Ribosome Quality Control Mechanism Mitigates the Cytotoxic Impacts of Ribosome Collisions Induced by 5-Fluorouracil

Abstract

Translation of aberrant or damaged mRNAs results in ribosome stalling and collisions. The Ribosome Quality Control (RQC) mechanism detects collided ribosomes and removes aberrant mRNAs and nascent peptides, thus preventing their cytotoxic effects. Conversely, excessive or unresolved ribosome collisions can induce apoptosis. 5-Fluorouracil (5FU) forms the backbone of standard-of-care chemotherapeutic regimens for several types of cancer. Although best known for its incorporation into DNA and inhibition of thymidylate synthase, a major determinant of 5FUs anticancer activity is its incorporation into RNAs. Nevertheless, the mechanism(s) underlying RNA-dependent 5FU cytotoxicity and the cellular response to its impact on RNA metabolism remain unclear. Here, we report a key role for RQC in mitigating the cytotoxic effects of 5FU-induced dysregulation of mRNA translation. We show that acute 5FU treatment results in the rapid induction of the mTOR signalling pathway, an enhanced rate of mRNA translation initiation, and increased ribosome collisions that trigger RQC. We also found that RQC deficiency, caused by the depletion of ZNF598, results in increased 5FU-induced cell death, a phenotype that is reversed by inhibition of mTOR or repression of mRNA translation initiation. Importantly, 5FU treatment enhances the expression of key RQC factors, including ZNF598 and GIGYF2, via an mTOR-dependent post-translational regulation mechanism. This acute adaptation likely mitigates the cytotoxic consequences of increased ribosome collisions upon 5FU treatment. Overall, our data indicate a heretofore unknown mTOR-dependent mechanism that augments the RQC process, mitigating the cytotoxicity of 5FU and undermining its anticancer efficacy.