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.     

Ganglioside GM3 inhibits hepatoma cell motility via down‐regulating activity of EGFR and PI3K/AKT signaling pathway

Two related sublines derived from murine ascites hepatoma cell lines Hca‐F25, which were selected for their markedly different metastatic potential to lymph nodes, were found to be distinct in their ganglioside patterns. The low metastatic cell line (HcaP) contained a major ganglioside GM3, whereas the high metastatic cell line (HcaF) contained a major ganglioside GM2. Suppression of GM3 by P4 enhanced the mobility and migration of the low metastatic HcaP cells in vitro. Increase in GM3 content in high metastatic HcaF cells by addition of exogenous GM3 inhibited the mobility and migration. These results suggested that the differences in lymphatic metastasis potential between these two cell lines could be attributed to the differences in their ganglioside compositions, and GM3 could suppress the motility and migration of these cells. Further, we investigated the mechanism by which GM3 suppressed the cell mobility and migration. The results showed that suppression of GM3 synthesis by P4 in low metastatic HcaP cells promoted PKB/Akt phosphorylation at Ser473 and Thr308, and phosphorylation of EGFR at the Tyr1173. In contrast, increase in GM3 content in high metastatic HcaF cells by addition of exogenous GM3 into the culture medium suppressed phosphorylation of PKB/Akt and EGFR at the same residues. Taken together, these results suggested that the mechanism of GM3‐suppressed cell motility and migration may involve the inhibition of phosphorylation of EGFR and the activity of PI3K/AKT signaling pathway. J. Cell. Biochem. 114: 1616–1624, 2013. © 2013 Wiley Periodicals, Inc.     

Regulation of dendritic cell function by insulin/IGF-1/PI3K/Akt signaling through klotho expression

Insulin or insulin-like growth factor 1 (IGF-1) promotes the activation of phosphoinositide 3 kinase (PI3K)/Akt signaling in immune cells including dendritic cells (DCs), the most potent professional antigen-presenting cells for naive T cells. Klotho, an anti-aging protein, participates in the regulation of the PI3K/Akt signaling, thus the Ca²⁺-dependent migration is reduced in klotho-deficient DCs. The present study explored the effects of insulin/IGF-1 on DC function through klotho expression. To this end, the mouse bone marrow cells were isolated and cultured with GM-CSF to attain bone marrow-derived DCs (BMDCs). Cells were treated with insulin or IGF-1 and followed by stimulating with lipopolysaccharides (LPS). Tumor necrosis factor (TNF)-α formation was examined by enzyme-linked immunosorbent assay (ELISA). Phagocytosis was analyzed by FITC-dextran uptake assay. The expression of klotho was determined by quantitative PCR, immunoprecipitation and western blotting. As a result, treatment of the cells with insulin/IGF-1 resulted in reducing the klotho expression as well as LPS-stimulated TNF-α release and increasing the FITC-dextran uptake but unaltering reactive oxygen species (ROS) production in BMDCs. The effects were abolished by using pharmacological inhibition of PI3K/Akt with LY294002 and paralleled by transfecting DCs with klotho siRNA. In conclusion, the regulation of klotho sensitive DC function by IGF-1 or insulin is mediated through PI3K/Akt signaling pathway in BMDCs.     

Iron-saturated lactoferrin stimulates cell cycle progression through PI3K/Akt pathway

Iron binding lactoferrin (Lf) is involved in the control of cell cycle progression. However, the molecular basis underlying the effects of Lf on cell cycle control, as well as its target genes, remains incompletely understood. In this study, we have demonstrated that a relatively low level of ironsaturated Lf, Lf(Fe³⁺), can stimulate S phase cell cycle entry, and requires Akt activation in MCF-7 cells. Lf(Fe³⁺) immediately induced Akt phosphorylation at Ser473, which subsequently induced the phosphorylation of two G1-checkpoint Cdk inhibitors, p21^Cip/WAF1 and p27^kip1. The Lf(Fe³⁺)-induced phosphorylation of Cdk inhibitors impaired their nuclear import behavior, thereby inducing cell cycle progression. However, the treatment of cells with a PI3K inhibitor, LY294002, almost completely blocked Lf(Fe³⁺)-stimulated cell cycle progression. LY294002 treatment abrogated Lf(Fe³⁺)-induced Akt activation, and prevented the cytoplasmic localization of p27^kip1. Higher levels of p21^Cip/WAF1 were also detected in the cytoplasmic sub-cellular compartment as a measure of cellular response to Lf(Fe³⁺). Consequently, the degree of phosphorylation of retinoblastoma protein was enhanced in response to Lf(Fe³⁺). Therefore, we conclude that Lf(Fe³⁺), as a potential antagonist of Cdk inhibitors, can facilitate the functions of E2F during progression to S phase via the Akt signaling pathway.     

G protein-independent Ras/PI3K/F-actin circuit regulates basic cell motility

Phosphoinositide 3-kinase (PI3K)gamma and Dictyostelium PI3K are activated via G protein-coupled receptors through binding to the Gbetagamma subunit and Ras. However, the mechanistic role(s) of Gbetagamma and Ras in PI3K activation remains elusive. Furthermore, the dynamics and function of PI3K activation in the absence of extracellular stimuli have not been fully investigated. We report that gbeta null cells display PI3K and Ras activation, as well as the reciprocal localization of PI3K and PTEN, which lead to local accumulation of PI(3,4,5)P(3). Simultaneous imaging analysis reveals that in the absence of extracellular stimuli, autonomous PI3K and Ras activation occur, concurrently, at the same sites where F-actin projection emerges. The loss of PI3K binding to Ras-guanosine triphosphate abolishes this PI3K activation, whereas prevention of PI3K activity suppresses autonomous Ras activation, suggesting that PI3K and Ras form a positive feedback circuit. This circuit is associated with both random cell migration and cytokinesis and may have initially evolved to control stochastic changes in the cytoskeleton.     

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。     

Magnolol induces apoptosis via inhibiting the EGFR/PI3K/Akt signaling pathway in human prostate cancer cells

We observed that treatment of prostate cancer cells for 24 h with magnolol, a phenolic component extracted from the root and stem bark of the oriental herb Magnolia officinalis, induced apoptotic cell death in a dose‐ and time‐dependent manner. A sustained inhibition of the major survival signal, Akt, occurred in magnolol‐treated cells. Treatment of PC‐3 cells with an apoptosis‐inducing concentration of magnolol (60 µM) resulted in a rapid decrease in the level of phosphorylated Akt leading to inhibition of its kinase activity. Magnolol treatment (60 µM) also caused a decrease in Ser(¹³⁶) phosphorylation of Bad (a proapoptotic protein), which is a downstream target of Akt. Protein interaction assay revealed that Bcl‐xL, an anti‐apoptotic protein, was associated with Bad during treatment with magnolol. We also observed that during treatment with magnolol, translocation of Bax to the mitochondrial membrane occurred and the translocation was accompanied by cytochrome c release, and cleavage of procaspase‐8, ‐9, ‐3, and poly(ADP‐ribose) polymerase (PARP). Similar results were observed in human colon cancer HCT116Bax^+/? cell line, but not HCT116Bax^?/? cell line. Interestingly, at similar concentrations (60 µM), magnolol treatment did not affect the viability of normal human prostate epithelial cell (PrEC) line. We also observed that apoptotic cell death by magnolol was associated with significant inhibition of pEGFR, pPI3K, and pAkt. These results suggest that one of the mechanisms of the apoptotic activity of magnolol involves its effect on epidermal growth factor receptor (EGFR)‐mediated signaling transduction pathways. J. Cell. Biochem. 106: 1113–1122, 2009. © 2009 Wiley‐Liss, Inc.     

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.

     

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.     

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。     

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.