Abstract LB-334: Signals from the microenvironment induce a malignant program accompanied by de novo epigenetic remodeling

Abstract

Abstract Introduction: The active acquisition of epigenetic changes is a poorly understood but important process in development, differentiation, and disease. Our work has recently demonstrated that repression of the p16/pRb pathway in human epithelial cells, a condition common to stem cells and many tumor cells, induces dynamic epigenetic remodeling resulting in the targeted methylation of selected CpG islands. We hypothesized that cells in this epigenetically-plastic state can be programmed by the microenvironment to acquire epigenetic changes that promote tumorigenesis. Methods: Normal human mammary epithelial cells (HMEC) and HMEC with repressed p16 were first transduced with constitutively active Ha-rasV12. In order to mimic the secretory aspects of the extracellular environment, the cells were subsequently cultured in a serum-rich environment. Results: When p16-repressed cells were challenged with oncogenic stress, they failed to undergo the classic proliferative arrest as documented in normal cells. When further stressed by being cultured in a serum-rich environment, they spontaneously immortalized and exhibited phenotypic changes indicative of epithelial to mesenchymal transition (EMT). The EMT was accompanied by de novo methylation of the E-cadherin promoter and increased motility. Conclusions: These data demonstrate that signals from the microenvironment can induce phenotypic and gene expression changes that result in de novo epigenetic alterations important in tumor progression.