Rapamycin inhibits cell motility by suppression of mTOR-mediated S6K1 and 4E-BP1 pathways

Review: The PI3K-AKT-mTOR signal transduction pathway in canine cancer

Tumors in dogs and humans share many similar molecular and genetic features, incentivizing a better understanding of canine neoplasms not only for the purpose of treating companion animals, but also to facilitate research of spontaneously developing tumors with similar biologic behavior and treatment approaches in an immunologically competent animal model. Multiple tumor types of both species have similar dysregulation of signal transduction through phosphatidylinositol 3-kinase (PI3K), protein kinase B (PKB; AKT), and mechanistic target of rapamycin (mTOR), collectively known as the PI3K-AKT-mTOR pathway. This review aims to delineate the pertinent aspects of the PI3K-AKT-mTOR signaling pathway in health and in tumor development. It will then present a synopsis of current understanding of PI3K-AKT-mTOR signaling in important canine cancers and advancements in targeted inhibitors of this pathway.

Poncirus trifoliata (L.) Raf. Seed Extract Induces Cell Cycle Arrest and Apoptosis in the Androgen Receptor Positive LNCaP Prostate Cancer Cells

Prostate cancer (PCa) is the second most common male cancer. Its incidence derives from the interaction between modifiable and non-modifiable factors. The progression of prostate cancer into a more aggressive phenotype is associated with chronic inflammation and increased ROS production. For their biological properties, some phytochemicals from fruits and vegetable emerge as a promise strategy for cancer progression delay. These bioactive compounds are found in the highest amounts in peels and seeds. Poncirus trifoliata (L.) Raf. (PT) has been widely used in traditional medicine and retains anti-inflammatory, anti-bacterial, and anticancer effects. The seeds of P. trifoliata were exhaustively extracted by maceration with methanol as the solvent. The cell proliferation rate was performed by MTT and flow cytometry, while the apoptosis signals were analyzed by Western blotting and TUNEL assay. P. trifoliata seed extract reduced LNCaP and PC3 cell viability and induced cell cycle arrest at the G0/G1phase and apoptosis. In addition, a reduction in the AKT/mTOR pathway has been observed together with the up-regulation of stress-activated MAPK (p38 and c-Jun N-terminal kinase). Based on the study, the anti-growth effects of PT seed extract on prostate tumor cells give indications on the potential of the phytochemical drug for the treatment of this type of cancer. However, future in-depth studies are necessary to identify which components are mainly responsible for the anti-neoplastic response.

Role of Akt/Protein Kinase B in Cancer Metastasis

Metastasis is a critical step in the process of carcinogenesis and a vast majority of cancer-related mortalities result from metastatic disease that is resistant to current therapies. Cell migration and invasion are the first steps of the metastasis process, which mainly occurs by two important biological mechanisms, i.e., cytoskeletal remodelling and epithelial to mesenchymal transition (EMT). Akt (also known as protein kinase B) is a central signalling molecule of the PI3K-Akt signalling pathway. Aberrant activation of this pathway has been identified in a wide range of cancers. Several studies have revealed that Akt actively engages with the migratory process in motile cells, including metastatic cancer cells. The downstream signalling mechanism of Akt in cell migration depends upon the tumour type, sites, and intracellular localisation of activated Akt. In this review, we focus on the role of Akt in the regulation of two events that control cell migration and invasion in various cancers including head and neck squamous cell carcinoma (HNSCC) and the status of PI3K-Akt pathway inhibitors in clinical trials in metastatic cancers.

mLST8 is essential for coronavirus replication and regulates its replication through the mTORC1 pathway

Coronaviruses (CoVs), which pose a serious threat to human and animal health worldwide, need to hijack host factors to complete their replicative cycles. However, the current study of host factors involved in CoV replication remains unknown. Here, we identified a novel host factor, mammalian lethal with sec-13 protein 8 (mLST8), which is a common subunit of mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), and is critical for CoV replication. Inhibitor and knockout (KO) experiments revealed that mTORC1, but not mTORC2, is essential for transmissible gastroenteritis virus replication. Furthermore, mLST8 KO reduced the phosphorylation of unc-51-like kinase 1 (ULK1), a factor downstream of the mTORC1 signaling pathway, and mechanistic studies revealed that decreased phosphorylation of the mTORC1 downstream factor ULK1 promoted the activation of autophagy, which is responsible for antiviral replication in mLST8 KO cells. Then, transmission electron microscopy indicated that both mLST8 KO and autophagy activator inhibited the formation of double-membrane vesicles in early viral replication. Finally, mLST8 KO and autophagy activator treatment could also inhibit the replication of other CoVs, indicating a conserved relationship between autophagy activation and CoV replication. In summary, our work reveals that mLST8 is a novel host regulator of CoV replication, which provides new insights into the mechanism of CoV replication and can facilitate the development of broad-spectrum antiviral drugs. IMPORTANCE CoVs are highly variable, and existing CoV vaccines are still limited in their ability to address mutations in CoVs. Therefore, the need to improve our understanding of the interaction of CoVs with the host during viral replication and to find targets for drugs against CoVs is urgent. Here, we found that a novel host factor, mLST8, is critical for CoV infection. Further studies showed that mLST8 KO inhibited the mTORC1 signaling pathway, and we found that autophagy activation downstream of mTORC1 was the main cause of antiviral replication in mLST8 KO cells. Autophagy activation impaired the formation of DMVs and inhibited early viral replication. These findings deepen our understanding of the CoV replication process and provide insights into potential therapeutic applications.

Mitochondrial Hydrogen Peroxide Activates PTEN and Inactivates Akt Leading to Autophagy Inhibition-Dependent Cell Death in Neuronal Models of Parkinson's Disease

Defective autophagy relates to the pathogenesis of Parkinson's disease (PD), a typical neurodegenerative disease. Our recent study has demonstrated that PD toxins (6-OHDA, MPP+, or rotenone) induce neuronal apoptosis by impeding the AMPK/Akt-mTOR signaling. Here, we show that treatment with 6-OHDA, MPP+, or rotenone triggered decreases of ATG5/LC3-II and autophagosome formation with a concomitant increase of p62 in PC12, SH-SY5Y cells, and primary neurons, suggesting inhibition of autophagy. Interestingly, overexpression of wild-type ATG5 attenuated the inhibitory effect of PD toxins on autophagy, reducing neuronal apoptosis. The effects of PD toxins on autophagy and apoptosis were found to be associated with activation of PTEN and inactivation of Akt. Overexpression of dominant negative PTEN, constitutively active Akt and/or pretreatment with rapamycin rescued the cells from PD toxins-induced downregulation of ATG5/LC3-II and upregulation of p62, as well as consequential autophagosome diminishment and apoptosis in the cells. The effects of PD toxins on autophagy and apoptosis linked to excessive intracellular and mitochondrial hydrogen peroxide (H2O2) production, as evidenced by using a H2O2-scavenging enzyme catalase, a mitochondrial superoxide indicator MitoSOX and a mitochondria-selective superoxide scavenger Mito-TEMPO. Furthermore, we observed that treatment with PD toxins reduced the protein level of Parkin in the cells. Knockdown of Parkin alleviated the effects of PD toxins on H2O2 production, PTEN/Akt activity, autophagy, and apoptosis in the cells, whereas overexpression of wild-type Parkin exacerbated these effects of PD toxins, implying the involvement of Parkin in the PD toxins-induced oxidative stress. Taken together, the results indicate that PD toxins can elicit mitochondrial H2O2, which can activate PTEN and inactivate Akt leading to autophagy inhibition-dependent neuronal apoptosis, and Parkin plays a critical role in this process. Our findings suggest that co-manipulation of the PTEN/Akt/autophagy signaling by antioxidants may be exploited for the prevention of neuronal loss in PD.

A noncommutative combinatorial protein logic circuit controls cell orientation in nanoenvironments

Single-protein-based devices that integrate signal sensing with logical operations to generate functional outputs offer exceptional promise for monitoring and modulating biological systems. Engineering such intelligent nanoscale computing agents is challenging, as it requires the integration of sensor domains into a functional protein via intricate allosteric networks. We incorporate a rapamycin-sensitive sensor (uniRapR) and a blue light-responsive LOV2 domain into human Src kinase, creating a protein device that functions as a noncommutative combinatorial logic circuit. In our design, rapamycin activates Src kinase, causing protein localization to focal adhesions, whereas blue light exerts the reverse effect that inactivates Src translocation. Focal adhesion maturation induced by Src activation reduces cell migration dynamics and shifts cell orientation to align along collagen nanolane fibers. Using this protein device, we reversibly control cell orientation by applying the appropriate input signals, a framework that may be useful in tissue engineering and regenerative medicine.

Therapeutic silencing of mTOR by systemically administered siRNA-loaded neutral liposomal nanoparticles inhibits DMBA-induced mammary carcinogenesis

BACKGROUND

Mammary carcinogenesis possesses great challenges due to the lack of effectiveness of the multiple therapeutic options available. Gene therapy-based cancer treatment strategy provides more targeting accuracy, fewer side effects, and higher therapeutic efficiency. Downregulation of the oncogene mTOR by mTOR-siRNA is an encouraging approach to reduce cancer progression. However, its employment as means of therapeutic strategy has been restricted due to the unavailability of a suitable delivery system.

METHODS

A suitable nanocarrier system made up of 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) has been developed to prevent degradation and for proficient delivery of siRNA. This was followed by in vitro and in vivo anti-breast cancer efficiency analysis of the mTOR siRNA-loaded neutral liposomal formulation (NL-mTOR-siRNA).

RESULTS

In our experiment, a profound reduction in MCF-7 cell growth, proliferation and invasion was ascertained following extensive downregulation of mTOR expression. NL-mTOR-siRNA suppressed tumour growth and restored morphological alterations of DMBA-induced breast cancer. In addition, neutral liposome enhanced accumulation of siRNA in mammary cancer tissues facilitating its deep cytosolic distribution within the tumour, which allows apoptosis thereby facilitating its anti-tumour potential.

CONCLUSION

Hence, the current study highlighted the augmented ground for therapies aiming toward cancerous cells to diminish mTOR expression by RNAi in managing mammary carcinoma.

Neuroprotection of resveratrol against cadmium-poisoning acts through dual inhibition of mTORC1/2 signaling

Resveratrol is a natural polyphenol with neuroprotective function. The underlying mechanism is not well understood. Our previous studies have identified that resveratrol antagonizes cadmium (Cd) neurotoxicity via targeting PP2A/PP5-mediated Erk1/2 and JNK pathways. Here we show that resveratrol protected against Cd-poisoning also by blocking Cd-induced activation of mTORC1 and mTORC2 pathways in PC12 cells and murine primary neurons. Co-treatment with inhibitors of mTORC1 (rapamycin), mTORC1/2 (PP242), Erk1/2 (U0126) and/or JNK (SP600125), knockdown of mTOR, or disruption of mTORC1 and/or mTORC2 by silencing raptor, rictor or raptor/rictor, respectively, markedly potentiated the inhibitory effects of resveratrol on Cd-induced phosphorylation of S6K1/4E-BP1 (mTORC1 substrates), Akt (mTORC2 substrate), Erk1/2 and/or JNK/c-Jun, cleavage of caspase-3 and cell death in PC12 cells and/or primary neurons. Knockdown of S6K1 or 4E-BP1, or ectopic expression of constitutively hypophosphorylated 4E-BP1 (4E-BP1-5A) reinforced the resveratrol's inhibition on Cd-evoked cell death, whereas ectopic expression of constitutively active S6K1 or knockdown of 4E-BP1 attenuated the resveratrol's inhibition on Cd-induced cell death. Co-treatment with Akt inhibitor or overexpression of dominant negative Akt (dn-Akt) strengthened the resveratrol's suppression on Cd-induced ROS, Erk1/2 activation and apoptosis, whereas overexpression of constitutively active Akt (myr-Akt) conferred high resistance to the resveratrol's inhibitory effects in the neuronal cells. Taken together, the results indicate that resveratrol attenuates Cd-induced neuronal apoptosis partly through inhibition of mTORC1/2 pathways. Our studies highlight that resveratrol can be exploited for the prevention of Cd toxicity related to neurodegenerative diseases.

Targeting mTOR as a Cancer Therapy: Recent Advances in Natural Bioactive Compounds and Immunotherapy

The mammalian target of rapamycin (mTOR) is a highly conserved serine/threonine-protein kinase, which regulates many biological processes related to metabolism, cancer, immune function, and aging. It is an essential protein kinase that belongs to the phosphoinositide-3-kinase (PI3K) family and has two known signaling complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Even though mTOR signaling plays a critical role in promoting mitochondria-related protein synthesis, suppressing the catabolic process of autophagy, contributing to lipid metabolism, engaging in ribosome formation, and acting as a critical regulator of mRNA translation, it remains one of the significant signaling systems involved in the tumor process, particularly in apoptosis, cell cycle, and cancer cell proliferation. Therefore, the mTOR signaling system could be suggested as a cancer biomarker, and its targeting is important in anti-tumor therapy research. Indeed, its dysregulation is involved in different types of cancers such as colon, neck, cervical, head, lung, breast, reproductive, and bone cancers, as well as nasopharyngeal carcinoma. Moreover, recent investigations showed that targeting mTOR could be considered as cancer therapy. Accordingly, this review presents an overview of recent developments associated with the mTOR signaling pathway and its molecular involvement in various human cancer types. It also summarizes the research progress of different mTOR inhibitors, including natural and synthetised compounds and their main mechanisms, as well as the rational combinations with immunotherapies.

Effects of the Exposure of Human Non-Tumour Cells to Sera of Pancreatic Cancer Patients

Pancreatic ductal adenocarcinoma (PDAC) has high metastatic potential. The “genometastasis” theory proposes that the blood of some cancer patients contains elements able to transform healthy cells by transferring oncogenes. Since findings on genometastasis in PDAC are still scarce, we sought supporting evidence by treating non-tumour HEK293T and hTERT-HPNE human cell lines with sera of PDAC patients. Here, we showed that HEK293T cells have undergone malignant transformation, increased the migration and invasion abilities, and acquired a partial chemoresistance, whereas hTERT-HPNE cells were almost refractory to transformation by patients’ sera. Next-generation sequencing showed that transformed HEK293T cells gained and lost several genomic regions, harbouring genes involved in many cancer-associated processes. Our results support the genometastasis theory, but further studies are needed for the identification of the circulating transforming elements. Such elements could also be useful biomarkers in liquid biopsy assays.

Downregulation of miR-1270 mediates endothelial progenitor cell function in preeclampsia: Role for ATM in the Src/VE-cadherin axis

Preeclampsia, a pregnancy-related hypertensive disorder, is associated with endothelial dysfunction and increased cardiovascular risk of the offspring in adulthood. In preeclampsia, endothelial colony-forming cells (ECFC) are reduced in number and function. Recently, we have shown that miR-1270, which is involved in cancer in vitro proliferation, migration, and tumor progression, is downregulated in fetal ECFC from preeclamptic pregnancies. We now hypothesize that miR-1270 dysregulation contributes to vascular endothelial dysfunction occurring after preeclampsia via ATM (ataxia telangiectasia mutated) overexpression, the key kinase of DNA damage repair. Here, we show that miR-1270 silencing in normal ECFC and downregulation in preeclamptic ECFC are accompanied by an increase in the expression levels of ATM. Furthermore, ATM activation correlates with upregulated tyrosine kinase Src leading to phosphorylation and internalization of VE-cadherin (vascular endothelial-cadherin) which subsequently compromises endothelial barrier permeability and morphodynamic cell parameters. Treatment with specific ATM inhibitors reveals a novel role of ATM upstream of tyrosine kinase Src activation. Subsequently, Src phosphorylation and internalization of VE-cadherin compromise endothelial barrier permeability. Our findings suggest that downregulation of miR-1270 contributes to impaired ECFC function via the associated ATM overexpression, which further identifies ATM as a novel and critical factor for ECFC defects in preeclampsia. Our study provides new insights into the understanding of ECFC impairment associated with cardiovascular risk in preeclamptic offspring and identifies potential novel therapeutic targets.

NOX2-derived hydrogen peroxide impedes the AMPK/Akt-mTOR signaling pathway contributing to cell death in neuronal cells

Oxidative stress is closely related to the pathogenesis of Parkinson's disease (PD), a typical neurodegenerative disease. NADPH oxidase 2 (NOX2) is involved in hydrogen peroxide (H₂O₂) generation. Recently, we have reported that treatment with H₂O₂ and PD toxins, including 6-hydroxydopamine (6-OHDA), 1-Methyl-4-phenylpyridin-1-ium (MPP⁺) and rotenone, induces neuronal apoptosis by inhibiting the mTOR pathway. Here, we show that treatment with 6-OHDA, MPP⁺ or rotenone induced H₂O₂ generation by upregulating the levels of NOX2 and its regulatory proteins (p22^phox, p40^phox, p47^phox, p67^phox, and Rac1), leading to apoptotic cell death in PC12 cells and primary neurons. Inhibition of NOX2 with apocynin or diphenyleneiodonium, or knockdown of NOX2 powerfully attenuated PD toxins-evoked NOX2 and H2O2, thereby hindering activation of AMPK, inhibition of Akt/mTOR, and induction of apoptosis in neuronal cells. Pretreatment with catalase, a H₂O₂-scavenging enzyme, blocked the effects of PD toxins on NOX2-dependent H₂O₂ production, AMPK/Akt/mTOR signaling and apoptosis in the cells. Similar effects were also seen in the cells pretreated with Mito-TEMPO, a mitochondria-selective superoxide scavenger, implying a mitochondrial H₂O₂-dependent mechanism involved. Further research revealed that ectopic expression of constitutively active Akt or dominant negative AMPKα, or inhibition of AMPK with compound C suppressed PD toxins-induced expression of NOX2 and its regulatory proteins, as well as consequential H₂O₂ production and apoptosis in the cells. Taken together, these results indicate that certain PD toxins can impede the AMPK/Akt-mTOR signaling pathway leading to neuronal apoptosis by eliciting NOX2-derived H₂O₂ production. Our findings suggest that neuronal loss in PD may be prevented by regulating the NOX2, AMPK/Akt-mTOR signaling and/or applying antioxidants to ameliorate oxidative stress.

Dual Inhibition of mTORC1/2 Reduces Migration of Cholangiocarcinoma Cells by Regulation of Matrixmetalloproteinases

Cholangiocarcinoma (CCA) is a rare but highly aggressive tumor entity for which systemic therapies only showed limited efficacy so far. As OSI-027—a dual kinase inhibitor targeting both mTOR complexes, mTORC1 and mTORC2 - showed improved anti-cancer effects, we sought to evaluate its impact on the migratory and metastatic capacity of CCA cells in vitro. We found that treatment with OSI-027 leads to reduced cell mobility and migration as well as a reduced surviving fraction in colony-forming ability. While neither cell viability nor proliferation rate was affected, OSI-027 decreased the expression of MMP2 and MMP9. Moreover, survival as well as anti-apoptotic signaling was impaired upon the use of OSI-027 as determined by AKT and MAPK blotting. Dual targeting of mTORC1/2 might therefore be a viable option for anti-neoplastic therapy in CCA.

EBV LMP1-activated mTORC1 and mTORC2 Coordinately Promote Nasopharyngeal Cancer Stem Cell Properties

Epstein-Barr Virus (EBV) is associated with several malignant diseases, including Burkitt's lymphoma, nasopharyngeal carcinoma (NPC), certain types of lymphomas, and a portion of gastric cancers. Virus-encoded oncoprotein LMP1 induces the epithelial-to-mesenchymal transition (EMT), leading to cancer stem cell formation. In the current study, we investigated how LMP1 contributes to cancer stem cell development in NPC. We found that LMP1 plays an essential role in acquiring CSC characteristics, including tumor initiation, metastasis, and therapeutic resistance by activating the PI3K/mTOR/Akt signaling pathway. We dissected the functions of distinct signaling (mTORC1 and mTORC2) in the acquisition of different CSC characteristics. Side population (SP) formation, which represents the chemotherapy resistance feature of CSC, requires mTORC1 signaling. Tumor initiation capability is mainly attributed to mTORC2, which confers on NPC the capabilities of proliferation and survival by activating mTORC2 downstream genes c-Myc. Both mTORC1 and mTORC2 enhance cell migration and invasion of NPC cells, suggesting that mTORC1/2 co-regulate metastasis of NPC. The revelation of the roles of the mTOR signaling pathways in distinct tumorigenic features provides a guideline for designing efficient therapies by choosing specific mTOR inhibitors targeting mTORC1, mTORC2, or both to achieve durable remission of NPC in patients. Importance LMP1 endows NPC to gain cancer stem cell characteristics through activating mTORC1 and mTORC2 pathways. The different mTOR pathways are responsible for distinct tumorigenic features. Rapamycin-insensitive mTORC1 is essential for CSC drug resistance. NPC tumor initiation capacity is mainly attributed to mTORC2 signaling. mTORC1 and mTORC2 co-regulate NPC cell migration and invasion. The revelation of the roles of mTOR signaling in NPC CSC establishment has implications for novel therapeutic strategies to treat relapsed and metastatic NPC and achieve durable remission.

Copper depletion modulates mitochondrial oxidative phosphorylation to impair triple negative breast cancer metastasis

Copper serves as a co-factor for a host of metalloenzymes that contribute to malignant progression. The orally bioavailable copper chelating agent tetrathiomolybdate (TM) has been associated with a significant survival benefit in high-risk triple negative breast cancer (TNBC) patients. Despite these promising data, the mechanisms by which copper depletion impacts metastasis are poorly understood and this remains a major barrier to advancing TM to a randomized phase II trial. Here, using two independent TNBC models, we report a discrete subpopulation of highly metastatic SOX2/OCT4+ cells within primary tumors that exhibit elevated intracellular copper levels and a marked sensitivity to TM. Global proteomic and metabolomic profiling identifies TM-mediated inactivation of Complex IV as the primary metabolic defect in the SOX2/OCT4+ cell population. We also identify AMPK/mTORC1 energy sensor as an important downstream pathway and show that AMPK inhibition rescues TM-mediated loss of invasion. Furthermore, loss of the mitochondria-specific copper chaperone, COX17, restricts copper deficiency to mitochondria and phenocopies TM-mediated alterations. These findings identify a copper-metabolism-metastasis axis with potential to enrich patient populations in next-generation therapeutic trials.

Correlation of the AKT/mTOR signaling pathway with the clinicopathological features and prognosis of nasopharyngeal carcinoma

The primary aim of this study was to examine the correlation of the AKT/mTOR signaling pathway with the clinicopathological features and prognostic significance in nasopharyngeal carcinoma (NPC). The study tissues were collected from 285 patients with NPC and normal mucosal tissues were obtained from 289 individuals with normal nasopharynxes. Immunohistochemical staining was used to detected the expression of the AKT, mTOR, and p70 ribosomal S6 kinase (P70S6K) proteins. Follow-up was performed for between 8 and 60 months. Spearman’s rank correlation analysis was performed to evaluate the correlation of the expression of the AKT, mTOR, and P70S6K proteins in NPC tissues. Kaplan-Meier curves were plotted to show the survival of patients with NPC. A Cox proportional hazards model was used to explore the independent risk factors for prognosis. The expression of the AKT, mTOR, and P70S6K proteins in NPC tissues was higher than that in healthy nasopharyngeal mucosal tissues, and was correlated with T-staging, N-staging, clinical stage, distant metastasis, and differentiation. The positive expression of the AKT, mTOR, and P70S6K proteins was higher in patients with stage III/IV NPC, low differentiation, and metastasis. The survival rates of patients with NPC with AKT-positive, mTOR-positive, and P70S6K-positive expression were considerably lower than those without the expression of these proteins. Distant metastasis and the overexpression of the AKT, mTOR, and P70S6K proteins were independent risk factors for the prognosis of patients with NPC. The results obtained from this study indicated an association between the AKT/mTOR signaling pathway and the progression of NPC. The upregulation of the AKT/mTOR pathway in patients with NPC is a predictor of poor prognosis.

Dysregulation of myelin synthesis and actomyosin function underlies aberrant myelin in CMT4B1 neuropathy

Charcot-Marie-Tooth type 4B1 (CMT4B1) is a severe autosomal recessive demyelinating neuropathy with childhood onset, caused by loss-of-function mutations in the myotubularin-related 2 (MTMR2) gene. MTMR2 is a ubiquitously expressed catalytically active 3-phosphatase, which in vitro dephosphorylates the 3-phosphoinositides PtdIns3P and PtdIns(3,5)P ₂, with a preference for PtdIns(3,5)P ₂ A hallmark of CMT4B1 neuropathy are redundant loops of myelin in the nerve termed myelin outfoldings, which can be considered the consequence of altered growth of myelinated fibers during postnatal development. How MTMR2 loss and the resulting imbalance of 3'-phosphoinositides cause CMT4B1 is unknown. Here we show that MTMR2 by regulating PtdIns(3,5)P ₂ levels coordinates mTORC1-dependent myelin synthesis and RhoA/myosin II-dependent cytoskeletal dynamics to promote myelin membrane expansion and longitudinal myelin growth. Consistent with this, pharmacological inhibition of PtdIns(3,5)P ₂ synthesis or mTORC1/RhoA signaling ameliorates CMT4B1 phenotypes. Our data reveal a crucial role for MTMR2-regulated lipid turnover to titrate mTORC1 and RhoA signaling thereby controlling myelin growth.

Inhibition of the mTOR pathway and reprogramming of protein synthesis by MDM4 reduce ovarian cancer metastatic properties

Epithelial ovarian cancer (EOC) is a highly heterogeneous disease with a high death rate mainly due to the metastatic spread. The expression of MDM4, a well-known p53-inhibitor, is positively associated with chemotherapy response and overall survival (OS) in EOC. However, the basis of this association remains elusive. We show that in vivo MDM4 reduces intraperitoneal dissemination of EOC cells, independently of p53 and an immune-competent background. By 2D and 3D assays, MDM4 impairs the early steps of the metastatic process. A 3D-bioprinting system, ad hoc developed by co-culturing EOC spheroids and endothelial cells, showed reduced dissemination and intravasation into vessel-like structures of MDM4-expressing cells. Consistent with these data, high MDM4 levels protect mice from ovarian cancer-related death and, importantly, correlate with increased 15 y OS probability in large data set analysis of 1656 patients. Proteomic analysis of EOC 3D-spheroids revealed decreased protein synthesis and mTOR signaling, upon MDM4 expression. Accordingly, MDM4 does not further inhibit cell migration when its activity towards mTOR is blocked by genetic or pharmacological approaches. Importantly, high levels of MDM4 reduced the efficacy of mTOR inhibitors in constraining cell migration. Overall, these data demonstrate that MDM4 impairs EOC metastatic process by inhibiting mTOR activity and suggest the usefulness of MDM4 assessment for the tailored application of mTOR-targeted therapy.

PI3K/mTOR Dual Inhibitor PF-04691502 Is a Schedule-Dependent Radiosensitizer for Gastroenteropancreatic Neuroendocrine Tumors

Patients with advanced-stage gastroenteropancreatic neuroendocrine tumors (GEP-NETs) have a poor overall prognosis despite chemotherapy and radiotherapy (e.g., peptide receptor radionuclide therapy (PRRT)). Better treatment options are needed to improve disease regression and patient survival. The purpose of this study was to examine a new treatment strategy by combining PI3K/mTOR dual inhibition and radiotherapy. First, we assessed the efficacy of two PI3K/mTOR dual inhibitors, PF-04691502 and PKI-402, to inhibit pAkt and increase apoptosis in NET cell lines (BON and QGP-1) and patient-derived tumor spheroids as single agents or combined with radiotherapy (XRT). Treatment with PF-04691502 decreased pAkt (Ser473) expression for up to 72 h compared with the control; in contrast, decreased pAkt expression was noted for less than 24 h with PKI-402. Simultaneous treatment with PF-04691502 and XRT did not induce apoptosis in NET cells; however, the addition of PF-04691502 48 h after XRT significantly increased apoptosis compared to PF-04691502 or XRT treatment alone. Our results demonstrate that schedule-dependent administration of a PI3K/mTOR inhibitor, combined with XRT, can enhance cytotoxicity by promoting the radiosensitivity of NET cells. Moreover, our findings suggest that radiotherapy, in combination with timed PI3K/mTOR inhibition, may be a promising therapeutic regimen for patients with GEP-NET.

Inhibitory effects of terrein on lung cancer cell metastasis and angiogenesis

Cancer metastasis is the leading cause of mortality in cancer patients. Over 70% of lung cancer patients are diagnosed at advanced or metastatic stages, and this results in an increased incidence of mortality. Terrein is a secondary bioactive fungal metabolite isolated from Aspergillus terreus. Numerous studies have demonstrated that terrein has anticancer properties, but in the present study, the cellular mechanisms underlying the inhibition of lung cancer cell metastasis by terrein was investigated for the first time. Using MTT assays, the cytotoxic effects of terrein were first examined in human lung cancer cells (A549 cells) and then compared with its cytotoxic effects in three noncancer control cell lines (Vero kidney, L6 skeletal muscle and H9C2 cardiomyoblast cells). The results indicated that terrein significantly reduced the viability of all these cells but exhibited a different level of toxicity in each cell type; these results revealed a specific concentration range in which the effect of terrein was specific to A549 cells. This significant cytotoxic effect of terrein in A549 cells was verified using LDH assays. It was then demonstrated that terrein attenuated the proliferation of A549 cells using IncuCyte image analysis. Regarding its antimetastatic effects, terrein significantly inhibited A549 cell adhesion, migration and invasion. In addition, terrein suppressed the angiogenic processes of A549 cells, including vascular endothelial growth factor (VEGF) secretion, capillary-like tube formation and VEGF/VEGFR2 interaction. These phenomena were accompanied by reduced protein levels of integrins, FAK, and their downstream mediators (e.g., PI3K, AKT, mTORC1 and P70S6K). All these data indicated that terrein was able to inhibit all the major metastatic processes in human lung cancer cells, which is crucial for cancer treatment.

Potent antitumour of the mTORC1/2 dual inhibitor AZD2014 in docetaxel-sensitive and docetaxel-resistant castration-resistant prostate cancer cells

Recent studies indicate mammalian target of rapamycin (mTOR) may play an important role in PCa progression and drug resistance. Here, we investigated the effects of a novel mTORC1/C2 dual inhibitor, AZD2014, on naive and docetaxel (Doc)‐pre‐treated castration‐resistant PCa (CRPC) cells and explored its therapeutic potential in CRPCs. In the current study, AZD2014 has a greater inhibitory effect against 4EBP1 and AKT phosphorylation than rapamycin in CRPC cells and prevented the feedback activation of AKT signalling. Importantly, AZD2014 suppressed CRPC cell growth in vitro by suppressing proliferation, apoptosis, cell cycle arrest at G1 phase and autophagy to a greater extent than rapamycin. Moreover, AZD2014 was more efficacious than rapamycin in inhibiting migration, invasion and EMT progression in Doc‐sensitive and Doc‐resistant CRPC cells. Overall, AZD2014 showed significant antitumour effects. Thereby, the current study highlights a reliable theoretical basis for the clinical application of AZD2014 in both Doc‐sensitive and Doc‐resistant CRPCs.

Bortezomib activation of mTORC1 pathway mediated by NOX2-drived reactive oxygen species results in apoptosis in primary dorsal root ganglion neurons

Bortezomib (Bort), a chemotherapeutic agent, is widely used for the clinical treatment of cancers. However, Bort-induced peripheral neurotoxicity (BIPN) significantly restricts its clinical application, which is difficult to deal with since the underlying mechanisms of BIPN are unclear. Here, we showed that Bort activates mTORC1 pathway leading to dorsal root ganglion (DRG) neuronal apoptosis. Inhibition of mTORC1 with rapamycin or knockdown of raptor, regulatory-associated protein of mTORC1, with shRNA dramatically rescued the cells from Bort-caused apoptosis. In addition, we found that Bort-activated mTORC1 pathway was attributed to Bort elevation of reactive oxygen species (ROS). This is supported by the evidence that using ROS scavenger N-acetyl cysteine (NAC) significantly alleviated Bort-activated mTORC1 pathway. Furthermore, we revealed that upregulation of NOX2 contributed to Bort-elicited ROS overproduction, leading to mTORC1 pathway-dependent apoptosis in DRG neurons. Inhibition of NOX2 with apocynin remarkably diminished Bort-induced overgeneration of ROS, activation of mTORC1 pathway and apoptosis in the cells. Taken together, these results indicate that Bort activation of mTORC1 pathway mediated by NOX2-drived ROS leads to apoptotic death in DRG neurons. Our findings highlight that manipulation of intracellular ROS level or NOX2 or mTORC1 activity may be exploited for prevention of BIPN.

Translational Regulation of Cancer Metastasis

Deregulation of the mRNA translational process has been observed during tumorigenesis. However, recent findings have shown that deregulation of translation also contributes specifically to cancer cell spread. During metastasis, cancer cells undergo changes in cellular state, permitting the acquisition of features necessary for cell survival, dissemination, and outgrowth. In addition, metastatic cells respond to external cues, allowing for their persistence under significant cellular and microenvironmental stresses. Recent work has revealed the importance of mRNA translation to these dynamic changes, including regulation of cell states through epithelial-to-mesenchymal transition and tumor dormancy and as a response to external stresses such as hypoxia and immune surveillance. In this review, we focus on examples of altered translation underlying these phenotypic changes and responses to external cues and explore how they contribute to metastatic progression. We also highlight the therapeutic opportunities presented by aberrant mRNA translation, suggesting novel ways to target metastatic tumor cells.

Chemokine (C-C Motif) Ligand 1 Derived from Tumor-Associated Macrophages Contributes to Esophageal Squamous Cell Carcinoma Progression via CCR8-Mediated Akt/Proline-Rich Akt Substrate of 40 kDa/Mammalian Target of Rapamycin Pathway

Tumor-associated macrophages (TAMs) promote tumor progression. The number of infiltrating TAMs is associated with poor prognosis in esophageal squamous cell carcinoma (ESCC) patients; however, the mechanism underlying this phenomenon is unclear. cDNA microarray analysis indicates that the expression of chemokine (C-C motif) ligand 1 (CCL1) is up-regulated in peripheral blood monocyte-derived macrophages stimulated using conditioned media from ESCC cells (TAM-like macrophages). Here, we evaluated the role of CCL1 in ESCC progression. CCL1 was overexpressed in TAM-like macrophages, and CCR8, a CCL1 receptor, was expressed on ESCC cell surface. TAM-like macrophages significantly enhanced the motility of ESCC cells, and neutralizing antibodies against CCL1 or CCR8 suppressed this increased motility. Recombinant human CCL1 promoted ESCC cell motility via the Akt/proline-rich Akt substrate of 40 kDa/mammalian target of rapamycin pathway. Phosphatidylinositol 3-kinase or Akt inhibitors, CCR8 silencing, and neutralizing antibody against CCR8 could significantly suppress these effects. The overexpression of CCL1 in stromal cells or CCR8 in ESCC cells was significantly associated with poor overall survival (P = 0.002 or P = 0.009, respectively) and disease-free survival (P = 0.009 or P = 0.047, respectively) in patients with ESCC. These results indicate that the interaction between stromal CCL1 and CCR8 on cancer cells promotes ESCC progression via the Akt/proline-rich Akt substrate of 40 kDa/mammalian target of rapamycin pathway, thereby providing novel therapeutic targets.

Directly imaging the localisation and photosensitization properties of the pan-mTOR inhibitor, AZD2014, in living cancer cells

The range of cellular functions the mechanistic target of rapamycin (mTOR) protein performs makes it an attractive drug target for cancer therapy. However, the cellular localisation and mode of action of second generation inhibitors of mTOR is poorly understood despite the level of attention there is in targeting the mTOR protein. We have therefore studied the properties of the pan-mTOR inhibitor AZD2014, an ideal candidate to study because it is naturally fluorescent, characterising its photochemical properties in solution phase (DMSO, PBS and BSA) and within living cells, where it localises within both the nucleus and the cytoplasm but with different excited state lifetimes of 4.8 (+/- 0.5) and 3.9 (+/- 0.4) ns respectively. We measure the uptake of the inhibitor AZD2014 (7 μM) in monolayer HEK293 cells occurring with a half-life of 1 min but observe complex behaviour for 3D spheroids with the core of the spheroid showing a slower uptake and a slow biphasic behaviour at longer times. From a cellular perspective using fluorescence lifetime imaging microscopy AZD2014 was found to interact directly with GFP-tagged mTORC1 proteins including the downstream target, S6K1. We observe light sensitive behaviour of the cells containing AZD2014 which leads to cell death, in both monolayer and spheroids cells, demonstrating the potential of AZD2014 to act as a possible photodynamic drug under both single photon and multiphoton excitation and discuss its use as a photosensitizer. We also briefly characterise another pan-mTOR inhibitor, INK128.

Integrating Mathematical Modeling with High-Throughput Imaging Explains How Polyploid Populations Behave in Nutrient-Sparse Environments

Breast cancer progresses in a multistep process from primary tumor growth and stroma invasion to metastasis. Nutrient-limiting environments promote chemotaxis with aggressive morphologies characteristic of invasion. It is unknown how coexisting cells differ in their response to nutrient limitations and how this impacts invasion of the metapopulation as a whole. In this study, we integrate mathematical modeling with microenvironmental perturbation data to investigate invasion in nutrient-limiting environments inhabited by one or two cancer cell subpopulations. Subpopulations were defined by their energy efficiency and chemotactic ability. Invasion distance traveled by a homogeneous population was estimated. For heterogeneous populations, results suggest that an imbalance between nutrient efficacy and chemotactic superiority accelerates invasion. Such imbalance will spatially segregate the two populations and only one type will dominate at the invasion front. Only if these two phenotypes are balanced, the two subpopulations compete for the same space, which decelerates invasion. We investigate ploidy as a candidate biomarker of this phenotypic heterogeneity and discuss its potential to inform the dose of mTOR inhibitors (mTOR-I) that can inhibit chemotaxis just enough to facilitate such competition. SIGNIFICANCE: This study identifies the double-edged sword of high ploidy as a prerequisite to personalize combination therapies with cytotoxic drugs and inhibitors of signal transduction pathways such as mTOR-Is. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/22/5109/F1.large.jpg.

TIPRL, a Novel Tumor Suppressor, Suppresses Cell Migration, and Invasion Through Regulating AMPK/mTOR Signaling Pathway in Gastric Cancer

Invasion and metastasis of gastric cancer after curative resection remain the most common lethal outcomes. However, our current understanding of the molecular mechanism underlying gastric cancer metastasis is far from complete. Herein, we identified TOR signaling pathway regulator (TIPRL) as a novel metastasis suppressor in gastric cancer through genome-wide gene expression profiling analysis using mRNA microarray. Decreased TIPRL expression was detected in clinical gastric cancer specimens, and low TIPRL expression was correlated with more-advanced TNM stage, distant metastasis, and poor clinical outcome. Moreover, TIPRL was identified as a direct target of miR-216a-5p and miR-383-5p. Functional study revealed that re-expression of TIPRL in gastric cancer cell lines suppressed their migratory and invasive capacities, whereas inverse effects were observed in TIPRL-deficient models. Mechanistically, TIPRL downstream effectors and signaling pathways were investigated using mRNA microarray. Gene expression profiling revealed that TIPRL could not modulate the downstream genes at transcriptional levels, thereby implying that the regulation might occur at the post-transcriptional levels. We further demonstrated that TIPRL induced phosphorylation/activation of AMPK, which in turn attenuated phosphorylation of mTOR, p70S6K, and 4E-BP1, thereby leading to inactivation of mTOR signaling and subsequent suppression of cell migration/invasion in gastric cancer. Taken together, TIPRL acts as a novel metastasis suppressor in gastric cancer, at least in part, through regulating AMPK/mTOR signaling, likely representing a promising target for new therapies in gastric cancer.

p70S6K Promotes Acquired Resistance of Erlotinib Through Induction of Epithelial-Mesenchymal Transition in Non-Small Cell Lung Carcinoma

Background

Lung cancer is the leading cause of cancer-related deaths. EGFR tyrosine kinase inhibitors, such as erlotinib, were approved for non-small cell lung carcinoma patients with EGFR mutations. However, the acquired resistance of these inhibitors has not been fully clarified. Therefore, clarifying the mechanism and developing new rationales to overcome the drug resistance are urgently needed.

Methods

A pair of erlotinib sensitive and resistant cells was used to identify the key molecules in mediating erlotinib resistance. Loss- or gain-of-function study was used to confirm the effects of the key molecules. Xenograft mouse model and human cancer tissue sample studies were conducted for further corroboration.

Results

HCC827 cells with acquired resistance to erlotinib underwent epithelial-mesenchymal transition and exhibited enhanced p70S6K signaling compared to parental sensitive cells. Moreover, in erlotinib resistant cells, downregulation of p70S6K expression using either siRNA or shRNA reversed EMT and partially overcame erlotinib resistance. Meanwhile, in erlotinib sensitive cells, overexpression of p70S6K promoted EMT and induced erlotinib resistance. Upregulation of p70S6K signaling in erlotinib resistant cells was caused by reduced GSK3β-mediated protein degradation of mTOR and raptor. Additionally, p70S6K silencing suppressed the growth of erlotinib resistant cells in a xenograft mouse model. Finally, we found a correlation between p70S6K and E-cadherin expression in human non-small-cell lung cancer (NSCLC) tissue samples.

Conclusion

Our findings suggest that p70S6K-induced EMT plays an important role in the acquired resistance of erlotinib and provides a novel therapeutic rationale of targeting p70S6K in NSCLC therapy.

Tanshinone IIA Suppresses Proliferation and Inflammatory Cytokine Production of Synovial Fibroblasts from Rheumatoid Arthritis Patients Induced by TNF-α and Attenuates the Inflammatory Response in AIA Mice

Rheumatoid arthritis (RA) is a chronic and progressive autoimmune disease in which activated RA fibroblast-1ike synoviocytes (RA-FLSs) are one of the main factors responsible for inducing morbidity. Previous reports have shown that RA-FLSs have proliferative features similar to cancer cells, in addition to causing cartilage erosion that eventually causes joint damage. Thus, new therapeutic strategies and drugs that can effectively contain the abnormal hyperplasia of RA-FLSs and restrain RA development are necessary for the treatment of RA. Tanshinone IIA (Tan IIA), one of the main phytochemicals isolated from Salvia miltiorrhiza Bunge, is capable of promoting RA-FLS apoptosis and inhibiting arthritis in an AIA mouse model. In addition, RA patients treated at our clinic with Tan IIA showed significant improvements in their clinical symptoms. However, the details of the molecular mechanism by which Tan IIA effects RA are unknown. To clarify this mechanism, we evaluated the antiproliferative and inhibitory effects of proinflammatory factor production caused by Tan IIA to RA-FLSs. We demonstrated that Tan IIA can restrict the proliferation, migration, and invasion of RA-FLSs in a time- and dose-dependent manner. Moreover, Tan IIA effectively suppressed the increase in mRNA expression of some matrix metalloproteinases and proinflammatory factors induced by TNF-α in RA-FLSs, resulting in inflammatory reactivity inhibition and blocking the destruction of the knee joint. Through the integration of network pharmacology analyses with the experimental data obtained, it is revealed that the effects of Tan IIA on RA can be attributed to its influence on different signaling pathways, including MAPK, AKT/mTOR, HIF-1, and NF-kB. Taken together, these data suggest that the compound Tan IIA has great therapeutic potential for RA treatment.

Spatial regulation of mTORC1 signalling: Beyond the Rag GTPases

The mechanistic (or mammalian) Target of Rapamycin Complex 1 (mTORC1) is a central regulator of cell growth and metabolism. By integrating mitogenic signals, mTORC1-dependent phosphorylation of substrates dictates the balance between anabolic, pro-growth and catabolic, recycling processes in the cell. The discovery that amino acids activate mTORC1 by promoting its translocation to the lysosome was a fundamental advance in the understanding of mTORC1 signalling. It has since become clear that the lysosome-cytoplasm shuttling of mTORC1 represents just one layer of spatial control of this signalling pathway. This review will focus on exploring the subcellular localisation of mTORC1 and its regulators to multiple sites within the cell. We will discuss how these spatially distinct regions such as endoplasmic reticulum, plasma membrane and the endosomal pathway co-operate to transduce nutrient availability to mTORC1, allowing for tight control of cell growth.

Ivermectin reverses the drug resistance in cancer cells through EGFR/ERK/Akt/NF-κB pathway

Background

Discovery and development of novel drugs that are capable of overcoming drug resistance in tumor cells are urgently needed clinically. In this study, we sought to explore whether ivermectin (IVM), a macrolide antiparasitic agent, could overcome the resistance of cancer cells to the therapeutic drugs.

Methods

We used two solid tumor cell lines (HCT-8 colorectal cancer cells and MCF-7 breast cancer cells) and one hematologic tumor cell line (K562 chronic myeloid leukemia cells), which are resistant to the chemotherapeutic drugs vincristine and adriamycin respectively, and two xenograft mice models, including the solid tumor model in nude mice with the resistant HCT-8 cells and the leukemia model in NOD/SCID mice with the resistant K562 cells to investigate the reversal effect of IVM on the resistance in vitro and in vivo. MTT assay was used to investigate the effect of IVM on cancer cells growth in vitro. Flow cytometry, immunohistochemistry, and immunofluorescence were performed to investigate the reversal effect of IVM in vivo. Western blotting, qPCR, luciferase reporter assay and ChIP assay were used to detect the molecular mechanism of the reversal effect. Octet RED96 system and Co-IP were used to determine the interactions between IVM and EGFR.

Results

Our results indicated that ivermectin at its very low dose, which did not induce obvious cytotoxicity, drastically reversed the resistance of the tumor cells to the chemotherapeutic drugs both in vitro and in vivo. Mechanistically, ivermectin reversed the resistance mainly by reducing the expression of P-glycoprotein (P-gp) via inhibiting the epidermal growth factor receptor (EGFR), not by directly inhibiting P-gp activity. Ivermectin bound with the extracellular domain of EGFR, which inhibited the activation of EGFR and its downstream signaling cascade ERK/Akt/NF-κB. The inhibition of the transcriptional factor NF-κB led to the reduced P-gp transcription.

Conclusions

These findings demonstrated that ivermectin significantly enhanced the anti-cancer efficacy of chemotherapeutic drugs to tumor cells, especially in the drug-resistant cells. Thus, ivermectin, a FDA-approved antiparasitic drug, could potentially be used in combination with chemotherapeutic agents to treat cancers and in particular, the drug-resistant cancers.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1251-7) contains supplementary material, which is available to authorized users.

Cadmium results in accumulation of autophagosomes-dependent apoptosis through activating Akt-impaired autophagic flux in neuronal cells

Environmental exposure to cadmium (Cd) links to neurodegenerative disorders. Autophagy plays an important role in controlling cell survival/death. However, how autophagy contributes to Cd's neurotoxicity remains enigmatic. Here, we show that Cd induced significant increases in autophagosomes with a concomitant elevation of LC3-II and p62 in PC12 cells and primary neurons. Using autophagy inhibitor 3-MA, we demonstrated that Cd-increased autophagosomes contributed to neuronal apoptosis. Impairment of Cd on autophagic flux was evidenced by co-localization of mCherry and GFP tandem-tagged LC3 puncta in the cells. This is further supported by the findings that administration of chloroquine (CQ) potentiated the basic and Cd-elevated LC3-II and p62 levels, autophagosome accumulation and cell apoptosis, whereas rapamycin relieved the effects in the cells in response to Cd. Subsequently, we noticed that Cd evoked the phosphorylation of Akt and BECN1. Silencing BECN1 and especially expression of mutant BECN1 (Ser295A) attenuated Cd-increased autophagosomes and cell death. Of note, inhibition of Akt with Akt inhibitor X, or ectopic expression of dominant negative Akt (dn-Akt), in the presence or absence of 3-MA, significantly alleviated Cd-triggered phosphorylation of Akt and BECN1, autophagosomes, and apoptosis. Importantly, we found that Cd activation of Akt functioned in impairing autophagic flux. Collectively, these results indicate that Cd results in accumulation of autophagosomes-dependent apoptosis through activating Akt-impaired autophagic flux in neuronal cells. Our findings underscore that inhibition of Akt to improve autophagic flux is a promising strategy against Cd-induced neurotoxicity and neurodegeneration.

Endothelial Function: A Short Guide for the Interventional Cardiologist

An impaired function of the coronary endothelium is an important determinant of all stages of atherosclerosis, from initiation, to mediation of functional phenomena—such as spasm and plaque erosion, to atherothrombotic complications. Endothelial function is modified by therapies, including stent implantation. Finally, endothelial function changes over time, in response to physical stimuli and pharmocotherapies, and its assessment might provide information on how individual patients respond to specific therapies. In this review, we describe the role of the endothelium in the continuum of coronary atherosclerosis, from the perspective of the interventional cardiologist. In the first part, we review the current knowledge of the role of endothelial (dys)function on atherosclerotic plaque progression/instabilization and on the mechanisms of ischemia, in the absence of coronary artery stenosis. In the second part of this review, we describe the impact of coronary artery stenting on endothelial function, platelet aggregation, and inflammation.

Analysis of clinical factors and PDGFR-β in predicting prognosis of patients with clival chordoma

OBJECTIVE

In this study, the authors’ aim was to research clinical features and prognostic factors in patients harboring clival chordomas and explore the relationship between platelet-derived growth factor receptor-β (PDGFR-β) expression and tumor invasion and prognosis of clival chordoma.

METHODS

A total of 242 patients were retrospectively analyzed. Clinical information, including extent of resection, Al-Mefty classification, postoperative complications, and postoperative radiotherapy, was reviewed. Kaplan-Meier analysis was used to estimate survival time. Immunohistochemical analysis, quantitative reverse transcription polymerase chain reaction, and Western blotting were used to measure the expression level of proteins or mRNA. Transwell assaying was performed to measure the invasive ability of the tumor cells.

RESULTS

According to the Al-Mefty classification, there were 37, 112, and 93 type I, II, and III tumors, respectively. Gross-total resection (GTR) was achieved in 86 cases (35.5%), subtotal resection (STR) in 63 cases (26.0%), and partial resection (PR) in 93 cases (38.4%). The 5-year progression-free survival (PFS) and overall survival (OS) rates in the GTR group were significantly higher than those in the non–total resection (NTR; i.e., STR and PR) group (p < 0.001). The 5-year PFS and OS rates for patients with type I tumors were significantly higher than those for patients harboring types II and III tumors (p < 0.001). In the NTR group, the median PFS and OS of patients with lower PDGFR-β expression were significantly longer than those of patients with higher PDGFR-β expression. Reduction of PDGFR-β suppressed the invasion ability of cells in vitro. In addition, reduction of PDGFR-β can obviously downregulate the expression levels of mammalian target of rapamycin (mTOR) or phospho-mTOR.

CONCLUSIONS

Extent of resection, Al-Mefty classification, primary tumor, postoperative radiotherapy, and PDGFR-β expression level are valuable prognostic factors in patients with clival chordomas. PDGFR-β could regulate invasion through the mTOR pathway in clival chordoma cells.

Employing the Sirolimus-Eluting Poly (Propylene Carbonate) Mesh for the Prevention of Arteriovenous Graft Stenosis in Rats

Poly (propylene carbonate, PPC) is a new member of the aliphatic polyester family. An outstanding feature of PPC is that it produces mainly water and carbon dioxide when degraded in vivo, causing minimal side effects. This unique property together with excellent biocompatibility and biodegradability makes PPC a promising material for drug delivery. In this study, we explored the effect of the sirolimus (an inhibitor of cell growth)-eluting PPC mesh on graft stenosis and its possible mechanisms in a rat arteriovenous grafting model. The PPC mesh was prepared by electrospinning. A jugular vein to abdominal aortic autograft transplantation model was established in rats. The graft was then treated by wrapping with the drug mesh or the drug-free mesh or left untreated. Four weeks posttransplantation, neointima was measured with hematoxylin and eosin staining, matrix metalloproteinase-2 (MMP-2), and MMP-9, and proliferating cell nuclear antigen (PCNA) in the grafts were assayed by Western blotting and immunohistochemistry, respectively. In vitro rat aortic adventitial fibroblast cell (RAAFC) migration was assessed using the Boyden chamber assay, and phospho-mammalian target of rapamycin (mTOR) levels in RAAFCs were determined by Western blotting. Animals with the drug mesh had an intimal area index of 4.87% ± 0.98%, significantly lower than that of the blank group (14.21% ± 2.56%) or the PPC group (15.03% ± 2.35%, both P < .05). The sirolimus mesh markedly suppressed MMP-2 and MMP-9 expression, decreased PCNA-positive cell numbers, inhibited RAAFC migration, and reduced phospho-mTOR levels. Our data suggest that the sirolimus-eluting PPC mesh might be potentially applied for the management of grafting stenosis.

mTORC1 is a key mediator of RON-dependent breast cancer metastasis with therapeutic potential

Metastasis is the biggest challenge in treating breast cancer, and it kills >40,000 breast cancer patients annually in the US. Aberrant expression of the RON receptor tyrosine kinase in breast tumors correlates with poor prognosis and has been shown to promote metastasis. However, the molecular mechanisms that govern how RON promotes metastasis, and how to block it, are still largely unknown. We sought to determine critical effectors of RON using a combination of mutational and pharmacologic strategies. High-throughput proteomic analysis of breast cancer cells upon activation of RON showed robust phosphorylation of ribosomal protein S6. Further analysis revealed that RON strongly signals through mTORC1/p70S6K, which is mediated predominantly by the PI3K pathway. A targeted mutation approach to modulate RON signaling validated the importance of PI3K/mTORC1 pathway for spontaneous metastasis in vivo. Finally, inhibition of mTORC1 with an FDA-approved drug, everolimus, resulted in transient shrinkage of established RON-dependent metastases, and combined blockade of mTORC1 and RON delayed progression. These studies have identified a key downstream mediator of RON-dependent metastasis in breast cancer cells and revealed that inhibition of mTORC1, or combined inhibition of mTORC1 and RON, may be effective for treatment of metastatic breast cancers with elevated expression of RON.

Loss of Leucyl-tRNA synthetase b leads to ILFS1-like symptoms in zebrafish

Leucyl-tRNA synthetase (LARS) is a kind of aminoacyl-tRNA synthetases (aaRSs), which is important for protein synthesis. Following the discovery of three clinical cases which carry LARS mutations, it has been designated as the infantile liver failure syndrome type 1 (ILFS1) gene. ILFS1 is a kind of infantile hepatopathy, which is difficult to diagnose and manage. As the mechanism underlying this disease is poorly understood and LARS is conserved among vertebrates, we obtained zebrafish larsb^cq68 mutant via CRISPR/Cas9 technology to investigate the role of larsb in vivo. In mutant, the proliferation ability of liver was drastically decreased at later stages accompanied with severe DNA damage. Further studies demonstrated that the mTORC1 signaling was hyperactivated in larsb^cq68 mutant. Inhibition of mTORC1 signaling pathway by Rapamycin or mTORC1 morpholino can partially rescue the liver failure of the mutants. These data revealed that larsb mutation caused ILFS1-like phenotype in zebrafish, and indicated this mutant may serve as a potential model for ILFS1. Furthermore, we demonstrated that rapamycin treatment can partially rescue the liver defect in mutants, thus providing a practicable therapeutic plan for ILFS1.

Resveratrol inhibits Erk1/2-mediated adhesion of cancer cells via activating PP2A-PTEN signaling network

Resveratrol, a natural polyphenol compound, has been shown to possess anticancer activity. However, how resveratrol inhibits cancer cell adhesion has not been fully elucidated. Here, we show that resveratrol suppressed the basal or type I insulin-like growth factor (IGF)-1-stimulated adhesion of cancer cells (Rh1, Rh30, HT29, and HeLa cells) by inhibiting the extracellular signal-regulated kinase 1/2 (Erk1/2) pathway. Inhibition of Erk1/2 with U0126, knockdown of Erk1/2, or overexpression of dominant-negative mitogen-activated protein kinase kinase 1 (MKK1) strengthened resveratrol's inhibition of the basal or IGF-1-stimulated of Erk1/2 phosphorylation and cell adhesion, whereas ectopic expression of constitutively active MKK1 attenuated the inhibitory effects of resveratrol. Further research revealed that both protein phosphatase 2A (PP2A) and phosphatase and tensin homolog (PTEN)-Akt were implicated in resveratrol-inactivated Erk1/2-dependent cell adhesion. Inhibition of PP2A with okadaic acid or overexpression of dominant-negative PP2A rendered resistance to resveratrol's suppression of the basal or IGF-1-stimulated phospho-Erk1/2 and cell adhesion, whereas expression of wild-type PP2A enhanced resveratrol's inhibitory effects. Overexpression of wild-type PTEN or dominant-negative Akt or inhibition of Akt with Akt inhibitor X strengthened resveratrol's inhibition of the basal or IGF-1-stimulated Erk1/2 phosphorylation and cell adhesion. Furthermore, inhibition of mechanistic/mammalian target of rapamycin (mTOR) with rapamycin or silencing mTOR enhanced resveratrol's inhibitory effects on the basal and IGF-1-induced inhibition of PP2A-PTEN, activation of Akt-Erk1/2, and cell adhesion. The results indicate that resveratrol inhibits Erk1/2-mediated adhesion of cancer cells via activating PP2A-PTEN signaling network. Our data highlight that resveratrol has a great potential in the prevention of cancer cell adhesion.

Comparative oncology approach to drug repurposing in osteosarcoma

BACKGROUND

Osteosarcoma is an orphan disease for which little improvement in survival has been made since the late 1980s. New drug discovery for orphan diseases is limited by the cost and time it takes to develop new drugs. Repurposing already approved FDA-drugs can help overcome this limitation. Another limitation of cancer drug discovery is the lack of preclinical models that accurately recapitulate what occurs in humans. For OS using dogs as a model can minimize this limitation as OS in canines develops spontaneously, is locally invasive and metastasizes to the lungs as it does in humans.

METHODS

In our present work we used high-throughput screens to identify drugs from a library of 2,286 FDA-approved drugs that demonstrated selective growth inhibition against both human and canine OS cell lines. The identified lead compound was then tested for synergy with 7 other drugs that have demonstrated activity against OS. These results were confirmed with in vitro assays and an in vivo murine model of OS.

RESULTS

We identified 13 drugs that demonstrated selective growth inhibition against both human and canine OS cell lines. Auranofin was selected for further in vitro combination drug screens. Auranofin showed synergistic effects with vorinostat and rapamycin on OS viability and apoptosis induction. Auranofin demonstrated single-agent growth inhibition in both human and canine OS xenografts, and cooperative growth inhibition was observed in combination with rapamycin or vorinostat. There was a significant decrease in Ki67-positive cells and an increase in cleaved caspase-3 levels in tumor tissues treated with a combination of auranofin and vorinostat or rapamycin.

CONCLUSIONS

Auranofin, alone or in combination with rapamycin or vorinostat, may be useful new treatment strategies for OS. Future studies may evaluate the efficacy of auranofin in dogs with OS as a prelude to human clinical evaluation.

p70S6K promotes IL-6-induced epithelial-mesenchymal transition and metastasis of head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the fifth most common cancer worldwide and a common cause of cancer-related death, with a 5-year survival rate of less than 60%. IL-6 has been suggested to play an important role in cancer metastasis, but its mechanism in HNSCC has not been fully clarified. p70S6K has been reported to induce epithelial-mesenchymal transition (EMT) of ovarian cancer, but its role in HNSCC remains unknown. In this study, we found that p70S6K and IL-6 were upregulated in high-metastatic HNSCC cell lines that underwent EMT when compared to paired low-metastatic cell lines. Overexpression of p70S6K promoted EMT and migration of HNSCC cells, while downregulation of p70S6K attenuated IL-6-induced EMT and cell migration. Furthermore, IL-6-induced p70S6K activation was attenuated by inhibitors of the PI3K/Akt/mTOR, MAPK/ERK, and JAK/STAT3 signaling pathways, suggesting that it located downstream of these pathways. These findings suggest that p70S6K promotes IL-6-induced EMT and metastasis of HNSCC. Targeting p70S6K for HNSCC therapy may benefit patients through the inhibition of tumor growth, as well as metastasis.

Protein profiling and angiogenic effect of hypoxia-cultured human umbilical cord blood-derived mesenchymal stem cells in hindlimb ischemia

The aim of the present study was to investigate protein profiles of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) cultured in normoxic (21% O₂) and hypoxic (1% O₂) conditions, and evaluate oxygenation effects on angiogenesis in an ischemic hindlimb mouse model using a modified ischemic scoring system. Hypoxic conditions did not change the expression of phenotypic markers and increased adipogenesis and chondrogenesis. Epidermal growth factor (EGF), transforming growth factor alpha (TGF-α), TGF-β RII, and vascular endothelial growth factor (VEGF) were upregulated in the conditioned medium of hypoxic hUCB-MSCs, which are commonly related to angiogenesis and proliferation of biological processes by Gene Ontology. In the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, significant enrichment of the phosphorylation of abelson murine leukemia viral oncogene homolog 1 (ABL1) (Phospho-Tyr204) and B-cell lymphoma-extra large (BCL-XL) (Phospho-Thr47) as anti-apoptotic pathways was observed in hypoxic hUCB-MSCs. Furthermore, hypoxic conditions induced proliferation and migration, and reduced apoptosis of hUCB-MSCs in vitro. Based on the results of protein antibody array, we evaluated the angiogenic effects of injecting normoxic or hypoxic hUCB-MSCs (1×10⁶) into the ischemic hindlimb muscles of mice. Ischemic scores and capillary generation were significantly greater in the hypoxic hUCB-MSC injection group than in the normoxic hUCB-MSC group. Our findings demonstrate that culturing hUCB-MSCs in hypoxic conditions not only significantly enriches phosphorylation in the anti-apoptosis pathway and enhances the secretion of several angiogenic proteins from cells, but also alleviates ischemic injury of hindlimb of mice.

Dual TORCs driven and B56 orchestrated signaling network guides eukaryotic cell migration

Different types of eukaryotic cells may adopt seemingly distinct modes of directional cell migration. However, several core aspects are regarded common whether the movement is either ameoboidal or mesenchymal. The region of cells facing the attractive signal is often termed leading edge where lamellipodial structures dominates and the other end of the cell called rear end is often mediating cytoskeletal F-actin contraction involving Myosin-II. Dynamic remodeling of cell-to-matrix adhesion involving integrin is also evident in many types of migrating cells. All these three aspects of cell migration are significantly affected by signaling networks of TorC2, TorC1, and PP2A/B56. Here we review the current views of the mechanistic understanding of these regulatory signaling networks and how these networks affect eukaryotic cell migration.

Rapamycin attenuates BAFF-extended proliferation and survival via disruption of mTORC1/2 signaling in normal and neoplastic B-lymphoid cells

B cell activating factor from the TNF family (BAFF) stimulates B-cell proliferation and survival, but excessive BAFF promotes the development of aggressive B cells leading to malignant and autoimmune diseases. Recently, we have reported that rapamycin, a macrocyclic lactone, attenuates human soluble BAFF (hsBAFF)-stimulated B-cell proliferation/survival by suppressing mTOR-mediated PP2A-Erk1/2 signaling pathway. Here, we show that the inhibitory effect of rapamycin on hsBAFF-promoted B cell proliferation/survival is also related to blocking hsBAFF-stimulated phosphorylation of Akt, S6K1, and 4E-BP1, as well as expression of survivin in normal and B-lymphoid (Raji and Daudi) cells. It appeared that both mTORC1 and mTORC2 were involved in the inhibitory activity of rapamycin, as silencing raptor or rictor enhanced rapamycin's suppression of hsBAFF-induced survivin expression and proliferation/viability in B cells. Also, PP242, an mTORC1/2 kinase inhibitor, repressed survivin expression, and cell proliferation/viability more potently than rapamycin (mTORC1 inhibitor) in B cells in response to hsBAFF. Of interest, ectopic expression of constitutively active Akt (myr-Akt) or constitutively active S6K1 (S6K1-ca), or downregulation of 4E-BP1 conferred resistance to rapamycin's attenuation of hsBAFF-induced survivin expression and B-cell proliferation/viability, whereas overexpression of dominant negative Akt (dn-Akt) or constitutively hypophosphorylated 4E-BP1 (4EBP1-5A), or downregulation of S6K1, or co-treatment with Akt inhibitor potentiated the inhibitory effects of rapamycin. The findings indicate that rapamycin attenuates excessive hsBAFF-induced cell proliferation/survival via blocking mTORC1/2 signaling in normal and neoplastic B-lymphoid cells. Our data underscore that rapamycin may be a potential agent for preventing excessive BAFF-evoked aggressive B-cell malignancies and autoimmune diseases.

Periostin suppresses in vivo invasiveness via PDK1/Akt/mTOR signaling pathway in a mouse orthotopic model of bladder cancer

Periostin is an extracellular matrix protein involved in the regulation of intercellular adhesion. The present study investigated the in vivo tumor suppressor function of periostin in a mouse orthotopic model of bladder cancer. Retroviral vectors were used to transfect human bladder cancer UMUC-3 cell line with periostin. Bladders of nude mice that were transurethrally instilled with periostin-expressing UMUC-3 cells were revealed to weigh less compared with bladders instilled with vector control cells. In total, five (83.3%) of six vector control UMUC-3 bladder tumors exhibited histological evidence of muscle invasion. However, none of the five periostin-expressing UMUC-3 bladder tumors revealed muscle invasion. Thick edematous lesions were present in the submucosa of periostin-expressing UMUC-3 bladder tumors. The expression of periostin also suppressed in vitro cell invasiveness of UMUC-3 cells without affecting cellular proliferation. The level of phosphorylation of phosphoinositide-dependent kinase-1 (PDK1), protein kinase B (Akt) and S6 ribosomal protein, a downstream protein of mammalian target of rapamycin (mTOR) was decreased in periostin-expressing UMUC-3 cells compared with vector control cells. Treatment with 100 ng/ml recombinant human periostin protein also suppressed cell invasiveness and phosphorylation of PDK1, Akt and S6 in UMUC-3 cells, consistent with results using periostin-expressing UMUC-3 cells. Treatment with PDK1, Akt and mTOR inhibitors significantly suppressed UMUC-3 cell invasiveness. These results demonstrate that periostin suppresses in vivo and in vitro invasiveness of bladder cancer via the PDK1/Akt/mTOR signaling pathway. Periostin may be useful as a potent chemotherapeutic agent by suppressing bladder cancer invasiveness.

Systems Biology Reveals NS4B-Cyclophilin A Interaction: A New Target to Inhibit YFV Replication

Yellow fever virus (YFV) replication is highly dependent on host cell factors. YFV NS4B is reported to be involved in viral replication and immune evasion. Here interactions between NS4B and human proteins were determined using a GST pull-down assay and analyzed using 1-DE and LC-MS/MS. We present a total of 207 proteins confirmed using Scaffold 3 Software. Cyclophilin A (CypA), a protein that has been shown to be necessary for the positive regulation of flavivirus replication, was identified as a possible NS4B partner. 59 proteins were found to be significantly increased when compared with a negative control, and CypA exhibited the greatest difference, with a 22-fold change. Fisher's exact test was significant for 58 proteins, and the p value of CypA was the most significant (0.000000019). The Ingenuity Systems software identified 16 pathways, and this analysis indicated sirolimus, an mTOR pathway inhibitor, as a potential inhibitor of CypA. Immunofluorescence and viral plaque assays showed a significant reduction in YFV replication using sirolimus and cyclosporine A (CsA) as inhibitors. Furthermore, YFV replication was strongly inhibited in cells treated with both inhibitors using reporter BHK-21-rep-YFV17D-LucNeoIres cells. Taken together, these data suggest that CypA-NS4B interaction regulates YFV replication. Finally, we present the first evidence that YFV inhibition may depend on NS4B-CypA interaction.

Celastrol ameliorates Cd-induced neuronal apoptosis by targeting NOX2-derived ROS-dependent PP5-JNK signaling pathway

Celastrol, a plant-derived triterpene, has neuroprotective benefit in the models of neurodegenerative disorders that are characterized by overproduction of reactive oxygen species (ROS). Recently, we have reported that cadmium (Cd) activates c-Jun N-terminal kinase (JNK) pathway leading to neuronal cell death by inducing ROS inactivation of protein phosphatase 5 (PP5), and celastrol prevents Cd-activated JNK pathway against neuronal apoptosis. Therefore, we hypothesized that celastrol could hinder Cd induction of ROS-dependent PP5-JNK signaling pathway from apoptosis in neuronal cells. Here, we show that celastrol attenuated Cd-induced expression of NADPH oxidase 2 (NOX2) and its regulatory proteins (p22^phox , p40^phox , p47^phox , p67^phox , and Rac1), as well as the generation of ROS in PC12 cells and primary neurons. Also, N-acetyl-l-cysteine, a ROS scavenger, potentiated celastrol's inhibition of the events in the cells triggered by Cd, implying neuroprotection by celastrol via blocking Cd-evoked NOX2-derived ROS. Further research revealed that celastrol was involved in the regulation of PP5 inactivation and JNK/c-Jun activation induced by Cd, as celastrol prevented Cd from reducing PP5 expression, and over-expression of wild-type PP5 or dominant negative c-Jun strengthened celastrol's inhibition of Cd-induced phosphorylation of JNK and/or c-Jun, as well as apoptosis in neuronal cells. Of importance, inhibiting NOX2 with apocynin or silencing NOX2 by RNA interference enhanced the inhibitory effects of celastrol on Cd-induced inactivation of PP5, activation of JNK/c-Jun, ROS, and apoptosis in the cells. Furthermore, we noticed that expression of wild-type PP5 or dominant negative c-Jun, or pretreatment with JNK inhibitor SP600125 reinforced celastrol's suppression of Cd-induced NOX2 and its regulatory proteins, and consequential ROS in neuronal cells. These findings indicate that celastrol ameliorates Cd-induced neuronal apoptosis via targeting NOX2-derived ROS-dependent PP5-JNK signaling pathway. Our data highlight a beneficial role of celastrol in the prevention of Cd-induced oxidative stress and neurodegenerative diseases.

Underlying Mechanisms for Distant Metastasis - Molecular Biology

BACKGROUND

The formation of distant metastases constitutes a complex process with a variety of different genes and pathways involved. To improve patient survival, it is necessary to understand the underlying mechanisms of metastasis to allow for targeted intervention.

METHODS

This review provides an overview of the general concepts of metastasis, focusing on the most important genes and pathways involved and on interventional strategies.

RESULTS

Cancer cells undergo different steps to form metastasis: most prominently, local invasion, intravasation, survival in the circulation, arrest at a distant organ site and extravasation, micrometastasis formation, and metastatic colonization. In order to pass these steps, different molecular pathways are of major importance: EGF/RAS/RAF/MEK/ERK, PI3K/Akt/mTOR, HGF/Met, Wnt/β-catenin, and VEGF signaling. The HGF/Met regulator MACC1 and the Wnt signaling target S100A4 have been shown to play a major role in the metastatic process. Each gene and pathway provides an opportunity for therapeutic intervention.

CONCLUSION

Since metastasis represents a highly limiting factor in cancer therapy causing 90% of cancer deaths, it is imperative to reveal the underlying mechanisms. This is fundamental for uncovering prognostic markers and new targeted therapy options.

Exercise increases mTOR signaling in brain regions involved in cognition and emotional behavior

Exercise can enhance learning and memory and produce resistance against stress-related psychiatric disorders such as depression and anxiety. In rats, these beneficial effects of exercise occur regardless of exercise controllability: both voluntary and forced wheel running produce stress-protective effects. The mechanisms underlying these beneficial effects of exercise remain unknown. The mammalian target of rapamycin (mTOR) is a translation regulator important for cell growth, proliferation, and survival. mTOR has been implicated in enhancing learning and memory as well as antidepressant effects. Moreover, mTOR is sensitive to exercise signals such as metabolic factors. The effects of exercise on mTOR signaling, however, remain unknown. The goal of the present study was to test the hypothesis that exercise, regardless of controllability, increases levels of phosphorylated mTOR (p-mTOR) in brain regions important for learning and emotional behavior. Rats were exposed to 6 weeks of either sedentary (locked wheel), voluntary, or forced wheel running conditions. At 6 weeks, rats were sacrificed during peak running and levels of p-mTOR were measured using immunohistochemistry. Overall, both voluntary and forced exercise increased p-mTOR-positive neurons in the medial prefrontal cortex, striatum, hippocampus, hypothalamus, and amygdala compared to locked wheel controls. Exercise, regardless of controllability, also increased numbers of p-mTOR-positive glia in the striatum, hippocampus, and amygdala. For both neurons and glia, the largest increase in p-mTOR positive cells was observed after voluntary running, with forced exercise causing a more modest increase. Interestingly, voluntary exercise preferentially increased p-mTOR in astrocytes (GFAP+), while forced running increased p-mTOR in microglia (CD11+) in the inferior dentate gyrus. Results suggest that mTOR signaling is sensitive to exercise, but subtle differences exist depending on exercise controllability. Increases in mTOR signaling could contribute to the beneficial effects of exercise on cognitive function and mental health.

Cryptotanshinone activates AMPK-TSC2 axis leading to inhibition of mTORC1 signaling in cancer cells

Background

Cryptotanshinone (CPT), a fat-soluble phenanthraquinone from Salvia miltiorrhiza Bunge, has been demonstrated to inhibit phosphorylation of p70 S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1), a couple of direct downstream effectors of the mammalian target of rapamycin complex 1 (mTORC1), resulting in cancer cell arrested in G0 phase and subsequent inhibition of proliferation. However, its concrete molecular mechanism about how CPT inhibits mTORC1 signaling pathway is unclear.

Methods

one solution was used to check cell viability and western blotting for determining expression of the indicated proteins. Molecular docking was performed to assess the binding of CPT with mTOR. The co-immunoprecipitation assay was to analyze whether CPT could disrupt the mTORC1 and TSC1/TSC2 complex. Recombinant adenoviral dominant-negative AMPKα was used to downregulate expression of AMPKα and lentiviral AMPK and TSC2 to silence the AMPK and TSC2 in Rh30 cells.

Results

Primarily, Rh30 cells expressing rapamycin-resistant mutant mTOR are also sensitive to CPT, while the molecular docking result for CPT binding to mTOR is negative, suggesting that CPT inhibition of mTORC1 is different from rapamycin. Then the related proteins of PTEN-PI3K pathway was proved not to be affected, but the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) was activated by a concentration- and time- dependent manner, meaning that it may be associated with AMPK. Further results indicated that compound C, inhibitor of AMPK, could clearly reversed CPT inhibitory effect on Rh30 cells, and dominant-negative AMPK in cancer cells conferred resistance to CPT inhibition of 4E-BP1 and phosphorylation of S6K1, as well as sh-AMPK. Furthermore, compared with AMPK-positive MEF cells, AMPK-negative MEF cells are less sensitive to CPT by the findings that 4E-BP1 and phosphorylation of S6K1 express comparatively more. Additionally, phosphorylation of tuberous sclerosis complex 2 (TSC2) was activated under the treatment of CPT, and down-expression of TSC2 by shRNA slightly recovered expression of 4E-BP1 and phosphorylation of S6K1, while co-immunoprecipitation of TSC2 did not alter expression of TSC1 by CPT.

Conclusion

CPT inhibiting mTORC1 pathway was mostly due to activation of AMPK-TSC2 axis rather than specific binding to mTORC1. CPT is a potent anticancer agent targeting AMPK.