Abstract 841: UTR analysis identifies Musashi1 as a translational regulator of radiation-induced Golgi-related gene expression

The cellular radioresponse is regulated by post-translational modification of constitutively expressed proteins and by changes in gene expression. Although the role of constitutively expressed proteins, such as those involved in the DNA damage response and cell cycle checkpoints, is well-understood in the context of the radioresponse, radiation-induced changes in gene expression are not as clearly defined. We have previously demonstrated that glioblastoma stem-like cells (GSCs) alter their gene expression at the translational level in response to ionizing radiation (IR). In particular, the NSC11 GSC line demonstrated thousands of genes differentially translated at one hour after a dose of 2 Gy, while considerably fewer were modified at the transcriptome level. Furthermore, there was little overlap between the transcriptome and the translatome. Genes undergoing translational regulation in response to IR fell into distinct functional categories, including mitochondrial structure and function, Golgi function, and translational regulation. Here, we aimed to elucidate the mechanism by which IR induces translational changes in the NSC11 GSC line. NSC11 cells were either exposed to 2 Gy or mock irradiated, and polysomes were isolated by sucrose gradient fractionation one hour later. Polysome-bound mRNA was purified and analyzed by microarray. The 5’ and 3’ untranslated regions (UTRs) of the top 75 up- and down-regulated genes were analyzed for the presence of regulatory elements. The most frequently occurring element in the UTRs of both the top up- and down-regulated genes was the Musashi1 binding site. Musashi1 is an RNA binding protein that typically binds to 3’ UTRs to regulate mRNA translation. It is a neural stem cell marker, and its expression is correlated with the grade of malignancy in glioma. GO term analysis of known Musashi1 target genes that were translationally regulated in response to IR revealed an enrichment of genes involved in Golgi function and vesicular trafficking. Knockdown of Musashi1 prevented IR-induced Golgi dispersal in NSC11 cells. Musashi1 knockdown also radiosensitized NSC11 cells, indicating a role for the protein in the cellular radioresponse. Together, these data demonstrate that in the NSC11 GSC line, Musashi1 contributes to radiation-induced translational regulation, specifically in the context of Golgi-related genes, and suggests that Musashi1 is a novel target for radiosensitization. Citation Format: Stacey L. Lehman, John W.