CD44 enhances the epithelial-mesenchymal transition in association with colon cancer invasion

The metastatic process involves the migration and invasion of cancer cells throughout the body to produce secondary tumors at distant sites. Through of epithelial-mesenchymal transition (EMT), cancer cells employ developmental processes to gain migratory and invasive properties. CD44 is the transmembrane adhesion receptor for Hyaluronan (HA) and plays a central role in the remodeling and degradation of HA that leads to cell migration, as well as to cancer invasion and metastasis. CD44 is highly expressed in primary and metastatic colon cancer but lowly expressed in normal tissues. We evaluated the impact of CD44 on EMT and invasion of colon cancer cells. The functional role of CD44 in EMT was determined by the overexpression or knockdown of CD44. CD44 was overexpressed by transfection with plasmid-RT-PCR product and knockdown of CD44 by small hairpin RNA (shRNA)-mediated depletion of CD44 in SW480 colon cancer cells. Morphological changes were evaluated by confocal laser microscopy in the culture media. The expression of EMT markers (E-cadherin/N-cadherin/vimentin/fibronectin/actin/MMPs) and CD44/EGFR/PI3K-Akt signaling were evaluated using western blotting. The influence of EMT in tumor biology was assessed with proliferation, migration and invasion assays. EMT changes increased in CD44-overexpressing SW480 cells and decreased in CD44 knockdown cells. CD44 activation induced expression of EGFR and activation of phosphatidylinositol 3' kinase (PI3K)/Akt and expression of glycogen synthase kinase-3 beta (GSK-3 beta). In terms of EMT markers, CD44 downregulated E-cadherin expression, upregulated N-cadherin, alpha-actin, vimentin, fibronectin and MT1-MMP, and inhibited the formation of the membrane-associated E-cadherin-beta-catenin complex, which resulted in cell invasion and migration.