Selectin-mediated interactions in the vasculature promote metastatic spread by facilitating
circulating tumor cell binding to
selectin-expressing host cells. Therefore, identifying the
selectin ligand(s) on
tumor cells is critical to the prevention of blood-borne
metastasis. A current challenge is to distinguish between structures expressed by
circulating tumor cells that can bind
selectins in vitro from the functional
ligands whose depletion suppresses
selectin-dependent binding under flow in vivo. Interestingly,
podocalyxin (PODXL), which can bind E- and
L-selectin, is upregulated in a number of
cancers, including those of the breast, colon, and pancreas. In this work, we show that metastatic
pancreatic cancer cells overexpress PODXL compared with nonmalignant pancreatic epithelial cells. We further demonstrate via tissue microarray that 69% of pancreatic ductal
adenocarcinomas stain positive for PODXL. In cases of focal expression, positive staining is restricted to the invasive front of primary
tumors. By combining immunoblot, immunodepletion,
short-hairpin RNA-mediated gene silencing, and flow-based adhesion assays, we evaluated the functional role of sialofucosylated PODXL in
selectin-mediated adhesion under flow. Our data indicate that sialofucosylated PODXL is a functional E- and
L-selectin ligand expressed by metastatic
pancreatic cancer cells, as specific depletion of this molecule from the cell surface significantly interferes with
selectin-dependent interactions. Cumulatively, these data support a correlation between sialofucosylated PODXL expression and enhanced binding to
selectins by metastatic
pancreatic cancer cells and offer additional perspective on the upregulation of PODXL in aggressive
cancers.