title: A transmembrane tight junction protein selectively expressed on endothelial cells and platelets.
abstract: Searching for cell surface proteins expressed at interendothelial cell contacts, we have raised monoclonal antibodies against intact mouse endothelial cells. We obtained two monoclonal antibodies, 1G8 and 4C10, that stain endothelial cell contacts and recognize a protein of 55 kDa. Purification and identification by mass spectrometry of this protein revealed that it contains two extracellular Ig domains, reminiscent of the JAM family, but a much longer 120-amino acid cytoplasmic domain. The antigen is exclusively expressed on endothelial cells of various organs as was analyzed by immunohistochemistry. Immunogold labeling of ultrathin sections of brain as well as skeletal muscle revealed that the antigen strictly colocalizes in capillaries with the tight junction markers occludin, claudin-5, and ZO-1. Upon transfection into MDCK cells, the antigen was restricted to the most apical tip of the lateral cell surface, where it colocalized with ZO-1 but not with beta-catenin. In contrast to JAM-1, however, the 1G8 antigen does not associate with the PDZ domain proteins ZO-1, AF-6, or ASIP/PAR-3, despite the presence of a PDZ-binding motif. The 1G8 antigen was not detected on peripheral blood mouse leukocytes, whereas similar to JAM-1 it was strongly expressed on platelets and megakaryocytes. The 1G8 antigen supports homophilic interactions on transfected Chinese hamster ovary cells. Based on the similarity to the JAM molecules, it is plausible that the 1G8 antigen might be involved in interendothelial cell adhesion.
authors.affiliation: Institute of Cell Biology, ZMBE, University of Münster, 48149 Münster, Germany.
authors.forename: Ines
authors.initials: I
authors.lastname: Nasdala
authors.forename: Karen
authors.initials: K
authors.lastname: Wolburg-Buchholz
authors.forename: Hartwig
authors.initials: H
authors.lastname: Wolburg
authors.forename: Annegret
authors.initials: A
authors.lastname: Kuhn
authors.forename: Klaus
authors.initials: K
authors.lastname: Ebnet
authors.forename: Gertrud
authors.initials: G
authors.lastname: Brachtendorf
authors.forename: Ulrike
authors.initials: U
authors.lastname: Samulowitz
authors.forename: Bernhard
authors.initials: B
authors.lastname: Kuster
authors.forename: Britta
authors.initials: B
authors.lastname: Engelhardt
authors.forename: Dietmar
authors.initials: D
authors.lastname: Vestweber
authors.forename: Stefan
authors.initials: S
authors.lastname: Butz
mesh_terms: D000818:Animals; D000906:Antibodies; D000911:Antibodies, Monoclonal; D001792:Blood Platelets / Q000378:metabolism*; D001921:Brain / Q000378:metabolism; D015815:Cell Adhesion Molecules / Q000032:analysis / Q000502:physiology*; D004730:Endothelium, Vascular / Q000378:metabolism*; D013058:Mass Spectrometry; D008533:Megakaryocytes / Q000378:metabolism* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D016253:Microscopy, Immunoelectron; D018482:Muscle, Skeletal / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D019108:Tight Junctions / Q000502:physiology*
chemical_list: D000906:Antibodies; D000911:Antibodies, Monoclonal; D015815:Cell Adhesion Molecules; C428190:Esam protein, mouse; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins