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Frontiers in Immunology 2021Phagocytosis is the cellular defense mechanism used to eliminate antigens derived from dysregulated or damaged cells, and microbial pathogens. Phagocytosis is therefore...
Phagocytosis is the cellular defense mechanism used to eliminate antigens derived from dysregulated or damaged cells, and microbial pathogens. Phagocytosis is therefore a pillar of innate immunity, whereby foreign particles are engulfed and degraded in lysolitic vesicles. In hexacorallians, phagocytic mechanisms are poorly understood, though putative anthozoan phagocytic cells (amoebocytes) have been identified histologically. We identify and characterize phagocytes from the coral and the sea anemone . Using fluorescence-activated cell sorting and microscopy, we show that distinct populations of phagocytic cells engulf bacteria, fungal antigens, and beads. In addition to pathogenic antigens, we show that phagocytic cells engulf self, damaged cells. We show that target antigens localize to low pH phagolysosomes, and that degradation is occurring within them. Inhibiting actin filament rearrangement interferes with efficient particle phagocytosis but does not affect small molecule pinocytosis. We also demonstrate that cellular markers for lysolitic vesicles and reactive oxygen species (ROS) correlate with hexacorallian phagocytes. These results establish a foundation for improving our understanding of hexacorallian immune cell biology.
Topics: Animals; Anthozoa; Biomarkers; Cytokines; Cytoplasmic Vesicles; Flow Cytometry; Hydrogen-Ion Concentration; Immunity, Innate; Phagocytes; Phagocytosis; Phagosomes; Sea Anemones
PubMed: 34381444
DOI: 10.3389/fimmu.2021.662803 -
Investigative Ophthalmology & Visual... Jan 2017Autophagy and macropinocytosis are processes that are vital for cellular homeostasis, and help cells respond to stress and take up large amounts of material,... (Review)
Review
Autophagy and macropinocytosis are processes that are vital for cellular homeostasis, and help cells respond to stress and take up large amounts of material, respectively. The limbal and corneal epithelia have the machinery necessary to carry out both processes; however, autophagy and macropinocytosis are relatively understudied in these two epithelia. In this Perspectives, we describe the basic principles behind macropinocytosis and autophagy, discuss how these two processes are regulated in the limbal and corneal epithelia, consider how these two processes impact on the physiology of limbal and corneal epithelia, and elaborate on areas of future research in autophagy and macropinocytosis as related to the limbal/corneal epithelia.
Topics: Animals; Autophagy; Epithelium, Corneal; Humans; Limbus Corneae; Pinocytosis
PubMed: 28118670
DOI: 10.1167/iovs.16-21111 -
Philosophical Transactions of the Royal... Feb 2019Macropinocytosis-the large-scale, non-specific uptake of fluid by cells-is used by Dictyostelium discoideum amoebae to obtain nutrients. These cells form circular... (Review)
Review
Macropinocytosis-the large-scale, non-specific uptake of fluid by cells-is used by Dictyostelium discoideum amoebae to obtain nutrients. These cells form circular ruffles around regions of membrane defined by a patch of phosphatidylinositol (3,4,5)-trisphosphate (PIP3) and the activated forms of the small G-proteins Ras and Rac. When this ruffle closes, a vesicle of the medium is delivered to the cell interior for further processing. It is accepted that PIP3 is required for efficient macropinocytosis. Here, we assess the roles of Ras and Rac in Dictyostelium macropinocytosis. Gain-of-function experiments show that macropinocytosis is stimulated by persistent Ras activation and genetic analysis suggests that RasG and RasS are the key Ras proteins involved. Among the activating guanine exchange factors (GEFs), GefF is implicated in macropinocytosis by an insertional mutant. The individual roles of Rho family proteins are little understood but activation of at least some may be independent of PIP3. This article is part of the Theo Murphy meeting issue 'Macropinocytosis'.
Topics: Dictyostelium; Monomeric GTP-Binding Proteins; Pinocytosis
PubMed: 30967009
DOI: 10.1098/rstb.2018.0150 -
Autophagy May 2017Macroautophagy/autophagy is vital for cellular homeostasis and helps cells respond to various stress situations. Macropinocytosis enables cells to nonselectively engulf... (Review)
Review
Macroautophagy/autophagy is vital for cellular homeostasis and helps cells respond to various stress situations. Macropinocytosis enables cells to nonselectively engulf and take up large volumes of fluid and is known to supply amino acids to cells. The stem cell-enriched limbal epithelium has the machinery necessary to carry out both autophagy and macropinocytosis; however, both processes are relatively understudied in this tissue. We have demonstrated that these processes are linked via MIR103-MIR107, a microRNA family that is limbal epithelial-preferred. Loss of MIR103-MIR107 causes the accumulation of large vacuoles that originate, in part, from a dysregulation in macropinocytosis via activation of SRC-RAS signaling. We found that these vacuoles were autophagic in nature and retained in cells due to inappropriate regulation of end-stage autophagy. Specifically, MIR103-MIR107 regulates diacylglycerol-PRKC/protein kinase C and CDK5 (cyclin dependent kinase 5) signaling, which enables DNM1 (dynamin 1) to function in vacuole clearance.
Topics: Animals; Autophagy; Epithelial Cells; Humans; MicroRNAs; Pinocytosis; Stem Cells; Vacuoles
PubMed: 28402214
DOI: 10.1080/15548627.2017.1287658 -
The FEBS Journal Nov 2017Macropinocytosis is a mechanism for the nonspecific bulk uptake and internalisation of extracellular fluid. This plays specific and distinct roles in diverse cell types... (Review)
Review
Macropinocytosis is a mechanism for the nonspecific bulk uptake and internalisation of extracellular fluid. This plays specific and distinct roles in diverse cell types such as macrophages, dendritic cells and neurons, by allowing cells to sample their environment, extract extracellular nutrients and regulate plasma membrane turnover. Macropinocytosis has recently been implicated in several diseases including cancer, neurodegenerative diseases and atherosclerosis. Uptake by macropinocytosis is also exploited by several intracellular pathogens to gain entry into host cells. Both capturing and subsequently processing large volumes of extracellular fluid poses a number of unique challenges for the cell. Macropinosome formation requires coordinated three-dimensional manipulation of the cytoskeleton to form shaped protrusions able to entrap extracellular fluid. The following maturation of these large vesicles then involves a complex series of membrane rearrangements to shrink and concentrate their contents, while delivering components required for digestion and recycling. Recognition of the diverse importance of macropinocytosis in physiology and disease has prompted a number of recent studies. In this article, we summarise advances in our understanding of both macropinosome formation and maturation, and seek to highlight the important unanswered questions.
Topics: Animals; Carrier Proteins; Cell Surface Extensions; Endosomes; Humans; Pinocytosis
PubMed: 28544479
DOI: 10.1111/febs.14115 -
Biochemical and Biophysical Research... Jun 2024Platelets endocytose many molecules from their environment. However, this process of pinocytosis in platelets is poorly understood. Key endocytic regulators such as...
Platelets endocytose many molecules from their environment. However, this process of pinocytosis in platelets is poorly understood. Key endocytic regulators such as dynamin, clathrin, CDC42 and Arf6 are expressed in platelets but their roles in pinocytosis is not known. Stimulated platelets form two subpopulations of pro-aggregatory and procoagulant platelets. The effect of stimulation on pinocytosis is also poorly understood. In this study, washed human platelets were treated with a range of endocytosis inhibitors and stimulated using different activators. The rate of pinocytosis was assessed using pHrodo green, a pH-sensitive 10 kDa dextran. In unstimulated platelets, pHrodo fluorescence increased over time and accumulated as intracellular puncta indicating constituently active pinocytosis. Stimulated platelets (both pro-aggregatory and procoagulant) had an elevated pinocytosis rate compared to unstimulated platelets. Dynamin inhibition blocked pinocytosis in unstimulated, pro-aggregatory and procoagulant platelets indicating that most platelet pinocytosis is dynamin dependent. Although pinocytosis was clathrin-independent in unstimulated and procoagulant populations, clathrin partially contributed to pinocytosis in pro-aggregatory platelets.
PubMed: 38870846
DOI: 10.1016/j.bbrc.2024.150250 -
The Journal of Cell Biology Jul 2021Actin organization underpins conserved functions at the leading edge of cells. In this issue, Yang et al. (2021. J. Cell Biol.https://doi.org/10.1083/jcb.202010096)...
Actin organization underpins conserved functions at the leading edge of cells. In this issue, Yang et al. (2021. J. Cell Biol.https://doi.org/10.1083/jcb.202010096) characterize Leep1 as a bi-functional regulator of migration and macropinocytosis through PIP3 and the Scar/WAVE complex.
Topics: Actins; Pinocytosis
PubMed: 34128957
DOI: 10.1083/jcb.202105141 -
Biomedicine & Pharmacotherapy =... Sep 2020Human epidermal growth factor receptor 2 (HER2) is overexpressed in 15-20% of patients with breast cancer. HER2 overexpression is the result of a genetic alteration and... (Review)
Review
PURPOSE
Human epidermal growth factor receptor 2 (HER2) is overexpressed in 15-20% of patients with breast cancer. HER2 overexpression is the result of a genetic alteration and this marker is associated with poor clinical outcomes. HER2-targeted therapy can significantly improve the prognosis of patients with either early or advanced HER2-positive breast cancer. One such therapy is the antibody drug conjugate (ADC) trastuzumab emtansine (T-DM1), a combination of trastuzumab and the cytotoxic antimicrotubule agent DM1. After T-DM1 binds HER2, DM1 is subsequently released into the cell. T-DM1 is generally well tolerated and has a relatively low incidence of adverse events. However, there are clinical concerns regarding T-DM1-induced high-grade thrombocytopenia.
METHODS
Here, we summarize the incidence of thrombocytopenia from several clinical trials and review experimental studies to explore the causes for T-DM1-induced thrombocytopenia. Progress in several other ADCs targeting HER2-positive breast cancer was also reviewed.
CONCLUSIONS
We conclude that T-DM1 uptake by megakaryocytes occurs through either Fcγ receptor binding or through pinocytosis, and we suggest several methods through which these processes could be interrupted to potentially improve the clinical safety of T-DM1. More generally, we recommend that toxicity should be carefully addressed during the development of ADCs.
Topics: Ado-Trastuzumab Emtansine; Animals; Antineoplastic Agents, Immunological; Breast Neoplasms; Female; Humans; Immunoconjugates; Incidence; Megakaryocytes; Pinocytosis; Receptors, IgG; Thrombocytopenia; Treatment Outcome
PubMed: 32570117
DOI: 10.1016/j.biopha.2020.110407 -
Frontiers in Neuroscience 2015The chemical and electrical microenvironment of neurons within the central nervous system is protected and segregated from the circulation by the vascular blood-brain... (Review)
Review
The chemical and electrical microenvironment of neurons within the central nervous system is protected and segregated from the circulation by the vascular blood-brain barrier. This barrier operates on the level of endothelial cells and includes regulatory crosstalk with neighboring pericytes, astrocytes, and neurons. Within this neurovascular unit, the endothelial cells form a formidable, highly regulated barrier through the presence of inter-endothelial tight junctions, the absence of fenestrations, and the almost complete absence of fluid-phase transcytosis. The potent psychostimulant drug methamphetamine transiently opens the vascular blood-brain barrier through either or both the modulation of inter-endothelial junctions and the induction of fluid-phase transcytosis. Direct action of methamphetamine on the vascular endothelium induces acute opening of the blood-brain barrier. In addition, striatal effects of methamphetamine and resultant neuroinflammatory signaling can indirectly lead to chronic dysfunction of the blood-brain barrier. Breakdown of the blood-brain barrier may exacerbate the neuronal damage that occurs during methamphetamine abuse. However, this process also constitutes a rare example of agonist-induced breakdown of the blood-brain barrier and the adjunctive use of methamphetamine may present an opportunity to enhance delivery of chemotherapeutic agents to the underlying neural tissue.
PubMed: 25999807
DOI: 10.3389/fnins.2015.00156 -
Molecular Cell Jun 2024Circular RNAs (circRNAs) are stable RNAs present in cell-free RNA, which may comprise cellular debris and pathogen genomes. Here, we investigate the phenomenon and...
Circular RNAs (circRNAs) are stable RNAs present in cell-free RNA, which may comprise cellular debris and pathogen genomes. Here, we investigate the phenomenon and mechanism of cellular uptake and intracellular fate of exogenous circRNAs. Human myeloid cells and B cells selectively internalize extracellular circRNAs. Macrophage uptake of circRNA is rapid, energy dependent, and saturable. CircRNA uptake can lead to translation of encoded sequences and antigen presentation. The route of internalization influences immune activation after circRNA uptake, with distinct gene expression programs depending on the route of RNA delivery. Genome-scale CRISPR screens and chemical inhibitor studies nominate macrophage scavenger receptor MSR1, Toll-like receptors, and mTOR signaling as key regulators of receptor-mediated phagocytosis of circRNAs, a dominant pathway to internalize circRNAs in parallel to macropinocytosis. These results suggest that cell-free circRNA serves as an "eat me" signal and danger-associated molecular pattern, indicating orderly pathways of recognition and disposal.
Topics: RNA, Circular; Humans; Macrophages; Signal Transduction; Phagocytosis; TOR Serine-Threonine Kinases; Animals; Toll-Like Receptors; B-Lymphocytes; Scavenger Receptors, Class A; Antigen Presentation; Pinocytosis; Mice
PubMed: 38761795
DOI: 10.1016/j.molcel.2024.04.022