Podocalyxin Is a Glycoprotein Ligand of the Human Pluripotent Stem Cell‐Specific Probe rBC2LCN

This study demonstrates that podocalyxin, a heavily glycosylated type 1 transmembrane protein, is a glycoprotein ligand of rBC2LCN on human induced pluripotent stem (iPS) cells and embryonic stem (ES) cells. When analyzed by DNA microarray, podocalyxin was found to be highly expressed in both iPS cells and ES cells. The carbohydrate antigens of rBC2LCN are expressed on O‐glycans of podocalyxin, since alkaline hydrolysis greatly reduced the binding of rBC2LCN to human iPS cells and ES cells. rBC2LCN bound to an O‐glycan carrying H type 3 epitope structure isolated from iPS cells, suggesting that H type 3 is a novel pluripotency glycan marker. In comprehensive glycome analysis with a high‐density lectin microarray, we have previously shown that the recombinant N‐terminal domain of the lectin BC2L‐C from Burkholderia cenocepacia (rBC2LCN) binds exclusively to undifferentiated human induced pluripotent stem (iPS) cells and embryonic stem (ES) cells but not to differentiated somatic cells. Here we demonstrate that podocalyxin, a heavily glycosylated type 1 transmembrane protein, is a glycoprotein ligand of rBC2LCN on human iPS cells and ES cells. When analyzed by DNA microarray, podocalyxin was found to be highly expressed in both iPS cells and ES cells. Western and lectin blotting revealed that rBC2LCN binds to podocalyxin with a high molecular weight of more than 240 kDa in undifferentiated iPS cells of six different origins and four ES cell lines, but no binding was observed in either differentiated mouse feeder cells or somatic cells. The specific binding of rBC2LCN to podocalyxin prepared from a large set of iPS cells (138 types) and ES cells (15 types) was also confirmed using a high‐throughput antibody‐overlay lectin microarray. Alkaline digestion greatly reduced the binding of rBC2LCN to podocalyxin, indicating that the major glycan ligands of rBC2LCN are presented on O‐glycans. Furthermore, rBC2LCN was found to exhibit significant affinity to a branched O‐glycan comprising an H type 3 structure (Ka, 2.5 × 104 M−1) prepared from human 201B7 iPS cells, indicating that H type 3 is a most probable potential pluripotency marker. We conclude that podocalyxin is a glycoprotein ligand of rBC2LCN on human iPS cells and ES cells.