New responsibilities for the PI3K regulatory subunit p85 alpha

Targeting the RAS upstream and downstream signaling pathway for cancer treatment

Cancer often involves the overactivation of RAS/RAF/MEK/ERK (MAPK) and PI3K-Akt-mTOR pathways due to mutations in genes like RAS, RAF, PTEN, and PIK3CA. Various strategies are employed to address the overactivation of these pathways, among which targeted therapy emerges as a promising approach. Directly targeting specific proteins, leads to encouraging results in cancer treatment. For instance, RTK inhibitors such as imatinib and afatinib selectively target these receptors, hindering ligand binding and reducing signaling initiation. These inhibitors have shown potent efficacy against Non-Small Cell Lung Cancer. Other inhibitors, like lonafarnib targeting Farnesyltransferase and GGTI 2418 targeting geranylgeranyl Transferase, disrupt post-translational modifications of proteins. Additionally, inhibition of proteins like SOS, SH2 domain, and Ras demonstrate promising anti-tumor activity both in vivo and in vitro. Targeting downstream components with RAF inhibitors such as vemurafenib, dabrafenib, and sorafenib, along with MEK inhibitors like trametinib and binimetinib, has shown promising outcomes in treating cancers with BRAF-V600E mutations, including myeloma, colorectal, and thyroid cancers. Furthermore, inhibitors of PI3K (e.g., apitolisib, copanlisib), AKT (e.g., ipatasertib, perifosine), and mTOR (e.g., sirolimus, temsirolimus) exhibit promising efficacy against various cancers such as Invasive Breast Cancer, Lymphoma, Neoplasms, and Hematological malignancies. This review offers an overview of small molecule inhibitors targeting specific proteins within the RAS upstream and downstream signaling pathways in cancer.

Role of microRNAs in epidermal growth factor receptor signaling pathway in cervical cancer

Cervical cancer is one of the most common disorders in females all around the world. Similar to other types of cancer, several signaling pathways are demonstrated to be involved in the progression of this cancer including ERK/MAPK, PI3K/AKT, apoptotic signaling pathways, Wnt, and epidermal growth factor receptor (EGFR). Various microRNAs (miRNAs) and their target genes involved in cervical cancer have been extracted from the kinds of literature of Scopus, Pubmed and Google scholar databases. Regarding the targets, some of them were found to belong in EGFR signaling pathways. The regulation patterns of these miRNA are different in cervical cancer; however, their main aim is to trigger EGFR signaling to proceed with cancer. Moreover, several predicted miRNAs were found to have some interactions with the differentially expressed genes of cervical cancer which are the members of the EGFR signaling pathway by using miRWalk 3.0 (https://mirwalk.umm.uni-heidelberg.de/) and TargetScan 7.1 (https://www.targetscan.org/vert_71/). Also, the microarray data were obtained from the NCBI-Gene Expression Omnibus (GEO) datasets of cervical cancer. In the present review, we highlight the miRNAs involved in cervical cancer and the role of their targets in the EGFR signaling pathway. Furthermore, some predicted miRNAs were the candidate to target EGFR signaling pathway members differentially expressed in cervical cancer samples compared to normal samples.

Isoform-specific activities of the regulatory subunits of phosphatidylinositol 3-kinases - potentially novel therapeutic targets

INTRODUCTION

The main regulatory subunits of Class IA phosphatidylinositol 3-kinase (PI3K), p85α and p85β, initiate diverse cellular activities independent of binding to the catalytic subunit p110. Several of these signaling processes directly or indirectly contribute to a regulation of PI3K and could become targets for therapeutic efforts. Areas covered: This review will highlight two general areas of p85 activity: (1) direct interaction with regulatory proteins and with determinants of the cytoskeleton, and (2) a genetic analysis by deletion and domain switches identifying new functions for p85 domains. Expert Opinion: Isoform-specific activities of regulatory subunits have long been at the periphery of the PI3K field. Our understanding of these unique functions of the regulatory subunits is fragmentary and raises many important questions. At this time, there is insufficient information to translate this knowledge into the clinic, but some tempting targets have emerged that could move the field forward with the help of novel technologies in drug design and identification.

Calorie Restriction-Induced Increase in Skeletal Muscle Insulin Sensitivity Is Not Prevented by Overexpression of the p55α Subunit of Phosphoinositide 3-Kinase

Introduction: The Phosphoinositide 3-kinase (PI3K) signaling pathway plays an important role in skeletal muscle insulin-stimulated glucose uptake. While whole-body and tissue specific knockout (KO) of individual or combinations of the regulatory subunits of PI3K (p85α, p55α, and p50α or p85β); increase insulin sensitivity, no study has examined whether increasing the expression of the individual regulatory subunits would inhibit insulin action in vivo. Therefore, the objective of this study was to determine whether skeletal muscle-specific overexpression of the p55α regulatory subunit of PI3K impairs skeletal muscle insulin sensitivity, or prevents its enhancement by caloric restriction. Methods: We developed a novel "floxed" mouse that, through the Cre-LoxP approach, allows for tamoxifen (TMX)-inducible and skeletal muscle-specific overexpression of the p55α subunit of PI3K (referred to as, 'p55α-mOX'). Beginning at 10 weeks of age, p55α-mOX mice and their floxed littermates (referred to as wildtype [WT]) either continued with free access to food (ad libitum; AL), or were switched to a calorie restricted diet (CR; 60% of AL intake) for 20 days. We measured body composition, whole-body energy expenditure, oral glucose tolerance and ex vivo skeletal muscle insulin sensitivity in isolated soleus and extensor digitorum longus muscles using the 2-deoxy-glucose (2DOG) uptake method. Results: p55α mRNA and protein expression was increased ∼2 fold in muscle from p55α-mOX versus WT mice. There were no differences in energy expenditure, total activity, or food intake of AL-fed mice between genotypes. Body weight, fat and lean mass, tissue weights, and fasting glucose and insulin were comparable between p55α-mOX and WT mice on AL, and were decreased equally by CR. Interestingly, overexpression of p55α did not impair oral glucose tolerance or skeletal muscle insulin signaling or sensitivity, nor did it impact the ability of CR to enhance these parameters. Conclusion: Skeletal muscle-specific overexpression of p55α does not impact skeletal muscle insulin action, suggesting that p85α and/or p50α may be more important regulators of skeletal muscle insulin signaling and sensitivity.

Key Molecular Mechanisms of Chaiqinchengqi Decoction in Alleviating the Pulmonary Albumin Leakage Caused by Endotoxemia in Severe Acute Pancreatitis Rats

To reveal the key molecular mechanisms of Chaiqinchengqi decoction (CQCQD) in alleviating the pulmonary albumin leakage caused by endotoxemia in severe acute pancreatitis (SAP) rats. Rats models of SAP endotoxemia-induced acute lung injury were established, the studies in vivo provided the important evidences that the therapy of CQCQD significantly ameliorated the increases in plasma levels of lipopolysaccharide (LPS), sCd14, and Lbp, the elevation of serum amylase level, the enhancements of systemic and pulmonary albumin leakage, and the depravation of airways indicators, thus improving respiratory dysfunction and also pancreatic and pulmonary histopathological changes. According to the analyses of rats pulmonary tissue microarray and protein-protein interaction network, c-Fos, c-Src, and p85α were predicted as the target proteins for CQCQD in alleviating pulmonary albumin leakage. To confirm these predictions, human umbilical vein endothelial cells were employed in in vitro studies, which provide the evidences that (1) LPS-induced paracellular leakage and proinflammatory cytokines release were suppressed by pretreatment with inhibitors of c-Src (PP1) or PI3K (LY294002) or by transfection with siRNAs of c-Fos; (2) fortunately, CQCQD imitated the actions of these selective inhibitions agents to inhibit LPS-induced high expressions of p-Src, p-p85α, and c-Fos, therefore attenuating paracellular leakage and proinflammatory cytokines release.

Signaling in Effector Lymphocytes: Insights toward Safer Immunotherapy

Receptors on T and NK cells systematically propagate highly complex signaling cascades that direct immune effector functions, leading to protective immunity. While extensive studies have delineated hundreds of signaling events that take place upon receptor engagement, the precise molecular mechanism that differentially regulates the induction or repression of a unique effector function is yet to be fully defined. Such knowledge can potentiate the tailoring of signal transductions and transform cancer immunotherapies. Targeted manipulations of signaling cascades can augment one effector function such as antitumor cytotoxicity while contain the overt generation of pro-inflammatory cytokines that contribute to treatment-related toxicity such as “cytokine storm” and “cytokine-release syndrome” or lead to autoimmune diseases. Here, we summarize how individual signaling molecules or nodes may be optimally targeted to permit selective ablation of toxic immune side effects.

Disrupted PI3K p110δ Signaling Dysregulates Maternal Immune Cells and Increases Fetal Mortality In Mice

Maternal immune cells are an integral part of reproduction, but how they might cause pregnancy complications remains elusive. Macrophages and their dual function in inflammation and tissue repair are thought to play key yet undefined roles. Altered perinatal growth underpins adult morbidity, and natural killer (NK) cells may sustain fetal growth by establishing the placental blood supply. Using a mouse model of genetic inactivation of PI3K p110δ, a key intracellular signaling molecule in leukocytes, we show that p110δ regulates macrophage dynamics and NK-cell-mediated arterial remodeling. The uterus of dams with inactive p110δ had decreased IFN-γ and MHC class II^low macrophages but enhanced IL-6. Poor vascular remodeling and a pro-inflammatory uterine milieu resulted in fetal death or growth retardation. Our results provide one mechanism that explains how imbalanced adaptations of maternal innate immune cells to gestation affect offspring well-being with consequence perinatally and possibly into adulthood.

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Genetic inactivation of p110δ in pregnant mice perturbs maternal immune cells

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Uterine NK cells produce less cytokines, resulting in fetal growth restriction

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Inflammatory macrophages are overrepresented, resulting in increased fetal loss

Dipterocarpus tuberculatus ethanol extract strongly suppresses in vitro macrophage-mediated inflammatory responses and in vivo acute gastritis

ETHNOPHARMACOLOGICAL RELEVANCE

Dipterocarpus tuberculatus Roxb. (Dipterocarpaceae) has been traditionally used to treat various inflammatory symptoms. However, no mechanistic studies on the anti-inflammatory actions of D. tuberculatus have been reported. This study is therefore aimed at exploring the anti-inflammatory effects of 95% ethanol extracts (Dt-EE) of this plant.

MATERIALS AND METHODS

The regulatory activity of Dt-EE and its molecular mechanism on the release of nitric oxide (NO) and prostaglandin (PG)E2 in lipopolysaccharide (LPS)-treated macrophage-like RAW264.7 cells were elucidated by evaluating the activation of transcription factors and their upstream signals and by analyzing the kinase activities of target enzymes. Furthermore, to confirm its availability for oral use, an EtOH/HCl-induced acute gastritis model was tested with this extract.

RESULTS

Dt-EE effectively suppressed LPS-mediated inflammatory responses such as the production of NO and PGE2 from macrophages in a dose-dependent manner. In particular, Dt-EE clearly blocked the activation of NF-κB by blocking the phosphorylation of its upstream enzymes IKK and Akt. Using a direct enzyme assay, Dt-EE was shown to block the enzyme activity of PDK1. Finally, this extract also remarkably ameliorated inflammatory lesions in the stomach induced by EtOH/HCl.

CONCLUSION

Our data strongly suggest that Dt-EE can be considered as a novel anti-inflammatory remedy with PDK1/NF-κB inhibitory properties and can also be used to treat gastritis symptoms. In addition, our findings can serve as a basis for further phytochemical and pharmacological studies in the future.

Surfing the big WAVE: Insights into the role of WAVE3 as a driving force in cancer progression and metastasis

WAVE3 belongs to the WASP/WAVE family of actin cytoskeleton remodeling proteins. These proteins are known to be involved in several biological functions ranging from controlling cell shape and movement, to being closely associated with pathological conditions such as cancer progression and metastasis. Last decade has seen an explosion in the literature reporting significant scientific advances on the molecular mechanisms whereby the WASP/WAVE proteins are regulated both in normal physiological as well as pathological conditions. The purpose of this review is to present the major findings pertaining to how WAVE3 has become a critical player in the regulation of signaling pathways involved in cancer progression and metastasis. The review will conclude with suggesting options for the potential use of WAVE3 as a therapeutic target to prevent the progression of cancer to the lethal stage that is the metastatic disease.

Regulation of PTEN activity by p38δ-PKD1 signaling in neutrophils confers inflammatory responses in the lung

Deletion of p38 MAP kinase p38 d results in decreased alveolar neutrophil accumulation and attenuation of acute lung injury through activation of protein kinase D1 and PTEN.

Despite their role in resolving inflammatory insults, neutrophils trigger inflammation-induced acute lung injury (ALI), culminating in acute respiratory distress syndrome (ARDS), a frequent complication with high mortality in humans. Molecular mechanisms underlying recruitment of neutrophils to sites of inflammation remain poorly understood. Here, we show that p38 MAP kinase p38δ is required for recruitment of neutrophils into inflammatory sites. Global and myeloid-restricted deletion of p38δ in mice results in decreased alveolar neutrophil accumulation and attenuation of ALI. p38δ counteracts the activity of its downstream target protein kinase D1 (PKD1) in neutrophils and myeloid-restricted inactivation of PKD1 leads to exacerbated lung inflammation. Importantly, p38δ and PKD1 conversely regulate PTEN activity in neutrophils, thereby controlling their extravasation and chemotaxis. PKD1 phosphorylates p85α to enhance its interaction with PTEN, leading to polarized PTEN activity, thereby regulating neutrophil migration. Thus, aberrant p38δ–PKD1 signaling in neutrophils may underlie development of ALI and life-threatening ARDS in humans.

Neuregulin 1-ErbB4-PI3K signaling in schizophrenia and phosphoinositide 3-kinase-p110δ inhibition as a potential therapeutic strategy

Neuregulin 1 (NRG1) and ErbB4, critical neurodevelopmental genes, are implicated in schizophrenia, but the mediating mechanisms are unknown. Here we identify a genetically regulated, pharmacologically targetable, risk pathway associated with schizophrenia and with ErbB4 genetic variation involving increased expression of a PI3K-linked ErbB4 receptor (CYT-1) and the phosphoinositide 3-kinase subunit, p110δ (PIK3CD). In human lymphoblasts, NRG1-mediated phosphatidyl-inositol,3,4,5 triphosphate [PI(3,4,5)P3] signaling is predicted by schizophrenia-associated ErbB4 genotype and PIK3CD levels and is impaired in patients with schizophrenia. In human brain, the same ErbB4 genotype again predicts increased PIK3CD expression. Pharmacological inhibition of p110δ using the small molecule inhibitor, IC87114, blocks the effects of amphetamine in a mouse pharmacological model of psychosis and reverses schizophrenia-related phenotypes in a rat neonatal ventral hippocampal lesion model. Consistent with these antipsychotic-like properties, IC87114 increases AKT phosphorylation in brains of treated mice, implicating a mechanism of action. Finally, in two family-based genetic studies, PIK3CD shows evidence of association with schizophrenia. Our data provide insight into a mechanism of ErbB4 association with schizophrenia; reveal a previously unidentified biological and disease link between NRG1-ErbB4, p110δ, and AKT; and suggest that p110δ is a previously undescribed therapeutic target for the treatment of psychiatric disorders.

p85β regulatory subunit of class IA PI3 kinase negatively regulates mast cell growth, maturation, and leukemogenesis

We show that loss of p85α inhibits the growth and maturation of mast cells, whereas loss of p85β enhances this process. Whereas restoring the expression of p85α in P85α(-/-) cells restores these functions, overexpression of p85β has the opposite effect. Consistently, overexpression of p85β in WT mast cells represses KIT-induced proliferation and IL-3-mediated maturation by inhibiting the expression of Microphthalmia transcription factor. Because p85α and p85β differ in their N-terminal sequences, chimeric proteins consisting of amino or carboxy-terminal of p85α and/or p85β do not rescue the growth defects of p85α(-/-) cells, suggesting cooperation between these domains for normal mast cell function. Loss of p85β impaired ligand induced KIT receptor internalization and its overexpression enhanced this process, partly because of increased binding of c-Cbl to p85β relative to p85α. In vivo, loss of p85β resulted in increased mast cells, and bone marrow transplantation of cells overexpressing p85β resulted in significant reduction in some tissue mast cells. Overexpression of p85β suppressed the growth of oncogenic KIT-expressing cells in vitro and prolonged the survival of leukemic mice in vivo. Thus, p85α and p85β differentially regulate SCF and oncogenic KIT-induced signals in myeloid lineage-derived mast cells.

Phosphoinositides in chemotaxis

Phosphatidylinositol lipids generated through the action of phosphinositide 3-kinase (PI3K) are key mediators of a wide array of biological responses. In particular, their role in the regulation of cell migration has been extensively studied and extends to amoeboid as well as mesenchymal migration. Through the emergence of fluorescent probes that target PI3K products as well as the use of specific inhibitors and knockout technologies, the spatio-temporal distribution of PI3K products in chemotaxing cells has been shown to represent a key anterior polarity signal that targets downstream effectors to actin polymerization. In addition, through intricate cross-talk networks PI3K products have been shown to regulate signals that control posterior effectors. Yet, in more complex environments or in conditions where chemoattractant gradients are steep, a variety of cell types can still chemotax in the absence of PI3K signals. Indeed, parallel signal transduction pathways have been shown to coordinately regulate cell polarity and directed movement. In this chapter, we will review the current role PI3K products play in the regulation of directed cell migration in various cell types, highlight the importance of mathematical modeling in the study of chemotaxis, and end with a brief overview of other signaling cascades known to also regulate chemotaxis.

A new approach to the molecular analysis of docking, priming, and regulated membrane fusion

Studies using isolated sea urchin cortical vesicles have proven invaluable in dissecting mechanisms of Ca(2+)-triggered membrane fusion. However, only acute molecular manipulations are possible in vitro. Here, using selective pharmacological manipulations of sea urchin eggs ex vivo, we test the hypothesis that specific lipidic components of the membrane matrix selectively affect defined late stages of exocytosis, particularly the Ca(2+)-triggered steps of fast membrane fusion. Egg treatments with cholesterol-lowering drugs resulted in the inhibition of vesicle fusion. Exogenous cholesterol recovered fusion extent and efficiency in cholesterol-depleted membranes; α-tocopherol, a structurally dissimilar curvature analogue, selectively restored fusion extent. Inhibition of phospholipase C reduced vesicle phosphatidylethanolamine and suppressed both the extent and kinetics of fusion. Although phosphatidylinositol-3-kinase inhibition altered levels of polyphosphoinositide species and reduced all fusion parameters, sequestering polyphosphoinositides selectively inhibited fusion kinetics. Thus, cholesterol and phosphatidylethanolamine play direct roles in the fusion pathway, contributing negative curvature. Cholesterol also organizes the physiological fusion site, defining fusion efficiency. A selective influence of phosphatidylethanolamine on fusion kinetics sheds light on the local microdomain structure at the site of docking/fusion. Polyphosphoinositides have modulatory upstream roles in priming: alterations in specific polyphosphoinositides likely represent the terminal priming steps defining fully docked, release-ready vesicles. Thus, this pharmacological approach has the potential to be a robust high-throughput platform to identify molecular components of the physiological fusion machine critical to docking, priming, and triggered fusion.

Regulatory subunits of class IA PI3K

All class I PI3K enzymes are obligate heterodimers, consisting of a catalytic subunit tightly bound to a regulatory subunit. The regulatory subunit influences the subcellular location, binding partners, and activity of the catalytic subunit. Regulatory subunits also possess adaptor functions in cellular signaling, which are largely independent of their role in regulating PI3K activity. This chapter reviews the structure and function of PI3K regulatory subunits, focusing on the class IA subgroup.

Phosphatidylinositol 3-kinase signaling in thymocytes: the need for stringent control

The thymus serves as the primary site for the lifelong formation of new T lymphocytes; hence, it is essential for the maintenance of an effective immune system. Although thymocyte development has been widely studied, the mechanisms involved are incompletely defined. A comprehensive understanding of the molecular events that control regular thymocyte development will not only shed light on the physiological control of T cell differentiation but also probably provide insight into the pathophysiology of T cell immunodeficiencies, the molecular basis that underpins autoimmunity, and the mechanisms that instigate the formation of T cell lymphomas. Phosphatidylinositol 3-kinases (PI3Ks) play a critical role in thymocyte development, although not all of their downstream mediators have yet been identified. Here, we discuss experimental evidence that argues for a critical role of the PI3K-phosphoinositide-dependent protein kinase (PDK1)-protein kinase B (PKB) signaling pathway in the development of both normal and malignant thymocytes, and we highlight molecules that can potentially be targeted therapeutically.

The regulatory subunits of PI3K, p85alpha and p85beta, interact with XBP-1 and increase its nuclear translocation

Despite the fact that X-box binding protein-1 (XBP-1) is one of the main regulators of the unfolded protein response (UPR), the modulators of XBP-1 are poorly understood. Here, we show that the regulatory subunits of phosphotidyl inositol 3-kinase (PI3K), p85alpha (encoded by Pik3r1) and p85beta (encoded by Pik3r2) form heterodimers that are disrupted by insulin treatment. This disruption of heterodimerization allows the resulting monomers of p85 to interact with, and increase the nuclear translocation of, the spliced form of XBP-1 (XBP-1s). The interaction between p85 and XBP-1s is lost in ob/ob mice, resulting in a severe defect in XBP-1s translocation to the nucleus and thus in the resolution of endoplasmic reticulum (ER) stress. These defects are ameliorated when p85alpha and p85beta are overexpressed in the liver of ob/ob mice. Our results define a previously unknown insulin receptor signaling pathway and provide new mechanistic insight into the development of ER stress during obesity.

Dominant role of the p110beta isoform of PI3K over p110alpha in energy homeostasis regulation by POMC and AgRP neurons

PI3K signaling is thought to mediate leptin and insulin action in hypothalamic pro-opiomelanocortin (POMC) and agouti-related protein (AgRP) neurons, key regulators of energy homeostasis, through largely unknown mechanisms. We inactivated either p110alpha or p110beta PI3K catalytic subunits in these neurons and demonstrate a dominant role for the latter in energy homeostasis regulation. In POMC neurons, p110beta inactivation prevented insulin- and leptin-stimulated electrophysiological responses. POMCp110beta null mice exhibited central leptin resistance, increased adiposity, and diet-induced obesity. In contrast, the response to leptin was not blocked in p110alpha-deficient POMC neurons. Accordingly, POMCp110alpha null mice displayed minimal energy homeostasis abnormalities. Similarly, in AgRP neurons, p110beta had a more important role than p110alpha. AgRPp110alpha null mice displayed normal energy homeostasis regulation, whereas AgRPp110beta null mice were lean, with increased leptin sensitivity and resistance to diet-induced obesity. These results demonstrate distinct metabolic roles for the p110alpha and p110beta isoforms of PI3K in hypothalamic energy regulation.

LRP1 regulates architecture of the vascular wall by controlling PDGFRbeta-dependent phosphatidylinositol 3-kinase activation

BACKGROUND

Low density lipoprotein receptor-related protein 1 (LRP1) protects against atherosclerosis by regulating the activation of platelet-derived growth factor receptor beta (PDGFRbeta) in vascular smooth muscle cells (SMCs). Activated PDGFRbeta undergoes tyrosine phosphorylation and subsequently interacts with various signaling molecules, including phosphatidylinositol 3-kinase (PI3K), which binds to the phosphorylated tyrosine 739/750 residues in mice, and thus regulates actin polymerization and cell movement.

METHODS AND PRINCIPAL FINDINGS

In this study, we found disorganized actin in the form of membrane ruffling and enhanced cell migration in LRP1-deficient (LRP1-/-) SMCs. Marfan syndrome-like phenotypes such as tortuous aortas, disrupted elastic layers and abnormally activated transforming growth factor beta (TGFbeta) signaling are present in smooth muscle-specific LRP1 knockout (smLRP1-/-) mice. To investigate the role of LRP1-regulated PI3K activation by PDGFRbeta in atherogenesis, we generated a strain of smLRP1-/- mice in which tyrosine 739/750 of the PDGFRbeta had been mutated to phenylalanines (PDGFRbeta F2/F2). Spontaneous atherosclerosis was significantly reduced in the absence of hypercholesterolemia in these mice compared to smLRP1-/- animals that express wild type PDGFR. Normal actin organization was restored and spontaneous SMC migration as well as PDGF-BB-induced chemotaxis was dramatically reduced, despite continued overactivation of TGFbeta signaling, as indicated by high levels of nuclear phospho-Smad2.

CONCLUSIONS AND SIGNIFICANCE

Our data suggest that LRP1 regulates actin organization and cell migration by controlling PDGFRbeta-dependent activation of PI3K. TGFbeta activation alone is not sufficient for the expression of the Marfan-like vascular phenotype. Thus, regulation of PI3 Kinase by PDGFRbeta is essential for maintaining vascular integrity, and for the prevention of atherosclerosis as well as Marfan syndrome.

Sprouty 2 regulates DNA damage-induced apoptosis in Ras-transformed human fibroblasts

We have reported that expression of Sprouty 2 (Spry2) is necessary for tumor formation by HRas(V12)-transformed fibroblasts. We now report on the role of Spry2 in the inhibition of UV(254 nm) radiation-induced apoptosis in HRas(V12)-transformed human fibroblasts. Silencing Spry2 in this context resulted in increased apoptosis, associated with decreased Akt activation and decreased phosphorylation of HDM2 at Ser-166, which has been shown to stabilize HDM2. As a consequence, when cells with silenced Spry2 were UV-irradiated, they exhibited diminished levels of HDM2 and elevated levels of p53. In agreement with these findings, overexpression of Spry2 in the parental non-transformed fibroblasts led to increased Akt activation and to the stabilization of HDM2. It also led to diminished expression of p53 and decreased apoptosis following UV irradiation. Silencing Spry2 in HRas-transformed cells decreased Rac1 activation, but independent expression of Spry2 in the non-transformed parental cells had no effect on Rac1, suggesting a specific involvement in the activation of Rac1 by Ras. Silencing Spry2 in HRas(V12)-transformed cells resulted in diminished interaction between HRas and Tiam1, a Rac1-specific nucleotide exchange factor. Expression of constitutively active Rac1 in cells with silenced Spry2 partly reversed the effect of Spry2 down-regulation. Furthermore, loss of Spry2 expression in HRas(V12)-transformed cells augmented the cytotoxicity of the DNA-damaging, chemotherapeutic agent cisplatin, a process that was also reversed by active Rac1. Together, these data show that Spry2 inhibits apoptosis in response to DNA damage by regulating Akt, HDM2, and p53, by a process mediated partly by Rac1.

Mechanisms of nuclear vitamin D receptor resistance in Harvey-ras-transfected cells

The hormone 1,25 dihydroxyvitamin D (1,25(OH)(2)D) binds to the nuclear vitamin D receptor (nVDR), which heterodimerizes with retinoid X receptor alpha (RXRalpha), and this complex interacts with specific response elements [vitamin D response elements (VDREs)] to regulate gene transcription. Previous results show a significant reduction in 1,25(OH)(2)D-induced nVDR transcriptional activity in fibroblast (C3H10T1/2) cells transfected with the Harvey ras gene (ras cells) compared with parental cells. The purpose of this study was to investigate the mechanisms by which the H-ras gene interferes with nVDR transcriptional activity. Similar to the ras cells, transcriptional activity of the nVDR was reduced following induction of the H-ras gene for 9 days. The ras cells expressed similar protein levels of RXRalpha with the parent cells, and overexpression of the wild-type RXRalpha plasmid did not restore 1,25(OH)(2)D-mediated nVDR activity in ras cells. Inhibiting activation of extracellular signal-regulated kinase (ERK1/2) had no effect on nVDR activity in ras cells. Furthermore, the binding of nVDR to VDREs was reduced in 1,25(OH)(2)D-treated ras cells. In addition, neither treatment of ras cells with an inhibitor (ketoconazole) of the 1,25(OH)(2)D degradative enzyme, 24-hydroxylase, nor the protein kinase C inhibitors, bisindoylmaleimide I and Gö 6976, had an effect on nVDR activity. In contrast, inhibition of phosphatidylinositol 3-kinase (PI3K) with LY294002 resulted in a 1.6-fold significant increase in the nVDR activity in the ras cells. Taken together, these results indicate that PI3K may, at least in part, mediate the suppression of the 1,25(OH)(2)D regulation of nVDR transcriptional activity by the H-ras gene, leading to reduced ability to associate with response elements.

T cell Ig and mucin domain-1-mediated T cell activation requires recruitment and activation of phosphoinositide 3-kinase

Ligation of the transmembrane protein T cell Ig and mucin domain (Tim)-1 can costimulate T cell activation. Agonistic Abs to Tim-1 are also capable of inducing T cell activation without additional stimuli. However, little is known about the biochemical mechanisms underlying T cell stimulation or costimulation through Tim-1. We show that a tyrosine in Tim-1 becomes phosphorylated in a lck-dependent manner, whereupon it can directly recruit p85 adaptor subunits of PI3K. This results in PI3K activation, which is required for Tim-1 function. We also provide genetic evidence that p85 expression is required for optimal Tim-1 function. Thus, we describe a pathway from Tim-1 tyrosine phosphorylation to the PI3K signaling pathway, which appears to be a major effector of Tim-1-mediated T cell activation.

Outer membrane protein A expression in Enterobacter sakazakii is required to induce microtubule condensation in human brain microvascular endothelial cells for invasion

Enterobacter sakazakii (ES) causes neonatal meningitis and necrotizing enterocolitis with case-fatality rates among infected infants ranging from 40 to 80%. Very little is known about the mechanisms by which these organisms cause disease. Here, we demonstrate that ES invades human brain microvascular endothelial cells (HBMEC) with higher frequency when compared with epithelial cells and endothelial cells from different origins. The entry of ES into HBMEC requires the expression of outer membrane protein A (OmpA), as the OmpA-deletion mutant was sevenfold less invasive than the wild type ES and the bacterium does not multiply inside HBMEC. Anti-OmpA antibodies generated against the OmpA of Escherichia coli K1, which also recognize the OmpA of ES, did not prevent the invasion of ES in HBMEC. ES invasion depends on microtubule condensation in HBMEC and is independent of actin filament reorganization. Both PI3-kinase and PKC-alpha were activated during ES entry into HBMEC between 15 min and 30 min of infection. Concomitantly, overexpression of dominant negative forms of PI3-kinase and PKC-alpha significantly inhibited the invasion of ES into HBMEC. In summary, ES invasion of HBMEC is dependent on the expression of OmpA similar to that of E. coli K1; however, the epitopes involved in the interaction with HBMEC appears to be different.

Src kinase-targeted anti-inflammatory activity of davallialactone from Inonotus xeranticus in lipopolysaccharide-activated RAW264.7 cells

BACKGROUND AND PURPOSE

Mushrooms are popular both as food and as a source of natural compounds of biopharmaceutical interest. Some mushroom-derived compounds such as beta-glucan have been shown to be immunostimulatory; this study explores the anti-inflammatory properties of hispidin analogues derived from the mushroom, Inonotus xeranticus. We sought to identify the molecular mechanism of action of these hispidin analogues by determining their effects on lipopolysaccharide (LPS)-mediated inflammatory responses in a macrophage cell line.

EXPERIMENTAL APPROACH

The production of inflammatory mediators was determined by Griess assay, reverse transcription-PCR and ELISA. The inhibitory effect of davalliactone on LPS-induced activation of signalling cascades was assessed by western blotting, immunoprecipitation and direct kinase assay.

KEY RESULTS

In activated RAW264.7 cells, davallialactone strongly downregulated LPS-mediated inflammatory responses, including NO production, prostaglandin E2 release, expression of proinflammatory cytokine genes and cell surface expression of co-stimulatory molecules. Davallialactone treatment did not alter cell viability or morphology. Davallialactone was found to exert its anti-inflammatory effects by inhibiting a signalling cascade that activates nuclear factor kappa B via PI3K, Akt and IKK, but not mitogen-activated protein kinases. Treatment with davallialactone affected the phosphorylation of these signalling proteins, but not their level of expression. These inhibitory effects were not due to the interruption of toll-like receptor 4 binding to CD14. In particular, davallialactone strongly inhibited the LPS-induced phosphorylation and kinase activity of Src, implying that Src may be a potential pharmacological target of davallialactone.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that davallialactone, a small molecule found in edible mushrooms, has anti-inflammatory activity. Davallialactone can be developed as a pharmaceutically valuable anti-Src kinase agent.

A functional 14-3-3zeta-independent association of PI3-kinase with glycoprotein Ib alpha, the major ligand-binding subunit of the platelet glycoprotein Ib-IX-V complex

Engagement of the adhesion receptor glycoprotein (GP) Ib-IX-V by von Willebrand factor (VWF) mediates platelet adhesion to damaged vessels and triggers platelet activation and thrombus formation in heart attack and stroke. GPIb-IX-V contains distinct 14-3-3zeta-binding sites at the GPIb alpha C-terminus involving phosphorylation of Ser609, an upstream site involving phosphorylated Ser587/Ser590, and a protein kinase A (PKA)-dependent site on GPIb beta involving Ser166. 14-3-3zeta regulates the VWF-binding affinity of GPIb-IX-V and inhibiting 14-3-3zeta association blocks receptor signaling, suggesting a key functional role for 14-3-3zeta. We used deletion mutants of GPIb alpha expressed in Chinese hamster ovary (CHO) cells to define the relationship of 14-3-3zeta binding to another GPIb-IX-V-associated signaling protein, phosphoinositide 3-kinase (PI3-kinase). Pull-down experiments involving glutathione S-transferase (GST)-PI3-kinase/p85-subunit and GST-14-3-3zeta indicated that both proteins interacted with contiguous GPIb alpha sequences 580 to 590/591 to 610. Deleting these, but not upstream sequences of GPIb alpha expressed in CHO cells, inhibited VWF/ristocetin-dependent Akt phosphorylation, relative to wild-type receptor, confirming this region encompassed a functional PI3-kinase-binding site. Pull-down experiments with GST-p85 truncates indicated the GPIb alpha-binding region involved the p85 breakpoint cluster region (BCR) domain, containing RSXSXP. However, pull-down of GPIb-IX was unaltered by mutation/deletion/phosphorylation of this potential 14-3-3zeta-binding sequence in mutant constructs of GST-p85, suggesting PI3-kinase bound GPIb alpha independently of 14-3-3zeta; 14-3-3zeta inhibitor peptide R18 also blocked pull-down of receptor by GST-14-3-3zeta but not GST-p85, and GST-p85 pull-downs were unaffected by excess 14-3-3zeta. Together, these data suggest the GPIb alpha C-terminus regulates signaling through independent association of 14-3-3zeta and PI3-kinase.

Regulation of c-Met signaling by the tetraspanin KAI-1/CD82 affects cancer cell migration

It has been proposed that the metastasis suppressor CD82/KAI-1, which is a member of the tetraspanin superfamily, regulates biological activity by associating with cell surface receptors or proteins. We show a novel association between CD82 and the hepatocyte growth factor (HGF) receptor c-Met. Although ectopic expression of CD82 in nonsmall cell lung carcinoma cells did not affect the tyrosine phosphorylation of c-Met, these cells showed significant suppression of HGF-induced lamellipodial protrusion and cell migration. CD82 selectively attenuated c-Met signaling via the Ras-Cdc42/Rac and the phosphatidylinositol 3-kinase/Cdc42/Rac pathways. In contrast, another c-Met signaling pathway that involves phosphatidylinositol 3-kinase/Akt and phosphatidylinositol 3-kinase/mitogen activated protein kinase was not affected by CD82. Signaling adapter proteins for c-Met, such as Grb2 and p85, exhibited reduced association with c-Met in cells that ectopically expressed CD82. These results indicate that the CD82-c-Met complex inhibits HGF-induced cancer cell migration by the inactivation of small GTP-binding proteins of the Rho family via c-Met adapter proteins.

A microarray analysis of the emergence of embryonic definitive hematopoiesis

OBJECTIVE

Human embryonic stem (ES) cells provide a unique model for studying the development and function of human tissues and have proven utility in a number of areas. However, results from ES cell-based studies have been limited by the paucity of information available about early human hematopoietic development.

METHODS

To better understand early development of the hematopoietic lineage, we use microarray analysis to examine the temporal patterns of gene expression in embryoid bodies derived from human ES cells, focusing around the time of the emergence of definitive hematopoiesis. We use an empirical Bayes hierarchical modeling approach, called EBarrays, to classify genes into each of the possible temporal patterns of gene expression for five different time points, and correlate those patterns with the emergence of hematopoiesis.

RESULTS

We find a distinct group of genes previously identified as important in adult hematopoietic self-renewal (such as PIK3R1, ABCB1/MDR-1, RGS18, IRS1, SENP6/SUMO-1, and Wnt5A, etc.) temporally correlates with the emergence of the definitive hematopoiesis. Microarray-based results are further supported via flow cytometry and reverse transcription-polymerase chain reaction studies.

CONCLUSION

The novel genes demonstrating the same expression pattern as this group could further facilitate the understanding of the molecular mechanisms of embryonic hematopoiesis.

Mechanism of two classes of cancer mutations in the phosphoinositide 3-kinase catalytic subunit

Many human cancers involve up-regulation of the phosphoinositide 3-kinase PI3Kalpha, with oncogenic mutations identified in both the p110alpha catalytic and the p85alpha regulatory subunits. We used crystallographic and biochemical approaches to gain insight into activating mutations in two noncatalytic p110alpha domains-the adaptor-binding and the helical domains. A structure of the adaptor-binding domain of p110alpha in a complex with the p85alpha inter-Src homology 2 (inter-SH2) domain shows that oncogenic mutations in the adaptor-binding domain are not at the inter-SH2 interface but in a polar surface patch that is a plausible docking site for other domains in the holo p110/p85 complex. We also examined helical domain mutations and found that the Glu545 to Lys545 (E545K) oncogenic mutant disrupts an inhibitory charge-charge interaction with the p85 N-terminal SH2 domain. These studies extend our understanding of the architecture of PI3Ks and provide insight into how two classes of mutations that cause a gain in function can lead to cancer.

The p85alpha regulatory subunit of phosphoinositide 3-kinase potentiates c-Jun N-terminal kinase-mediated insulin resistance

Insulin resistance is a defining feature of type 2 diabetes and the metabolic syndrome. While the molecular mechanisms of insulin resistance are multiple, recent evidence suggests that attenuation of insulin signaling by c-Jun N-terminal kinase (JNK) may be a central part of the pathobiology of insulin resistance. Here we demonstrate that the p85alpha regulatory subunit of phosphoinositide 3-kinase (PI3K), a key mediator of insulin's metabolic actions, is also required for the activation of JNK in states of insulin resistance, including high-fat diet-induced obesity and JNK1 overexpression. The requirement of the p85alpha regulatory subunit for JNK occurs independently of its role as a component of the PI3K heterodimer and occurs only in response to specific stimuli, namely, insulin and tunicamycin, a chemical that induces endoplasmic reticulum stress. We further show that insulin and p85 activate JNK by via cdc42 and MKK4. The activation of this cdc42/JNK pathway requires both an intact N terminus and functional SH2 domains within the C terminus of the p85alpha regulatory subunit. Thus, p85alpha plays a dual role in regulating insulin sensitivity and may mediate cross talk between the PI3K and stress kinase pathways.

Phosphatidylinositol 3-kinase C2alpha is essential for ATP-dependent priming of neurosecretory granule exocytosis

Neurotransmitter release and hormonal secretion are highly regulated processes culminating in the calcium-dependent fusion of secretory vesicles with the plasma membrane. Here, we have identified a role for phosphatidylinositol 3-kinase C2alpha (PI3K-C2alpha) and its main catalytic product, PtdIns3P, in regulated exocytosis. In neuroendocrine cells, PI3K-C2alpha is present on a subpopulation of mature secretory granules. Impairment of PI3K-C2alpha function specifically inhibits the ATP-dependent priming phase of exocytosis. Overexpression of wild-type PI3K-C2alpha enhanced secretion, whereas transfection of PC12 cells with a catalytically inactive PI3K-C2alpha mutant or a 2xFYVE domain sequestering PtdIns3P abolished secretion. Based on these results, we propose that production of PtdIns3P by PI3K-C2alpha is required for acquisition of fusion competence in neurosecretion.

Topographical expression of class IA and class II phosphoinositide 3-kinase enzymes in normal human tissues is consistent with a role in differentiation

Background

Growth factor, cytokine and chemokine-induced activation of PI3K enzymes constitutes the start of a complex signalling cascade, which ultimately mediates cellular activities such as proliferation, differentiation, chemotaxis, survival, trafficking, and glucose homeostasis. The PI3K enzyme family is divided into 3 classes; class I (subdivided into IA and IB), class II (PI3K-C2α, PI3K-C2β and PI3K-C2γ) and class III PI3K. Expression of these enzymes in human tissue has not been clearly defined.

Methods

In this study, we analysed the immunohistochemical topographical expression profile of class IA (anti-p85 adaptor) and class II PI3K (PI3K-C2α and PI3K-C2β) enzymes in 104 formalin-fixed, paraffin embedded normal adult human (age 33–71 years, median 44 years) tissue specimens including those from the gastrointestinal, genitourinary, hepatobiliary, endocrine, integument and lymphoid systems. Antibody specificity was verified by Western blotting of cell lysates and peptide blocking studies. Immunohistochemistry intensity was scored from undetectable to strong.

Results

PI3K enzymes were expressed in selected cell populations of epithelial or mesenchymal origin. Columnar epithelium and transitional epithelia were reactive but mucous secreting and stratified squamous epithelia were not. Mesenchymal elements (smooth muscle and endothelial cells) and glomerular epithelium were only expressed PI3K-C2α while ganglion cells expressed p85 and PI3K-C2β. All three enzymes were detected in macrophages, which served as an internal positive control. None of the three PI3K isozymes was detected in the stem cell/progenitor compartments or in B lymphocyte aggregates.

Conclusions

Taken together, these data suggest that PI3K enzyme distribution is not ubiquitous but expressed selectively in fully differentiated, non-proliferating cells. Identification of the normal in vivo expression pattern of class IA and class II PI3K paves the way for further analyses which will clarify the role played by these enzymes in inflammatory, neoplastic and other human disease conditions.

Impaired B and T cell antigen receptor signaling in p110delta PI 3-kinase mutant mice

Class IA phosphoinositide 3-kinases (PI3Ks) are a family of p85/p110 heterodimeric lipid kinases that generate second messenger signals downstream of tyrosine kinases, thereby controlling cell metabolism, growth, proliferation, differentiation, motility, and survival. Mammals express three class IA catalytic subunits: p110alpha, p110beta, and p110delta. It is unclear to what extent these p110 isoforms have overlapping or distinct biological roles. Mice expressing a catalytically inactive form of p110delta (p110delta(D910A)) were generated by gene targeting. Antigen receptor signaling in B and T cells was impaired and immune responses in vivo were attenuated in p110delta mutant mice. They also developed inflammatory bowel disease. These results reveal a selective role for p110delta in immunity.

Synthesis and function of 3-phosphorylated inositol lipids

The 3-phosphorylated inositol lipids fulfill roles as second messengers by interacting with the lipid binding domains of a variety of cellular proteins. Such interactions can affect the subcellular localization and aggregation of target proteins, and through allosteric effects, their activity. Generation of 3-phosphoinositides has been documented to influence diverse cellular pathways and hence alter a spectrum of fundamental cellular activities. This review is focused on the 3-phosphoinositide lipids, the synthesis of which is acutely triggered by extracellular stimuli, the enzymes responsible for their synthesis and metabolism, and their cell biological roles. Much knowledge has recently been gained through structural insights into the lipid kinases, their interaction with inhibitors, and the way their 3-phosphoinositide products interact with protein targets. This field is now moving toward a genetic dissection of 3-phosphoinositide action in a variety of model organisms. Such approaches will reveal the true role of the 3-phosphoinositides at the organismal level in health and disease.