Resumen de Lutheran Blood Group Antigen as a Receptor for α5 Laminins in Gingival Epithelia
Jaana Willberg, Marketta Hormia, Minna Takkunen, Ismo Virtanen
Background: Lutheran blood group glycoprotein (Lu) is a transmembrane receptor of the immunoglobulin superfamily. Lu serves as a receptor for α5 laminins (Lm). The Lm α5 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 α3 and β1 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 α5 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 α5 preparations was diminished with monoclonal antibodies (MAbs) against integrin α3 and even more effectively with MAbs against the β1 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 α3 antibody. Lm-511 did not induce lamellipodia or focal contacts in cultured gingival keratinocytes.
Conclusions: Lu was in coalignment with Lm α5 chain in gingival epithelia. Lu also seemed to have a role in gingival epithelial cell adhesion together with integrin α3β1.
