mTOR and cancer: many loops in one pathway.

The mammalian target of rapamycin (mTOR) is a master regulator of cell growth and division that responds to a variety of stimuli, including nutrient, energy, and growth factors. In the last years, a significant number of pieces have been added to the puzzle of how mTOR coordinates and executes its functions. Extensive research on mTOR has also uncovered a complex network of regulatory loops that impact the therapeutic approaches aimed at targeting mTOR.

Systematic RNA interference reveals that oncogenic KRAS-driven cancers require TBK1.

The proto-oncogene KRAS is mutated in a wide array of human cancers, most of which are aggressive and respond poorly to standard therapies. Although the identification of specific oncogenes has led to the development of clinically effective, molecularly targeted therapies in some cases, KRAS has remained refractory to this approach. A complementary strategy for targeting KRAS is to identify gene products that, when inhibited, result in cell death only in the presence of an oncogenic allele.

Growth signaling at the nexus of stem cell life and death.

Stress can activate tumor-suppressive mechanisms, causing the loss of adult stem cell function with age. In this issue of Cell Stem Cell and in Nature, Castilho et al. (2009) and Harrison et al.

Involvement of vps33a in the fusion of uroplakin-degrading multivesicular bodies with lysosomes.

The apical surface of the terminally differentiated mouse bladder urothelium is largely covered by urothelial plaques, consisting of hexagonally packed 16-nm uroplakin particles. These plaques are delivered to the cell surface by fusiform vesicles (FVs) that are the most abundant cytoplasmic organelles. We have analyzed the functional involvement of several proteins in the apical delivery and endocytic degradation of uroplakin proteins.

A UV-transparent passive concentrator/spectrum deconvolution method for simultaneous detection of endocrine disrupting chemicals (EDCs) and related contaminants in natural waters.

Suspected endocrine disrupting chemicals (EDCs) have been widely detected in the environment, and are a source of increasing concern. One of the major challenges in assessing the risk associated with EDCs in the environment is that their environmental concentrations are typically extremely low - on the order of ngL(-1) to microgL(-1) - making them difficult to quantify without extensive pre-concentration procedures. Further complicating their detection is the fact that they are present in mixtures, sometimes with tens to hundreds of other compounds (pharmaceuticals, personal care products, detergents, natural organic matter).

Multipass membrane air-stripping (MAS) for removing volatile organic compounds (VOCs) from surfactant micellar solutions.

Air-stripping is one of the most effective technologies for removing volatile organic compounds (VOCs) from surfactant solutions, although the presence of surfactant poses some unique challenges. This study evaluated the effect of a mixed surfactant system on the apparent Henry's law constant of tetrachloroethylene (PCE) and the efficiency of PCE removal from surfactant solutions using a lab-scale hollow fiber membrane contactor. Results show that the presence of surfactant significantly reduced the apparent Henry's law constant of PCE, and the reduction was proportional to the total surfactant concentration.

DEPTOR is an mTOR inhibitor frequently overexpressed in multiple myeloma cells and required for their survival.

The mTORC1 and mTORC2 pathways regulate cell growth, proliferation, and survival. We identify DEPTOR as an mTOR-interacting protein whose expression is negatively regulated by mTORC1 and mTORC2. Loss of DEPTOR activates S6K1, Akt, and SGK1, promotes cell growth and survival, and activates mTORC1 and mTORC2 kinase activities.

Rapamycin inhibits mTORC1, but not completely.

Rapamycin is widely used as a complete inhibitor of the mTORC1 nutrient-sensitive signaling complex. Using a novel ATP-competitive inhibitor named Torin1, we have found that many mTORC1 functions that regulate cap-dependent translation and autophagy are resistant to inhibition by rapamycin.

The pharmacology of mTOR inhibition.

A flurry of reports indicates that we are entering a new phase in the development of mammalian target of rapamycin (mTOR)-based therapies for oncology. Here, we summarize exciting findings regarding mTOR signaling and the outlook for mTOR inhibitors as tools to study the mTOR pathway and as drugs in the clinic.

Tumours with PI3K activation are resistant to dietary restriction.

Dietary restriction delays the incidence and decreases the growth of various types of tumours, but the mechanisms underlying the sensitivity of tumours to food restriction remain unknown. Here we show that certain human cancer cell lines, when grown as tumour xenografts in mice, are highly sensitive to the anti-growth effects of dietary restriction, whereas others are resistant. Cancer cells that form dietary-restriction-resistant tumours carry mutations that cause constitutive activation of the phosphatidylinositol-3-kinase (PI3K) pathway and in culture proliferate in the absence of insulin or insulin-like growth factor 1.

Scoring diverse cellular morphologies in image-based screens with iterative feedback and machine learning.

Many biological pathways were first uncovered by identifying mutants with visible phenotypes and by scoring every sample in a screen via tedious and subjective visual inspection. Now, automated image analysis can effectively score many phenotypes. In practical application, customizing an image-analysis algorithm or finding a sufficient number of example cells to train a machine learning algorithm can be infeasible, particularly when positive control samples are not available and the phenotype of interest is rare.

mTOR complex 2 is required for the development of prostate cancer induced by Pten loss in mice.

mTOR complex 2 (mTORC2) contains the mammalian target of rapamycin (mTOR) kinase and the Rictor regulatory protein and phosphorylates Akt. Whether this function of mTORC2 is critical for cancer progression is unknown. Here, we show that transformed human prostate epithelial cells lacking PTEN require mTORC2 to form tumors when injected into nude mice.

An ATP-competitive mammalian target of rapamycin inhibitor reveals rapamycin-resistant functions of mTORC1.

The mammalian target of rapamycin (mTOR) kinase is the catalytic subunit of two functionally distinct complexes, mTORC1 and mTORC2, that coordinately promote cell growth, proliferation, and survival. Rapamycin is a potent allosteric mTORC1 inhibitor with clinical applications as an immunosuppressant and anti-cancer agent. Here we find that Torin1, a highly potent and selective ATP-competitive mTOR inhibitor that directly inhibits both complexes, impairs cell growth and proliferation to a far greater degree than rapamycin.

Rag proteins regulate amino-acid-induced mTORC1 signalling.

The serum- and nutrient-sensitive protein kinase mTOR (mammalian target of rapamycin) is a master regulator of cell growth and survival. The mechanisms through which nutrients regulate mTOR have been one of the major unanswered questions in the mTOR field. Identification of the Rag (Ras-related GTPase) family of GTPases as mediators of amino acid signalling to mTOR is an important step towards our understanding of this mechanism.

Highly parallel identification of essential genes in cancer cells.

More complete knowledge of the molecular mechanisms underlying cancer will improve prevention, diagnosis and treatment. Efforts such as The Cancer Genome Atlas are systematically characterizing the structural basis of cancer, by identifying the genomic mutations associated with each cancer type. A powerful complementary approach is to systematically characterize the functional basis of cancer, by identifying the genes essential for growth and related phenotypes in different cancer cells.

CellProfiler Analyst: data exploration and analysis software for complex image-based screens.

Background: Image-based screens can produce hundreds of measured features for each of hundreds of millions of individual cells in a single experiment.

Results: Here, we describe CellProfiler Analyst, open-source software for the interactive exploration and analysis of multidimensional data, particularly data from high-throughput, image-based experiments.

Conclusion: The system enables interactive data exploration for image-based screens and automated scoring of complex phenotypes that require combinations of multiple measured features per cell.

Cancer cell metabolism: Warburg and beyond.

Described decades ago, the Warburg effect of aerobic glycolysis is a key metabolic hallmark of cancer, yet its significance remains unclear. In this Essay, we re-examine the Warburg effect and establish a framework for understanding its contribution to the altered metabolism of cancer cells.

Hydrophilic-lipophilic deviation (HLD) method for characterizing conventional and extended surfactants.

An accurate determination of the hydrophilic-lipophilic nature of surfactants plays an essential role in guiding the formulation of microemulsion with the goal of achieving low interfacial tension (IFT) and high solubilization. While several empirical models have been proposed as simple tools for predicting surfactant characteristics and microemulsion conditions, only a few of these models are fundamentally based yet convenient to use. In this work, the hydrophilic-lipophilic deviation (HLD) approach was used with mixed surfactant systems to determine the surfactant characteristic (sigma) and the sigmaK parameter of conventional and extended surfactants.

The Rag GTPases bind raptor and mediate amino acid signaling to mTORC1.

The multiprotein mTORC1 protein kinase complex is the central component of a pathway that promotes growth in response to insulin, energy levels, and amino acids and is deregulated in common cancers. We find that the Rag proteins--a family of four related small guanosine triphosphatases (GTPases)--interact with mTORC1 in an amino acid-sensitive manner and are necessary for the activation of the mTORC1 pathway by amino acids. A Rag mutant that is constitutively bound to guanosine triphosphate interacted strongly with mTORC1, and its expression within cells made the mTORC1 pathway resistant to amino acid deprivation.

Plakoglobin is required for effective intermediate filament anchorage to desmosomes.

Desmosomes are adhesive junctions that provide mechanical coupling between cells. Plakoglobin (PG) is a major component of the intracellular plaque that serves to connect transmembrane elements to the cytoskeleton. We have used electron tomography and immunolabeling to investigate the consequences of PG knockout on the molecular architecture of the intracellular plaque in cultured keratinocytes.

Role of the air-water interface in the retention of TiO2 nanoparticles in porous media during primary drainage.

The increasing use of nanomaterials in commercial products has resulted in increased concerns about their potential environmental impacts. The overall mobility of nanomaterials in the environment may depend in part on their mobility in the unsaturated zone of the subsurface, which may provide a sink for nanomaterials, preventing their spread, or a long-term contaminant source. The objective of this work was to study the dynamic unsaturated transport of titanium dioxide (TiO2) during primary drainage to examine the role of air-water interface formation on nanomaterial retention.

Increased mTORC1 signaling UPRegulates stress.

In this issue of Molecular Cell, Ozcan et al. (2008) show that the loss of the tuberous sclerosis tumor suppressor complex induces endoplasmic reticulum stress, leading to attenuation of insulin receptor signaling activity via the unfolded protein response.

Rhamnolipid biosurfactant mixtures for environmental remediation.

This study investigated the efficiency of rhamnolipid biosurfactant and synthetic surfactant mixtures for improving the interfacial activity of the surfactant system against several light non-aqueous-phase liquids (LNAPLs). Since the rhamnolipid biosurfactant proved to be relatively hydrophilic, we hypothesized that mixtures of rhamnolipid biosurfactants with more hydrophobic synthetic surfactants would produce lower interfacial tensions (IFTs) than an individual rhamnolipid biosurfactant. The minimum IFT observed for rhamnolipid alone and toluene (0.