title: An antibody to the lutheran glycoprotein (Lu) recognizing the LU4 blood type variant inhibits cell adhesion to laminin α5.
abstract: BACKGROUND
  The Lutheran blood group glycoprotein (Lu), an Ig superfamily (IgSF) transmembrane receptor, is also known as basal cell adhesion molecule (B-CAM). Lu/B-CAM is a specific receptor for laminin α5, a major component of basement membranes in various tissues. Previous reports have shown that Lu/B-CAM binding to laminin α5 contributes to sickle cell vaso-occlusion. However, as there are no useful tools such as function-blocking antibodies or drugs, it is unclear how epithelial and sickled red blood cells adhere to laminin α5 via Lu/B-CAM.
  
  
  RESULTS
  In this study, we discovered a function-blocking antibody that inhibits Lu binding to laminin α5 using a unique binding assay on tissue sections. To characterize the function-blocking antibody, we identified the site on Lu/B-CAM recognized by this antibody. The extracellular domain of Lu/B-CAM contains five IgSF domains, D1-D2-D3-D4-D5. The antibody epitope was localized to D2, but not to the D3 domain containing the major part of the laminin α5 binding site. Furthermore, mutagenesis studies showed that Arg(175), the LU4 blood group antigenic site, was crucial for forming the epitope and the antibody bound sufficiently close to sterically hinder the interaction with α5. Cell adhesion assay using the antibody also showed that Lu/B-CAM serves as a secondary receptor for the adhesion of carcinoma cells to laminin α5.
  
  
  CONCLUSIONS
  This function-blocking antibody against Lu/B-CAM should be useful for not only investigating cell adhesion to laminin α5 but also for developing drugs to inhibit sickle cell vaso-occlusion.
authors.affiliation: Laboratory of Clinical Biochemistry, Tokyo University of Pharmacy and Life Sciences, Tokyo, Japan. kikkawa@toyaku.ac.jp
authors.forename: Yamato
authors.initials: Y
authors.lastname: Kikkawa
authors.forename: Takahiro
authors.initials: T
authors.lastname: Miwa
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Tohara
authors.forename: Takayuki
authors.initials: T
authors.lastname: Hamakubo
authors.forename: Motoyoshi
authors.initials: M
authors.lastname: Nomizu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000378:metabolism / Q000494:pharmacology; D001665:Binding Sites / Q000235:genetics; D002448:Cell Adhesion / Q000187:drug effects / Q000276:immunology; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D045744:Cell Line, Tumor; D018604:Epitope Mapping; D000939:Epitopes / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D039222:Integrin alpha1beta1 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D039201:Integrin alpha3beta1 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D039121:Integrin alpha6beta1; D007668:Kidney / Q000276:immunology / Q000378:metabolism; D007797:Laminin / Q000276:immunology* / Q000378:metabolism; D008188:Lutheran Blood-Group System / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000276:immunology / Q000378:metabolism; D009154:Mutation; D009469:Neuromuscular Junction / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects / Q000276:immunology; D017386:Sequence Homology, Amino Acid
chemical_list: D000911:Antibodies, Monoclonal; C090228:BCAM protein, human; D015815:Cell Adhesion Molecules; D000939:Epitopes; D039222:Integrin alpha1beta1; D039201:Integrin alpha3beta1; D039121:Integrin alpha6beta1; D007797:Laminin; D008188:Lutheran Blood-Group System; C097043:laminin alpha5