title: Identification of rat yolk sac target protein of teratogenic antibodies, gp280, as intrinsic factor-cobalamin receptor.
abstract: Previous studies in the rat have shown that antibodies to gp280, a protein > 200 kD and closely associated with the early endocytic system can induce fetal malformations. Although gp280 is thought to act as a receptor, its ligand(s) is not known. In the current study, we report that purified gp280 from rat kidney, like the intrinsic factor-Cobalamin receptor (IFCR), binds to the intrinsic factor-cobalamin (IFCbl) complex with an association constant of 0.3 x 10(9) M-1 and mediates its internalization. Furthermore, antibodies raised to purified gp280 and IFCR inhibited the binding of IF-[57Co]Cbl complex to intestinal, renal, and yolk sac apical membranes and revealed a single identically sized protein on immunoblotting of the renal membranes. Both antibodies precipitated a single radiolabeled protein > 200 kD from cellular extract from [35S]methionine-labeled yolk sac epithelial cells, and antibody to gp280 inhibited the uptake and internalization of 125IF-Cbl. Immunoelectron microscopy using the two antibodies revealed that in the kidney, both proteins were colocalized. These observations suggest that IF-Cbl complex is a ligand for gp280 and that gp280 and IFCR are identical proteins.
authors.affiliation: Department of Medicine and Biochemistry, Medical College of Wisconsin, and Veterans Affairs Medical Center, Milwaukee, Wisconsin 53226, USA. seethara@its.post.mcw.edu
authors.forename: B
authors.initials: B
authors.lastname: Seetharam
authors.forename: E I
authors.initials: EI
authors.lastname: Christensen
authors.forename: S K
authors.initials: SK
authors.lastname: Moestrup
authors.forename: T G
authors.initials: TG
authors.lastname: Hammond
authors.forename: P J
authors.initials: PJ
authors.lastname: Verroust
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism / Q000633:toxicity*; D002478:Cells, Cultured; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000502:physiology; D007668:Kidney / Q000502:physiology; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism; D008970:Molecular Weight; D051381:Rats; D011956:Receptors, Cell Surface / Q000276:immunology / Q000302:isolation & purification / Q000502:physiology*; D013723:Teratogens; D015017:Yolk Sac / Q000502:physiology*
chemical_list: D000911:Antibodies, Monoclonal; D011956:Receptors, Cell Surface; D013723:Teratogens; C029486:intrinsic factor-cobalamin receptor