PI3K/Akt信号传导通路与肿瘤

信号转导通路的异常激活是肿瘤细胞的发生、发展重要步骤,PI3K/Akt 信号通路在人类绝大多数恶性肿瘤中被异常激活,其在肿瘤的增殖、存活、细胞运动、抵抗凋亡、血管发生和转移以及对化疗耐药、放疗抗拒中发挥了重要作用.因此,通过对PI3K/Akt 通路的研究进一步了解肿瘤的发生、发展机制,并寻求抗肿瘤药物的新靶点,本文就 PI3K/Akt 信号转导通路的结构特点、与肿瘤发生、发展的关系及其时放化疗的影响作一综述.     

Gadolinium promoted proliferation in mouse embryo fibroblast NIH3T3 cells through Rac and PI3K/Akt signaling pathways

Nephrogenic systemic fibrosis (NSF) is a fibrosing disorder disease developed in patients with underlying renal insufficiency following exposure to gadolinium-based contrast agents (GBCAs). Previous studies have demonstrated that GdCl₃ can promote NIH3T3 fibroblast cell proliferation, which provide a new clue to the role of GBCAs in the development of NSF. In the present study, we further clarify the molecular mechanism of Gd-promoted proliferation. The results showed that intervention with the Rac inhibitor NSC23766 abrogated Gd-promoted proliferation. The levels of active Rac1 significantly increased in Gd-treated cells detected by pull-down assays. In addition, the phosphorylation of Akt was significantly elevated in the treatment group, which was blocked by NSC23766. NSC23766 also reduced the migration of NIH3T3 cells enhanced by Gd. Moreover, the F-actin cytoskeleton was strengthened and the mitotic cell numbers was significantly increased after exposure to Gd. These results suggest that Rac and PI3K/Akt signaling pathways, as well as integrin-mediated signal pathway may play important roles in Gd-induced cell proliferation. In addition, under serum-free condition, Gd could decrease ROS accumulation and increase NIH3T3 cell survival.     

Regulation of survivin by PI3K/Akt/p70S6K1 pathway

PI3K activation is commonly observed in many human cancer cells. Survivin expression is elevated in cancer cells, and induced by some growth factors through PI3K activation. However, it is not clear whether PI3K activation is sufficient to induce survivin expression. To investigate the role of PI3K pathway in the regulation of survivin, we expressed an active form of PI3K, v-P3k in chicken embryonic fibroblast cells (CEF), and found that overexpression of PI3K-induced survivin mRNA expression. Forced expression of wild-type but not mutant tumor suppressor PTEN in CEF decreased survivin mRNA levels. PI3K regulates survivin expression through Akt activation. To further investigate downstream target of PI3K and Akt in regulating the expression of survivin mRNA, we found that PI3K and Akt-induced p70S6K1 activation and that overexpression of p70S6K1 alone was sufficient to induce survivin expression. The treatment of CEF cells by rapamycin decreased the survivin mRNA expression. This result demonstrated that p70S6K1 is an important target downstream of PI3K and Akt in regulating suvivin mRNA expression. The knockdown of survivin mRNA expression by its specific siRNA induced apoptosis of cancer cells when the cells were treated with LY294002 or taxol. Taken together, these results demonstrated that PI3K/Akt/p70S6K1 pathway is essential for regulating survivin mRNA expression.     

PI3K/Akt信号通路与肺纤维化

肺纤维化(pulmonary fibrosis)是进行性、致命性的疾病。其致病机制不明,治疗效果差。PI3K/Akt信号通路主要与细胞的生长、增殖、分化、凋亡及血管形成等有关。近年来,随着对PI3K/Akt信号通路的深入研究,发现其活化后可激活下游中的一些因子参与肺纤维化,且与其他通路协同作用促进肺纤维化的形成。因此该通路有可能成为治疗肺纤维化的新靶点。将PI3K/Akt信号通路参与肺纤维化形成的研究进展作一综述。     

Roxarsone induces angiogenesis via PI3K/Akt signaling

Background

3-Nitro-4-hydroxy phenyl arsenic acid, roxarsone, is widely used as an organic arsenic feed additive for livestock and poultry, which may increase the level of arsenic in the environment and the risk of exposure to arsenic in human. Little information is focused on the angiogenesis roxarsone-induced and its mechanism at present. This paper aims to study the role of PI3K/Akt signaling in roxarsone-induced angiogenesis in rat vascular endothelial cells and a mouse B16–F10 melanoma xenograft model.

Results

The results showed that treatment with 0.1–10.0 µmol/L roxarsone resulted in an increase in the OD rate in the MTT assay, the number of BrdU-positive cells in the proliferation assay, the migration distance in the scratch test and the number of meshes in tube formation assay. Further, treatment with 1.0 µmol/L roxarsone was associated with significantly higher phosphorylation of PI3K/Akt and expression of VEGF than the control treatment. The PI3K inhibitor was found to significantly combat the effects of 1.0 µmol/L roxarsone. Furthermore, roxarsone treatment was observed to increase the weight and volume of B16–F10 xenografts and VEGF expression and PI3K/Akt phosphorylation in a dose-dependent manner, with the 25 mg/kg dose having significant effects.

Conclusions

These results demonstrate that roxarsone has the ability to promote growth and tube formation in vascular endothelial cells and the growth of mouse B16–F10 xenografts. Further, the findings also indicate that PI3K/Akt signaling plays a regulatory role in roxarsone-induced angiogenesis in vivo and in vitro.

     

PI3K和Akt蛋白在异丙肾上腺素所致大鼠心肌肥厚中的表达

目的研究异丙肾上腺素(ISO)致大鼠心肌肥厚中PI3K和Akt在心肌组织中的表达,为探讨心肌肥厚的信号转导机制和逆转心肌肥厚提供形态学资料.方法健康成年SD大鼠20只,随机分为实验组、对照组,每组10只.实验组给予异丙肾上腺素处理.1周后处死大鼠,取心肌组织,常规石蜡切片,HE染色,观察心肌组织的病理变化,测量心肌肥厚指标;免疫组织化学染色和免疫荧光染色,检测p-PI3K和p-Akt的表达及分布.结果实验组大鼠心肌肥厚指标与对照组相比均明显升高;免疫组织化学检测显示,实验组心肌组织p-PI3K和p-Akt蛋白表达面积和平均光密度较对照组高.免疫荧光检测实验组心肌组织p-PI3K和p-Akt蛋白表达较对照组高.结论小剂量持续给予 ISO 能建立大鼠心肌肥厚模型;p-PI3K和p-Akt蛋白表达均与心肌肥厚的发生和发展过程相关,PI3K/Akt信号通路激活,可能是导致心肌肥厚的机制之一.     

Integrin αIIb-Mediated PI3K/Akt Activation in Platelets

Integrin αIIbβ3 mediated bidirectional signaling plays a critical role in thrombosis and haemostasis. Signaling mediated by the β3 subunit has been extensively studied, but αIIb mediated signaling has not been characterized. Previously, we reported that platelet granule secretion and TxA2 production induced by αIIb mediated outside-in signaling is negatively regulated by the β3 cytoplasmic domain residues R₇₂₄KEFAKFEEER₇₃₄. In this study, we identified part of the signaling pathway utilized by αIIb mediated outside-in signaling. Platelets from humans and gene deficient mice, and genetically modified CHO cells as well as a variety of kinase inhibitors were used for this work. We found that aggregation of TxA2 production and granule secretion by β3Δ724 human platelets initiated by αIIb mediated outside-in signaling was inhibited by the Src family kinase inhibitor PP2 and the PI3K inhibitor wortmannin, respectively, but not by the MAPK inhibitor U0126. Also, PP2 and wortmannin, and the palmitoylated β3 peptide R₇₂₄KEFAKFEEER₇₃₄, each inhibited the phosphorylation of Akt residue Ser473 and prevented TxA2 production and storage granule secretion. Similarly, Akt phosphorylation in mouse platelets stimulated by the PAR4 agonist peptide AYPGKF was αIIbβ3-dependent, and blocked by PP2, wortmannin and the palmitoylated peptide p-RKEFAKFEEER. Akt was also phosphorylated in response to mAb D3 plus Fg treatment of CHO cells in suspension expressing αIIbβ3-Δ724 or αIIbβ3E₇₂₄AERKFERKFE₇₃₄, but not in cells expressing wild type αIIbβ3. In summary, SFK(s) and PI3K/Akt signaling is utilized by αIIb-mediated outside-in signaling to activate platelets even in the absence of all but 8 membrane proximal residues of the β3 cytoplasmic domain. Our results provide new insight into the signaling pathway used by αIIb-mediated outside-in signaling in platelets.     

Apelin reduces myocardial reperfusion injury independently of PI3K/Akt and P70S6 kinase

Apelin, the endogenous ligand of the G protein-coupled APJ receptor, is a peptide mediator with emerging regulatory actions in the heart. The aim of the present studies was to explore potential roles of the apelin/APJ system in myocardial ischaemia/reperfusion injury. To determine the cardiac expression of apelin/APJ and potential regulation by acute ischaemic insult, Langendorff perfused rat hearts were subjected to regional ischaemia (left coronary artery occlusion, 35 min) or ischaemia followed by reperfusion (30 min). Apelin and APJ mRNA expression were then determined in ventricular myocardium by rt-PCR. Unlike APJ mRNA expression, which remained unchanged, apelin mRNA was upregulated 2.4 fold in ventricular myocardium from isolated rat hearts undergoing ischaemia alone, but returned back to control levels after 30 min reperfusion. We then proceeded to test the hypothesis that treatment with exogenous apelin is protective against ischaemia/reperfusion injury. Perfused hearts were subjected to 35 min left main coronary artery occlusion and 120 min reperfusion, after which infarct size was determined by tetrazolium staining. Exogenous Pyr(1)-apelin-13 (10(-8 )M) was perfused either from 5 min prior to 15 min after coronary occlusion, or from 5 min prior to 15 min after reperfusion. Whilst ineffective when used during ischaemia alone, apelin administered during reperfusion significantly reduced infarct size (47.6+/-2.6% of ischaemic risk zone compared to 62.6+/-2.8% in control, n=10 each, p<0.05) in hearts subject to temporary coronary occlusion followed by reperfusion. This protective effect was not abolished by co-administration of the PI3K inhibitor wortmannin (10(-7 )M, infarct size 49.8+/-4.1%, n=4) or the P70S6 kinase inhibitor rapamycin (10(-9 )M, 41.8+/-8.8%, n=4). In conclusion these results suggest that apelin may be a new and potentially important cardioprotective autacoid, upregulated rapidly after myocardial ischaemia and acting through an unknown pathway.     

The PI3K/Akt pathway contributes to arenavirus budding

Several arenaviruses, chiefly Lassa virus (LASV), cause hemorrhagic fever (HF) disease in humans and pose a significant public health concern in regions where they are endemic. On the other hand, evidence indicates that the globally distributed prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) is a neglected human pathogen. The phosphatidylinositol 3-kinase (PI3K)/Akt pathway participates in many cellular processes, including cell survival and differentiation, and also has been shown to play important roles in different steps of the life cycles of a variety of viruses. Here we report that the inhibition of the PI3K/Akt pathway inhibited budding and to a lesser extent RNA synthesis, but not cell entry, of LCMV. Accordingly, BEZ-235, a PI3K inhibitor currently in cancer clinical trials, inhibited LCMV multiplication in cultured cells. These findings, together with those previously reported for Junin virus (JUNV), indicate that targeting the PI3K/Akt pathway could represent a novel antiviral strategy to combat human-pathogenic arenaviruses.     

PI3K/Akt信号通路的调控与肿瘤血管生成

肿瘤对人类的生存危害极大,恶性肿瘤的治疗一直是世界性的难题。肿瘤血管生成是肿瘤赖以生长、转移的基础,受多种因子的调节。目前发现有多条信号网络参与调控肿瘤血管生成,PI3K/Akt是其中比较重要的一条信号传导途径,该通路与肿瘤的发生发展密切相关。本文介绍了PI3K/Akt信号通路的结构组成与活性调控,并重点阐述PI3K/Akt信号途径与肿瘤血管生成的关系。     

Effects of PI3K catalytic subunit and Akt isoform deficiency on mTOR and p70S6K activation in myoblasts

The PI3K/Akt/mTOR signaling pathway is critical for cellular growth and survival in skeletal muscle, and is activated in response to growth factors such as insulin-like growth factor-I (IGF-I). We found that in C2C12 myoblasts, deficiency of PI3K p110 catalytic subunits or Akt isoforms had distinct effects on phosphorylation of mTOR and p70S6K. siRNA-mediated knockdown of PI3K p110α, p110β, and simultaneous knockdown of p110α and p110β resulted in increased basal and IGF-I-stimulated phosphorylation of mTOR S2448 and p70S6K T389; however, phosphorylation of S6 was reduced in p110β-deficient cells, possibly due to reductions in total S6 protein. We found that IGF-I-stimulated Akt1 activity was enhanced in Akt2- or Akt3-deficient cells, and that knockdown of individual Akt isoforms increased mTOR/p70S6K activation in an isoform-specific fashion. Conversely, levels of IGF-I-stimulated p70S6K phosphorylation in cells simultaneously deficient in both Akt1 and Akt3 were increased beyond those seen with loss of any single Akt isoform, suggesting an alternate, Akt-independent mechanism that activates mTOR/p70S6K. Our results collectively suggest that mTOR/p70S6K is activated in a PI3K/Akt-dependent manner, but that in the absence of p110α or Akt, alternate pathway(s) may mediate activation of mTOR/p70S6K in C2C12 myoblasts.     

L-threonine regulates G1/S phase transition of mouse embryonic stem cells via PI3K/Akt, MAPKs, and mTORC pathways

Although amino acids can function as signaling molecules in the regulation of many cellular processes, mechanisms surrounding L-threonine involvement in embryonic stem cell (ESC) functions have not been explored. Thus, we investigated the effect of L-threonine on regulation of mouse (m)ESC self-renewal and related signaling pathways. In L-threonine-depleted mESC culture media mRNA of self-renewal marker genes, [(3)H]thymidine incorporation, expression of c-Myc, Oct4, and cyclins protein was attenuated. In addition, resupplying L-threonine (500 μM) after depletion restores/maintains the mESC proliferation. Disruption of the lipid raft/caveolae microdomain through treatment with methyl-β-cyclodextrin or transfection with caveolin-1 specific small interfering RNA blocked L-threonine-induced proliferation of mESCs. Addition of L-threonine induced phosphorylation of Akt, ERK, p38, JNK/SAPK, and mTOR in a time-dependent manner. This activity was blocked by LY 294002 (PI3K inhibitor), wortmannin (PI3K inhibitor), or an Akt inhibitor. L-threonine-induced activation of mTOR, p70S6K, and 4E-BP1 as well as cyclins and Oct4 were blocked by PD 98059 (ERK inhibitor), SB 203580 (p38 inhibitor) or SP 600125 (JNK inhibitor). Furthermore, L-threonine induced phosphorylation of raptor and rictor binding to mTOR was completely inhibited by 24 h treatment with rapamycin (mTOR inhibitor); however, a 10 min treatment with rapamycin only partially inhibited rictor phosphorylation. L-threonine induced translocation of rictor from the membrane to the cytosol/nuclear, which blocked by pretreatment with rapamycin. In addition, rapamycin blocked L-threonine-induced increases in mRNA expressions of trophoectoderm and mesoderm marker genes and mESC proliferation. In conclusion, L-threonine stimulated ESC G(1)/S transition through lipid raft/caveolae-dependent PI3K/Akt, MAPKs, mTOR, p70S6K, and 4E-BP1 signaling pathways.     

PI3K/Akt/mTOR信号通路及临床相关肿瘤抑制剂

哺乳动物雷帕霉素靶（mTOR）和蛋白激酶B（Akt/PKB）与肿瘤发生的密切关系已被广泛地认可.mTOR是一种丝/苏氨酸激酶,可以通过影响mRNA转录、代谢、自噬等方式调控细胞的生长.它既是PI3K的效应分子,也可以是PI3K的反馈调控因子.mTORC1 和mTORC2是mTOR的两种不同复合物. 对雷帕霉素敏感的mTORC1受到营养、生长因子、能量和应激4种因素的影响.生长因子通过PI3K/Akt信号通路调控mTORC1是最具特征性调节路径.而mTORC2最为人熟知的是作为Akt473磷酸化位点的上游激酶. 同样,Akt/PKB在细胞增殖分化、迁移生长过程中发挥着重要作用. 随着Thr308和Ser473两个位点激活,Akt/PKB也得以全面活化.因此,mTORC2-Akt-mTORC1的信号通路在肿瘤形成和生长中是可以存在的.目前临床肿瘤治疗中,PI3K/Akt/mTOR是重要的靶向治疗信号通路.然而,仅抑制mTORC1活性,不是所有的肿瘤都能得到预期控制.雷帕霉素虽然能抑制mTORC1,但也能反馈性地增加PI3K信号活跃度,从而影响治疗预后.近来发现的第二代抑制剂可以同时抑制mTORC1/2和PI3K活性,这种抑制剂被认为在肿瘤治疗上颇具前景.本综述着重阐述了PI3K/Akt/mTOR信号通路的传导、各因子之间的相互调控以及相关抑制剂的发展.     

缺氧诱导因子1与PI3K/Akt/mTOR信号转导通路

缺氧诱导因子1（HIF-1）是参与缺氧调节的核心因子,可调控一系列缺氧诱导基因的表达,与机体许多生理和病理过程也密切相关。尽管一些研究显示缺氧和非缺氧性刺激可通过PI3K/Akt/mTOR信号途径诱导HIF-1的表达和活性,PI3K信号途径是否参与对HIF-1的调节仍然是个有争议的研究热点。明确HIF-1和PI3K的相互作用关系,能进一步为肿瘤等相关疾病的防治提供新的思路和方法。本文主要就HIF-1和PI3K/Akt/mTOR关系作一简要综述。     

Kinetic analysis of the MAPK and PI3K/Akt signaling pathways

Computational modeling of signal transduction is currently attracting much attention as it can promote the understanding of complex signal transduction mechanisms. Although several mathematical models have been used to examine signaling pathways, little attention has been given to crosstalk mechanisms. In this study, an attempt was made to develop a computational model for the pathways involving growth-factor-mediated mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3'-kinase/protein kinase B (PI3K/Akt). In addition, the dynamics of the protein activities were analyzed based on a set of kinetic data. The simulation approach integrates the information on several levels and predicts systems behavior. The in-silico analysis conducted revealed that the Raf and Akt pathways act independently.     

Axl is essential for VEGF-A-dependent activation of PI3K/Akt

Herein, we report that vascular endothelial growth factor A (VEGF-A) engages the PI3K/Akt pathway by a previously unknown mechanism that involves three tyrosine kinases. Upon VEGF-A-dependent activation of VEGF receptor-2 (VEGFR-2), and subsequent TSAd-mediated activation of Src family kinases (SFKs), SFKs engage the receptor tyrosine kinase Axl via its juxtamembrane domain to trigger ligand-independent autophosphorylation at a pair of YXXM motifs that promotes association with PI3K and activation of Akt. Other VEGF-A-mediated signalling pathways are independent of Axl. Interfering with Axl expression or function impairs VEGF-A- but not bFGF-dependent migration of endothelial cells. Similarly, Axl null mice respond poorly to VEGF-A-induced vascular permeability or angiogenesis, whereas other agonists induce a normal response. These results elucidate the mechanism by which VEGF-A activates PI3K/Akt, and identify previously unappreciated potential therapeutic targets of VEGF-A-driven processes.     

PI3K-Akt信号传导通路对糖代谢的调控作用

磷脂酰肌醇3-激酶(PI3Ks)作为酪氨酸激酶和G蛋白偶联受体的主要下游分子,通过催化产生第二信使3,4,5-三磷酸磷脂酰肌醇(PIP3)并激活Akt、糖原合酶激酶-3(GSK-3)、Forkhead转录因子FoxO1、mTOR(mammalian target of rapamycin)等下游分子,将多种生长因子及细胞因子的信号传递到细胞内,从而对细胞增殖、分化、凋亡和葡萄糖转运等多种生物过程起重要的调节作用.PTEN(phosphatase and tensin homologue)是PI3K信号通路的重要负调节因子.本文将对PI3K-Akt信号通路在糖代谢中的作用予以简要综述.     

Role of PI3K/Akt signaling pathway in cardiac fibrosis

Molecular and Cellular Biochemistry - Heart failure (HF) is considered as a severe health problem worldwide, while cardiac fibrosis is one of the main driving factors for the progress of HF....