mTORC2信号通路调节上皮细胞钠通道的研究进展

哺乳动物雷帕霉素靶蛋白(mammalian target of rapamycin,mTOR)是一种丝氨酸/苏氨酸蛋白激酶,属于磷脂酰肌醇激酶相关激酶蛋白质家族成员。mTOR进化上高度保守,可整合营养、能量及生长因子等多种细胞外信号,在细胞生长、增殖、凋亡及自噬等过程中发挥极为重要的作用。在生物体内,mTOR有2种多蛋白复合物:mTORC1和mTORC2,目前mTORC1信号通路与肿瘤的关系研究较多,而对mTORC2的研究相对较少,近年来有研究发现mTORC2信号通路参与了上皮细胞钠通道的调节作用。     

Rictor与糖代谢的研究进展

雷帕霉素靶蛋白(mTOR)是一种非典型的丝氨酸/苏氨酸蛋白激酶,对机体细胞的生长、代谢有调节作用。mTOR在哺乳动物中形成两种蛋白复合物,mTORC1和mTORC2,均可调节糖脂代谢。Rictor是雷帕霉素靶蛋白复合物2(mTORC2)的核心蛋白之一,可通过mTORC2直接磷酸化Akt调节糖代谢。当Rictor缺乏时,会通过影响胰岛素信号传导通路、胰岛β细胞的增殖和凋亡等造成葡萄糖耐受不良。     

哺乳动物雷帕霉素靶蛋白C1(mTORC1)在非酒精性脂肪性肝病治疗中的作用机制及潜力

非酒精性脂肪性肝病(NAFLD)已成为全球最常见的慢性肝病，可进展为非酒精性脂肪性肝炎、肝硬化和肝癌。哺乳动物雷帕霉素靶蛋白(mTOR)是一种非典型丝氨酸/苏氨酸蛋白激酶，在细胞生长、凋亡、自噬及代谢等过程中发挥了极为重要的作用。本文阐述mTORC1信号通路在NAFLD发病过程中对细胞代谢和生长分化的作用，进一步提出mTORC1通路对于NAFLD治疗药物的研究价值和潜力。     

哺乳动物雷帕霉素靶蛋白信号通路在心脏发育和重构中作用的研究进展

哺乳动物雷帕霉素靶蛋白(mTOR)是一种非典型的丝氨酸/苏氨酸蛋白激酶,其行使生理功能主要通过两种不同的蛋白质复合体mTORC1和mTORC2。mTORC1调节蛋白质的合成、细胞的生长增殖,而mTORC2调节细胞的存活。研究表明,mTOR在心脏发育和重构中发挥关键调节作用。寻找心脏特异性mTORC1的抑制剂,而不损害其生理功能,可能为心血管疾病治疗提供新思路。     

磷脂酰肌醇-3-激酶/蛋白激酶B/雷帕霉素靶蛋白信号转导研究进展及与自身免疫病的关系

磷脂酰肌醇-3-激酶/蛋白激酶B/雷帕霉素靶蛋白(PI3K/Akt/mTOR)信号通路介导许多在肿瘤和自身免疫病发生中至关重要的细胞生物学过程,对于细胞增殖、细胞活化、血管生成起到重要作用.PI3 K/Akt/mTOR信号通路作为药物治疗靶点进行抗细胞增殖活化的研究近年来发展迅速.本文从PI3K/Akt/mTOR信号通路的上下游、信号通路抑制剂以及与信号通路相关的自身免疫病等方面作一综述.     

哺乳动物雷帕霉素靶蛋白及其与肝脏肿瘤关系的研究进展

哺乳动物雷帕霉素靶蛋白（mammalian target of rapamycin，mTOR）是一种丝氨酸／苏氨酸蛋白激酶。在细胞的生长、分化、增殖、迁移和存活上扮演了重要的角色。由于mTOR信号通路在细胞周期进程中发挥了重要作用，而细胞周期进程调节异常与许多疾病尤其是癌症的发生、发展有关，因此mTOR信号通路的失调可引起多种癌症。mTOR的特异性抑制剂雷帕霉素及其衍生物CCI-779能抑制mTOR的功能，使细胞阻滞在G1期，并引起凋亡。本文就mTOR信号通路及其与肝脏肿瘤的关系作一综述。     

mTORC1信号通路在花生四烯酸代谢产物致乳腺癌过程中的作用

目的：探讨花生四烯酸（ AA）代谢产物5-羟二十烷四烯酸（ HETE）、12-HETE促进乳腺癌发生过程中雷帕霉素靶蛋白1（ mTOR）信号通路的作用。方法将体外培养乳腺癌MCF-7细胞随机分为4组,对照组加入0．1％DMSO,HETE组加入5-HETE及12-HETE 15μmol/L,Rap组加入mTORC1抑制剂雷帕霉素（ Rap）100μmol/L,HETE＋Rap组加入Rap 100μmol/L及5-HETE＋12-HETE 15μmol/L。 CCK-8法检测各组细胞增殖率,免疫印迹法检测各组细胞mTORC1信号通路下游蛋白P-S6活性,细胞划痕实验检测各组细胞迁移能力。结果细胞增殖率HETE组高于对照组,HETE＋Rap组低于HETE组（P均＜0．05）。 P-S6蛋白灰度值HETE组高于对照组,HETE＋Rap组低于HETE组（ P均＜0．01）。 MCF-7细胞迁移距离 HETE 组大于对照组（P＜0．01）。 HETE＋Rap组小于HETE组（P＜0．05）。结论 mTORC1信号通路参与了 AA代谢产物乳腺癌发生的过程。     

mTOR信号通路相关蛋白在胰腺癌中的表达及其临床意义

目的 探讨mTOR信号通路相关蛋白在胰腺癌中的表达及其临床意义。方法 采用免疫组织化学技术测定并比较mTOR信号通路相关蛋白Akt、mTOR及P70S6K在胰腺癌和非胰腺癌组织中的磷酸化水平,应用Spearman相关分析探讨mTOR信号通路相关蛋白磷酸化水平与胰腺癌患者年龄、性别、肿瘤大小、组织学分级、淋巴结转移及肿瘤分期的相关性。结果 p-Akt和p-mTOR蛋白阳性着色定位于细胞质内,而p-P70S6K蛋白阳性着色定位于细胞核。p-mTOR、p-Akt和p-P70S6K蛋白在胰腺癌组织中表达水平显著高于非胰腺癌组织（P均< 0.01）。Spearman 相关分析显示,p-Akt、p-mTOR和p-P70S6K蛋白表达与患者年龄、性别、肿瘤大小、组织学分级无关（P均>0.05）,与淋巴结转移和分期有关（P均<0.05）。结论 mTOR信号通路与胰腺癌的发生发展相关,但mTOR信号通路相关蛋白磷酸化水平在胰腺癌临床分型及转归中的意义不大。     

mTOR信号通路与胃癌的相关性研究

正哺乳动物雷帕霉素靶蛋白(mTOR)属于丝氨酸/苏氨酸蛋白激酶的一种,其自酵母中分离出来,在P13K/AKT/mTOR信号通路中是蛋白激酶B(Akt)的下游底物。mTOR是一种含有2549个氨基酸残基的蛋白质分子,生理状态下,该蛋白在各种刺激因子的作用下发挥调控细胞周期、细胞生长增殖等作用,因此mTOR在多种肿瘤组织中表达异     

mTOR信号通路在心血管系统中作用研究的进展

哺乳动物雷帕霉素靶蛋白(mTOR)是一种非典型的丝氨酸/苏氨酸蛋白激酶,它是调控细胞生长、增殖、翻译、代谢及自噬的关键蛋白激酶,最初因为其能被雷帕霉素抑制而被认识。研究表明,mTOR在调节心血管系统的生理与病理过程中起到关键的作用。本文重点回顾了mTOR信号通路在心血管系统中作用研究的进展。     

Mammalian target of rapamycin inhibition in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death worldwide. It is associated with a poor prognosis and has limited treatment options. Sorafenib, a multi-targeted kinase inhibitor, is the only available systemic agent for treatment of HCC that improves overall survival for patients with advanced stage disease; unfortunately, an effective second-line agent for the treatment of progressive or sorafenib-resistant HCC has yet to be identified. This review focuses on components of the mammalian target of rapamycin (mTOR) pathway, its role in HCC pathogenesis, and dual mTOR inhibition as a therapeutic option with potential efficacy in advanced HCC. There are several important upstream and downstream signals in the mTOR pathway, and alternative tumor-promoting pathways are known to exist beyond mTORC1 inhibition in HCC. This review analyzes the relationships of the upstream and downstream regulators of mTORC1 and mTORC2 signaling; it also provides a comprehensive global picture of the interaction between mTORC1 and mTORC2 which demonstrates the pre-clinical relevance of the mTOR pathway in HCC pathogenesis and progression. Finally, it provides scientific rationale for dual mTORC1 and mTORC2 inhibition in the treatment of HCC. Clinical trials utilizing mTORC1 inhibitors and dual mTOR inhibitors in HCC are discussed as well. The mTOR pathway is comprised of two main components, mTORC1 and mTORC2; each has a unique role in the pathogenesis and progression of HCC. In phase III studies, mTORC1 inhibitors demonstrate anti-tumor activity in advanced HCC, but dual mTOR (mTORC1 and mTORC2) inhibition has greater therapeutic potential in HCC treatment which warrants further clinical investigation.     

mTOR inhibitor for the treatment of hepatocellular carcinoma

Mammalian target of rapamycin (mTOR) plays a central role in the regulation of cellular growth, proliferation, and survival via a cytoplasmic serine/threonine kinase. mTOR also works as a nutrition sensor to monitor cellular metabolism. mTOR is located downstream in the PI3K/Akt pathway, in which Akt and the tuberous sclerosis complex (TSC) 1/2 are involved, to form a signal transduction pathway. New anticancer agents that target mTOR in the PI3K/Akt pathway of the signal transduction pathways involved in cell proliferation control have recently been developed and are already commercially available. A phase III clinical trial of mTOR inhibitor for hepatocellular carcinoma (HCC) is now ongoing worldwide to expand indications. RAD001 is a signal-transduction inhibitor (STI) that targets mTOR (more specifically, mTORC1). mTORC1 signaling is intricately regulated by mitogens, growth factors, energy, and nutrients. mTORC1 is a regulator essential for general protein synthesis, located downstream of the PI3K/AKT/mTOR pathway, which is dysregulated in most human cancers. Inhibiting mTOR with molecules, such as RAD001, generates additive effects that accompany upstream and downstream target inhibition; alternatively, upstream receptor inhibition is compensated for by inhibiting the downstream pathway, even if some resistance develops against receptor inhibition regardless of initial or acquired resistance. In conclusion, RAD001 is a potential targeted agent for HCC and therefore final results of a phase III study are awaited.     

Control of mTORC1 signaling by the Opitz syndrome protein MID1

Mutations in the MID1 gene are causally linked to X-linked Opitz BBB/G syndrome (OS), a congenital disorder that primarily affects the formation of diverse ventral midline structures. The MID1 protein has been shown to function as an E3 ligase targeting the catalytic subunit of protein phosphatase 2A (PP2A-C) for ubiquitin-mediated degradation. However, the molecular pathways downstream of the MID1/PP2A axis that are dysregulated in OS and that translate dysfunctional MID1 and elevated levels of PP2A-C into the OS phenotype are poorly understood. Here, we show that perturbations in MID1/PP2A affect mTORC1 signaling. Increased PP2A levels, resulting from proteasome inhibition or depletion of MID1, lead to disruption of the mTOR/Raptor complex and down-regulated mTORC1 signaling. Congruously, cells derived from OS patients that carry MID1 mutations exhibit decreased mTORC1 formation, S6K1 phosphorylation, cell size, and cap-dependent translation, all of which is rescued by expression of wild-type MID1 or an activated mTOR allele. Our findings define mTORC1 signaling as a downstream pathway regulated by the MID1/PP2A axis, suggesting that mTORC1 plays a key role in OS pathogenesis.     

Inhibition of the mTORC1 pathway suppresses intestinal polyp formation and reduces mortality in ApcDelta716 mice

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that regulates cell growth via mTOR complex 1 (mTORC1), whose activation has been implicated in many human cancers. However, mTORC1's status in gastrointestinal tumors has not been characterized thoroughly. We have found that the mTORC1 pathway is activated with increased expression of the mTOR protein in intestinal polyps of the Apc^Δ716 heterozygous mutant mouse, a model for human familial adenomatous polyposis. An 8-week treatment with RAD001 (everolimus) suppressed the mTORC1 activity in these polyps and inhibited proliferation of the adenoma cells as well as tumor angiogenesis, which significantly reduced not only the number of polyps but also their size. β-Catenin knockdown in the colon cancer cell lines reduced the mTOR level and thereby inhibited the mTORC1 signaling. These results suggest that the Wnt signaling contributes to mTORC1 activation through the increased level of mTOR and that the activation plays important roles in the intestinal polyp formation and growth. Indeed, long-term RAD001 treatment significantly reduced mortality of the Apc^Δ716 mice. Thus, we propose that the mTOR inhibitors may be efficacious for therapy and prevention of colonic adenomas and cancers with Wnt signaling activation.     

mTOR complex 2 in adipose tissue negatively controls whole-body growth

Mammalian target of rapamycin (mTOR), a highly conserved protein kinase that controls cell growth and metabolism in response to nutrients and growth factors, is found in 2 structurally and functionally distinct multiprotein complexes termed mTOR complex 1 (mTORC1) and mTORC2. mTORC2, which consists of rictor, mSIN1, mLST8, and mTOR, is activated by insulin/IGF1 and phosphorylates Ser-473 in the hydrophobic motif of Akt/PKB. Though the role of mTOR in single cells is relatively well characterized, the role of mTOR signaling in specific tissues and how this may contribute to overall body growth is poorly understood. To examine the role of mTORC2 in an individual tissue, we generated adipose-specific rictor knockout mice (rictor^ad−/−). Rictor^ad−/− mice are increased in body size due to an increase in size of nonadipose organs, including heart, kidney, spleen, and bone. Furthermore, rictor^ad−/− mice have a disproportionately enlarged pancreas and are hyperinsulinemic, but glucose tolerant, and display elevated levels of insulin-like growth factor 1 (IGF1) and IGF1 binding protein 3 (IGFBP3). These effects are observed in mice on either a high-fat or a normal diet, but are generally more pronounced in mice on a high-fat diet. Our findings suggest that adipose tissue, in particular mTORC2 in adipose tissue, plays an unexpectedly central role in controlling whole-body growth.     

Alcohol-induced modulation of rictor and mTORC2 activity in C2C12 myoblasts

Background: The mammalian target of rapamycin (mTOR) kinase controls cell growth, proliferation, and metabolism through 2 distinct multiprotein complexes, mTORC1 and mTORC2. We reported that alcohol (EtOH) inhibits mTORC1 activity and protein synthesis in C2C12 myoblasts. However, the role that mTORC2 plays in this process has not been elucidated. In this study, we investigated whether mTORC2 functions as part of a feedback regulator in response to EtOH, acting to maintain the balance between the functions of Akt, mTORC2, and mTORC1. Methods: C2C12 myoblasts were incubated with EtOH for 18 to 24 hours. Levels of various mTORC2 proteins and mRNA were assessed by immunoblotting and real‐time PCR, respectively, while protein–protein interactions were determined by immunoprecipitation and immunoblotting. An in vitro mTORC2 kinase activity assay was performed using Akt as a substrate. The rate of protein synthesis was determined by ³⁵S‐methionine/cysteine incorporation into cellular protein. Results: EtOH (100 mM) increased the protein and mRNA levels of the mTORC2 components rictor, mSin1, proline‐rich repeat protein 5, and Deptor. There was also an increased association of these proteins with mTOR. EtOH increased the in vitro kinase activity of mTORC2, and this was correlated with decreased binding of rictor with 14‐3‐3 and Deptor. Reduced rictor phosphorylation at T1135 by EtOH was most likely due to decreased S6K1 activity. Knockdown of rictor elevated mTORC1 activity, as indicated by increased S6K1 phosphorylation and protein synthesis. Likewise, there were decreased amounts and/or phosphorylation levels of various mTORC1 and mTORC2 components including raptor, proline‐rich Akt substrate 40 kDa, mSin1, Deptor, and GβL. Activated PP2A was associated with decreased Akt and eukaryotic elongation factor 2 phosphorylation. Collectively, our results provide evidence of a homeostatic balance between the 2 mTOR complexes following EtOH treatments in myoblasts . Conclusions: EtOH increased the activity of mTORC2 by elevating levels of various components and their interaction with mTOR. Decreased rictor phosphorylation at T1135 acts as mTORC1‐dependent feedback mechanisms, functioning in addition to the insulin receptor substrate‐I/PI3K signaling pathway to regulate protein synthesis.     

SAD-A kinase controls islet β-cell size and function as a mediator of mTORC1 signaling

The mammalian target of rapamycin (mTOR) plays an important role in controlling islet β-cell function. However, the underlying molecular mechanisms remain poorly elucidated. Synapses of amphids defective kinase-A (SAD-A) is a 5′ adenosine monophosphate-activated protein kinase-related protein kinase that is exclusively expressed in pancreas and brain. In this study, we investigated a role of the kinase in regulating pancreatic β-cell morphology and function as a mediator of mTOR complex 1 (mTORC1) signaling. We show that global SAD-A deletion leads to defective glucose-stimulated insulin secretion and petite islets, which are reminiscent of the defects in mice with global deletion of ribosomal protein S6 kinase 1, a downstream target of mTORC1. Consistent with these findings, selective deletion of SAD-A in pancreas decreased islet β-cell size, whereas SAD-A overexpression significantly increased the size of mouse insulinomas cell lines β-cells. In direct support of SAD-A as a unique mediator of mTORC1 signaling in islet β-cells, we demonstrate that glucose dramatically stimulated SAD-A protein translation in isolated mouse islets, which was potently inhibited by rapamycin, an inhibitor of mTORC1. Moreover, the 5′-untranslated region of SAD-A mRNA is highly structured and requires mTORC1 signaling for its translation initiation. Together, these findings identified SAD-A as a unique pancreas-specific effector protein of mTORC1 signaling.     

The splicing-factor oncoprotein SF2/ASF activates mTORC1

The splicing factor SF2/ASF is an oncoprotein that is up-regulated in many cancers and can transform immortal rodent fibroblasts when slightly overexpressed. The mTOR signaling pathway is activated in many cancers, and pharmacological blockers of this pathway are in clinical trials as anticancer drugs. We examined the activity of the mTOR pathway in cells transformed by SF2/ASF and found that this splicing factor activates the mTORC1 branch of the pathway, as measured by S6K and eIF4EBP1 phosphorylation. This activation is specific to mTORC1 because no activation of Akt, an mTORC2 substrate, was detected. mTORC1 activation by SF2/ASF bypasses upstream PI3K/Akt signaling and is essential for SF2/ASF-mediated transformation, as inhibition of mTOR by rapamycin blocked transformation by SF2/ASF in vitro and in vivo. Moreover, shRNA-mediated knockdown of mTOR, or of the specific mTORC1 and mTORC2 components Raptor and Rictor, abolished the tumorigenic potential of cells overexpressing SF2/ASF. These results suggest that clinical tumors with SF2/ASF up-regulation could be especially sensitive to mTOR inhibitors.     

Dueling for dual inhibition: Means to enhance effectiveness of PI3K/Akt/mTOR inhibitors in AML

The phosphatidylinositol 3-kinase/protein kinase B (Akt)/mechanistic target of rapamycin (PI3K/Akt/mTOR) pathway is amplified in 60–80% of patients with acute myelogenous leukemia (AML). Since this complex pathway is crucial to cell functions such as growth, proliferation, and survival, inhibition of this pathway would be postulated to inhibit leukemia initiation and propagation. Inhibition of the mTORC1 pathway has met with limited success in AML due to multiple resistance mechanisms including direct insensitivity of the mTORC1 complex, feedback activation of the PI3k/Akt signaling network, insulin growth factor-1 (IGF-1) activation of PI3K, and others. This review explores the role of mTOR inhibition in AML, mechanisms of resistance, and means to improve outcomes through use of dual mTORC1/2 inhibitors or dual TORC/PI3K inhibitors. How these inhibitors interface with currently available therapies in AML will require additional preclinical experiments and conduct of well-designed clinical trials.