mTORC1 and mTORC2 in cancer and the tumor microenvironment

LAT2 regulates glutamine-dependent mTOR activation to promote glycolysis and chemoresistance in pancreatic cancer

BACKGROUND

Reprogrammed energy metabolism has become an emerging hallmark of cancer in recent years. Transporters have been reported to be amino acid sensors involved in controlling mTOR recruitment and activation, which is crucial for the growth of both normal and tumor cells. L-type amino acid transporter 2 (LAT2), encoded by the SLC7A8 gene, is a Na⁺-independent neutral amino acid transporter and is responsible for transporting neutral amino acids, including glutamine, which can activate mTOR. Previous studies have shown that LAT2 was overexpressed in gemcitabine-resistant pancreatic cancer cells. However, the role of LAT2 in chemoresistance in pancreatic cancer remains uncertain and elusive.

METHODS

The effects of LAT2 on biological behaviors were analyzed. LAT2 and LDHB levels in tissues were detected, and the clinical value was evaluated.

RESULTS

We demonstrated that LAT2 emerged as an oncogenic protein and could decrease the gemcitabine sensitivity of pancreatic cancer cells in vitro and in vivo. The results of a survival analysis indicated that high expression levels of both LAT2 and LDHB predicted a poor prognosis in patients with pancreatic cancer. Furthermore, we found that LAT2 could promote proliferation, inhibit apoptosis, activate glycolysis and alter glutamine metabolism to activate mTOR in vitro and in vivo. Next, we found that gemcitabine combined with an mTOR inhibitor (RAD001) could reverse the decrease in chemosensitivity caused by LAT2 overexpression in pancreatic cancer cells. Mechanistically, we demonstrated that LAT2 could regulate two glutamine-dependent positive feedback loops (the LAT2/p-mTOR^Ser2448 loop and the glutamine/p-mTOR^Ser2448/glutamine synthetase loop) to promote glycolysis and decrease gemcitabine (GEM) sensitivity in pancreatic cancer.

CONCLUSION

Taken together, our data reveal that LAT2 functions as an oncogenic protein and could regulate glutamine-dependent mTOR activation to promote glycolysis and decrease GEM sensitivity in pancreatic cancer. The LAT2-mTOR-LDHB pathway might be a promising therapeutic target in pancreatic cancer.

Protective effect of docosahexaenoic acid on lipotoxicity-mediated cell death in Schwann cells: Implication of PI3K/AKT and mTORC2 pathways

BACKGROUND AND AIM

Docosahexaenoic acid (DHA) exhibits neuroprotective properties and has been shown to preserve nerve cells following trauma and ischemic injury. Recently, we showed that DHA pretreatment improved locomotion and reduced neuropathic pain after acute spinal cord injury in adult rats. These improvements were associated with an increase in the levels of AKT in spinal cord injury neurons. In this study, we investigate the implication of PI3K/AKT and mTOR pathway in DHA-mediated protection of primary cultured Schwann cells (pSC) undergoing palmitic acid-induced lipotoxicity (PA-LTx).

METHODS

Primary cultured Schwann cells were treated with PA (PA:BSA, 2:1) in the presence or absence of DHA (1-200 µM) for 24-48 hr. Cell viability was determined by crystal violet staining and nuclear morphology was examined using Hoechst staining.

RESULTS

We found that pSC cultures exposed to palmitic acid (PA) overload showed chromatin condensation, a decrease in cell viability and an inhibition of AKT phosphorylation in a time-dependent manner. Next, pSC exposed to PA overload were treated with DHA. The data show that co-treatment with DHA inhibited the loss of cell viability and apoptosis caused by PA. Moreover, treatment with DHA inhibited chromatin condensation, significantly stimulated p-AKT phosphorylation under PA-LTx condition, and DHA alone increased AKT phosphorylation. Additionally, when these pSC cultures were treated with PI3K inhibitors LY294002 and, BKM120 and mTOR inhibitors Torin 1 (mTORC1/mTORC2), but not rapamycin (mTORC1), the protective effects of DHA were not observed.

CONCLUSION

These findings suggest PI3K/AKT and mTORC2 kinase pathways are involved in the protective function (s) of DHA in PA-induced Schwann cell death.

Quantitative Proteomics Implicates Rictor/mTORC2 in Cell Adhesion

The mammalian target of rapamycin complex 2 (mTORC2) plays critical roles in various biological processes. To better understand the functions of mTORC2 and the underlying molecular mechanisms, we established a stable cell line with reduced Rictor, a specific component in mTORC2, and investigated the quantitative changes of the cellular proteome. As a result, we observed that 101 proteins were down-regulated and 50 proteins were up-regulated in Rictor knockdown cells. A protein-protein interaction network regulated by Rictor/mTORC2 was established, showing that Rictor/mTORC2 was involved in various cellular processes. Intriguingly, gene ontology analysis indicated that the proteome regulated by Rictor/mTORC2 was significantly involved with cell adhesion. Rictor knockdown affected the expressions of multiple cell adhesion associated molecules, e.g. integrin α-5 (ITGA5), transforming growth factor beta-1-induced transcript 1 protein (TGFB1I1), lysyl oxidase homologue 2 (LOXL2), etc. Further study suggested that Rictor/mTORC2 may regulate cell adhesion and invasion by modulating the expressions of these cell adhesion molecules through AKT. Taken together, this study maps the proteome regulated by Rictor/mTORC2 and reveals its role in promoting renal cancer cell invasion through modulating cell adhesion and migration.

Hypoxia and Selective Autophagy in Cancer Development and Therapy

Low oxygen availability, a condition known as hypoxia, is a common feature of various pathologies including stroke, ischemic heart disease, and cancer. Hypoxia adaptation requires coordination of intricate pathways and mechanisms such as hypoxia-inducible factors (HIFs), the unfolded protein response (UPR), mTOR, and autophagy. Recently, great effort has been invested toward elucidating the interplay between hypoxia-induced autophagy and cancer cell metabolism. Although novel types of selective autophagy have been identified, including mitophagy, pexophagy, lipophagy, ERphagy and nucleophagy among others, their potential interface with hypoxia response mechanisms remains poorly understood. Autophagy activation facilitates the removal of damaged cellular compartments and recycles components, thus promoting cell survival. Importantly, tumor cells rely on autophagy to support self-proliferation and metastasis; characteristics related to poor disease prognosis. Therefore, a deeper understanding of the molecular crosstalk between hypoxia response mechanisms and autophagy could provide important insights with relevance to cancer and hypoxia-related pathologies. Here, we survey recent findings implicating selective autophagy in hypoxic responses, and discuss emerging links between these pathways and cancer pathophysiology.

Morphology regulation in vascular endothelial cells

Morphological change in endothelial cells is an initial and crucial step in the process of establishing a functional vascular network. Following or associated with differentiation and proliferation, endothelial cells elongate and assemble into linear cord-like vessels, subsequently forming a perfusable vascular tube. In vivo and in vitro studies have begun to outline the underlying genetic and signaling mechanisms behind endothelial cell morphology regulation. This review focuses on the transcription factors and signaling pathways regulating endothelial cell behavior, involved in morphology, during vascular development.

Role of mTOR Signaling in Tumor Microenvironment: An Overview

The mammalian target of rapamycin (mTOR) pathway regulates major processes by integrating a variety of exogenous cues, including diverse environmental inputs in the tumor microenvironment (TME). In recent years, it has been well recognized that cancer cells co-exist and co-evolve with their TME, which is often involved in drug resistance. The mTOR pathway modulates the interactions between the stroma and the tumor, thereby affecting both the tumor immunity and angiogenesis. The activation of mTOR signaling is associated with these pro-oncogenic cellular processes, making mTOR a promising target for new combination therapies. This review highlights the role of mTOR signaling in the characterization and the activity of the TME’s elements and their implications in cancer immunotherapy.

Targeted Therapies in Type II Endometrial Cancers: Too Little, but Not Too Late

Type II endometrial carcinomas (ECs) are responsible for most endometrial cancer-related deaths due to their aggressive nature, late stage detection and high tolerance for standard therapies. However, there are no targeted therapies for type II ECs, and they are still treated the same way as the clinically indolent and easily treatable type I ECs. Therefore, type II ECs are in need of new treatment options. More recently, molecular analysis of endometrial cancer revealed phosphorylation-dependent oncogenic signalling in the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways to be most frequently altered in type II ECs. Consequently, clinical trials tested pharmacologic kinase inhibitors targeting these pathways, although mostly with rather disappointing results. In this review, we highlight the most common genetic alterations in type II ECs. Additionally, we reason why most clinical trials for ECs using targeted kinase inhibitors had unsatisfying results and what should be changed in future clinical trial setups. Furthermore, we argue that, besides kinases, phosphatases should no longer be ignored in clinical trials, particularly in type II ECs, where the tumour suppressive phosphatase protein phosphatase type 2A (PP2A) is frequently mutated. Lastly, we discuss the therapeutic potential of targeting PP2A for (re)activation, possibly in combination with pharmacologic kinase inhibitors.

SIRT7 promotes thyroid tumorigenesis through phosphorylation and activation of Akt and p70S6K1 via DBC1/SIRT1 axis

SIRT7 is an NAD⁺-dependent histone/non-histone deacetylase, which is highly expressed in different types of cancer including thyroid cancer; however, its biological function in thyroid cancer is still undiscovered. In this study, we found that SIRT7 expression was elevated in papillary thyroid cancers (PTCs), and demonstrated that SIRT7 knockdown dramatically inhibited the proliferation, colony formation, migration and invasion of thyroid cancer cells, and induced thyroid cancer cell cycle arrest and apoptosis. Conversely, SIRT7 re-expression markedly enhanced thyroid cancer cell growth, invasiveness and tumorigenic potential in nude mice. Further studies revealed that SIRT7 exerted an oncogenic function in thyroid tumorigenesis by phosphorylation of Akt and p70S6K1. Mechanistically, SIRT7 binds to the promoter of deleted in breast cancer-1 (DBC1), an endogenous inhibitor of SIRT1, and represses its transcription via deacetylation of H3K18Ac. This results in enhanced interactions between SIRT1 and Akt or p70S6K1, thereby promoting deacetylation and subsequent phosphorylation of Akt and p70S6K1 through a SIRT1-dependent manner. Altogether, our results show that DBC1 is a downstream target of SIRT7, and first uncover that SIRT7 promotes thyroid tumorigenesis through phosphorylation and activation of Akt and p70S6K1 via the modulation of DBC1/SIRT1 axis.

mTORC Inhibitors as Broad-Spectrum Therapeutics for Age-Related Diseases

Chronological age represents the greatest risk factor for many life-threatening diseases, including neurodegeneration, cancer, and cardiovascular disease; ageing also increases susceptibility to infectious disease. Current efforts to tackle individual diseases may have little impact on the overall healthspan of older individuals, who would still be vulnerable to other age-related pathologies. However, recent progress in ageing research has highlighted the accumulation of senescent cells with chronological age as a probable underlying cause of pathological ageing. Cellular senescence is an essentially irreversible proliferation arrest mechanism that has important roles in development, wound healing, and preventing cancer, but it may limit tissue function and cause widespread inflammation with age. The serine/threonine kinase mTOR (mechanistic target of rapamycin) is a regulatory nexus that is heavily implicated in both ageing and senescence. Excitingly, a growing body of research has highlighted rapamycin and other mTOR inhibitors as promising treatments for a broad spectrum of age-related pathologies, including neurodegeneration, cancer, immunosenescence, osteoporosis, rheumatoid arthritis, age-related blindness, diabetic nephropathy, muscular dystrophy, and cardiovascular disease. In this review, we assess the use of mTOR inhibitors to treat age-related pathologies, discuss possible molecular mechanisms of action where evidence is available, and consider strategies to minimize undesirable side effects. We also emphasize the urgent need for reliable, non-invasive biomarkers of senescence and biological ageing to better monitor the efficacy of any healthy ageing therapy.

mTORC2 contributes to the metabolic reprogramming in EGFR tyrosine-kinase inhibitor resistant cells in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) patients with activating EGFR mutations are often successfully treated with EGFR tyrosine kinase inhibitor (TKI) such as erlotinib; however, treatment resistance inevitably occurs. Given tumor metabolism of glucose and therapeutic response are intimately linked, we explored the metabolic differences between isogenic erlotinib-sensitive and -resistant NSCLC cell lines. We discovered that the growth of erlotinib-resistant cells is more sensitive to glucose deprivation. Seahorse metabolic assay revealed erlotinib-resistant cells have lower spare respiratory capacity (SRC), an indicator of metabolic flexibility, compared to erlotinib-sensitive cells. Additionally, we found downstream components of mTORC2 signaling to be phosphorylated in erlotinib-resistant cells. Knockdown of an mTORC2 component, Rictor, enhanced the SRC and rescued the growth rate of erlotinib-resistant cells during glucose deprivation. Among NSCLCs with activating EGFR mutations, gene sets involved in glucose metabolism were enriched in patients with high expression of p-NDGR1, a readout of mTORC2 activity. Furthermore, overall survival was negatively correlated with p-NDRG1. Our work uncovers a link between mTORC2 and metabolic reprogramming in EGFR TKI-resistant cells and highlights the significance of mTORC2 in the progression of EGFR-mutated NSCLC.

Novel mechanism of cannabidiol-induced apoptosis in breast cancer cell lines

Studies have emphasized an antineoplastic effect of the non-psychoactive, phyto-cannabinoid, Cannabidiol (CBD). However, the molecular mechanism underlying its antitumor activity is not fully elucidated. Herein, we have examined the effect of CBD on two different human breast cancer cell lines: the ER-positive, well differentiated, T-47D and the triple negative, poor differentiated, MDA-MB-231 cells. In both cell lines, CBD inhibited cell survival and induced apoptosis in a dose dependent manner as observed by MTT assay, morphological changes, DNA fragmentation and ELISA apoptosis assay. CBD-induced apoptosis was accompanied by down-regulation of mTOR, cyclin D1 and up-regulation and localization of PPARγ protein expression in the nuclei and cytoplasmic of the tested cells. The results suggest that CBD treatment induces an interplay among PPARγ, mTOR and cyclin D1 in favor of apoptosis induction in both ER-positive and triple negative breast cancer cells, proposing CBD as a useful treatment for different breast cancer subtypes.

Facile construction of fused benzimidazole-isoquinolinones that induce cell-cycle arrest and apoptosis in colorectal cancer cells

Colorectal cancer (CRC) is one of the most frequent, malignant gastrointestinal tumors, and strategies and effectiveness of current therapy are limited. A series of benzimidazole-isoquinolinone derivatives (BIDs) was synthesized and screened to identify novel scaffolds for CRC. Of the compounds evaluated, 7g exhibited the most promising anti-cancer properties. Employing two CRC cell lines, SW620 and HT29, 7g was found to suppress growth and proliferation of the cell lines at a concentration of ∼20 µM. Treatment followed an increase in G₂/M cell cycle arrest, which was attributed to cyclin B1 and cyclin-dependent kinase 1 (CDK1) signaling deficiencies with simultaneous enhancement in p21 and p53 activity. In addition, mitochondrial-mediated apoptosis was induced in CRC cells. Interestingly, 7g decreased phosphorylated AKT, mTOR and 4E-BP1 levels, while promoting the expression/stability of PTEN. Since PTEN controls input into the PI3K/AKT/mTOR pathway, antiproliferative effects can be attributed to PTEN-mediated tumor suppression. Collectively, these results suggest that BIDs exert antitumor activity in CRC by impairing PI3K/AKT/mTOR signaling. Against a small kinase panel, 7g exhibited low affinity at 5 µM suggesting anticancer properties likely stem through a non-kinase mechanism. Because of the novelty of BIDs, the structure can serve as a lead scaffold to design new CRC therapies.

High miR-100 expression is associated with aggressive features and modulates TORC1 complex activation in lung carcinoids

PURPOSE

Mammalian target of rapamycin (mTOR) is a promising therapeutic target in advanced lung carcinoid patients. However, the mechanisms of mTOR modulation and of responsiveness to mTOR inhibitors are largely unclear. Our aim was to analyze the expression and functional role of specific miRNAs in lung carcinoids as an alternative mechanism targeting mTOR pathway.

EXPERIMENTAL DESIGN

Seven miRNAs, selected by bioinformatic tools and literature search, were analyzed in 142 lung neuroendocrine neoplasms (92 carcinoids and a control group of 50 high grade neuroendocrine carcinomas), and compared with mTOR mRNA expression and clinical/pathological parameters. Tissue results were validated in vitro in two lung carcinoid cell lines by specific RNA interference and biological/pharmacological tests.

RESULTS

Tissutal expression of five miRNAs (miR-99b, miR-100, miR-155, miR-193a-3p, miR-193a-5p) was inversely correlated with mTOR mRNA expression, supporting their role in the negative regulation of mTOR transcription. High expression of miR-100, miR-193a-3p and miR-193a-5p was associated with aggressive features and, for the former two, with shorter time to progression. In H727 and UMC11 lung carcinoid cells, miR-100 modulated mTOR RNA and TORC1 complex protein expression, positively promoted cell migration and negatively influenced cell proliferation. Moreover, miR-100 directly influenced responsiveness of H727 and UMC11 cells to rapamycin.

CONCLUSIONS

MiR-100 actively participates to the regulation of mTOR expression in lung carcinoids and represents a novel candidate prognostic biomarker for this tumor type; moreover, inhibition of its expression is associated to increased responsiveness to mTOR inhibitors and might represent a novel strategy to sensitize lung carcinoids to these target agents.

Deoxyribonucleotide Triphosphate Metabolism in Cancer and Metabolic Disease

The maintenance of a healthy deoxyribonucleotide triphosphate (dNTP) pool is critical for the proper replication and repair of both nuclear and mitochondrial DNA. Temporal, spatial, and ratio imbalances of the four dNTPs have been shown to have a mutagenic and cytotoxic effect. It is, therefore, essential for cell homeostasis to maintain the balance between the processes of dNTP biosynthesis and degradation. Multiple oncogenic signaling pathways, such as c-Myc, p53, and mTORC1 feed into dNTP metabolism, and there is a clear role for dNTP imbalances in cancer initiation and progression. Additionally, multiple chemotherapeutics target these pathways to inhibit nucleotide synthesis. Less is understood about the role for dNTP levels in metabolic disorders and syndromes and whether alterations in dNTP levels change cancer incidence in these patients. For instance, while deficiencies in some metabolic pathways known to play a role in nucleotide synthesis are pro-tumorigenic (e.g., p53 mutations), others confer an advantage against the onset of cancer (G6PD). More recent evidence indicates that there are changes in nucleotide metabolism in diabetes, obesity, and insulin resistance; however, whether these changes play a mechanistic role is unclear. In this review, we will address the complex network of metabolic pathways, whereby cells can fuel dNTP biosynthesis and catabolism in cancer, and we will discuss the potential role for this pathway in metabolic disease.

Low-Protein Diet Induces IRE1α-Dependent Anticancer Immunosurveillance

Dietary restriction (DR) was shown to impact on tumor growth with very variable effects depending on the cancer type. However, how DR limits cancer progression remains largely unknown. Here, we demonstrate that feeding mice a low-protein (Low PROT) isocaloric diet but not a low-carbohydrate (Low CHO) diet reduced tumor growth in three independent mouse cancer models. Surprisingly, this effect relies on anticancer immunosurveillance, as depleting CD8⁺ T cells, antigen-presenting cells (APCs), or using immunodeficient mice prevented the beneficial effect of the diet. Mechanistically, we established that a Low PROT diet induces the unfolded protein response (UPR) in tumor cells through the activation of IRE1α and RIG1 signaling, thereby resulting in cytokine production and mounting an efficient anticancer immune response. Collectively, our data suggest that a Low PROT diet induces an IRE1α-dependent UPR in cancer cells, enhancing a CD8-mediated T cell response against tumors.

Drug discovery targeting the mTOR pathway

Mechanistic target of rapamycin (mTOR) is the kinase subunit of two structurally and functionally distinct large multiprotein complexes, referred to as mTOR complex 1 (mTORC1) and mTORC2. mTORC1 and mTORC2 play key physiological roles as they control anabolic and catabolic processes in response to external cues in a variety of tissues and organs. However, mTORC1 and mTORC2 activities are deregulated in widespread human diseases, including cancer. Cancer cells take advantage of mTOR oncogenic signaling to drive their proliferation, survival, metabolic transformation, and metastatic potential. Therefore, mTOR lends itself very well as a therapeutic target for innovative cancer treatment. mTOR was initially identified as the target of the antibiotic rapamycin that displayed remarkable antitumor activity in vitro Promising preclinical studies using rapamycin and its derivatives (rapalogs) demonstrated efficacy in many human cancer types, hence supporting the launch of numerous clinical trials aimed to evaluate the real effectiveness of mTOR-targeted therapies. However, rapamycin and rapalogs have shown very limited activity in most clinical contexts, also when combined with other drugs. Thus, novel classes of mTOR inhibitors with a stronger antineoplastic potency have been developed. Nevertheless, emerging clinical data suggest that also these novel mTOR-targeting drugs may have a weak antitumor activity. Here, we summarize the current status of available mTOR inhibitors and highlight the most relevant results from both preclinical and clinical studies that have provided valuable insights into both their efficacy and failure.

Comparative aspects of GnRH-Stimulated signal transduction in the vertebrate pituitary - Contributions from teleost model systems

Gonadotropin-releasing hormone (GnRH) is a major regulator of reproduction through actions on pituitary gonadotropin release and synthesis. Although it is often thought that pituitary cells are exposed to only one GnRH, multiple GnRH forms are delivered to the pituitary of teleost fishes; interestingly this can include the cGnRH-II form usually thought to be non-hypophysiotropic. GnRHs can regulate other pituitary cell-types, both directly as well as indirectly, and multiple GnRH receptors (GnRHRs) may also be expressed in the pituitary, and even within a single pituitary cell-type. Literature on the differential actions of native GnRH isoforms in primary pituitary cells is largely derived from teleost fishes. This review will outline the diversity and complexity of GnRH-GnRHR signal transduction found within vertebrate gonadotropes as well as extra-gonadotropic sites with special emphasis on comparative studies from fish models. The implications that GnRHR transduction mechanisms are GnRH isoform-, function-, and cell-specific are also discussed.

Genomic landscape of pancreatic neuroendocrine tumours: the International Cancer Genome Consortium

Neuroendocrine tumours (NETs) may arise throughout the body and are a highly heterogeneous, relatively rare class of neoplasms difficult to study also for the lack of disease models. Despite this, knowledge on their molecular alterations has expanded in the latest years, also building from genetic syndromes causing their onset. Pancreatic NETs (PanNETs) have been among the most studied, and research so far has outlined a series of recurring features, as inactivation of MEN1, VHL, TSC1/2 genes and hyperactivation of the PI3K/mTOR pathway. Next-generation sequencing has added new information by showing the key role of alternative lengthening of telomeres, driven in a fraction of PanNETs by inactivation of ATRX/DAXX. Despite this accumulation of knowledge, single studies often relied on few cases or were limited to the DNA, RNA, protein or epigenetic level with lack of integrative analysis. The International Cancer Genome Consortium aimed at removing these barriers through a strict process of data and samples collection, to produce whole-genome integrated analyses for many tumour types. The results of this effort on PanNETs have been recently published and, while confirming previous observations provide a first snapshot of how heterogeneous is the combination of genetic alterations that drive this tumour type, yet converging into four pathways whose alteration has been enriched by newly discovered mechanisms. While calling for further integration of genetic and epigenetic analyses, these data allow to reconcile previous findings in a defined frame and may provide clinical research with markers for patients stratification and to guide targeted therapy decisions.

Targeted reduction of the EGFR protein, but not inhibition of its kinase activity, induces mitophagy and death of cancer cells through activation of mTORC2 and Akt

The oncogenic epidermal growth factor receptor (EGFR) is commonly overexpressed in solid cancers. The tyrosine kinase activity of EGFR has been a major therapeutic target for cancer; however, the efficacy of EGFR tyrosine kinase inhibitors to treat cancers has been challenged by innate and acquired resistance at the clinic. Accumulating evidence suggests that EGFR possesses kinase-independent pro-survival functions, and that cancer cells are more vulnerable to reduction of EGFR protein than to inhibition of its kinase activity. The molecular mechanism underlying loss-of-EGFR-induced cell death remains largely unknown. In this study, we show that, unlike inhibiting EGFR kinase activity that is known to induce pro-survival non-selective autophagy, downregulating EGFR protein, either by siRNA, or by a synthetic EGFR-downregulating peptide (Herdegradin), kills prostate and ovarian cancer cells via selective mitophagy by activating the mTORC2/Akt axis. Furthermore, Herdegradin induced mitophagy and inhibited the growth of orthotopic ovarian cancers in mice. This study identifies anti-mitophagy as a kinase-independent function of EGFR, reveals a novel function of mTORC2/Akt axis in promoting mitophagy in cancer cells, and offers a novel approach for pharmacological downregulation of EGFR protein as a potential treatment for EGFR-positive cancers.

Selective mTORC2 Inhibitor Therapeutically Blocks Breast Cancer Cell Growth and Survival

Small-molecule inhibitors of the mTORC2 kinase (torkinibs) have shown efficacy in early clinical trials. However, the torkinibs under study also inhibit the other mTOR-containing complex mTORC1. While mTORC1/mTORC2 combined inhibition may be beneficial in cancer cells, recent reports describe compensatory cell survival upon mTORC1 inhibition due to loss of negative feedback on PI3K, increased autophagy, and increased macropinocytosis. Genetic models suggest that selective mTORC2 inhibition would be effective in breast cancers, but the lack of selective small-molecule inhibitors of mTORC2 have precluded testing of this hypothesis to date. Here we report the engineering of a nanoparticle-based RNAi therapeutic that can effectively silence the mTORC2 obligate cofactor Rictor. Nanoparticle-based Rictor ablation in HER2-amplified breast tumors was achieved following intratumoral and intravenous delivery, decreasing Akt phosphorylation and increasing tumor cell killing. Selective mTORC2 inhibition in vivo, combined with the HER2 inhibitor lapatinib, decreased the growth of HER2-amplified breast cancers to a greater extent than either agent alone, suggesting that mTORC2 promotes lapatinib resistance, but is overcome by mTORC2 inhibition. Importantly, selective mTORC2 inhibition was effective in a triple-negative breast cancer (TNBC) model, decreasing Akt phosphorylation and tumor growth, consistent with our findings that RICTOR mRNA correlates with worse outcome in patients with basal-like TNBC. Together, our results offer preclinical validation of a novel RNAi delivery platform for therapeutic gene ablation in breast cancer, and they show that mTORC2-selective targeting is feasible and efficacious in this disease setting.Significance: This study describes a nanomedicine to effectively inhibit the growth regulatory kinase mTORC2 in a preclinical model of breast cancer, targeting an important pathogenic enzyme in that setting that has been undruggable to date. Cancer Res; 78(7); 1845-58. ©2018 AACR.

mTOR Cross-Talk in Cancer and Potential for Combination Therapy

The mammalian Target of Rapamycin (mTOR) pathway plays an essential role in sensing and integrating a variety of exogenous cues to regulate cellular growth and metabolism, in both physiological and pathological conditions. mTOR functions through two functionally and structurally distinct multi-component complexes, mTORC1 and mTORC2, which interact with each other and with several elements of other signaling pathways. In the past few years, many new insights into mTOR function and regulation have been gained and extensive genetic and pharmacological studies in mice have enhanced our understanding of how mTOR dysfunction contributes to several diseases, including cancer. Single-agent mTOR targeting, mostly using rapalogs, has so far met limited clinical success; however, due to the extensive cross-talk between mTOR and other pathways, combined approaches are the most promising avenues to improve clinical efficacy of available therapeutics and overcome drug resistance. This review provides a brief and up-to-date narrative on the regulation of mTOR function, the relative contributions of mTORC1 and mTORC2 complexes to cancer development and progression, and prospects for mTOR inhibition as a therapeutic strategy.

Loss of Pten synergizes with c-Met to promote hepatocellular carcinoma development via mTORC2 pathway

Hepatocellular carcinoma (HCC) is a deadly malignancy with limited treatment options. Activation of the AKT/mTOR cascade is one of the most frequent events along hepatocarcinogenesis. mTOR is a serine/threonine kinase and presents in two distinct complexes: mTORC1 and mTORC2. While mTORC1 has been extensively studied in HCC, the functional contribution of mTORC2 during hepatocarcinogenesis has not been well characterized, especially in vivo. Pten expression is one of the major mechanisms leading to the aberrant activation of the AKT/mTOR signaling. Here, we show that concomitant downregulation of Pten and upregulation of c-Met occurs in a subset of human HCC, mainly characterized by poor prognosis. Using CRISPR-based gene editing in combination with hydrodynamic injection, Pten was deleted in a subset of mouse hepatocytes (sgPten). We found that loss of Pten synergizes with overexpression of c-Met to promote HCC development in mice (sgPten/c-Met). At the molecular level, sgPten/c-Met liver tumor tissues display increased AKT and mTOR signaling. Using Rictor conditional knockout mice, we demonstrate that sgPten/c-Met-driven HCC development strictly depends on an intact mTORC2 complex. Our findings therefore support the critical role of mTORC2 in hepatocarcinogenesis. sgPten/c-Met mouse model represents a novel valuable system that can be used for the development of targeted therapy against this deadly malignancy.

Ribosome biogenesis in cancer: new players and therapeutic avenues

The ribosome is a complex molecular machine composed of numerous distinct proteins and nucleic acids and is responsible for protein synthesis in every living cell. Ribosome biogenesis is one of the most multifaceted and energy- demanding processes in biology, involving a large number of assembly and maturation factors, the functions of which are orchestrated by multiple cellular inputs, including mitogenic signals and nutrient availability. Although causal associations between inherited mutations affecting ribosome biogenesis and elevated cancer risk have been established over the past decade, mechanistic data have emerged suggesting a broader role for dysregulated ribosome biogenesis in the development and progression of most spontaneous cancers. In this Opinion article, we highlight the most recent findings that provide new insights into the molecular basis of ribosome biogenesis in cancer and offer our perspective on how these observations present opportunities for the design of new targeted cancer treatments.

Andersen C. Characterization of genetic intratumor heterogeneity in colorectal cancer and matching patient-derived spheroid cultures

Patient-derived in vitro cultures of colorectal cancer (CRC) may help guide treatment strategies prior to patient treatment. However, most previous studies have been performed on a single biopsy per tumor. The purpose of this study was to analyze multiple spatially distinct biopsies from CRCs and see how well intratumor heterogeneity (ITH) was recapitulated in matching patient-derived spheroids. Three to five biopsies were collected from six CRC tumors. Each biopsy was split in two; one half was used for spheroid culturing, while the other half was used for DNA and RNA purification. For two patients, lymph node metastases were analyzed. Somatic mutations were called from whole exome sequencing data. Each tumor contained mutations shared across all biopsies and spheroids, including major CRC drivers such as APC, KRAS, and TP53. At the same time, all tumors exhibited ITH on both mutation and copy number level. The concordance between biopsies and spheroids ranged between 40 and 70% for coding mutations. For three patients, the biopsy and spheroid from matching areas clustered together, meaning that the spheroid resembled the area of origin more than the other areas. However, all biopsies and spheroids contained private mutations. Therefore, multiple cultures from spatially distinct sites of the tumor increase the insight into the genetic profile of the entire tumor. Molecular subtypes were called from RNA sequencing data. When based on transcripts from both cancer and noncancerous cells, the subtypes were largely independent of sampling site. In contrast, subtyping based on cancer cell transcripts alone was dependent on sample site and genetic ITH. In conclusion, all examined CRC tumors showed genetic ITH. Spheroid cultures partly reflected this ITH, and having multiple cultures from distinct tumor sites improved the representation of the genetic tumor subclones. This should be taken into account when establishing patient-derived models for drug screening.

hnRNPM guides an alternative splicing program in response to inhibition of the PI3K/AKT/mTOR pathway in Ewing sarcoma cells

Ewing sarcomas (ES) are biologically aggressive tumors of bone and soft tissues for which no cure is currently available. Most ES patients do not respond to chemotherapeutic treatments or acquire resistance. Since the PI3K/AKT/mTOR axis is often deregulated in ES, its inhibition offers therapeutic perspective for these aggressive tumors. Herein, by using splicing sensitive arrays, we have uncovered an extensive splicing program activated upon inhibition of the PI3K/AKT/mTOR signaling pathway by BEZ235. Bioinformatics analyses identified hnRNPM as a key factor in this response. HnRNPM motifs were significantly enriched in introns flanking the regulated exons and proximity of binding represented a key determinant for hnRNPM-dependent splicing regulation. Knockdown of hnRNPM expression abolished a subset of BEZ235-induced splicing changes that contained hnRNPM binding sites, enhanced BEZ235 cytotoxicity and limited the clonogenicity of ES cells. Importantly, hnRNPM up-regulation correlates with poor outcome in sarcoma patients. These findings uncover an hnRNPM-dependent alternative splicing program set in motion by inhibition of the mTOR/AKT/PI3K pathway in ES cells that limits therapeutic efficacy of pharmacologic inhibitors, suggesting that combined inhibition of the PI3K/AKT/mTOR pathway and hnRNPM activity may represent a novel approach for ES treatment.

Unraveling the human protein atlas of metastatic melanoma in the course of ultraviolet radiation-derived photo-therapy

To explore the photo-therapeutic capacity of UV radiation in solid tumors, we herein employed an nLC-MS/MS technology to profile the proteomic landscape of irradiated WM-266-4 human metastatic-melanoma cells. Obtained data resulted in proteomic catalogues of 5982 and 7280 proteins for UVB- and UVC-radiation conditions, respectively, and indicated the ability of UVB/C-radiation forms to eliminate metastatic-melanoma cells through induction of synergistically operating programs of apoptosis and necroptosis. However, it seems that one or more WM-266-4 cell sub-populations may escape from UV-radiation's photo-damaging activity, acquiring, besides apoptosis tolerance, an EMT phenotype that likely offers them the advantage of developing resistance to certain chemotherapeutic drugs. Low levels of autophagy may also critically contribute to the selective survival and growth of UV-irradiated melanoma-cell escapers. These are the cells that must be systemically targeted with novel therapeutic schemes, like the one of UV radiation and Irinotecan herein suggested to be holding strong promise for the effective treatment of metastatic-melanoma patients. Given the dual nature of UV radiation to serve as both anti-tumorigenic and tumorigenic agent, all individuals being subjected to risk factors for melanoma development have to be appropriately informed and educated, in order to integrate the innovative PPPM concept in their healthcare-sector management.

SIGNIFICANCE

This study reports the application of nLC-MS/MS technology to deeply map the proteomic landscape of UV-irradiated human metastatic-melanoma cells. Data bioinformatics processing led to molecular-network reconstructions that unearthed the dual nature of UV radiation to serve as both anti-tumorigenic and tumorigenic factor in metastatic-melanoma cellular environments. Our UV radiation-derived "photo-proteomic" atlas may prove valuable for the identification of new biomarkers and development of novel therapies for the disease. Given that UV radiation represents a major risk factor causing melanoma, a PPPM-based life style and clinical practice must be embraced by all individuals being prone to disease's appearance and expansion.

Structural basis for the assembly of the Ragulator-Rag GTPase complex

The mechanistic target of rapamycin complex 1 (mTORC1) plays a central role in regulating cell growth and metabolism by responding to cellular nutrient conditions. The activity of mTORC1 is controlled by Rag GTPases, which are anchored to lysosomes via Ragulator, a pentameric protein complex consisting of membrane-anchored p18/LAMTOR1 and two roadblock heterodimers. Here we report the crystal structure of Ragulator in complex with the roadblock domains of RagA-C, which helps to elucidate the molecular basis for the regulation of Rag GTPases. In the structure, p18 wraps around the three pairs of roadblock heterodimers to tandemly assemble them onto lysosomes. Cellular and in vitro analyses further demonstrate that p18 is required for Ragulator-Rag GTPase assembly and amino acid-dependent activation of mTORC1. These results establish p18 as a critical organizing scaffold for the Ragulator-Rag GTPase complex, which may provide a platform for nutrient sensing on lysosomes.

mTORC1 activity is controlled through Rag GTPases, which are anchored to the lysosome through the Ragulator. Here, the authors give molecular insights into Ragulator-Rag GTPase assembly and present the crystal structures of the Ragulator alone and in complex with the RagA-C roadblock domains.

Coronarin D induces reactive oxygen species-mediated cell death in human nasopharyngeal cancer cells through inhibition of p38 MAPK and activation of JNK

Background and Purpose

Nasopharyngeal carcinoma (NPC) belongs to squamous cell carcinoma that occurs in the epithelial lining of the nasopharynx. Because of the anatomical position close to the cervical lymph node, some patients have a distant metastasis at the time of diagnosis that leads to treatment failure. Although early stages have a high curability and excellent prognosis, advanced NPC urgently requires new drugs developed to reinforce the effectiveness of therapy without noticeable side effects.

Experimental approach

Coronarin D (CD), a natural product extracted from the rhizomes of Hedychium coronarium, has been reported to possess anticancer potential. The aim of the present study was to determine the anticancer activity of CD and further elucidate the underlying molecular mechanisms.

Key Results

In this study, we first demonstrated that CD potently suppressed cell viability in various NPC cell lines. Treatment of cells with CD induced G2/M arrest, apoptosis, and autophagy. Further studies showed that CD increased the production of reactive oxygen species and subsequently activated both autophagy and apoptosis. Moreover, we found that CD-induced activation of p38 and JNK constituted major mechanisms involved in the apoptosis and autophagy triggered by CD. In particular, inhibition of autophagy could strengthen the cytotoxicity of CD, implying that autophagy seems to play a valuable survival and protective role in cancer cells.

Conclusions & Implications

These findings provide a promise for the use of CD in combination with autophagy inhibitors for treatment of human NPC cell lines.

Metabolic reprogramming ensures cancer cell survival despite oncogenic signaling blockade

Lue et al. show that although inhibition of PI3K–AKT–mTOR signaling markedly decreased glycolysis and restrained tumor growth, these signaling and metabolic restrictions triggered autophagy. Survival of cancer cells was critically dependent on phospholipase A2 (PLA2) to mobilize lysophospholipids and free fatty acids to sustain fatty acid oxidation and oxidative phosphorylation.

There is limited knowledge about the metabolic reprogramming induced by cancer therapies and how this contributes to therapeutic resistance. Here we show that although inhibition of PI3K–AKT–mTOR signaling markedly decreased glycolysis and restrained tumor growth, these signaling and metabolic restrictions triggered autophagy, which supplied the metabolites required for the maintenance of mitochondrial respiration and redox homeostasis. Specifically, we found that survival of cancer cells was critically dependent on phospholipase A2 (PLA2) to mobilize lysophospholipids and free fatty acids to sustain fatty acid oxidation and oxidative phosphorylation. Consistent with this, we observed significantly increased lipid droplets, with subsequent mobilization to mitochondria. These changes were abrogated in cells deficient for the essential autophagy gene ATG5. Accordingly, inhibition of PLA2 significantly decreased lipid droplets, decreased oxidative phosphorylation, and increased apoptosis. Together, these results describe how treatment-induced autophagy provides nutrients for cancer cell survival and identifies novel cotreatment strategies to override this survival advantage.

Uncoupling TORC2 from AGC kinases inhibits tumour growth

Mammalian target of rapamycin (mTOR) is a central regulator of growth and metabolism. mTOR resides in two distinct multi-protein complexes - mTORC1 and mTORC2 - with distinct upstream regulators and downstream targets. While it is possible to specifically inhibit mTORC1 with rapamycin, or inhibit both mTOR complexes together with ATP pocket directed mTOR kinase inhibitors, it is not possible to assess the specific roles for mTORC2 pharmacologically. To overcome this, we have developed a novel, inducible, dominant negative system for disrupting substrate recruitment to mTORC2. Previously we identified the mTORC2 specific subunit Sin1 as a direct binding partner for AGC kinases Akt and PKC. Sin1 mutants, which retain the ability to bind Rictor and mTOR, but fail to recruit their AGC client kinases, inhibit AKT and PKC priming and block cell growth. In this study, we demonstrate that uncoupling mTORC2 from AGC kinases in DLD1 colon cancer cells inhibits Akt activation and blocks tumour growth in vivo. Further we demonstrate, using time resolved two-site amplified FRET (A-FRET) analysis of xenograft tumours, that inhibition of tumour growth correlates with the degree of mTORC2 uncoupling from its downstream targets, as demonstrated for Akt. These data add weight to the body of evidence that mTORC2 represents a pharmacological target in cancer independently of mTORC1.

mTOR Controls Mitochondrial Dynamics and Cell Survival via MTFP1

The mechanisms that link environmental and intracellular stimuli to mitochondrial functions, including fission/fusion, ATP production, metabolite biogenesis, and apoptosis, are not well understood. Here, we demonstrate that the nutrient-sensing mechanistic/mammalian target of rapamycin complex 1 (mTORC1) stimulates translation of mitochondrial fission process 1 (MTFP1) to control mitochondrial fission and apoptosis. Expression of MTFP1 is coupled to pro-fission phosphorylation and mitochondrial recruitment of the fission GTPase dynamin-related protein 1 (DRP1). Potent active-site mTOR inhibitors engender mitochondrial hyperfusion due to the diminished translation of MTFP1, which is mediated by translation initiation factor 4E (eIF4E)-binding proteins (4E-BPs). Uncoupling MTFP1 levels from the mTORC1/4E-BP pathway upon mTOR inhibition blocks the hyperfusion response and leads to apoptosis by converting mTOR inhibitor action from cytostatic to cytotoxic. These data provide direct evidence for cell survival upon mTOR inhibition through mitochondrial hyperfusion employing MTFP1 as a critical effector of mTORC1 to govern cell fate decisions.

c‑Myc promotes cholangiocarcinoma cells to overcome contact inhibition via the mTOR pathway

The loss of contact inhibition is a hallmark of a wide range of human cancer cells. Yet, the precise mechanism behind this process is not fully understood. c‑Myc plays a pivotal role in carcinogenesis, but its involvement in regulating contact inhibition has not been explored to date. Here, we report that c‑Myc plays an important role in abrogating contact inhibition in human cholangiocarcinoma (CCA) cells. Our data show that the protein level of c‑Myc obviously decreased in contact-inhibited normal biliary epithelial cells. However, CCA cells sustain high protein levels of c‑Myc and keep strong proliferation ability in confluent conditions. Importantly, the suppression of c‑Myc by inhibitor or siRNA induced G0/G1 phase cell cycle arrest in confluent CCA cells. We demonstrate that the inhibition of c‑Myc suppressed the activity of mammalian target of rapamycin (mTOR) in confluent CCA cells, and mTOR inhibition induced G0/G1 phase cell cycle arrest in confluent CCA cells. In confluent CCA cells, the activity of Merlin is downregulated, and Yes-associated protein (YAP) sustains high levels of activity. Furthermore, YAP inhibition not only induced G0/G1 phase cell cycle arrest, but also decreased c‑Myc expression in confluent CCA cells. These results indicate that Merlin/YAP/c‑Myc/mTOR signaling axis promotes human CCA cell proliferation by overriding contact inhibition. We propose that overriding c‑Myc‑mediated contact inhibition is implicated in the development of CCA.

MiR-15a/16 deficiency enhances anti-tumor immunity of glioma-infiltrating CD8+ T cells through targeting mTOR

MiR-15a/16, a miRNA cluster located at chromosome 13q14, has been reported to act as an immune regulator in inflammatory disorders besides its aberrant expression in cancers. However, little is known about its regulation in tumor-infiltrating immune cells. In our study, using an orthotropic GL261 mouse glioma model, we found that miR-15a/16 deficiency in host inhibited tumor growth and prolonged mice survival, which might be associated with the accumulation of tumor-infiltrating CD8+ T cells. More importantly, tumor-infiltrating CD8+ T cells without miR-15a/16 showed lower expression of PD-1, Tim-3 and LAG-3, and stronger secretion of IFN-γ, IL-2 and TNF-α than WT tumor-infiltrating CD8+ T cells. Also, our in vitro experiments further confirmed that miR-15a/16^-/- CD8+ T displayed higher active phenotypes, more cytokines secretion and faster expansion, compared to WT CD8+ T cells. Mechanismly, mTOR was identified as a target gene of miR-15a/16 to negatively regulate the activation of CD8+ T cells. Taken together, these data suggest that miR-15a/16 deficiency resists the exhaustion and maintains the activation of glioma-infiltrating CD8+ T cells to alleviate glioma progression via targeting mTOR. Our findings provide evidence for the potential immunotherapy through targeting miR-15a/16 in tumor-infiltrating immune cells.

Brain-derived neurotrophic factor promotes VEGF-C-dependent lymphangiogenesis by suppressing miR-624-3p in human chondrosarcoma cells

Chondrosarcoma is the second most common primary malignancy of bone, and one of the most difficult bone tumors to diagnose and treat. It is well known that increased levels of vascular endothelial growth factor-C (VEGF-C) promote active tumor lymphangiogenesis and lymphatic tumor spread to regional lymph nodes. Brain-derived neurotrophic factor (BDNF) is known to promote metastasis in human chondrosarcoma cells. Knowing more about the mechanism of BDNF in VEGF-C expression and lymphangiogenesis in human chondrosarcoma would improve our understanding as how to prevent chondrosarcoma angiogenesis and metastasis, which currently lacks effective adjuvant treatment. Here, we found that BDNF expression was at least 2.5-fold higher in the highly migratory JJ012(S10) cell line as compared with the primordial cell line (JJ012). In addition, VEGF-C expression and secretion was markedly increased in JJ012(S10) cells. Conditioned medium from JJ012(S10) cells significantly promoted migration and tube formation of human lymphatic endothelial cells (LECs), whereas knockdown of BDNF attenuated LEC migration and tube formation by suppressing VEGF-C production in JJ012(S10) cells. Mechanistic investigations indicated that BDNF facilitated VEGF-C-dependent lymphangiogenesis through the MEK/ERK/mTOR signaling pathway. We also showed that microRNA (miR)-624-3p expression was negatively regulated by BDNF via the MEK/ERK/mTOR cascade. Importantly, BDNF knockdown profoundly inhibited tumor-associated lymphangiogenesis in vivo. Further analyses identified that BDNF promoted tumor lymphangiogenesis by downregulating miR-624-3p in human chondrosarcoma tissues. In conclusion, this study is the first to reveal the mechanism underlying BDNF-induced lymphangiogenesis. We suggest that BDNF may serve as a promising therapeutic target for the restriction of VEGF-C-mediated tumor lymphangiogenesis and lymphatic metastasis.

Small molecules to the rescue: Inhibition of cytokine signaling in immune-mediated diseases

Cytokines are small, secreted proteins associated with the maintenance of immune homeostasis but also implicated with the pathogenesis of several autoimmune and inflammatory diseases. Biologic agents blocking cytokines or their receptors have revolutionized the treatment of such pathologies. Nonetheless, some patients fail to respond to these drugs or do not achieve complete remission. The signal transduction originating from membrane-bound cytokine receptors is an intricate network of events that lead to gene expression and ultimately regulate cellular functionality. Our understanding of the intracellular actions that molecules such as interleukins, interferons (IFNs) and tumor necrosis factor (TNF) set into motion has greatly increased in the past few years, making it possible to interfere with cytokines' signaling cascades. The Janus kinase (JAK)/signal transducer and activator of transcription (STAT), the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB), the mitogen activated protein kinase (MAPK) and the Phosphatidylinositol-3'-kinases (PI3K) pathways have all been intensively studied and key steps as well as molecules have been identified. These research efforts have led to the development of a new generation of small molecule inhibitors. Drugs capable of blocking JAK enzymatic activity or interfering with the proteasome-mediated degradation of intermediates in the NF-kB pathway have already entered the clinical arena confirming the validity of this approach. In this review, we have recapitulated the biochemical events downstream of cytokine receptors and discussed some of the drugs which have already been successfully utilized in the clinic. Moreover, we have highlighted some of the new molecules that are currently being developed for the treatment of immune-mediated pathologies and malignancies.

Host Serine/Threonine Kinases mTOR and Protein Kinase C-α Promote InlB-Mediated Entry of Listeria monocytogenes

The bacterial pathogen Listeria monocytogenes causes foodborne illnesses resulting in gastroenteritis, meningitis, or abortion. Listeria induces its internalization into some human cells through interaction of the bacterial surface protein InlB with the host receptor tyrosine kinase Met. InlB-dependent entry requires localized polymerization of the host actin cytoskeleton. The signal transduction pathways that act downstream of Met to regulate actin filament assembly or other processes during Listeria uptake remain incompletely characterized. Here, we demonstrate important roles for the human serine/threonine kinases mTOR and protein kinase C-α (PKC-α) in InlB-dependent entry. Experiments involving RNA interference (RNAi) indicated that two multiprotein complexes containing mTOR, mTORC1 and mTORC2, are each needed for efficient internalization of Listeria into cells of the human cell line HeLa. InlB stimulated Met-dependent phosphorylation of mTORC1 or mTORC2 substrates, demonstrating activation of both mTOR-containing complexes. RNAi studies indicated that the mTORC1 effectors 4E-BP1 and hypoxia-inducible factor 1α (HIF-1α) and the mTORC2 substrate PKC-α each control Listeria uptake. Genetic or pharmacological inhibition of PKC-α reduced the internalization of Listeria and the accumulation of actin filaments that normally accompanies InlB-mediated entry. Collectively, our results identify mTOR and PKC-α to be host factors exploited by Listeria to promote infection. PKC-α controls Listeria entry, at least in part, by regulating the actin cytoskeleton downstream of the Met receptor.

Caspase involvement in autophagy

Caspases are a family of cysteine proteases widely known as the principal mediators of the apoptotic cell death response, but considerably less so as the contributors to the regulation of pathways outside cellular demise. In regards to autophagy, the modulatory roles of caspases have only recently begun to be adequately described. In contrast to apoptosis, autophagy promotes cell survival by providing energy and nutrients through the lysosomal degradation of cytoplasmic constituents. Under basal conditions autophagy and apoptosis cross-regulate each other through an elaborate network of interconnections which also includes the interplay between autophagy-related proteins (ATGs) and caspases. In this review we focus on the effects of this crosstalk at the cellular level, as we aim to concentrate the main observations from research conducted so far on the fine-tuning of autophagy by caspases. Several members of this protease-family have been found to directly interact with key ATGs involved in different tiers across the autophagic cascade. Therefore, we firstly outline the core mechanism of macroautophagy in brief. In an effort to emphasize the importance of the intricate cross-regulation of ATGs and caspases, we also present examples of autophagy's contribution to apoptotic cell death during development.

Control of B lymphocyte development and functions by the mTOR signaling pathways

Mechanistic target of rapamycin (mTOR) is a serine/threonine kinase originally discovered as the molecular target of the immunosuppressant rapamycin. mTOR forms two compositionally and functionally distinct complexes, mTORC1 and mTORC2, which are crucial for coordinating nutrient, energy, oxygen, and growth factor availability with cellular growth, proliferation, and survival. Recent studies have identified critical, non-redundant roles for mTORC1 and mTORC2 in controlling B cell development, differentiation, and functions, and have highlighted emerging roles of the Folliculin-Fnip protein complex in regulating mTOR and B cell development. In this review, we summarize the basic mechanisms of mTOR signaling; describe what is known about the roles of mTORC1, mTORC2, and the Folliculin/Fnip1 pathway in B cell development and functions; and briefly outline current clinical approaches for targeting mTOR in B cell neoplasms. We conclude by highlighting a few salient questions and future perspectives regarding mTOR in B lineage cells.

Transcriptional Dependencies in Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine glioma (DIPG) is a fatal pediatric cancer with limited therapeutic options. The majority of cases of DIPG exhibit a mutation in histone-3 (H3K27M) that results in oncogenic transcriptional aberrancies. We show here that DIPG is vulnerable to transcriptional disruption using bromodomain inhibition or CDK7 blockade. Targeting oncogenic transcription through either of these methods synergizes with HDAC inhibition, and DIPG cells resistant to HDAC inhibitor therapy retain sensitivity to CDK7 blockade. Identification of super-enhancers in DIPG provides insights toward the cell of origin, highlighting oligodendroglial lineage genes, and reveals unexpected mechanisms mediating tumor viability and invasion, including potassium channel function and EPH receptor signaling. The findings presented demonstrate transcriptional vulnerabilities and elucidate previously unknown mechanisms of DIPG pathobiology.

Signaling pathways regulating blood-tissue barriers - Lesson from the testis

Signaling pathways that regulate blood-tissue barriers are important for studying the biology of various blood-tissue barriers. This information, if deciphered and better understood, will provide better therapeutic management of diseases particularly in organs that are sealed by the corresponding blood-tissue barriers from systemic circulation, such as the brain and the testis. These barriers block the access of antibiotics and/or chemotherapeutical agents across the corresponding barriers. Studies in the last decade using the blood-testis barrier (BTB) in rats have demonstrated the presence of several signaling pathways that are crucial to modulate BTB function. Herein, we critically evaluate these findings and provide hypothetical models regarding the underlying mechanisms by which these signaling molecules/pathways modulate BTB dynamics. This information should be carefully evaluated to examine their applicability in other tissue barriers which shall benefit future functional studies in the field. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Metformin exhibits the anti-proliferation and anti-invasion effects in hepatocellular carcinoma cells after insufficient radiofrequency ablation

Background

The mechanisms and prevention of progression of hepatocellular carcinoma (HCC) after insufficient radiofrequency ablation (RFA) has been preliminarily investigated, therefore, new strategy needs to be investigated to prevent the process. Whether metformin could be used to inhibit the growth of HCC after insufficient RFA and further prevent the progression of residual HCC remains unclearly.

Methods

MTT assay, colony formation assay and transwell assay were used to observe the cell viability, migration and invasion. Western blot and immunohistochemistry methods were used to observe the expression of proteins. Xenograft model was used to evaluate the growth of HCC cells in vivo.

Results

Metformin inhibited the enhanced proliferation, migration and invasion of HepG2 and SMMC7721 cells after insufficient RFA (named as HepG2-H and SMMC7721-H). Metformin deregulated the expression of p-Akt in HepG2 and SMMC7721 cells after insufficient RFA through AMPK/PTEN pathway. HepG2-H cells also exhibited larger tumor size in vivo. Higher expression of Ki-67 and CD31 and lower expression of E-cadherin were observed in HepG2-H tumors. Metformin blocked the enhanced growth of HepG2 cells in vivo after insufficient RFA. Metformin had no apparent toxicity on nude mice.

Conclusions

Metfromin inhibited the growth of HCC cells after insufficient RFA, and may be used to prevent the progression of HCC after RFA.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-017-0418-6) contains supplementary material, which is available to authorized users.

Regulation of PI3K effector signalling in cancer by the phosphoinositide phosphatases

Class I phosphoinositide 3-kinase (PI3K) generates phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P₃) at the plasma membrane in response to growth factors, activating a signalling cascade that regulates many cellular functions including cell growth, proliferation, survival, migration and metabolism. The PI3K pathway is commonly dysregulated in human cancer, and drives tumorigenesis by promoting aberrant cell growth and transformation. PtdIns(3,4,5)P₃ facilitates the activation of many pleckstrin homology (PH) domain-containing proteins including the serine/threonine kinase AKT. There are three AKT isoforms that are frequently hyperactivated in cancer through mutation, amplification or dysregulation of upstream regulatory proteins. AKT isoforms have converging and opposing functions in tumorigenesis. PtdIns(3,4,5)P₃ signalling is degraded and terminated by phosphoinositide phosphatases such as phosphatase and tensin homologue (PTEN), proline-rich inositol polyphosphate 5-phosphatase (PIPP) (INPP5J) and inositol polyphosphate 4-phosphatase type II (INPP4B). PtdIns(3,4,5)P₃ is rapidly hydrolysed by PIPP to generate phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P₂), which is further hydrolysed by INPP4B to form phosphatidylinositol 3-phosphate (PtdIns3P). PtdIns(3,4)P₂ and PtdIns3P are also important signalling molecules; PtdIns(3,4)P₂ together with PtdIns(3,4,5)P₃ are required for maximal AKT activation and PtdIns3P activates PI3K-dependent serum and glucocorticoid-regulated kinase (SGK3) signalling. Loss of Pten, Pipp or Inpp4b expression or function promotes tumour growth in murine cancer models through enhanced AKT isoform-specific signalling. INPP4B inhibits PtdIns(3,4)P₂-mediated AKT activation in breast and prostate cancer; however, INPP4B expression is increased in acute myeloid leukaemia (AML), melanoma and colon cancer where it paradoxically promotes cell proliferation, transformation and/or drug resistance. This review will discuss how PTEN, PIPP and INPP4B distinctly regulate PtdIns(3,4,5)P₃ signalling downstream of PI3K and how dysregulation of these phosphatases affects cancer outcomes.

Resistance to mTORC1 Inhibitors in Cancer Therapy: From Kinase Mutations to Intratumoral Heterogeneity of Kinase Activity

Targeting mTORC1 has been thoroughly explored in cancer therapy. Following encouraging preclinical studies, mTORC1 inhibitors however failed to provide substantial benefits in cancer patients. Several resistance mechanisms have been identified including mutations of mTOR and activation of alternate proliferation pathways. Moreover, emerging evidence discloses intratumoral heterogeneity of mTORC1 activity that further contributes to a reduced anticancer efficacy of mTORC1 inhibitors. Genetic heterogeneity as well as heterogeneous conditions of the tumor environment such as hypoxia profoundly modifies mTORC1 activity in tumors and hence influences the response of tumors to mTORC1 inhibitors. Intriguingly, the heterogeneity of mTORC1 activity also occurs towards its substrates at the single cell level, as mutually exclusive pattern of activation of mTORC1 downstream effectors has been reported in tumors. After briefly describing mTORC1 biology and the use of mTORC1 inhibitors in patients, this review will give an overview on concepts of resistance to mTORC1 inhibition in cancer with a particular focus on intratumoral heterogeneity of mTORC1 activity.

Deptor: not only a mTOR inhibitor

Deptor is an important protein that belongs to the mTORC1 and mTORC2 complexes, able to interact with mTOR and to inhibit its kinase activity. As a natural mTOR inhibitor, Deptor is involved in several molecular pathways, such as cell growth, apoptosis, autophagy and ER stress response. For this reason, Deptor seems to play an important role in controlling cellular homeostasis. Despite several recent insights characterizing Deptor functions and regulation, its complete role within cells has not yet been completely clarified. Indeed, quite recently, Deptor has been associated with chromatin, and it has been demonstrated having a role in transcriptional regulation, controlling in such way endoplasmatic reticulum activity.

From all these observations it is not surprising that Deptor can behave either as an oncogene or oncosuppressor, depending on the cell- or tissue-contexts. This review highlights recent progresses made in our understanding of the many activities of Deptor, describing its transcriptional and post-transcriptional regulation in different cancer cell types. Moreover, here we discuss the possibility of using compounds able to inhibit Deptor or to disrupt its interaction with mTOR as novel approaches for cancer therapy.

Transcriptional Profiling and Identification of Heat-Responsive Genes in Perennial Ryegrass by RNA-Sequencing

Perennial ryegrass (Lolium perenne) is one of the most widely used forage and turf grasses in the world due to its desirable agronomic qualities. However, as a cool-season perennial grass species, high temperature is a major factor limiting its performance in warmer and transition regions. In this study, a de novo transcriptome was generated using a cDNA library constructed from perennial ryegrass leaves subjected to short-term heat stress treatment. Then the expression profiling and identification of perennial ryegrass heat response genes by digital gene expression analyses was performed. The goal of this work was to produce expression profiles of high temperature stress responsive genes in perennial ryegrass leaves and further identify the potentially important candidate genes with altered levels of transcript, such as those genes involved in transcriptional regulation, antioxidant responses, plant hormones and signal transduction, and cellular metabolism. The de novo assembly of perennial ryegrass transcriptome in this study obtained more total and annotated unigenes compared to previously published ones. Many DEGs identified were genes that are known to respond to heat stress in plants, including HSFs, HSPs, and antioxidant related genes. In the meanwhile, we also identified four gene candidates mainly involved in C₄ carbon fixation, and one TOR gene. Their exact roles in plant heat stress response need to dissect further. This study would be important by providing the gene resources for improving heat stress tolerance in both perennial ryegrass and other cool-season perennial grass plants.