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SNARE-mediated Fusion of Single Proteoliposomes with Tethered Supported Bilayers in a Microfluidic Flow Cell Monitored by Polarized TIRF Microscopy
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Rab11 promotes docking and fusion of multivesicular bodies in a calcium-dependent manner

Ariel Savina1, Claudio M Fader, María T Damiani

  • 1Laboratorio de Biología Celular y Molecular-Instituto de Histología y Embriología, Facultad de Ciencias Médicas, Universidad Nacional de Cuyo--CONICET, Mendoza, 5500, Argentina.

Traffic (Copenhagen, Denmark)
|January 7, 2005
PubMed

Insights

Calcium influx promotes multivesicular body (MVB) fusion and exosome release in K562 cells. Rab11 protein and calcium are key regulators of this process, influencing MVB development and secretion.

Area of Science:

  • Cell Biology
  • Membrane Trafficking
  • Exosome Biology

Background:

  • Multivesicular bodies (MVBs) are key intracellular structures involved in protein sorting and secretion.
  • Exosomes are released from cells via the fusion of MVBs with the plasma membrane.
  • The role of intracellular calcium in MVB development and exosome release remains incompletely understood.

Purpose of the Study:

  • To investigate the effect of increased cytosolic calcium on MVB development and exosome release in K562 cells.
  • To elucidate the involvement of Rab11 and calcium in the homotypic fusion of MVBs.

Main Methods:

  • K562 cells overexpressing GFP-Rab11 wild-type or mutants were treated with monensin to increase cytosolic calcium.
  • MVB morphology and enlargement were assessed.
  • Time-lapse confocal microscopy was used to observe MVB behavior in living cells.
  • Calcium chelators (BAPTA-AM) were employed to study calcium's role.

Main Results:

  • Increased cytosolic calcium caused significant enlargement of MVBs in cells expressing Rab11 wt or Rab11Q70L mutant.
  • This calcium-induced enlargement was blocked by BAPTA-AM.
  • Rab11-decorated MVBs were observed to be docked and ready for fusion, suggesting Rab11's role in tethering/docking.
  • Calcium was found to be essential for the final fusion step of MVBs.
  • Elevated intracellular calcium enhanced exosome secretion in Rab11 wt cells and rescued the inhibitory effect of Rab11 mutants.

Conclusions:

  • Rab11 plays a role in the tethering and docking of MVBs, preparing them for fusion.
  • Cytosolic calcium is critical for the homotypic fusion of MVBs.
  • Both Rab11 and calcium are integral components regulating MVB homotypic fusion and subsequent exosome release.

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