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Factor XII binding to endothelial cells depends on caveolae
Inger Schousboe1, Peter Thomsen, Bo van Deurs
1Department of Medical Biochemistry & Genetics, The Panum Institute, University of Copenhagen, Denmark. schousboe@imbg.ku.dk
European Journal of Biochemistry
|July 6, 2004
Summary
Factor XII (FXII) binding to human umbilical vein endothelial cells (HUVEC) occurs in specific membrane patches rich in caveolae. This binding depends on intact caveolae, suggesting their crucial role in FXII interactions.
Area of Science:
- Vascular Biology
- Cellular Biology
- Biochemistry
Background:
- Factor XII (FXII) is known to bind to vascular cellular surfaces.
- Urokinase-like plasminogen activator (u-PAR), anchored by glycosylphosphatidylinositol, is a proposed receptor for FXII, often found in caveolae/lipid rafts.
- Previous studies have not confirmed FXII binding localization to these specialized membrane structures in HUVEC.
Purpose of the Study:
- To investigate and confirm the localization of FXII binding to caveolae in HUVEC.
- To elucidate the role of caveolae and u-PAR in FXII binding to endothelial cells.
Main Methods:
- Microscopy techniques were employed to visualize FXII binding sites on HUVEC.
- Sucrose density-gradient centrifugation was used to analyze the co-localization of FXII with caveolae markers.
- Experiments involving cholesterol-depleted HUVEC were conducted to assess the dependence of FXII binding on caveolae integrity.
Main Results:
- FXII was observed to bind to specific patches on the HUVEC plasma membrane characterized by a high density of caveolae.
- Sucrose density-gradient centrifugation revealed that FXII co-localizes with caveolin-1 (a caveolae marker) in HUVEC.
- Cholesterol depletion significantly reduced FXII binding to HUVEC, indicating a dependence on intact caveolae.
- A minority of u-PAR was found in caveolae with FXII, suggesting secondary binding.
Conclusions:
- FXII binding to HUVEC is localized to membrane areas rich in caveolae.
- The integrity of caveolae is essential for FXII binding to endothelial cells.
- FXII-u-PAR interaction may be secondary and dependent on caveolae structural components.