Abstract 291: Activated AKT signaling exerts epigenetic effects on cell motility and epithelial-mesenchymal transition in breast epithelia

Abstract

Abstract Growing body of evidence demonstrates that AKT signaling plays a pivotal role in orchestrating various neoplastic phenotypes of breast carcinomas. Although the question of how tumorigenic activities are attributed to the respective AKT isoforms (namely AKT1, AKT2, and AKT3) has not been well delineated, AKT1 seems to impede transwell migration as well as epithelial-mesenchymal transition (EMT), whereas AKT2 exerts an opposing effect. Yet, the role that AKT3 plays remains poorly understood. Moreover, activated PI3K/AKT signaling augments the stem/progenitor subpopulation, which is presumably influenced from enhanced EMT. However, these findings were merely inferred from the results of ablating PTEN (one of AKT antagonists) and implementing PI3K as well as AKT inhibitors, but without ectopic delivery of activated AKT. As such, we aimed to substantiate the aforementioned outcomes by overly expressing various constitutive AKT isoforms and then observing their respective effects on cell motility, EMT, and stem/progenitor cell enrichment. To our surprise, rather than exerting an activation as previously reported, overexpression of all three AKT isoforms in the noncancerous breast epithelial cell line MCF10A consistently resulted in an inhibitory effect on the expression of EMT hallmarks, including upregulation of E-cadherin as well as down-regulation of N-cadherin and Vimentin. Importantly, inclusion of an EMT-inducer namely TGF-beta exerted a relatively more prominent suppressive effect. In addition to MCF10A, a similar outcome was rendered in another breast cancer cell line, namely SUM159, indicating that AKT can exert comparable effects on both normal and neoplastic breast epithelia in an isoform-independent manner. Regarding stem cell enrichment, we observed that AKT activation surprisingly manifested negligible effects in both MCF10A and SUM159 cells, as opposed to an increase appraised by knocking-down PTEN. Furthermore, as we have reported that activated AKT signaling can impose epigenetic silencing on a tumor suppressor gene CST6 by promoter hypermethylation, whether or not and which AKT isoforms can exert epigenetic effects on motility, or on EMT, were evaluated. Interestingly, expression of EMT hallmarks can be partially restored by using epigenetic drugs (DAC and TSA); a finding thereby indicates the likelihood of epigenetic regulation. Together, we highlighted a novelty that activated AKT signaling unlikely promotes EMT or enriches stem cells. Our data will be further clinically validated in breast tissues procured from women and thus the effect of AKT on both non-cancerous and malignant primary mammary epithelia can be investigated. Future therapeutic regimens implementing AKT-inhibiting drugs should require extra precautions as they might exert opposite effects of reactivating EMT followed by enriching stem cell subpopulation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 291.