Characterizing the interactions between the two subunits of the p101/p110gamma phosphoinositide 3-kinase and their role in the activation of this enzyme by G beta gamma subunits

MrgprF acts as a tumor suppressor in cutaneous melanoma by restraining PI3K/Akt signaling

The incidence of cutaneous melanoma (CM) has been increasing annually worldwide. In this study, we identify that MrgprF, a MAS related GPR family member, is decreased in cutaneous melanoma tissues and cell lines due to hypermethylation of its promoter region, and show that patients with CM expressing high levels of MrgprF exhibit an improved clinical outcome. We demonstrate that MrgprF forced expression inhibits tumor cell proliferation, migration, xenograft tumor growth, and metastasis. On the contrary, MrgprF knockdown promotes tumor cell proliferation and transformation of immortalized human keratinocyte-HaCaT cells, supporting the inhibitory role of MrgprF during tumor progression. Mechanistic studies reveal that MrgprF reduces the phosphoinositol‑3‑kinase (PI3K) complex formation between p101 and p110γ subunits, the critical step for phosphatidylinositol-(3, 4)-P2 (PIP2) conversion to phosphatidylinositol-(3, 4, 5)-P3 (PIP3), and then reduces the activation of PI3K/Akt signaling. This effect can be reversed by Akt specific agonist SC79. In addition, AMG 706, a previously documented inhibitor for endothelial cell proliferation, is identified as a potential agonist for MrgprF, and can impede tumor growth both in vitro and in vivo. Taken together, our findings suggest that MrgprF, a novel tumor suppressor in cutaneous melanoma, may be useful as a therapeutic target in the future.

Discovery of novel selective PI3Kγ inhibitors through combining machine learning-based virtual screening with multiple protein structures and bio-evaluation

Introduction

Phosphoinositide 3-kinase gamma (PI3Kγ) has been regarded as a promising drug target for the treatment of various diseases, and the diverse physiological roles of class I PI3K isoforms (α, β, δ, and γ) highlight the importance of isoform selectivity in the development of PI3Kγ inhibitors. However, the high structural conservation among the PI3K family makes it a big challenge to develop selective PI3Kγ inhibitors.

Objectives

A novel machine learning-based virtual screening with multiple PI3Kγ protein structures was developed to discover novel PI3Kγ inhibitors.

Methods

A large chemical database was screened using the virtual screening model, the top-ranked compounds were then subjected to a series of bio-evaluations, which led to the discovery of JN-KI3. The selective inhibition mechanism of JN-KI3 against PI3Kγ was uncovered by a theoretical study.

Results

49 hits were identified through virtual screening, and the cell-free enzymatic studies found that JN-KI3 selectively inhibited PI3Kγ at a concentration as low as 3,873 nM but had no inhibitory effect on Class IA PI3Ks, leading to the selective cytotoxicity on hematologic cancer cells. Meanwhile, JN-KI3 potently blocked the PI3K signaling, finally led to distinct apoptosis of hematologic cell lines at a low concentration. Lastly, the key residues of PI3Kγ and the structural characteristics of JN-KI3, which both would influence γ isoform-selective inhibition, were highlighted by systematic theoretical studies.

Conclusion

The developed virtual screening model strongly manifests the robustness to find novel PI3Kγ inhibitors. JN-KI3 displays a specific cytotoxicity on hematologic tumor cells, and significantly promotes apoptosis associated with the inhibition of the PI3K signaling, which depicts PI3Kγ as a potential target for the hematologic tumor therapy. The theoretical results reveal that those key residues interacting with JN-KI3 are less common compared to most of the reported PI3Kγ inhibitors, indicating that JN-KI3 has novel structural characteristics as a selective PIK3γ inhibitor.

PI3K Isoform Signalling in Platelets

Platelets are unique anucleated blood cells that constantly patrol the vasculature to seal and prevent injuries in a process termed haemostasis. Thereby they rapidly adhere to the subendothelial matrix and recruit further platelets, resulting in platelet aggregates. Apart from their central role in haemostasis, they also kept some of their features inherited by their evolutionary ancestor-the haemocyte, which was also involved in immune defences. Together with leukocytes, platelets fight pathogenic invaders and guide many immune processes. In addition, they rely on several signalling pathways which are also relevant to immune cells. Among these, one of the central signalling hubs is the PI3K pathway. Signalling processes in platelets are unique as they lack a nucleus and therefore transcriptional regulation is absent. As a result, PI3K subclasses fulfil distinct roles in platelets compared to other cells. In contrast to leukocytes, the central PI3K subclass in platelet signalling is PI3K class Iβ, which underlines the uniqueness of this cell type and opens new ways for potential platelet-specific pharmacologic inhibition. An overview of platelet function and signalling with emphasis on PI3K subclasses and their respective inhibitors is given in this chapter.

Targeting phosphatidylinositol 3-kinase gamma (PI3Kγ): Discovery and development of its selective inhibitors

Phosphatidylinositol 3-kinase gamma (PI3Kγ) has been regarded as a promising drug target for the treatment of advanced solid tumors, leukemia, lymphoma, and inflammatory and autoimmune diseases. However, the high level of structural conservation among the members of the PI3K family and the diverse physiological roles of Class I PI3K isoforms (α, β, δ, and γ) highlight the importance of isoform selectivity in the development of PI3Kγ inhibitors. In this review, we provide an overview of the structural features of PI3Kγ that influence γ-isoform selectivity and discuss the structure-selectivity-activity relationship of existing clinical PI3Kγ inhibitors. Additionally, we summarize the experimental and computational techniques utilized to identify PI3Kγ inhibitors. The insights gained so far could be used to overcome the main challenges in development and accelerate the discovery of PI3Kγ-selective inhibitors.

The prognostic value of PI3K mutational status in breast cancer: A meta-analysis

Breast cancer (BC) is the second most common cause of cancer-related deaths in women worldwide. The availability of reliable biomarkers of response/resistance to cancer treatments would benefit patients and clinicians allowing for a better selection of BC patients most likely to respond to a specific treatment. Phosphatidylinositol 3-kinase (PI3K) enzymes are involved in numerous cellular- functions and processes. The gene encoding for PI3K catalytic subunit p110α is mutated in 20-40% of BC. We performed a meta-analysis of the current literature on randomized clinical trials, investigating the role of PIK3CA mutational status as prognostic factor, and predictor of response to anti-cancer treatments. Overall 1929 cases were included. The pooled analysis confirmed that the presence of a PIK3CA mutation represents an independent negative prognostic factor (HR = 1.67, 95%CI: 1.15-2.43; P = 0.007) in BC, as previously reported. As PI3K signaling is also a result of other pathways' hyperactivation, further investigation of potential biomarkers able to predict likelihood of response to anti-PI3K/mTOR, anti-HER2, and other TKRs is warranted in future randomized clinical trials.

Modeling of RAS complexes supports roles in cancer for less studied partners

Background

RAS protein interactions have predominantly been studied in the context of the RAF and PI3kinase oncogenic pathways. Structural modeling and X-ray crystallography have demonstrated that RAS isoforms bind to canonical downstream effector proteins in these pathways using the highly conserved switch I and II regions. Other non-canonical RAS protein interactions have been experimentally identified, however it is not clear whether these proteins also interact with RAS via the switch regions.

Results

To address this question we constructed a RAS isoform-specific protein-protein interaction network and predicted 3D complexes involving RAS isoforms and interaction partners to identify the most probable interaction interfaces. The resulting models correctly captured the binding interfaces for well-studied effectors, and additionally implicated residues in the allosteric and hyper-variable regions of RAS proteins as the predominant binding site for non-canonical effectors. Several partners binding to this new interface (SRC, LGALS1, RABGEF1, CALM and RARRES3) have been implicated as important regulators of oncogenic RAS signaling. We further used these models to investigate competitive binding and multi-protein complexes compatible with RAS surface occupancy and the putative effects of somatic mutations on RAS protein interactions.

Conclusions

We discuss our findings in the context of RAS localization to the plasma membrane versus within the cytoplasm and provide a list of RAS protein interactions with possible cancer-related consequences, which could help guide future therapeutic strategies to target RAS proteins.

Electronic supplementary material

The online version of this article (doi:10.1186/s13628-017-0037-6) contains supplementary material, which is available to authorized users.

Characterization and mechanism of phosphoinositide 3-kinases (PI3Ks) members in insulin-induced changes of protein metabolism in yellow catfish Pelteobagrus fulvidraco

In the present study, seven phosphoinositide 3-kinase (PI3K) members (PI3KCa, PI3KCb, PI3KCd, PI3KCg, PI3KC2a, PI3KC2b and PI3KC3, respectively) were isolated and characterized from yellow catfish Pelteobagrus fulvidraco, and their roles in insulin-induced changes of protein metabolism were determined. These seven PI3Ks can be divided into three classes, class I (including PI3KCa, PI3KCb, PI3KCd and PI3KCg), class II (including PI3KC2a and PI3KC2b) and class III (only including PI3KC3). Compared with mammals, all of these members share similar domain structure. Their mRNAs were widely expressed across ten tested tissues (liver, white muscle, spleen, brain, gill, mesenteric fat, intestine, heart, kidney and ovary), but at variable levels. In the in vivo study, insulin treatment significantly increased hepatic protein content at 3h, accompanied with reduced plasma total amino acid contents and liver ALT activity, and with increased total RNA content and the mRNA levels of PI3KCb, PI3KC2a, AKT2, mTORC1 and S6K1 in liver. At 6h and 12h, insulin injection showed no significant effect on liver protein content and plasma total amino acid, but reduced liver ALT activity and increased liver total RNA and the mRNA levels of AKT2, mTORC1 and S6K1 in liver at 6h. In the in vitro study, insulin incubation also tended to increase protein content of hepatocytes, accompanied with reduced cell medium total amino acid contents and hepatocytes ALT activity, and increased total RNA content and the mRNA levels of PI3KCb, PI3KC2a, AKT2, mTORC1 and S6K1 in hepatocytes. However, insulin treatment showed no significant effect on GDH activity and mRNA expression of PI3KCa, PI3KCd, PI3KCg, PI3KC2b, PI3KC3 and eEF2 both in the in vivo and in vitro studies. Effects of insulin on the mRNA levels of eIF-4E and 4E-BP1 were different between the in vivo and in vitro studies, and also time-dependent. Compared to single insulin group, insulin+wortmannin group increased ALT activity at 6h but reduced T-RNA content at 6 and 12h. AKT2 and S6K1 mRNA levels at 6 and 12h, mRNA levels of mTORC1, 4E-BP1 and eEF2 at 3 and 6h, and EIF-4E mRNA levels at 3 and 12h, PI3KCb and PI3KC2a mRNA levels were significantly lower in insulin+wortmannin group than those in single insulin group. Thus, our study demonstrated that among seven PI3K members, PI3KCb and PI3KC2a were more sensitive to the insulin signaling pathway, and insulin stimulated hepatic protein synthesis in yellow catfish through PI3K signaling pathway.

Focus on PTEN Regulation

The role of phosphatase and tensin homolog on chromosome 10 (PTEN) as a tumor suppressor has been for a long time attributed to its lipid phosphatase activity against PI(3,4,5)P₃, the phospholipid product of the class I PI3Ks. Besides its traditional role as a lipid phosphatase at the plasma membrane, a wealth of data has shown that PTEN can function independently of its phosphatase activity and that PTEN also exists and plays a role in the nucleus, in cytoplasmic organelles, and extracellularly. Accumulating evidence has shed light on diverse physiological functions of PTEN, which are accompanied by a complex regulation of its expression and activity. PTEN levels and function are regulated transcriptionally, post-transcriptionally, and post-translationally. PTEN is also sensitive to regulation by its interacting proteins and its localization. Herein, we summarize the current knowledge on mechanisms that regulate the expression and enzymatic activity of PTEN and its role in human diseases.

The Potential of Vitamin D-Regulated Intracellular Signaling Pathways as Targets for Myeloid Leukemia Therapy

The current standard regimens for the treatment of acute myeloid leukemia (AML) are curative in less than half of patients; therefore, there is a great need for innovative new approaches to this problem. One approach is to target new treatments to the pathways that are instrumental to cell growth and survival with drugs that are less harmful to normal cells than to neoplastic cells. In this review, we focus on the MAPK family of signaling pathways and those that are known to, or potentially can, interact with MAPKs, such as PI3K/AKT/FOXO and JAK/STAT. We exemplify the recent studies in this field with specific relevance to vitamin D and its derivatives, since they have featured prominently in recent scientific literature as having anti-cancer properties. Since microRNAs also are known to be regulated by activated vitamin D, this is also briefly discussed here, as are the implications of the emerging acquisition of transcriptosome data and potentiation of the biological effects of vitamin D by other compounds. While there are ongoing clinical trials of various compounds that affect signaling pathways, more studies are needed to establish the clinical utility of vitamin D in the treatment of cancer.

Targeting the phosphoinositide 3-kinase pathway in hematologic malignancies

The phosphoinositide 3-kinase pathway represents an important anticancer target because it has been implicated in cancer cell growth, survival, and motility. Recent studies show that PI3K may also play a role in the development of resistance to currently available therapies. In a broad range of cancers, various components of the phosphoinositide 3-kinase signaling axis are genetically modified, and the pathway can be activated through many different mechanisms. The frequency of genetic alterations in the phosphoinositide 3-kinase pathway, coupled with the impact in oncogenesis and disease progression, make this signaling axis an attractive target in anticancer therapy. A better understanding of the critical function of the phosphoinositide 3-kinase pathway in leukemias and lymphomas has led to the clinical evaluation of novel rationally designed inhibitors in this setting. Three main categories of phosphoinositide 3-kinase inhibitors have been developed so far: agents that target phosphoinositide 3-kinase and mammalian target of rapamycin (dual inhibitors), pan-phosphoinositide 3-kinase inhibitors that target all class I isoforms, and isoform-specific inhibitors that selectively target the α, -β, -γ, or -δ isoforms. Emerging data highlight the promise of phosphoinositide 3-kinase inhibitors in combination with other therapies for the treatment of patients with hematologic malignancies. Further evaluation of phosphoinositide 3-kinase inhibitors in first-line or subsequent regimens may improve clinical outcomes. This article reviews the role of phosphoinositide 3-kinase signaling in hematologic malignancies and the potential clinical utility of inhibitors that target this pathway.

Molecular determinants of PI3Kγ-mediated activation downstream of G-protein-coupled receptors (GPCRs)

Phosphoinositide 3-kinase gamma (PI3Kγ) has profound roles downstream of G-protein-coupled receptors in inflammation, cardiac function, and tumor progression. To gain insight into how the enzyme's activity is shaped by association with its p101 adaptor subunit, lipid membranes, and Gβγ heterodimers, we mapped these regulatory interactions using hydrogen-deuterium exchange mass spectrometry. We identify residues in both the p110γ and p101 subunits that contribute critical interactions with Gβγ heterodimers, leading to PI3Kγ activation. Mutating Gβγ-interaction sites of either p110γ or p101 ablates G-protein-coupled receptor-mediated signaling to p110γ/p101 in cells and severely affects chemotaxis and cell transformation induced by PI3Kγ overexpression. Hydrogen-deuterium exchange mass spectrometry shows that association with the p101 regulatory subunit causes substantial protection of the RBD-C2 linker as well as the helical domain of p110γ. Lipid interaction massively exposes that same helical site, which is then stabilized by Gβγ. Membrane-elicited conformational change of the helical domain could help prepare the enzyme for Gβγ binding. Our studies and others identify the helical domain of the class I PI3Ks as a hub for diverse regulatory interactions that include the p101, p87 (also known as p84), and p85 adaptor subunits; Rab5 and Gβγ heterodimers; and the β-adrenergic receptor kinase.

BST-2/tetherin is overexpressed in mammary gland and tumor tissues in MMTV-induced mammary cancer

BST-2 restricts MMTV replication, but once infection has established, MMTV modulates BST-2 levels. MMTV-directed BST-2 modulation is tissue-specific and dependent on infection and neoplastic transformation status of cells. In the lymphoid compartment of infected mice, BST-2 expression is first upregulated and then significantly downregulated regardless of absence or presence of mammary tumors. However, in mammary gland tissues, upregulation of BST-2 expression is dependent on the presence of mammary tumors and tumor tissues themselves have high BST-2 levels. Elevated BST-2 expression in these tissues is not attributable to IFN since levels of IFNα and IFNγ negatively correlate with BST-2. Importantly, soluble factors released by tumor cells suppress IFNα and IFNγ but induce BST-2. These data suggest that overexpression of BST-2 in carcinoma tissues could not be attributed to IFNs but to a yet to be determined factor that upregulates BST-2 once oncogenesis is initiated.

PKCβ phosphorylates PI3Kγ to activate it and release it from GPCR control

All class I phosphoinositide 3-kinases (PI3Ks) associate tightly with regulatory subunits through interactions that have been thought to be constitutive. PI3Kγ is key to the regulation of immune cell responses activated by G protein-coupled receptors (GPCRs). Remarkably we find that PKCβ phosphorylates Ser582 in the helical domain of the PI3Kγ catalytic subunit p110γ in response to clustering of the high-affinity IgE receptor (FcεRI) and/or store-operated Ca²⁺- influx in mast cells. Phosphorylation of p110γ correlates with the release of the p84 PI3Kγ adapter subunit from the p84-p110γ complex. Ser582 phospho-mimicking mutants show increased p110γ activity and a reduced binding to the p84 adapter subunit. As functional p84-p110γ is key to GPCR-mediated p110γ signaling, this suggests that PKCβ-mediated p110γ phosphorylation disconnects PI3Kγ from its canonical inputs from trimeric G proteins, and enables p110γ to operate downstream of Ca²⁺ and PKCβ. Hydrogen deuterium exchange mass spectrometry shows that the p84 adaptor subunit interacts with the p110γ helical domain, and reveals an unexpected mechanism of PI3Kγ regulation. Our data show that the interaction of p110γ with its adapter subunit is vulnerable to phosphorylation, and outline a novel level of PI3K control.

p110δ PI3 kinase pathway: emerging roles in cancer

Class IA PI3Ks consists of three isoforms of the p110 catalytic subunit designated p110α, p110β, and p110δ which are encoded by three separate genes. Gain-of-function mutations on PIK3CA gene encoding for p110α isoform have been detected in a wide variety of human cancers whereas no somatic mutations of genes encoding for p110β or p110δ have been reported. Unlike p110α and p110β which are ubiquitously expressed, p110δ is highly enriched in leukocytes and thus the p110δ PI3K pathway has attracted more attention for its involvement in immune disorders. However, findings have been accumulated showing that the p110δ PI3K plays a seminal role in the development and progression of some hematologic malignancies. A wealth of knowledge has come from studies showing the central role of p110δ PI3K in B-cell functions and B-cell malignancies. Further data have documented that wild-type p110δ becomes oncogenic when overexpressed in cell culture models and that p110δ is the predominant isoform expressed in some human solid tumor cells playing a prominent role in these cells. Genetic inactivation of p110δ in mice models and highly-selective inhibitors of p110δ have demonstrated an important role of this isoform in differentiation, growth, survival, motility, and morphology with the inositol phosphatase PTEN to play a critical role in p110δ signaling. In this review, we summarize our understanding of the p110δ PI3K signaling pathway in hematopoietic cells and malignancies, we highlight the evidence showing the oncogenic potential of p110δ in cells of non-hematopoietic origin and we discuss perspectives for potential novel roles of p110δ PI3K in cancer.

The determinants of head and neck cancer: Unmasking the PI3K pathway mutations

Studies attempting to identify and understand the function of mutated genes and deregulated molecular pathways in cancer have been ongoing for many years. The PI3K-PTEN-mTOR signaling pathway is one of the most frequently deregulated pathways in cancer. PIK3CA mutations are found 11%-33% of head and neck cancer (HNC). The hotspot mutation sites for PIK3CA are E542K, E545K and H1047R/L. The PTEN somatic mutations are in 9-23% of HNC, and they frequently cluster in the phosphatase domain of PTEN protein. PTEN loss of heterozygosity (LOH) ranges from 41%-71% and loss of PTEN protein expression occurs in 31.2% of the HNC samples. PIK3CA and PTEN are key molecules in the PI3K-PTEN-mTOR signaling pathway. In this review, we provided a comprehensive overview of mutations in the PI3K-PTEN-mTOR molecular circuitry in HNC, including PI3K family members, TSC1/TSC2, PTEN, AKT, and mTORC1 and mTORC2 complexes. We discussed how these genetic alterations may affect protein structure and function. We also highlight the latest discoveries in protein kinase and tumor suppressor families, emphasizing how mutations in these families interfere with PI3K signaling. A better understanding of the mechanisms underlying cancer formation, progression and resistance to therapy will inform selection of novel genomic-based personalized therapies for head and neck cancer patients.

PI3Ks-drug targets in inflammation and cancer

Phosphoinositide 3-kinases (PI3Ks) control cell growth, proliferation, cell survival, metabolic activity, vesicular trafficking, degranulation, and migration. Through these processes, PI3Ks modulate vital physiology. When over-activated in disease, PI3K promotes tumor growth, angiogenesis, metastasis or excessive immune cell activation in inflammation, allergy and autoimmunity. This chapter will introduce molecular activation and signaling of PI3Ks, and connections to target of rapamycin (TOR) and PI3K-related protein kinases (PIKKs). The focus will be on class I PI3Ks, and extend into current developments to exploit mechanistic knowledge for therapy.

The role of PI3K/protein kinase B (PKB/c-akt) in migration and homing of hematopoietic stem and progenitor cells

PURPOSE OF REVIEW

Hematopoietic stem cell (HSC) transplantation is the most powerful treatment modality for a variety of hematological disorders. Successful hematopoietic recovery after transplantation depends on optimal homing of HSCs to the bone marrow and subsequent lodging in the HSC niche. The molecular mechanisms underlying bone marrow homing are, thus far, incompletely understood. This review focuses on recent studies that extended our understanding of how the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (PKB/c-akt) signaling module can regulate migration and homing of HSCs.

RECENT FINDINGS

In addition to regulation of HSC maintenance and lineage development, it has recently become apparent that the PI3K/PKB signaling module plays a critical role in regulation of migration and adhesion of hematopoietic stem and progenitor cells. Activation of this signaling pathway enhances firm adhesion, reduces migration and inhibits bone marrow homing, whereas inhibition of PKB conversely induces bone marrow homing.

SUMMARY

These findings clearly implicate the PI3K/PKB signaling module in playing a critical role in regulation of bone marrow homing, suggesting that pharmacological modulation of this signaling molecule prior to transplantation may provide a clinical means of improving engraftment levels and accelerating hematopoietic recovery.

Differential roles for the p101 and p84 regulatory subunits of PI3Kγ in tumor growth and metastasis

Phosphoinositide 3-kinase γ (PI3Kγ) consists of a catalytic subunit p110γ, which forms mutually exclusive dimers with one of the regulatory subunits called p101 and p84/p87(PIKAP). Recently, PI3Kγ emerged as being a potential oncogene because overexpression of the catalytic subunit p110γ or the regulatory subunit p101 leads to oncogenic cellular transformation and malignancy. However, the contribution of the individual subunits to tumor growth and metastasis and the mechanisms involved are not understood. We therefore individually knocked down the PI3Kγ subunits (p84, p101 and p110γ) in MDA-MB-231 cells, which reduced in vitro migration of the cell lines. Knockdown of p110γ or p101 inhibited apoptosis, Akt phosphorylation and lung colonization in SCID mice. Similarly, the knockdown of p110γ and p101 in murine epithelial carcinoma 4T1.2 cells inhibited primary tumor growth and spontaneous metastasis, as well as lung colonization. In contrast, knockdown of p84 in MDA-MB-231 cells enhanced Akt phosphorylation and lung colonization. These findings are the first to implicate differential functions of the two PI3Kγ regulatory subunits in the process of oncogenesis, and indicate that loss of p101 is sufficient to reduce in vivo tumor growth and metastasis to the same extent as that of p110γ.

Relaxin induces rapid dilation of rodent small renal and human subcutaneous arteries via PI3 kinase and nitric oxide

The peptide hormone relaxin is a potent vasodilator with therapeutic potential in diseases complicated by vasoconstriction, including heart failure. However, the molecular mediators and magnitude of vasodilation may vary according to duration of exposure and artery type. The objective of these studies was to determine mechanisms of rapid (within minutes) relaxin-induced vasodilation and to examine whether relaxin dilates arteries from different animal species and vascular beds. Rat and mouse small renal, rat mesenteric, and human sc arteries were isolated, mounted in a pressure arteriograph, and treated with recombinant human relaxin (rhRLX; 1-100 ng/ml) after preconstriction with phenylephrine. Rat and mouse small renal as well as human sc arteries dilated in response to rhRLX, whereas rat mesenteric arteries did not. Endothelial removal or pretreatment with l-N(G)-monomethyl arginine (L-NMMA) abolished rapid relaxin-induced vasodilation; phosphatidylinositol-3-kinase (PI3K) inhibitors also prevented it. In cultured human endothelial cells, rhRLX stimulated nitric oxide (assessed using 4-amino-5-methylamino-2'7'-difluorofluorescein) as well as Akt and endothelial NO synthase (eNOS) phosphorylation by Western blotting but not increases in intracellular calcium (evaluated by fura-2). NO production was attenuated by inhibition of Gα(i/o) and Akt (using pertussis toxin and the allosteric inhibitor MK-2206, respectively), PI3K, and NOS. Finally, the dilatory effect of rhRLX in rat small renal arteries was unexpectedly potentiated, rather than inhibited, by pretreatment with the vascular endothelial growth factor receptor inhibitor SU5416. We conclude that relaxin rapidly dilates select arteries across a range of species. The mechanism appears to involve endothelial Gα(i/o) protein coupling to PI3K, Akt, and eNOS but not vascular endothelial growth factor receptor transactivation or increased calcium.

Regulation of p110delta PI 3-kinase gene expression

BACKGROUND

Despite an intense interest in the biological functions of the phosphoinositide 3-kinase (PI3K) signalling enzymes, little is known about the regulation of PI3K gene expression. This also applies to the leukocyte-enriched p110delta catalytic subunit of PI3K, an enzyme that has attracted widespread interest because of its role in immunity and allergy.

PRINCIPAL FINDINGS

We show that p110delta expression is mainly regulated at the transcriptional level. In fibroblasts, lymphocytes and myeloid cells, p110delta gene transcription appears to be constitutive and not subject to acute stimulation. 5'RACE experiments revealed that p110delta mRNA transcripts contain distinct upstream untranslated exons (named exon -1, -2a, -2b, -2c and -2d), which are located up to 81 kb upstream of the translational start codon in exon 1. The levels of all the different p110delta transcripts are higher in leukocytes compared to non-leukocytes, with the p110delta transcript containing exon -2a most abundantly expressed. We have identified a highly conserved transcription factor (TF) binding cluster in the p110delta gene which has enhanced promoter activity in leukocytes compared to non-leukocytes. In human, this TF cluster is located immediately upstream of exon -2a whilst in mouse, it is located within exon -2a.

CONCLUSION

This study identifies a conserved PIK3CD promoter region that may account for the predominant leukocyte expression of p110delta.

Endosomal colocalization of melanocortin-3 receptor and beta-arrestins in CAD cells with altered modification of AKT/PKB

The melanocortin 3-receptor is involved in regulating energy metabolism, body fluid composition and inflammatory responses. Melanocortin receptors function by activating membrane bound adenylate cyclase. However, the literature reports indicate that some G protein coupled receptors (GPCRs) can also activate mitogen activated protein kinase (MAPK) or phosphoinositide 3 kinase (PI3K) signaling pathways consequent to their endocytosis. These studies were undertaken to evaluate the role of these pathways in MC3R signaling in brain-stem neuronal cells. Recruitment of arrestins is implicated in the activation of secondary pathways by GPCRs and our data shows the colocalization of either arrestin B1 or B2 with MC3R in endosomes. An alteration in PKB phosphorylation pattern was observed in MC3R expressing cells independent of agonist stimulation. MC3R transfectants exhibited increased proliferation rates and inhibition of PKB pathway with triciribine abrogated cell proliferation in both vector control and MC3R transfectants. PKB is constitutively active in proliferating CAD cells but could be further activated by culturing the cells in differentiation medium. These studies suggest that the AKT/PKB pathway plays an important role in the proliferation of CAD cells and suggest a link between MC3R and cell growth pathways that may involve the alteration of AKT/PKB signaling pathway.

PI3Kgamma inhibition: towards an 'aspirin of the 21st century'?

Class IB phosphatidylinositol 3-kinase p110gamma (PI3Kgamma) has gained increasing attention as a promising drug target for the treatment of inflammatory disease. Extensive target-validation data are available, which are derived from studies using both pharmacological and genetic tools. More recent findings have uncovered further therapeutic applications for PI3Kgamma inhibitors, opening up potentially huge opportunities for these drugs. Several companies have been pursuing small-molecule PI3Kgamma inhibitor projects, but none of them has progressed to the clinic yet. Here, we discuss the insights gained so far and the main challenges that are emerging on the path to developing PI3Kgamma inhibitors for the treatment of human disease.

Action mechanisms and structure-activity relationships of PI3Kgamma inhibitors on the enzyme: a molecular modeling study

Action mechanisms of four types of PI3Kgamma inhibitors were investigated on the ligand-binding pocket (LBP) of PI3Kgamma with molecular modeling method. At first five compounds whose complex structures with PI3Kgamma were available experimentally were used to validate the reliability of docking program Autodock3.0. The results demonstrated that the program could reproduce the bound conformations of those compounds in crystal structures. Then the program was used to dock all the four types of PI3Kgamma inhibitors into the LBP of the enzyme. The predicted activities of these compounds were in agreement with their experimental activities, and a pharmacophore model was hence derived for these compounds, which consisted of one hydrophobic portion flanked by two symmetric hydrophilic portions. Furthermore, the structure-activity relationships of PI3Kgamma inhibitors were elucidated and the activity differences between them were discussed.

Targeting the signaling pathway of acylation stimulating protein

Acylation stimulating protein (ASP; C3adesArg) stimulates triglyceride synthesis (TGS) and glucose transport in preadipocytes/adipocytes through C5L2, a G-protein-coupled receptor. Here, ASP signaling is compared with insulin in 3T3-L1 cells. ASP stimulation is not Galpha(s) or Galpha(i) mediated (pertussis and cholera toxin insensitive), suggesting G(alphaq) as a candidate. Phospholipase C (PLC) is required, because the Ca(2+) chelator 1,2-bis(o-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester and the PLC inhibitor U73122 decreased ASP stimulation of TGS by 93.1% (P < 0.0.001) and 86.1% (P < 0.004), respectively. Wortmannin and LY294002 blocked ASP effect by 69% (P < 0.001) and 116.1% (P < 0.003), respectively, supporting phosphatidylinositol 3-kinase (PI3K) involvement. ASP induced rapid, transient Akt phosphorylation (maximal, 5 min; basal, 45 min), which was blocked by Akt inhibition, resembling treatment by insulin. Downstream of PI3K, mamalian target of rapaycin (mTOR) is required for insulin but not ASP action. By contrast, both ASP and insulin activate the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK(1/2)) pathway, with rapid, pronounced increases in ERK(1/2) phosphorylation, effects partially blocked by PD98059 (64.7% and 65.9% inhibition, respectively; P < 0.001). Time-dependent (maximal, 30 min) transient calcium-dependent phospholipase A(2) (cPLA(2))(-Ser505) phosphorylation (by MAPK/ERK(1/2)) was demonstrated by Western blot analysis. ASP signaling involves sequential activation of PI3K and PLC, with downstream activation of protein kinase C, Akt, MAPK/ERK(1/2), and cPLA(2), all of which leads to an effective and prolonged stimulation of TGS.

BCR-ABL Regulates Phosphatidylinositol 3-Kinase-p110γ Transcription and Activation and Is Required for Proliferation and Drug Resistance

The BCR-ABL oncogene is the hallmark of chronic myeloid leukemia, a clonal hematopoietic stem cell disorder. BCR-ABL displays constitutive tyrosine kinase activity, required for its transformation ability. Although the molecular mechanisms behind this malignancy are not fully understood, a role for phosphatidylinositol (PI) 3-kinase has been repeatedly described. Here we report the specific up-regulation of the class I(B) catalytic subunit of PI 3-kinase (p110gamma) in response to BCR-ABL expression. We demonstrate that this upregulation is due to increased transcription and is dependent on both PI 3-kinase and MEK activity. We performed in vitro kinase activity assays and show that BCR-ABL also leads to increased p110gamma activity and that this activation requires both G protein-coupled receptor and Ras signaling. In addition, by transfection of cells with dominant negative p110gamma, we determined that this specific PI 3-kinase isoform is involved in both proliferation and the apoptosis resistance associated with chronic myeloid leukemia. The data presented here define for the first time the ability of BCR-ABL to alter the expression levels of PI 3-kinase isoforms and also demonstrate a previously unreported link between BCR-ABL and p110gamma.

Leukocytes on the move with phosphoinositide 3-kinase and its downstream effectors

Cell signalling mediators derived from membrane phospholipids are frequent participants in biological processes. The family of phosphoinositide 3-kinases (PI3Ks) phosphorylate the membrane lipid phosphatidylinositol, generating second messengers that direct diverse responses. These PI3K products are fundamental for leukocyte migration or chemotaxis, a pivotal event during the immune response. This system is therefore of significant biomedical interest. This review focuses on the biochemistry and signalling pathways of PI3K, with particular emphasis on chemokine (chemotactic cytokine)-directed responses. The key objectives of chemotaxis are motility and direction. The latter--direction--requires distinct events at the front and back of a cell. In light of this, the coordinated localisation of signalling factors, an event choreographed by a sharp intracellular gradient of PI3K-derived products, is a common theme.

p84, a New Gβγ-Activated Regulatory Subunit of the Type IB Phosphoinositide 3-Kinase p110γ

A variety of genetic and inhibitor studies have shown that phosphoinositide 3-kinase gamma (PI3Kgamma) plays an essential role in a number of physiological responses, including neutrophil chemotaxis, mast cell degranulation, and cardiac function []. PI3Kgamma is currently thought to be composed of a p110gamma catalytic subunit and a single regulatory subunit, p101. The binding of p110gamma to p101 dramatically increases the activation of the complex by Gbetagamma subunits and, hence, is thought to be critical for the coupling of PI3Kgamma to G protein coupled receptors []. Here, we characterize a new regulatory subunit for PI3Kgamma. p84 is present in human, mouse, chicken, frog, and fugu genomes and is located beside the p101 locus. It is broadly expressed in cells of the murine immune system. Both recombinant and endogenous p84 bind p110gamma specifically and with high affinity. Binding of p84 to p110gamma substantially increases the ability of Gbetagamma to stimulate phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P(3)) production both in vitro and in vivo. However, the p84/p110gamma heterodimer is approximately 4-fold less sensitive to Gbetagammas than p101/p110gamma. Endogenous murine p84 expression is substantially reduced in the absence of p110gamma expression. We conclude that p110gamma has two potential regulatory subunits in vivo, p84 and p101.

Assigning functional domains within the p101 regulatory subunit of phosphoinositide 3-kinase gamma

Phosphoinositide 3-Kinase (PI3K) gamma is a lipid kinase that is regulated by G-protein-coupled receptors. It plays a crucial role in inflammatory and allergic processes. Activation of PI3Kgamma is primarily mediated by Gbetagamma subunits. The regulatory p101 subunit of PI3Kgamma binds to Gbetagamma and, thereby, recruits the catalytic p110gamma subunit to the plasma membrane. Despite its crucial role in the activation of PI3Kgamma, the structural organization of p101 is still largely elusive. Employing fluorescence resonance energy transfer measurements, coimmunoprecipitation and colocalization studies with p101 deletion mutants, we show here that distinct regions within the p101 primary structure are responsible for interaction with p110gamma and Gbetagamma. The p110gamma binding site is confined to the N terminus, whereas binding to Gbetagamma is mediated by a C-terminal domain of p101. These domains appear to be highly conserved among various species ranging from Xenopus to men. In addition to establishing a domain structure for p101, our results point to the existence of a previously unknown, p101-related regulatory subunit for PI3Kgamma.

Regulation of P-Rex1 by phosphatidylinositol (3,4,5)-trisphosphate and Gbetagamma subunits

P-Rex1 is a guanine-nucleotide exchange factor (GEF) for the small GTPase Rac. We have investigated here the mechanisms of stimulation of P-Rex1 Rac-GEF activity by the lipid second messenger phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3) and the Gbetagamma subunits of heterotrimeric G proteins. We show that a P-Rex1 mutant lacking the PH domain (DeltaPH) cannot be stimulated by PtdIns(3,4,5)P3, which implies that the PH domain confers PtdIns(3,4,5)P3 regulation of P-Rex1 Rac-GEF activity. Consistent with this, we found that PtdIns(3,4,5)P3 binds to the PH domain of P-Rex1 and that the DH/PH domain tandem is sufficient for PtdIns(3,4,5)P3-stimulated P-Rex1 activity. The Rac-GEF activities of the DeltaPH mutant and the DH/PH domain tandem can both be stimulated by Gbetagamma subunits, which infers that Gbetagamma subunits regulate P-Rex1 activity by binding to the catalytic DH domain. Deletion of the DEP, PDZ, or inositol polyphosphate 4-phosphatase homology domains has no major consequences on the abilities of either PtdIns(3,4,5)P3 or Gbetagamma subunits to stimulate P-Rex1 Rac-GEF activity. However, the presence of any of these domains impacts on the levels of basal and/or stimulated P-Rex1 Rac-GEF activity, suggesting that there are important functional interactions between the DH/PH domain tandem and the DEP, PDZ, and inositol polyphosphate 4-phosphatase homology domains of P-Rex1.

ARAP3 is a PI3K- and rap-regulated GAP for RhoA

Rho and Arf family small GTPases are well-known regulators of cellular actin dynamics. We recently identified ARAP3, a member of the ARAP family of dual GTPase activating proteins (GAPs) for Arf and Rho family GTPases, in a screen for PtdIns(3,4,5)P(3) binding proteins. PtdIns(3,4,5)P(3) is the lipid product of class I phosphoinositide 3OH-kinases (PI3Ks) and is a signaling molecule used by growth factor receptors and integrins in the regulation of cell dynamics. We report here that as a Rho GAP, ARAP3 prefers RhoA as a substrate and that it can be activated in vitro by the direct binding of Rap proteins to a neighbouring Ras binding domain (RBD). This activation by Rap is GTP dependent and specific for Rap versus other Ras family members. We found no evidence for direct regulation of ARAP3's Rho GAP activity by PtdIns(3,4,5)P(3) in vitro, but PI3K activity was required for activation by Rap in a cellular context, suggesting that PtdIns(3,4,5)P(3)-dependent translocation of ARAP3 to the plasma membrane may be required for further activation by Rap. Our results indicate that ARAP3 is a Rap-effector that plays an important role in mediating PI3K-dependent crosstalk between Ras, Rho, and Arf family small GTPases.

A versatile high-throughput screen for inhibitors of lipid kinase activity: development of an immobilized phospholipid plate assay for phosphoinositide 3-kinase gamma

The family of phosphoinositide 3-kinases (PI3K) regulates fundamental cellular responses such as proliferation, apoptosis, motility, and adhesion. In particular, the PI3K gamma isoform plays a critical role in the control of cell migration. Despite the attractiveness of PI3-kinases as drug targets, drug discovery efforts have been hampered by the lack of appropriate lipid kinase assay formats suitable for high-throughput screening. The authors report the development of a simple and robust 384-well plate assay that is based on(33) P-phosphate transfer from radiolabeled [gamma(33) P]ATP to phosphatidylinositol immobilized on Maxisorp plates. The established assay format for PI3K gamma was easily adapted to the automated screening platform and was successfully employed for high-throughput screening. Enzymatic and inhibition characteristics of recombinant human PI3K gamma determined with the plate assay are in very good agreement with previously reported values determined in other assay formats. Maximal catalytic activity of PI3K gamma was observed at pH 7.0. The apparent K(m) value for ATP using a 1:1 mixture of phosphatidylinositol and phosphatidylserine was determined to be 7.3 microM (6.0-8.6 microM, 95% confidence interval [CI]). IC(50) values for known PI3-kinase inhibitors were determined to be 1.45 nM (1.17-1.80 nM, 95% CI) for wortmannin and estimated from partial inhibition data to be 1400, 2830, and 21,400 nM for quercetin, LY294002, and staurosporine, respectively. This novel assay approach allows for screening of inhibitors of lipid kinases in high-throughput mode and thereby may facilitate the identification of novel inhibitory structures for drug development.

Platelet-derived growth factor-BB-mediated activation of Akt suppresses smooth muscle-specific gene expression through inhibition of mitogen-activated protein kinase and redistribution of serum response factor

Platelet-derived growth factor (PDGF) inhibits expression of smooth muscle (SM) genes in vascular smooth muscle cells and blocks induction by arginine vasopressin (AVP). We have previously demonstrated that suppression of SM-alpha-actin by PDGF-BB is mediated in part through a Ras-dependent pathway. This study examined the role of phosphatidylinositol 3-kinase (PI3K)y and its downstream effector, Akt, in regulating SM gene expression. PDGF caused a rapid sustained activation of Akt, whereas AVP caused only a small transient increase. PDGF selectively caused a sustained stimulation of p85/p110 alpha PI3K. In contrast, p85/110 beta PI3K activity was not altered by either PDGF or AVP, whereas both agents caused a delayed activation of Class IB p101/110 gamma PI3K. Expression of a gain-of-function PI3K or myristoylated Akt (myr-Akt) mimicked the inhibitory effect of PDGF on SM-alpha-actin and SM22 alpha expression. Pretreatment with LY 294002 reversed the inhibitory effect of PDGF. Expression of myr-Akt selectively inhibited AVP-induced activation of c-Jun N-terminal kinase and p38 mitogen-activated protein kinases, which we have shown are critical for induction of these genes. Nuclear extracts from PDGF-stimulated or myr-Akt expressing cells showed reduced serum response factor binding to SM-specific CArG elements. This was associated with appearance of serum response factor in the cytoplasm. These data indicate that activation of p85/p110 alpha/Akt mediates suppression of SM gene expression by PDGF.

Requirement for PI 3-kinase γ in macrophage migration to MCP-1 and CSF-1

Phosphoinositide 3-kinases (PI3Ks) are important regulators of cell migration. The PI3K isoform gamma is primarily expressed in haematopoietic cells, and is activated by G protein-coupled receptors (GPCRs). Here, we investigate the contribution of PI3Kgamma to macrophage responses to chemoattractants, using bone marrow-derived macrophages from wild-type and PI3Kgamma-null mice. We observe that early membrane ruffling induced by MCP-1, which activates a GPCR, or by CSF-1, which activates a tyrosine kinase receptor, is unaltered in PI3Kgamma(-/-) mice, although by 30 min MCP-1-induced cell polarization was strongly reduced in PI3Kgamma(-/-) compared to wild-type macrophages. The migration behaviour of the macrophages was analysed by time-lapse microscopy in Dunn chemotaxis chambers. PI3Kgamma(-/-) macrophages showed reduced migration speed and translocation, and no chemotaxis to MCP-1. Interestingly, there was also a reduction in migration efficiency in PI3Kgamma(-/-) macrophages stimulated with CSF-1 although early CSF-1R signalling was normal. These results indicate that the initial actin reorganization induced by either a GPCR or tyrosine kinase receptor agonist is not dependent on PI3Kgamma, whereas PI3Kgamma is needed for optimal migration of macrophages to either agonist.

Novel pathways of F-actin polymerization in the human neutrophil

Recently we demonstrated the existence of a phosphatidylinositol 3-kinase (PI3K)-independent F-actin polymerization during neutrophil pseudopod extension. Here we examine the use of the PI3K-dependent and PI3K-independent pathways of activation by the N-formyl peptide receptor and the chemokine receptors, and the priming of the 2 pathways by granulocyte-macrophage colony-stimulating factor (GM-CSF) and insulin. The inhibition of PI3K activity with wortmannin showed that rate of pseudopod extension stimulated with N-formyl-Met-Leu-Phe (fMLP was mostly dependent on PI3K, while the rate of interleukin-8 (IL-8)-stimulated pseudopod extension was less dependent on PI3K. The incubation of cells with either GM-CSF or insulin increased the rate of pseudopod extension by 50% when the cells were stimulated with IL-8 but not with fMLP. The stimulation with IL-8 phosphorylated the PI3K regulatory subunit. This phosphorylation was enhanced by GM-CSF, which increased PI3K activity and total phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) production. The effect of GM-CSF was blocked with wortmannin. In contrast, insulin did not increase p85 phosphorylation and did not enhance PI3K activity or PtdIns(3,4,5)P3 production. The effect of insulin was insensitive to wortmannin; however, it was blocked by an Src homology 2 (SH2)-binding peptide. These data indicate that priming of IL-8 activation with GM-CSF was mediated via the PI3Ks of class IA, while priming with insulin used a PI3K-independent pathway.

Neuroprotective effect of postischemic administration of sodium orthovanadate in rats with transient middle cerebral artery occlusion

Orthovanadate is a competitive inhibitor of protein tyrosine phosphatases. Some of its reported biologic effects are its insulin mimetic property and its activation of phosphoinositide 3-kinase and extracellular-signal regulated kinase (ERK). The authors previously reported its neuroprotective effect on delayed neuronal death of gerbil hippocampal CA1 neurons via Akt and ERK activation after transient forebrain ischemia. In the present study, the neuroprotective effect of postischemic intraperitoneal administration of sodium orthovanadate (2 l/kg of 50-mmol/l sodium orthovanadate in saline) was investigated in rats with transient middle cerebral artery occlusion. Ischemic neuronal injury was evaluated 1 day and 28 days after ischemia. The neuroprotective effect of orthovanadate was significant in the cortex but not the caudate putamen (ischemic core) at both 1 and 28 days after ischemia. In orthovanadate group, the activities of Akt and ERK were maintained after reperfusion; they were decreased in saline group. Blood glucose level decreased but within normal range. Regional cerebral blood flow was lower than that of saline group only at 0 hours after reperfusion. These data suggest that orthovanadate has neuroprotective effects in rats with transient middle cerebral artery occlusion and that these effects are mediated by Akt and ERK activation. Furthermore, low blood glucose levels and gradual recovery of regional cerebral blood flow may contribute to neuroprotection.

Role of phosphoinositide 3-kinase signaling in mast cells: new insights from knockout mouse studies

Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases essential for diverse physiological reactions. In recent years a series of gene-targeted mice lacking different types of PI3Ks and related molecules have been generated which enable us to understand the role of PI3K pathways, particularly class I members, in vivo. Analyses of such gene-targeted mice have led to major discoveries in the physiological roles of PI3K signaling in mast cell biology. In particular the role of PI3Ks has been extensively studied in signaling through the high-affinity IgE receptor (FcepsilonRI), since mast cells are the main effector cells in type I allergic reaction associated with IgE-dependent mechanisms. Furthermore, the knockout mice have provided significant information concerning the role of PI3K signals in mast cell differentiation. This review presents several new insights into mast cell biology, which have been elucidated by the analyses of these knockout mice.

Hyaluronan-mediated CD44 interaction with RhoGEF and Rho kinase promotes Grb2-associated binder-1 phosphorylation and phosphatidylinositol 3-kinase signaling leading to cytokine (macrophage-colony stimulating factor) production and breast tumor progression

In this study we have examined CD44 (a hyaluronan (HA) receptor) interaction with a RhoA-specific guanine nucleotide exchange factor (p115RhoGEF) in human metastatic breast tumor cells (MDA-MB-231 cell line). Immunoprecipitation and immunoblot analyses indicate that both CD44 and p115RhoGEF are expressed in MDA-MB-231 cells and that these two proteins are physically associated as a complex in vivo. The binding of HA to MDA-MB-231 cells stimulates p115RhoGEF-mediated RhoA signaling and Rho kinase (ROK) activity, which, in turn, increases serine/threonine phosphorylation of the adaptor protein, Gab-1 (Grb2-associated binder-1). Phosphorylated Gab-1 promotes PI 3-kinase recruitment to CD44v3. Subsequently, PI 3-kinase is activated (in particular, alpha, beta, gamma forms but not the delta form of the p110 catalytic subunit), AKT signaling occurs, the cytokine (macrophage-colony stimulating factor (M-CSF)) is produced, and tumor cell-specific phenotypes (e.g. tumor cell growth, survival and invasion) are up-regulated. Our results also demonstrate that HA/CD44-mediated oncogenic events (e.g. AKT activation, M-CSF production and breast tumor cell-specific phenotypes) can be effectively blocked by a PI 3-kinase inhibitor (LY294002). Finally, we have found that overexpression of a dominant-negative form of ROK (by transfection of MBA-MD-231 cells with the Rho-binding domain cDNA of ROK) not only inhibits HA/CD44-mediated RhoA-ROK activation and Gab-1 phosphorylation but also down-regulates oncogenic signaling events (e.g. Gab-1.PI 3-kinase-CD44v3 association, PI 3-kinase-mediated AKT activation, and M-CSF production) and tumor cell behaviors (e.g. cell growth, survival, and invasion). Taken together, these findings strongly suggest that CD44 interaction with p115RhoGEF and ROK plays a pivotal role in promoting Gab-1 phosphorylation leading to Gab-1.PI 3-kinase membrane localization, AKT signaling, and cytokine (M-CSF) production during HA-mediated breast cancer progression.

Akt is a molecular target for signal transduction therapy in brain ischemic insult

Growth factors including insulin-like growth factor-1 (IGF-1) promote cell survival in ischemic brain injury. Stimulation of IGF-1 receptor coupled with tyrosine kinase activates phosphatidylinositol 3-kinase and subsequently, protein kinase B (Akt) in hippocampal neurons. Here we introduce a new approach of signal transduction therapy for brain damage occurring in ischemic insult. As has been shown for IGF-1, intracerebroventricular injection of sodium orthovanadate, a protein tyrosine phosphatase inhibitor, prior to ischemic insult blocked delayed neuronal death in the CA1 region. The neuroprotective effects of orthovanadate and IGF-1 were associated with an increased Akt activity in the CA1 region. We discuss here potential targets for Akt relevant to such neuroprotective activity. Our findings lead to the conclusion that Akt activity is a potential target for neuroprotective drugs in brain ischemic insult and other episodes of excitotoxic neuronal apoptosis such as seizure and Huntington's and Parkinson's diseases.

Phosphatidic acid production, required for cholecystokinin octapeptide-stimulated amylase secretion from pancreatic acinar AR42J cells, is regulated by a wortmannin-sensitive process

To investigate the role of phospholipids in exocytotic secretory events, we utilized rat pancreatic acinar AR42J cells that secreted amylase in response to cholecystokinin octapeptide (CCK-8). Wortmannin, an inhibitor of phosphoinositide 3-kinase (PI3K), was found to inhibit the secretion in a dose-dependent manner. When changes in cell membrane phospholipids were investigated before and after CCK-8 stimulation using [32P]orthophosphoric acid-labeled AR42J cells, we observed a rapid increase in phosphatidic acid (PtdOH) levels right after stimulation, which was not observed in non-stimulated cells. The increase, however, was suppressed by wortmannin pre-treatment, which also inhibited amylase secretion. Changes in other major phospholipids were not significant. These results indicate that CCK-8 induces amylase secretion through PI3K-regulated production of PtdOH in cell membranes.

The p110 gamma PI-3 kinase is required for EphA8-stimulated cell migration

This study provides evidence that treatment with preclustered ephrin A5-Fc results in a substantial increase in the stability of the p110 gamma PI-3 kinase associated with EphA8, thereby enhancing PI-3 kinase activity and cell migration on a fibronectin substrate. In contrast, co-expression of a lipid kinase-inactive p110 gamma mutant together with EphA8 inhibits ligand-stimulated PI-3 kinase activity and cell migration on a fibronectin substrate, suggesting that the mutant has a dominant negative effect against the endogenous p110 gamma PI-3 kinase. Significantly, the tyrosine kinase activity of EphA8 is not important for either of these processes. Taken together, our results demonstrate that the stimulation of cell migration on a fibronectin substrate by the EphA8 receptor depends on the p110 gamma PI-3 kinase but is independent of a tyrosine kinase activity.

Roles of G beta gamma in membrane recruitment and activation of p110 gamma/p101 phosphoinositide 3-kinase gamma

Receptor-regulated class I phosphoinositide 3-kinases (PI3K) phosphorylate the membrane lipid phosphatidylinositol (PtdIns)-4,5-P2 to PtdIns-3,4,5-P3. This, in turn, recruits and activates cytosolic effectors with PtdIns-3,4,5-P3-binding pleckstrin homology (PH) domains, thereby controlling important cellular functions such as proliferation, survival, or chemotaxis. The class IB p110 gamma/p101 PI3K gamma is activated by G beta gamma on stimulation of G protein-coupled receptors. It is currently unknown whether in living cells G beta gamma acts as a membrane anchor or an allosteric activator of PI3K gamma, and which role its noncatalytic p101 subunit plays in its activation by G beta gamma. Using GFP-tagged PI3K gamma subunits expressed in HEK cells, we show that G beta gamma recruits the enzyme from the cytosol to the membrane by interaction with its p101 subunit. Accordingly, p101 was found to be required for G protein-mediated activation of PI3K gamma in living cells, as assessed by use of GFP-tagged PtdIns-3,4,5-P3-binding PH domains. Furthermore, membrane-targeted p110 gamma displayed basal enzymatic activity, but was further stimulated by G beta gamma, even in the absence of p101. Therefore, we conclude that in vivo, G beta gamma activates PI3K gamma by a mechanism assigning specific roles for both PI3K gamma subunits, i.e., membrane recruitment is mediated via the noncatalytic p101 subunit, and direct stimulation of G beta gamma with p110 gamma contributes to activation of PI3K gamma.

Chemotactic signaling pathways in neutrophils: from receptor to actin assembly

In this review, we present an overview of the signaling elements between neutrophil chemotactic receptors and the actin cytoskeleton that drives cell motility. From receptor-ligand interactions, activation of heterotrimeric G-proteins, their downstream effectors PLC and PI-3 kinase, the activation of small GTPases of the Rho family, and their regulation of particular cytoskeletal regulatory proteins, we describe pathways specific to the chemotaxing neutrophil and elements documented to be important for neutrophil function.

Translational control: implications for skeletal muscle hypertrophy

Skeletal muscle hypertrophy is characterized, in part, by increases in protein mass per fiber. This increased accumulation of protein results from a net increase in protein synthesis relative to breakdown. Increases in rates of protein synthesis (translation) have been reported across different models of resistance exercise and across all species studied. However, although an increase in protein synthesis after exercise is reported commonly, the mechanisms underlying this response are not understood clearly. Therefore, the aim of the current review was to select areas of research within which translational control has been well-studied. The logic is that the mechanisms described in this review have the potential to contribute to the changes seen in protein synthesis after high-resistance exercise. The field of translational control has seen rapid growth in the past 5 to 10 years and although attempts have been made to include all contributing studies, apologies are given from the start because many have undoubtedly been overlooked.

Structural insight into substrate specificity and regulatory mechanisms of phosphoinositide 3-kinases

Phosphoinositide 3-kinases (PI3Ks) are implicated in a variety of fundamental cellular processes. These enzymes catalyse phosphorylation of the 3'-OH position of myo-inositol lipids that serve as secondary messengers. The catalytic subunit for one of the family members, PI3K gamma, has been structurally characterized, independently, in complexes with kinase inhibitors and with the p21(Ras) GTPase. These atomic structures provide a basis for the rationalization of some PI3K substrate specificities and regulatory mechanisms, establishing links to functional and cellular data. Ongoing comprehensive structural and functional studies are essential to realize the promise of PI3K isozyme-specific therapeutic agents.

Activation of phosphoinositide 3-kinase gamma by Ras

BACKGROUND

Type I phosphoinositide 3-kinases are responsible for the hormone-sensitive synthesis of the lipid messenger phosphatidylinositol(3,4,5)-trisphosphate. Type IA and IB subfamily members contain a Ras binding domain and are stimulated by activated Ras proteins both in vivo and in vitro. The mechanism of Ras activation of type I PI3Ks is unknown, in part because no robust in vitro assay of this event has been established and characterized. Other Ras effectors, such as Raf and phosphoinositide-phospholipase Cepsilon, have been shown to be translocated into the plasma membrane, leading to their activation.

RESULTS

We show that posttranslationally lipid-modified, activated N-, H-, K-, and R-Ras proteins can potently and substantially activate PI3Kgamma when using a stripped neutrophil membrane fraction as a source of phospholipid substrate. We have found GTPgammaS-loaded Ras can significantly (6- to 8-fold) activate PI3Kgamma when using artificial phospholipid vesicles containing their substrate, and this effect is a result of both a decrease in apparent Km for phosphatidylinositol(4,5)-bisphosphate and an increase in the apparent Vmax. However, neither in vivo nor in the two in vitro assays of Ras activation of PI3Kgamma could we detect any evidence of a Ras-dependent translocation of PI3Kgamma to its source of phospholipid substrate.

CONCLUSIONS

Our data suggest that Ras activate PI3Kgamma at the level of the membrane, by allosteric modulation and/or reorientation of the PI3Kgamma, implying that Ras can activate PI3Kgamma without its membrane translocation. This view is supported by structural work that has suggested binding of Ras to PI3Kgamma results in a change in the structure of the catalytic pocket.