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Related Concept Videos

Pinocytosis00:38

Pinocytosis

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Cells use energy-requiring bulk transport mechanisms to transfer large particles or large numbers of small particles into or out of the cell. The cells envelop the particles in spherical membranes called vesicles or vacuoles. Vesicles that transport material into the cell are built from the cell membrane. These vesicles encapsulate external molecules and transport them into the cell in a process called endocytosis.
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Phagocytosis00:41

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Cells pull particles inward and engulf them in spherical vesicles in an energy-requiring process called endocytosis. Phagocytosis ("cellular eating") is one of three major types of endocytosis. Cells use phagocytosis to take in large objects, such as other cells (or their debris), bacteria, and even viruses.
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Eukaryotic cells use different mechanisms to eliminate toxic waste obsolete and worn-out substances. Lysosomes play a pivotal role in this, and hence, these substances are carried to the lysosome from other parts of the cell and extracellular space through different pathways. The most elaborately studied pathways to the lysosome are the endocytic pathways.
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Eukaryotic cells acquire nutrients for growth and proliferation. Nutrients and other molecules that require degradation are internalized from the extracellular space by a process called endocytosis. The term ‘endocytosis' was first coined by Christian de Duve in 1963.
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Vesicle budding is orchestrated by distinct cytosolic proteins such as adaptor proteins, coat proteins, and GTPases. To initiate vesicle budding, membrane-bending proteins containing crescent-shaped BAR domains bind to the lipid heads in the bilayer and distort the membrane to form a protein-coated vesicle bud. Adaptors proteins such as AP2 for clathrin-coated vesicles can nucleate on the deformed membrane. Finally, coat proteins such as clathrin or COPI and COPII assemble into a coat forming...
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Introduction to Membrane Traffic

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The ER, Golgi apparatus, endosomes, and lysosomes work in tandem to modify, sort, and package proteins and lipids. An integrated membrane trafficking network facilitates the back and forth shuttling of molecules within different organelles in the same cell or across the cell membrane.
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The Amoebal Model for Macropinocytosis.

Robert R Kay1, Josiah Lutton2, Helena Coker3

  • 1MRC Laboratory of Molecular Biology, Cambridge, UK. rrk@mrc-lmb.cam.ac.uk.

Sub-Cellular Biochemistry
|April 5, 2022
PubMed
Summary

Dictyostelium amoebae use macropinocytosis for feeding, engulfing large fluid volumes. Actin cytoskeleton dynamics and specific signaling pathways, including PIP3 and Ras, are crucial for forming and shaping these feeding structures.

Keywords:
Dictyostelium discoideumEndocytosisMacropinocytosisNF1PI3-kinasePIP3RasSCAR/WAVE

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Area of Science:

  • Cell Biology
  • Biochemistry
  • Molecular Biology

Background:

  • Macropinocytosis is a large-scale endocytosis process driven by the actin cytoskeleton.
  • Dictyostelium amoebae utilize macropinocytosis for nutrient uptake, facilitating experimental studies due to high fluid uptake rates.

Purpose of the Study:

  • To identify and characterize the cytoskeletal and signaling proteins involved in macropinocytosis in Dictyostelium.
  • To elucidate the molecular mechanisms governing the formation and dynamics of macropinocytic cups.

Main Methods:

  • Analysis of mutant strains to identify essential genes and proteins.
  • Investigation of signaling pathways, including phosphoinositide 3-kinase (PI3K) and Ras GTPases, at the plasma membrane.
  • Microscopy and biochemical assays to study actin polymerization and membrane dynamics.

Main Results:

  • Macropinocytic cups form around plasma membrane domains enriched in phosphoinositide 3-phosphate (PIP3), Ras, and Rac signaling.
  • Proteins such as NF1, RGP2, PTEN, Akt, SGK, PDK1, TORC2, and Rho proteins are critical for proper cup formation.
  • PIP3 domains recruit the SCAR/WAVE complex, activating the Arp2/3 complex for dendritic actin polymerization, which shapes the cups.

Conclusions:

  • The dynamics of PIP3 domains are central to shaping macropinocytic cups throughout the process.
  • The Ras-PI3-kinase module's role in organizing feeding structures in unicellular organisms likely represents an ancient evolutionary origin for growth factor signaling pathways.