| Popis: |
Currently accepted models for metastatic progression involve several steps. The first of these, local invasion of the primary tumor, requires detachment from the tumor mass and increased mobility. Epithelial to Mesenchymal Transition (EMT) is believed to play an important role in this increased mobility and consequent local invasion. Following local invasion, the tumor cells must intravasate and survive in the bloodstream prior to extravasation. Once the metastatic tumor cells have completed these steps, it is believed that the invading cells must undergo Mesenchymal to Epithelial Transition (MET), returning to their epithelial phenotype, in order to effectively establish metastasis. Importantly, E-cadherin expression positively correlates with the epithelial status of the cell. As part of the EMT mechanism, the change from E-cadherin to N-cadherin is driven by the ZEB and SNAIL family transcription factors. Loss of E-cadherin contributes to the increased cell motility associated with EMT by reducing the number of cell-cell contacts, allowing the cell to emerge from its local tissue environment. On the contrary, during MET, the re-expression of E-cadherin reestablishes cell connections.In order to test the requirement of MET during the final stages of metastasis, we used Cas9 to knock-out E-cadherin in the murine breast cancer cell line 4T1. As a result, the cells converted to a mesenchymal-like morphology. We hypothesized that the permanent disruption of the E-cadherin gene would prevent the cancer cells from undergoing MET thereby suppressing their ability to form metastasis. Surprisingly, upon implantation of the modified 4T1 cells, there was no difference in the appearance of metastasis as compared to the control. Both parental and E-cadherin knock-out 4T1 cells were able to form metastasis in the lung. These results demonstrate that E-cadherin is not necessary for the metastatic process in 4T1 cells. Further, the study suggests that MET may not be crucial during the final stages of metastasis. More detailed understanding of when MET is required, if at all, during metastatic progression will help to shape treatment strategies and continued research of metastatic disease. |
