The PI3K-PDK1 connection: more than just a road to PKB. Biochem J. 2000;346 Pt 3:561-576. [PMID: 10698680 DOI: 10.1042/0264-6021:3460561]

Effects of Cyanobacterial Harmful Algal Bloom Toxin Microcystin-LR on Gonadotropin-Dependent Ovarian Follicle Maturation and Ovulation in Mice

BACKGROUND

Cyanobacterial harmful algal blooms (CyanoHABs) originate from the excessive growth or bloom of cyanobacteria often referred to as blue-green algae. They have been on the rise globally in both marine and freshwaters in recently years with increasing frequency and severity owing to the rising temperature associated with climate change and increasing anthropogenic eutrophication from agricultural runoff and urbanization. Humans are at a great risk of exposure to toxins released from CyanoHABs through drinking water, food, and recreational activities, making CyanoHAB toxins a new class of contaminants of emerging concern.

OBJECTIVES

We investigated the toxic effects and mechanisms of microcystin-LR (MC-LR), the most prevalent CyanoHAB toxin, on the ovary and associated reproductive functions.

METHODS

Mouse models with either chronic daily oral or acute intraperitoneal exposure, an engineered three-dimensional ovarian follicle culture system, and human primary ovarian granulosa cells were tested with MC-LR of various dose levels. Single-follicle RNA sequencing, reverse transcription-quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, western blotting, immunohistochemistry (IHC), and benchmark dose modeling were used to examine the effects of MC-LR on follicle maturation, hormone secretion, ovulation, and luteinization.

RESULTS

Mice exposed long term to low-dose MC-LR did not exhibit any differences in the kinetics of folliculogenesis, but they had significantly fewer corpora lutea compared with control mice. Superovulation models further showed that mice exposed to MC-LR during the follicle maturation window had significantly fewer ovulated oocytes. IHC results revealed ovarian distribution of MC-LR, and mice exposed to MC-LR had significantly lower expression of key follicle maturation mediators. Mechanistically, in both murine and human granulosa cells exposed to MC-LR, there was reduced protein phosphatase 1 (PP1) activity, disrupted PP1-mediated PI3K/AKT/FOXO1 signaling, and less expression of follicle maturation-related genes.

DISCUSSION

Using both in vivo and in vitro murine and human model systems, we provide data suggesting that environmentally relevant exposure to the CyanoHAB toxin MC-LR interfered with gonadotropin-dependent follicle maturation and ovulation. We conclude that MC-LR may pose a nonnegligible risk to women's reproductive health by heightening the probability of irregular menstrual cycles and infertility related to ovulatory disorders. https://doi.org/10.1289/EHP12034.

Pten associates with important gene regulatory network to fine-tune Müller glia-mediated zebrafish retina regeneration

Unlike mammals, zebrafish possess a remarkable ability to regenerate damaged retina after an acute injury. Retina regeneration in zebrafish involves the induction of Müller glia-derived progenitor cells (MGPCs) exhibiting stem cell-like characteristics, which are capable of restoring all retinal cell-types. The induction of MGPC through Müller glia-reprograming involves several cellular, genetic and biochemical events soon after a retinal injury. Despite the knowledge on the importance of Phosphatase and tensin homolog (Pten), which is a dual-specificity phosphatase and tumor suppressor in the maintaining of cellular homeostasis, its importance during retina regeneration remains unknown. Here, we explored the importance of Pten during zebrafish retina regeneration. The Pten gets downregulated upon retinal injury and is absent from the MGPCs, which is essential to trigger Akt-mediated cellular proliferation essential for retina regeneration. We found that the downregulation of Pten in the post-injury retina accelerates MGPCs formation, while its overexpression restricts the regenerative response. We observed that Pten regulates the proliferation of MGPCs not only through Akt pathway but also by Mmp9/Notch signaling. Mmp9-activity is essential to induce the proliferation of MGPCs in the absence of Pten. Lastly, we show that expression of Pten is fine-tuned through Mycb/histone deacetylase1 and Tgf-β signaling. The present study emphasizes on the stringent regulation of Pten and its crucial involvement during the zebrafish retina regeneration.

Putative Roles of SETBP1 Dosage on the SET Oncogene to Affect Brain Development

Mutations in SET BINDING PROTEIN 1 (SETBP1) cause two different clinically distinguishable diseases called Schinzel–Giedion syndrome (SGS) or SETBP1 deficiency syndrome (SDD). Both disorders are disorders of protein dosage, where SGS is caused by decreased rate of protein breakdown due to mutations in a proteosome targeting domain, and SDD is caused by heterozygous loss-of-function mutations leading to haploinsufficiency. While phenotypes of affected individuals support a role for SETBP1 in brain development, little is known about the mechanisms that might underlie this. The binding partner which gave SETBP1 its name is SET and there is extensive literature on this important oncogene in non-neural tissues. Here we describe different molecular complexes in which SET is involved as well as the role of these complexes in brain development. Based on this information, we postulate how SETBP1 protein dosage might influence these SET-containing molecular pathways and affect brain development. We examine the roles of SET and SETBP1 in acetylation inhibition, phosphatase activity, DNA repair, and cell cycle control. This work provides testable hypotheses for how altered SETBP1 protein dosage affects brain development.

Covalent Allosteric Inhibitors of Akt Generated Using a Click Fragment Approach

Akt is a protein kinase that has been implicated in the progression of cancerous tumours. A number of covalent allosteric Akt inhibitors are known, and based on these scaffolds, a small library of novel potential covalent allosteric imidazopyridine-based inhibitors was designed. The envisaged compounds were synthesised, with click chemistry enabling a modular approach to a number of the target compounds. The binding modes, potencies and antiproliferative activities of these synthesised compounds were explored, thereby furthering the structure activity relationship knowledge of this class of Akt inhibitors. Three novel covalent inhibitors were identified, exhibiting moderate activity against Akt1 and various cancer cell lines, potentially paving the way for future covalent allosteric inhibitors with improved properties.

Role of PI3K/Akt/mTOR pathway in mediating endocrine resistance: concept to clinic

The majority of breast cancers express the estrogen receptor (ER) and for this group of patients, endocrine therapy is the cornerstone of systemic treatment. However, drug resistance is common and a focus for breast cancer preclinical and clinical research. Over the past 2 decades, the PI3K/Akt/mTOR axis has emerged as an important driver of treatment failure, and inhibitors of mTOR and PI3K are now licensed for the treatment of women with advanced ER-positive breast cancer who have relapsed on first-line hormonal therapy. This review presents the preclinical and clinical data that led to this new treatment paradigm and discusses future directions.

Revealing Calcium Signaling Pathway as Novel Mechanism of Danhong Injection for Treating Acute Myocardial Infarction by Systems Pharmacology and Experiment Validation

Introduction: Danhong injection (DHI) is a traditional Chinese medicine preparation commonly used in the clinical treatment of acute myocardial infarction (AMI). In this study, the active components of DHI and its mechanism in the treatment of AMI were investigated.

Methods: The chemical components of DHI were detected by the ultra-high-performance liquid chromatography-linear trap quadrupole-orbitrap-tandem mass spectrometry (UHPLC-LTQ-Orbitrap-MS/MS), and the targets and pathways of DHI in the treatment of AMI were analyzed by systems pharmacology, which was verified by molecular docking and animal experiments.

Results: A total of 12 active components of DHI were obtained, and 158 common targets of component and disease were identified by systems pharmacology. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results showed that DHI is closely related to the calcium signaling pathway in the treatment of AMI. Molecular docking showed that the key target protein has good binding affinity to related compounds. The experimental results showed that compared with the model group, LVAWs, EF, and FS significantly (p < 0.05) increased in the DHI group. The percentage of myocardial infarction significantly (p < 0.01) decreased, both in the ventricular and total cardiac regions, and the pathological damage of myocardial tissue also decreased. In addition, the expression of the protein CaMK II decreased (p < 0.01) and the expression of SERCA significantly increased (p < 0.01).

Conclusion: This study revealed that ferulic acid, caffeic acid and rosmarinic acid could inhibit AMI by regulating PLB, CaMK II, SERCA, etc. And mechanistically, calcium signaling pathway was critically involved. Combination of systems pharmacology prediction with experimental validation may provide a scientific basis for in-depth clinical investigation of the material basis of DHI.

Lipid raft involvement in signal transduction in cancer cell survival, cell death and metastasis

Lipid rafts are cholesterol‐ and sphingolipid‐enriched specialized membrane domains within the plasma membrane. Lipid rafts regulate the density and activity of signal receptors by compartmentalizing them, promoting signalling cascades that play important roles in the survival, death and metastasis of cancer cells. In this review, we emphasize the current concept initially postulated by F. Mollinedo and C. Gajate on the importance of lipid rafts in cancer survival, death and metastasis by describing representative signalling pathways, including the IGF system and the PI3K/AKT, Fas/CD95, VEGF/VEGFR2 and CD44 signalling pathways, and we also discuss the concept of CASMER (cluster of apoptotic signalling molecule‐enriched rafts), coined, originally introduced and further advanced by F. Mollinedo and C. Gajate in the period 2005–2010. Then, we summarize relevant research progress and suggest that lipid rafts play important roles in the survival, death and metastasis of cancer cells, making them promising targets for cancer therapy.

mTOR-dependent immunometabolism as Achilles' heel of anticancer therapy

Immune cells are important constituents of the tumor microenvironment and essential in eradicating tumor cells during conventional therapies or novel immunotherapies. The mechanistic target of rapamycin (mTOR) signaling pathway senses the intra- and extracellular nutrient status, growth factor supply, and cell stress-related changes to coordinate cellular metabolism and activation dictating effector and memory functions in mainly all hematopoietic immune cells. In addition, the mTOR complex 1 (mTORC1) and mTORC2 are frequently deregulated and become activated in cancer cells to drive cell transformation, survival, neovascularization, and invasion. In this review, we provide an overview of the influence of mTOR complexes on immune and cancer cell function and metabolism. We discuss how mTOR inhibitors aiming to target cancer cells will influence immunometabolic cell functions participating either in antitumor responses or favoring tumor cell progression in individual immune cells. We suggest immunometabolism as the weak spot of anticancer therapy and propose to evaluate patients according to their predominant immune cell subtype in the cancer tissue. Advances in metabolic drug development that hold promise for more effective treatments in different types of cancer will have to consider their effects on the immune system.

Conditional knockout of the PDK-1 gene in osteoblasts affects osteoblast differentiation and bone formation

Osteoblasts are the main functional cells of bone formation, and they are responsible for the synthesis, secretion, and mineralization of the bone matrix. Phosphatidylinositol-3-kinase/Akt is an important signaling pathway involved in the regulation of cell proliferation, death, and survival. Some studies have shown that 3-phosphoinositide-dependent protein kinase-1 (PDK-1) plays an important role in the phosphorylation of Akt. In the present study, an osteocalcin (OCN) promoter-driven Cre-LoxP system was established to specifically delete the PDK-1 gene in osteoblasts. It was found that the size and weight of PDK-1 conditional gene knockout (cKO) mice were significantly reduced. von Kossa staining and microcomputed tomography showed that the trabecular thickness, trabecular number, and bone volume were significantly decreased, whereas trabecular separation was increased, as compared with wide-type littermates, which were characterized by a decreased bone mass. A model of distal femoral defect was established, and it was found that cKO mice delayed bone defect repair. In osteoblasts derived from PDK-1 cKO mice, the alkaline phosphatase (ALP) secretion and ability of calcium mineralization were significantly decreased, and the expressions of osteoblast-related proteins, runt-related transcription factor 2, OCN, and ALP were also clearly decreased. Moreover, the phosphorylation level of Akt and downstream factor GSK3β and their response to insulin-like growth factor-1 (IGF-1) decreased clearly. Therefore, we believe that PDK-1 plays a very important role in osteoblast differentiation and bone formation by regulating the PDK-1/Akt/GSK3β signaling pathway.

IGF family effects on development, stability, and treatment of hematological malignancies

Multiple factors, including growth factors, are shown to be culprits of cancer outset and persistence. Among growth factors, insulin-like growth factors (IGFs) family are of more importance in the prognosis of blood malignancies. After binding to their corresponding receptor, IGFs initiate PI3K/AKT signaling pathway and increase the translation of intracellular proteins, such as cell division-related proteins. They also stimulate the transcription of cell division-related genes using the Ras-GTP pathway. In addition to organs such as the liver, IGFs are secreted by tumor cells and can cause growth and proliferation of self or tumor cells via autocrine and paracrine methods. Current studies indicate that decreasing the effects of IGF by blocking them, their receptors, or PI3K/AKT pathway using various drugs could help to suppress the division of tumor cells. Here, we delineate the role of the IGF family in hematologic malignancies and their potential mechanisms.

The PI3K pathway induced by αMSH exerts a negative feedback on melanogenesis and contributes to the release of pigment

The melanocortin-1 receptor (MC1R) belongs to the family of the G protein-coupled receptor (GPCR). Activated GPCRs can promote the phosphoinositide 3-kinase (PI3K) pathway. Few studies deal with the role of the PI3K pathway activation in response to αMSH. On B16-F10 cell line, we investigated the αMSH-dependent modulation of pAKT/AKT, as a key element of the PI3K pathway after rapid and prolonged stimulation. We demonstrated that αMSH triggers a rapid modulation of AKT which culminates in an increase in its phosphorylation. We highlighted a comparable upregulation of pAKT after exposure to αMSH on primary cultures of normal human melanocytes (NHMs) expressing a wild-type MC1R. On B16-F10 cells, NHMs, and an ex vivo model of human skin biopsies, we explored the influence of PI3K/AKT signaling triggered by αMSH, focusing on the control of melanogenesis and pigment release. We showed that the αMSH-dependent PI3K/AKT pathway exerts a negative feedback on melanogenesis and promotes the extracellular release of pigment. We strengthened the role of the PI3K/AKT pathway triggered by αMSH in preserving redox equilibrium and genome integrity, highlighting its role in affecting cell survival.

Targeting Mouse Double Minute 2: Current Concepts in DNA Damage Repair and Therapeutic Approaches in Cancer

Defects in DNA damage repair may cause genome instability and cancer development. The tumor suppressor gene p53 regulates cell cycle arrest to allow time for DNA repair. The oncoprotein mouse double minute 2 (MDM2) promotes cell survival, proliferation, invasion, and therapeutic resistance in many types of cancer. The major role of MDM2 is to inhibit p53 activity and promote its degradation. In this review, we describe the influence of MDM2 on genomic instability, the role of MDM2 on releasing p53 and binding DNA repair proteins to inhibit repair, and the regulation network of MDM2 including its transcriptional modifications, protein stability, and localization following DNA damage in genome integrity maintenance and in MDM2-p53 axis control. We also discuss p53-dependent and p53 independent oncogenic function of MDM2 and the outcomes of clinical trials that have been used with clinical inhibitors targeting p53-MDM2 to treat certain cancers.

Design, synthesis, and biological evaluation of novel 3-(thiophen-2-ylthio)pyridine derivatives as potential multitarget anticancer agents

A series of novel 3-(thiophen-2-ylthio)pyridine derivatives as insulin-like growth factor 1 receptor (IGF-1R) inhibitors was designed and synthesized. IGF-1R kinase inhibitory activities and cytotoxicities against HepG2 and WSU-DLCL2 cell lines were tested. For all of these compounds, potent cancer cell proliferation inhibitory activities were observed, but not through the inhibition of IGR-1R. Selected compounds were further screened against various kinases. Typical compound 22 (50% inhibitory concentration [IC₅₀ ] values, HepG2: 2.98 ± 1.11 μM and WSU-DLCL2: 4.34 ± 0.84 μM) exhibited good inhibitory activities against fibroblast growth factor receptor-2 (FGFR2), FGFR3, epidermal growth factor receptor, Janus kinase, and RON (receptor originated from Nantes), with IC₅₀ values ranging from 2.14 to 12.20 μM. Additionally, the cell-cycle analysis showed that compound 22 could arrest HepG2 cells in the G1/G0 phase. Taken together, all the experiments confirmed that the compounds in this series were multitarget anticancer agents worth further optimizing.

Regulation of TORC2 function and localization by Rab5 GTPases in Saccharomyces cerevisiae

The evolutionarily conserved Target of Rapamycin (TOR) complex-2 (TORC2) is an essential regulator of plasma membrane homeostasis in budding yeast (Saccharomyces cerevisiae). In this yeast, TORC2 phosphorylates and activates the effector protein kinase Ypk1 and its paralog Ypk2. These protein kinases, in turn, carry out all the crucial functions of TORC2 by phosphorylating and thereby controlling the activity of at least a dozen downstream substrates. A previously uncharacterized interplay between the Rab5 GTPases and TORC2 signaling was uncovered through analysis of a newly suspected Ypk1 target. Muk1, one of two guanine nucleotide exchange factors for the Rab5 GTPases, was found to be a physiologically relevant Ypk1 substrate; and, genetic analysis indicates that Ypk1-mediated phosphorylation activates the guanine nucleotide exchange activity of Muk1. Second, it was demonstrated both in vivo and in vitro that the GTP-bound state of the Rab5 GTPase Vps21/Ypt51 physically associates with TORC2 and acts as a direct positive effector required for full TORC2 activity. These interrelationships provide a self-reinforcing control circuit for sustained up-regulation of TORC2-Ypk1 signaling. In this overview, we summarize the experimental basis of these findings, their implications, and speculate as to the molecular basis for Rab5-mediated TORC2 activation.

Mutational Analysis of Oncogenic AKT1 Gene Associated with Breast Cancer Risk in the High Altitude Ecuadorian Mestizo Population

Breast cancer is the leading cause of cancer-related death among women worldwide. AKT1 encodes the kinase B alpha protein. The rs121434592, rs12881616, rs11555432, rs11555431, rs2494732, and rs3803304 single nucleotide polymorphisms have been identified in the AKT1 kinase gene. Activated AKT1 phosphorylates downstream substrates regulating cell growth, metabolism, apoptosis, angiogenesis, and drug responses. It is essential to know how breast cancer risk is associated with histopathological and immunohistochemical characteristics and genotype polymorphisms in a high altitude Ecuadorian mestizo population. This is a retrospective case-control study. DNA was extracted from 185 healthy and 91 affected women who live 2,800 meters above sea level. Genotypes were determined by genomic sequencing. We found a possible association between the noncoding intronic variant rs3803304 and breast cancer risk development: GG (odds ratio [OR] = 5.2; 95% confidence interval [CI] = 1.3-20.9; P ≤ 0.05; Q > 0.05). Regarding pathologic characteristics, we found significant risk between estrogen receptor, progesterone receptor, and HER2 status and molecular subtypes (P ≤ 0.001; Q ≤ 0.05). On the other hand, we did not find risk between variants and histopathological characteristics. Despite the small sample size, we found that the intronic variant, AKT1 rs3803304, may act as a predictive biomarker in the risk of developing breast cancer in the high altitude Ecuadorian mestizo population.

A triangular connection between Cyclin G, PP2A and Akt1 in the regulation of growth and metabolism in Drosophila

Size and weight control is a tightly regulated process, involving the highly conserved Insulin receptor/target of rapamycin (InR/TOR) signaling cascade. We recently identified Cyclin G (CycG) as an important modulator of InR/TOR signaling activity in Drosophila. cycG mutant flies are underweight and show a disturbed fat metabolism resembling TOR mutants. In fact, InR/TOR signaling activity is disturbed in cycG mutants at the level of Akt1, the central kinase linking InR and TORC1. Akt1 is negatively regulated by protein phosphatase PP2A. Notably the binding of the PP2A B′-regulatory subunit Widerborst (Wdb) to Akt1 is differentially regulated in cycG mutants, presumably by a direct interaction of CycG and Wdb. Since the metabolic defects of cycG mutant animals are abrogated by a concomitant loss of Wdb, CycG presumably influences Akt1 activity at the PP2A nexus. Here we show that Well rounded (Wrd), another B' subunit of PP2A in Drosophila, binds CycG similar to Wdb, and that its loss ameliorates some, but not all, of the metabolic defects of cycG mutants. We propose a model, whereby the binding of CycG to a particular B′-regulatory subunit influences the tissue specific activity of PP2A, required for the fine tuning of the InR/TOR signaling cascade in Drosophila.

Neuritic complexity of hippocampal neurons depends on WIP-mediated mTORC1 and Abl family kinases activities

INTRODUCTION

Neuronal morphogenesis is governed mainly by two interconnected processes, cytoskeletal reorganization, and signal transduction. The actin-binding molecule WIP (Wiskott-Aldrich syndrome protein [WASP]-interacting protein) was identified as a negative regulator of neuritogenesis. Although WIP controls activity of the actin-nucleation-promoting factor neural WASP (N-WASP) during neuritic differentiation, its implication in signal transduction remains unknown.

METHODS

Using primary neurons from WIP-deficient and wild-type mice we did an immunofluorescence, morphometric, and biochemical analysis of the signaling modified by WIP deficiency.

RESULTS

Here, we describe the WIP contribution to the regulation of neuritic elaboration and ramification through modification in phosphorylation levels of several kinases that participate in the mammalian target of rapamycin complex 1 (mTORC1)-p70S6K (phosphoprotein 70 ribosomal protein S6 kinase, S6K) intracellular signaling pathway. WIP deficiency induces an increase in the number of neuritic bifurcations and filopodial protrusions in primary embryonic neurons. This phenotype is not due to modifications in the activity of the phosphoinositide 3 kinase (PI3K)-Akt pathway, but to reduced phosphorylation of the S6K residues Ser(411) and Thr(389). The resulting decrease in kinase activity leads to reduced S6 phosphorylation in the absence of WIP. Incubation of control neurons with pharmacological inhibitors of mTORC1 or Abl, two S6K regulators, conferred a morphology resembling that of WIP-deficient neurons. Moreover, the preferential co-distribution of phospho-S6K with polymerized actin is altered in WIP-deficient neurons.

CONCLUSION

These experiments identify WIP as a member of a signaling cascade comprised of Abl family kinases, mTORC1 and S6K, which regulates neuron development and specifically, neuritic branching and complexity. Thus, we postulated a new role for WIP protein.

The Neuroprotective Role of Insulin Against MPP(+) -Induced Parkinson's Disease in Differentiated SH-SY5Y Cells

Parkinson's disease (PD) is a common chronic neurodegenerative disorder associated with aging that primarily caused by the death of dopaminergic neurons in the substantia nigra pars compacta (SN). Retinoic acid (RA)-differentiated human neuroblastoma SH-SY5Y cells (SH-SY5Y+RA) have been broadly utilized in studies of mechanisms of the pathogenesis underlying 1-Methyl-4-phenyl pyridinium (MPP(+))-induced PD models. Here, we investigated the neuroprotective mechanisms of insulin on MPP(+)-induced neurotoxicity on SH-SY5Y+RA cells. Recent studies suggest that insulin has a protective effect against oxidative stress but not been elucidated for PD. In this study, pretreatment of insulin prevented the cell death in a dose dependent manner and lowered nitric oxide (NO) release, reactive oxygen species (ROS), and calcium ion (Ca(2+)) influx induced by MPP(+). Insulin also elevated tyrosine hydroxylase (TH) and insulin signaling pathways in dopaminergic neuron through activating PI3K/Akt/GSK-3 survival pathways which in turn inhibits MPP(+)-induced iNOS and ERK activation, and Bax to Bcl-2 ratio. These results suggest that insulin has a protective effect on MPP(+)-neurotoxicity in SH-SY5Y+RA cells.

De novo resistance biomarkers to anti-HER2 therapies in HER2-positive breast cancer

Therapies targeting HER2 receptor, overexpressed in 20% breast cancer (BC), improved prognosis, however ~62% patients experiment progression during the first year. Molecular mechanisms proposed to be responsible for this de novo resistance include HER2 modifications, defects in the antibody dependent cellular cytotoxicity or in cell arrest and apoptosis or alterations in HER2 signaling components. This article will review the influence of genetic markers investigated to date as cause of de novo resistance to HER2-targeted drugs in HER2-positive BC patients. Biomarkers like p95HER2, CCND1 and CDC25A have demonstrated clinical relevance and prognostic value in HER2-positive BC patients. However, the prognostic value of most biomarkers investigated to date, such as PIK3CA or AKT1, cannot be fully established yet.

Vitamin B₂ Sensitizes Cancer Cells to Vitamin-C-Induced Cell Death via Modulation of Akt and Bad Phosphorylation

Vitamin C is an essential dietary nutrient that has a variety of biological functions. Recent studies have provided promising evidence for its additional health benefits, including anticancer activity. Vitamin B2, another essential dietary nutrient, often coexists with vitamin C in some fruits, vegetables, or dietary supplements. The objective of the present study is to determine whether the combination of vitamin C and B2 can achieve a synergistic anticancer activity. MDA-MB-231, MCF-7, and A549 cells were employed to evaluate the combinatory effects of vitamin C and B2. We found that the combination of vitamin C and B2 resulted in a synergistic cell death induction in all cell lines tested. Further mechanistic investigations revealed that vitamin B2 sensitized cancer cells to vitamin C through inhibition of Akt and Bad phosphorylation. Our findings identified vitamin B2 as a promising sensitizer for improving the efficacy of vitamin-C-based cancer chemoprevention and chemotherapy.

Daucosterol protects neurons against oxygen-glucose deprivation/reperfusion-mediated injury by activating IGF1 signaling pathway

We previously reported that daucosterol (a sterolin) up-regulates the expression of insulin-like growth factor I (IGF1)(1) protein in neural stem cells. In this study, we investigated the effects of daucosterol on the survival of cultured cortical neurons after neurons were subjected to oxygen and glucose deprivation and simulated reperfusion (OGD/R)(2), and determined the corresponding molecular mechanism. The results showed that post-treatment of daucosterol significantly reduced neuronal loss, as well as apoptotic rate and caspase-3 activity, displaying the neuroprotective activity. We also found that daucosterol increased the expression level of IGF1 protein, diminished the down-regulation of p-AKT(3) and p-GSK-3β(4), thus activating the AKT(5) signal pathway. Additionally, it diminished the down-regulation of the anti-apoptotic proteins Mcl-1(6) and Bcl-2(7), and decreased the expression level of the pro-apoptotic protein Bax(8), thus raising the ratio of Bcl-2/Bax. The neuroprotective effect of daucosterol was inhibited in the presence of picropodophyllin (PPP)(9), the inhibitor of insulin-like growth factor I receptors (IGF1R)(10). Our study provided information about daucosterol as an efficient and inexpensive neuroprotectants, to which the IGF1-like activity of daucosterol contributes. Daucosterol could be potentially developed as a medicine for ischemic stroke treatment.

Layered double hydroxide nanoparticles promote self-renewal of mouse embryonic stem cells through the PI3K signaling pathway

Embryonic stem cells (ESCs) hold great potential for regenerative medicine due to their two unique characteristics: self-renewal and pluripotency. Several groups of nanoparticles have shown promising applications in directing the stem cell fate. Herein, we investigated the cellular effects of layered double hydroxide nanoparticles (LDH NPs) on mouse ESCs (mESCs) and the associated molecular mechanisms. Mg-Al-LDH NPs with an average diameter of ∼100 nm were prepared by hydrothermal methods. To determine the influences of LDH NPs on mESCs, cellular cytotoxicity, self-renewal, differentiation potential, and the possible signaling pathways were explored. Evaluation of cell viability, lactate dehydrogenase release, ROS generation and apoptosis demonstrated the low cytotoxicity of LDH NPs. The alkaline phosphatase activity and the expression of pluripotency genes in mESCs were examined, which indicated that exposure to LDH NPs could support self-renewal and inhibit spontaneous differentiation of mESCs under feeder-free culture conditions. The self-renewal promotion was further proved to be independent of the leukemia inhibitory factor (LIF). Furthermore, cells treated with LDH NPs maintained the potential to differentiate into all three germ layers both in vitro and in vivo through formation of embryoid bodies and teratomas. In addition, we observed that LDH NPs initiated the activation of the PI3K/Akt pathway, while treatment with the PI3K inhibitor LY294002 could block the effects of LDH NPs on mESCs. The results confirmed that the promotion of self-renewal by LDH NPs was associated with activation of the PI3K/Akt signaling pathway. Altogether, our studies identified a new role of LDH NPs in maintaining self-renewal of mouse ES cells which could potentially be applied in stem cell research.

Computational identification of significant missense mutations in AKT1 gene

The AKT1 gene is of supreme importance in cell signaling and human cancer. In the present study, we aim to understand the phenotype variations that were believed to have the highest impact in AKT1 gene by different computational approaches. The analysis was initiated with SIFT tool followed by PolyPhen 2.0, I-Mutant 2.0, and SNPs&GO tools with the aid of 22 nonsynonymous (nsSNPs) retrieved from dbSNP. A total of five AKT1 variants such as E17K, E17S, E319G, L357P, and P388T are found to exert deleterious effects on the protein structure and function. Furthermore, the molecular docking study indicates the lesser binding affinity of inhibitor with the mutant structure than the native type. In addition, root mean square deviation and hydrogen bond details were also analyzed in the 10 ns molecular dynamics simulation study. These computational evidences suggested that E17K, E17S, E319G, L357P, and P388T variants of AKT1 could destabilize the protein networks, thus causing functional deviations of protein to some extent. Moreover, the findings strongly indicate that screening for AKT1, E17K, E17S, E319G, L357P, and P388T variants may be useful for disease molecular diagnosis and also to design the potential AKT inhibitors.

Association between AKT1 Gene Polymorphism rs2498794 and Smoking-Related Traits with reference to Cancer Susceptibility

To clarify the potential role of variability within and around the AKT1 gene in smoking behaviors, we performed a single-nucleotide polymorphism (SNP) analysis of the AKT1 gene in an elderly Japanese cohort. Genotypes of the rs2498794 SNP, which is located in the fifth intron region of the AKT1 gene, were marginally but significantly associated with smoking duration in the total 999 samples of former and current smokers. Interestingly, this SNP had a marginally significant association with individual cancer history (past and current), especially in groups with a shorter smoking duration (<44 years) and fewer cigarettes per day (≤20). These data suggest that the rs2498794 polymorphism of the AKT1 gene is associated with a long smoking duration and may be involved in the predisposition to cancer when the smoking duration is short or the cigarettes per day is rate low.

The different role of sex hormones on female cardiovascular physiology and function: not only oestrogens

Human response to different physiologic stimuli and cardiovascular (CV) adaptation to various pathologies seem to be gender specific. Sex-steroid hormones have been postulated as the major contributors towards these sex-related differences. This review will discuss current evidence on gender differences in CV function and remodelling, and will present the different role of the principal sex-steroid hormones on female heart. Starting from a review of sex hormones synthesis, receptors and CV signalling, we will summarize the current knowledge concerning the role of sex hormones on the regulation of our daily activities throughout the life, via the modulation of autonomic nervous system, excitation-contraction coupling pathway and ion channels activity. Many unresolved questions remain even if oestrogen effects on myocardial remodelling and function have been extensively studied. So this work will focus attention also on the controversial and complex relationship existing between androgens, progesterone and female heart.

A carbazole alkaloid deactivates mTOR through the suppression of rictor and that induces apoptosis in lung cancer cells

Non-small cell lung cancer (NSCLC) is known to be a difficult cancer to treat because of its poor prognosis, limited option for surgery, and resistance to chemo or radiotherapy. In this study, we have demonstrated that suppression of rictor expression in A549 and H1299 NSCLC cells by mahanine, a carbazole alkaloid, disrupted constitutive activation of mTOR and Akt. Mahanine suppression of rictor gene expression and consequent attenuation of its protein expression affected the inhibition of mTOR (Ser-2481) and Akt (Ser-473) phosphorylation. Since mahanine treatment revealed this new insight of rictor-mTOR relationship, we examined an association between mTOR activation with rictor expression. Interestingly, in rictor knockdown (KD) NSCLC cells, mTOR activation was significantly impaired. Transfection of rictor over-expression vector into the NSCLC cells reversed this situation. In fact, both rictor KD and mahanine treated cells showed considerably depleted phospho-mTOR level. These results indicate that rictor is required to maintain constitutive activation of mTOR in lung cancer cells. When mTOR kinase activity in rictor KD cells was examined with Akt as substrate, a significant reduction of Akt phosphorylation indicated impairment of mTOR kinase potentiality. Disruption of mTOR and Akt activation caused drastic mortality of NSCLC cancer cells through apoptosis. Hence, our study reveals a new dimension in mTOR-rictor relationship, where rictor stands to be a suitable therapeutic target for lung cancer.

PI3K/AKT pathway-mediated regulation of p27(Kip1) is associated with cell cycle arrest and apoptosis in cervical cancer

BACKGROUND

The cyclin-dependent kinase inhibitor p27(Kip1) is known to act as a putative tumor suppressor in several human cancers, including cervical cancer. Down-regulation of p27(Kip1) may occur either through transcription inhibition or through phosphorylation-dependent proteolytic degradation. As yet, the mechanism underlying p27(Kip1) down-regulation and its putative downstream effects on cervical cancer development are poorly understood. Here we assessed the expression and sub-cellular localization of p27(Kip1) and its effects on proliferation, cell cycle progression and (inhibition of) apoptosis in cervical cancer cells.

METHODS

Primary cervical cancer samples (n = 70), normal cervical tissue samples (n = 30) and cervical cancer-derived cell lines (n = 8) were used to assess the expression of p27(Kip1) and AKT1 by RT-PCR, Western blotting and immunohistochemistry, respectively. The effects of the PI3K inhibitor LY294004 and the proteasome inhibitor MG132 on cervical cancer cell proliferation were investigated using a MTT assay. Apoptosis and cell cycle analyses were carried out using flow cytometry, and sub-cellular p27(Kip1) localization analyses were carried out using immunofluorescence assays.

RESULTS

We observed p27(Kip1) down-regulation (p = 0.045) and AKT1 up-regulation (p = 0.046) in both the primary cervical cancer samples and the cervical cancer-derived cell lines, compared to the normal cervical tissue samples tested. Treatment of cervical cancer-derived cell lines with the PI3K inhibitor LY294002 resulted in a reduced AKT1 activity. We also observed a dose-dependent inhibition of cell viability after treatment of these cell lines with the proteasome inhibitor MG132. Treatment of the cells with LY294002 resulted in a G1 cell cycle arrest, a nuclear expression of p27(Kip1), and a cytoplasmic p27(Kip1) accumulation after subsequent treatment with MG132. Additionally, we found that the synergistic effect of MG132 and LY294002 resulted in a sub-G1 cell cycle arrest and apoptosis induction through poly (ADP-ribose) polymerase (PARP) cleavage.

CONCLUSION

Our data suggest that p27(Kip1) down-regulation in cervical cancer cells is primarily regulated through PI3K/AKT-mediated proteasomal degradation. The observed synergistic effect of the MG132 and LY294002 inhibitors may form a basis for the design of novel cervical cancer therapies.

A generalised enzyme kinetic model for predicting the behaviour of complex biochemical systems

•

We propose the dQSSA model as a novel way of modelling complex biological networks.

•

No low enzyme concentration assumption, covering more biological settings.

•

Reduces the number of parameters, which simplifies optimisation.

•

dQSSA was validated both in silico and in vitro.

•

Both biochemical and signalling pathways can be modelled accurately and simply.

Quasi steady-state enzyme kinetic models are increasingly used in systems modelling. The Michaelis Menten model is popular due to its reduced parameter dimensionality, but its low-enzyme and irreversibility assumption may not always be valid in the in vivo context. Whilst the total quasi-steady state assumption (tQSSA) model eliminates the reactant stationary assumptions, its mathematical complexity is increased. Here, we propose the differential quasi-steady state approximation (dQSSA) kinetic model, which expresses the differential equations as a linear algebraic equation. It eliminates the reactant stationary assumptions of the Michaelis Menten model without increasing model dimensionality. The dQSSA was found to be easily adaptable for reversible enzyme kinetic systems with complex topologies and to predict behaviour consistent with mass action kinetics in silico. Additionally, the dQSSA was able to predict coenzyme inhibition in the reversible lactate dehydrogenase enzyme, which the Michaelis Menten model failed to do. Whilst the dQSSA does not account for the physical and thermodynamic interactions of all intermediate enzyme-substrate complex states, it is proposed to be suitable for modelling complex enzyme mediated biochemical systems. This is due to its simpler application, reduced parameter dimensionality and improved accuracy.

Neuroprotection induced by sevoflurane-delayed post-conditioning is attributable to increased phosphorylation of mitochondrial GSK-3β through the PI3K/Akt survival pathway

BACKGROUND AND PURPOSE

Post-conditioning with volatile anesthetics can create ischemic tolerance against cerebral ischemia-reperfusion injury. The present study was designed to determine whether delayed exposure to sevoflurane could induce ischemic tolerance and if this effect was dependent on increasing phosphorylated Akt-Ser473 and GSK-3β-Ser9 expression in the mitochondria, via a mechanism involving the PI3K/Akt pathway.

METHODS

Adult male Sprague-Dawley rats were subjected to focal cerebral ischemia. Sevoflurane post-conditioning was achieved by administration of 2.5% sevoflurane for 60 min, 15 min after reperfusion. Phosphorylated Akt-Ser473 and GSK-3β-Ser9 in the cytosol and mitochondria of the ischemic penumbra were evaluated 4, 12, 24, and 72 h after reperfusion. Neurological deficit score and activity of caspase-3 and -9 were evaluated 24 and 72 h after reperfusion. Apoptosis, as measured by TUNEL staining and cerebral infarct size,was determined 24h after reperfusion.

RESULTS

Sevoflurane-delayed post-conditioning significantly increased levels of phosphorylated Akt-Ser473 and GSK-3β-Ser9 in the mitochondria and inhibited the activities of caspase-3 and -9, showing an improved neurological deficit score and a decreased infarct size. However, LY294002, a selective PI3K inhibitor, not only eliminated the neuroprotection of sevoflurane, as indicated by an increased infarct size and a larger number of TUNEL-positive cells, but also reversed the elevation of p-Akt and p-GSK-3β expression in the mitochondria induced by sevoflurane post-conditioning.

CONCLUSIONS

Our data suggested that delayed application of sevoflurane after reperfusion provides neuroprotection by activating phosphorylated Akt-Ser473 and GSK-3β-Ser9 in the mitochondria via the PI3K/Akt pathway.

Targeting mTOR signaling pathways and related negative feedback loops for the treatment of acute myeloid leukemia

An accumulating understanding of the complex pathogenesis of acute myeloid leukemia (AML) continues to lead to promising therapeutic approaches. Among the key aberrant intracellular signaling pathways involved in AML, the phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin (PI3K/AKT/mTOR) axis is of major interest. This axis modulates a wide array of critical cellular functions, including proliferation, metabolism, and survival. Pharmacologic inhibitors of components of this pathway have been developed over the past decade, but none has an established role in the treatment of AML. This review will discuss the preclinical data and clinical results driving ongoing attempts to exploit the PI3K/AKT/mTOR pathway in patients with AML and address issues related to negative feedback loops that account for leukemic cell survival. Targeting the PI3K/AKT/mTOR pathway is of high interest for the treatment of AML, but combination therapies with other targeted agents may be needed to block negative feedback loops in leukemia cells.

Phosphorylation of AKT(Ser473) serves as an independent prognostic marker for radiosensitivity in advanced head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is frequently characterized by high resistance to radiotherapy, which critically depends on both altered signaling pathways within tumor cells and their dynamic interaction with the tumor microenvironment. This study evaluated the prognostic value of the phosphorylation status of AKT on Ser473 and Thr308 for the clinical outcome of patients with advanced HNSCC on radiotherapy. Furthermore, we investigated the impact of AKT(Ser473) phosphorylation [p-AKT(Ser473)] in the context of radioresistance using ex vivo tissue cultures that resemble the complex tissue architecture and paracrine interaction with the tumor microenvironment. In a cohort of 120 patients with advanced HNSCC, who were treated with primary or adjuvant radiotherapy, a significant association was found between relative p-AKT(Ser473) levels and overall survival (p = 0.006) as well as progression-free survival (p = 0.021), while no significant correlation was revealed for relative p-AKT(Thr308) levels. In ex vivo tissue cultures p-AKT(Ser473) levels were increased upon irradiation and treatment with the PI3K inhibitor LY294002 inhibited both basal and irradiation induced AKT(Ser473) phosphorylation. Strikingly, pretreatment with LY294002 sensitized tissue cultures derived from primary and recurrent tumors to radiotherapy as determined by impaired tumor cell proliferation and enhanced DNA damage. In conclusion, phosphorylation status of AKT(Ser473) in tumor specimens serves as a novel biomarker to identify patients with advanced HNSCC at high risk for treatment failure following radiotherapy, and our data from ex vivo tissue cultures support the assumption that pharmacological inhibition of AKT(Ser473) phosphorylation might circumvent radioresistance to improve efficiency and reduce toxicity of current treatment modalities.

Aberrant mTOR activation in senescence and aging: A mitochondrial stress response?

Unexpected activation of mTOR signaling, measured by ribosomal S6 phosphorylation or ribosomal S6 kinase (p70S6K) activity, has been reported in aging-related settings. Evidence of elevated mTOR activity has been reported in the heart and muscle tissue in aged mice and humans, mouse models of progeria, and senescent human fibroblasts. We explore these reports and the possibility that activation of the mTOR/p70S6K kinase pathway may represent a ROS-mediated response to mitochondrial stress leading to the activation of senescence. This activation is a hallmark of both aged tissue and senescent human cells.

The regulation of osteoclast function and bone resorption by small GTPases

Osteoclasts are multinucleated cells that are responsible for resorption of bone, and increased activity of these cells is associated with several common bone diseases, including postmenopausal osteoporosis. Upon adhesion to bone, osteoclasts become polarized and reorganise their cytoskeleton and membrane to form unique domains including the sealing zone (SZ), which is a dense ring of F-actin-rich podosomes delimiting the ruffled border (RB), where protons and proteases are secreted to demineralise and degrade the bone matrix, respectively. These processes are dependent on the activity of small GTPases. Rho GTPases are well known to control the organization of F-actin and adhesion structures of different cell types, affecting subsequently their migration. In osteoclasts, RhoA, Rac, Cdc42, RhoU and also Arf6 regulate podosome assembly and their organization into the SZ. By contrast, the formation of the RB involves vesicular trafficking pathways that are regulated by the Rab family of GTPases, in particular lysosomal Rab7. Finally, osteoclast survival is dependent on the activity of Ras GTPases. The correct function of almost all these GTPases is absolutely dependent on post-translational prenylation, which enables them to localize to specific target membranes. Bisphosphonate drugs, which are widely used in the treatment of bone diseases such as osteoporosis, act by preventing the prenylation of small GTPases, resulting in the loss of the SZ and RB and therefore inhibition of osteoclast activity, as well as inducing osteoclast apoptosis. In this review we summarize current understanding of the role of specific prenylated small GTPases in osteoclast polarization, function and survival.

Skeletal muscle tissue engineering: methods to form skeletal myotubes and their applications

Skeletal muscle tissue engineering (SMTE) aims to repair or regenerate defective skeletal muscle tissue lost by traumatic injury, tumor ablation, or muscular disease. However, two decades after the introduction of SMTE, the engineering of functional skeletal muscle in the laboratory still remains a great challenge, and numerous techniques for growing functional muscle tissues are constantly being developed. This article reviews the recent findings regarding the methodology and various technical aspects of SMTE, including cell alignment and differentiation. We describe the structure and organization of muscle and discuss the methods for myoblast alignment cultured in vitro. To better understand muscle formation and to enhance the engineering of skeletal muscle, we also address the molecular basics of myogenesis and discuss different methods to induce myoblast differentiation into myotubes. We then provide an overview of different coculture systems involving skeletal muscle cells, and highlight major applications of engineered skeletal muscle tissues. Finally, potential challenges and future research directions for SMTE are outlined.

Application of insulin-like growth factor-1 in the treatment of inner ear disorders

Sensorineural hearing loss (SNHL) is considered an intractable disease, given that hair and supporting cells (HCs and SCs) of the postnatal mammalian cochlea are unable to regenerate. However, with progress in regenerative medicine in the 21st century, several innovative approaches for achieving regeneration of inner ear HCs and SCs have become available. These methods include stem cell transplantation, overexpression of specific genes, and treatment with growth factors. Insulin-like growth factor-1 (IGF-1) is one of the growth factors that are involved in the development of the inner ear. Treatment with IGF-1 maintains HC numbers in the postnatal mammalian cochlea after various types of HC injuries, with activation of two major pathways downstream of IGF-1 signaling. In the aminoglycoside-treated neonatal mouse cochlear explant culture, promotion of the cell-cycle in SCs as well as inhibition of HC apoptosis was observed in the IGF-1-treated group. Activation of downstream molecules was observed in SCs and, in turn, SCs contribute to the maintenance of HC numbers. Using comprehensive analysis of the gene expression, the candidate effector molecules of the IGF-1 signaling pathway in the protection of HCs were identified as Netrin1 and Gap43. Based on these studies, a clinical trial has sought to investigate the effects of IGF-1 on SNHL. Sudden SNHL (SSHL) that was refractory to systemic steroids was treated with IGF-1 in a gelatin hydrogel and the outcome was compared with a historical control of hyperbaric oxygen therapy. The proportion of patients showing hearing improvement was significantly higher in the IGF-1-treatment group at 24 weeks after treatment than in the control group. A randomized clinical trial is ongoing to compare the effect of IGF-1 treatment with that of intra-tympanic steroids for SSHL that is refractory to systemic steroids.

The links between AKT and two intracellular proteolytic cascades: ubiquitination and autophagy

The serine threonine kinase AKT plays a central role in the regulation of cell survival in a variety of human neoplastic diseases. A series of studies have revealed a connection between AKT signaling and two important protein degradation pathways in mammalian cells: the ubiquitin-proteasome system and autophagy. Two distinct ubiquitination systems have been reported to regulate AKT signaling: K63-linked ubiquitination, which promotes the oncogenic activation of AKT, and K48-linked ubiquitination, which triggers the proteasomal degradation of phosphorylated AKT. Autophagy is an evolutionarily conserved mechanism for the gross disposal and recycling of intracellular proteins in mammalian cells. AKT signaling may play a regulatory role in autophagy; however, the underlying mechanisms have not been fully clarified. Recently, AKT was shown to phosphorylate key molecules involved in the regulation of autophagy. Furthermore, lysosomal co-localization of the AKT-Phafin2 complex is reportedly critical for the induction of autophagy. In this review, we will discuss the connection between AKT, a core intracellular survival regulator, and two major intracellular proteolytic signaling pathways in mammalian cells.

PI3K/AKT/mTOR signaling pathway as a therapeutic target for ovarian cancer

BACKGROUND

Ovarian cancer is one of the major causes of death in women worldwide. Despite improvements in conventional treatment approaches, such as surgery and chemotherapy, a majority of patients with advanced ovarian cancer experience relapse and eventually succumb to the disease; the outcome of patients remains poor. Hence, new therapeutic strategies are urgently required. The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) is activated in approximately 70 % of ovarian cancers, resulting in hyperactive signaling cascades that relate to cellular growth, proliferation, survival, metabolism, and angiogenesis. Consistent with this, a number of clinical studies are focusing on PI3K pathway as an attractive target in the treatment of ovarian cancer. In this review, we present an overview of PI3K pathway as well as its pathological aberrations reported in ovarian cancer. We also discuss inhibitors of PI3K pathway that are currently under clinical investigations and the challenges these inhibitors face in future clinical utility.

METHODS

PubMed was searched for articles of relevance to ovarian cancer and the PI3K pathway. In addition, the ClinicalTrials.gov was also scanned for data on novel therapeutic inhibitors targeting the PI3K pathway.

RESULTS

Genetic aberrations at different levels of PI3K pathway are frequently observed in ovarian cancer, resulting in hyperactivation of this pathway. The alterations of this pathway make the PI3K pathway an attractive therapeutic target in ovarian cancer. Currently, several inhibitors of PI3K pathway, such as PI3K/AKT inhibitors, rapamycin analogs for mTOR inhibition, and dual PI3K/mTOR inhibitors are in clinical testing in patients with ovarian cancer.

CONCLUSIONS

PI3K pathway inhibitors have shown great promise in the treatment of ovarian cancer. However, further researches on selection patients that respond to PI3K inhibitors and exploration of effective combinatorial therapies are required to improve the management of ovarian cancer.

Differential effects of Akt isoforms on somatic cell reprogramming

Akt plays an important role in cell growth, proliferation and survival. The specific roles of the three Akt isoforms in somatic cell reprogramming have not been investigated. Here we report that, during iPSC generation, enhanced Akt1 activity promotes complete reprogramming mainly through increased activation of Stat3 in concert with leukemia inhibitory factor (LIF) and, to a lesser extent, through promotion of colony formation. Akt1 augments Stat3 activity through activation of mTOR and upregulation of LIF receptor expression. Similarly, enhanced Akt2 or Akt3 activation also promotes reprogramming and coordinates with LIF to activate Stat3. Blocking Akt1 or Akt3 but not Akt2 expression prohibits cell proliferation and reprogramming. Furthermore, the halt in cell proliferation and reprogramming caused by mTOR and Akt inhibitors can be reversed by inhibition of GSK3. Finally, we found that expressing the GSK3β target Esrrb overrides inhibition of Akt and restores reprogramming. Our data demonstrated that during reprogramming, Akt promotes establishment of pluripotency through co-stimulation of Stat3 activity with LIF. Akt1 and Akt3 are essential for the proliferation of reprogrammed cells, and Esrrb supports cell proliferation and complete reprogramming during Akt signaling.

Substrate-selective inhibition of protein kinase PDK1 by small compounds that bind to the PIF-pocket allosteric docking site

The PIF-pocket of AGC protein kinases participates in the physiologic mechanism of regulation by acting as a docking site for substrates and as a switch for the transduction of the conformational changes needed for activation or inhibition. We describe the effects of compounds that bind to the PIF-pocket of PDK1. In vitro, PS210 is a potent activator of PDK1, and the crystal structure of the PDK1-ATP-PS210 complex shows that PS210 stimulates the closure of the kinase domain. However, in cells, the prodrug of PS210 (PS423) acts as a substrate-selective inhibitor of PDK1, inhibiting the phosphorylation and activation of S6K, which requires docking to the PIF-pocket, but not affecting PKB/Akt. This work describes a tool to study the dynamics of PDK1 activity and a potential approach for drug discovery.

The PPARβ/δ agonist GW0742 modulates signaling pathways associated with cardiac myocyte growth via a non-genomic redox mechanism

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily and appear to have beneficial effects in the cardiovascular system. PPARβ/δ has been shown previously to exert an inhibitory effect on cardiac myocyte hypertrophy in vivo and in vitro although the exact mechanism is not fully clear yet. The principal signaling pathways that have been involved in triggering cardiac hypertrophic response are mitogen-activated protein kinases (MAPKs) and PI3K/Akt cascades. In this study, we sought to evaluate the potential effects evoked by PPARβ/δ activation on signaling pathways that are implicated in cardiac myocyte growth responses. The selective PPARβ/δ agonist GW0742 attenuated ERK1/2 and Akt phosphorylation that was stimulated by growth promoting agonists (phenylephrine, insulin or IGF-1). This effect was not reversed by the specific PPARβ/δ antagonist, GSK0660, but was inhibited by vanadate, a potent protein tyrosine phosphatase inhibitor. In addition, GW0742 prevented the oxidation and inactivation of PTEN supporting further the notion that its inhibitory action on the agonist-induced kinase phosphorylation is mediated by the modulation of phosphatase activity. Furthermore, GW0742 abolished the agonist-induced intracellular generation of reactive oxygen species, independently of PPARβ/δ activation. Our data reveals a new non-genomic mechanism of GW0742, which ameliorates the generation of reactive oxygen species and attenuates ERK1/2 and PI3K/Akt signaling, with implications in the regulation of cardiac hypertrophic response.

Defect of insulin signal in peripheral tissues: Important role of ceramide

In healthy people, balance between glucose production and its utilization is precisely controlled. When circulating glucose reaches a critical threshold level, pancreatic β cells secrete insulin that has two major actions: to lower circulating glucose levels by facilitating its uptake mainly into skeletal muscle while inhibiting its production by the liver. Interestingly, dietary triglycerides are the main source of fatty acids to fulfill energy needs of oxidative tissues. Normally, the unconsumed fraction of excess of fatty acids is stored in lipid droplets that are localized in adipocytes to provide energy during fasting periods. Thus, adipose tissue acts as a trap for fatty acid excess liberated from plasma triglycerides. When the buffering action of adipose tissue to store fatty acids is impaired, fatty acids that build up in other tissues are metabolized as sphingolipid derivatives such as ceramides. Several studies suggest that ceramides are among the most active lipid second messengers to inhibit the insulin signaling pathway and this review describes the major role played by ceramide accumulation in the development of insulin resistance of peripherals tissues through the targeting of specific proteins of the insulin signaling pathway.

Neuroprotective effects of neuregulin-1 ß on oligodendrocyte type 2 astrocyte progenitors following oxygen and glucose deprivation

BACKGROUND

Hypoxic-ischemic brain injury in neonates, especially in premature infants, is one of the main contributors to the mortality of newborns and can cause nervous system dysfunction in children. The major pathogenesis seems to be cerebral ischemia/reperfusion in the immature white matter that preferentially targets vulnerable premyelinating oligodendrocytes.

OBJECTIVES

The goal of this study was to culture oligodendrocyte type 2 astrocyte cells in an oxygen and glucose deprivation environment to simulate ischemia injury and examine the cellular and molecular mechanisms involved in the neuroprotective effects of neuregulin-1ß on ischemia-induced immature oligodendrocytes.

METHODS

Oligodendrocyte type 2 astrocyte cells were cultured from neonatal Sprague-Dawley rat cerebra. The cells were divided into two groups: one was subjected to oxygen and glucose deprivation for 9 hours and the other was treated with 50 ng/mL or 100 ng/mL neuregulin-1β during oxygen and glucose deprivation. Cell survival was determined by Trypan Blue staining and cell apoptosis were observed by fluorescein isothiocyanate-Annexin V and propidium iodide double staining. To study if the PI3K-Akt signaling pathway was involved in the mechanism of protective effect of neuregulin-1ß, Western blot analysis was used to quantitative the changes of protein.

RESULTS

Treatment with neuregulin-1ß within the period of oxygen and glucose deprivation significantly increased cell survival and also resulted in a significant decrease in cell apoptosis. The neuroprotective effects of neuregulin-1ß were prevented by treatment with Ly294002, an inhibitor of the phosphatidylinositol-3-kinase/Akt pathway.

CONCLUSIONS

These results suggest that neuregulin-1ß could protect the oligodendrocyte type 2 astrocyte progenitors against hypoxic injury, and the mechanism may be associated with the PI3K-Akt signaling pathway.

Activation of PI3Kα by physiological effectors and by oncogenic mutations: structural and dynamic effects

PI3Kα, a heterodimeric lipid kinase, catalyzes the conversion of phosphoinositide-4,5-bisphosphate (PIP2) to phosphoinositide-3,4,5-trisphosphate (PIP3), a lipid that recruits to the plasma membrane proteins that regulate signaling cascades that control key cellular processes such as cell proliferation, carbohydrate metabolism, cell motility, and apoptosis. PI3Kα is composed of two subunits, p110α and p85, that are activated by binding to phosphorylated receptor tyrosine kinases (RTKs) or their substrates. The gene coding for p110α, PIK3CA, has been found to be mutated in a large number of tumors; these mutations result in increased PI3Kα kinase activity. The structure of the complex of p110α with a fragment of p85 containing the nSH2 and the iSH2 domains has provided valuable information about the mechanisms underlying the physiological activation of PI3Kα and its pathological activation by oncogenic mutations. This review discusses information derived from x-ray diffraction and theoretical calculations regarding the structural and dynamic effects of mutations in four highly mutated regions of PI3K p110α, as well as the proposed mechanisms by which these mutations increase kinase activity. During the physiological activation of PI3Kα, the phosphorylated tyrosine of RTKs binds to the nSH2 domain of p85, dislodging an inhibitory interaction between the p85 nSH2 and a loop of the helical domain of p110α. Several of the oncogenic mutations in p110α activate the enzyme by weakening this autoinhibitory interaction. These effects involve structural changes as well as changes in the dynamics of the enzyme. One of the most common p110α mutations, H1047R, activates PI3Kα by a different mechanism: it increases the interaction of the enzyme with the membrane, maximizing the access of the PI3Kα to its substrate PIP2, a membrane lipid.

The detection of risk pathways, regulated by miRNAs, via the integration of sample-matched miRNA-mRNA profiles and pathway structure

The use of genome-wide, sample-matched miRNA (miRNAs)-mRNA expression data provides a powerful tool for the investigation of miRNAs and genes involved in diseases. The identification of miRNA-regulated pathways has been crucial for analysis of the role of miRNAs. However, the classical identification method fails to consider the structural information of pathways and the regulation of miRNAs simultaneously. We proposed a method that simultaneously integrated the change in gene expression and structural information in order to identify pathways. Our method used fold changes in miRNAs and gene products, along with the quantification of the regulatory effect on target genes, to measure the change in gene expression. Topological characteristics were investigated to measure the influence of gene products on entire pathways. Through the analysis of multiple myeloma and prostate cancer expression data, our method was proven to be effective and reliable in identifying disease risk pathways that are regulated by miRNAs. Further analysis showed that the structure of a pathway plays a crucial role in the recognition of the pathway as a factor in disease risk.

mTOR/p70S6K signaling distinguishes routine, maintenance-level autophagy from autophagic cell death during influenza A infection

Autophagy, a stress response activated in influenza A virus infection helps the cell avoid apoptosis. However, in the absence of apoptosis infected cells undergo vastly expanded autophagy and nevertheless die in the presence of necrostatin but not of autophagy inhibitors. Combinations of inhibitors indicate that the controls of protective and lethal autophagy are different. Infection that triggers apoptosis also triggers canonical autophagy signaling exhibiting transient PI3K and mTORC1 activity. In terminal autophagy phospho-mTOR(Ser2448) is suppressed while mTORC1, PI3K and mTORC2 activities increase. mTORC1 substrate p70S6K becomes highly phosphorylated while its activity, now regulated by mTORC2, is required for LC3-II formation. Inhibition of mTORC2/p70S6K, unlike that of PI3K/mTORC1, blocks expanded autophagy in the absence of apoptosis but not moderate autophagy. Inhibitors of expanded autophagy limit virus reproduction. Thus expanded, lethal autophagy is activated by a signaling mechanism different from autophagy that helps cells survive toxic or stressful episodes.

Activation of PI3K/Akt signaling in rostral ventrolateral medulla impairs brain stem cardiovascular regulation that underpins circulatory depression during mevinphos intoxication

As the most widely used pesticides in the globe, the organophosphate compounds are understandably linked with the highest incidence of suicidal poisoning. Whereas the elicited toxicity is often associated with circulatory depression, the underlying mechanisms require further delineation. Employing the pesticide mevinphos as our experimental tool, we evaluated the hypothesis that transcriptional upregulation of nitric oxide synthase II (NOS II) by NF-κB on activation of the PI3K/Akt cascade in the rostral ventrolateral medulla (RVLM), the brain stem site that maintains blood pressure and sympathetic vasomotor tone, underpins the circulatory depressive effects of organophosphate poisons. Microinjection of mevinphos (10 nmol) bilaterally into the RVLM of anesthetized Sprague-Dawley rats induced a progressive hypotension that was accompanied sequentially by an increase (Phase I) and a decrease (Phase II) of an experimental index for the baroreflex-mediated sympathetic vasomotor tone. There were also progressive augmentations in PI3K or Akt enzyme activity and phosphorylation of p85 or Akt(Thr308) subunit in the RVLM that were causally related to an increase in NF-κB transcription activity and elevation in NOS II or peroxynitrite expression. Loss-of-function manipulations of PI3K or Akt in the RVLM significantly antagonized the reduced baroreflex-mediated sympathetic vasomotor tone and hypotension during Phase II mevinphos intoxication, and blunted the increase in NF-κB/NOS II/peroxynitrite signaling. We conclude that activation of the PI3K/Akt cascade, leading to upregulation of NF-κB/NOS II/peroxynitrite signaling in the RVLM, elicits impairment of brain stem cardiovascular regulation that underpins circulatory depression during mevinphos intoxication.