IMMUNOFUNCTIONAL PROPERTIES OF A YOLK-SAC EPITHELIAL-CELL LINE EXPRESSING 2 PROTEINS GP280 AND GP330 OF THE INTERMICROVILLAR AREA OF PROXIMAL TUBULE CELLS - INHIBITION OF ENDOCYTOSIS BY THE SPECIFIC ANTIBODIES

The apical domain of epithelial cells lining the proximal tubule and t he yolk sec is characterized by the development of extensive microvill i which limit intermicrovillar spaces backed on their cytoplasmic aspe ct by a coat of clathrin. These membrane areas which give rise to endo cytic vesicles rue characterized by the expression on their outer aspe ct of two high molecular weight glycoproteins: gp330 and gp280. In thi s study we report on an epithelial cell line, BN/MSV, derived from a y olk sac carcinoma which expresses these two glycoproteins. By indirect immunofluorescence, gp330 and gp280 were detectable on the cell surfa ce and after permeabilization in intracytoplasmic vesicles. At the ult rastructural level they were concentrated in clathrin-coated membrane areas although gp280 could also be detected in non-coated areas. The t wo proteins were synthesized independently in the form of high molecul ar weight polymers by biosynthetically labeled BN/MSV cells. Both were released in the supernatant, but, in spite of previously reported sim ilarities by peptide mapping, only gp330 coprecipitated with a 45 kDa protein comigrating with the alpha 2-macroglobulin receptor-associated protein (MRAP). Culture of the cells in the presence of antibodies to gp280 and to a lesser extent of antibodies to gp330 inhibited the int ernalization of [C-14]sucrose and peroxidase. When followed intracellu larly at the ultrastructural level, the compartments containing peroxi dase in the presence of anti-gp280 or gp330 antibodies mere morphologi cally distinct from those observed under control conditions: vesicles mere of smaller size and irregular shape and accumulation in lysosomes was delayed. This cellular system may be of value to understand the p hysiology of the 2 glycoproteins which may contribute to the specific endocytic properties of some epithelial cell types.