PI3K/Akt信号通路与肝纤维化

PI3K/AKT信号通路可以通过调控基因表达,从而在细胞的存活、分化、生长、运动和凋亡等多种生理和病理过程中起到重要作用。尤其在肝纤维化的进展中,此信号通路发挥了重要的调节作用。本文将对目前有关PI3K/AKT信号通路在参与肝纤维化形成中,如何调控细胞外基质的降解、影响HSC的活化及调节肝窦毛细血管化等作用机制作一综述。这些资料不仅可以揭示相关疾病条件下,多个细胞与信号因子之间复杂的相互作用机制,而且能够突出通过阻断PI3K/AKT信号通路可以保护和治疗肝纤维化这一潜在的临床意义。     

Small molecule inhibition of phosphatidylinositol-3,4,5-triphosphate (PIP3) binding to pleckstrin homology domains

The PI3-kinase (PI3K) pathway regulates many cellular processes, especially cell metabolism, cell survival, and apoptosis. Phosphatidylinositol-3,4,5-trisphosphate (PIP3), the product of PI3K activity and a key signaling molecule, acts by recruiting pleckstrin-homology (PH) domain-containing proteins to cell membranes. Here, we describe a new structural class of nonphosphoinositide small molecule antagonists (PITenins, PITs) of PIP3-PH domain interactions (IC(50) ranges from 13.4 to 31 μM in PIP3/Akt PH domain binding assay). PITs inhibit interactions of a number of PIP3-binding PH domains, including those of Akt and PDK1, without affecting several PIP2-selective PH domains. As a result, PITs suppress the PI3K-PDK1-Akt pathway and trigger metabolic stress and apoptosis. A PIT-1 analog displayed significant antitumor activity in vivo, including inhibition of tumor growth and induction of apoptosis. Overall, our studies demonstrate the feasibility of developing specific small molecule antagonists of PIP3 signaling.     

p-Akt和P27的生物学特性及其与鼻咽癌关系的研究进展

蛋白激酶B（PKB／Akt）磷酸化后激活为p-Akt,可以促进细胞存活、抑制细胞凋亡,并调控与细胞周期相关的蛋白,磷酸肌醇3-激酶（P13K）／AKT信号转导通路促进恶性肿瘤转移。P27蛋白作为细胞周期负性调控因子,能抑制各种细胞周期蛋白和激酶的活性。P27表达下降或者缺失,促进了肿瘤的增殖和侵袭。两者都在鼻咽癌的发病和转移中起作用,并对预后有影响。     

Cardiotrophin-1 phosphorylates akt and BAD, and prolongs cell survival via a PI3K-dependent pathway in cardiac myocytes

Growth factors and cytokines trigger survival signaling in a wide variety of cell systems, including cardiac myocytes. Participation of the phosphatidylinositol 3-OH kinase (PI3K)/Akt pathway in survival signaling has already been described in some cell types, but its involvement in the survival of cardiac myocytes is as yet unknown. Recently, CT-1, an interleukin 6-related cytokine, was shown to have survival-promoting, anti-apoptotic effects on cultured cardiac myocytes. However, roles of PI3K-dependent pathways in this signaling have not been elucidated. In the present study, therefore, we examined the participation of the PI3K/Akt pathway in CT-1-induced, survival-promoting signaling in cultured ventricular myocytes. It was found that CT-1 phosphorylated and activated Akt, and the effect was blocked by the PI3K inhibitors LY294002 and wortmannin. CT-1 also phosphorylated the pro-apoptotic factor, BAD, and the BAD phosphorylation was inhibited by LY294002, suggesting that phosphorylation of BAD is one of the key events by which the PI3K/Akt pathway mediates CT-1-induced survival signaling. Further, CT-1 PI3K-dependently prolonged the survival of serum-starved ventricular myocytes by preventing apoptosis. In summary, our findings show that PI3K-dependent survival signals contribute to CT-1-mediated ventricular myocyte survival. In vivo, the death of ventricular myocytes leads to heart failure, and downregulation of survival signals and/or augmentation of pro-apoptotic signals are likely to be important components of disease processes. Thus, the extent to which CT-1 and the PI3K/Akt pathway mitigate such pathological processes, in vivo, is an important question for the future.     

Calpain interacts with class IA phosphoinositide 3-kinases regulating their stability and signaling activity

Class IA phosphoinositide 3-kinases (PI3Ks) are signaling enzymes with key roles in the regulation of essential cellular functions and disease, including cancer. Accordingly, their activity is tightly controlled in cells to maintain homeostasis. The formation of multiprotein complexes is a ubiquitous mechanism to regulate enzyme activity but the contribution of protein-protein interactions to the regulation of PI3K signaling is not fully understood. We designed an affinity purification quantitative mass spectrometry strategy to identify proteins interacting dynamically with PI3K in response to pathway activation, with the view that such binding partners may have a functional role in pathway regulation. Our study reveals that calpain small subunit 1 interacts with PI3K and that the association between these proteins is lower in cells stimulated with serum compared to starved cells. Calpain and PI3K activity assays confirmed these results, thus demonstrating that active calpain heterodimers associate dynamically with PI3K. In addition, calpains were found to cleave PI3K proteins in vitro (resulting in a reduction of PI3K lipid kinase activity) and to regulate endogenous PI3K protein levels in vivo. Further investigations revealed that calpains have a role in the negative regulation of PI3K/Akt pathway activity (as measured by Akt and ribosomal S6 phosphorylation) and that their inhibition promotes cell survival during serum starvation. These results indicate that the interaction between calpain and PI3K is a novel mechanism for the regulation of class IA PI3K stability and activity.     

The IGF-1 Signaling Pathway in Viral Infections

Insulin-like growth factor-1 (IGF-1) and the IGF-1 receptor (IGF-1R) belong to the insulin-like growth factor family, and IGF-1 activates intracellular signaling pathways by binding specifically to IGF-1R. The interaction between IGF-1 and IGF-1R transmits a signal through a number of intracellular substrates, including the insulin receptor substrate (IRS) and the Src homology collagen (Shc) proteins, which activate two major intracellular signaling pathways: the phosphatidylinositol 3-kinase (PI3K)/AKT and mitogen-activated protein kinase (MAPK) pathways, specifically the extracellular signal-regulated kinase (ERK) pathways. The PI3K/AKT kinase pathway regulates a variety of cellular processes, including cell proliferation and apoptosis. IGF1/IGF-1R signaling also promotes cell differentiation and proliferation via the Ras/MAPK pathway. Moreover, upon IGF-1R activation of the IRS and Shc adaptor proteins, Shc stimulates Raf through the GTPase Ras to activate the MAPKs ERK1 and ERK2, phosphorylate and several other proteins, and to stimulate cell proliferation. The IGF-1 signaling pathway is required for certain viral effects in oncogenic progression and may be induced as an effect of viral infection. The mechanisms of IGF signaling in animal viral infections need to be clarified, mainly because they are involved in multifactorial signaling pathways. The aim of this review is to summarize the current data obtained from virological studies and to increase our understanding of the complex role of the IGF-1 signaling axis in animal virus infections.     

普伐他汀对骨髓间充质干细胞迁移和黏附能力的影响

目的观察普伐他汀干预对人骨髓间充质干细胞(bone marrow mesenchymal stem cells,BMMSCs)迁移和黏附能力的影响及其相关细胞信号传导通路。方法使用普伐他汀干预体外培养的第6代人BMMSCs,Western blotting检测作用前后ERK1/2、p38MAPK及PI3K/Akt通路蛋白的表达情况。将10μmol/L普伐他汀预处理人BMMSCs1h后,通过Transwell小室进行细胞迁移实验,并进行细胞黏附性测定,进一步用特异的细胞信号通路抑制剂或激动剂阻断或激活ERK1/2、p38MAPK及PI3K/AKT途径,观察其对普伐他汀作用的影响。结果普伐他汀可使人BMMSCs的PI3K/Akt通路磷酸化水平升高,抑制p38MAPK通路磷酸化水平,而其对人BMMSCs的ERK通路和总Akt、总p38MAPK水平无显著影响。经普伐他汀作用后迁移细胞显著增多(P<0.05),Ly294002预处理后这种作用消失,anisomycin预处理对这种作用影响不明显。普伐他汀作用后贴壁细胞显著增多(P<0.05),但Ly294002或anisomycin预处理对这种作用影响均不明显。结论普伐他汀具有增强人BMMSCs迁移和黏附能力的作用。其增强迁移能力的作用与激活人BMMSCs的PI3K/Akt通路有关。但是它对黏附能力的作用与PI3K/Akt和p38MAPK通路均无关。     

PI3K/Akt/mTOR信号转导通路在肝细胞癌发生发展中的作用

PI3K/Akt/mTOR信号转导通路可以通过调控基因表达,在肝细胞癌肿瘤细胞生成、增殖、转移和凋亡等过程中发挥重要作用。简述了PI3K/Akt/mTOR信号通路的组成及功能,对PI3K/Akt/mTOR通路在肝细胞癌进程中的作用机制及相关抑制剂的研究进展进行了综述,揭示阻断PI3K/Akt/mTOR通路可以成为肝细胞癌治疗新的靶点方向。     

PI3K/Akt信号通路调节心脏功能的研究进展

PI3K/Akt是调节心脏功能的一条重要的信号转导通路,主要通过血管内皮生长因子介导血管生成、抑制心肌细胞凋亡、重构心室、促进细胞能量代谢等方面调节心脏功能。研究发现PI3K/Akt信号通路在内分泌疾病、肾病、肝纤维化、肿瘤及心血管疾病的发生、发展中起着重要作用。本文就PI3K/Akt信号通路调节心脏功能的分子机制作一阐述。     

Akt Kinase Intervenes in Flavivirus Replication by Interacting with Viral Protein NS5

Arthropod-borne flaviviruses, such as Zika virus (ZIKV), Usutu virus (USUV), and West Nile virus (WNV), are a growing cause of human illness and death around the world. Presently, no licensed antivirals to control them are available and, therefore, search for broad-spectrum antivirals, including host-directed compounds, is essential. The PI3K/Akt pathway controls essential cellular functions involved in cell metabolism and proliferation. Moreover, Akt has been found to participate in modulating replication in different viruses including the flaviviruses. In this work we studied the interaction of flavivirus NS5 polymerases with the cellular kinase Akt. In vitro NS5 phosphorylation experiments with Akt showed that flavivirus NS5 polymerases are phosphorylated and co-immunoprecipitate by Akt. Polymerase activity assays of Ala- and Glu-generated mutants for the Akt-phosphorylated residues also indicate that Glu mutants of ZIKV and USUV NS5s present a reduced primer-extension activity that was not observed in WNV mutants. Furthermore, treatment with Akt inhibitors (MK-2206, honokiol and ipatasertib) reduced USUV and ZIKV titers in cell culture but, except for honokiol, not WNV. All these findings suggest an important role for Akt in flavivirus replication although with specific differences among viruses and encourage further investigations to examine the PI3K/Akt/mTOR pathway as an antiviral potential target.     

Mechanisms of disease: PI3K/AKT signaling in gastrointestinal cancers

The lipid kinase phosphoinositide 3-OH kinase (PI3K) and its downstream target Akt, also known as protein kinase B (PKB), are crucial effectors in oncogenic signaling induced by various receptor-tyrosine kinases. In recent years, data are accumulating that PI3K/Akt signaling components are frequently altered in a variety of human malignancies. This review summarizes the major effects of PI3K/Akt signaling on proliferation, survival and resistance to apoptosis, angiogenesis and cell motility in gastrointestinal cancers. In addition, activation of PI3K/Akt by various growth factors, the modulation of downstream targets by Akt-induced phosphorylation as well as novel treatment strategies targeting this pathway in gastrointestinal tumors are discussed.     

A member of Forkhead family transcription factor, FKHRL1, is one of the downstream molecules of phosphatidylinositol 3-kinase-Akt activation pathway in erythropoietin signal transduction

The phosphatidylinositol 3-kinase (PI3K) signaling pathway is important for the regulation of a number of cellular responses. Serine/threonine kinase Akt (protein kinase B; PKB) is downstream of PI3K and activated by growth factors. This study found that erythropoietin (EPO) induced tyrosine phosphorylation of Akt in a time- and dose-dependent manner in EPO-dependent human leukemia cell line UT-7/EPO. In vitro kinase assay using histone H2B and glucose synthase kinase as substrates demonstrated that Akt was actually activated by EPO. EPO-induced phosphorylation of Akt was completely blocked by a PI3K-specific inhibitor, LY294002, at 10 micromol/L, indicating that activation of Akt by EPO is dependent on PI3K activity. In addition, overexpression of the constitutively active form of Akt on UT-7/EPO cells partially blocked apoptosis induced by withdrawal of EPO from the culture medium. This finding suggested that the PI3K-Akt activation pathway plays some role in the antiapoptotic effect of EPO. EPO induced phosphorylation of a member of the trancription factor Forkhead family, FKHRL1, at threonine 32 and serine 253 in a dose- and time-dependent manner in UT-7/EPO cells. Moreover, results showed that Akt kinase activated by EPO directly phosphorylated FKHRL1 protein and that FKHRL1 phosphorylation was completely dependent on PI3K activity as is the case for Akt. In conjunction with the evidence that FKHRL1 is expressed in normal human erythroid progenitor cells and erythroblasts, the results suggest that FKHRL1 plays an important role in erythropoiesis as one of the downstream target molecules of PI3K-Akt.     

Murine cirrhosis induces hepatocyte epithelial mesenchymal transition and alterations in survival signaling pathways

Hepatocytes that reside in a chronically-injured liver have altered growth responses compared to hepatocytes in normal liver. Transforming growth factor beta (TGFbeta) is upregulated in the cirrhotic liver, and cirrhotic hepatocytes, unlike normal hepatocytes exposed to this cytokine, exhibit decreased apoptosis. In fetal hepatocytes, TGFbeta also induces epithelial-mesenchymal transition (EMT) and signaling changes in cell survival pathways. Here, chronic murine liver injury was induced by twice-weekly carbon tetrachloride administration for 8 weeks. Normal liver-derived hepatocytes (NLDH) and cirrhotic liver-derived hepatocytes (CLDH) were examined for EMT and the small mothers against decapentaplegic homolog (Smad), phosphatidylinositol-3-kinase (PI3K/Akt), and mitogen activated protein kinase (MAPK) pathways were investigated. Immunofluorescence imaging of cirrhotic livers demonstrated increased vimentin expression, which was confirmed by immunoblot analysis. In vitro, CLDH exhibited increased vimentin and type 1 collagen expression within cellular extensions consistent with EMT. Treatment with TGFbeta augmented the EMT response in CLDH. In contrast, untreated NLDH did not display features of EMT but responded to TGFbeta with increased vimentin expression and EMT characteristics. In response to PI3K/Akt inhibition, CLDH had decreased basal and insulin-stimulated p-Akt expression and decreased apoptosis compared to NLDH. In both NLDH and CLDH, vimentin expression was dependent on PI3K/Akt activity. CLDH demonstrated increased basal p-extracellular signal-regulated kinase expression that was independent of Smad and PI3K/Akt signaling. Inhibition of the MAPK pathway produced a marked increase in CLDH apoptosis. CONCLUSION: CLDH have increased vimentin and type 1 collagen expression and morphologic features consistent with EMT. In addition, compared to NLDH, the cellular signaling phenotype of CLDH changes from a MAPK-independent pathway to a MAPK-dependent cell survival pathway. These findings may have clinical implications for chemoprevention of hepatocellular carcinoma in the cirrhotic liver.     

非小细胞肺癌中PI3K/Akt信号通路通过Cdh1调控Skp2表达的机制研究

目的探讨非小细胞肺癌（NSCLC）中Cdc20同源蛋白1（Cdh1）参与磷脂酰肌醇三羟基激酶（PI3K）/Akt信号通路对S期激酶相关蛋白2（Skp2）表达调控的机制。方法体外培养NSCLC细胞系A549、LK2和H460,LY294002特异性阻断PI3K/Akt信号通路后,Western blot检测Skp2、Cdh1及p-Akt蛋白表达的变化,免疫荧光（IF）检测Cdh1在NSCLC中的定位变化。结果 LY294002处理后,与对照组相比3种细胞中Skp2蛋白表达和Akt磷酸化水平均降低（P〈0.01）,Cdh1在3种细胞的核内表达均增多。结论 NSCLC中PI3K/Akt信号通路抑制剂LY294002使Skp2蛋白表达下调与Cdh1由细胞质向细胞核转位有关。     

Virus-Induced Aggregates in Infected Cells

During infection, many viruses induce cellular remodeling, resulting in the formation of insoluble aggregates/inclusions, usually containing viral structural proteins. Identification of aggregates has become a useful diagnostic tool for certain viral infections. There is wide variety of viral aggregates, which differ by their location, size, content and putative function. The role of aggregation in the context of a specific virus is often poorly understood, especially in the case of plant viruses. The aggregates are utilized by viruses to house a large complex of proteins of both viral and host origin to promote virus replication, translation, intra- and intercellular transportation. Aggregated structures may protect viral functional complexes from the cellular degradation machinery. Alternatively, the activation of host defense mechanisms may involve sequestration of virus components in aggregates, followed by their neutralization as toxic for the host cell. The diversity of virus-induced aggregates in mammalian and plant cells is the subject of this review.     

Inactivation of Drosophila DJ-1 leads to impairments of oxidative stress response and phosphatidylinositol 3-kinase/Akt signaling

Parkinson's disease (PD) is the most common movement disorder characterized by dopaminergic dysfunction and degeneration. The cause of most PD cases is unknown, although postmortem studies have implicated the involvement of oxidative stress. The identification of familial PD-associated genes offers the opportunity to study mechanisms of PD pathogenesis in model organisms. Here, we show that DJ-1A, a Drosophila homologue of the familial PD-associated gene DJ-1, plays an essential role in oxidative stress response and neuronal maintenance. Inhibition of DJ-1A function through RNA interference (RNAi) results in cellular accumulation of reactive oxygen species, organismal hypersensitivity to oxidative stress, and dysfunction and degeneration of dopaminergic and photoreceptor neurons. To identify other genes that may interact with DJ-1A in regulating cell survival, we performed genetic interaction studies and identified components of the phosphatidylinositol 3-kinase (PI3K)/Akt-signaling pathway as specific modulators of DJ-1A RNAi-induced neurodegeneration. PI3K signaling suppresses DJ-1A RNAi phenotypes at least in part by reducing cellular reactive oxygen species levels. Consistent with the genetic interaction results, we also found reduced phosphorylation of Akt in DJ-1A RNAi animals, indicating an impairment of PI3K/Akt signaling by DJ-1A down-regulation. Together with recent findings in mammalian systems, these results implicate impairments of PI3K/Akt signaling and oxidative stress response in DJ-1-associated disease pathogenesis. We also observed impairment of PI3K/Akt signaling in the fly parkin model of PD, hinting at a common molecular event in the pathogenesis of PD. Manipulation of PI3K/Akt signaling may therefore offer therapeutic benefits for the treatment of PD.     

Cardioprotective stimuli mediate phosphoinositide 3-kinase and phosphoinositide dependent kinase 1 nuclear accumulation in cardiomyocytes

The phosphoinositide 3-kinase (PI3K)/phosphoinositide dependent kinase 1 (PDK1) signaling pathway exerts cardioprotective effects in the myocardium through activation of key proteins including Akt. Activated Akt accumulates in nuclei of cardiomyocytes suggesting that biologically relevant targets are located in that subcellular compartment. Nuclear Akt activity could be potentiated in both intensity and duration by the presence of a nuclear-associated PI3K/PDK1 signaling cascade as has been described in other non-myocyte cell types. PI3K/PDK1 distribution was determined in vitro and in vivo by immunostaining and nuclear extraction of cultured rat neonatal cardiomyocytes or transgenic mouse hearts. Results show that PI3K and PDK1 are present at a basal level in cardiomyocytes nuclei and that cardioprotective stimulation with atrial natriuretic peptide (ANP) increases their nuclear localization. In comparison, overexpression of nuclear-targeted Akt does not mediate increased translocation of either PI3K or PDK1 indicating that accumulation of Akt does not drive PI3K or PDK1 into the nuclear compartment. Furthermore, PI3K and phospho-Akt⁴⁷³ show parallel temporal accumulation in the nucleus following (MI) infarction challenge. These findings demonstrate the presence of a dynamically regulated nuclear-associated signaling cascade involving PI3K and PDK that presumably influences nuclear Akt activation.     

Functional characterization of the guanine nucleotide exchange factor (GEF) motif of GIV protein reveals a threshold effect in signaling

Heterotrimeric G proteins are critical signal-transducing molecules controlled by a complex network of regulators. GIV (a.k.a. Girdin) is a unique component of this network and a nonreceptor guanine nucleotide exchange factor (GEF) that functions via a signature motif. GIV's GEF motif is involved in the regulation of critical biological processes such as phosphoinositide 3 kinase (PI3K)-Akt signaling, actin cytoskeleton remodeling, cell migration, and cancer metastasis. Here we investigated how the GEF function of GIV affects the wiring of its signaling pathway to shape different biological responses. Using a structure-guided approach, we designed a battery of GIV mutants with different Gαi-binding and -activating properties and used it to dissect the specific impact of changes in GIV's GEF activity on several cellular responses. In vivo signaling assays revealed a threshold effect of GEF activity for the activation of Akt by GIV in different cell lines and by different stimuli. Akt signaling is minimal at low GEF activity and is sharply increased to reach a maximum above a threshold of GEF activity, suggesting that GIV is a critical signal amplifier and that activation of Akt is ultrasensitive to changes in GIV's GEF activity. A similar threshold dependence was observed for other biological functions promoted by GIV such as remodeling of the actin cytoskeleton and cell migration. This functional characterization of GIV's GEF motif provides insights into the molecular interactions between nonreceptor GEFs and G proteins and the mechanisms that govern this signal transduction pathway.     

Y-box binding protein 1 augments sorafenib resistance via the PI3K/Akt signaling pathway in hepatocellular carcinoma

BACKGROUNDSorafenib is the first-line treatment for patients with advanced hepatocellular carcinoma (HCC). Y-box binding protein 1 (YB-1) is closely correlated with tumors and drug resistance. However, the relationship between YB-1 and sorafenib resistance and the underlying mechanism in HCC remain unknown.AIMTo explore the role and related mechanisms of YB-1 in mediating sorafenib resistance in HCC.METHODSThe protein expression levels of YB-1 were assessed in human HCC tissues and adjacent nontumor tissues. Next, we constructed YB-1 overexpression and knockdown hepatocarcinoma cell lines with lentiviruses and stimulated these cell lines with different concentrations of sorafenib. Then, we detected the proliferation and apoptosis in these cells by terminal deoxynucleotidyl transferase dUTP nick end labeling, flow cytometry and Western blotting assays. We also constructed a xenograft tumor model to explore the effect of YB-1 on the efficacy of sorafenib in vivo. Moreover, we studied and verified the specific molecular mechanism of YB-1 mediating sorafenib resistance in hepatoma cells by digital gene expression sequencing (DGE-seq).RESULTSYB-1 protein levels were found to be higher in HCC tissues than in corresponding nontumor tissues. YB-1 suppressed the effect of sorafenib on cell proliferation and apoptosis. Consistently, the efficacy of sorafenib in vivo was enhanced after YB-1 was knocked down. Furthermore, KEGG pathway enrichment analysis of DGE-seq demonstrated that the phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt) signaling pathway was essential for the sorafenib resistance induced by YB-1. Subsequently, YB-1 interacted with two key proteins of the PI3K/Akt signaling pathway (Akt1 and PIK3R1) as shown by searching the BioGRID and HitPredict websites. Finally, YB-1 suppressed the inactivation of the PI3K/Akt signaling pathway induced by sorafenib, and the blockade of the PI3K/Akt signaling pathway by LY294002 mitigated YB-1-induced sorafenib resistance.CONCLUSIONOverall, we concluded that YB-1 augments sorafenib resistance through the PI3K/Akt signaling pathway in HCC and suggest that YB-1 is a key drug resistance-related gene, which is of great significance for the application of sorafenib in advanced-stage HCC.