bims-momema Biomed News
on Molecular mechanisms of macropinocytosis
Issue of 2022–04–10
eightteen papers selected by
Harilaos Filippakis, Harvard University
  1. Macropinocytosis and Cancer: From Tumor Stress to Signaling Pathways.
  2. KRAS Addiction Promotes Cancer Cell Adaptation in Harsh Microenvironment Through Macropinocytosis.
  3. KRASG12R-Independent Macropinocytosis in Pancreatic Cancer.
  4. Signaling Pathways that Regulate Macropinocytosis in Mammalian Cells.
  5. Wnt, GSK3, and Macropinocytosis.
  6. Functional Diversity of Macropinocytosis.
  7. An amino acid-defined diet impairs tumour growth in mice by promoting endoplasmic reticulum stress and mTOR inhibition.
  8. Extracellular ATP and Macropinocytosis: Their Interactive and Mutually Supportive Roles in Cell Growth, Drug Resistance, and EMT in Cancer.
  9. The Amoebal Model for Macropinocytosis.
  10. Metabolic profile of the Warburg effect as a tool for molecular prognosis and diagnosis of cancer.
  11. Roles for 3' Phosphoinositides in Macropinocytosis.
  12. Metabolic Reservoir Cycles in Cancer.
  13. Classification of KRAS-Activating Mutations and the Implications for Therapeutic Intervention.
  14. A novel anticancer pharmacological agent targeting mitochondrial complex I.
  15. Macropinocytosis and Cell Migration: Don't Drink and Drive….
  16. The PripA-TbcrA complex-centered Rab GAP cascade facilitates macropinosome maturation in Dictyostelium.
  17. ATP Recycling Fuels Sustainable Glycerol 3-Phosphate Formation in Synthetic Cells Fed by Dynamic Dialysis.
  18. Social experiences switch states of memory engrams through regulating hippocampal Rac1 activity.
  1. Subcell Biochem. 2022 ;98 15-40
    Macropinocytosis and Cancer: From Tumor Stress to Signaling Pathways.
    Guillem Lambies, Cosimo Commisso.
      Macropinocytosis is an evolutionarily conserved endocytic pathway that mediates the nonselective acquisition of extracellular material via large endocytic vesicles known as macropinosomes. In addition to other functions, this uptake pathway supports cancer cell metabolism through the uptake of nutrients. Cells harboring oncogene or tumor suppressor mutations are known to display heightened macropinocytosis, which confers to the cancer cells the ability to survive and proliferate despite the nutrient-scarce conditions of the tumor microenvironment. Thus, macropinocytosis is associated with cancer malignancy. Macropinocytic uptake can be induced in cancer cells by different stress stimuli, acting as an adaptive mechanism for the cells to resist stresses in the tumor milieu. Here, we review the cellular stresses that are known to promote macropinocytosis, as well as the underlying molecular mechanisms that drive this process.
    Keywords:  Cancer malignancy; Cell metabolism; Macropinocytosis; Nutrient scarcity; Nutrient uptake; Stress stimuli
    DOI:  https://doi.org/10.1007/978-3-030-94004-1_2
  2. Subcell Biochem. 2022 ;98 189-204
    KRAS Addiction Promotes Cancer Cell Adaptation in Harsh Microenvironment Through Macropinocytosis.
    Laetitia Seguin.
      KRAS is the most frequently mutated oncogene in cancer and despite intensive studies, attempts to develop effective therapies targeting KRAS or its downstream signaling have failed mostly due to the complexity of KRAS activation and function in cancer initiation and progression. Over the years, KRAS has been involved in several biological processes including cell survival, proliferation, and metabolism by promoting not only a favorable tumor environment but also a cell-microenvironment dialog to allow cancer cells to adapt to tumor microenvironment scarcity. One of the mechanisms involved in this adaption is KRAS-mediated macropinocytosis. Macropinocytosis is an evolutionarily conserved, large-scale, and nonselective form of endocytosis involving actin-driven cell membrane remodeling to engulf large amounts of extracellular fluids and proteins from the local environment. While macropinocytosis process has been known for decades, recent gain interest due to its regulation of KRAS-driven tumor growth in adverse microenvironments. By promoting extracellular protein and other macromolecules internalization, macropinocytosis provides a survival mechanism under nutrient scarce conditions and the potential for unrestricted tumor growth. Thus, a better understanding of macropinocytotic process is needed to develop alternative therapeutic strategies.
    Keywords:  Integrin; KRAS addiction; Macropinocytosis; Microenvironment sensing
    DOI:  https://doi.org/10.1007/978-3-030-94004-1_10
  3. Subcell Biochem. 2022 ;98 205-221
    KRASG12R-Independent Macropinocytosis in Pancreatic Cancer.
    G Aaron Hobbs, Channing J Der.
      Macropinocytosis is a critical route of nutrient acquisition in pancreatic cancer cells. Constitutive macropinocytosis is promoted by mutant KRAS, which activates the PI3Kα lipid kinase and RAC1, to drive membrane ruffling, macropinosome uptake and processing. However, our recent study on the KRASG12R mutant indicated the presence of a KRAS-independent mode of macropinocytosis in pancreatic cancer cell lines, thereby increasing the complexity of this process. We found that KRASG12R-mutant cell lines promote macropinocytosis independent of KRAS activity using PI3Kγ and RAC1, highlighting the convergence of regulation on RAC signaling. While macropinocytosis has been proposed to be a therapeutic target for the treatment of pancreatic cancer, our studies have underscored how little we understand about the activation and regulation of this metabolic process. Therefore, this review seeks to highlight the differences in macropinocytosis regulation in the two cellular subtypes while also highlighting the features that make the KRASG12R mutant atypical.
    Keywords:  KRAS; Macropinocytosis; Metabolism; Mutant-specific signaling; PI3K; Pancreatic cancer
    DOI:  https://doi.org/10.1007/978-3-030-94004-1_11
  4. Subcell Biochem. 2022 ;98 143-167
    Signaling Pathways that Regulate Macropinocytosis in Mammalian Cells.
    Wilhelm Palm.
      Macropinocytosis is an evolutionarily conserved endocytic pathway that mediates non-selective uptake of extracellular fluid in bulk. Macropinocytosis is initiated by localized polymerization of the actin cytoskeleton, which generates plasma membrane protrusions that enclose part of the environment into large endocytic vesicles. From amoebae to mammalian cells, the actin dynamics that drive macropinosome formation are regulated by a conserved set of intracellular signaling proteins including Ras superfamily GTPases and PI3-kinases. In mammalian cells, multiple upstream signaling pathways control activity of these core regulators in response to cell-extrinsic and cell-intrinsic stimuli. Growth factor signaling pathways play a central role in macropinocytosis induction. In addition, an increasing number of functionally diverse processes has been identified as macropinocytosis regulators, including several nutrient-sensing and developmental signaling pathways. Many of these signaling pathways have proto-oncogenic properties, and their dysregulation drives the high macropinocytic activity that is commonly observed in cancer cells. These regulatory principles illustrate how macropinocytosis is controlled by complex upstream inputs to exert diverse cellular functions in physiological and pathological contexts.
    Keywords:  AMPK; Macropinocytosis; PI3-kinase; Ras GTPase; developmental signaling; growth factor signaling; mTORC1; nutrient-sensing; oncogenic signaling
    DOI:  https://doi.org/10.1007/978-3-030-94004-1_8
  5. Subcell Biochem. 2022 ;98 169-187
    Wnt, GSK3, and Macropinocytosis.
    Nydia Tejeda-Muñoz, Edward M De Robertis.
      Here we review the regulation of macropinocytosis by Wnt growth factor signaling. Canonical Wnt signaling is normally thought of as a regulator of nuclear β-catenin, but emerging results indicate that there is much more than β-catenin to the Wnt pathway. Macropinocytosis is transiently regulated by EGF-RTK-Ras-PI3K signaling. Recent studies show that Wnt signaling provides for sustained acquisition of nutrients by macropinocytosis. Endocytosis of Wnt-Lrp6-Fz receptor complexes triggers the sequestration of GSK3 and components of the cytosolic destruction complex such as Axin1 inside multivesicular bodies (MVBs) through the action of the ESCRT machinery. Wnt macropinocytosis can be induced both by the transcriptional loop of stabilized β-catenin, and by the inhibition of GSK3 even in the absence of new protein synthesis. The cell is poised for macropinocytosis, and all it requires for triggering of Pak1 and the actin machinery is the inhibition of GSK3. Striking lysosomal acidification, which requires macropinocytosis, is induced by GSK3 chemical inhibitors or Wnt protein. Wnt-induced macropinocytosis requires the ESCRT machinery that forms MVBs. In cancer cells, mutations in the tumor suppressors APC and Axin1 result in extensive macropinocytosis, which can be reversed by restoring wild-type protein. In basal cellular conditions, GSK3 functions to constitutively repress macropinocytosis.
    Keywords:  Colorectal cancer; ESCRT; Endocytosis; GSK3; Hepatocellular carcinoma; Lysosome regulation; Macropinocytosis; Multivesicular bodies; Wnt-STOP
    DOI:  https://doi.org/10.1007/978-3-030-94004-1_9
  6. Subcell Biochem. 2022 ;98 3-14
    Functional Diversity of Macropinocytosis.
    Rajeev Mishra, Yamini Gupta, Garima Ghaley, Neil A Bhowmick.
      Eukaryotic cells are capable of internalizing different types of cargo by plasma membrane ruffling and forming vesicles in a process known as endocytosis. The most extensively characterized endocytic pathways are clathrin-coated pits, lipid raft/caveolae-mediated endocytosis, phagocytosis, and macropinocytosis. Macropinocytosis is unique among all the endocytic processes due to its nonselective internalization of extracellular fluid, solutes, and membrane in large endocytic vesicles known as macropinosomes with unique susceptibility toward Na+/H+ exchanger inhibitors. Range of cell types capable of macropinocytosis and known to play important role in different physiological processes, which include antigen presentation, nutrient sensing, migration, and signaling. Understanding the physiological function of macropinocytosis will be helpful in filling the gaps in our knowledge and which can be exploited to develop novel therapeutic targets. In this chapter, we discuss the different molecular mechanisms that initiate the process of macropinocytosis with special emphasis on proteins involved and their diversified role in different cell types.
    Keywords:  Clathrin; Endocytosis, Caveolae; Lipid rafts; Macropinocytosis; RAS
    DOI:  https://doi.org/10.1007/978-3-030-94004-1_1
  7. Mol Metab. 2022 Mar 30. pii: S2212-8778(22)00047-3. [Epub ahead of print] 101478
    An amino acid-defined diet impairs tumour growth in mice by promoting endoplasmic reticulum stress and mTOR inhibition.
    Maurizio Ragni, Chiara Ruocco, Laura Tedesco, Michele O Carruba, Alessandra Valerio, Enzo Nisoli.
       OBJECTIVE: Profound metabolic alterations characterize cancer development and, beyond glucose addiction, amino acid (AA) dependency is now recognized as a hallmark of tumour growth. Therefore, targeting the metabolic addiction of tumours by reprogramming their substrate utilization is an attractive therapeutic strategy. We hypothesized that a dietary approach targeted to stimulate oxidative metabolism could reverse the metabolic inflexibility of tumours and represent a proper adjuvant therapy.
    METHODS: We measured tumour development in xenografted mice fed with a designer, casein-deprived diet enriched in free essential amino acids (EAAs; SFA-EAA diet), or two control isocaloric, isolipidic, and isonitrogenous diets, identical to the SFA-EAA diet except for casein presence (SFA diet), or casein replacement by the free AA mixture designed on the AA profile of casein (SFA-CAA diet). Moreover, we investigated the metabolic, biochemical, and molecular effects of two mixtures that reproduce the AA composition of the SFA-EAA diet (i.e., EAAm) and SFA-CAA diet (i.e., CAAm) in diverse cancer and non-cancer cells.
    RESULTS: The SFA-EAA diet reduced tumour growth in vivo, promoted endoplasmic reticulum (ER) stress, and inhibited mechanistic/mammalian target of rapamycin (mTOR) activity in the tumours. Accordingly, in culture, the EAAm, but not the CAAm, activated apoptotic cell death in cancer cells without affecting the survival and proliferation of non-cancer cells. The EAAm increased branched-chain amino acid (BCAA) oxidation and decreased glycolysis, ATP levels, redox potential, and intracellular content of selective non-essential amino acids (NEAA) in cancer cells. The EAAm-induced NEAA starvation activated the GCN2-ATF4 stress pathway, leading to ER stress, mTOR inactivation, and apoptosis in cancer cells, unlike non-cancer cells.
    CONCLUSION: Together, these results confirm the efficacy of specific EAA mixtures in promoting cancer cells' death and suggest that manipulation of dietary EAA content and profile could be a valuable support to the standard chemotherapy for specific cancers.
    Keywords:  Branched-chain amino acids; Cancer metabolism; Essential amino acids; Glycolysis; Mechanistic/mammalian target of rapamycin; Mitochondria
    DOI:  https://doi.org/10.1016/j.molmet.2022.101478
  8. Subcell Biochem. 2022 ;98 61-83
    Extracellular ATP and Macropinocytosis: Their Interactive and Mutually Supportive Roles in Cell Growth, Drug Resistance, and EMT in Cancer.
    Maria Evers, Jingwen Song, Xiaozhuo Chen.
      Macropinocytosis is one of the major mechanisms by which cancer cells uptake extracellular nutrients from tumor microenvironment (TME) and plays very important roles in various steps of tumorigenesis. We previously reported the unexpected finding that intratumoral and extracellular ATP (eATP), as one of the major drastically upregulated extracellular nutrients and messengers in tumors, is taken up by cancer cells through macropinocytosis in large quantities and significantly contributing to cancer cell growth, survival, and increased resistance to chemo and target drugs. Inhibition of macropinocytosis substantially reduced eATP uptake by cancer cells and slowed down tumor growth in vivo. More recently, we have found the eATP also plays a very important role in inducing epithelial-to-mesenchymal transition (EMT), and that macropinocytosis is an essential facilitator in the induction. Thus, macropinocytosis and eATP, working in coordination, appear to play some previously unrecognized but very important roles in EMT and metastasis. As a result, they are likely to be interactive and communicative with each other, regulating each other's activity for various needs of host tumor cells. They are also likely to be an integral part of the future new anticancer therapeutic strategies. Moreover, it is undoubted that we have not identified all the important activities coordinated by ATP and macropinocytosis. This review describes our findings in how eATP and macropinocytosis work together to promote cancer cell growth, resistance, and EMT. We also list scientific challenges facing eATP research and propose to target macropinocytosis and eATP to reduce drug resistance and slow down metastasis.
    Keywords:  ABC transporters; ATP internalization; Cancer metabolism; Endocytosis; Epithelial–mesenchymal transition; Metastasis; Purinergic receptor signaling
    DOI:  https://doi.org/10.1007/978-3-030-94004-1_4
  9. Subcell Biochem. 2022 ;98 41-59
    The Amoebal Model for Macropinocytosis.
    Robert R Kay, Josiah Lutton, Helena Coker, Peggy Paschke, Jason S King, Till Bretschneider.
      Macropinocytosis is a relatively unexplored form of large-scale endocytosis driven by the actin cytoskeleton. Dictyostelium amoebae form macropinosomes from cups extended from the plasma membrane, then digest their contents and absorb the nutrients in the endo-lysosomal system. They use macropinocytosis for feeding, maintaining a high rate of fluid uptake that makes assay and experimentation easy. Mutants collected over the years identify cytoskeletal and signalling proteins required for macropinocytosis. Cups are organized around plasma membrane domains of intense PIP3, Ras and Rac signalling, proper formation of which also depends on the RasGAPs NF1 and RGBARG, PTEN, the PIP3-regulated protein kinases Akt and SGK and their activators PDK1 and TORC2, Rho proteins, plus other components yet to be identified. This PIP3 domain directs dendritic actin polymerization to the extending lip of macropinocytic cups by recruiting a ring of the SCAR/WAVE complex around itself and thus activating the Arp2/3 complex. The dynamics of PIP3 domains are proposed to shape macropinocytic cups from start to finish. The role of the Ras-PI3-kinase module in organizing feeding structures in unicellular organisms most likely predates its adoption into growth factor signalling, suggesting an evolutionary origin for growth factor signalling.
    Keywords:  Dictyostelium discoideum; Endocytosis; Macropinocytosis; NF1; PI3-kinase; PIP3; Ras; SCAR/WAVE
    DOI:  https://doi.org/10.1007/978-3-030-94004-1_3
  10. Expert Rev Mol Diagn. 2022 Apr 08.
    Metabolic profile of the Warburg effect as a tool for molecular prognosis and diagnosis of cancer.
    Gerardo M Nava, Luis Alberto Madrigal Perez.
       INTRODUCTION: Adaptations of eukaryotic cells to environmental changes are important for their survival. However, under some circumstances, microenvironmental changes promote that eukaryotic cells utilize a metabolic signature resembling a unicellular organism named the Warburg effect. Most cancer cells share the Warburg effect displaying lactic fermentation and high glucose uptake. The Warburg effect also induces a metabolic rewiring stimulating glutamine consumption and lipid synthesis, also considered cancer hallmarks. Amino acid metabolism alteration due to the Warburg effect increases plasma levels of proline and branched-chain amino acids in several cancer types. Proline and lipids are probably used as electron transfer molecules in carcinogenic cells. In addition, branched-chain amino acids fuel the Krebs cycle, protein synthesis, and signaling in cancer cells.
    AREAS COVERED: This review covers how metabolomics studies describe changes in some metabolites and proteins associated with the Warburg effect and related metabolic pathways.
    EXPERT OPINION: In this review, we analyze the metabolic signature of the Warburg effect and related phenotypes and propose some Warburg effect-related metabolites and proteins (lactate, glucose uptake, glucose transporters, glutamine, branched-chain amino acids, proline, and some lipogenic enzymes) as promising cancer biomarkers.
    Keywords:  Biomarker; Warburg effect; cancer; diagnosis; metabolism; molecular prognosis
    DOI:  https://doi.org/10.1080/14737159.2022.2065196
  11. Subcell Biochem. 2022 ;98 119-141
    Roles for 3' Phosphoinositides in Macropinocytosis.
    Joel A Swanson, Nobukazu Araki.
      The distinct movements of macropinosome formation and maturation have corresponding biochemical activities which occur in a defined sequence of stages and transitions between those stages. Each stage in the process is regulated by variously phosphorylated derivatives of phosphatidylinositol (PtdIns) which reside in the cytoplasmic face of the membrane lipid bilayer. PtdIns derivatives phosphorylated at the 3' position of the inositol moiety, called 3' phosphoinositides (3'PIs), regulate different stages of the sequence. 3'PIs are synthesized by numerous phosphoinositide 3'-kinases (PI3K) and other lipid kinases and phosphatases, which are themselves regulated by small GTPases of the Ras superfamily. The combined actions of these enzymes localize four principal species of 3'PI to distinct domains of the plasma membrane or to discrete organelles, with distinct biochemical activities confined to those domains. Phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3) and phosphatidylinositol (3,4)-bisphosphate (PtdIns(3,4)P2) regulate the early stages of macropinosome formation, which include cell surface ruffling and constrictions of circular ruffles which close into macropinosomes. Phosphatidylinositol 3-phosphate (PtdIns3P) regulates macropinosome fusion with other macropinosomes and early endocytic organelles. Phosphatidylinositol (3,5)-bisphosphate (PtdIns(3,5)P2) mediates macropinosome maturation and shrinkage, through loss of ions and water, and subsequent traffic to lysosomes. The different characteristic rates of macropinocytosis in different cell types indicate levels of regulation which may be governed by the cell's capacity to generate 3'PIs.
    Keywords:  Macrophage; Macropinosome closure; Phosphatidylinositol 3-kinase; Ruffling
    DOI:  https://doi.org/10.1007/978-3-030-94004-1_7
  12. Semin Cancer Biol. 2022 Apr 04. pii: S1044-579X(22)00079-7. [Epub ahead of print]
    Metabolic Reservoir Cycles in Cancer.
    Cissy Zhang, Addison Quinones, Anne Le.
      Cancer cells possess various biological processes to ensure survival and proliferation even under unfavorable conditions such as hypoxia, nutrient deprivation, and oxidative stress. One of the defining hallmarks of cancer cells is their ability to reprogram their metabolism to suit their needs. Building on over a decade of research in the field of cancer metabolism, numerous unique metabolic capabilities are still being discovered in the present day. One recent discovery in the field of cancer metabolism that was hitherto unexpected is the ability of cancer cells to store vital metabolites in forms that can be readily converted to glucose and glutamine for later use. We called these forms "metabolic reservoirs." While many studies have been conducted on storage molecules such as glycogen, triglyceride, and phosphocreatine (PCr), few have explored the concept of "metabolic reservoirs" for cancer as a whole. In this review, we will provide an overview of this concept, the previously known reservoirs including glycogen, triglyceride, and PCr, and the new discoveries made including the newly discovered reservoirs such as N-acetyl-aspartyl-glutamate (NAAG), lactate, and γ- aminobutyric acid (GABA). We will also discuss whether disrupting these reservoir cycles may be a new avenue for cancer treatment.
    Keywords:  Metabolic reservoir; N-acetyl-aspartyl-glutamate (NAAG); cancer metabolism; gamma aminobutyric acid (GABA); lactate
    DOI:  https://doi.org/10.1016/j.semcancer.2022.03.023
  13. Cancer Discov. 2022 Apr 01. 12(4): 913-923
    Classification of KRAS-Activating Mutations and the Implications for Therapeutic Intervention.
    Christian Johnson, Deborah L Burkhart, Kevin M Haigis.
      Members of the family of RAS proto-oncogenes, discovered just over 40 years ago, were among the first cancer-initiating genes to be discovered. Of the three RAS family members, KRAS is the most frequently mutated in human cancers. Despite intensive biological and biochemical study of RAS proteins over the past four decades, we are only now starting to devise therapeutic strategies to target their oncogenic properties. Here, we highlight the distinct biochemical properties of common and rare KRAS alleles, enabling their classification into functional subtypes. We also discuss the implications of this functional classification for potential therapeutic avenues targeting mutant subtypes.
    SIGNIFICANCE: Efforts in the recent past to inhibit KRAS oncogenicity have focused on kinases that function in downstream signal transduction cascades, although preclinical successes have not translated to patients with KRAS-mutant cancer. Recently, clinically effective covalent inhibitors of KRASG12C have been developed, establishing two principles that form a foundation for future efforts. First, KRAS is druggable. Second, each mutant form of KRAS is likely to have properties that make it uniquely druggable.
    DOI:  https://doi.org/10.1158/2159-8290.CD-22-0035
  14. Trends Pharmacol Sci. 2022 Apr 02. pii: S0165-6147(22)00057-8. [Epub ahead of print]
    A novel anticancer pharmacological agent targeting mitochondrial complex I.
    Gabriela Reyes-Castellanos, Alice Carrier.
      Targeting metabolic reprogramming has proven successful in oncology, but this field requires better identification of drugs that inhibit mitochondrial metabolism in cancer cells. Recent work from Dr Wolf's group reveals that the primary target of the antitumor compound SMIP004-7 is mitochondrial complex I (NDUFS2 subunit), inhibition of which promotes anticancer immune surveillance.
    Keywords:  anticancer therapies; cancer metabolism; complex I; mitochondria; oxidative phosphorylation system; tumor microenvironment
    DOI:  https://doi.org/10.1016/j.tips.2022.03.007
  15. Subcell Biochem. 2022 ;98 85-102
    Macropinocytosis and Cell Migration: Don't Drink and Drive….
    María-Graciela Delgado, Claudia A Rivera, Ana-María Lennon-Duménil.
      Macropinocytosis is a nonspecific mechanism by which cells compulsively "drink" the surrounding extracellular fluids in order to feed themselves or sample the molecules therein, hence gaining information about their environment. This process is cell-intrinsically incompatible with the migration of many cells, implying that the two functions are antagonistic. The migrating cell uses a molecular switch to stop and explore its surrounding fluid by macropinocytosis, after which it employs the same molecular machinery to start migrating again to examine another location. This cycle of migration/macropinocytosis allows cells to explore tissues, and it is key to a range of physiological processes. Evidence of this evolutionarily conserved antagonism between the two processes can be found in several cell types-immune cells, for example, being particularly adept-and ancient organisms (e.g., the social amoeba Dictyostelium discoideum). How macropinocytosis and migration are negatively coupled is the subject of this chapter.
    Keywords:  Actin; Arp2/3 complex; Barotaxis; Cytoskeleton; Dendritic cell; Macropinocytosis; Migration; Myosin II; Small GTPases
    DOI:  https://doi.org/10.1007/978-3-030-94004-1_5
  16. Nat Commun. 2022 Apr 04. 13(1): 1787
    The PripA-TbcrA complex-centered Rab GAP cascade facilitates macropinosome maturation in Dictyostelium.
    Hui Tu, Zhimeng Wang, Ye Yuan, Xilin Miao, Dong Li, Hu Guo, Yihong Yang, Huaqing Cai.
      Macropinocytosis, an evolutionarily conserved mechanism mediating nonspecific bulk uptake of extracellular fluid, has been ascribed diverse functions. How nascent macropinosomes mature after internalization remains largely unknown. By searching for proteins that localize on macropinosomes during the Rab5-to-Rab7 transition stage in Dictyostelium, we uncover a complex composed of two proteins, which we name PripA and TbcrA. We show that the Rab5-to-Rab7 conversion involves fusion of Rab5-marked early macropinosomes with Rab7-marked late macropinosomes. PripA links the two membrane compartments by interacting with PI(3,4)P2 and Rab7. In addition, PripA recruits TbcrA, which acts as a GAP, to turn off Rab5. Thus, the conversion to Rab7 is linked to inactivation of the upstream Rab5. Consistently, disruption of either pripA or tbcrA impairs Rab5 inactivation and macropinocytic cargo processing. Therefore, the PripA-TbcrA complex is the central component of a Rab GAP cascade that facilitates programmed Rab switch and efficient cargo trafficking during macropinosome maturation.
    DOI:  https://doi.org/10.1038/s41467-022-29503-1
  17. ACS Synth Biol. 2022 Apr 04.
    ATP Recycling Fuels Sustainable Glycerol 3-Phosphate Formation in Synthetic Cells Fed by Dynamic Dialysis.
    Eleonora Bailoni, Bert Poolman.
      The bottom-up construction of an autonomously growing, self-reproducing cell represents a great challenge for synthetic biology. Synthetic cellular systems are envisioned as out-of-equilibrium enzymatic networks encompassed by a selectively open phospholipid bilayer allowing for protein-mediated communication; internal metabolite recycling is another key aspect of a sustainable metabolism. Importantly, gaining tight control over the external medium is essential to avoid thermodynamic equilibrium due to nutrient depletion or waste buildup in a closed compartment (e.g., a test tube). Implementing a sustainable strategy for phospholipid biosynthesis is key to expanding the cellular boundaries. However, phospholipid biosynthesis is currently limited by substrate availability, e.g., of glycerol 3-phosphate, the essential core of phospholipid headgroups. Here, we reconstitute an enzymatic network for sustainable glycerol 3-phosphate synthesis inside large unilamellar vesicles. We exploit the Escherichia coli glycerol kinase GlpK to synthesize glycerol 3-phosphate from externally supplied glycerol. We fuel phospholipid headgroup formation by sustainable l-arginine breakdown. In addition, we design and characterize a dynamic dialysis setup optimized for synthetic cells, which is used to control the external medium composition and to achieve sustainable glycerol 3-phosphate synthesis.
    Keywords:  ATP recycling; continuous-flow dialysis; glycerol 3-phosphate; phospholipid headgroup synthesis; selectively open system; sustainable minimal metabolism
    DOI:  https://doi.org/10.1021/acssynbio.2c00075
  18. Proc Natl Acad Sci U S A. 2022 Apr 12. 119(15): e2116844119
    Social experiences switch states of memory engrams through regulating hippocampal Rac1 activity.
    Bo Lei, Li Lv, Shiqiang Hu, Yikai Tang, Yi Zhong.
      SignificanceIt is well known that silent memory engrams in pathological or artificial conditions can be artificially switched into the latent state for retrieval by natural recall cues. Thus, physiological strategies that depend on the underlying molecular mechanisms for switching between silent state and latent state are a subject for investigation. Here, we show that social experiences stimulated switching between latent and silent engrams to achieve flexible memory accessibility and also reveal the basic molecular mechanism of: 1) social reward turning silent engram to latent via suppression of Rac1 activity in CA1 neurons of the hippocampus; and 2) social stress switching latent memory engram into silent through activating Rac1. Together, this work demonstrates emotion-driven bidirectional switching between latent and silent engrams.
    Keywords:  Rac1; engram; forgetting; social reward; social stress
    DOI:  https://doi.org/10.1073/pnas.2116844119
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