Lutheran blood group antigen as a receptor for alpha5 laminins in gingival epithelia.
BACKGROUND
Lutheran blood group glycoprotein (Lu) is a transmembrane receptor of the immunoglobulin superfamily. Lu serves as a receptor for alpha5 laminins (Lm). The Lm alpha5 chain is a constituent of Lms-511 and -521. Lm-511 is found in most human basement membranes (BMs) and also is detected in BM of gingival epithelia. Recent studies indicated that Lu mediates cell adhesion to Lms-511/521 independently or in concert with integrins. This study focused on the expression of Lu in gingival epithelia and on cultured immortalized gingival keratinocytes. The role of Lu and alpha(3) and beta(1) integrin subunits in the adhesion of oral epithelial cells to Lms-511/521 was also studied.


METHODS
Immunofluorescence microscopy was used to study the expression of Lu in gingival tissues and in cultured gingival keratinocytes. Immunoprecipitation of radioactively metabolically labeled cells was used to detect Lu. Cell adhesion to Lm-511/521 preparation and to pure Lm-511 was studied in quantitative cell adhesion experiments. Morphological adhesion assays were carried out for visualization of the morphology and adhesion structure formation of the adhering cells.


RESULTS
Immunofluorescence studies on gingiva showed complete coalignment of Lu on basal epithelial cells with the BM Lm alpha5 chain. A surface-confined, punctate immunoreaction for Lu was detected throughout cell surfaces on cultured gingival cells. Immunoprecipitation showed a broad polypeptide with molecular weight 85,000. In quantitative cell adhesion assays, the adhesion of cells to both Lm alpha5 preparations was diminished with monoclonal antibodies (MAbs) against integrin alpha(3) and even more effectively with MAbs against the beta(1) subunit. When the adhesion sites were blocked with soluble recombinant Lu (sol-Lu), the adhesion of gingival epithelial cells to Lms-511/521 was reduced significantly, and sol-Lu increased the inhibition with integrin alpha(3) antibody. Lm-511 did not induce lamellipodia or focal contacts in cultured gingival keratinocytes.


CONCLUSIONS
Lu was in coalignment with Lm alpha5 chain in gingival epithelia. Lu also seemed to have a role in gingival epithelial cell adhesion together with integrin alpha(3)beta(1).
Willberg
Jaana
J
Department of Oral Pathology and Radiology, Institute of Dentistry, University of Turku, Turku, Finland. jaana.willberg@utu.fi
Hormia
Marketta
M
Takkunen
Minna
M
Kikkawa
Yamato
Y
Sekiguchi
Kiyotoshi
K
Virtanen
Ismo
I
D000328:Adult; D001485:Basement Membrane; D002448:Cell Adhesion / Q000502:physiology; D015815:Cell Adhesion Molecules / Q000378:metabolism*; D002461:Cell Line, Transformed; D005881:Gingiva / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D039201:Integrin alpha3beta1 / Q000378:metabolism; D015603:Keratinocytes / Q000378:metabolism; D007797:Laminin / Q000378:metabolism*; D008188:Lutheran Blood-Group System / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009363:Neoplasm Proteins / Q000378:metabolism*; D017474:Receptors, Laminin / Q000378:metabolism*
C090228:BCAM protein, human; D015815:Cell Adhesion Molecules; D039201:Integrin alpha3beta1; D007797:Laminin; D008188:Lutheran Blood-Group System; D009363:Neoplasm Proteins; D017474:Receptors, Laminin; C097043:laminin alpha5