Reversible disruption of cultured endothelial monolayers by sulphated fucans

We have examined the effects of a variety of polysaccharides and glycoconjugates on the organization and morphology of cultured A14CL-1 endothelial monolayers. The sulphated fucose-containing polysaccharides, fucoidin and sea-urchin egg jelly fucan, induce a dramatic disruption of the organization of the monolayers, characterized by the retraction of adjacent borders of cells exposing areas of the subendothelial matrix. This effect, which occurs at a fucoidin concentration of 10 micrograms/ml, is rapidly reversible after the fucoidin-containing medium is removed. Within 1 h after replacement with fresh medium many cell contacts are re-established; within 20 h the fucoidin-treated monolayers closely resemble the untreated controls. The effect of the sulphated fucose-containing polysaccharides is specific. Of a wide variety of sulphated polysaccharides and glycoconjugates tested, only fucoidin and the egg jelly fucan produce a detectable alteration in the morphology of cultured endothelial monolayers. The endothelial monolayer has specific binding sites for fucoidin. The binding of fucoidin is saturable and a maximum of 4.5 X 10(5) molecules of fucoidin are bound per cell with an apparent affinity of 2.3 X 10(-7) M. A significant proportion (26%) of the total monolayer-associated fucoidin is apparently internalized by the endothelial cells after incubation with fucoidin for 1 h at 37 degrees C. The morphological response to fucoidin is probably not due to its internalization, since the effect is observed at 7 degrees C where little uptake (3.5%) occurs. Fucoidin appears to bind at two distinct sites on endothelial monolayers. One site is inhibitable by heparin, while the other site seems to be specific for fucoidin. The observation that fucoidin still induces the retraction of the endothelial cells in the presence of a 100-fold excess of heparin, suggests that binding at the fucoidin-specific site is responsible for the morphological effect of fucoidin. In addition, fucoidin has no detectable effect on monolayers of 3T3 and BHK fibroblast-like cells at 1 mg/ml, 100-fold higher than the concentration required to produce an effect on endothelial cells. Among the possible interpretations of these results is that sulphated fucose-containing glycoconjugates may play a role in the adhesive interactions of endothelial cells.