The effects of microenvironmental stiffness on mouse epithelial mammary gland cells undergoing epithelial-mesenchymal transition were observed in this experiment. The stiffnesses used represented the range of stiffness found in normal mammary gland epithelial tissue and cancerous breast tissue. Transforming growth factor (TGF)-β was used to induce the transition in the cells and the expression of tropomyosin was used as a read out of change in cell phenotype. The increased stiffness induced a higher degree of EMT as compared to the softer environments as observed by the increased expression of tropomyosin by immunofluorescence while EMT was not observed in TGFβ treated cells on the soft environment as indicated by tropomyosin expression. There was no change in the cellular expression of tropomyosin in non EMT induced samples as stiffness varied. In TGFβ-treated cells, the increased stiffness increased the tropomyosin expressed. The RhoA/SRF inhibitor, CCG-1423 caused the expression of tropomyosin to decrease, indicating the involvement of the RhoA pathway in the regulation of tropomyosin expression in EMT. This experiment showed EMT is controlled by both TGFβ-signaling and the mechanical stiffness of the cellular microenvironment.
