Abstract 4994: An integrated stress response activator causes cellular senescence and inhibits growth in multiple tumor cell types

Abstract

Abstract The Integrated Stress Response (ISR) is a program elicited by mammalian cells to attenuate global translation in response to a variety of stressors. There are four branches of the ISR, including those mediated by PERK, which responds to endoplasmic reticulum stress, and GCN2, which is activated by amino acid deprivation. Activation of these kinases ultimately leads to translational upregulation of the transcription factor ATF4, which modulates the expression of genes involved in amino acid transport and synthesis, oxidative stress, and differentiation. Complete abrogation of the ISR or its overactivation by pharmacological agents in the presence of hypoxic or nutrient stress has been shown to lead to cell death. Here, we employed a small molecule screen to identify modulators of ATF4 expression via a reporter construct with the 5′-UTR of ATF4 fused to the luciferase gene. From this screen, a compound with ATF4-activating properties was identified. Multiple assays have been used to characterize the effects of this drug, referred to as E235, on both transformed and normal cells. Specifically, we have shown that E235 induces the ISR in a dose-dependent manner in tumor cell lines (HT1080 fibrosarcoma, B16F10 melanoma) but not in normal human diploid cells. The drug also reduces cell viability and proliferation at low μM concentrations, which does not appear to be dependent on apoptosis. By performing live cell microscopy, we observed that after prolonged (>24h) treatment with 1μM E235, the majority of cells displayed senescence-like morphology. This was confirmed by additional experiments, such as staining for senescence-associated β-galactosidase activity and immunoblotting for the upregulation of the cdk inhibitor p21. Future experiments will focus on establishing the roles of ATF4, p21 and p53 in E235-mediated senescence. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4994. doi:1538-7445.AM2012-4994