TGFβ1-mediated epithelial to mesenchymal transition is accompanied by invasion in the SiHa cell line

It has recently been suggested by several investigators that the epithelial-mesenchymal transition-inducing capacity of TGFβs contributes to invasive transition of tumors at later stages of carcinogenesis. In the present study, we examined the possibility of TGFβ1-stimulated epithelial-mesenchymal transition in SiHa cell line, detailed molecular events in the process, and its possible contribution to the invasive transition of tumors. TGFβ1-induced epithelial-mesenchymal transition of SiHa cells was based on morphological and biochemical criteria; actin stress fiber formation, focal translocalization of integrin αv, talin, and vinculin, fibronectin-based matrix assembly at the cell periphery, and translocalization and down-regulation of E-cadherin. TGFβ1 also stimulated surface expression of integrin αvβ3 and FAK activation. Focal translocalization of integrin αv preceded actin reorganization and fibronectin matrix assembly, and functional blocking of the integrin suppressed actin stress fiber formation. Furthermore, induction of actin reorganization and fibronectin matrix assembly by TGFβ1 were shown to be mutually independent events. These changes were irreversible because 5 minutes pulse exposure to TGFβ1 was sufficient to stimulate progress of actin reorganization and fibronectin matrix assembly. In further studies with raft culture, TGFβ1 was found to stimulate invasion of SiHa cells into a type I collagen gel matrix. In conclusion, TGFβ1 stimulated epithelial-mesenchymal transition of SiHa cells, indicating a positive role in the invasive transition of tumors.