by Yamato Kikkawa, Takahiro Miwa, Yukiko Tohara, Takayuki Hamakubo, Motoyoshi Nomizu
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 a5, a major component of basement membranes in various tissues. Previous reports have shown that Lu/B-CAM binding to laminin a5 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 a5 via Lu/B-CAM. Methodology/Principal Findings
In this study, we discovered a function-blocking antibody that inhibits Lu binding to laminin a5 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 a5 binding site. Furthermore, mutagenesis studies showed that Arg175, the LU4 blood group antigenic site, was crucial for forming the epitope and the antibody bound sufficiently close to sterically hinder the interaction with a5. 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 a5. Conclusion/Significance
This function-blocking antibody against Lu/B-CAM should be useful for not only investigating cell adhesion to laminin a5 but also for developing drugs to inhibit sickle cell vaso-occlusion.