Enhanced expression of sialylated, fucosylated oligosaccharides such as sialyl Lewis x (sLe x) or sialyl Lewis a (sLe a) on the tumor cell surface correlates with poor prognosis because of tumor progression and metastatic spread ( 27, 42, 43). A variety of tumor cells, including colon carcinoma, express sialofucosylated molecules that can be recognized by selectins ( 16, 17, 38, 52). The selectins (E-, L-, and P-selectin) constitute a family of structurally related transmembrane glycoproteins that mainly recognize specific glycoconjugates on apposing cell surfaces ( 28, 34, 49, 54). Selectins play a pivotal role in the hematogenous dissemination of tumor cells in the vasculature by mediating specific interactions between selectin-expressing host cells and selectin ligands on tumor cells.

The novel finding that PCLP is an E-/L-selectin ligand on carcinoma cells offers a unifying perspective on the apparent enhanced metastatic potential associated with tumor cell PCLP overexpression and the role of selectins in metastasis. The enhanced expression of HECA-452 reactivity on PCLP from CD44-knockdown cells correlates with the increased avidity of PCLP for E- but not L-selectin. PCLP on CD44-knockdown LS174T cells exhibits higher HECA-452 immunoreactivity than PCLP on wild-type cells, suggesting that PCLP functions as an alternative acceptor for selectin-binding glycans. The selectin-binding determinants on LS174T PCLP are non-MECA-79-reactive sialofucosylated structures displayed on O-linked glycans, distinct from the MECA-79-reactive O-glycans on PCLP expressed by high endothelial venules, which is an L-selectin ligand.

Blot rolling and cell-free flow-based adhesion assays disclose that PCLP on LS174T colon carcinoma cells possesses E-/L-, but not P-, selectin binding activity. Using immunoaffinity chromatography and tandem mass spectrometry, we identify podocalyxin-like protein (PCLP) as an alternative selectin ligand. Furthermore, a в€ј180-kDa sialofucosylated glycoprotein(s) mediated selectin binding in CD44-knockdown cells. We recently identified CD44 variant isoforms as functional P-, but not E-/L-, selectin ligands on colon carcinoma cells. Selectins facilitate metastasis and tumor cell arrest in the microvasculature by mediating binding of selectin-expressing host cells to ligands on tumor cells.

Pclp login