CD44v4 is a major E-selectin ligand that mediates breast cancer cell transendothelial migration.
BACKGROUND
Endothelial E-selectin has been shown to play a pivotal role in mediating cell-cell interactions between breast cancer cells and endothelial monolayers during tumor cell metastasis. However, the counterreceptor for E-selectin and its role in mediating breast cancer cell transendothelial migration remain unknown.


RESULTS
By assessing migration of various breast cancer cells across TNF-alpha pre-activated human umbilical vein endothelial cells (HUVECs), we found that breast cancer cells migrated across HUVEC monolayers differentially and that transmigration was E-selectin dependent. Cell surface labeling with the E-selectin extracellular domain/Fc chimera (exE-selectin/Fc) showed that the transmigration capacity of breast cancer cells was correlated to both the expression level and localization pattern of E-selectin binding protein(s) on the tumor cell surface. The exE-selectin/Fc strongly bound to metastatic MDA-MB-231, MDA-MB-435 and MDA-MB-468 cells, but not non-metastatic MCF-7 and T47D cells. Binding of exE-selectin/Fc was abolished by removal of tumor cell surface sialyl lewis x (sLe(x)) moieties. Employing an exE-selectin/Fc affinity column, we further purified the counterreceptor of E-selectin from metastatic breast cancer cells. The N-terminal protein sequence and cDNA sequence identified this E-selectin ligand as a approximately 170 kD human CD44 variant 4 (CD44v4). Purified CD44v4 showed a high affinity for E-selectin via sLe(x) moieties and, as expected, MDA-MB-231 cell adhesion to and migration across HUVEC monolayers were significantly reduced by down-regulation of tumor cell CD44v4 via CD44v4-specific siRNA.


CONCLUSIONS
We demonstrated, for the first time, that breast cancer cell CD44v4 is a major E-selectin ligand in facilitating tumor cell migration across endothelial monolayers. This finding offers new insights into the molecular basis of E-selectin-dependent adhesive interactions that mediate breast cancer cell transendothelial metastasis.
Zen
Ke
K
State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu, China. kzen@nju.edu.cn
Liu
Dan-Qing
DQ
Guo
Ya-Lan
YL
Wang
Chen
C
Shan
Jun
J
Fang
Ming
M
Zhang
Chen-Yu
CY
Liu
Yuan
Y
D001943:Breast Neoplasms / Q000473:pathology*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D019040:E-Selectin / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000473:pathology*; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism* / Q000502:physiology; D008024:Ligands; D009362:Neoplasm Metastasis
C497483:CD44 protein, human; D019040:E-Selectin; D018960:Hyaluronan Receptors; D008024:Ligands