Abstract 999: PTEN/PI-3 kinase pathway's regulation of β-catenin in epithelial to mesenchymal transition (EMT)
Authors: Sidhu Jaskiran , Persad Amit , Hao Li , Persad Sujata 
Published: June 2012

INTRODUCTION: Cancer metastasis is responsible for 90% of cancer-related deaths. For metastasis to occur, cells must shed their epithelial phenotype and acquire a mesenchymal phenotype in order to gain the characteristic motility and invasiveness. These alterations are referred to as “Epithelial- Mesenchymal Transition (EMT)”. Beta-Catenin (β-cat) is a dual-role protein. It serves a role in cell-cell adhesion; it links E-cadherin to the actin cytoskeleton. The second role is its involvement in the canonical Wnt-signaling pathway. It acts as a co-activator of the lymphoid enhancer factor/ T-cell factor family of DNA-binding proteins. The binding of this complex activates transcription of genes that control cell proliferation and invasiveness. Excessive transcription of these genes mediated by excess β-cat is associated with the oncogenic properties of cancer cells and β-cat has been widely implicated as an oncogene in human cancers. We determined the role of β-cat and the regulation of its expression and activity by the PTEN/ Phosphatidyl-inositol-3 Kinase (PI3K) pathway during EMT associated with melanoma progression. PTEN is a dual lipid/protein phosphatase which functions to oppose the kinase function of PI3K. Absence of PTEN allows for the deregulation of the pathway, leading to sustenance of pro-survival and anti-apoptotic cellular response.

METHODS: Our studies were done using a panel of cell lines representative of the various phases of melanoma progression as a model of EMT (Melanocyte=HeMaLp; Mixed Radial & Vertical Growth Phase = A375; Radial Growth Phase = WM35; Vertical Growth Phase = WM793; Metastatic Melanoma = A2058). We determined alterations in cellular expression, sub cellular distribution and activity of β -Cat, and PTEN during EMT progression.

RESULTS: We determined that there was a loss in the expression of the tumor suppressor PTEN in the melanoma cell lines with complete absence of its expression in the vertical and metastatic melanoma cell lines. This was correlated with an increase in total cellular levels of β-Cat and active β-Cat. We then carried out the transient transfection of the PTEN-null metastatic melanoma cell line (A2058) with a vector containing wild type PTEN tagged with GFP. Our results show a decrease in overall β-Cat and active-β-Cat levels. There was an increase in phospho-β-Cat at ser-33/37 and thr-41 without any alteration to the phosphorylation at ser-45. These changes are associated with a decrease in cellular levels of β-Cat with a significant attenuation of nuclear levels of active β-Cat.

CONCLUSIONS: Our results show a direct regulatory role of PTEN/PI3K pathway upon the levels and activity of β-Cat.

SIGNIFICANCE: Components of the PTEN/PI3-Kinase pathway involved in regulating β-Cat levels and activity represent potential molecular targets, which could be intercepted to limit progression to metastatic disease.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 999. doi:10.1158/1538-7445.AM2011-999