Inhibitor Of mTOR Signaling Pathway Research Articles

SNAT2-mediated regulation of estrogen and progesterone in the proliferation of goat mammary epithelial cells

The development of the goat mammary gland is mainly under the control of ovarian hormones particularly estrogen and progesterone (P4). Amino acids play an essential role in mammary gland development and milk production, and sodium-coupled neutral amino acid transporter 2 (SNAT2) was reported to be expressed in the mammary gland of rats and bovine mammary epithelial cells, which may affect the synthesis of milk proteins or mammary cell proliferation by mediating prolactin, 17β-estradiol (E2) or methionine function. However, whether SNAT2 mediates the regulatory effects of E2 and P4 on the development of the ruminant mammary gland is still unclear. In this study, we show that E2 and P4 could increase the proliferation of goat mammary epithelial cells (GMECs) and regulate SNAT2 mRNA and protein expression in a dose-dependent manner. Further investigation revealed that SNAT2 is abundantly expressed in the mammary gland during late pregnancy and early lactation, while knockdown and overexpression of SNAT2 in GMECs could inhibit or enhance E2- and P4-induced cell proliferation as well as mammalian target of rapamycin (mTOR) signaling. We also found that the accelerated proliferation induced by SNAT2 overexpression in GMECs was suppressed by the mTOR signaling pathway inhibitor rapamycin. This indicates that the regulation of GMECs proliferation mediated by SNAT2 in response to E2 and P4 is dependent on the mTOR signaling pathway. Finally, we found that the total content of the amino acids in GMECs changed after knocking-down and overexpressing SNAT2. In summary, the results demonstrate that the regulatory effects of E2 and P4 on GMECs proliferation may be mediated by the SNAT2-transported amino acid pathway. These results may offer a novel nutritional target for improving the development of the ruminant mammary gland and milk production.

Sestrin 2 protects human lens epithelial cells from oxidative stress and apoptosis induced by hydrogen peroxide by regulating the mTOR/Nrf2 pathway.

We aimed to explore the effect and potential mechanism of Sestrin 2 (SESN2) in human lens epithelial cells (HLECs). To mimic the oxidative stress environment, SAR01/04 cells were treated with 200μM hydrogen peroxide (H2O2) for 24h. Cell viability and apoptosis were checked by cell counting kit-8 and flow cytometry. Western blot was taken to check the protein changes of SESN2, B-cell lymphoma-2 (Bcl-2), Bcl-2-associated X (Bax), mechanistic target of rapamycin (mTOR), phosphorylated (p)-mTOR, ribosomal protein S6 kinase B1 (p70S6K), p-p70S6K, and nuclear factor erythroid 2-related factor 2 (Nrf2). Superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and reactive oxygen species (ROS) were detected via the corresponding reagent kit. The levels of interleukin (IL)-1β, IL-18, and tumor necrosis factor (TNF)-α were measured using enzyme-linked immunosorbent assay. SESN2 was down-regulated in cataract lens tissue and up-regulated in SAR01/04 cells treated with H2O2. Under treatment of H2O2, up-regulation of SESN2 improved cell viability, enhanced the activity of SOD and CAT, inhibited cell apoptosis, and reduced the levels of MDA, ROS, IL-1β, IL-18, and TNF-α, while down-regulation of SESN2 caused the contrary effects. Further bioinformatics analysis suggested that SESN2 regulated the mTOR signaling pathway. Treatment of H2O2 inhibited p-mTOR and p-p70S6K protein expression, while overexpression of SESN2 increased p-mTOR and p-p70S6K protein expression in the H2O2 group and down-regulation of SESN2 further decreased p-mTOR and p-p70S6K protein expression in the H2O2 group. Additionally, H2O2 increased Nrf2 protein expression, and overexpression of SESN2 further increased Nrf2 protein expression in the H2O2 group. Importantly, rapamycin (an inhibitor of mTOR signaling pathway) and knockdown of Nrf2 reversed the promotive effects of SESN2 on cell viability and the inhibitive effects of SESN2 on cell apoptosis, oxidative stress, and inflammatory reaction. SESN2 protected HLECs damage induced by H2O2, which was related to the activation of mTOR/Nrf2 pathway.

Xenon post-conditioning protects against spinal cord ischemia-reperfusion injury in rats by downregulating mTOR pathway and inhibiting endoplasmic reticulum stress-induced neuronal apoptosis

The purpose of this study was to determine whether xenon post-conditioning affects mTOR signaling as well as endoplasmic reticulum stress (ERS)-apoptosis pathway in rats with spinal cord ischemia/reperfusion injury. Fifty male rats were randomized equally into sham-operated group (Sham group), I/R model group (I/R group), I/R model+ xenon post-conditioning group (Xe group), I/R model+rapamycin (a mTOR signaling pathway inhibitor) treatment group (I/R+ Rapa group), and I/R model + xenon post- conditioning with rapamycin treatment group (Xe + Rapa group).. In the latter 4 groups, SCIRI was induced by clamping the abdominal aorta for 85 min followed by reperfusion for 4 h. Rapamycin (or vehicle) was administered by daily intraperitoneal injection (4 mg/kg) for 3 days before SCIRI, and xenon post-conditioning by inhalation of 1∶1 mixture of xenon and oxygen for 1 h at 1 h after initiation of reperfusion; the rats without xenon post-conditioning were given inhalation of nitrogen and oxygen (1∶ 1). After the reperfusion, motor function and histopathologic changes in the rats were examined. Western blotting and real-time PCR were used to detect the protein and mRNA expressions of GRP78, ATF6, IRE1α, PERK, mTOR, p-mTOR, Bax, Bcl-2 and caspase-3 in the spinal cord. The rats showed significantly lowered hind limb motor function following SCIRI (P < 0.01) with a decreased count of normal neurons, increased mRNA and protein expressions of GRP78, ATF6, IRE1α, PERK, and caspase-3, and elevated p-mTOR/mTOR ratio and Bax/Bcl-2 ratio (P < 0.01). Xenon post-conditioning significantly decreased the mRNA and protein levels of GRP78, ATF6, IRE1α, PERK and caspase-3 (P < 0.05 or 0.01) and reduced p-mTOR/mTOR and Bax/Bcl-2 ratios (P < 0.01) in rats with SCIRI; the mRNA contents and protein levels of GRP78 and ATF6 were significantly decreased in I/R+Rapa group (P < 0.01). Compared with those in Xe group, the rats in I/R+Rapa group and Xe+Rapa had significantly lowered BBB and Tarlov scores of the hind legs (P < 0.01), and caspase-3 protein level and Bax/Bcl-2 ratio were significantly lowered in Xe+Rapa group (P < 0.05 or 0.01). By inhibiting ERS and neuronal apoptosis, xenon post- conditioning may have protective effects against SCIRI in rats. The mTOR signaling pathway is partially involved in this process.

Cost-effectiveness analysis of the use of mTOR signaling pathway inhibitors x mycophenolate in kidney transplantation recipients without cytomegalovirus prophylaxis

Objetivo: Avaliar a relação de custo-efetividade dos regimes imunossupressores utilizados em pacientes receptores de transplante renal, no Hospital Santa Casa de Misericórdia de Juiz de Fora, MG, basiliximabe, micofenolato de sódio, tacrolimo e prednisona (Grupo 1 = 93 pacientes), comparados com a associação de timoglobulina, everolimo, tacrolimo e prednisona (Grupo 2 = 91 pacientes). Métodos: Para a análise farmacoeconômica, foi utilizado o modelo de Árvore de Decisão, desenvolvido no software Treeage Suite 2011. Foi considerada uma coorte real de pacientes submetidos ao transplante renal entre janeiro de 2013 e março de 2017, os quais foram acompanhados por um período de um ano, sendo mensurados os benefícios clínicos, bem como os custos associados, na perspectiva do Sistema Único de Saúde. O método de custeio utilizado foi o botton-up. Foram adotados os limiares de custo-efetividade (LCEs) equivalentes a 1 PIB per capita e 1 a 3 PIB, considerando o ano de 2017. Resultados: No que diz respeito à sobrevida, a RCEI foi de cerca de R$ 214.234,12 para 1 ano de vida ganho. Em relação aos eventos adversos, a RCEI foi de cerca de R$ 43.682,98 para 1 ano sem incidência de eventos adversos. Conclusões: Ao avaliar a sobrevida e a incidência de eventos adversos, timoglobulina+everolimo não é considerado custo-efetivo em relação ao esquema contendo basiliximabe+micofenolato de sódio diante do LCE de 1 PIB per capita. No entanto, ao adotarmos o LCE até 3 PIB per capita, o regime contendo timoglobulina+everolimo é custo-efetivo, ultrapassando cerca de 38% do PIB per capita.

MTOR pathway mediates endoplasmic reticulum stress-induced CD4+ T cell apoptosis in septic mice

Endoplasmic reticulum stress (ERS) has been well documented to participate in the pathophysiological processes of apoptosis in many diseases. Inhibition of ERS ameliorates pathological organ injury. However, the upstream signaling pathways and molecular regulatory mechanisms of which are still unknown. mTOR, an evolutionarily conserved protein kinase, is a key regulator of apoptosis. Hence, in this study, a classical cecal ligation and puncture (CLP) sepsis model was constructed by using the T cell-specific knockout mTOR and TSC1 (Tuberous Sclerosis Complex, the inhibitor of mTOR signaling pathway) mice to explore the underlying signaling pathway and molecular mechanism of host immune imbalance caused by apoptosis in sepsis. We found that mTOR may modulate septic T cell apoptosis by regulating Akt–IRE1–JNK pathway. To further clarify the possible mechanism, the specific inhibitors of PI3K-Akt and IRE1–JNK were used to intervene in mice before/after CLP, respectively. By analyzing the proteins of mTOR-ERS signaling pathway and the expression of apoptosis-related proteins and genes, we found that mTOR mediated the ER stress induced CD4+ T cell apoptosis in Septic mice by negatively regulating the Akt–IRE1–JNK-Caspase 3 signaling cascades. These results indicate that mTOR–Akt–IRE1α–JNK signaling pathway mediated the Endoplasmic reticulum stress induced CD4+ T cell apoptosis in Septic mice.

Serum-derived exosomes from SD rats induce inflammation in macrophages through the mTOR pathway.

Inhalation of beryllium and its compounds can cause lung injuries, resulting from inflammation and oxidative stress. Multivesicular bodies (MVB), such as exosomes, are membrane vesicles produced by early and late endosomes that mediate intercellular communications. However, the role of exosomes in beryllium toxicity has not been elucidated. This current study aimed to investigate the functional role of exosomes in lung injury resulting from beryllium sulfate (BeSO4 ). Here, Sprague-Dawley (SD) rats were exposed to 4, 8, and 12 mg/kg BeSO4 by nonexposed intratracheal instillation. Murine macrophage (RAW 264.7) cells were pretreated with 50 nmol/L rapamycin (an mTOR signaling pathway inhibitor) for 30 min and then cultured for 24 h with 100 μg/mL exosomes, which had been previously isolated from the serum of 12 mg/kg BeSO4 -treated SD rats. Compared with those of the controls, exposure to BeSO4 in vivo increased LDH activity, elevated levels of inflammatory cytokines (IL-10, TNF-α, and IFN-γ) alongside inflammation-related proteins expression (COX-2 and iNOS), and enhanced secretion of exosomes from the SD rat's serum. Moreover, the BeSO4 -Exos-induced upregulation of LDH activity and inflammatory responses in RAW 264.7 cells can be alleviated following pretreatment with rapamycin. Collectively, these results suggest that serum exosomes play an important role in pulmonary inflammation induced by BeSO4 in RAW 264.7 cells via the mTOR pathway.

Structural Basis of DEPTOR to Recognize Phosphatidic Acid Using its Tandem DEP Domains

DEP domain containing mTOR-interacting protein (DEPTOR) plays pivotal roles in regulating metabolism, growth, autophagy and apoptosis by functions as an endogenous inhibitor of mTOR signaling pathway. Activated by phosphatidic acid, a second messenger in mTOR signaling, DEPTOR dissociates from mTORC1 complex with unknown mechanism. Here, we present a 1.5 Å resolution crystal structure, which shows that the N-terminal two tandem DEP domains of hDEPTOR fold into a dumbbell-shaped structure, protruding the characteristic β-hairpin arms of DEP domains on each side. An 18 amino acids DDEX motif at the end of DEP2 interacts with DEP1 and stabilizes the structure. Biochemical studies showed that the tandem DEP domains directly interact with phosphatidic acid using two distinct positively charged patches. These results provide insights into mTOR activation upon phosphatidic acid stimulation.

Optimized rapamycin-loaded PEGylated PLGA nanoparticles: Preparation, characterization and pharmacokinetics study

Rapamycin (RAP), an inhibitor of mTOR signaling pathway, has been widely used for its immunosuppressive activity over its anti-tumor and anti-inflammatory properties. The objective of this study was to encapsulate RAP into appropriately sized PEGylated nanoparticles, using biodegradable polyethylene glycol-poly (D, l-lactide-co-glycolide) copolymer (PEG-PLGA), for preferential tumor delivery through the enhanced permeability and retention (EPR) effect. Taguchi experimental design was used to determine the optimum preparation conditions for desirable sized nanoparticles and particle size was set as characteristic response. Nanoprecipitation method was used to prepare nanoparticles and the effects of stirring time, Tween 80 concentration, and RAP/PEG-PLGA ratio on nanoparticles size were investigated. The particle size of RAP-loaded PEGylated PLGA nanoparticles (RPP NPs) prepared using optimum conditions was about 118.8 nm. The release of RAP from optimized RPP NPs followed a non-Fickian sustained release pattern over a period of 7 days. In addition, the in vitro cytotoxicity of RPP NPs was investigated on various cell lines, and human leukemic Jurkat T cells revealed the lowest IC50 value. RPP NPs showed a good stability when stored for one month at 4 °C. The in vivo study on mice model showed enhanced pharmacokinetic profile of loaded RAP compared to its free form. Therefore, RPP NPs could be a potential therapeutic system for cancer and inflammatory disorder therapies.

Inhibitory effects of ursolic acid from Bushen Yijing Formula on TGF-β1-induced human umbilical vein endothelial cell fibrosis via AKT/mTOR signaling and Snail gene

The present study aimed to investigate the functional components from Bushen Yijing Formula and their inhibition of endothelial–mesenchymal transition (EndMT) and fibrosis in human umbilical vascular endothelial cells (HUVECs). HUVEC fibrosis was induced by treatment of transforming growth factor β (TGF-β) as the cellular model. Expression of EndMT biomarker gene and cofactors were determined by quantitative real-time-PCR, western blotting, and immunofluorescence. Angiogenesis capacity of vein endothelial cells was evaluated using tube formation assay. Ursolic acid and drug-contained serum ameliorated EndMT biomarker gene expression changes and angiogenesis capacity suppression induced by TGF-β treatment. Slug, Snail, and Twist gene expression and phosphorylation of mammalian target of rapamycin (mTOR) and AKT altered by TGF-β in HUVECs were suppressed by ursolic acid and drug-contained serum. Treatment with the mTOR signaling pathway inhibitor, rapamycin, inhibited the phosphorylation of mTOR and AKT, decreased Snail and Vimentin protein levels, and increased VE-cad protein levels. Overexpression of Snail gene promoted expression of EndMT-related genes and suppressed angiogenesis in HUVECs, which were attenuated by application of ursolic acid and drug-contained serum. Ursolic acid from Bushen Yijing Formula inhibits human umbilical vein endothelial cell EndMT and fibrosis, mediated by AKT/mTOR signaling and Snail gene expression.

Influence of mTOR signaling pathway on ketamine-induced injuries in the hippocampal neurons of rats

ABSTRACTObjective: To explore the influences of mammalian target of rapamycin (mTOR) signaling pathway on ketamine-induced apoptosis, oxidative stress and Ca2+ concentration in the hippocampal neurons of rats.Methods: The primary hippocampal neurons isolated from fetal Sprague Dawley rats were treated with ketamine (0, 50, 100 and 500 μM) for 4 days to observe its effect on mTOR signaling pathway and apoptosis of rat hippocampal neurons. Then, the hippocampal neurons were divided into C (Control), R (Rapamycin, an inhibitor of mTOR signaling pathway), K (Ketamine) and R + K (Rapamycin + Ketamine) groups to detect the apoptosis, reactive oxygen species (ROS) production, and Ca2+ concentration via the terminal transferase uridyl nick end labelling (TUNEL) assay, dichloro-dihydro-fluorescein diacetate (DCFH-DA) method and Fluo-3 acetoxymethyl ester (Fluo-3AM) staining, respectively. The expressions of mTOR signaling pathway and apoptosis-related proteins in hippocampal neurons were examined by qRT-PCR and Western blot.Results: Ketamine could dose-dependently promote the apoptosis of rat hippocampal neurons with upregulation of p-mTOR and its downstream regulators (p-4E-BP-1 and p-p70S6K). However, ketamine-induced apoptosis in hippocampal neurons was reversed significantly by the administration of rapamycin, as evident by the decrease in expressions of pro-apoptotic proteins (Bax and cleaved Caspase-3) and the increase in anti-apoptotic protein (Bcl-2). Meanwhile, the ROS generation and Ca2+ concentration was inhibited accompanied with reduced malonildialdehyde levels but elevated superoxide and glutathione peroxidase activities.Conclusion: Inhibition of mTOR signaling pathway protected rat hippocampal neurons from ketamine-induced injuries via reducing apoptosis, oxidative stress, as well as Ca2+ concentration.Abbreviations: mTOR: mammalian target of rapamycin; SD: Sprague-Dawley; SPF: Specific-pathogen free; ROS: reactive oxygen species; TUNEL: terminal transferase uridyl nick end labelling; DCFH-DA: Dichloro-dihydro-fluorescein diacetate; Fluo-3A: Fluo-3 acetoxymethyl ester; NMDAR: non-competitive N-methyl-D-aspartame glutamate receptor; 4E-BP1: 4E binding protein 1; p70S6K: p70 S6 Kinase; PCR: Polymerase chain reaction; MDA: malonildialdehyde; GSH-PX: glutathione peroxidase; ANOVA: One-way Analysis of Variance.

Human cytomegalovirus infection-induced autophagy was associated with the biological behavioral changes of human umbilical vein endothelial cell (HUVEC)

In this study, we investigated the enacted role of autophagy in biological behavioral changes of human umbilical vein endothelial cell (HUVEC) infected with human cytomegalovirus (HCMV). It was found that in HCMV-infected cells, the number of punctuate structures increased from 24 h to 48 h p.i. while decreased at 60 h p.i. by GFP-LC3 tranfecting, Monodansylcadaverine (MDC), acridine orange (AO) staining, which suggested that autophagy was induced at early stage, but it was inhibited at later stage in responding to HCMV infection. By real-time qPCR assay, it was revealed that mTOR autophagy pathway inhibitor rapamycin could promote HCMV proliferation in HUVEC cells. After the treatment of autophagy promoting agent, autophagy inhibitor, and mTOR signaling pathway inhibitor in HCMV-infected HUVECs showed similar results to the above findings by Western Blotting assay. Moreover, invasion assay showed that HCMV infection promoted HUVEC cell migration, and ELISA assay showed that HCMV infection increased the expression of adhesion molecules of HUVEC cells. In conclusion, HCMV infection induced autophagy in a time-dependent manner in HUVECs with the involvement of mTOR signaling pathway. The autophagy of HUVEC may enhance its cell invasiveness and the expression of ICAM-1 and VCAM-1. Thus, HCMV infection-induced autophagy was associated with the biological behavioral changes of HUVECs.

Phosphorylated p70S6K expression is an independent prognosticator for patients with esophageal squamous cell carcinoma

Although marked improvements have been made in surgical technique and chemoradiotherapy, the prognosis for patients with esophageal squamous cell carcinoma (ESCC) is still unsatisfactory. The mammalian target of rapamycin (mTOR) and its downstream signaling, p70 ribosomal S6 protein kinase (p70S6K) and eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4E-BP1), seem to play central roles in the regulation of cancer cell proliferation and survival. The significance of mTOR and its downstream targets, p70S6K and 4E-BP1, on the prognosis of ESCC remains uncertain, but this pathway is of particular concern because effective inhibitors are already available. Immunohistochemistry performed to evaluate the expression of phosphorylated mTOR (p-mTOR), phosphorylated p70S6K (p-p70S6K), phosphorylated 4E-binding protein 1 (p-4E-BP1), and Ki-67 using 105 surgically resected ESCC correlated with treatment outcome. The effect of the mTOR signaling pathway inhibitor everolimus on ESCC cell lines were investigated invitro by the 3-(4.5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and invivo by a nude mouse xenograft model. Univariate analysis showed that p-mTOR overexpression (P=.022), p-p70S6K overexpression (P=.002), and Ki-67 labeling index >50% (P=.045) were associated with inferior overall survival (OS). In a multivariate comparison, p-p70S6K overexpression (P=.001; hazard ratio, 2.247) remained independently associated with worse OS. In cell lines and the xenograft model, everolimus significantly inhibited ESCC growth. Overexpression of p-p70S6K is associated independently with a poor prognosis among patients with ESCC. The mTOR signaling pathway inhibitor everolimus can inhibit ESCC growth invitro and invivo. Our findings suggest that inhibition of mTOR signaling pathway may be a promising novel target for ESCC.

The microRNA 132 Regulates Fluid Shear Stress-Induced Differentiation in Periodontal Ligament Cells through mTOR Signaling Pathway

Background/Aims: Once tissue destruction has occurred, the differentiation of periodontal ligament (PDL) cells into osteoblasts plays an important role in repairing the oral cavity. Methods: In this work, we measured the proliferation and differentiation of PDL cells after fluid shear stress (FSS) treatment by ALP activity assays and in vitro mineralization assays respectively. The levels of miRNA in PDL cells treated with FSS or not were detected by using microRNA arrays. The possible signaling pathway was determined by western-blot. Results: This study demonstrates that FSS modulates several functions of human PDL cells. Specifically, increasing FSS in fixed increments regulates the proliferation and differentiation of PDL cells. Through microRNA arrays, we find that FSS induced-differentiation is accompanied by a significantly higher level of miR-132 compared to untreated controls. Phosphorylated levels of the P13K, AKT, mTOR, and p70S6K proteins also significantly increases in FSS-treated PDL cells. Finally, the FSS-induced differentiation of PDL cells is inhibited by miR-132 knockdown probe and the mTOR signaling pathway inhibitor BEZ235. Conclusion: Our data support the hypothesis that FSS-induced differentiation and proliferation involves the PI3K/AKT/mTOR signaling axis, through a process involving mir-132.

Identification of two novel inhibitors of mTOR signaling pathway based on high content screening

Mammalian target of rapamycin (mTOR) signaling pathway plays a critical role in regulating cell growth, proliferation and survival. Dysregulation of mTOR signaling pathway is closely involved in cancer development and chemotherapy resistance. Inhibitors of mTOR signaling pathway have been demonstrated to be attractive therapeutics for cancer therapy. In the present study, we aim to discover novel mTOR signaling pathway inhibitors from a natural compound library. Inhibitors of mTOR signaling pathway were discovered via high content screen assay based on the subcellular localization of eukaryotic initiation factor 4E (eIF4E) in mouse embryonic fibroblast cells. Candidate compounds were further assessed in cancer cells. Phosphorylation levels of mTOR complexes downstream targets were analyzed using Western blot. Cell cytotoxicity and apoptosis were evaluated using MTS assay and flow cytometry, respectively. Two compounds, 1,4-O-diferuloylsecoisolariciresinol (IM-1) and Pierreione B (IM-2), were identified which induced significant nuclear translocation of eIF4E in a panel of cancer cells. Both of the compounds decreased the phosphorylation levels of p70 ribosomal protein S6 kinase (S6K) and eIF4E binding protein 1 (4E-BP1), resulting in cancer cell cytotoxicity and apoptosis. Via high content screen assay, two novel inhibitors of mTOR signaling, IM-1 and IM-2, were identified with strong anticancer activity. IM-1 and IM-2 could be potential candidates for anticancer therapeutics by targeting mTOR signaling pathway and as such warrants further exploration.

Rapamycin, an inhibitor of mTOR signaling pathway, reverses lithium‐induced cell proliferation in renal collecting ducts

The most common side effect in patients undergoing lithium therapy is nephrogenic diabetes insipidus (NDI), in addition, lithium treatment can cause collecting duct cells to proliferate. The mammalian target of rapamycin (mTOR) signaling pathway is a key regulator of cell proliferation. We hypothesized that the mTOR signaling pathway may be playing a role in lithium‐induced cell proliferation of renal collecting duct. We fed mice lithium for 14d; AQP2 protein expression was significantly decreased (16 ± 4.0% vs control 100 ± 8.8%) and proliferating cell nuclear antigen (PCNA) protein expression was significantly increased (172 ± 8.6% vs control 100 ± 1.4%) in renal inner medulla (IM). We demonstrate that p‐mTOR (Ser 2448) was increased (154 ± 26.5%), as was phosphorylation of ribosomal S6 protein (p‐rS6), a downstream component of mTOR pathway (404 ± 151.4%) in renal IM of lithium‐treated mice. To test whether the inhibition of mTOR signaling pathway could reverse lithium‐induced cell proliferation, we treated mice with Rapamycin (Rapa), an inhibitor of mTOR. Rapa reversed lithium‐induced proliferation of IM collecting duct cells and decreased lithium‐induced p‐mTOR and p‐rS6 levels. Rapa had no effect on the upstream components of mTOR; p‐Akt and p‐TSC2 remained elevated by lithium. In conclusion, the mTOR signaling pathway is involved in lithium‐induced collecting duct cell proliferation.

The mTOR protein as a target in thyroid cancer

Introduction: The mammalian target of rapamycin (mTOR) protein is a downstream effector of the phosphatidilinositol-3 kinase (PI3K)/Akt pathway, which regulates not only cell proliferation and viability, but also iodide uptake in thyroid cells. Genetic alterations in the PI3K/Akt/mTOR pathway are common during thyroid cancer progression, and thus, these proteins are attractive targets for cancer therapy. So far, specific mTOR inhibitors, such as rapamycin analogs, have been developed and studied as anti-cancer agents.Areas covered: This review discusses evidence that justifies the potential use of mTOR signaling pathway inhibitors as therapeutic agents for thyroid cancer.Expert opinion: In the near future, mTOR-targeted drugs might represent a new approach for the therapy of thyroid cancer patients; rapamycin analogs have already been developed and are currently being clinically tested. Besides the antiproliferative action of mTOR inhibition, the stimulatory effect on thyroid iodide uptake can also be useful in the treatment of recurrent thyroid cancer. Therefore, if rapamycin analogs are able to increase iodide uptake in thyroid cancer, either alone or in combination with other agents, this will represent a new approach for the treatment of thyroid cancer, which may possibly improve the treatment of patients in which radioiodine therapy is not effective.