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Proceedings of the National Academy of... May 2022Mammalian target of rapamycin complex 1 (mTORC1) senses amino acids to control cell growth, metabolism, and autophagy. Some amino acids signal to mTORC1 through the Rag...
Mammalian target of rapamycin complex 1 (mTORC1) senses amino acids to control cell growth, metabolism, and autophagy. Some amino acids signal to mTORC1 through the Rag GTPase, whereas glutamine and asparagine activate mTORC1 through a Rag GTPase-independent pathway. Here, we show that the lysosomal glutamine and asparagine transporter SNAT7 activates mTORC1 after extracellular protein, such as albumin, is macropinocytosed. The N terminus of SNAT7 forms nutrient-sensitive interaction with mTORC1 and regulates mTORC1 activation independently of the Rag GTPases. Depletion of SNAT7 inhibits albumin-induced mTORC1 lysosomal localization and subsequent activation. Moreover, SNAT7 is essential to sustain KRAS-driven pancreatic cancer cell growth through mTORC1. Thus, SNAT7 links glutamine and asparagine signaling from extracellular protein to mTORC1 independently of the Rag GTPases and is required for macropinocytosis-mediated mTORC1 activation and pancreatic cancer cell growth.
Topics: Amino Acid Transport Systems, Neutral; Asparagine; Glutamine; Humans; Lysosomes; Mechanistic Target of Rapamycin Complex 1; Pancreatic Neoplasms; Pinocytosis; Signal Transduction
PubMed: 35561222
DOI: 10.1073/pnas.2123261119 -
Nature Jun 2017Mammalian cells are surrounded by diverse nutrients, such as glucose, amino acids, various macromolecules and micronutrients, which they can import through transmembrane... (Review)
Review
Mammalian cells are surrounded by diverse nutrients, such as glucose, amino acids, various macromolecules and micronutrients, which they can import through transmembrane transporters and endolysosomal pathways. By using different nutrient sources, cells gain metabolic flexibility to survive periods of starvation. Quiescent cells take up sufficient nutrients to sustain homeostasis. However, proliferating cells depend on growth-factor-induced increases in nutrient uptake to support biomass formation. Here, we review cellular nutrient acquisition strategies and their regulation by growth factors and cell-intrinsic nutrient sensors. We also discuss how oncogenes and tumour suppressors promote nutrient uptake and thereby support the survival and growth of cancer cells.
Topics: Animals; Cell Proliferation; Cells; Endocytosis; Glucose; Glutamine; Intercellular Signaling Peptides and Proteins; Lysosomes; Neoplasms; Pinocytosis; Proteins; Tumor Microenvironment
PubMed: 28593971
DOI: 10.1038/nature22379 -
Philosophical Transactions of the Royal... Feb 2019Macropinosome formation occurs as a localized sequence of biochemical activities and associated morphological changes, which may be considered a form of signal... (Review)
Review
Macropinosome formation occurs as a localized sequence of biochemical activities and associated morphological changes, which may be considered a form of signal transduction leading to the construction of an organelle. Macropinocytosis may also convey information about the availability of extracellular nutrients to intracellular regulators of metabolism. Consistent with this idea, activation of the metabolic regulator mechanistic target of rapamycin complex-1 (mTORC1) in response to acute stimulation by growth factors and extracellular amino acids requires internalization of amino acids by macropinocytosis. This suggests that macropinocytosis is necessary for mTORC1-dependent growth of metazoan cells, both as a route for delivery of amino acids to sensors associated with lysosomes and as a platform for growth factor-dependent signalling to mTORC1 via phosphatidylinositol 3-kinase (PI3K) and the Akt pathway. Because the biochemical signals required for the construction of macropinosomes are also required for cell growth, and inhibition of macropinocytosis inhibits growth factor signalling to mTORC1, we propose that signalling by growth factor receptors is organized into stochastic, structure-dependent cascades of chemical reactions that both build a macropinosome and stimulate mTORC1. More generally, as discrete units of signal transduction, macropinosomes may be subject to feedback regulation by metabolism and cell dimensions. This article is part of the Theo Murphy meeting issue 'Macropinocytosis'.
Topics: Animals; Cell Proliferation; Endosomes; Humans; Pinocytosis; Signal Transduction
PubMed: 30967006
DOI: 10.1098/rstb.2018.0157 -
Trends in Cancer Jun 2021The mevalonate synthesis inhibitors, statins, are mainstay therapeutics for cholesterol management and cardiovascular health. Thirty years of research have uncovered... (Review)
Review
The mevalonate synthesis inhibitors, statins, are mainstay therapeutics for cholesterol management and cardiovascular health. Thirty years of research have uncovered supportive roles for the mevalonate pathway in numerous cellular processes that support oncogenesis, most recently macropinocytosis. Central to the diverse mechanisms of statin sensitivity is an acquired dependence on one mevalonate pathway output, protein geranylgeranylation. New chemical prenylation probes and the discovery of a novel geranylgeranyl transferase hold promise to deepen our understanding of statin mechanisms of action. Further, insights into statin selection and the counterproductive role of dietary geranylgeraniol highlight how we should assess statins in the clinic. Lastly, rational combination strategies preview how statins will enter the oncology toolbox.
Topics: Alkyl and Aryl Transferases; Animals; Antineoplastic Combined Chemotherapy Protocols; Cell Line, Tumor; Cell Proliferation; Cell Survival; Disease Models, Animal; Diterpenes; Farnesyltranstransferase; Feeding Behavior; Food-Drug Interactions; Humans; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Metabolic Networks and Pathways; Mevalonic Acid; Mice; Neoplasms; Pinocytosis; Polyisoprenyl Phosphates; Prenylation
PubMed: 33358111
DOI: 10.1016/j.trecan.2020.11.008 -
Cellular and Molecular Life Sciences :... Apr 2018The growth and proliferation of metazoan cells are driven by cellular nutrient status and by extracellular growth factors. Growth factor receptors on cell surfaces... (Review)
Review
The growth and proliferation of metazoan cells are driven by cellular nutrient status and by extracellular growth factors. Growth factor receptors on cell surfaces initiate biochemical signals that increase anabolic metabolism and macropinocytosis, an actin-dependent endocytic process in which relatively large volumes of extracellular solutes and nutrients are internalized and delivered efficiently into lysosomes. Macropinocytosis is prominent in many kinds of cancer cells, and supports the growth of cells transformed by oncogenic K-Ras. Growth factor receptor signaling and the overall metabolic status of the cell are coordinated in the cytoplasm by the mechanistic target-of-rapamycin complex-1 (mTORC1), which positively regulates protein synthesis and negatively regulates molecular salvage pathways such as autophagy. mTORC1 is activated by two distinct Ras-related small GTPases, Rag and Rheb, which associate with lysosomal membranes inside the cell. Rag recruits mTORC1 to the lysosomal surface where Rheb directly binds to and activates mTORC1. Rag is activated by both lysosomal luminal and cytosolic amino acids; Rheb activation requires phosphoinositide 3-kinase, Akt, and the tuberous sclerosis complex-1/2. Signals for activation of Rag and Rheb converge at the lysosomal membrane, and several lines of evidence support the idea that growth factor-dependent endocytosis facilitates amino acid transfer into the lysosome leading to the activation of Rag. This review summarizes evidence that growth factor-stimulated macropinocytosis is essential for amino acid-dependent activation of mTORC1, and that increased solute accumulation by macropinocytosis in transformed cells supports unchecked cell growth.
Topics: Amino Acids; Animals; Cell Proliferation; Humans; Intercellular Signaling Peptides and Proteins; Mechanistic Target of Rapamycin Complex 1; Pinocytosis; Signal Transduction
PubMed: 29119228
DOI: 10.1007/s00018-017-2710-y -
Cellular Microbiology Oct 2014Cellular engulfment of particles, cells or solutes displaces large domains of plasma membrane into intracellular membranous vacuoles. This transfer of membrane is... (Review)
Review
Cellular engulfment of particles, cells or solutes displaces large domains of plasma membrane into intracellular membranous vacuoles. This transfer of membrane is accompanied by major transitions of the phosphoinositide (PI) species that comprise the cytoplasmic face of membrane bilayers. Mapping of membrane PIs during engulfment reveals distinct patterns of protein and PI distributions associated with each stage of engulfment, which correspond with activities that regulate the actin cytoskeleton, membrane movements and vesicle secretion. Experimental manipulation of PI chemistry during engulfment indicates that PIs integrate organelle identity and orient signal transduction cascades within confined subdomains of membrane. These pathways are exploited by microbial pathogens to direct or redirect the engulfment process.
Topics: Actin Cytoskeleton; Bacteria; Biological Transport; Cell Membrane; Phagocytosis; Phosphatidylinositols; Pinocytosis; Signal Transduction; Vacuoles
PubMed: 25073505
DOI: 10.1111/cmi.12334 -
Drug Design, Development and Therapy 2017Antibody-drug conjugate (ADC) is a milestone in targeted cancer therapy that comprises of monoclonal antibodies chemically linked to cytotoxic drugs. Internalization of... (Review)
Review
Antibody-drug conjugate (ADC) is a milestone in targeted cancer therapy that comprises of monoclonal antibodies chemically linked to cytotoxic drugs. Internalization of ADC takes place via clathrin-mediated endocytosis, caveolae-mediated endocytosis, and pinocytosis. Conjugation strategies, endocytosis and intracellular trafficking optimization, linkers, and drugs chemistry present a great challenge for researchers to eradicate tumor cells successfully. This inventiveness of endocytosis and intracellular trafficking has given considerable momentum recently to develop specific antibodies and ADCs to treat cancer cells. It is significantly advantageous to emphasize the endocytosis and intracellular trafficking pathways efficiently and to design potent engineered conjugates and biological entities to boost efficient therapies enormously for cancer treatment. Current studies illustrate endocytosis and intracellular trafficking of ADC, protein, and linker strategies in unloading and also concisely evaluate practically applicable ADCs.
Topics: Animals; Antibodies, Monoclonal; Antineoplastic Agents; Humans; Immunoconjugates; Neoplasms
PubMed: 28814834
DOI: 10.2147/DDDT.S135571 -
Frontiers in Cell and Developmental... 2021The volumes of a cell [cell volume (CV)] and its organelles are adjusted by osmoregulatory processes. During pinocytosis, extracellular fluid volume equivalent to its CV... (Review)
Review
The volumes of a cell [cell volume (CV)] and its organelles are adjusted by osmoregulatory processes. During pinocytosis, extracellular fluid volume equivalent to its CV is incorporated within an hour and membrane area equivalent to the cell's surface within 30 min. Since neither fluid uptake nor membrane consumption leads to swelling or shrinkage, cells must be equipped with potent volume regulatory mechanisms. Normally, cells respond to outwardly or inwardly directed osmotic gradients by a volume decrease and increase, respectively, i.e., they shrink or swell but then try to recover their CV. However, when a cell death (CD) pathway is triggered, CV persistently decreases in isotonic conditions in apoptosis and it increases in necrosis. One type of CD associated with cell swelling is due to a dysfunctional pinocytosis. Methuosis, a non-apoptotic CD phenotype, occurs when cells accumulate too much fluid by macropinocytosis. In contrast to functional pinocytosis, in methuosis, macropinosomes neither recycle nor fuse with lysosomes but with each other to form giant vacuoles, which finally cause rupture of the plasma membrane (PM). Understanding methuosis longs for the understanding of the ionic mechanisms of cell volume regulation (CVR) and vesicular volume regulation (VVR). In nascent macropinosomes, ion channels and transporters are derived from the PM. Along trafficking from the PM to the perinuclear area, the equipment of channels and transporters of the vesicle membrane changes by retrieval, addition, and recycling from and back to the PM, causing profound changes in vesicular ion concentrations, acidification, and-most importantly-shrinkage of the macropinosome, which is indispensable for its proper targeting and cargo processing. In this review, we discuss ion and water transport mechanisms with respect to CVR and VVR and with special emphasis on pinocytosis and methuosis. We describe various aspects of the complex mutual interplay between extracellular and intracellular ions and ion gradients, the PM and vesicular membrane, phosphoinositides, monomeric G proteins and their targets, as well as the submembranous cytoskeleton. Our aim is to highlight important cellular mechanisms, components, and processes that may lead to methuotic CD upon their derangement.
PubMed: 34249909
DOI: 10.3389/fcell.2021.651982 -
Scientific Reports Oct 2023Vesicular transport driven by membrane trafficking systems conserved in eukaryotes is critical to cellular functionality and homeostasis. It is known that homotypic...
Vesicular transport driven by membrane trafficking systems conserved in eukaryotes is critical to cellular functionality and homeostasis. It is known that homotypic fusion and vacuole protein sorting (HOPS) and class C core endosomal vacuole tethering (CORVET) interact with Rab-GTPases and SNARE proteins to regulate vesicle transport, fusion, and maturation in autophagy and endocytosis pathways. In this study, we identified two novel "Hybrid" tethering complexes in mammalian cells in which one of the subunits of HOPS or CORVET is replaced with the subunit from the other. Substrates taken up by receptor-mediated endocytosis or pinocytosis were transported by distinctive pathways, and the newly identified hybrid complexes contributed to pinocytosis in the presence of HOPS, whereas receptor-mediated endocytosis was exclusively dependent on HOPS. Our study provides new insights into the molecular mechanisms of the endocytic pathway and the function of the vacuolar protein sorting-associated (VPS) protein family.
Topics: Animals; Vacuoles; Vesicular Transport Proteins; Endosomes; Endocytosis; SNARE Proteins; Membrane Fusion; Saccharomyces cerevisiae Proteins; Mammals
PubMed: 37907479
DOI: 10.1038/s41598-023-45418-3 -
The International Journal of... 2019Macropinocytosis is used by a variety of amoebae for feeding on liquid medium. The amoebae project cups and ruffles from their plasma membrane, driven by actin... (Review)
Review
Macropinocytosis is used by a variety of amoebae for feeding on liquid medium. The amoebae project cups and ruffles from their plasma membrane, driven by actin polymerization, and eventually fuse these back to the membrane, entrapping droplets of medium into internal vesicles. These vesicles are of up to several microns in diameter and are processed through the lysosomal digestive system to extract nutrients. Recognizably the same process is used in metazoan cells for a number of medically important purposes, including the pathological growth of cancer cells. We describe the discovery of macropinocytosis in Dictyostelium amoebae, its genetic regulation by the NF1 RasGAP, and the tools available for its investigation. Work on Dictyostelium over the last 30 years has identified many genes that may be important for macropinocytosis, which are listed at dictyBase, and give a basis for mechanistic studies. We argue that the actin cytoskeleton is organized for macropinocytosis by a signalling patch of PIP3 and active Ras and Rac, together with their regulatory proteins and effectors, including the protein kinases Akt and SGK. The Scar/WAVE complex is recruited to the periphery of this patch, triggering the formation of a hollow ring of protrusive actin polymerization, and eventually a macropinocytic cup. Major problems to be addressed include: the dynamics sustaining macropinocytic patches and the mechanism of Scar/WAVE recruitment; the mechanisms of cup closure and of membrane fusion; the ecological situations where amoebae feed by macropinocytosis; and the evolutionary relationship between macropinocytosis and growth factor signalling.
Topics: Actin Cytoskeleton; Actins; Animals; Cell Membrane; Dictyostelium; Lysosomes; Microscopy; Phosphatidylinositol 3-Kinases; Pinocytosis; Signal Transduction; rac GTP-Binding Proteins; ras Proteins
PubMed: 31840785
DOI: 10.1387/ijdb.190220rk