Roles of AP4 in Cell Migration
Student thesis: Doctoral Thesis
Related Research Unit(s)
|Award date||3 Dec 2015|
Tumor metastasis is known to be the primary cause of mortality in most cancer patients. To disassociate from the original tumor site to other non-adjacent sites, most malignant tumor cells undergo the epithelial-mesenchymal transition (EMT) to break away from the adhesions between the cells and their surrounding extracellular matrix and penetrate into the blood vessels or lymphatic vessels. Therefore, the abilities of cell migration and invasion are crucial for the cancer cells during tumor development. Recently, activator protein 4 (AP4) has been shown to be a mediator of EMT in colorectal cancer and high level of AP4 correlates with poor prognosis of cancer patients. It has been found that AP4 can up-regulate the genes involved in EMT and cell proliferation in colorectal cancer cells. Therefore, we tested the hypothesis that AP4 may also affect cell migration. Three different assays, including the wound healing assay, the Boyden chamber assay and the cell tracking assay, were employed to examine whether AP4 can regulate both cell migration and invasion. Immunofluorescence staining and Western blot analysis revealed that MDA-MB-231 cells underwent EMT when AP4 was up-regulated. On the other hand, MDA-MB-231 cells migration were down-regulated when DN-AP4 (dominant-negative AP4, lacking DNA binding domain) was expressed, which forms dimers with endogenous AP4 and inactivates the DNA binding ability of AP4. Interestingly, AP4 regulated retinal pigment epithelium (RPE) cell migration opposite of that of MDA-MB-231 cells. Migration of RPE cells was down-regulated by AP4 and up-regulated by DN-AP4. Further experiments reveal that p53 was involved during AP4-mediated cell migration. Mutant p53 and wild type p53 were activated by AP4 in MDA-MB-231 and RPE cells, respectively. Knockdown of p53 by siRNA significantly diminished the activation of cell migration by AP4 in MDA-MB-231, indicating that AP4 regulates cell migration via the activity of p53.