Mechanism of phosphatidylinositol 3-kinase-dependent increases in BAC1.2F5 macrophage-like cell density in response to M-CSF: Phosphatidylinositol 3-kinase inhibitors increase the rate of apoptosis rather than inhibit DNA synthesis

OBJECTIVE AND DESIGN: To determine the role of phosphatidylinositol 3-kinase (PI 3-kinase) in macrophagecolony stimulating factor (M-CSF)-induced macrophage proliferation. MATERIALS: The M-CSF-dependent BAC1.2F5 murine macrophage cell line was used. METHODS: PI 3-kinase activity, Protein kinase B activation, increased cell numbers, induction of DNA synthesis and apoptosis were measured in response to serum, M-CSF and PI 3-kinase inhibitors. RESULTS: Wortmannin or LY294002 inhibited M-CSF-stimulated increases in BAC1.2F5 cell density. Further analysis showed that inhibition of PI 3-kinase had an insignificant effect on DNA synthesis, but significantly induced apoptosis. Other co-factors in serum mediated cell survival and prevented programmed cell death, in a PI 3-kinase-dependent manner. Stimulation of BAC1.2F5 macrophages with M-CSF induced phosphorylation of PKB/Akt as detected by activation-specific antibodies. Activation of PKB/Akt correlated with PI 3-kinase activation, suggesting that the protection from apoptosis in these cells is mediated by PKB/Akt. CONCLUSIONS: These results indicate that the lack of increase in cell numbers when cells are stimulated with M-CSF in the presence of PI 3-kinase inhibitors is due to a preferential PI 3-kinase requirement for protection against apoptosis, rather than a requirement for PI 3-kinase activation during the proliferation signal.     

PI3-K/Akt信号通路对阿尔茨海默病神经元凋亡的调节作用

磷脂酰肌醇3-激酶(PI3-K/Akt)途径是细胞内重要的促细胞存活通路之一,PI3-K被细胞外信号活化后,激活下游蛋白激酶Akt。在阿尔茨海默病(AD)的发病过程中,凋亡相关基因Bad、GSK-3、转录因子家族、caspases家族等参与了神经元的凋亡,导致神经元的大量丢失。而活化的Akt通过磷酸化Bad、GSK-3、转录因子家族、IB、caspases等使促凋亡基因失活,从而起到抑制神经元凋亡及促进神经元存活的作用,进而减少AD神经元的大量丢失,改善AD的病理变化。     

Ligation of the T cell co-stimulatory receptor CD28 activates the serine-threonine protein kinase protein kinase B

The intracellular signaling pathways activated upon ligation of the co-stimulatory receptor CD28 remain relatively ill-defined, although CD28 ligation does result in the strong association with, and activation of, phosphatidylinositol (PI) 3-kinase. The downstream effector targets of the CD28-activated PI 3-kinase-dependent signaling pathway remain poorly defined, but recent evidence from other systems has shown that Akt/protein kinase B (PKB) is a major target of PI 3-kinase and have indicated that a major function of PKB is the regulation of cell survival events. Given the strong coupling of CD28 to PI 3-kinase and the known protective effects of both CD28 and PI 3-kinase against apoptosis in different cell models, we investigated the effects of CD28 on PKB activation. We demonstrate that ligation of CD28 by either anti-CD28 monoclonal antibodies or the natural ligand B7.1, results in the marked activation of PKB in both the leukemic T cell line Jurkat and freshly isolated human peripheral blood-derived normal T lymphocytes. Our data suggest therefore, that PKB may be an important intracellular signal involved in CD28 signal transduction and demonstrate CD28 coupling to downstream elements of a signaling cascade known to promote cell survival.     

Phosphatidylinositol 3-kinase activity is not essential for CD28 costimulatory activity in Jurkat T cells: studies with a selective inhibitor,wortmannin

The interaction of CD28 with its counter-receptor, B7-1 (CD 80), on antigenpresenting cells induces a co-signal in T cells required to promote antigendependent interleukin-2 (IL-2) production and to prevent clonal anergy. CD28 stimulation causes both protein-tyrosine kinase and phosphatidylinositol3-kinase (PI3-K) activation, suggesting a possible role for these enzyme activities in CD28 co-signal transduction. Here, we investigate the effect of wortmannin, a selective and irreversible PI3-K inhibitor on CD28 co-signaling events in the Jurkat T cell line. Wortmannin added to cell cultures partially inhibits CD28-induced tyrosine phosphorylation of the putative p110 catalytic subunit of PI3-K, but does not block CD28-induced association of the p85 PI3-K regulatory subunit with the CD28 receptor. Wortmannin inhibits in a dose-dependent manner both total cellular PI3-K activity and CD28-induced receptor-associated PI3-K activity. Wortmannin (1 μM) inhibits cellular PI3-K activity by 90% with complete inhibition achieved at 10 μM. The inhibitory effect of wortmannin on cellular PI3-K activity is prolonged (> 18 h), suggesting that the drug is not readily metabolized by Jurkat T cells. Wortmannin, at concentrations that blocked PI3-K activity, fails to inhibit the synergistic effect of CD28 on IL-2 secretion in the presence of phorbol 12-myristate 13-acetate and ionomycin. These data demonstrate that CD28-induced signaling events other than the activation of PI3-K catalytic activity contribute to the control of IL-2 secretion.     

Signal transduction involved in CTGF-induced production of chemokines in mesangial cells

Objective and design. This study investigates the regulatory role of connective tissue growth factor (CTGF) on production of fractalkine, monocyte-chemoattractant protein-1 (MCP-1) and regulated on activation, normal T cell expressed and secreted (RANTES) in human mesangial cells, and explore the mechanisms of CTGF action.

Methods. Cultured human mesangial cells were treated with CTGF. Expressions of mRNA and proteins of fractalkine, MCP-1 and RANTES were analyzed by real-time polymerase chain reaction (PCR) and by enzyme-linked immunosorbent assay, respectively. Expressions of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2), phosphoinositide 3-kinase (PI3-K) and protein kinase B (PKB) were assessed by Western blotting. Activities of nuclear factor-κB (NF-κB) were determined by NF-κB luciferase reporter assay.

Results. CTGF enhanced the mRNA expressions and protein release of fractalkine, MCP-1 and RANTES, and the expressions of phosphorylated ERK1/2, PI3-K and PKB, and activities of NF-κB. Blockade of ERK1/2 inhibited the CTGF-induced expression of phosphorylated ERK1/2 and NF-κB, and partially decreased the expressions of the above chemokines. PI3-K blockade downregulated the CTGF-stimulated expressions of phosphorylated PI3-K, PKB and NF-κB but not phosphorylated ERK1/2, partially decreased the expressions of the above chemokines. NF-κB blockade abrogated the CTGF-activated NF-κB and partially decreased the expressions of the above chemokines. Soluble heparin and K252a, an inhibitor of Trk, blocked CTGF-induced production of the above chemokines and the activation of the above signaling proteins.

Conclusion. These results demonstrated that CTGF induces production of fractalkine, MCP-1 and RANTES via ERK1/2 and PI3-K/PKB/NF-κB-dependent signal pathway mediated by cell surface heparin sulfate proteoglycans and the tyrosine kinase receptor TrkA in human mesangial cells.     

Exogenous human immunodeficiency virus type-1 Tat protein selectively stimulates a phosphatidylinositol-specific phospholipase C nuclear pathway in the Jurkat T cell line

We investigated the effect of extracellular Tat protein of human immunodeficiency virus-type 1 (HIV-1) on the phosphatidylinositol (PI) cycle, which represents a major signal transduction pathway in lymphoid cells. Recombinant Tat, recombinant HIV-1 p24 and cross-linked anti-CD3 monoclonal antibody (mAb) were added in culture for 1–60 min to Jurkat lymphoblastoid CD4⁺ T cells. The stimulation of T cell receptor by cross-linked anti-CD3 mAb resulted in a rapid increase of the phosphatidylinositol-specific phospholipase C (PI-PLC) activity in whole cell lysates. On the other hand, Tat protein, either alone or in combination with anti-CD3 mAb, showed little effect on the PI turnover of whole cell extracts. Tat, however, selectively stimulated a nuclear-specific PI-PLC with a peak of activity after 30 min from the addition in culture to Jurkat cells. Interestingly, this time corresponded to that required for the uptake and nuclear localization of recombinant Tat protein, as demonstrated by electron microscope immunocytochemistry experiments with anti-Tat mAb. Moreover, exogenous Tat reached the nucleus of Jurkat cells in a bioactive form, as shown in a HIV-1 long terminal repeat-chloramphenicol acetyl transferase transactivation assay. The specific increase of a nuclear PI-PLC activity was further demonstrated by the ability of Tat to stimulate PI turnover also when added directly to isolated nuclei. As a whole, these data demonstrate that Tat selectively stimulates a nuclear polyphosphoinositide hydrolysis, which appears to be independent of the cellular PI turnover. The relevance of these findings for a better understanding of the biological functions of extracellular Tat is discussed.     

Ang II attenuates IGF-1-stimulated Na+, K(+)-ATPase activity via PI3K/Akt pathway in vascular smooth muscle cells

We have investigated the role of phosphatidylinositol 3-kinase (PI3K) and serine/threonine protein kinase B (Akt) in mediating vascular smooth muscle cells (VSMC) sodium pump (Na+, K(+)-ATPase) regulatory interactions between insulin-like growth factor-1 (IGF-1) and angiotensin II (Ang II). Treatment with IGF-1 (100 nM) for 30 min or Ang II (100 nM) for 10 min increased sodium pump activity. Pretreatment with Ang II for 10 min, abolished IGF-1 increased sodium pump activity. Given separately for 6 h, Ang II and IGF-1 stimulated alpha1 mRNA accumulation. Phosphorylation on Ser473 of Akt was increased after treatment with both IGF-1 and Ang II. Pretreatment with 100 nM of PI3K inhibitor Wortmannin (WT) for 30 min decreased: IGF-1 and Ang II-stimulated pump activity, phosphorylation of Akt and PI3K protein expression. Pretreatment with Ang II attenuated IGF-1-stimulated sodium pump activity, phosphorylation of Akt and PI3K protein expression. IGF-1 increased the association between IRS-1 and p85, and Ang II as well as PI3K inhibition decreased this IGF-1 effect. These results suggest that Ang II, which increases pump activity alone, reduces the IGF-1 stimulation of sodium pump activity by attenuating PI3K/Akt signaling. These results implicate PI3K/Akt pathways in Ang II/IGF-1 regulation of the sodium pump in VSMC.     

The effects of dehydrocostus lactone on osteoblastic MC3T3-E1 cells in redox changes and PI3K/Akt/CREB

Antimycin A (AMA) inhibits mitochondrial electron transport chain between cytochrome b and c. In the present study, we investigated the effects of dehydrocostus lactone on osteoblastic MC3T3-E1 cells in the presence of AMA with a focus on redox changes and PI3K/Akt/CREB signaling. AMA increased nitrotyrosin level and decreased NADPH level, activities of thioredoxin reductase, phosphoinositide 3-kinase (PI3K), and Akt (protein kinase B [PKB]), and phosphorylated cAMP-response element-binding protein (CREB). Pretreatment with dehydrocostus lactone prior to AMA exposure significantly prevented the loss of NADPH, production of nitrotyrosine, and thioredoxin reductase inactivation induced by AMA. Moreover, dehydrocostus lactone increased activities of PI3K and Akt, and CREB phosphorylation inhibited by AMA. These results suggest that antioxidant activity and PI3K/Akt/CREB activation are related to the protective effect of dehydrocostus lactone against osteoblast damage induced by AMA.     

Insulin facilitates repetitive spike firing in rat insular cortex via phosphoinositide 3-kinase but not mitogen activated protein kinase cascade

The insular cortex (IC) processes gustatory and visceral information, which functionally correlate to feeding behavior. Insulin, a well-known hormone controlling glucose metabolism, is released by elevation of blood glucose concentration following feeding behavior. The IC expresses dense insulin receptors and receives projection from the hypothalamus, which monitors changes in glucose concentration. Therefore, it is likely that insulin modulates neural properties in the IC. However, little is known about the effects of insulin on electrophysiological properties of the neocortex including the IC. To explore the effects of insulin on subthreshold responses and action potential properties in the IC, intracellular recording with sharp glass electrodes was performed from IC pyramidal cells using slice preparations. Although application of insulin (100 nM) had little effect on the resting membrane potential, input resistance and rheobase, insulin significantly increased the frequency of repetitive spike firing in response to a long depolarizing current pulse injection: the slope of the frequency-current curve was increased from 23.7±2.3 Hz/nA to 29.5±3.4 Hz/nA. Insulin slightly decreased the action potential threshold without affecting the amplitude of medium-duration and slow afterhyperpolarization (sAHP) s. The insulin-induced facilitation of repetitive spike firing was dose-dependent and blocked by pre-application of 200 nM lavendustin A, a tyrosine kinase inhibitor. Moreover, when combined with 200 nM wortmannin, a phosphoinositide 3-kinase (PI3-K) inhibitor, or 500 nM deguelin, an inhibitor of protein kinase B (PKB/Akt) downstream of PI3-K, insulin failed to increase the frequency of repetitive spike firing. In contrast, co-application of insulin and (10 μM) PD 98059, an inhibitor of mitogen activated protein kinase (MAPK), exerted facilitation of repetitive spike firing. These results suggest that acute insulin-induced facilitation of firing frequency is at least partially induced by hyperpolarizing effects on the action potential threshold, and that this facilitation is induced by activation of PI3-K but not MAPK cascade.     

The effect of epidermal growth factor on production of vascular endothelial growth factor by amnion-derived (WISH) cells

Our objective was to clarify the physiological role of vascular endothelial growth factor (VEGF) by amnion-derived (WISH) cells. WISH cells were cultured, and the effect of epidermal growth factor (EGF), mitogen-activated protein (MAP) kinase kinase or extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitors (U0126) or phosphatidylinositol (PI) 3-kinase on the production of VEGF was examined. VEGF was assayed by ELISA. The activation of MAP kinase and akt, which is phosphorylated by PI 3-kinase, were detected by Western blot analysis using anti-phosphorylated MAP kinase antibody and anti-phosphorylated akt antibody. In the time course of VEGF production following EGF treatment, VEGF production showed a significant increase only after 16 (p < 0.01)–32?h (p < 0.01). EGF increased the production of VEGF by WISH cells in a dose-dependent manner. The MAP kinase and akt activity were determined by treatment with EGF. VEGF production was significantly decreased following pretreatment with U0126 or wortmannin for two hours before treatment with EGF (p < 0.01, p < 0.01). WISH cells appeared to produce VEGF via a mechanism involving tyrosine kinase activation of EGF receptor and MAP kinase or PI 3-kinase. It is suggested that VEGF may contribute to the neovascularization and proliferation of the placenta and gestational tissue, and EGF may play an important role in regulation of VEGF production in the placenta.     

Phosphatidylinositol 3-kinase and ERK1/2 are not involved in adenosine A1, A2A or A3 receptor-mediated preconditioning in rat ventricle strips

Mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase 1 and 2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3-kinase)/protein kinase B (PKB; also known as Akt) are important antiapoptotic signalling pathways which have recently been implicated in cardioprotection. However, at present the involvement of ERK1/2 and PI3-kinase/PKB in adenosine receptor-mediated cardioprotection is poorly understood. In this study we used isolated rat right ventricular strips, contracted by electrical-field stimulation, in order to investigate the role of ERK1/2 and PI3-kinase/PKB in adenosine receptor-induced cardioprotection. Ventricle strips were pretreated for 2 min with the agonists adenosine (non-selective), CPA (A1 selective), CGS 21680 (A2A selective) and Cl-IB-MECA (A3 selective) before 30 min hypoxia followed by 30 min reoxygenation. Each agonist significantly improved posthypoxic percentage contraction recovery compared to control strips. Similarly hypoxic preconditioning (10 min hypoxia followed by 20 min reoxygenation) significantly improved posthypoxic percentage contraction recovery compared to non-preconditioned strips. The selective adenosine receptor antagonists DPCPX (A1), ZM 241385 (A2A) and MRS 1220 (A3) attenuated cardioprotection induced by CPA, CGS 21680 and Cl-IB-MECA, respectively. Pre-incubation (30 min) of ventricle strips with the MEK1 inhibitor PD 98059 (50 microM) or the PI3-kinase inhibitor wortmannin (100 nM) significantly reduced posthypoxic percentage contraction recovery induced by hypoxic preconditioning. In contrast, PD 98059 and wortmannin had no significant effect on cardioprotection induced by CPA, Cl-IB-MECA or CGS 21680. Overall these data indicate that although selective A1, A2A and A3 adenosine receptor agonists induce preconditioning in rat right ventricular strips the effects are independent of ERK1/2- and PI3-kinase-dependent pathways. In contrast ERK1/2 and PI3-kinase-dependent pathways do appear to be involved in early hypoxic preconditioning.     

脂联素激活AKT抑制H2O2诱导的大鼠心肌细胞凋亡

目的: 观察脂联素(adiponectin)对H₂O₂诱导的大鼠心肌细胞(H9c2)凋亡的影响并探讨其作用机制。方法: 应用脱氧三磷酸尿苷缺口末端标记(TUNEL)法观察脂联素对H₂O₂诱导的H9c2细胞凋亡的影响;应用Western blotting法观察脂联素对Akt和caspase-3活性的影响。结果: 脂联素对H₂O₂诱导的H9c2细胞凋亡具有显著的抑制作用(P<0.01)。脂联素直接激活Akt并增加了H₂O₂诱导的Akt活性,对H₂O₂诱导的caspase-3激活有显著抑制作用(P<0.01)。 Akt上游激酶PI3K的特异抑制剂LY294002 不但增加了H₂O₂诱导的H9c2细胞凋亡率,而且消除了脂联素的抗凋亡作用。结论: 脂联素对H₂O₂诱导的H9c2细胞凋亡具有抑制作用,其机制可能与其激活PI3K/Akt通路、抑制caspase凋亡信号通路有关。     

Protective effect of nicotine on tunicamycin-induced apoptosis of PC12h cells

Nicotine has been reported to have neuroprotective effects. The present study deals with the neuroprotective effect of nicotine on the tunicamycin-induced apoptosis of PC12h cells. Treatment of PC12h cells with tunicamycin causes endoplasmic reticulum stress leading to apoptosis. Nicotine dose-dependently prevented the tunicamycin-induced apoptosis. Hoechst 33258 staining demonstrated the protective effect of nicotine against tunicamycin-induced apoptosis. Treatment with nicotinic acetylcholine receptor (nAChR) and L-type voltage-sensitive calcium channel (L-VSCC) antagonists prevented the nicotine-induced protective effect. A phosphatidylinositol 3-kinase (PI3-K) inhibitor had no influence on the nicotine-induced neuroprotective effect. These results show that the neuroprotective effect of nicotine occurs through nAChRs including the alpha 7 subtype and L-VSCC in PC12h cells and not through the PI3-K/Akt pathway.     

Testosterone up-regulates seladin-1 expression by iAR and PI3-K/Akt signaling pathway in C6 cells

The previous study indicated that DHCR24/seladin-1 was an important neuroprotective effector. However, the molecular mechanisms that androgen modulates the expression of seladin-1 remain incompletely defined. In this paper, we showed that the expression of seladin-1 was significantly increased by testosterone at all concentrations tested at the protein and mRNA levels in C6 cells, the selective AR antagonist flutamide obviously inhibited the effect in a concentration-dependent manner. Furthermore, we found that testosterone significantly increased the phosphorylation level of V-akt murine thymoma viral oncogene (Akt), a key effector of the phosphoinositide 3-kinase (PI3-K)/Akt signaling pathway, while a specific PI3-K inhibitor LY294002 obviously prevented the activation of Akt phosphorylation. In addition, the PI3-K inhibitor LY294002 also markedly blocked the up-regulation expression of seladin-1 gene induced by testosterone at the protein and mRNA levels. Collectively, the above results suggested that testosterone regulated the expression of seladin-1 by the intracellular androgen receptor (iAR)-mediated genomic signaling pathway and the non-genomic PI3-K/Akt signaling pathway in C6 glial cells.     

Protection of CD95-mediated apoptosis by activation of phosphatidylinositide 3-kinase and protein kinase B

Apoptosis may be triggered, in a variety of tissues, by interaction of the cell surface molecule CD95 with its specific ligand, CD95L. CD95 plays a physiological role in the regulation of the immune response; furthermore, alterations in CD95/CD95L function may contribute to the pathogenesis of a number of human diseases, including cancer, autoimmune diseases and viral infections. Many cells that express CD95, however, are not susceptible to CD95-mediated apoptosis. It is therefore important to identify the mechanisms that counteract the CD95 apoptotic process that are still poorly understood. Growth factors and lymphokines such as interleukin (IL)-4 that counteract CD95-mediated apoptosis may activate phosphatidylinositide 3-kinase (PI 3-kinase). We therefore used two different approaches to investigate the role of PI 3-kinase on CD95-mediated apoptosis. First we tested the effect of two pharmacological PI 3-kinase inhibitors, wortmannin and LY294002, on CD95 agonistic antibody-induced apoptosis in three different cell lines. Second, we co-expressed in COS7 cells CD95 with constitutively active PI 3-kinase. Results of both approaches indicate that active PI 3-kinase effectively protects against CD95-mediated apoptosis. Furthermore we extended our studies on the CD95 downstream mediator, FADD, and on the PI 3-kinase downstream mediator, the serine/threonine protein kinase PKB, using the co-expression approach in COS7 cells. We provide evidence that apoptosis induced by triggering the CD95 cell death receptor is counteracted by PI 3-kinase activation; moreover, PKB but not p70S6K represents the relevant downstream target of PI 3-kinase signaling.     

The effects of dehydrocostus lactone on osteoblastic MC3T3-E1 cells in redox changes and PI3K/Akt/CREB

Antimycin A (AMA) inhibits mitochondrial electron transport chain between cytochrome b and c. In the present study, we investigated the effects of dehydrocostus lactone on osteoblastic MC3T3-E1 cells in the presence of AMA with a focus on redox changes and PI3K/Akt/CREB signaling. AMA increased nitrotyrosin level and decreased NADPH level, activities of thioredoxin reductase, phosphoinositide 3-kinase (PI3K), and Akt (protein kinase B [PKB]), and phosphorylated cAMP-response element-binding protein (CREB). Pretreatment with dehydrocostus lactone prior to AMA exposure significantly prevented the loss of NADPH, production of nitrotyrosine, and thioredoxin reductase inactivation induced by AMA. Moreover, dehydrocostus lactone increased activities of PI3K and Akt, and CREB phosphorylation inhibited by AMA. These results suggest that antioxidant activity and PI3K/Akt/CREB activation are related to the protective effect of dehydrocostus lactone against osteoblast damage induced by AMA.     

Integrating signals from T-cell receptor and serum by T cells enhance translation of tumour necrosis factor-alpha

Tumour necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine produced by several cell types, including T cells upon antigen stimulation. Its production is crucial for the development of an early defence against many pathogens, but its beneficial effects are dependent on the strength and duration of its expression. In this paper we present evidence indicating that serum increases translational efficiency of TNF-alpha in human peripheral blood mononuclear cells stimulated with superantigen. The increase in translation of TNF-alpha due to serum could be inhibited by the phosphatidylinositol (PI) 3-K inhibitors, wortmannin and LY294002, suggesting that PI 3-K is involved in the translational control of TNF-alpha by serum. Similarly to primary T cells, stimulation of Jurkat T cells with superantigen led to TNF-alpha secretion and this was up-regulated by serum. Transfection of Jurkat cells with a constitutively active form of PI 3-Kalpha increased the production of TNF-alpha in cells stimulated with superantigen. Additionally, we used the specific inhibitors targeting ERK kinase and p38 mitogen-activated protein kinase (MAPK), potentially downstream of PI 3-kinase, PD98059 and SB203580. Differently from with PI 3-K inhibitors, the accumulation of TNF-alpha mRNA was inhibited by PD98059 or SB203580. These results suggest that, in T cells, activation of PI 3-K is an important step in controlling TNF-alpha protein synthesis in response to growth factors.