Abstract 3480: 2'-O-ribose tRNA methylation in S. cerevisiae and implications for ovarian cancer
Authors: Doyle Frank , Rose Rebecca E. , Fabris Daniele , Endres Lauren 
Published: July 2017

Abstract
tRNAs are among the most chemically modified molecules of the cell, yet our understanding of how these modifications influence cell behavior remains poor. Much of the research to date has been focused on identifying specific modification events, particularly those that increase or decrease in response to oxidative stress. Less attention has been given to understanding how tRNA modifications, and their modifying enzymes (tRNA methyltransferases, or TRMs), regulate the cell's response to reactive oxygens, molecules that are known to influence cancer initiation, survival and malignant progression. Our overall idea is that tRNA modifying enzymes respond to oxidative stress by catalyzing the modification of target tRNAs, and that this in turn influences the translation of transcripts that encode proteins that limit the potentially harmful effects of reactive oxygens. Here we used S. cerevisiae as a model eukaryote system to test the hypothesis that 2'-O-ribose tRNA methylation protects cells against the cytotoxic effects of reactive oxygens. 2'-O-ribose TRM deletion mutants (TRMs 3Δ, 7Δ, 13Δ and 44Δ) were exposed to H2O2, rotenone and acetic acid in order to produce intracellular reactive oxygens. In growth and colony forming assays, each deletion strain was more sensitive to the killing effects of these toxicants when compared to the wild-type strain (BY4741), and the most pronounced effect was observed for the TRM3Δ mutant. We next performed a quantitative analysis of global changes in tRNA modifications in response to H2O2 using mass spectrometry. We found that several methyl-based modifications (i.e. 2'-O-methyl -adenosine, -guanosine, and -cytidine) were significantly decreased in TRM3Δ and 7Δ mutants, providing a direct link between oxidative stress and 2'-O-ribose tRNA methylation. These results support that 2'-O-ribose methyltransferase activity plays a cytoprotective role against oxidative stress in S. cerevisiae. Given the connections between reactive oxygens and cancer, we used cBioPortal to search for gene alterations of the human homolog of TRM3, TARBP1, in the genome datasets of The Cancer Genome Atlas. Interestingly, TARBP1 was found to be amplified in a significant proportion of breast, ovarian and liver cancers. From these observations, a new hypothesis emerged: increased 2'-O-ribose methyltransferase activity contributes to a cancer phenotype by enabling cancer cells to maintain reactive oxygens at sub-lethal levels that promote survival and malignant progression. Thus far, preliminary results show that cultured ovarian cancer cells have elevated levels of TARBP1 relative to normal ovarian cancer epithelial cells, providing a useful model system to test this hypothesis in future studies.
Citation Format: Frank Doyle, Rebecca E. Rose, Daniele Fabris, Lauren Endres. 2'-O-ribose tRNA methylation in S. cerevisiae and implications for ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3480. doi:10.1158/1538-7445.AM2017-3480