α3/4 fucosyltransferase 3-dependent synthesis of sialyl lewis A on CD44 variant containing exon 6 mediates polymorphonuclear leukocyte detachment from intestinal epithelium during transepithelial migration

Polymorphonuclear leukocyte (PMN) migration across the intestinal epithelium closely parallels disease symptoms in patients with inflammatory bowel disease. PMN transepithelial migration (TEM) is a multistep process that terminates with PMN detachment from the apical epithelium into the lumen. Using a unique mAb (GM35), we have previously demonstrated that engagement of the CD44 variant containing exon 6 (CD44v6) blocks both PMN detachment and cleavage of CD44v6. In this article, we report that PMN binding to CD44v6 is mediated by protein-specific O-glycosylation with sialyl Lewis A (sLe^a). Analyses of glycosyltransferase expression identified fucosyltransferase 3 (Fut3) as the key enzyme driving sLe^a biosynthesis in human intestinal epithelial cells (IECs). Fut3 transfection of sLe^a-deficient IECs resulted in robust expression of sLe^a. However, this glycan was not expressed on CD44v6 in these transfected IECs; therefore, engagement of sLe^a had no effect on PMN TEM across these cells. Analyses of sLe^a in human colonic mucosa revealed minimal expression in noninflamed areas, with striking upregulation under colitic conditions that correlated with increased expression of CD44v6. Importantly, intraluminal administration of mAb GM35 blocked PMN TEM and attenuated associated increases in intestinal permeability in a murine intestinal model of inflammation. These findings identify a unique role for protein-specific O-glycosylation in regulating PMN-epithelial interactions at the luminal surface of the intestine.