Expression of E-selectin and its ligand ESL–1 in rat hepatic stellate cells (HSC): implications for leukocyte extravasation and liver metastasis

Abstract

HSC are pericytes of liver sinusoidal endothelial cells. Activation of HSC seems to be involved in repair of liver tissue injury, in liver regeneration and in angiogenesis of liver metastases. Entry of leukocytes but also of tumor cells is controlled by cell adhesion events in particular between the invading cells and endothelial cells. The cytokine-inducible E-selectin mediates binding of neutrophiles to endothelial cells and is implicated in colon cancer metastasis. Binding to E-selectin depends on the presence of sialylated and fucosylated carbohydrate structures which are generated by a(1,3)-fucosyltransferases (FucT). E-selectin ligand–1 (ESL–1) is the major E-selectin ligand on neutrophiles and almost exclusively modified by FucTIV and FucTVII. Here we report for the first time expression of E-selectin and of its ligand ESL–1 in HSC. Since HSC appear to be oxygen-sensing cells, the expression of E-selectin binding activity was analyzed by using an E-selectin-IgG fusion protein and a rabbit polyclonal anti-ESL–1 antibody in primary rat HSC under hypoxic atmosphere. While expression of the glycoprotein ESL–1 was unaffected by hypoxia, E-selectin binding activity decreased. However under the same conditions, mRNA expression of the modifying enzyme fucTVII was 2, 5 fold increased. FucTVII up-regulation was accompanied by increased expression of VEGF (9-fold) and by a strong induction of E-selectin expression (14 fold). The lost of E-selectin binding activity therefore appears neither to be the result of reduced expression of the modifying transferase nor the expression of the backbone glycoprotein. Analysis of expression and secretion of ESL–1 in the established human HSC cell line LX–2 transient transfected with ESL–1 cDNAs revealed that ESL-was efficiently produced into the supernatant. Therefore, we hypothese that ESL–1 may be shedded from or be secreted by hypoxia activated HSC. The in vitro hypoxic condition reproduces the avascular microenvironment present during tumor metastasis, the early stages of liver regeneration and during wound healing. Activated HSC may be a new cell type expressing E-selectin and its major ligand ESL–1 supporting leukocyte extravasation on one hand but also on the other hand may contribute to the liver colonization of tumor cells.