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The Journal of Biological Chemistry Nov 2019How cells utilize nutrients to produce the ATP needed for bioenergetic homeostasis has been well-characterized. What is less well-studied is how resting cells... (Review)
Review
How cells utilize nutrients to produce the ATP needed for bioenergetic homeostasis has been well-characterized. What is less well-studied is how resting cells metabolically shift from an ATP-producing catabolic metabolism to a metabolism that supports anabolic growth. In metazoan organisms, the discovery of growth factors and the ability of their receptors to induce new transcription and translation led to the hypothesis that the bioenergetic and synthetic demands of cell growth were primarily met through the replacement of nutrients consumed during net macromolecular synthesis, a demand-based system of nutrient uptake. Recent data have challenged this hypothesis. Instead, there is increasing evidence that cellular nutrient uptake is a push system. Growth factor signaling has been linked to direct stimulation of nutrient uptake. The ability of growth factor signaling to increase the uptake of glucose, lipids, and amino acids to levels that exceed a cell's bioenergetic and synthetic needs has been documented in a wide variety of settings. In some tissues, this leads to the storage of the excess nutrients in the form of glycogen or fat. In others, the excess is secreted as lactate and certain nonessential amino acids. When growth factor signaling stimulates nutrient uptake to levels that exceed a cell's bioenergetic needs, adaptive changes in intermediate metabolism lead to the production of anabolic precursors that fuel the net synthesis of protein, lipids, and nucleic acids. Through the increased production of these precursors, growth factor signaling provides a supply-side stimulation of cell growth and proliferation.
Topics: Animals; Cell Cycle; Glycolysis; Homeostasis; Humans; Intercellular Signaling Peptides and Proteins; Nutrients; Pinocytosis
PubMed: 31628187
DOI: 10.1074/jbc.AW119.008146 -
The FEBS Journal Sep 2020The quest for the effective treatment against coronavirus disease 2019 pneumonia caused by the severe acute respiratory syndrome (SARS)-coronavirus 2(CoV-2) coronavirus... (Review)
Review
The quest for the effective treatment against coronavirus disease 2019 pneumonia caused by the severe acute respiratory syndrome (SARS)-coronavirus 2(CoV-2) coronavirus is hampered by the lack of knowledge concerning the basic cell biology of the infection. Given that most viruses use endocytosis to enter the host cell, mechanistic investigation of SARS-CoV-2 infection needs to consider the diversity of endocytic pathways available for SARS-CoV-2 entry in the human lung epithelium. Taking advantage of the well-established methodology of membrane trafficking studies, this research direction allows for the rapid characterisation of the key cell biological mechanism(s) responsible for SARS-CoV-2 infection. Furthermore, 11 clinically approved generic drugs are identified as potential candidates for repurposing as blockers of several potential routes for SARS-CoV-2 endocytosis. More broadly, the paradigm of targeting a fundamental aspect of human cell biology to protect against infection may be advantageous in the context of future pandemic outbreaks.
Topics: Alveolar Epithelial Cells; Amiloride; Antiviral Agents; COVID-19; Caveolae; Chlorpromazine; Clathrin-Coated Vesicles; Drug Repositioning; Endocytosis; Endosomes; Humans; Itraconazole; Lung; Lysosomes; Nystatin; Pinocytosis; SARS-CoV-2; Vinblastine; Virus Internalization; COVID-19 Drug Treatment
PubMed: 32428379
DOI: 10.1111/febs.15369 -
Philosophical Transactions of the Royal... Feb 2019Macrophages respond to several stimuli by forming florid membrane ruffles that lead to fluid uptake by macropinocytosis. This type of induced macropinocytosis, executed... (Review)
Review
Macrophages respond to several stimuli by forming florid membrane ruffles that lead to fluid uptake by macropinocytosis. This type of induced macropinocytosis, executed by a variety of non-malignant and malignant cells, is initiated by transmembrane receptors and is involved in nutrient acquisition and mTOR signalling. However, macrophages also perform a unique type of constitutive ruffling and macropinocytosis that is dependent on the presence of extracellular calcium. Calcium-sensing receptors are responsible for this activity. This distinct form of macropinocytosis enables macrophages to continuously sample their microenvironment for antigenic molecules and for pathogen- and danger-associated molecular patterns, as part of their immune surveillance functions. Interestingly, even within the monocyte lineage, there are differences in macropinocytic ability that reflect the polarized functional roles of distinct macrophage subsets. This review discusses the shared and distinct features of both induced and constitutive macropinocytosis displayed by the macrophage lineage and their roles in physiology, immunity and pathophysiology. In particular, we analyse the role of macropinocytosis in the uptake of modified low-density lipoprotein (LDL) and its contribution to foam cell and atherosclerotic plaque formation. We propose a combined role of scavenger receptors and constitutive macropinocytosis in oxidized LDL uptake, a process we have termed 'receptor-assisted macropinocytosis'. This article is part of the Theo Murphy meeting issue 'Macropinocytosis'.
Topics: Animals; Atherosclerosis; Humans; Immunity; Macrophages; Pinocytosis
PubMed: 30967001
DOI: 10.1098/rstb.2018.0147 -
Scientific Reports Jan 2021Neutrophil activation is an integral process to acute inflammation and is associated with adverse clinical sequelae. Identification of neutrophil activation in real time... (Clinical Trial)
Clinical Trial
Neutrophil activation is an integral process to acute inflammation and is associated with adverse clinical sequelae. Identification of neutrophil activation in real time in the lungs of patients may permit biological stratification of patients in otherwise heterogenous cohorts typically defined by clinical criteria. No methods for identifying neutrophil activation in real time in the lungs of patients currently exist. We developed a bespoke molecular imaging probe targeting three characteristic signatures of neutrophil activation: pinocytosis, phagosomal alkalinisation, and human neutrophil elastase (HNE) activity. The probe functioned as designed in vitro and ex vivo. We evaluated optical endomicroscopy imaging of neutrophil activity using the probe in real-time at the bedside of healthy volunteers, patients with bronchiectasis, and critically unwell mechanically ventilated patients. We detected a range of imaging responses in vivo reflecting heterogeneity of condition and severity. We corroborated optical signal was due to probe function and neutrophil activation.
Topics: Animals; Bronchiectasis; Humans; Inflammation; Lung; Male; Neutrophil Activation; Neutrophils; Pancreatic Elastase; Pinocytosis; Spectrometry, Fluorescence
PubMed: 33441792
DOI: 10.1038/s41598-020-80083-w -
Nature Communications Oct 2015Macrophages play a pivotal role in tissue fibrogenesis, which underlies the pathogenesis of many end-stage chronic inflammatory diseases. MicroRNAs are key regulators of...
Macrophages play a pivotal role in tissue fibrogenesis, which underlies the pathogenesis of many end-stage chronic inflammatory diseases. MicroRNAs are key regulators of immune cell functions, but their roles in macrophage's fibrogenesis have not been characterized. Here we show that IL-4 and IL-13 induce miR-142-5p and downregulate miR-130a-3p in macrophages; these changes sustain the profibrogenic effect of macrophages. In vitro, miR-142-5p mimic prolongs STAT6 phosphorylation by targeting its negative regulator, SOCS1. Blocking miR-130a relieves its inhibition of PPARγ, which coordinates STAT6 signalling. In vivo, inhibiting miR-142-5p and increasing miR-130a-3p expression with locked nucleic acid-modified oligonucleotides inhibits CCL4-induced liver fibrosis and bleomycin-induced lung fibrosis in mice. Furthermore, macrophages from the tissue samples of patients with liver cirrhosis and idiopathic pulmonary fibrosis display increased miR-142-5p and decreased miR-130a-3p expression. Therefore, miR-142-5p and miR-130a-3p regulate macrophage profibrogenic gene expression in chronic inflammation.
Topics: Animals; Blotting, Northern; Blotting, Western; Chromatin Immunoprecipitation; Down-Regulation; Electrophoretic Mobility Shift Assay; Enzyme-Linked Immunosorbent Assay; Fibroblasts; Flow Cytometry; Gene Expression Regulation; Humans; Interleukin-13; Interleukin-4; Liver Cirrhosis; Macrophages; Mice; MicroRNAs; PPAR gamma; Phosphorylation; Pinocytosis; Pulmonary Fibrosis; Real-Time Polymerase Chain Reaction; STAT6 Transcription Factor; Suppressor of Cytokine Signaling 1 Protein; Suppressor of Cytokine Signaling Proteins; Up-Regulation
PubMed: 26436920
DOI: 10.1038/ncomms9523 -
Biochemical Society Transactions Dec 2020Endocytosis is an essential process where proteins and lipids are internalised from the plasma membrane in membrane-bound carriers, such as clathrin-coated vesicles.... (Review)
Review
Endocytosis is an essential process where proteins and lipids are internalised from the plasma membrane in membrane-bound carriers, such as clathrin-coated vesicles. Once internalised into the cell these vesicles fuse with the endocytic network where their contents are sorted towards degradation in the lysosome or recycling to their origin. Initially, it was thought that cargo recycling is a passive process, but in recent years the identification and characterisation of specialised recycling complexes has established a hitherto unthought-of level of complexity that actively opposes degradation. This review will summarise recent developments regarding the composition and regulation of the recycling machineries and their relationship with the degradative pathways of the endosome.
Topics: Actin Cytoskeleton; Amino Acid Motifs; Animals; Biological Transport; Cell Membrane; Clathrin; Clathrin-Coated Vesicles; Endocytosis; Endosomes; Golgi Apparatus; Humans; Ligands; Lysosomes; Models, Biological; Organelles; Phosphorylation; Pinocytosis; Protein Transport; Signal Transduction; Ubiquitin
PubMed: 33300959
DOI: 10.1042/BST20180255 -
Drug Delivery Dec 2021Native nanostructured lipoproteins such as low- and high-density lipoproteins (LDL and HDL) are powerful tools for the targeted delivery of drugs and imaging agents.... (Review)
Review
Native nanostructured lipoproteins such as low- and high-density lipoproteins (LDL and HDL) are powerful tools for the targeted delivery of drugs and imaging agents. While the cellular recognition of well-known HDL-based carriers occurs via interactions with an HDL receptor, the selective delivery and uptake of LDL particles by target cells are more complex. The most well-known mode of LDL-based delivery is via the interaction between apolipoprotein B (Apo-B) - the main protein of LDL - and the low-density lipoprotein receptor (LDLR). LDLR is expressed in the liver, adipocytes, and macrophages, and thus selectively delivers LDL carriers to these cells and tissues. Moreover, the elevated expression of LDLR in tumor cells indicates a role for LDL in the targeted delivery of chemotherapy drugs. In addition, chronic inflammation associated with hypercholesterolemia (i.e., high levels of endogenous LDL) can be abated by LDL carriers, which outcompete the deleterious oxidized LDL for uptake by macrophages. In this case, synthetic LDL nanocarriers act as 'eat-me' signals and exploit mechanisms of native LDL uptake for targeted drug delivery and imaging. Lastly, recent studies have shown that the delivery of LDL-based nanocarriers to macrophages via fluid-phase pinocytosis is a promising tool for atherosclerosis imaging. Hence, the present review summarizes the use of natural and synthetic LDL-based carriers for drug delivery and imaging and discusses various mechanisms of targeting.
Topics: Animals; Atherosclerosis; Drug Carriers; Humans; Hypercholesterolemia; Lipoproteins, HDL; Lipoproteins, LDL; Macrophages; Nanomedicine; Receptors, Lipoprotein
PubMed: 33594923
DOI: 10.1080/10717544.2021.1886199 -
Cancer Cell May 2021Su et al. demonstrate that upon inhibiting autophagy, an intracellular nutrient recycling pathway, pancreatic ductal adenocarcinoma cells upregulate NRF2-mediated...
Su et al. demonstrate that upon inhibiting autophagy, an intracellular nutrient recycling pathway, pancreatic ductal adenocarcinoma cells upregulate NRF2-mediated transcription of macropinocytosis pathway components, thereby triggering an alternate route for tumors to scavenge nutrients from extracellular sources. Accordingly, the combined inhibition of autophagy and macropinocytosis may improve cancer treatment.
Topics: Autophagy; Carcinoma, Pancreatic Ductal; Humans; NF-E2-Related Factor 2; Pancreatic Neoplasms; Pinocytosis
PubMed: 33974856
DOI: 10.1016/j.ccell.2021.03.011 -
Traffic (Copenhagen, Denmark) Dec 2018Macropinosomes, phagosomes and autolysosomes are comparatively large, quasi-spherical organelles that play essential functions in immunity and homeostasis. These... (Review)
Review
Macropinosomes, phagosomes and autolysosomes are comparatively large, quasi-spherical organelles that play essential functions in immunity and homeostasis. These vacuolar organelles are relatively short-lived, promptly fragmenting into smaller structures. Vacuolar resolution is mediated by tubulation and vesiculation, processes orchestrated by protein complexes that are recruited to highly curved membranes. Importantly, the surface-to-volume ratios of the tubules and vesicles generated during the resolution process are considerably larger than that of the parental vacuole. Because membranes under high hydrostatic tension resist deformation, an active, concomitant loss of volume is required to sustain the resolution process and may even initiate tubulation and vesiculation. Despite its fundamental role in membrane remodeling, the mechanisms that account for organellar volume loss are poorly understood, but are likely to involve the export of solutes followed by osmotically obliged water. In this review, we describe the principles and possible mechanisms underlying the resolution of organelles, with particular attention paid to the osmolytes they contain and the pathways mediating their exit.
Topics: Animals; Cytoplasmic Vesicles; Humans; Microtubules; Osmotic Pressure; Phagocytosis; Pinocytosis
PubMed: 30159984
DOI: 10.1111/tra.12614 -
ACS Nano May 2023The RAS-transformed cells utilize macropinocytosis to acquire amino acids to support their uncontrolled growth. However, targeting RAS to inhibit macropinocytosis...
The RAS-transformed cells utilize macropinocytosis to acquire amino acids to support their uncontrolled growth. However, targeting RAS to inhibit macropinocytosis remains a challenge. Here, we report that gold nanoparticles (GNP) inhibit macropinocytosis by decreasing KRAS activation. Using surface-modified and unmodified GNP, we showed that unmodified GNP specifically sequestered both wild-type and mutant KRAS and inhibited its activation, irrespective of growth factor stimulation, while surface-passivated GNP had no effect. Alteration of KRAS activation is reflected on downstream signaling cascades, macropinocytosis and tumor cell growth , and two independent preclinical human xenograft models of pancreatic cancer . The current study demonstrates NP-mediated inhibition of macropinocytosis and KRAS activation and provides translational opportunities to inhibit tumor growth in a number of cancers where activation of KRAS plays a major role.
Topics: Humans; Gold; Proto-Oncogene Proteins p21(ras); Metal Nanoparticles; Pinocytosis; Pancreatic Neoplasms; Cell Proliferation; Cell Line, Tumor; Mutation
PubMed: 37129853
DOI: 10.1021/acsnano.3c00920