Abstract 3332: Radiation-induced translational control of gene expression in glioblastoma stem-like cells
Authors: Wahba Amy , Rath Barbara H. , Camphausen Kevin , Tofilon Philip J. 
Published: August 2015

Radiation-induced gene expression has long been assumed to comprise a protective response against radiation-induced cell death. However, whereas radiation-induced changes in total cellular mRNA (i.e., the transcriptome) have been studied extensively, the vast majority of mRNA changes detected do not correlate with changes in the corresponding protein, a situation that has made it difficult to assign functional significance to radiation-induced gene expression. In contrast, analysis of polysome-bound RNA in established cell lines indicates that radiation selectively regulates gene translation, a process that operates independently from changes in the transcriptome. Moreover, characteristics of the radiation-induced translatome include a correlation between the genes whose translational activity is affected by radiation and the expression of their corresponding protein. To investigate the role of the translational control of gene expression in the radioresponse of glioblastoma (GBM), we have focused on a series of human glioblastoma stem-like cells (GSCs). Radiation-induced translatomes and transcriptomes were defined using microarray analysis of polysome-bound RNA and total RNA, respectively, for 4 GSCs and 2 normal cell types (astrocytes and pericytes). For each cell type, there was little overlap between the radiation-induced translatomes and transcriptomes. Subsequent analyses focused on those genes whose expression was only modified in the translatome, i.e., those subject to radiation-induced translational control. Hierarchical clustering of radiation-induced changes in KEGG Pathways showed that while the radiation-induced changes in the GSC lines were more similar to each other than to the normal CNS cells, there were also cell line-dependent changes. Rather than screen individual proteins, Ingenuity Pathway Analysis (IPA) was used to identify potential functional consequences of radiation-induced translational control. A significant network activated in all GSC translatomes was Response to DNA Damage. Consistent with activation of this pathway, post- irradiation addition of the mTOR inhibitor INK128, which inhibits translational control, slowed the dispersal of γH2AX foci. Among the radiation-induced translatome networks activated in a cell line specific manner was Mitochondrial Function. This was validated by the detection of radiation-induced changes in mitochondrial DNA and mass, which were prevented by addition of INK128 after irradiation. These results suggest that analysis of radiation-induced translatomes may provide novel insight into the general as well as cell specific mechanisms mediating radioresponse. In addition, they suggest that the translational control of gene expression may provide a source of molecular targets for GBM radiosensitization.

Citation Format: Amy Wahba, Barbara H. Rath, Kevin Camphausen, Philip J. Tofilon. Radiation-induced translational control of gene expression in glioblastoma stem-like cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3332. doi:10.1158/1538-7445.AM2015-3332