The endocytic hyaluronan receptor in rat liver sinusoidal endothelial cells is Ca+2-independent and distinct from a Ca+2-dependent hyaluronan binding activity
✍ Scribed by Judith Yannariello-Brown; Carl T. McGary; Paul H. Weigel
- Publisher
- John Wiley and Sons
- Year
- 1992
- Tongue
- English
- Weight
- 818 KB
- Volume
- 48
- Category
- Article
- ISSN
- 0730-2312
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✦ Synopsis
Isolated and cultured rat liver sinusoidal endothelial cells (LECs) retain the ability to specifically bind '251-hyalur~nan (HA) and internalize it using a coated pit pathway [Biochem J, 257:875-884, 19891. Here we have determined the effect of Ca+' on the binding and endocytosis of HA by LECs. '251-HA binding to intact LECs at 4°C occurred both in the absence (1 0 m M EGTA) or the presence of physiologic concentrations of Ca+' (1.8 mM). However, the specific binding of '*%HA to LECs increased linearly with increasing Ca+' concentrations. After permeabilization with the nonionic detergent digitonin, the Ca''-independent HA binding activity increased -743%, while the Ca+'-dependent binding activity was enhanced only -46%. Therefore, the Ca''-dependent HA binding activity appears not to be intracellular, whereas the Ca+*-independent HA receptor i s found both inside LECs and on the cell surface. When LECs were allowed to endocytose '2SI-HA at 37°C in 10 m M EGTA or in 1.8 m M Cat*, no differences were seen in the extent or rate of endocytosis. When LECs were allowed to endocytose "'I-HA in the presence of 10 mM Ca+*, the amount of cell-associated radioactivity increased approximately 20-50-fold. However, this additional cell-associated 12' 1-HA was not sensitive to hyperosmolarity and was removed by washing the cells in I 0 rnM EGTA at 4°C. Therefore, the Ca''-dependent cell-associated '251-HA had accumulated on the cell surface and had not been internalized. From these studies we conclude that LECs have at least two types of specific HA binding sites. One, the previously characterized HA receptor, is Ca+'-independent, localized both extracellularly and intracellulary, and mediates the efficient binding and subsequent endocytosis of HA using a coated pit pathway. The other newly recognized HA binding activity is Ca+*-dependent, localized extracellularly, and is not responsible for the endocytosis of HA in rat LECs.