The expression and role of circulating galectins in colorectal cancer

• Main Author: Barrow, Hannah Elizabeth
• Published: University of Liverpool 2011
• Subjects: 616.994347
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.569204

Adhesion of circulating tumour cells to the blood vascular endothelium is a pivotal step in metastasis. This study shows that the levels of free circulating galectin- 2, -3, -4, and -8, but not galectin-9 and -1, were markedly increased up to 31-fold in the bloodstream of colon and breast cancer patients and in particular those with metastasis. The presence in vitro of each of these galectins at pathological concentrations induced dose-dependent increases of cancer cell adhesion to monolayers of human macro- and micro-vascular endothelial cells, an effect that was abolished by the presence of galectin inhibitor, by pre- fixation of the cells, or by pre- treatment of the cells with O-glycanase to remove cell surface TF (Galβ1,3GalNAcα-) antigen. Suppression of the TF-expressing mucin protein MUCl by siRNA reduced, while overexpression of MUC 1 increased, the galectin-mediated cancer cell adhesion. Higher levels of circulating galectin-2 were associated with a significantly increased mortality risk in colorectal cancer patients and this association was diminished by serum co-existence of auto-anti-MUCl antibody specifically against the TF epitope of MUCl. Thus, the increased circulations of galectin members are common features in cancer and promote metastatic spread. Circulating galectins therefore represent a novel class of therapeutic targets for the development of effective agents to reduce metastasis and increase patient's survival. The possible role of modified heparins as inhibitors of the galectin3-ligand interaction that leads to increased vascular adhesion was therefore investigated. ELISA assays showed that chemically modified heparin derivatives successfully blocked galectin-3 adhesion to asialo-bovine mucin, and also galectin-3-mediated cellular adhesion to endothelial cell monolayers and extracellular matrix components, which suggests a possible role for heparin derivatives in cancer therapeutics. Finally in this study, the functional importance of Core 1 Gal-transferase (C 1 Ga1T) was investigated. It has long been presumed that there is a competition between Core 1 Gal-transferase (C1GalT), Core 3 G1cNAc-transferase (C3GnT) and sialyl-transferase (ST6Ga1NAc- T) for elongation of O-linked mucin-type glycans that initiate with GalNAcα-Ser/Thr. However, evidence that supports such a competition among these glyco-transferases is surprisingly lacking. This study shows that selective suppression of the CIGalT caused over 80% reduction of Galβ1,3GaINAcα- (Core 1, Thomsen-Friedenreich, TF antigen) expression in human colon cancer HT29 ary-based lecti. Suppression of Cl GalT was also associated with 198±8%, 136±24% 136±24% and 231±6% increase of sialyl-GalNAca- (sialyl-Tn), G1cNAcβ1 ,3GaINAcα- (Core 3) and GalNAcα- (Tn) expression in HT29 and 174±11 %, 155±37% and 200±5% increase in SW620 cells. These results provide direct evidence of a competition between CIGalT, C3GnT and ST6GalNAcT transferases for modification of the GaINAcα-Ser/Thr in O-glycan biosynthesis. As Tn, TF and sialyl- Tn are all oncofetal carbohydrate antigens and over-expressed in up to 90% of all human cancers, this information may also be useful for future development of glyco-transferase-targeted therapeutic strategies for cancer treatment.