Abstract LB-39: Phenotypic switching and molecular anatomy of malignant progression (E-M-T/M-E-T).

Abstract

Abstract Proliferation and invasion are two fundamental phenotypes required for malignancy while phenotypic switching is required for malignant progression. Thus, during malignant progression primary tumor cells switch from proliferative to invasive phenotypes and switch again to form proliferating metastases. The acquisition of the invasive phenotype through epithelial-mesenchymal-transition (E-M-T) is a crucial step in tumor progression, as is mesenchymal-epithelial-transition (M-E-T) or switching to become tumor metastases. Using a reductionist approach, we have been able to reproduce these steps through a combination of in vitro and in vivo methods: Beginning with prostate and ovarian carcinoma cells, we show that the majority are epithelial (E) cells, grow as acini in three dimensional (3D) Matrigel and are nonresponsive to hepatocyte growth factor/scatter factor (HGF/SF). These E cells grow in soft agar and are tumorigenic in immunocompromised mice. However, there is a second cell population which also grows as acini in 3D Matrigel, but display extensive branching morphogenesis when HGF/SF is present. These subclones are mesenchymal (M), are highly invasive in response to HGF/SF, but do not grow in soft agar and display low or no tumorigenicity in vivo. We show that M cells can originate in vitro from the non-invasive E subclones. However, M subclones undergo M-E-T only in vivo, at low frequency mimicking tumor progression to proliferating metastases. We show that E-M-T switching events occur with loss of E-Cadherin and the gain of c-MET expression. Expression of β-Catenin does not change with phenotypic switching, but with the loss of E-Cadherin, its localization shifts from the cell membrane to nuclear/cytoplasmic location, activating β-Catenin dependent expression. Moreover, depleting E-Cadherin in E cells triggers nuclear/cytoplasmic shift of β-Catenin and enhanced HGF/SF-c-Met signaling, while ectopic expression of E-Cadherin in M cells restores E phenotype and decreases HGF/SF-Met signaling. Importantly, we show that phenotypic switching occurs with distinct changes in karyotype that dictate changes in the chromosome transcriptome and the expression of genes that account for changes to M or to E phenotypes, thereby implicating chromosome instability as a key mechanism for phenotypic switching. We conclude that chromosome instability generates the transcriptome diversity in vitro or in vivo, which in the appropriate environment, leads to expansion of clonal variants responsible for phenotypic switching. 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 LB-39. doi:10.1158/1538-7445.AM2011-LB-39