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1.
2.
By using purified preparations we show that nanomolar concentrations of Gbetagamma significantly stimulated lipid kinase activity of phosphatidylinositol 3-kinase (PI3K) beta and PI3Kgamma in the presence as well as in the absence of non-catalytic subunits such as p85alpha or p101. Concomitantly, Gbetagamma stimulated autophosphorylation of the catalytic subunit of PI3Kgamma (EC(50), 30 nM; stoichiometry >/=0.6 mol of P(i)/mol of p110gamma), which also occurred in the absence of p101. Surprisingly, we found that p101 affected the lipid substrate preference of PI3Kgamma in its Gbetagamma-stimulated state. With phosphatidylinositol as substrate, p110gamma but not p101/p110gamma was significantly stimulated by Gbetagamma to form PI-3-phosphate (EC(50), 20 nM). The opposite situation was found when PI-4,5-bisphosphate served as substrate. Gbetagamma efficiently and potently (EC(50), 5 nM) activated the p101/p110gamma heterodimer but negligibly stimulated the p110gamma monomer to form PI-3,4,5-trisphosphate. However, this weak stimulatory effect on p110gamma was overcome by excess concentrations of Gbetagamma (EC(50), 100 nM). This finding is in accordance with the in vivo situation, where activated PI3K catalyzes the formation of PI-3,4,5-trisphosphate but not PI-3-phosphate. We conclude that p101 is responsible for PI-4, 5-bisphosphate substrate selectivity of PI3Kgamma by sensitizing p110gamma toward Gbetagamma in the presence of PI-4,5-P(2).  相似文献   

3.
Previous results have shown that in rat portal vein myocytes the betagamma dimer of the G(13) protein transduces the angiotensin II-induced stimulation of calcium channels and increase in intracellular Ca(2+) concentration through activation of phosphoinositide 3-kinase (PI3K). In the present work we determined which class I PI3K isoforms were involved in this regulation. Western blot analysis indicated that rat portal vein myocytes expressed only PI3Kalpha and PI3Kgamma and no other class I PI3K isoforms. In the intracellular presence of an anti-p110gamma antibody infused by the patch clamp pipette, both angiotensin II- and Gbetagamma-mediated stimulation of Ca(2+) channel current were inhibited, whereas intracellular application of an anti-p110alpha antibody had no effect. The anti-PI3Kgamma antibody also inhibited the angiotensin II- and Gbetagamma-induced production of phosphatidylinositol 3,4,5-trisphosphate. In Indo-1 loaded cells, the angiotensin II-induced increase in [Ca(2+)](i) was inhibited by intracellular application of the anti-PI3Kgamma antibody, whereas the anti-PI3Kalpha antibody had no effect. The specificity of the anti-PI3Kgamma antibody used in functional experiments was ascertained by showing that this antibody did not recognize recombinant PI3Kalpha in Western blot experiments. Moreover, anti-PI3Kgamma antibody inhibited the stimulatory effect of intracellularly infused recombinant PI3Kgamma on Ca(2+) channel current without altering the effect of recombinant PI3Kalpha. Our results show that, although both PI3Kgamma and PI3Kalpha are expressed in vascular myocytes, the angiotensin II-induced stimulation of vascular L-type calcium channel and increase of [Ca(2+)](i) involves only the PI3Kgamma isoform.  相似文献   

4.
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.  相似文献   

5.
The phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway is frequently activated in human cancer and plays a crucial role in glioblastoma biology. We were interested in gaining further insight into the potential of targeting PI3K isoforms as a novel anti-tumor approach in glioblastoma. Consistent expression of the PI3K catalytic isoform PI3K p110α was detected in a panel of glioblastoma patient samples. In contrast, PI3K p110β expression was only rarely detected in glioblastoma patient samples. The expression of a module comprising the epidermal growth factor receptor (EGFR)/PI3K p110α/phosphorylated ribosomal S6 protein (p-S6) was correlated with shorter patient survival. Inhibition of PI3K p110α activity impaired the anchorage-dependent growth of glioblastoma cells and induced tumor regression in vivo. Inhibition of PI3K p110α or PI3K p110β also led to impaired anchorage-independent growth, a decreased migratory capacity of glioblastoma cells, and reduced the activation of the Akt/mTOR pathway. These effects were selective, because targeting of PI3K p110δ did not result in a comparable impairment of glioblastoma tumorigenic properties. Together, our data reveal that drugs targeting PI3K p110α can reduce growth in a subset of glioblastoma tumors characterized by the expression of EGFR/PI3K p110α/p-S6.  相似文献   

6.
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.  相似文献   

7.
The central role of phosphatidylinositol 3-kinase (PI3K, p110α) signaling in allowing cancer cells to bypass normal growth-limiting controls has led to the development of PI3K(p110α) inhibitors. A challenge in targeting PI3K(p110α) relates to the diverse actions of the PI3K pathway in numerous cell types. Recent findings in mice deficient in PI3K(p110α) activity in the heart, demonstrate the critical role of this pathway in protecting the heart against pathological insults. Mice deficient in PI3K(p110α) displayed accelerated heart failure in response to dilated or hypertrophic cardiomyopathy. These results help explain the association of cardiomyopathy in cancer patients given tyrosine kinase inhibitors and raise concerns for the use of PI3K(p110α) inhibitors in cancer patients with cardiovascular risk factors. Interestingly, an inhibitor of the mammalian target of rapamycin (a downstream effector of PI3K), did not have adverse effects on the heart. A more complete understanding of the complex arms and interactions of the PI3K pathway will hopefully lead to the development of anti-cancer agents without cardiac complications.  相似文献   

8.
Purinergic stimulation of cardiomyocytes turns on a Src family tyrosine kinase-dependent pathway that stimulates PLCgamma and generates IP(3), a breakdown product of phosphatidylinositol 4,5-bisphosphate (PIP2). This signaling pathway closely regulates cardiac cell autonomic activity (i.e., spontaneous cell Ca(2+) spiking). PIP2 is phosphorylated on 3' by phosphoinositide 3-kinases (PI3Ks) that belong to a broad family of kinase isoforms. The product of PI3K, phosphatidylinositol 3,4,5-trisphosphate, regulates activity of PLCgamma. PI3Ks have emerged as crucial regulators of many cell functions including cell division, cell migration, cell secretion, and, via PLCgamma, Ca(2+) homeostasis. However, although PI3Kalpha and -beta have been shown to mediate specific cell functions in nonhematopoietic cells, such a role has not been found yet for PI3Kgamma.We report that neonatal rat cardiac cells in culture express PI3Kalpha, -beta, and -gamma. The purinergic agonist predominantly activates PI3Kgamma. Both wortmannin and LY294002 prevent tyrosine phosphorylation, and membrane translocation of PLCgamma as well as IP(3) generation in ATP-stimulated cells. Furthermore, an anti-PI3Kgamma, but not an anti-PI3Kbeta, injected in the cells prevents the effect of ATP on cell Ca(2+) spiking. A dominant negative mutant of PI3Kgamma transfected in the cells also exerts the same action. The effect of ATP was observed on spontaneous Ca(2+) spiking of wild-type but not of PI3Kgamma(2/2) embryonic stem cell-derived cardiomyocytes. ATP activates the Btk tyrosine kinase, Tec, and induces its association with PLCgamma. A dominant negative mutant of Tec blocks the purinergic effect on cell Ca(2+) spiking. Tec is translocated to the T-tubes upon ATP stimulation of cardiac cells. Both an anti-PI3Kgamma antibody and a dominant negative mutant of PI3Kgamma injected or transfected into cells prevent the latter event.We conclude that PI3Kgamma activation is a crucial step in the purinergic regulation of cardiac cell spontaneous Ca(2+) spiking. Our data further suggest that Tec works in concert with a Src family kinase and PI3Kgamma to fully activate PLCgamma in ATP-stimulated cardiac cells. This cluster of kinases provides the cardiomyocyte with a tight regulation of IP(3) generation and thus cardiac autonomic activity.  相似文献   

9.
Phosphatidylinositol 3-kinase (PI3K), one member of lipid kinase family, has been demonstrated to play a key role in regulating cell proliferation, adhesion, survival, and motility. Recent studies indicate that PI3K related signaling pathway is one of the most commonly activated pathways in human cancers. Accordingly, pharmacological inhibition of key nodes in this signaling cascade has been a focus in developmental therapeutics. To date, Inhibitors targeting PI3K or nodes in this pathway, AKT and mTOR, are best studied and have reached clinical trials. In this review, we will focus on recent progress on understanding of PI3Ks signaling pathway and the development of PI3K inhibitors.  相似文献   

10.
Ras activation of phosphoinositide 3-kinase (PI3K) is important for survival of transformed cells. We find that PI3Kgamma is strongly and directly activated by H-Ras G12V in vivo or by GTPgammaS-loaded H-Ras in vitro. We have determined a crystal structure of a PI3Kgamma/Ras.GMPPNP complex. A critical loop in the Ras binding domain positions Ras so that it uses its switch I and switch II regions to bind PI3Kgamma. Mutagenesis shows that interactions with both regions are essential for binding PI3Kgamma. Ras also forms a direct contact with the PI3Kgamma catalytic domain. These unique Ras/PI3Kgamma interactions are likely to be shared by PI3Kalpha. The complex with Ras shows a change in the PI3K conformation that may represent an allosteric component of Ras activation.  相似文献   

11.
Lee HY  Bae GU  Jung ID  Lee JS  Kim YK  Noh SH  Stracke ML  Park CG  Lee HW  Han JW 《FEBS letters》2002,515(1-3):137-140
Autotaxin (ATX), an exo-nucleotide pyrophosphatase and phosphodiesterase, stimulates tumor cell motility at sub-nanomolar levels and augments invasiveness and angiogenesis. We investigated the role of G protein-coupled phosphoinositide 3-kinase gamma (PI3Kgamma) in ATX-mediated tumor cell motility stimulation. Pretreatment of human melanoma cell line A2058 with wortmannin or LY294002 inhibited ATX-induced motility. ATX increased the PI3K activity in p110gamma, but not p85, immunoprecipitates. This effect was abrogated by PI3K inhibitors or inhibited by pertussis toxin. Furthermore, stimulation of tumor cell motility by ATX was inhibited by catalytically inactive form of PI3Kgamma, strongly indicating the crucial role of PI3Kgamma for ATX-mediated motility in human melanoma cells  相似文献   

12.
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.  相似文献   

13.
Lysophosphatidic acid (LPA), one of the naturally occurring phospholipids, stimulates cell motility through the activation of Rho family members, but the signaling mechanisms remain to be elucidated. In the present study, we investigated the roles of p21-activated kinase 1 (PAK1) on LPA-induced focal adhesion kinase (FAK) phosphorylation and cell motility. Treatment of human melanoma cells A2058 with LPA increased phosphorylation and activation of PAK1, which was blocked by treatment with pertussis toxin and by inhibition of phosphoinositide 3-kinase (PI3K) with an inhibitor LY294002 or by overexpression of catalytically inactive mutant of PI3Kgamma, indicating that LPA-induced PAK1 activation was mediated via a Gi protein and the PI3Kgamma signaling pathway. In addition, we demonstrated that Rac1/Cdc42 signals acted as upstream effector molecules of LPA-induced PAK activation. However, Rho-associated kinase, MAP kinase kinase 1/2 or phospholipase C might not be involved in LPA-induced PAK1 activation or cell motility stimulation. Furthermore, PAK1 was necessary for FAK phosphorylation by LPA, which might cause cell migration, as transfection of the kinase deficient mutant of PAK1 or PAK auto-inhibitory domain significantly abrogated LPA-induced FAK phosphorylation. Taken together, these findings strongly indicated that PAK1 activation was necessary for LPA-induced cell motility and FAK phosphorylation that might be mediated by sequential activation of Gi protein, PI3Kgamma and Rac1/Cdc42.  相似文献   

14.
Class I phosphoinositide 3-kinases (PI3Ks) are bifunctional enzymes possessing lipid kinase activity and the capacity to phosphorylate their catalytic and/or regulatory subunits. In this study, in vitro autophosphorylation of the G protein-sensitive p85-coupled class I(A) PI3K beta and p101-coupled class I(B) PI3K gamma was examined. Autophosphorylation sites of both PI3K isoforms were mapped to C-terminal serine residues of the catalytic p110 subunit (i.e. serine 1070 of p110 beta and serine 1101 of p110 gamma). Like other class I(A) PI3K isoforms, autophosphorylation of p110 beta resulted in down-regulated PI3K beta lipid kinase activity. However, no inhibitory effect of p110 gamma autophosphorylation on PI3K gamma lipid kinase activity was observed. Moreover, PI3K beta and PI3K gamma differed in the regulation of their autophosphorylation. Whereas p110 beta autophosphorylation was stimulated neither by G beta gamma complexes nor by a phosphotyrosyl peptide derived from the platelet-derived growth factor receptor, autophosphorylation of p110 gamma was significantly enhanced by G beta gamma in a time- and concentration-dependent manner. In summary, we show that autophosphorylation of both PI3K beta and PI3K gamma occurs in a C-terminal region of the catalytic p110 subunit but differs in its regulation and possible functional consequences, suggesting distinct roles of autophosphorylation of PI3K beta and PI3K gamma.  相似文献   

15.
Type I phosphatidylinositol 4-phosphate (PI(4)P) 5-kinases (PIP5Ks) catalyze the synthesis of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)), an essential lipid molecule involved in various cellular processes such as regulation of actin cytoskeleton and membrane traffic. The protein localizes to the plasma membrane where its activity has been shown to be regulated by small GTPase ARFs and/or phosphatidic acid. Deletion analysis of amino- or carboxy-terminal sequences of PIP5Kgamma fused with EGFP demonstrated that the presence of central kinase homology domain (KHD), a 380 amino acid-long region highly conserved among PIP5K family, was necessary and sufficient for the plasma membrane localization of PIP5Kgamma. Particularly, the dibasic Arg-Lys sequence located at the carboxy-terminal end of KHD was shown to be crucial for the plasma membrane targeting of PIP5Kgamma, since the deletion or charge-reversal mutation of this dibasic sequence resulted in the mislocalization of the protein to the cytoplasm. Mislocalized mutants also failed to complement the temperature-sensitive growth of Saccharomyces cerevisiae mss4-1 mutant defective in PIP5K function. The presence of dibasic residues at the C-terminal end of KHD was conserved among mammalian as well as invertebrate PIP5K family members, but not in the type II PIPKs that are not targeted to the plasma membrane, suggesting that the conserved dibasic motif provides a mechanism essential for the proper localization and cellular function of PIP5Ks.  相似文献   

16.
Through their ability to regulate production of the key lipid messenger PtdIns(3,4,5)P(3), the class I phosphatidylinositol-3-OH kinases (PI(3)Ks) support many critical cell responses. They, in turn, can be regulated by cell-surface receptors through signals acting on either their adaptor subunits (for example, through phosphotyrosine or Gbetagammas) or their catalytic subunits (for example, through GTP-Ras). The relative significance of these controlling inputs is undefined in vivo. Here, we have studied the roles of Gbetagammas, the adaptor p101, Ras and the Ras binding domain (RBD) in the control of the class I PI(3)K, PI(3)Kgamma, in mouse neutrophils. Loss of p101 leads to major reductions in the accumulation of PtdIns(3,4,5)P(3), activation of protein kinase B (PKB) and in migration towards G-protein activating ligands in vitro, and to an aseptically inflamed peritoneum in vivo. Loss of sensitivity of PI(3)Kgamma to Ras unexpectedly caused similar reductions, but additionally caused a substantial loss in production of reactive oxygen species (ROS). We conclude that Gbetagammas, p101 and the Ras-RBD interaction all have important roles in the regulation of PI(3)Kgamma in vivo and that they can simultaneously, but differentially, control distinct PI(3)Kgamma effectors.  相似文献   

17.
Resistance to thromboembolism in PI3Kgamma-deficient mice.   总被引:14,自引:0,他引:14  
Platelet aggregation and subsequent thrombosis are the major cause of ischemic diseases such as heart attack and stroke. ADP, acting via G protein-coupled receptors (GPCRs), is an important signal in thrombus formation and involves activation of phosphoinositide 3-kinases (PI3K). When platelets from mice lacking the G protein-activated PI3Kgamma isoform were stimulated with ADP, aggregation was impaired. Collagen or thrombin, however, evoked a normal response. ADP stimulation of PI3Kgamma-deficient platelets resulted in decreased PKB/Akt phosphorylation and alpha(IIb)beta(3) fibrinogen receptor activation. These effects did not influence bleeding time but protected PI3Kgamma-null mice from death caused by ADP-induced platelet-dependent thromboembolic vascular occlusion. This result demonstrates an unsuspected, well-defined role for PI3Kgamma downstream of ADP and suggests that pharmacological targeting of PI3Kgamma has a potential use as antithrombotic therapy.  相似文献   

18.
We addressed the role of class 1B phosphatidylinositol 3-kinase (PI3K) isoform PI3Kgamma in mediating NADPH oxidase activation and reactive oxidant species (ROS) generation in endothelial cells (ECs) and of PI3Kgamma-mediated oxidant signaling in the mechanism of NF-kappaB activation and intercellular adhesion molecule (ICAM)-1 expression. We used lung microvascular ECs isolated from mice with targeted deletion of the p110gamma catalytic subunit of PI3Kgamma. Tumor necrosis factor (TNF) alpha challenge of wild type ECs caused p110gamma translocation to the plasma membrane and phosphatidylinositol 1,4,5-trisphosphate production coupled to ROS production; however, this response was blocked in p110gamma-/- ECs. ROS production was the result of TNFalpha activation of Ser phosphorylation of NADPH oxidase subunit p47(phox) and its translocation to EC membranes. NADPH oxidase activation failed to occur in p110gamma-/- ECs. Additionally, the TNFalpha-activated NF-kappaB binding to the ICAM-1 promoter, ICAM-1 protein expression, and PMN adhesion to ECs required functional PI3Kgamma. TNFalpha challenge of p110gamma-/- ECs failed to induce phosphorylation of PDK1 and activation of the atypical PKC isoform, PKCzeta. Thus, PI3Kgamma lies upstream of PKCzeta in the endothelium, and its activation is crucial in signaling NADPH oxidase-dependent oxidant production and subsequent NF-kappaB activation and ICAM-1 expression.  相似文献   

19.
AT/RTs (atypical teratoid/rhabdoid tumours) of the CNS (central nervous system) are childhood malignancies associated with poor survival rates due to resistance to conventional treatments such as chemotherapy. We characterized a panel of human AT/RT and MRT (malignant rhabdoid tumour) cell lines for expression of RTKs (receptor tyrosine kinases) and their involvement in tumour growth and survival. When compared with normal brain tissue, AT/RT cell lines overexpressed the IR (insulin receptor) and the IGFIR (insulin-like growth factor-I receptor). Moreover, insulin was secreted by AT/RT cells grown in serum-free medium. Insulin potently activated Akt (also called protein kinase B) in AT/RT cells, as compared with other growth factors, such as epidermal growth factor. Pharmacological inhibitors, neutralizing antibodies, or RNAi (RNA interference) targeting the IR impaired the growth of AT/RT cell lines and induced apoptosis. Inhibitors of the PI3K (phosphoinositide 3-kinase)/Akt pathway also impaired basal and insulin-stimulated AT/RT cell proliferation. Experiments using RNAi and isoform-specific pharmacological inhibitors established a key role for the class I(A) PI3K p110alpha isoform in AT/RT cell growth and insulin signalling. Taken together, our results reveal a novel role for autocrine signalling by insulin and the IR in growth and survival of malignant human CNS tumour cells via the PI3K/Akt pathway.  相似文献   

20.
由磷脂酰肌醇3- 激酶(PI3K)、丝氨酸/ 苏氨酸蛋白激酶(Akt)和哺乳动物雷帕霉素靶蛋白(mTOR)组成的PI3K-Akt-mTOR通路是细胞内非常重要的信号转导途径,该通路的紊乱会引起一系列的疾病,包括癌症、神经病变、自身免疫性疾病和血液淋巴系统疾病。近年来,PI3K-Akt-mTOR 通路作为药物靶点备受关注。结合汤森路透数据库资源——Thomson Reuters Integrity 和Cortellis for Competitive Intelligence,对PI3K-Akt-mTOR 通路的机制、相关药物研究进展、适应证、研发公司、交易、专利、文献等情报进行了数据层面的分析。  相似文献   

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