Abstract 1887: MDM2 induces a partial/hybrid EMT phenotype switching through TGFβ1-Smad signaling pathway

Epithelial-Mesenchymal Transition (EMT) is a key step in the induction of metastasis, which is critical for the conversion of early-stage prostate tumors into metastatic malignancies. Therefore, identifying the signaling pathways promoting EMT is crucial for the prediction of disease progression and consequently treatment outcomes. The role of MDM2 proto-oncogene was investigated in regulating EMT in LNCaP prostate cancer cells. MDM2 over-expression in LNCaP-MST (MDM2 transfected prostate cancer cells) caused a reduction in epithelial characteristics, by altering the expression levels of proteins that are involved in cell adhesion, cell polarity and cell-ECM interactions. While forcing the loss of epithelial characteristics, the MDM2 oncogene seems to facilitate the gain of mesenchymal properties (such as increased motility, invasive properties, and a spindle-like morphology etc.). These phenotypic changes are generally due to cytoskeletal rearrangements and increased expression of mesenchymal markers, which was clearly identified through our western blotting and fluorescence microscopy imaging analysis in LNCaP-MST cells compared to the LNCaP cells. Nutlin-3, an MDM2 specific inhibitor was able to reverse the expression of mesenchymal markers, which further confirmed the role of MDM2 in phenotype switching. Analysis of cell culture supernatants using ELISA indicated that LNCaP-MST cells secreted two folds higher levels of TGFβ1 compared to LNCaP cells, which appears to cause the activation of downstream Smad signaling pathway leading to EMT. Activation of the TGFβ1-Smad pathway also results in the increased transcription of mesenchymal markers (N-cadherin, vimentin, and fibronectin) while retaining the epithelial characteristics as evidenced by the unaltered levels of E-cadherin. Recent reports have established that, while transitioning between the epithelial and mesenchymal phenotypes, cells can also attain a hybrid, partial, or intermediate EMT phenotypes. Cancer cells in this hybrid phenotype can migrate collectively as clusters (epithelial) or as a single cell (mesenchymal) and exhibit stemness and drug resistance. In addition, these migratory cells with hybrid characteristics can attain the necessary phenotype and growth depending on the microenvironment that is surrounding the metastatic sites. So far, our results have clearly demonstrated that MDM2 could serve as a key regulator to drive the EMT of prostate cancer cells, and this process seems to be aided by the elevation of TGFβ1 signaling. Thus, the pro-metastatic role of MDM2 oncoprotein has been steadily expanding in the last few years, and the newest knowledge acquired through our experiments is the confirmation of its ability to induce hybrid EMT phenotype in prostate cancer cells, (This project was supported by the generous financial support from The Royal Dames of Cancer Research Inc., Ft. Lauderdale, Florida) Citation Format: Priya Dondapati, Simran Agarwal, Deepthi Gangaram, Appu Rathinavelu. MDM2 induces a partial/hybrid EMT phenotype switching through TGFβ1-Smad signaling pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1887.