Explore the vast range of titles available.

Our understanding of the downstream effectors and upstream regulators of target of rapamycin (TOR) signalling continues to grow. In particular, recent global 'omics' studies have revealed physiological roles of mammalian TOR (mTOR) in protein, nucleotide and lipid synthesis, and other studies showed that Hippo, WNT and Notch signalling are novel regulators of mTOR. More than 20 years after its discovery, our understanding of target of rapamycin (TOR) signalling continues to grow. Recent global 'omics' studies have revealed physiological roles of mammalian TOR (mTOR) in protein, nucleotide and lipid synthesis. Furthermore, emerging evidence provides new insight into the control of mTOR by other pathways such as Hippo, WNT and Notch signalling. Together, this progress has expanded the list of downstream effectors and upstream regulators of mTOR signalling.

Key Points Acetate can be used by tumour cells as an important bioenergetic fuel or as a nutritional source to support lipid biosynthesis. Acetate can be a precursor for acetylation of histones and other proteins and hence can serve as an epigenetic and post-translational modifier. Despite the low circulating concentration of acetate, acetate may still exert its effects through intra- and intercellular recycling of acetate molecules within the tumour microenvironment or at sites with high local acetate concentrations. Acetyl-CoA synthetase 2 (ACSS2) is emerging as an important enzyme in the growth of many different types of cancers and is induced by cancer cells in response to nutrient stress conditions. Targeting ACSS2 may prove to be a powerful therapeutic modality. ACSS2 is highly upregulated in multiple cancer types and may be a useful biomarker for anti-ACSS2 therapies. [ 11 C]acetate has demonstrated excellent potential as an alternative positron emission tomography imaging probe for cancer. More studies on why some but not other tumours are [ 11 C]acetate avid, and correlating these data with the expression of acetyl-CoA synthetases will aid in deciphering the exact manner by which acetate metabolism supports tumour growth and help in stratifying patients for future anti-ACSS2 therapy. This Review discusses how acetate functions as a nutritional source for tumours and as a regulator of cancer cell stress, and how preventing its (re)capture by cancer cells may provide an opportunity for therapeutic intervention. Recent high-profile reports have reignited an interest in acetate metabolism in cancer. Acetyl-CoA synthetases that catalyse the conversion of acetate to acetyl-CoA have now been implicated in the growth of hepatocellular carcinoma, glioblastoma, breast cancer and prostate cancer. In this Review, we discuss how acetate functions as a nutritional source for tumours and as a regulator of cancer cell stress, and how preventing its (re)capture by cancer cells may provide an opportunity for therapeutic intervention.

Folate receptor-α (FRα) is overexpressed in many cancer cells and is therefore an important therapeutic target: here the X-ray crystal structure of folate-bound FRα is presented, revealing details of the ligand-binding pocket that may be useful in the development of small-molecule inhibitors for anticancer therapy. Folic acid receptor structure Folic acid, or folate, is an essential vitamin that is needed for many biological processes, including DNA synthesis, DNA repair and cell division. 'Normal' cells express relatively low amounts of the three folate receptors α, β and γ, but they are commonly overexpressed in cancer cell lines; for this reason, they are potential targets for new chemotherapeutics and cancer-imaging reagents. In this manuscript, the authors solve the X-ray crystal structure of the folate-bound form of human folate receptor α, which mediates folate uptake into cells. The authors map the ligand-binding pocket, providing data that should be useful for the development of new small molecules to target the receptor. Folate receptors (FRα, FRβ and FRγ) are cysteine-rich cell-surface glycoproteins that bind folate with high affinity to mediate cellular uptake of folate. Although expressed at very low levels in most tissues, folate receptors, especially FRα, are expressed at high levels in numerous cancers to meet the folate demand of rapidly dividing cells under low folate conditions 1 , 2 , 3 . The folate dependency of many tumours has been therapeutically and diagnostically exploited by administration of anti-FRα antibodies, high-affinity antifolates 4 , 5 , folate-based imaging agents and folate-conjugated drugs and toxins 6 , 7 , 8 . To understand how folate binds its receptors, we determined the crystal structure of human FRα in complex with folic acid at 2.8 Å resolution. FRα has a globular structure stabilized by eight disulphide bonds and contains a deep open folate-binding pocket comprised of residues that are conserved in all receptor subtypes. The folate pteroate moiety is buried inside the receptor, whereas its glutamate moiety is solvent-exposed and sticks out of the pocket entrance, allowing it to be conjugated to drugs without adversely affecting FRα binding. The extensive interactions between the receptor and ligand readily explain the high folate-binding affinity of folate receptors and provide a template for designing more specific drugs targeting the folate receptor system.

Advances in sequencing and high-throughput techniques have provided an unprecedented opportunity to interrogate human diseases on a genome-wide scale. The list of disease-causing mutations is expanding rapidly, and mutations affecting mRNA translation are no exception. Translation (protein synthesis) is one of the most complex processes in the cell. The orchestrated action of ribosomes, tRNAs and numerous translation factors decodes the information contained in mRNA into a polypeptide chain. The intricate nature of this process renders it susceptible to deregulation at multiple levels. In this Review, we summarize current evidence of translation deregulation in human diseases other than cancer. We discuss translation-related diseases on the basis of the molecular aberration that underpins their pathogenesis (including tRNA dysfunction, ribosomopathies, deregulation of the integrated stress response and deregulation of the mTOR pathway) and describe how deregulation of translation generates the phenotypic variability observed in these disorders.

Breast cancer is a leading cause of cancer-related death in women. Small open reading frame (sORF)-encoded proteins or microproteins constitute a new class of molecules often transcribed from presumed long non-coding RNA transcripts (lncRNAs). The translation of some of these sORFs has been confirmed, but their cellular function and importance remains largely unknown. Here, we report the identification and characterization of a novel microprotein of 10 kDa, which we named Cancer-Associated Small Integral Membrane Open reading frame 1 (CASIMO1). CASIMO1 RNA is overexpressed predominantly in hormone receptor-positive breast tumors. Its knockdown leads to decreased proliferation in multiple breast cancer cell lines. Its loss disturbs the organization of the actin cytoskeleton, leads to inhibition of cell motility, and causes a G 0 /G 1 cell cycle arrest. The proliferation phenotype upon overexpression is observed only with CASIMO1 protein expression, but not with a non-translatable mutant attributing the effects to the sORF-derived protein rather than a lncRNA function. CASIMO1 microprotein interacts with squalene epoxidase (SQLE), a key enzyme in cholesterol synthesis and a known oncogene in breast cancer. Overexpression of CASIMO1 leads to SQLE protein accumulation without affecting its RNA levels and increased lipid droplet clustering, while knockdown of CASIMO1 decreased SQLE protein abundance and ERK phosphorylation downstream of SQLE. Importantly, SQLE knockdown mimicked the CASIMO1 knockdown phenotype and in turn SQLE overexpression fully rescued the effect of CASIMO1 knockdown. These findings establish CASIMO1 as the first functional microprotein that plays a role in carcinogenesis and is implicated in the cell lipid homeostasis.

Heavy metals are both integral parts of cells and environmental toxicants, and their deregulation is associated with severe cellular dysfunction and various diseases. Here we show that the Hippo pathway plays a critical role in regulating heavy metal homeostasis. Hippo signalling deficiency promotes the transcription of heavy metal response genes and protects cells from heavy metal-induced toxicity, a process independent of its classic downstream effectors YAP and TAZ. Mechanistically, the Hippo pathway kinase LATS phosphorylates and inhibits MTF1, an essential transcription factor in the heavy metal response, resulting in the loss of heavy metal response gene transcription and cellular protection. Moreover, LATS activity is inhibited following heavy metal treatment, where accumulated zinc directly binds and inhibits LATS. Together, our study reveals an interplay between the Hippo pathway and heavy metals, providing insights into this growth-related pathway in tissue homeostasis and stress response. Han et al. report that the Hippo pathway kinases LATS1 and LATS2 phosphorylate the heavy metal response transcription factor MTF1, leading to attenuation of heavy metal response gene transcription and cellular detoxification.

mTORC1 in the fasting liver During periods of fasting, the liver breaks down fatty acids to produce acetone and other ketone bodies that the peripheral tissues can use as a source of energy. A study of the role in the liver of mTORC1, the target of the immunosuppressant rapamycin, shows that fasting inhibits the activity of multicomponent mTORC1. Inhibition of mTORC1 is required for activation of PPARα, a master regulator that switches on genes involved in ketogenesis. Livers from aged mice have increased mTORC1 signalling, reduced PPARα activity and reduced ketone production. The observation that mTORC1 promotes an ageing phenotype in the liver fits well with the observation that inhibition of this pathway increases lifespan in several organisms. During periods of fasting the liver produces ketone bodies, which the peripheral tissues can use as a source of energy. Here it is shown that fasting inhibits multi-component mTOR complex 1 (mTORC1) in the liver. Inhibition of mTORC1 is required for activation of PPARα, a master regulator that switches on genes involved in ketogenesis. Livers from aged mice have increased mTORC1 signalling, reduced PPARα activity, and reduced ketone production. The observation that mTORC1 promotes an ageing phenotype in the liver fits well with the observation that inhibition of this pathway increases lifespan in several organisms. The multi-component mechanistic target of rapamycin complex 1 (mTORC1) kinase is the central node of a mammalian pathway that coordinates cell growth with the availability of nutrients, energy and growth factors 1 . Progress has been made in the identification of mTORC1 pathway components and in understanding their functions in cells, but there is relatively little known about the role of the pathway in vivo . Specifically, we have little knowledge regarding the role mTOCR1 has in liver physiology. In fasted animals, the liver performs numerous functions that maintain whole-body homeostasis, including the production of ketone bodies for peripheral tissues to use as energy sources. Here we show that mTORC1 controls ketogenesis in mice in response to fasting. We find that liver-specific loss of TSC1 (tuberous sclerosis 1), an mTORC1 inhibitor 1 , leads to a fasting-resistant increase in liver size, and to a pronounced defect in ketone body production and ketogenic gene expression on fasting. The loss of raptor (regulatory associated protein of mTOR, complex 1) an essential mTORC1 component 1 , has the opposite effects. In addition, we find that the inhibition of mTORC1 is required for the fasting-induced activation of PPARα (peroxisome proliferator activated receptor α), the master transcriptional activator of ketogenic genes 2 , and that suppression of NCoR1 (nuclear receptor co-repressor 1), a co-repressor of PPARα 3 , reactivates ketogenesis in cells and livers with hyperactive mTORC1 signalling. Like livers with activated mTORC1, livers from aged mice have a defect in ketogenesis 4 , 5 , which correlates with an increase in mTORC1 signalling. Moreover, we show that the suppressive effects of mTORC1 activation and ageing on PPARα activity and ketone production are not additive, and that mTORC1 inhibition is sufficient to prevent the ageing-induced defect in ketogenesis. Thus, our findings reveal that mTORC1 is a key regulator of PPARα function and hepatic ketogenesis and suggest a role for mTORC1 activity in promoting the ageing of the liver.

The Hippo-YAP signaling pathway is a critical regulator of proliferation, apoptosis, and cell fate. The main downstream effector of this pathway, YAP, has been shown to be misregulated in human cancer and has emerged as an attractive target for therapeutics. A significant insufficiency in our understanding of the pathway is the identity of transcriptional targets of YAP that drive its potent growth phenotypes. Here, using liver cancer as a model, we identify NUAK2 as an essential mediator of YAP-driven hepatomegaly and tumorigenesis in vivo. By evaluating several human cancer cell lines we determine that NUAK2 is selectively required for YAP-driven growth. Mechanistically, we found that NUAK2 participates in a feedback loop to maximize YAP activity via promotion of actin polymerization and myosin activity. Additionally, pharmacological inactivation of NUAK2 suppresses YAP-dependent cancer cell proliferation and liver overgrowth. Importantly, our work here identifies a specific, potent, and actionable target for YAP-driven malignancies. Hippo-YAP pathway plays an important role in cancers; however the in vivo relevance of YAP/TAZ target genes is unclear. Here, the authors show that NUAK2 is a target of YAP and participates in a feedback loop to maximize YAP activity. Inhibition of NUAK2 suppresses YAP-driven hepatomegaly and liver cancer growth, offering a new target for cancer therapy.

The role of the unfolded protein response (UPR) in tissue homeostasis remains largely unknown. Here we find that loss of Mst1/2, the mammalian Hippo orthologues, or their regulator WW45, leads to a remarkably enlarged endoplasmic reticulum (ER) size-associated UPR. Intriguingly, attenuation of the UPR by tauroursodeoxycholic acid (TUDCA) diminishes Mst1/2 mutant-driven liver overgrowth and tumorigenesis by promoting nuclear exit and degradation of Hippo downstream effector Yap. Yap is required for UPR activity and ER expansion to alleviate ER stress. During the adaptive stage of the UPR, PERK kinase-eIF2α axis activates Yap, while prolonged ER stress-induced Hippo signalling triggers assembly of the GADD34/PP1 complex in a negative feedback loop to inhibit Yap and promote apoptosis. Significantly, the deregulation of UPR signals associated with Yap activation is found in a substantial fraction of human hepatocellular carcinoma (HCC). Thus, we conclude Yap integrates Hippo and UPR signalling to control liver size and tumorigenesis. The Hippo pathway is a major regulator of organ size and growth control. Here Wu et al . provide evidence for a novel link between the Hippo signalling pathway and the unfolded protein response (UPR) in regulating organ growth and tumorigenesis.