tailieunhanh - Báo cáo khoa học: Factor XII binding to endothelial cells depends on caveolae

It is now generally accepted that factor XII (FXII) binds to cellular surfaces in the vascular system. One of the suggested receptors of this binding is the glycosylphosphatidylinositol-anchored urokinase-like plasminogen activator (u-PAR) harbored in caveolae/lipid rafts. However, binding of FXII to human umbilical vein endothelial cells (HUVEC) has never been shown to be localized to these specialized mem-brane structures. Using microscopical techniques, we here report that FXII binds to specific patches of the HUVEC plasma membrane with a high density of caveolae | Eur. J. Biochem. 271 2998-3005 2004 FEBS 2004 doi Factor XII binding to endothelial cells depends on caveolae Inger Schousboe1 Peter Thomsen2 and Bo van Deurs2 1 Department of Medical Biochemistry Genetics and 2Structural Cell Biology Unit Department of Medical Anatomi The Panum Institute University of Copenhagen Denmark It is now generally accepted that factor XII FXII binds to cellular surfaces in the vascular system. One of the suggested receptors of this binding is the glycosylphosphatidylinositol-anchored urokinase-like plasminogen activator u-PAR harbored in caveolae lipid rafts. However binding of FXII to human umbilical vein endothelial cells HUVEC has never been shown to be localized to these specialized membrane structures. Using microscopical techniques we here report that FXII binds to specific patches of the HUVEC plasma membrane with a high density of caveolae. Further investigations of FXII binding to caveolae were performed by sucrose density-gradient centrifugations. This showed that the majority of FXII chemically cross-linked to HUVEC could be identified in the same fractions of the gradient as caveolin-1 a marker of caveolae while the majority of u-PAR was identified in noncaveolae lipid rafts. Accordingly cholesterol-depleted cells were found to bind significantly reduced amounts of FXII. These observations combined with the presence of a minority of u-PAR in caveolae concomitant with FXII binding indicate that FXII binding to u-PAR may be secondary and depends upon the structural elements within caveolae. Thus FXII binding to HUVEC depends on intact caveolae on the cellular surface. Keywords factor XII HUVEC lipid rafts caveolae u-PAR. Factor XII FXII is a zymogen present in plasma at a concentration of w 350 nM. At local increases in the Zn2 concentration above the normal plasma level of 25 M FXII binds to endothelial cells along with plasma prekallikrein. The latter becomes attached to the cells via complex .