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Homotypic fusion between aggregated lysosomes triggered by elevated [Ca2+]i in fibroblasts
A C Bakker1, P Webster, W A Jacob
1Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Journal of Cell Science
|October 24, 1997
Summary
Antibodies targeting lysosomal glycoprotein 120 (lgp120) aggregate lysosomes. Calcium ionophores trigger lysosome-lysosome fusion, forming larger vesicles, indicating calcium
Area of Science:
- Cell Biology
- Lysosome Biology
- Membrane Trafficking
Background:
- Lysosomal glycoprotein 120 (lgp120) plays a role in lysosome function.
- Antibodies to lgp120's cytoplasmic domain induce lysosome aggregation in NRK cells.
Purpose of the Study:
- To investigate the role of calcium in lysosome fusion.
- To determine if aggregated lysosomes can fuse.
Main Methods:
- Microinjection of anti-lgp120 antibodies into NRK cells.
- Transmission and high-voltage electron microscopy.
- Confocal microscopy.
- Treatment with calcium ionophores (ionomycin) and intracellular calcium-mobilizing agents (thapsigargin, bombesin, thrombin).
- Streptolysin O permeabilization to control intracellular calcium.
Main Results:
- Antibody-clustered vesicles were confirmed as lysosomes.
- Lysosome aggregation did not involve MPR or ss-COP.
- Calcium ionophores induced the formation of large vesicles from fused lysosomes.
- Thapsigargin, bombesin, and thrombin also promoted lysosome fusion.
- An intracellular free calcium concentration of 1 µM was sufficient to trigger fusion.
Conclusions:
- Calcium influx is a key trigger for lysosome-lysosome fusion.
- lgp120-mediated lysosome aggregation can lead to fusion events upon calcium stimulation.
- This study elucidates a calcium-dependent mechanism for lysosome fusion.