Abstract 3954: SAT1 (Spermidine/spermine-N1-acetyltrasferase 1) promotes radiation resistance in glioblastoma multiforme
Authors: Brett-Morris Adina , Welford Scott M. , Bar Eli , Spina Raffaella , Wright Bradley , Zhang Junran , Lu Jun , Seo Yuji 
Published: May 2015

Abstract
Glioblastoma multiforme (GBM), is the most common and severe form of brain cancer. The median survival time is approximately 14 months due to poor responses to surgery, radiation and chemotherapy. GBM cells have been shown to exhibit high resistance to radiation. In order to understand the mechanisms involved in radioresistance, we conducted a genetic screen using a shRNA library on GBM cell lines to identify genes whose inhibition would sensitize cells to radiation. The results were cross-referred with the Oncomine and Rembrandt databases to focus on genes that are highly expressed in GBM tumors, and are associated with poor patient outcomes. Spermidine/spermine-N1-acetyltransferase 1 (SAT1), an enzyme involved in polyamine catabolism, was identified as a gene that promotes resistance to ionizing radiation (IR), is overexpressed in brain tumors and its high expression correlates with poor outcomes. The objective of this study is to explore the role of SAT1 in radioresistance with the purpose of targeting SAT1 as a means to sensitize tumors. The knockdown of SAT1 using, shRNA and siRNA approaches, in multiple cell lines and neurosphere lines results in sensitization of GBM cells to radiation in colony formation assays. This was seen specifically in G2/M and S phases, leading to the hypothesis that SAT1 plays a role in homologous recombination (HR). By measuring HR in the DR-GFP reporter system, we confirmed that SAT1 promotes HR, since depletion of SAT1 results in decrease in HR. To test whether SAT1 depletion sensitizes cells to S-phase poisons, SAT1 knockdown GBM cells were then exposed to camptothecin, and were found to be sensitized. To explore the mechanisms of interaction of SAT1 with the DNA damage pathway, chromatin immunoprecipitation (ChIP) was performed under the theory that polyamine-DNA interactions may be altered during DNA repair. The results show that polyamines are decreased in the chromatin of the HR site following induction of double-strand breaks. Interestingly, western blot analyses show that SAT1 knockdown decreases the levels of acetylated histone 3 (H3) proteins, suggesting a new role of SAT1 in chromatin remodeling. Overall the results suggest that SAT1 is involved in radioresistance in GBM through regulation of HR and alterations in chromatin remodeling at sites of damage. Our findings suggest that the biological significance of SAT1 expression in GBM lies in its contribution to cell radioresistance and SAT1 may potentially be a therapeutic target to sensitize GBM to cancer therapies.
Citation Format: Adina Brett-Morris, Scott M. Welford, Eli Bar, Raffaella Spina, Bradley Wright, Junran Zhang, Jun Lu, Yuji Seo. SAT1 (Spermidine/spermine-N1-acetyltrasferase 1) promotes radiation resistance in glioblastoma multiforme. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3954. doi:10.1158/1538-7445.AM2014-3954