ANTIBODIES TO THE 280-KD COATED PIT PROTEIN, TARGET OF TERATOGENIC ANTIBODIES, PRODUCE ALTERATIONS IN THE TRAFFIC OF INTERNALIZED PROTEINS

Previous studies have identified two high-molecular weight (280 and 33 0 kd) glycoproteins expressed by coated Pits of the proximal renal tub ule and yolk sac and have further established that, in vivo, antibodie s to gp280 but not to gp330 induce fetal malformations. In the present study, we report the effect of these antibodies on the endocytic proc ess by yolk sac visceral epithelial cells of rat embryos explanted at day 10 of gestation Antibodies to gp280 markedly altered development o f the yolk sac and embryo, induced malformations, inhibited by 40% the uptake of [C-14] sucrose and perturbed the intracellular traffic of i nternalized proteins. Under control conditions, rat immunoglobulin G p resent in the culture medium was immunolocalized in lysosomes of epith elial cells, whereas in the presence of antibody, it was detected in s mall vesicles scattered through the apical cytoplasm Alterations of th e endocytic pathway were confirmed by experiments analyzing the uptake of peroxidase added to the medium for 2 to 60 minutes. The initial co mpartments of endocytosis visualized by peroxidase were increased in s ize and abnormal in shape and the transfer of the internalized peroxid ase to the lysosomal compartment was delayed. In contrast, antibodies to gp330 had a minimal effect on embryonic development and did not ind uce fetal malformations. Endocytosis was only modestly altered; uptake of[C-14] sucrose was decreased by 25%, and only minor modifications o f the intracellular transit of peroxidase could be detected. we sugges t that the key role of anti-gp280 antibodies is via trapping of the ta rget antigen in the early endocytic compartment thus preventing its no rmal function in lysosomal transfer.