Inhibition of PI3 kinase/Akt pathway is required for BMP2-induced EMT and invasion

Although dysregulation of bone morphogenetic protein (BMP) signaling has been linked to various types of cancers, the relationship between abnormal activation of these signaling pathways and tumorigenesis is not clear. The purpose of the current study was to clarify how BMP2 is involved in colon cancer aggressiveness. The data showed that SW480 and DLD-1 cells displayed different responses to short- and long-term exposure to BMP2. During the first 24 h of exposure to BMP2, these cells were growth-inhibited, whereas surviving cells became resistant to growth inhibition, showing epithelial-to-mesenchymal transformation (EMT) and enhanced motility and invasiveness. Interestingly, in highly metastatic mesenchymal colon carcinoma cells (CT26), blockade of BMP2 signaling by BMP2 siRNA prevented EMT, motility and invasiveness; rather, blockade of BMP2 signaling caused a mesenchymal-to-epithelial transition (MET). The levels of phosphorylated Akt were very different between the two cell types; the BMP2-sensitive SW480 and DLD-1 cells had much higher levels of expression than the BMP2-resistant SW480 and DLD-1 and CT26 cells. CT26 cells, following exposure to BMP2 and activation of Akt, escaped the EMT-induced cellular motility and invasiveness. Moreover, LY294002 treatment of BMP2-sensitive SW480 cells blocked cell growth and enhanced motility and invasiveness. Together, these results suggest that suppression of the PI3 kinase/Akt pathway is correlated with the development of BMP2 resistance and invasion in BMP2-induced EMT in colon cancer.