Insensitivity of PI3K/Akt/GSK3 signaling in peripheral blood mononuclear cells of age-related macular degeneration patients

Our recent studies with cultured retinal pigment epithelium cells suggested that overexpression of interleukin 17 receptor C (IL-17RC), a phenomenon observed in peripheral blood and chorioretinal tissues with age-related macular degeneration (AMD), was associated with altered activation of phosphatidylinositide 3-kinase (PI3K), Akt, and glycogen synthase kinase 3 (GSK3). We wondered whether or not altered PI3K, Akt, and GSK3 activities could be detected in peripheral blood mononuclear cells (PBMC) obtained from AMD patients. In the patients' PBMC, absentor reduced serine-phosphorylation of GSK3α or GSK3β was observed, which was accompanied with increased phosphorylation of GSK3 substrates (e.g. CCAAT enhancer binding protein α, insulin receptor substrate 1, and TAU), indicative of enhanced GSK3 activation. In addition, decreased protein mass of PI3K85α and tyrosinephosphorylation of PI3K50α was present in PBMC of the AMD patients, suggesting impaired PI3K activation. Moreover, abnormally lowered molecular weight forms of Akt and GSK3 were detected in PBMC of the AMD patients. These data demonstrate that despite the presence of high levels of IL-17RC, Wnt-3a and vascular endothelial growth factor, the PI3K/Akt/GSK3 signaling pathway is insensitive to these stimuli in PBMC of the AMD patients. Thus, measurement of PI3K/Akt/GSK3 expression and activity in PBMC may serve as a surrogate biomarker for AMD.     

Regulation of SHP2 by PTEN/AKT/GSK-3β signaling facilitates IFN-γ resistance in hyperproliferating gastric cancer

Oncogenic activation accompanied by escape from immune surveillance, such as IFN-γ resistance, is critical for cancer cell growth and survival. In this study, we investigated the crosstalk signaling between IFN-γ resistance and signaling of hyperproliferation in gastric cancer cells. IFN-γ inhibited the cell growth of MKN45 cells but not hyperproliferating AGS cells. AGS cells did not respond to IFN-γ because of a decrease in STAT1 but not due to dysfunctional IFN-γ receptors. Signaling of PI3K/AKT, as well as MEK/ERK, was required for the hyperproliferation; notably, PI3K/AKT alone mediated the IFN-γ resistance. Aberrant Src homology-2 domain-containing phosphatase (SHP) 2 determined IFN-γ resistance but unexpectedly had no effects on hyperproliferation or ERK activation. In the IFN-γ resistant cells, inactivation of glycogen synthase kinase (GSK)-3β by PI3K/AKT was important for SHP2 activation but not for hyperproliferation. An imbalance of AKT/GSK-3β/SHP2 caused by a reduction of PTEN was important for the crosstalk between IFN-γ resistance and hyperproliferation. PI3K is constitutively expressed in AGS cells and immunohistochemical staining showed a correlation between hyperproliferation and expression of SHP2 and STAT1 in gastric tumors. These results demonstrate the effects of PTEN/AKT/GSK-3β/SHP2 signaling on IFN-γ resistance in hyperproliferating gastric cancer cells.     

Glycogen synthase kinase-3β inactivation is an intracellular marker and regulator for endotoxemic neutrophilia

Neutrophilia, defined as a large number of neutrophils in the circulating blood, is caused by increased differentiation and survival from activation-induced apoptosis. Regulation of apoptosis is essential for neutrophil homeostasis; however, the molecular signaling that regulates this process needs further investigation. Unlike TLR4 wild-type C3H/HeN mice, TLR4 mutated C3H/HeJ mice were insusceptible to LPS-induced blood neutrophilia. LPS prevented constitutive apoptosis in neutrophils and partly involved a blockade of the mitochondrial pathway including mitochondria transmembrane potential loss, myeloid cell leukemia sequence (Mcl) 1 degradation, and caspase-3 activation. In apoptotic neutrophils, glycogen synthase kinase (GSK)-3β was activated, and inhibiting GSK-3β decreased Mcl-1 degradation and apoptosis. LPS caused p38 MAPK-, JNK-, and PI3K/AKT-mediated Mcl-1 stabilization and prevented apoptosis, and LPS induced GSK-3β inactivation mainly through p38 MAPK and PI3K/AKT. Neutrophils in the neutrophilia showed increased GSK-3β inactivation and Mcl-1 stabilization accompanied by activation of p38 MAPK, JNK, and AKT. Notably, LPS-induced ROS generation can partly facilitate p38 MAPK/JNK/AKT activation to regulate GSK-3β-mediated Mcl-1 stability, apoptosis, and neutrophilia. These results demonstrate that the molecular basis of endotoxemic neutrophilia is through a direct action on neutrophils involving GSK-3β inactivation to prevent constitutive apoptosis.     

Activation of the PKB/AKT pathway by ICAM-2

We identified intracellular adhesion molecule-2 (ICAM-2) in a genetic screen as an activator of the PI3K/AKT pathway leading to inhibition of apoptosis. ICAM-2 induced tyrosine phosphorylation of ezrin and PI3K kinase membrane translocation, resulting in phosphatidylinositol 3,4,5 production, PDK-1 and AKT activation, and subsequent phosphorylation of AKT targets BAD, GSK3, and FKHR. ICAM-2 clustering protected primary human CD19+ cells from TNFalpha- and Fas-mediated apoptosis as determined by single-cell analysis. ICAM-2 engagement by CD19+ cells of its natural receptor, LFA-1, on CD4+ naive cells specifically induced AKT activity in the absence of an MHC-peptide interaction. These results attribute a novel signaling function to ICAM-2 that might suggest mechanisms by which ICAM-2 signals intracellular communication at various immunological synapses.     

PI3Kγ kinase activity is required for optimal T‐cell activation and differentiation

Phosphatidylinositol‐3‐kinase gamma (PI3Kγ) is a leukocyte‐specific lipid kinase with signaling function downstream of G protein‐coupled receptors to regulate cell trafficking, but its role in T cells remains unclear. To investigate the requirement of PI3Kγ kinase activity in T‐cell function, we studied T cells from PI3Kγ kinase‐dead knock‐in (PI3Kγ^KD/KD) mice expressing the kinase‐inactive PI3Kγ protein. We show that CD4⁺ and CD8⁺ T cells from PI3Kγ^KD/KD mice exhibit impaired TCR/CD28‐mediated activation that could not be rescued by exogenous IL‐2. The defects in proliferation and cytokine production were also evident in naïve and memory T cells. Analysis of signaling events in activated PI3Kγ^KD/KD T cells revealed a reduction in phosphorylation of protein kinase B (AKT) and ERK1/2, a decrease in lipid raft formation, and a delay in cell cycle progression. Furthermore, PI3Kγ^KD/KD CD4⁺ T cells displayed compromised differentiation toward Th1, Th2, Th17, and induced Treg cells. PI3Kγ^KD/KD mice also exhibited an impaired response to immunization and a reduced delayed‐type hypersensitivity to Ag challenge. These findings indicate that PI3Kγ kinase activity is required for optimal T‐cell activation and differentiation, as well as for mounting an efficient T cell‐mediated immune response. The results suggest that PI3Kγ kinase inhibitors could be beneficial in reducing the undesirable immune response in autoimmune diseases.     

CD5 enhances Th17‐cell differentiation by regulating IFN‐γ response and RORγt localization

Mechanisms that modulate the generation of Th17 cells are incompletely understood. We report that the activation of casein kinase 2 (CK2) by CD5 is essential for the efficient generation of Th17 cells in vitro and in vivo. In our study, the CD5–CK2 signaling pathway enhanced TCR‐induced activation of AKT and promoted the differentiation of Th17 cells by two independent mechanisms: inhibition of glycogen synthase kinase 3 (GSK3) and activation of mTOR. Genetic ablation of the CD5–CK2 signaling pathway attenuated TCR‐induced AKT activation and consequently increased activity of GSK3 in Th17 cells. This resulted in increased sensitivity of Th17 cells to IFN‐γ‐mediated inhibition. In the absence of CD5‐CK2 signaling, we observed decreased activity of S6K and attenuated nuclear translocation of RORγt (ROR is retinoic acid receptor related orphan receptor). These results reveal a novel and essential function of the CD5–CK2 signaling pathway and GSK3–IFN‐γ axis in regulating Th‐cell differentiation and provide a possible means to dampen Th17‐type responses in autoimmune diseases.     

Development of highly sensitive cell-based AKT kinase ELISA for monitoring PI3K beta activity and compound efficacy

Phosphatidylinositol-3 kinase (PI3K) pathway regulates multiple cellular functions involving cell survival, growth, motility proliferation, apoptosis, and adhesion. These are deregulated in various diseases such as cancer, atherosclerosis, and inflammation. PI3Ks phosphorylate phosphatidylinositol 4,5-biphosphate (PIP2) yielding phosphatidylinositol 3, 4, 5 triphosphate (PIP3) which in turn activate AKT kinase (serine/threonine kinase), the central enzyme in regulation of metabolic functions. Due to their implications in disease pathophysiology, PI3K/AKT inhibitors became attractive targets for pharmaceutical industries. In order to assess the functional response generated by PI3K inhibitors, an appropriate cell-based screening system is essential in any screening cascade. Here we report the development of highly sensitive in-vitro cell-based kinase ELISA which quantifies the phosphorylated AKT kinase (serine 473) and total AKT kinase directly within the cells upon compound treatment. PI3Kβ overexpressing NIH3T3 cells stimulated by lysophosphatidic acid was used for PI3K/Akt pathway activation. Assay performance reliability and robustness were determined by percentage coefficient of variation (%CV) and Z factor which demonstrated an excellent agreement with assay guidelines. This 96-well plate medium throughput assay methodology was used to screen novel molecules and proved a commendable tool to study the mechanism of action property and target engagement of novel PI3K inhibitors in drug discovery.     

磷脂酰肌醇3激酶β(PI3Kβ)和PI3Kδ在KIT突变介导的细胞转化中起不同作用

目的 探究磷脂酰肌醇3激酶(PI3K)的不同亚型在三型酪氨酸激酶受体KIT突变介导的信号传递及细胞增殖中的作用.方法 在BaF3细胞中稳定表达野生型KIT及胃肠间质瘤中常见的KIT突变V560D、W557K558del,分别用PI3Kα、PI3Kβ、PI3Kδ亚型特异性抑制剂或者广谱PI3K抑制剂处理细胞,免疫沉淀法和...     

Hypoxic inactivation of glycogen synthase kinase‐3β promotes gastric tumor growth and angiogenesis by facilitating hypoxia‐inducible factor‐1 signaling

Since the molecular mechanism of hypoxic adaptation in cancer cells is cell‐type specific, we investigated whether glycogen synthase kinase‐3β (GSK‐3β) activation is involved in hypoxia‐induced gastric tumor promotion. Stable gastric cancer cell lines (SNU‐638, SNU‐484, MKN1, and MKN45) were cultured under hypoxic conditions. Cells overexpressing wild‐type GSK‐3β (WT‐GSK‐3β) or kinase‐dead mutant of GSK‐3β (KD‐GSK‐3β) were generated and used for cell culture and animal studies. In cell culture experiments, hypoxia decreased GSK‐3β activation in gastric cancer cells. Cell viability and the expressions of HIF‐1α protein and VEGF mRNA in gastric cancer cells were higher in KD‐GSK‐3β transfectants than in WT‐GSK‐3β transfectants under hypoxic conditions, but not under normoxic conditions. Gastric cancer xenografts showed that tumor growth, microvessel area, HIF‐1α activation, and VEGF expression were higher in KD‐GSK‐3β tumors than in WT‐GSK‐3β tumors in vivo. In addition, the expression of hypoxia‐induced HIF‐1α protein was regulated by GSK‐3β at the translational level. Our data suggest that GSK‐3β is involved in hypoxic adaptation of gastric cancer cells as an inhibitory upstream regulator of the HIF‐1α/VEGF signaling pathway.     

TREM‐2 Promotes Macrophage‐Mediated Eradication of Pseudomonas aeruginosa via a PI3K/Akt Pathway

Triggering receptor expressed on myeloid cells 2 (TREM‐2) is a cell surface receptor abundantly expressed on myeloid lineage cells such as macrophages and dendritic cells. It is reported that TREM‐2 functions as an inflammatory inhibitor in macrophages and dendritic cells. However, the role of TREM‐2 in bacterial killing remains unclear. This study explored the role of TREM‐2 in bacterial eradication of Pseudomonas aeruginosa (PA), a Gram‐negative bacterium which causes various opportunistic infections. Phagocytosis assay assessed by flow cytometry suggested that TREM‐2 was not involved in the uptake of PA by macrophages, while bacterial plate count data showed that TREM‐2 was required for macrophage‐mediated intracellular killing of PA. Moreover, our results demonstrated that TREM‐2 promoted macrophage killing by enhancing reactive oxygen species (ROS), but not nitric oxygen (NO) production. Treatment with N‐acetylcysteine, a ROS scavenger, diminished the TREM‐2‐mediated intracellular killing of PA. To further investigate the underlined mechanisms of TREM‐2‐promoted bacterial killing, we examined the activation of downstream mitogen‐activated protein kinases and PI3K/Akt pathway. Western blot data showed that silencing of TREM‐2 inhibited phosphorylation of Akt, but not ERK, JNK or P38. In addition, pretreatment with PI3K active product PIP3 DiC16 reversed the elevation of intracellular bacterial load in TREM‐2‐silenced macrophages, while PI3K inhibitor wortmannin restored the decline of bacterial load in TREM‐2‐overexpressed macrophages. These data together suggested that the TREM‐2‐mediated bacterial killing is dependent on the activation of PI3K/Akt signalling, which may provide a better understanding of the host antibacterial immune defence.     

Post‐ischaemic activation of kinases in the pre‐conditioning‐like cardioprotective effect of the platelet‐activating factor

Aim: Platelet‐activating factor (PAF) triggers cardiac pre‐conditioning against ischemia/reperfusion injury. The actual protection of ischaemic pre‐conditioning occurs in the reperfusion phase. Therefore, we studied in this phase the kinases involved in PAF‐induced pre‐conditioning. Methods: Langendorff‐perfused rat hearts underwent 30 min of ischaemia and 2 h of reperfusion (group 1, control). Before ischaemia, group 2 hearts were perfused for 19 min with PAF (2 × 10^?11 m ); groups 3–5 hearts were co‐infused during the initial 20 min of reperfusion, with the protein kinase C (PKC) inhibitor chelerythrine (5 × 10^?6 m ) or the phosphoinositide 3‐kinase (PI3K) inhibitor LY294002 (5 × 10^?5 m ) and atractyloside (2 × 10^?5 m ), a mitochondrial permeability transition pore (mPTP) opener respectively. Phosphorylation of PKCε, PKB/Aκt, GSK‐3β and ERK1/2 at the beginning of reperfusion was also checked. Left ventricular pressure and infarct size were determined. Results: PAF pre‐treatment reduced infarct size (33 ± 4% vs. 64 ± 5% of the area at risk of control hearts) and improved pressure recovery. PAF pre‐treatment enhanced the phosphorylation/activation of PKCε, PKB/Aκt and the phosphorylation/inactivation of GSK‐3β at reperfusion. Effects on ERK1/2 phosphorylation were not consistent. Infarct‐sparing effect and post‐ischaemic functional improvement induced by PAF pre‐treatment were abolished by post‐ischaemic infusion of either chelerythrine, LY294002 or atractyloside. Conclusions: The cardioprotective effect exerted by PAF pre‐treatment involves activation of PKC and PI3K in post‐ischaemic phases and might be mediated by the prevention of mPTP opening in reperfusion via GSK‐3β inactivation.     

Phosphoinositide‐dependent protein kinase 1 (PDK1) mediates potent inhibitory effects on eosinophils

Prostaglandin E₂ (PGE₂) protects against allergic responses via binding to prostanoid receptor EP4, which inhibits eosinophil migration in a PI3K/PKC‐dependent fashion. The phosphoinositide‐dependent protein kinase 1 (PDK1) is known to act as a downstream effector in PI3K signaling and has been implicated in the regulation of neutrophil migration. Thus, here we elucidate whether PDK1 mediates inhibitory effects of E‐type prostanoid receptor 4 (EP4) receptors on eosinophil function. Therefore, eosinophils were isolated from human peripheral blood or differentiated from mouse BM. PDK1 signaling was investigated in shape change, chemotaxis, CD11b, respiratory burst, and Ca²⁺ mobilization assays. The specific PDK1 inhibitors BX‐912 and GSK2334470 prevented the inhibition by prostaglandin E₂ and the EP4 agonist ONO‐AE1‐329. Depending on the cellular function, PDK1 seemed to act through PI3K‐dependent or PI3K‐independent mechanisms. Stimulation of EP4 receptors caused PDK1 phosphorylation at Ser396 and induced PI3K‐dependent nuclear translocation of PDK1. EP4‐induced inhibition of shape change and chemotaxis was effectively reversed by the Akt inhibitor triciribine. In support of this finding, ONO‐AE1‐329 induced a PI3K/PDK1‐dependent increase in Akt phosphorylation. In conclusion, our data illustrate a critical role for PDK1 in transducing inhibitory signals on eosinophil effector function. Thus, our results suggest that PDK1 might serve as a novel therapeutic target in diseases involving eosinophilic inflammation.     

Glycogen synthase kinase‐3β ablation limits pancreatitis‐induced acinar‐to‐ductal metaplasia

Acinar‐to‐ductal metaplasia (ADM) is a reversible epithelial transdifferentiation process that occurs in the pancreas in response to acute inflammation. ADM can rapidly progress towards pre‐malignant pancreatic intraepithelial neoplasia (PanIN) lesions in the presence of mutant KRas and ultimately pancreatic adenocarcinoma (PDAC). In the present work, we elucidate the role and related mechanism of glycogen synthase kinase‐3beta (GSK‐3β) in ADM development using in vitro 3D cultures and genetically engineered mouse models. We show that GSK‐3β promotes TGF‐α‐induced ADM in 3D cultured primary acinar cells, whereas deletion of GSK‐3β attenuates caerulein‐induced ADM formation and PanIN progression in Kras^G12D transgenic mice. Furthermore, we demonstrate that GSK‐3β ablation influences ADM formation and PanIN progression by suppressing oncogenic KRas‐driven cell proliferation. Mechanistically, we show that GSK‐3β regulates proliferation by increasing the activation of S6 kinase. Taken together, these results indicate that GSK‐3β participates in early pancreatitis‐induced ADM and thus could be a target for the treatment of chronic pancreatitis and the prevention of PDAC progression. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

MicroRNA-145通过丝裂原活化蛋白激酶和磷脂酰肌醇3激酶/蛋白质丝氨酸苏氨酸激酶通路调控肺癌A549细胞系转移及侵袭

目的 探讨microRNA-145(miR-145)对非小细胞肺癌A549细胞转移、侵袭及对丝裂原活化蛋白激酶(MAPK)和磷脂酰肌醇3激酶/蛋白质丝氨酸苏氨酸激酶（PI3K/AKT）通路的作用。 方法 将非小细胞肺癌A549细胞分成miR-145模拟物（mimics）组和negative-mimics组（miR-NC）以及antago miR-145组（抑制剂组）和antago miR control 组（antago-NC）,采用Transwell迁移实验及基质胶侵袭实验等检测miR-145对人非小细胞肺癌A549迁移、侵袭能力的影响;Western blotting方法分析miR-145对MAPK和PI3K/AKT通路的影响。此外,采用细胞外调节蛋白激酶（ERK）及AKT的通路抑制剂分别作用于A549细胞系,检测A549细胞迁移、侵袭能力的改变。 结果 miR-145 mimics组穿过细胞数（90.67±10.33）明显少于miR-NC组（175.33±23.67）,miR-145 mimics组穿过基质胶的细胞数（153.33±22.33）少于miR-NC组 (77.33±13.67）,P<0.05;antago-NC组通过小室的细胞数量以及穿过基质胶的细胞数量明显少于antago miR-145组（P<0.05）,结果说明,miR-145具有抑制非小细胞肺癌A549细胞迁移、侵袭的能力;miR-145 mimics转染可分别抑制A549细胞中90%、78%以及73%的ERK1/2、AKT的ser-473位点和thr-308位点的磷酸化,antago miR-145转染可促进A549细胞中ERK1/2、AKT的ser-473位点和thr-308位点的磷酸化,增加115%、125%以及129%,而当抑制MAPK通路及PI3K/AKT通路的激活后,A549细胞的转移及侵袭能力下降。 结论 miR-145通过MAPK和PI3K/AKT通路调控肺癌A549细胞转移及侵袭。