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Apical topography and modulation of ICAM-1 expression on activated endothelium
A Almenar-Queralt1, A Duperray, L A Miles
1Department of Cell Biology, Scripps Research Institute, La Jolla, California, USA.
Insights
Intercellular adhesion molecule-1 (ICAM-1) is found on the apical membrane of activated endothelial cells. Its internalization rate depends on expression levels, suggesting a role in vascular injury responses.
Area of Science:
- Immunology
- Cell Biology
- Vascular Biology
Background:
- Leukocyte-endothelium interactions and inflammation involve intercellular adhesion molecule-1 (ICAM-1) on endothelial cells.
- Regulated expression of ICAM-1 is crucial for inflammatory responses.
Purpose of the Study:
- To investigate the precise localization of ICAM-1 on cytokine-activated human umbilical vein endothelial cells.
- To analyze the internalization dynamics and regulation of ICAM-1.
- To understand the role of ICAM-1 trafficking in vascular injury and endothelial cell activation.
Main Methods:
- Confocal fluorescence microscopy and immunogold transmission electron microscopy were used to determine ICAM-1 localization.
- Kinetic binding studies with a radiolabeled monoclonal antibody assessed ICAM-1 internalization.
- Experiments utilized cytokine-activated endothelial cells and genetically engineered ICAM-1 transfectants.
Main Results:
- ICAM-1 was exclusively localized on the apical (luminal) membrane of activated endothelial cells, unlike basolateral beta 1 integrins.
- Approximately 8% of ICAM-1 was internalized via vesicles at 37°C with a half-life of ~18 min.
- Internalization rate increased significantly with higher ICAM-1 expression in transfectants, indicating density-dependent uptake.
Conclusions:
- ICAM-1 exhibits polarized localization on activated endothelium.
- Receptor trafficking and internalization are key regulatory mechanisms for ICAM-1 function.
- These processes likely play a critical role in ICAM-1-mediated adhesion during vascular injury and inflammation.
Abstract:
Leukocyte-endothelium interactions and general inflammatory responses are contributed by the regulated expression of intercellular adhesion molecule-1 (ICAM-1) on endothelium. It is now shown by confocal fluorescence microscopy and immunogold transmission electron microscopy that ICAM-1 was exclusively localized on the apical (luminal) membrane of cytokine-activated human umbilical vein endothelial cells. In contrast, other cell adhesion-promoting molecules, including beta 1 integrins, were expressed exclusively on the basolateral endothelial cell membrane, under the same experimental conditions. Kinetic binding studies of a 125I-labeled monoclonal antibody to ICAM-1 revealed that approximately 8% of membrane ICAM-1 on cytokine-activated endothelium was internalized in both coated and non-coated vesicles at 37 degrees C, with a t1/2 of approximately 18 min and a rate of approximately 3200 molecules/minute. This internalization pathway was directly dependent upon the level of ICAM-1 expression on the cell surface. Genetically engineered ICAM-1 transfectants, expressing a 10-fold higher receptor density than activated endothelium, internalized approximately 18% of membrane ICAM-1 at a rate of 75,000 molecules/minute with a t1/2 of approximately 22 min. These findings suggest that a combined pathway of polarized membrane topography and receptor trafficking may regulate ICAM-1-dependent adhesion at the site of vascular injury and endothelial cell activation.
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