Am J Physiol Cell Physiol AJP: Cell Physiology
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Am J Physiol Cell Physiol (December 31, 2008). doi:10.1152/ajpcell.00472.2008
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Submitted on September 13, 2008
Revised on December 24, 2008
Accepted on December 25, 2008

Podocalyxin-like protein is an E-/L-selectin ligand on colon carcinoma cells: Comparative biochemical properties of selectin ligands in host and tumor cells

Susan Napier Thomas1, Ronald L. Schnaar2, and Konstantinos Konstantopoulos1*

1 The Johns Hopkins University
2 Johns Hopkins School Of Medicine

* To whom correspondence should be addressed. E-mail: kkonsta1{at}jhu.edu.

Selectins facilitate metastasis and tumor cell arrest in the microvasculature by mediating binding of selectin-expressing host cells to ligands on tumor cells. We recently identified CD44 variant isoforms as functional P-, but not E-/L-, selectin ligands on colon carcinoma cells. Furthermore, a ~180-kDa sialofucosylated glycoprotein(s) mediated selectin binding in CD44-knockdown cells. Using immunoaffinity chromatography and tandem mass spectrometry, we identify podocalyxin-like protein (PCLP) as an alternative 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. 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. PCLP on CD44-knockdown LS174T cells exhibits higher HECA-452 immuno-reactivity than PCLP on wild-type cells, suggesting that PCLP functions as an alternative acceptor for selectin-binding glycans. 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. 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.







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