Thymosin β4 triggers an epithelial-mesenchymal transition in colorectal carcinoma by upregulating integrin-linked kinase

The epithelial-mesenchymal transition (EMT) is crucial for the invasion and metastasis of many epithelial tumors including colorectal carcinoma (CRC). In the present study, a scattering and fibroblastic morphology with reduced intercellular contacts was found in the SW480 colon cancer cells overexpressing the gene encoding thymosin beta 4 (T beta(4)), which was accompanied by a loss of E-cadherin as well as a cytosolic accumulation of beta-catenin, two most prominent markers of EMT. Whereas E-cadherin downregulation was likely to be accounted by a ZEB1-mediated transcriptional repression, the accumulation of beta-catenin was a result of glycogen synthase kinase-3 beta inactivation mediated by integrin-linked kinase (ILK) and/or its downstream effector, Akt. Intriguingly, ILK upregulation in T beta(4)-overexpressing SW480 cells seemed to be attributed mainly to a stabilization of this kinase by complexing with particularly interesting new Cys-His protein (PINCH) more efficiently. In the meantime, a strong correlation between the expression levels of T beta(4), ILK and E-cadherin in CRC patients was also revealed by immunohistochemical analysis. Taken together, these data suggest a novel role of T beta(4) in promoting CRC progression by inducing an EMT in tumor cells via upregulating ILK and consequentially its signal transduction.