF-2-stimulated OPG synthesis through the suppression of the Akt pathway in osteoblasts and that the inhibitory effect of resveratrol is mediated at least in part by SIRT1 activation.

Akt inhibitors: mechanism of action and implications for anticancer therapeutics

Akt, better known as protein kinase B (PKB), is a serine/threonine-specific protein kinase which acts as mediator via PI3K/Akt pathway in many biological processes like glucose metabolism, apoptosis, cell differentiation and transcription. Akt1 gene amplification has been implicated in gastric carcinoma while Akt2 amplification has been linked with ovarian, pancreas, breast and stomach tumors. The use of Akt inhibitors as monotherapy or in combination with other anticancer drugs could be useful for combating drug resistance and improving response. Thus, comprehensive understanding of Akt and its linked signaling pathways (PI3K, PKB, mTOR etc.) is necessary to lead to newer drug development and use.

PI 3-kinase independent role for AKT in F-actin regulation during outer segment phagocytosis by RPE cells

Daily phagocytosis of photoreceptor outer segment fragments (POS) by the retinal pigment epithelium (RPE) is essential for vision. RPE cells use an uptake machinery that is highly similar to the one macrophages use to phagocytose apoptotic cells. In both forms of phagocytosis, particle binding induces phagocyte signaling that is required for F-actin assembly and re-arrangement beneath bound particles. Macrophage binding of apoptotic cells stimulates PI3 kinases (PI3K) and AKT kinases (AKT), which may be downstream of PI3K, and PI3K inhibition decreases engulfment. Here, we used specific inhibitory agents to investigate whether and how PI3K and AKT contribute to RPE phagocytosis. Either PI3K or AKT inhibition eliminated AKT activation by RPE cells in response to POS and increased the numbers of POS bound by RPE cells. Analyzing the quality of bound POS, we found a higher fraction of POS associated with F-actin phagocytic cups and myosin II in RPE receiving AKT inhibitor. In these cells, individual POS also recruited more F-actin and myosin II than POS in control cells. In contrast, PI3K inhibition did not alter frequency of phagocytic cups but individual cups contained less F-actin (but similar levels of myosin II) compared to control cups. Annexin AII, another phagocytic cup protein of RPE cells, associated with bound POS regardless of inhibitor treatment. POS engulfment proceeded normally if cells already carried surface-bound POS when receiving inhibitors. However, PI3K inhibition during POS binding blocked subsequent POS engulfment. In striking contrast, AKT inhibition had no effect on POS engulfment. Taken together, these results suggest distinct regulatory roles of PI3K and AKT during POS phagocytosis by RPE cells.

A novel function of protein kinase B as an inducer of the mismatch repair gene hPMS2 degradation

Human DNA mismatch repair (MMR) proteins correct DNA errors, which normally occur during DNA replication. Defects of MMR genes result in genomic instability and carcinogenesis. However, the mechanism of MMR proteins regulation has not yet been clearly explored, especially for the member of MutL-related protein, human post meiotic segregation increased 2 (hPMS2). In this study, an inverse correlation between hPMS2 level and activated Akt was detected in nine tumor cell lines by western blot. The negative regulation of hPMS2 expression by activated Akt was further verified by functional experiments manipulating Akt activity using siRNA targeting Akt, Akt Inhibitor I, Akt/PKB Signaling Inhibitor-2 (API-2) and Insulin-like Growth Factor-I (IGF-1). In addition, protein complex immunoprecipitation assays and protein stability assays using cycloheximide revealed that activated Akt (P-Akt1 S473) could bind to hPMS2 directly and induce hPMS2 degradation. Moreover, results of immunofluorescence assays showed blocking Akt activity resulted in accumulation of hPMS2 protein in nucleus. These observations indicate that activated Akt is the upstream signaling regulating hPMS2 expression, stability and nuclear localization, providing a novel insight into the regulation of hPMS2 in cancer cells.

HSP70 increases extracellular matrix production by human vascular smooth muscle through TGF-β1 up-regulation

The circulating levels of heat shock proteins (HSP) are increased in cardiovascular diseases; however, the implication of this for the fibrotic process typical of such diseases remains unclear. HSP70 can interact with the vascular smooth muscle cells (SMC), the major producer of extracellular matrix (ECM) proteins, through the Toll-like receptors 4 (TLR4). The transforming growth factor type-β1 (TGF-β1) is a well known vascular pro-fibrotic cytokine that is regulated in part by AP-1-dependent transcriptional mechanisms. We hypothesized that extracellular HSP70 could interact with SMCs, inducing TGF-β1 synthesis and subsequent changes in the vascular ECM. We demonstrate that extracellular HSP70 binds to human aorta SMC TLR4, which up-regulates the AP-1-dependent transcriptional activity of the TGF-β1 promoter. This is achieved through the mitogen activated protein kinases JNK and ERK, as demonstrated by the use of specific blockers and the knockdown of TLR4 with specific small interfering RNAs. The TGF-β1 upregulation increase the expression of the ECM proteins type I collagen and fibronectin. This novel observation may elucidate the mechanisms by which HSP70 contributes in the inflammation and fibrosis present in atherosclerosis and other fibrosis-related diseases.

CYLD negatively regulates transforming growth factor-β-signalling via deubiquitinating Akt

Lung injury, whether induced by infection or caustic chemicals, initiates a series of complex wound-healing responses. If uncontrolled, these responses may lead to fibrotic lung diseases and loss of function. Thus, resolution of lung injury must be tightly regulated. The key regulatory proteins required for tightly controlling the resolution of lung injury have yet to be identified. Here we show that loss of deubiquitinase CYLD led to the development of lung fibrosis in mice after infection with Streptococcus pneumoniae. CYLD inhibited transforming growth factor-β-signalling and prevented lung fibrosis by decreasing the stability of Smad3 in an E3 ligase carboxy terminus of Hsc70-interacting protein-dependent manner. Moreover, CYLD decreases Smad3 stability by deubiquitinating K63-polyubiquitinated Akt. Together, our results unveil a role for CYLD in tightly regulating the resolution of lung injury and preventing fibrosis by deubiquitinating Akt. These studies may help develop new therapeutic strategies for preventing lung fibrosis.

Salmonella enteritidis Rck-mediated invasion requires activation of Rac1, which is dependent on the class I PI 3-kinases-Akt signaling pathway

The Salmonella outer membrane protein Rck mediates a Zipper-like entry mechanism controlled by Rac, the Arp2/3 complex, and actin polymerization. However, little is known about the early steps leading to Rac activation and Rck-mediated internalization. The use of pharmacological inhibitors or PI 3-kinase dominant-negative mutant induced more than 80% less invasion without affecting attachment. Moreover, Rck-mediated internalization caused an increase in the association of p85 with at least one tyrosine-phosphorylated protein, indicating that class I PI 3-kinase activity was stimulated. We also report that this PI 3-kinase activity is essential for Rac1 activation. However, Rac recruitment at the Rck-mediated entry site was independent of its activation. Using a pharmacological approach or Akt-knockout cells, we also demonstrated that Akt was phosphorylated in response to Rck-mediated internalization as demonstrated by immunoblotting analysis and that all three Akt isoforms were required during this process. Overall, our results describe a signaling pathway involving tyrosine phosphorylation, class I PI 3-kinase, Akt activation, and Rac activation, leading to Rck-dependent Zipper entry. The specificity of this signaling pathway with regard to that of the type 3 secretion system, which is the other invasion process of Salmonella, is discussed.

PTEN regulates retinal interneuron morphogenesis and synaptic layer formation

The lipid phosphatase PTEN is a critical negative regulator of extracellular signal-induced PI3K activities, yet the roles of PTEN in the neural retina remain poorly understood. Here, we investigate the function of PTEN during retinal development. Deletion of Pten at the onset of neurogenesis in retinal progenitors results in the reduction of retinal ganglion cells and rod photoreceptors, but increased Müller glial genesis. In addition, PTEN deficiency leads to elevated phosphorylation of Akt, especially in the developing inner plexiform layer, where high levels of PTEN are normally expressed. In Pten mutant retinas, various subtypes of amacrine cells show severe dendritic overgrowth, causing specific expansion of the inner plexiform layer. However, the outer plexiform layer remains relatively undisturbed in the Pten deficient retina. Physiological analysis detects reduced rod function and augmented oscillatory potentials originating from amacrine cells in Pten mutants. Furthermore, deleting Pten or elevating Akt activity in individual amacrine cells is sufficient to disrupt dendritic arborization, indicating that Pten activity is required cell autonomously to control neuronal morphology. Moreover, inhibiting endogenous Akt activity attenuates inner plexiform layer formation in vitro. Together, these findings demonstrate that suppression of PI3K/Akt signaling by PTEN is crucial for proper neuronal differentiation and normal retinal network formation.

Akt acutely activates the cholesterogenic transcription factor SREBP-2

Akt is an essential protein kinase for cell growth, proliferation, and survival. Perturbed Akt regulation is associated with a number of human diseases, such as cancer and diabetes. Recently, evidence has emerged that Akt is involved in the regulation of the sterol-regulatory element binding proteins, which are master transcriptional regulators of lipid metabolism. This offers a means by which synthesis of new membrane can be coordinated with cell growth and proliferation. However, the link between Akt and sterol-regulatory element binding protein-2, the major isoform participating in cholesterol regulation, is relatively unexplored. In the present study, we employed insulin-like growth factor-1 as an inducer of Akt signalling, and showed that it increased sterol-regulatory element binding protein-2 activation acutely (within 1h). This insulin-like growth factor-1-induced sterol-regulatory element binding protein-2 activation was blunted when Akt was inhibited pharmacologically or molecularly with small interfering RNA. Furthermore, we employed a rapalog heterodimerisation system to specifically and rapidly activate Akt, and found that sterol-regulatory element binding protein-2 activation was increased in response to Akt activation. Together, this study provides compelling evidence that Akt contributes to the acute regulation of cholesterol metabolism through activating sterol-regulatory element binding protein-2.

Novel inhibitors of AKT: assessment of a different approach targeting the pleckstrin homology domain

Protein kinase B/AKT plays a central role in cancer. The serine/threonine kinase is overexpressed or constitutively active in many cancers and has been validated as a therapeutic target for cancer treatment. However, targeting the kinase activity has revealed itself to be a challenge due to non-selectivity of the compounds towards other kinases. This review summarizes other approaches scientists have developed to inhibit the activity and function of AKT. They consist in targeting the pleckstrin homology (PH) domain of AKT. Indeed, upon the generation of 3-phosphorylated phosphatidylinositol phosphates (PI3Ps) by PI3-kinase (PI3K), AKT translocates from the cytosol to the plasma membrane and binds to the PI3Ps via its PH domain. Thus, several analogs of PI3Ps (PI Analogs or PIAs), alkylphospholipids (APLs), such as edelfosine or inositol phophates (IPs) have been described that inhibit the binding of the PH domain to PI3Ps. Recent allostertic inhibitors and small molecules that do not bind the kinase domain but affect the kinase activity of AKT, presumably by interacting with the PH domain, have been also identified. Finally, several drug screening studies spawned novel chemical scaffolds that bind the PH domain of AKT. Together, these approaches have been more or less sucessfull in vitro and to some extent translated in preclinical studies. Several of these new AKT PH domain inhibitors exhibit promising anti-tumor activity in mouse models and some of them show synergy with ionizing radiation and chemotherapy. Early clinical trials have started and results will attest to the validity and efficacy of such approaches in the near future.

UVC radiation induces downregulation of EGF receptor via phosphorylation at serine 1046/1047 in human pancreatic cancer cells

Epidermal growth factor receptor (EGFR) is overexpressed in human pancreatic cancer and is one of the clinical targets in its treatment. In the present study we investigated the mechanism underlying ultraviolet C (UVC)-radiation-induced cell growth inhibition and downregulation of EGFR in human pancreatic cancer cells (Panc1 and KP3). The cell proliferation assay indicated that Panc1 and KP3 cells were more sensitive to UVC radiation, and their growth was significantly inhibited compared to cells of the normal human pancreatic epithelial cell line, PE. Although EGFR levels was extremely low in PE cells, EGFR were highly overexpressed in Panc1 and KP3 cells, and UVC radiation downregulated the expression of EGFR in a time-dependent manner and induced phosphorylation of EGFR at Ser1046/1047 (S1046/7) in Panc1 and KP3 cells. UVC radiation induced activation of p38 mitogen-activated protein kinase (MAPK), and EGFR phosphorylation at S1046/7 induced by UVC radiation was markedly attenuated by the inhibition of p38 MAPK. Moreover, fluorescence microscopy revealed that p38 MAPK activated by UVC radiation triggered EGFR internalization and that this was not correlated with c-Cbl, an ubiquitin ligase, which plays an important role in EGF-induced EGFR downregulation. Taken together, our results suggest that in pancreatic cancer cells UVC radiation induced desensitization of the cells to EGFR stimuli via phosphorylation of EGFR at S1046/7 by activation of p38 MAPK, independent of c-Cbl.

Recent development of anticancer therapeutics targeting Akt

The serine/threonine kinase Akt has proven to be a significant signaling target, involved in various biological functions. Because of its cardinal role in numerous cellular responses, Akt has been implicated in many human diseases, particularly cancer. It has been established that Akt is a viable and feasible target for anticancer therapeutics. Analysis of all Akt kinases reveals conserved homology for an N-terminal regulatory domain, which contains a pleckstrin-homology (PH) domain for cellular translocation, a kinase domain with serine/threonine specificity, and a C-terminal extension domain. These well defined regions have been targeted, and various approaches, including in silico methods, have been implemented to develop Akt inhibitors. In spite of unique techniques and a prolific body of knowledge surrounding Akt, no targeted Akt therapeutics have reached the market yet. Here we will highlight successes and challenges to date on the development of anticancer agents modulating the Akt pathway in recent patents as well as discuss the methods employed for this task. Special attention will be given to patents with focus on those discoveries using computer-aided drug design approaches.

Interleukin-2 induces NF-kappaB activation through BCL10 and affects its subcellular localization in natural killer lymphoma cells

Deregulation of nuclear factor (NF)-kappaB signalling is common in cancers and is essential for tumourigenesis. Constitutive NF-kappaB activation in extranodal natural killer (NK)-cell lymphoma, nasal type (ENKL) is known to be associated with aberrant nuclear translocation of BCL10. Here we investigated the mechanisms leading to NF-kappaB activation and BCL10 nuclear localization in ENKLs. Given that ENKLs are dependent on T-cell-derived interleukin-2 (IL2) for cytotoxicity and proliferation, we investigated whether IL2 modulates NF-kappaB activation and BCL10 subcellular localization in ENKLs. In the present study, IL2-activated NK lymphoma cells were found to induce NF-kappaB activation via the PI3K/Akt pathway, leading to an increase in the entry of G(2)/M phase and concomitant transcription of NF-kappaB-responsive genes. We also found that BCL10, a key mediator of NF-kappaB signalling, participates in the cytokine receptor-induced activation of NF-kappaB. Knockdown of BCL10 expression resulted in deficient NF-kappaB signalling, whereas Akt activation was unaffected. Our results suggest that BCL10 plays a role downstream of Akt in the IL2-triggered NF-kappaB signalling pathway. Moreover, the addition of IL2 to NK cells led to aberrant nuclear translocation of BCL10, which is a pathological feature of ENKLs. We further show that BCL10 can bind to BCL3, a transcriptional co-activator and nuclear protein. Up-regulation of BCL3 expression was observed in response to IL2. Similar to BCL10, the expression and nuclear translocation of BCL3 were induced by IL2 in an Akt-dependent manner. The nuclear translocation of BCL10 was also dependent on BCL3 because silencing BCL3 by RNA interference abrogated this translocation. We identified a critical role for BCL10 in the cytokine receptor-induced NF-kappaB signalling pathway, which is essential for NK cell activation. We also revealed the underlying mechanism that controls BCL10 nuclear translocation in NK cells. Our findings provide insight into a molecular network within the NF-kappaB signalling pathway that promotes the pathogenesis of NK cell lymphomas.

Killing of rat basophilic leukemia cells by lethal toxin from Clostridium sordellii: critical role of phosphatidylinositide 3'-OH kinase/Akt signaling

Clostridium sordellii lethal toxin (TcsL) belongs to the family of clostridial glucosylating toxins. TcsL exhibits glucosyltransferase activity to inactivate Rho and Ras proteins. On cultured cells, TcsL causes actin reorganization ("cytopathic effect") and apoptotic cell death ("cytotoxic effect"). This study is based on the concept that the cytotoxic effects of TcsL depend on the glucosylation of critical substrate proteins rather than on the glucosyltransferase activity per se. The cytotoxic effects of TcsL depend on the glucosyltransferase activity of TcsL, as neither chemically inactivated TcsL nor a glucosyltransferase-deficient mutant version of TcsL caused it. The TcsL homologous toxin B from Clostridium difficile serotype F strain 1470 (TcdBF) also failed to cause cytotoxic effects. Correlation of the toxins' respective protein substrate specificities highlighted (H/K/N)Ras as critical substrate proteins for the cytotoxic effects. (H/K/N)Ras are critical upstream regulators of phosphatidylinositide 3'-OH kinase (PI3K)/Akt survival signaling. Tauroursodeoxycholic acid (TUDCA) classified to activate PI3K/Akt signaling downstream of apoptosis-inducing stimuli prevented the cytotoxic effects of TcsL. In conclusion, (H/K/N)Ras glucosylation and subsequent inhibition of PI3K/Akt signaling are critical for the cytotoxic effects of TcsL.

Talin1 promotes tumor invasion and metastasis via focal adhesion signaling and anoikis resistance

Talin1 is a focal adhesion complex protein that regulates integrin interactions with ECM. This study investigated the significance of talin1 in prostate cancer progression to metastasis in vitro and in vivo. Talin1 overexpression enhanced prostate cancer cell adhesion, migration, and invasion by activating survival signals and conferring resistance to anoikis. ShRNA-mediated talin1 loss led to a significant suppression of prostate cancer cell migration and transendothelial invasion in vitro and a significant inhibition of prostate cancer metastasis in vivo. Talin1-regulated cell survival signals via phosphorylation of focal adhesion complex proteins, such as focal adhesion kinase and Src, and downstream activation of AKT. Targeting AKT activation led to a significant reduction of talin1-mediated prostate cancer cell invasion. Furthermore, talin1 immunoreactivity directly correlated with prostate tumor progression to metastasis in the transgenic adenocarcinoma mouse prostate mouse model. Talin1 profiling in human prostate specimens revealed a significantly higher expression of cytoplasmic talin1 in metastatic tissue compared with primary prostate tumors (P < 0.0001). These findings suggest (a) a therapeutic significance of disrupting talin1 signaling/focal adhesion interactions in targeting metastatic prostate cancer and (b) a potential value for talin1 as a marker of tumor progression to metastasis.

p70 S6 kinase limits tumor necrosis factor-alpha-induced interleukin-6 synthesis in osteoblast-like cells

Our previous study demonstrated that tumor necrosis factor-alpha (TNF-alpha) stimulates the synthesis of interleukin-6 (IL-6), a potent bone resorptive agent, via p44/p42 mitogen-activated protein (MAP) kinase and phosphatidylinositol 3-kinase/Akt in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether p70 S6 kinase is involved in TNF-alpha-stimulated IL-6 synthesis in MC3T3-E1 cells. TNF-alpha time dependently induced the phosphorylation of p70 S6 kinase. Rapamycin, an inhibitor of p70 S6 kinase, which attenuated the phosphorylation of p70 S6 kinase induced by TNF-alpha, significantly amplified the TNF-alpha-stimulated IL-6 synthesis. TNF-alpha-induced phosphorylations of both p44/p42 MAP kinase and Akt were markedly enhanced by rapamycin. The amplification by rapamycin of TNF-alpha-induced IL-6 synthesis was reduced by PD98059, a specific inhibitor of MEK1/2, or Akt inhibitor. Rapamycin enhanced the IL-6 synthesis and the phosphorylation of Akt induced by TNF-alpha also in human osteoblasts. Taken together, these results strongly suggest that p70 S6 kinase limits the TNF-alpha-stimulated IL-6 synthesis at a point upstream from p44/p42 MAP kinase and Akt in osteoblast-like cells.

Pharmacological manipulation of the akt signaling pathway regulates myxoma virus replication and tropism in human cancer cells

Viruses have evolved an assortment of mechanisms for regulating the Akt signaling pathway to establish a cellular environment more favorable for viral replication. Myxoma virus (MYXV) is a rabbit-specific poxvirus that encodes many immunomodulatory factors, including an ankyrin repeat-containing host range protein termed M-T5 that functions to regulate tropism of MYXV for rabbit lymphocytes and certain human cancer cells. MYXV permissiveness in these human cancer cells is dependent upon the direct interaction between M-T5 and Akt, which has been shown to induce the kinase activity of Akt. In this study, an array of compounds that selectively manipulate Akt signaling was screened and we show that only a subset of Akt inhibitors significantly decreased the ability of MYXV to replicate in previously permissive human cancer cells. Furthermore, reduced viral replication efficiency was correlated with lower levels of phosphorylated Akt. In contrast, the PP2A-specific phosphatase inhibitor okadaic acid promoted increased Akt kinase activation and rescued MYXV replication in human cancer cells that did not previously support viral replication. Finally, phosphorylation of Akt at residue Thr308 was shown to dictate the physical interaction between Akt and M-T5, which then leads to phosphorylation of Ser473 and permits productive MYXV replication in these human cancer cells. The results of this study further characterize the mechanism by which M-T5 exploits the Akt signaling cascade and affirms this interaction as a major tropism determinant that regulates the replication efficiency of MYXV in human cancer cells.

Receptor interacting protein 3 suppresses vascular smooth muscle cell growth by inhibition of the phosphoinositide 3-kinase-Akt axis

Proliferation of vascular smooth muscle cells (VSMCs) is a primary mechanism underlying cardiovascular proliferative disorders. Phosphoinositide 3-kinase (PI3K)-Akt (or protein kinase B) axis has been assigned at the center of pathways that regulate cell proliferation. Here we demonstrate that enhanced PI3K-Akt signaling by mitogenic stimulation or arterial injury profoundly elevates expression of receptor interacting protein 3 (RIP3) in primary cultured rat VSMCs and in vivo and that the up-regulation of RIP3 leads to VSMC growth arrest and apoptosis via inhibiting the PI3K-Akt signaling pathway, thereby alleviating balloon injury-induced neointimal formation. Specifically, mitogenic stimulation with platelet-derived growth factor-BB or angiotensin II leads to a profound increase in RIP3 expression, which is abolished by inhibition of PI3K or Akt, and increased PI3K-Akt signaling by expression of a constitutively active PI3K mutant also elevates RIP3 expression. Importantly, adenoviral overexpression of RIP3 not only triggers apoptosis but also causes cell cycle arrest at G(1)/G(0) phases that is associated with suppressed Akt activation. In sharp contrast, RIP3 gene silencing enhances serum- and platelet-derived growth factor-induced cell proliferation and Akt activation. In vivo adenoviral gene delivery of rat RIP3 (rRIP3) increased apoptosis and reduced VSMC proliferation, thus, effectively alleviating balloon injury-induced neointimal formation. The growth-suppressive and pro-apoptotic effects are independent of rRIP3 Ser/Thr kinase activity, because overexpression of a kinase-inactive mutant of rRIP3, similar to its wild type, is sufficient to induce growth arrest and apoptosis. These findings reveal a novel growth-suppressive action of RIP3, marking RIP3 as an important factor to prevent excessive mitogenic stimulation- or injury-induced vascular smooth muscle cells hyperplasia.

CCL5 promotes macrophage recruitment and survival in human adipose tissue

OBJECTIVE

To examine the role of adipose-produced chemokine, chemokine ligand (CCL) 5, on the recruitment and survival of macrophages in human white adipose tissue (WAT).

METHODS AND RESULTS

CCL5 levels measured by enzyme immunoassay in serum and by real-time polymerase chain reaction in WAT were higher in obese compared to lean subjects. CCL5, but not CCL2, secretion was higher in visceral compared to subcutaneous WAT. CCL5 mRNA expression was positively correlated with the inflammatory macrophage markers as CD11b, tumor necrosis factor-alpha, and IL-6 in visceral WAT (n=24 obese subjects), and was higher in macrophages than other WAT cells. We found that CCL5 triggered adhesion and transmigration of blood monocytes to/through endothelial cells of human WAT. Whereas in obese WAT apoptotic macrophages were located around necrotic adipocytes, we demonstrated that CCL5, but not CCL2, protected macrophages from free cholesterol-induced apoptosis via activation of the Akt/Erk pathways.

CONCLUSIONS

CCL5 could participate in the inflammation of obese WAT by recruiting blood monocytes and exerting antiapoptotic properties on WAT macrophages. This specific role of CCL5 on macrophage survival with maintenance of their lipid scavenging function should be taken into account for future therapeutic strategies in obesity-related diseases.

Intracellular signal transduction pathways in the regulation of fowl sperm motility: evidence for the involvement of phosphatidylinositol 3-kinase (PI3-K) cascade

The possible role of PI3-K in the reversible temperature-dependent immobilization of fowl sperm motility was investigated by using PI3-K inhibitor (LY294002) and its inactive analogue (LY303511). The existence of the PI3-K in fowl spermatozoa was also confirmed by Western blotting analysis. Fowl sperm motility in TES/NaCl buffer remained negligible at the avian body temperature of 40 degrees C but was maintained vigorously when the temperature was decreased to 30 degrees C. At 30 degrees C, no stimulation or inhibition of motility was observed after the addition of 2 mM CaCl2 and 10 microM LY294002 or LY303511: around 70-80% of spermatozoa remained motile. In contrast, at 40 degrees C, the motility of spermatozoa was activated immediately after the addition of Ca(2+), but the subsequent addition of LY294002 inhibited the motility again. The addition of LY303511 did not appreciably affect the Ca(2+)-supplemented sperm motility, which was maintained for at least 15 min. The ATP concentrations of spermatozoa after the addition of LY294002 + Ca(2+) or LY303511 + Ca(2+) were almost the same values compared with those of Ca(2+) alone at 40 degrees C, suggesting that the addition of LY294002 was not simply affecting membrane damage or inhibiting energy production in the spermatozoa, but may be acting on some part of the motility-regulating cascade. Immunoblotting of sperm extract using an antibody to PI3-K revealed a major cross-reacting protein of 85 kDa, which corresponds to the molecular weight of the subunit of PI3-K. These results suggest that PI3-K may be positively involved in the calcium-regulated maintenance of flagellar movement of fowl spermatozoa at 40 degrees C.

Characteristic response of astrocytes to plasminogen/plasmin to upregulate transforming growth factor beta 3 (TGFbeta3) production/secretion through proteinase-activated receptor-1 (PAR-1) and the downstream phosphatidylinositol 3-kinase (PI3K)-Akt/PKB signaling cascade

The effects of microglia-derived plasminogen (PLGn) on the neurotrophic role of astrocytes were investigated in vitro. The treatment of astrocytes with rat PLGn led to a significant increase in transforming growth factor beta3 (TGFbeta3) in the conditioned medium (CM). This response of astrocytes to PLGn was characteristic and different from that to other stimulators, including lipopolysaccharide, phorbol-12-myristate-13-acetate, interferon-gamma, and ATP. In surveying the signaling molecules that respond to PLGn in astrocytes, we found that Akt/PKB phosphorylation is promoted. The pretreatment of astrocytes with an Akt inhibitor prior to PLGn stimulation resulted in a significant decrease in TGFbeta3 amounts in the CM, suggesting an association of Akt with TGFbeta3 production/secretion. Further survey revealed that phosphatidylinositol 3 kinase (PI3K) is closely associated with TGFbeta3 production/secretion in astrocytes. In fact, PI3K inhibitor clearly depressed the phosphorylation of Akt, indicating that PI3K is localized upstream of Akt. Moreover, the effects of PLGn to increase TGFbeta3 were depressed by pretreatment with a proteinase-activated receptor-1 (PAR-1) inhibitor. Plasmin could mimic the PLGn effects to upregulate TGFbeta3, and the plasmin effects were suppressed by pretreatment with the PAR-1 inhibitor, suggesting the association of PLGn/plasmin effects with PAR-1. In addition, Akt phosphorylation caused by plasmin was inhibited in the presence of PAR-1 inhibitor. We have therefore demonstrated that PLGn/plasmin, probably plasmin, facilitates the production/secretion of TGFbeta3 in astrocytes through both PAR-1 and the subsequent signaling cascade including PI3K and Akt.

Role of phosphoinositide 3-kinase beta in glycoprotein VI-mediated Akt activation in platelets

Glycoprotein (GP) VI is a critical platelet collagen receptor. Phosphoinositide 3-kinase (PI3K) plays an important role in GPVI-mediated platelet activation, yet the major PI3K isoforms involved in this process have not been identified. In addition, stimulation of GPVI results in the activation of Akt, a downstream effector of PI3K. Thus, we investigated the contribution of PI3K isoforms to GPVI-mediated platelet activation and Akt activation. A protein kinase C inhibitor GF 109203X or a P2Y(12) receptor antagonist AR-C69931MX partly reduced GPVI-induced Akt phosphorylation. Platelets from mice dosed with clopidogrel also showed partial Akt phosphorylation, indicating that GPVI-mediated Akt phosphorylation is regulated by both secretion-dependent and -independent pathways. In addition, GPVI-induced Akt phosphorylation in the presence of ADP antagonists was completely inhibited by PI3K inhibitor LY294002 and PI3Kbeta inhibitor TGX-221 indicating an essential role of PI3Kbeta in Akt activation directly downstream of GPVI. Moreover, GPVI-mediated platelet aggregation, secretion, and intracellular Ca(2+) mobilization were significantly inhibited by TGX-221, and less strongly inhibited by PI3Kalpha inhibitor PIK75, but were not affected by PI3Kgamma inhibitor AS252424 and PI3Kdelta inhibitor IC87114. Consistently, GPVI-induced integrin alpha(IIb)beta(3) activation of PI3Kgamma(-/-) and PI3Kdelta(-/-) platelets also showed no significant difference compared with wild-type platelets. These results demonstrate that GPVI-induced Akt activation in platelets is dependent in part on G(i) stimulation through P2Y(12) receptor activation by secreted ADP. In addition, a significant portion of GPVI-dependent, ADP-independent Akt activation also exists, and PI3Kbeta plays an essential role in GPVI-mediated platelet aggregation and Akt activation.

Probing Akt-inhibitor interaction by chemical cross-linking and mass spectrometry

The serine/threonine kinase Akt is a critical enzyme that regulates cell survival. As high Akt activity has been shown to contribute to the pathogenesis of various human malignancies, inhibition of Akt activation is a promising therapeutic strategy for cancers. We have previously demonstrated that changes in Akt interdomain arrangements from a closed to open conformation occur upon Akt-membrane interaction, which in turn allows Akt phosphorylation/activation. In the present study, we demonstrate a novel strategy to discern mechanisms for Akt inhibition based on Akt conformational changes using chemical cross-linking and (18)O labeling mass spectrometry. By quantitative comparison of two interdomain cross-linked peptides, which represent the proximity of the domains involved, we found that the binding of Akt to an inhibitor (PI analog) caused the open interdomain conformation where the PH and regulatory domains moved away from the kinase domain, even before interacting with membranes, subsequently preventing translocation of Akt to the plasma membrane. In contrast, the interdomain conformation remained unchanged after incubating with another type of inhibitor (peptide TCL1). Subsequent interaction with unilamellar vesicles suggested that TCL1 impaired particularly the opening of the PH domain for exposing T308 for phosphorylation at the plasma membrane. This novel approach based on the conformation-based molecular interaction mechanism should be potentially useful for drug discovery efforts for specific Akt inhibitors or anti-tumor agents.

Phosphoinositide 3-kinase inhibitor (wortmannin) inhibits pancreatic cancer cell motility and migration induced by hyaluronan in vitro and peritoneal metastasis in vivo

In order to block peritoneal metastasis of pancreatic cancer cells, we have attempted to block the signal transduction pathway involving hyaluronan (HA), Src, phosphoinositide 3-kinase (PI3K) and Akt. We examined the effects of Src, PI3K and Akt inhibitors on pancreatic cancer cell motility, invasion and metastasis. The pancreatic cancer cell line SW1990, known to cause peritoneal metastasis efficiently in nude mice, was used in this study. SW1990 cells were stimulated by HA to induce Akt phosphorylation. Then, the inhibitory effects of PI3K and Src kinase inhibitors were examined. Cell motility and cell migration assays were adopted to assess the cancer cell motility and its migration capability. We also examined the therapeutic efficacies of PI3K inhibitor wortmannin on peritoneal metastasis of SW1990 cells in the nude mouse model. Stimulation of SW1990 cells by HA markedly induced the Src-PI3K-Akt signaling, thus enhancing cancer cell motility and its migration. Significantly, we found that wortmannin could exert marked inhibition of the peritoneal metastasis of SW1990 in nude mice in vivo. These findings indicate that the PI3K-Akt signaling pathway plays an essential role in peritoneal metastasis and PI3K inhibitors such as wortmannin can be novel modalities to prevent peritoneal metastasis of invasive cancers such as pancreatic cancer.

Pretreatment with insulin before ischaemia reduces infarct size in Langendorff-perfused rat hearts

AIM

To compare the possible role of Akt and mammalian target of rapamycin (mTOR) in mediating cardioprotection against ischaemia under three different conditions: (1) During ischaemic preconditioning (IPC), (2) when insulin was given as a pretreatment agent (InsPC) and (3) when insulin was given as a reperfusion cell survival agent (Ins(R)).

METHODS

Isolated perfused rat hearts were subjected to IPC (3 x 5 min) or InsPC (50 mU mL(-1); 3 x 5 min), before 30 min of regional ischaemia followed by 120 min of reperfusion +/- 1L-6-hydroxymethyl-chiro-inositol-2-[(R)-2-O-methyl-3-O-octadecylcarbonate] (HIMO) (20 microm; Akt inhibitor) or rapamycin (1 nm; mTOR inhibitor). In addition, insulin (3 mU mL(-1)) was given at the onset of reperfusion, +/- HIMO or rapamycin. Risk zone (R) and infarct size (I) were determined with Evans blue and tetrazolium staining respectively. Western blot analysis was performed on tissue from Langendorff-perfused rat hearts and cell lysates from cultured HL1 cells.

RESULTS

IPC, InsPC and InsR treatment resulted in a significant reduction in infarct size compared to controls (all P < 0.05). This protective effect of IPC and insulin was abolished by the inhibitors. However, the putative Akt inhibitor, although capable of abolishing cardioprotection induced by insulin, was not able to inhibit insulin-induced phosphorylation of Akt in Langendorff-perfused rat hearts and cultured HL1 cells. The target for this compound therefore remains to be determined.

CONCLUSION

IPC and insulin (either as InsPC or Ins(R)) appear to activate mTOR, and this kinase seems to play an essential role in cardioprotection against ischaemia and reperfusion injury as rapamycin blocked the protection.

Mycobacterium bovis Bacillus Calmette-Guérin (BCG)-induced activation of PI3K/Akt and NF-kB signaling pathways regulates expression of CXCL10 in epithelial cells

CXCL10 production is a critical step in limiting mycobacterial infection. Although induction of this chemokine by mycobacteria in epithelial cells has been reported, it is still unclear how CXCL10 is regulated in Mycobacterium bovis BCG-infected epithelial cells. In this study, we demonstrate that phosphatidylinoditol 3-kinase (PI3K)/Akt and the nuclear factor kB (NF-kB) signaling pathways play an important role in CXCL10 expression at the protein and mRNA level in A549 cells. We demonstrate that treatment of A549 cells with LY294002 and wortmannin, two PI3K inhibitors, inhibited M. bovis BCG-induced CXCL10 expression. In addition, treatment of A549 cells with an Akt inhibitor significantly blocked M. bovis BCG-induced CXCL10 production. Moreover, our data show that treatment of epithelial cells with CAPE, BAY 11-7082, and PDTC three selective inhibitors of NF-kB, significantly reduced the effect of M. bovis BCG on induced CXCL10 mRNA expression (74%, 69% and 83% inhibition by 8microM CAPE, 10microM BAY 11-7082 and 3microM PDTC as assessed by real-time PCR, respectively). In accordance with the gene induction, the production of CXCL10 was also significantly reduced by these inhibitors. Finally, the inhibition of PI3K affect NF-kB activation in M. bovis BCG-infected cells, indicating that PI3K activity is required for the M. bovis BCG-induced activation of NF-kB. The functional association between PI3K/Akt and NF-kB demonstrates another mechanism in the regulation of M. bovis BCG-induced CXCL10 in A549 cells.