Abstract 2016: Potential role of polo-like kinase 1 in epithelial-mesenchymal transition in melanoma

Abstract

Abstract Mammalian polo-like kinase 1 (Plk1), an important serine/threonine kinase, has been shown to be a critical regulator of mitosis and cytokinesis. A number of studies, including those from our laboratory, have shown that Plk1 is significantly overexpressed in several cancers, including melanoma. Plk1 has also been linked with poor disease prognosis in cancer patients. A limited number of recent studies have suggested that Plk1 may be involved in epithelial-mesenchymal transition (EMT) in different cancers. However, the role of Plk1 in EMT process in melanoma has not been studied. Indeed, EMT plays a driving role in the acquisition of cancer metastasis and an important hallmark of EMT is downregulation of epithelial marker E-cadherin, and upregulation of mesenchymal marker, N-cadherin. In this study, we investigated whether the kinase activity of Plk1 plays a role in EMT process by modulating EMT markers in melanoma cells. To determine this, we performed western blots, RT-qPCR, cell migration and cell invasion assays using A375 melanoma cells stably transfected with plasmids for wild-type (WT) Plk1 overexpression, constitutively active Plk1 (T210D) and kinase-inactive (K82R) Plk1, as well as shRNA-mediated Plk1 knockdown. We observed that overexpression of WT Plk1 upregulated the mesenchymal markers N-cadherin, Vimentin, and Fibronectin, and downregulated the epithelial marker E-cadherin. We also found that the modulation in EMT markers by Plk1 in melanoma cells was associated with the upregulation of transcription factors Snail and Zeb1. Interestingly, downregulation of endogenous Plk1 by specific shRNA resulted in a downregulation of N-cadherin, Vimentin, Fibronectin, Snail and Zeb1. Further, when we assessed the EMT-related molecular changes in A375 melanoma cells containing constitutively active and kinase-inactive Plk1, the cells containing constitutively active Plk1 showed a significant decrease in epithelial marker as well as marked increases in mesenchymal markers. However, the cells containing kinase-inactive Plk1 showed the opposite trend. Moreover, A375 melanoma cells containing constitutively active Plk1 showed higher migration and invasion potential, whereas cells containing kinase-inactive Plk1 showed limited cell migration and invasion. Overall, these results suggest that Plk1 is involved in the EMT process and its kinase activity is important for EMT-related changes in melanoma cells. Further studies are in progress to determine the cause-and-effect molecular mechanisms of Plk1 mediated EMT regulation. Citation Format: Gagan Chhabra, Chandra K. Singh, Mary A. Ndiaye, Nihal Ahmad. Potential role of polo-like kinase 1 in epithelial-mesenchymal transition in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2016.