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Rab GTPases act in a regulated cascade during membrane fusion, helping the lipid bilayers mix. The Rab family of proteins are active when bound to GTP, and inactive when bound to GDP. Hence, they act as guanine nucleotide-dependent molecular switches. Rab-GTP recognizes and binds to long or short-range tethering proteins to capture the target vesicle. These tethers coordinate with SNAREs on the vesicle and the target membrane to assemble the trans SNARE complex that locks the mixing bilayers.
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Rab Proteins01:14

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Rab proteins constitute the largest family of monomeric GTPases, of which 70 members are present in humans. Rab proteins and their effectors regulate consecutive stages of vesicle transport such as vesicle transport, docking, and fusion to the correct recipient membrane.
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Ras and Rho are small monomeric GTPases that act downstream of receptor tyrosine kinase (RTK) and regulate various cellular processes. These GTPases switch between active and inactive states by binding to guanine nucleotides.
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Cell polarity is the asymmetric distribution of cellular and membrane components, making one side of the cell different from the other. This polarity is essential to many processes such as embryogenesis, axon migration, glucose transport across epithelial cells, and directional cell migration. A migrating cell responds to intracellular or extracellular signals via molecular cascades that reorganize the actin cytoskeleton to establish this polarity. In these cells, the Rho family proteins Cdc42,...
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The destabilization of microtubules can occur during different stages of the microtubule lifecycle, such as nucleation or elongation. It can take place at either end of the microtubule or in the microtubule lattices as a whole. The lifespan of individual microtubules within a cell varies according to the cell type and stage of the cell cycle. During interphase, the lifespan of the microtubule is about 30 minutes, while during cell division, it is about 15 minutes. In axonal microtubules of...
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Spatio-Temporal Manipulation of Small GTPase Activity at Subcellular Level and on Timescale of Seconds in Living Cells
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Rac1-PAK1 regulation of Rab11 cycling promotes junction destabilization.

Jennifer C Erasmus1, Kasia Smolarczyk1, Helena Brezovjakova1

  • 1National Heart and Lung Institute, Faculty of Medicine, Imperial College London, London, UK.

The Journal of Cell Biology
|April 29, 2021
PubMed
Summary
This summary is machine-generated.

Rac1 GTPase and its effector PAK1 drive cancer cell malignancy by internalizing E-cadherin via micropinocytosis. This process involves Rab GTPase regulation, impacting cell adhesion and motility.

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Area of Science:

  • Cell Biology
  • Molecular Oncology
  • Cancer Research

Background:

  • Rac1 GTPase is hyperactivated in tumors, contributing to malignancy.
  • Rac1's disruption of cell junctions involves its effector PAK1, but mechanisms remain unclear.

Purpose of the Study:

  • To elucidate the mechanisms by which Rac1 and PAK1 regulate E-cadherin and cell junctions.
  • To investigate the role of small GTPases in Rac1-mediated membrane remodeling.

Main Methods:

  • Studied E-cadherin internalization via micropinocytosis in a PAK1-dependent manner.
  • Investigated PAK1 phosphorylation of RabGDIβ and its association with Rab5 and Rab11.
  • Assessed the impact of Rab11 inhibition on E-cadherin levels.

Main Results:

  • E-cadherin is internalized via micropinocytosis dependent on PAK1, without catenin dissociation.
  • PAK1 phosphorylates RabGDIβ, promoting its association with Rab5 and Rab11, and Rab retrieval from membranes.
  • Rac1 activation leads to Rab11 activation, reducing surface E-cadherin levels.

Conclusions:

  • Rac1 activation reduces surface E-cadherin by increasing membrane uptake and counteracting Rab11-dependent delivery.
  • This crosstalk between small GTPases regulates membrane remodeling in epithelial cells.
  • Findings impact understanding of Rac1 and PAK1 roles in cancer progression and cell motility.