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1.
Cell Mol Life Sci ; 79(6): 316, 2022 May 27.
Article in English | MEDLINE | ID: covidwho-1941440

ABSTRACT

AXL, a TAM receptor tyrosine kinase (RTK), and its ligand growth arrest-specific 6 (GAS6) are implicated in cancer metastasis and drug resistance, and cellular entry of viruses. Given this, AXL is an attractive therapeutic target, and its inhibitors are being tested in cancer and COVID-19 clinical trials. Still, astonishingly little is known about intracellular mechanisms that control its function. Here, we characterized endocytosis of AXL, a process known to regulate intracellular functions of RTKs. Consistent with the notion that AXL is a primary receptor for GAS6, its depletion was sufficient to block GAS6 internalization. We discovered that upon receptor ligation, GAS6-AXL complexes were rapidly internalized via several endocytic pathways including both clathrin-mediated and clathrin-independent routes, among the latter the CLIC/GEEC pathway and macropinocytosis. The internalization of AXL was strictly dependent on its kinase activity. In comparison to other RTKs, AXL was endocytosed faster and the majority of the internalized receptor was not degraded but rather recycled via SNX1-positive endosomes. This trafficking pattern coincided with sustained AKT activation upon GAS6 stimulation. Specifically, reduced internalization of GAS6-AXL upon the CLIC/GEEC downregulation intensified, whereas impaired recycling due to depletion of SNX1 and SNX2 attenuated AKT signaling. Altogether, our data uncover the coupling between AXL endocytic trafficking and AKT signaling upon GAS6 stimulation. Moreover, our study provides a rationale for pharmacological inhibition of AXL in antiviral therapy as viruses utilize GAS6-AXL-triggered endocytosis to enter cells.


Subject(s)
Endocytosis , Intercellular Signaling Peptides and Proteins , Proto-Oncogene Proteins , Receptor Protein-Tyrosine Kinases , Antiviral Agents/pharmacology , Antiviral Agents/therapeutic use , COVID-19/metabolism , COVID-19/therapy , Clathrin/metabolism , Clathrin/physiology , Endocytosis/drug effects , Endocytosis/genetics , Endocytosis/physiology , Humans , Intercellular Signaling Peptides and Proteins/genetics , Intercellular Signaling Peptides and Proteins/physiology , Neoplasms/metabolism , Neoplasms/therapy , Proto-Oncogene Proteins/antagonists & inhibitors , Proto-Oncogene Proteins/genetics , Proto-Oncogene Proteins/metabolism , Proto-Oncogene Proteins/physiology , Proto-Oncogene Proteins c-akt/genetics , Proto-Oncogene Proteins c-akt/metabolism , Proto-Oncogene Proteins c-akt/physiology , Receptor Protein-Tyrosine Kinases/antagonists & inhibitors , Receptor Protein-Tyrosine Kinases/genetics , Receptor Protein-Tyrosine Kinases/physiology
2.
Eur J Cell Biol ; 101(2): 151222, 2022 Apr.
Article in English | MEDLINE | ID: covidwho-1881962

ABSTRACT

Clathrin-mediated endocytosis (CME) is the major route through which cells internalise various substances and recycle membrane components. Via the coordinated action of many proteins, the membrane bends and invaginates to form a vesicle that buds off-along with its contents-into the cell. The contribution of the actin cytoskeleton to this highly dynamic process in mammalian cells is not well understood. Unlike in yeast, where there is a strict requirement for actin in CME, the significance of the actin cytoskeleton to mammalian CME is variable. However, a growing number of studies have established the actin cytoskeleton as a core component of mammalian CME, and our understanding of its contribution has been increasing at a rapid pace. In this review, we summarise the state-of-the-art regarding our understanding of the endocytic cytoskeleton, its physiological significance, and the questions that remain to be answered.


Subject(s)
Actin Cytoskeleton , Clathrin , Actin Cytoskeleton/metabolism , Actins/metabolism , Animals , Cell Membrane/metabolism , Clathrin/metabolism , Cytoskeleton/metabolism , Endocytosis/physiology , Mammals/metabolism , Saccharomyces cerevisiae/metabolism
3.
Virol Sin ; 37(3): 380-389, 2022 Jun.
Article in English | MEDLINE | ID: covidwho-1730151

ABSTRACT

The recent COVID-19 pandemic poses a global health emergency. Cellular entry of the causative agent SARS-CoV-2 is mediated by its spike protein interacting with cellular receptor-human angiotensin converting enzyme 2 (ACE2). Here, by using lentivirus based pseudotypes bearing spike protein, we demonstrated that entry of SARS-CoV-2 into host cells was dependent on clathrin-mediated endocytosis, and phosphoinositides played essential roles during this process. In addition, we showed that the intracellular domain and the catalytic activity of ACE2 were not required for efficient virus entry. Finally, we showed that the current predominant Delta variant, although with high infectivity and high syncytium formation, also entered cells through clathrin-mediated endocytosis. These results provide new insights into SARS-CoV-2 cellular entry and present proof of principle that targeting viral entry could be an effective way to treat different variant infections.


Subject(s)
Angiotensin-Converting Enzyme 2 , COVID-19 , Clathrin/metabolism , Endocytosis , Humans , Pandemics , Peptidyl-Dipeptidase A/genetics , Peptidyl-Dipeptidase A/metabolism , Protein Binding , SARS-CoV-2 , Spike Glycoprotein, Coronavirus/genetics , Spike Glycoprotein, Coronavirus/metabolism , Virus Internalization
4.
Biochem Biophys Res Commun ; 587: 69-77, 2022 01 08.
Article in English | MEDLINE | ID: covidwho-1540389

ABSTRACT

The clathrin coat assembly protein AP180 drives endocytosis, which is crucial for numerous physiological events, such as the internalization and recycling of receptors, uptake of neurotransmitters and entry of viruses, including SARS-CoV-2, by interacting with clathrin. Moreover, dysfunction of AP180 underlies the pathogenesis of Alzheimer's disease. Therefore, it is important to understand the mechanisms of assembly and, especially, disassembly of AP180/clathrin-containing cages. Here, we identified AP180 as a novel phosphatidic acid (PA)-binding protein from the mouse brain. Intriguingly, liposome binding assays using various phospholipids and PA species revealed that AP180 most strongly bound to 1-stearoyl-2-docosahexaenoyl-PA (18:0/22:6-PA) to a comparable extent as phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), which is known to associate with AP180. An AP180 N-terminal homology domain (1-289 aa) interacted with 18:0/22:6-PA, and a lysine-rich motif (K38-K39-K40) was essential for binding. The 18:0/22:6-PA in liposomes in 100 nm diameter showed strong AP180-binding activity at neutral pH. Notably, 18:0/22:6-PA significantly attenuated the interaction of AP180 with clathrin. However, PI(4,5)P2 did not show such an effect. Taken together, these results indicate the novel mechanism by which 18:0/22:6-PA selectively regulates the disassembly of AP180/clathrin-containing cages.


Subject(s)
Clathrin/metabolism , Docosahexaenoic Acids/metabolism , Monomeric Clathrin Assembly Proteins/metabolism , Phosphatidic Acids/metabolism , Animals , Binding Sites , Brain/metabolism , COVID-19/metabolism , COVID-19/virology , Cell Line , Clathrin/chemistry , Docosahexaenoic Acids/chemistry , Endocytosis/physiology , Host Microbial Interactions/physiology , Humans , Mice , Monomeric Clathrin Assembly Proteins/chemistry , Monomeric Clathrin Assembly Proteins/genetics , Phosphatidic Acids/chemistry , Protein Binding , Protein Interaction Domains and Motifs , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , SARS-CoV-2/physiology , Virus Internalization
5.
J Virol ; 95(24): e0134521, 2021 11 23.
Article in English | MEDLINE | ID: covidwho-1441856

ABSTRACT

Porcine deltacoronavirus (PDCoV), an emerging enteropathogenic coronavirus, causes serious diarrhea in suckling piglets and has the potential for cross-species transmission. Although extensive studies have been reported on the biology and pathogenesis of PDCoV, the mechanisms by which PDCoV enters cells are not well characterized. In this study, we investigated how PDCoV enters IPI-2I cells, a line of porcine intestinal epithelial cells derived from pig ileum. Immunofluorescence assays, small interfering RNA (siRNA) interference, specific pharmacological inhibitors, and dominant negative mutation results revealed that PDCoV entry into IPI-2I cells depended on clathrin, dynamin, and a low-pH environment but was independent of caveolae. Specific inhibition of phosphatidylinositol 3-kinase (PI3K) and the Na+/H+ exchanger (NHE) revealed that PDCoV entry involves macropinocytosis and depends on NHE rather than on PI3K. Additionally, Rab5 and Rab7, but not Rab11, regulated PDCoV endocytosis. This is the first study to demonstrate that PDCoV uses clathrin-mediated endocytosis and macropinocytosis as alternative endocytic pathways to enter porcine intestinal epithelial cells. We also discussed the entry pathways of PDCoV into other porcine cell lines. Our findings reveal the entry mechanisms of PDCoV and provide new insight into the PDCoV life cycle. IMPORTANCE An emerging enteropathogenic coronavirus, PDCoV, has the potential for cross-species transmission, attracting extensive attenuation. Characterizing the detailed process of PDCoV entry into cells will deepen our understanding of the viral infection and pathogenesis and provide clues for therapeutic intervention against PDCoV. With the objective, we used complementary approaches to dissect the process in PDCoV-infected IPI-2I cells, a line of more physiologically relevant intestinal epithelial cells to PDCoV infection in vivo. Here, we demonstrate that PDCoV enters IPI-2I cells via macropinocytosis, which does not require a specific receptor, and clathrin-mediated endocytosis, which requires a low-pH environment and dynamin, while a caveola-mediated endocytic pathway is used by PDCoV to enter swine testicular (ST) cells and porcine kidney (LLC-PK1) cells. These findings provide a molecular detail of the cellular entry pathways of PDCoV and may direct us toward novel antiviral drug development.


Subject(s)
Coronavirus Infections/virology , Deltacoronavirus/physiology , Dynamins/metabolism , Endocytosis , Epithelial Cells/virology , Animals , Cell Line , Cell Survival , Clathrin/metabolism , Coronavirus/genetics , Hydrogen-Ion Concentration , Ileum/virology , Kidney/virology , Phosphatidylinositol 3-Kinases/metabolism , Pinocytosis , RNA, Small Interfering/metabolism , Swine , Swine Diseases/virology , Virus Internalization , rab5 GTP-Binding Proteins/metabolism
6.
PLoS Pathog ; 17(7): e1009706, 2021 07.
Article in English | MEDLINE | ID: covidwho-1305581

ABSTRACT

Many viruses utilize the host endo-lysosomal network for infection. Tracing the endocytic itinerary of SARS-CoV-2 can provide insights into viral trafficking and aid in designing new therapeutic strategies. Here, we demonstrate that the receptor binding domain (RBD) of SARS-CoV-2 spike protein is internalized via the pH-dependent CLIC/GEEC (CG) endocytic pathway in human gastric-adenocarcinoma (AGS) cells expressing undetectable levels of ACE2. Ectopic expression of ACE2 (AGS-ACE2) results in RBD traffic via both CG and clathrin-mediated endocytosis. Endosomal acidification inhibitors like BafilomycinA1 and NH4Cl, which inhibit the CG pathway, reduce the uptake of RBD and impede Spike-pseudoviral infection in both AGS and AGS-ACE2 cells. The inhibition by BafilomycinA1 was found to be distinct from Chloroquine which neither affects RBD uptake nor alters endosomal pH, yet attenuates Spike-pseudovirus entry. By screening a subset of FDA-approved inhibitors for functionality similar to BafilomycinA1, we identified Niclosamide as a SARS-CoV-2 entry inhibitor. Further validation using a clinical isolate of SARS-CoV-2 in AGS-ACE2 and Vero cells confirmed its antiviral effect. We propose that Niclosamide, and other drugs which neutralize endosomal pH as well as inhibit the endocytic uptake, could provide broader applicability in subverting infection of viruses entering host cells via a pH-dependent endocytic pathway.


Subject(s)
COVID-19/drug therapy , COVID-19/virology , SARS-CoV-2/drug effects , SARS-CoV-2/pathogenicity , Virus Internalization/drug effects , Ammonium Chloride/pharmacology , Angiotensin-Converting Enzyme 2/genetics , Angiotensin-Converting Enzyme 2/physiology , Animals , Antiviral Agents/administration & dosage , Antiviral Agents/pharmacology , Cell Line , Chlorocebus aethiops , Chloroquine/pharmacology , Clathrin/metabolism , Drug Synergism , Endocytosis/drug effects , Endocytosis/physiology , Endosomes/drug effects , Endosomes/metabolism , Humans , Hydrogen-Ion Concentration/drug effects , Hydroxychloroquine/administration & dosage , Macrolides/pharmacology , Niclosamide/administration & dosage , Niclosamide/pharmacology , Protein Binding/drug effects , Protein Domains , SARS-CoV-2/physiology , Spike Glycoprotein, Coronavirus/chemistry , Spike Glycoprotein, Coronavirus/physiology , Vero Cells
7.
mBio ; 12(2)2021 03 30.
Article in English | MEDLINE | ID: covidwho-1160040

ABSTRACT

Coronaviruses (CoVs) have caused severe diseases in humans and animals. Endocytic pathways, such as clathrin-mediated endocytosis (CME) and caveolae-mediated endocytosis (CavME), play an important role for CoVs to penetrate the cell membrane barrier. In this study, a novel CoV entry manner is unraveled in which clathrin and caveolae can cooperatively mediate endocytosis of porcine epidemic diarrhea coronavirus (PEDV). Using multicolor live-cell imaging, the dynamics of the fluorescently labeled clathrin structures, caveolae structures, and PEDV were dissected. During CavME of PEDV, we found that clathrin structures can fuse with caveolae near the cell plasma membrane, and the average time of PEDV penetrating the cell membrane was within ∼3 min, exhibiting a rapid course of PEDV entry. Moreover, based on the dynamic recruitment of clathrin and caveolae structures and viral motility, the direct evidence also shows that about 20% of PEDVs can undergo an abortive entry via CME and CavME. Additionally, the dynamic trafficking of PEDV from clathrin and caveolae structures to early endosomes, and from early endosomes to late endosomes, and viral fusion were directly dissected, and PEDV fusion mainly occurred in late endosomes within ∼6.8 min after the transport of PEDV to late endosomes. Collectively, this work systematically unravels the early steps of PEDV infection, which expands our understanding of the mechanism of CoV infection.IMPORTANCE Emerging and re-emerging coronaviruses cause serious human and animal epidemics worldwide. For many enveloped viruses, including coronavirus, it is evident that breaking the plasma membrane barrier is a pivotal and complex process, which contains multiple dynamic steps. Although great efforts have been made to understand the mechanisms of coronavirus endocytic pathways, the direct real-time imaging of individual porcine epidemic diarrhea coronavirus (PEDV) internalization has not been achieved yet. In this study, we not only dissected the kinetics of PEDV entry via clathrin-mediated endocytosis and caveolae-mediated endocytosis and the kinetics of endosome trafficking and viral fusion but also found a novel productive coronavirus entry manner in which clathrin and caveolae can cooperatively mediate endocytosis of PEDV. Moreover, we uncovered the existence of PEDV abortive endocytosis. In summary, the productive PEDV entry via the cooperation between clathrin and caveolae structures and the abortive endocytosis of PEDV provide new insights into coronavirus penetrating the plasma membrane barrier.


Subject(s)
Caveolae/metabolism , Clathrin/metabolism , Endocytosis/physiology , Porcine epidemic diarrhea virus/metabolism , Virus Internalization , Animals , Cell Line , Cell Membrane/virology , Chlorocebus aethiops , Coronavirus Infections , Swine , Swine Diseases/virology , Vero Cells
8.
FASEB J ; 34(3): 4653-4669, 2020 03.
Article in English | MEDLINE | ID: covidwho-832736

ABSTRACT

Transmissible gastroenteritis virus (TGEV) is a swine enteropathogenic coronavirus that causes significant economic losses in swine industry. Current studies on TGEV internalization mainly focus on viral receptors, but the internalization mechanism is still unclear. In this study, we used single-virus tracking to obtain the detailed insights into the dynamic events of the TGEV internalization and depict the whole sequential process. We observed that TGEVs could be internalized through clathrin- and caveolae-mediated endocytosis, and the internalization of TGEVs was almost completed within ~2 minutes after TGEVs attached to the cell membrane. Furthermore, the interactions of TGEVs with actin and dynamin 2 in real time during the TGEV internalization were visualized. To our knowledge, this is the first report that single-virus tracking technique is used to visualize the entire dynamic process of the TGEV internalization: before the TGEV internalization, with the assistance of actin, clathrin, and caveolin 1 would gather around the virus to form the vesicle containing the TGEV, and after ~60 seconds, dynamin 2 would be recruited to promote membrane fission. These results demonstrate that TGEVs enter ST cells via clathrin- and caveolae-mediated endocytic, actin-dependent, and dynamin 2-dependent pathways.


Subject(s)
Gastroenteritis, Transmissible, of Swine/metabolism , Gastroenteritis, Transmissible, of Swine/virology , Transmissible gastroenteritis virus/pathogenicity , Actins/metabolism , Animals , Caveolae/metabolism , Caveolin 1/metabolism , Cell Line , Cell Membrane/metabolism , Cell Membrane/physiology , Cell Membrane/virology , Clathrin/metabolism , Dynamin II/metabolism , Endocytosis/physiology , Membrane Fusion/physiology , Swine , Virus Internalization
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