Overexpression of Schizosaccharomyces pombe tRNA 3'-end processing enzyme Trz2 leads to an increased cellular iron level and apoptotic cell death.

The fission yeast Schizosaccharomyces pombe has two tRNase ZL genes (trz1 and trz2) involved in nuclear and mitochondrial tRNA 3′-end processing, respectively. Overexpression of trz2 but not trz1 is toxic to cells. In the present work, we showed that trz2 overexpression led to apoptotic cell death, as revealed by DAPI and Annexin V-FITC staining. Overexpression of trz2 also caused a loss of mitochondrial membrane potential and an increased reactive oxygen species (ROS) formation. These effects required mitochondrial localization but not its catalytic activity. RNA sequencing (RNA-seq) analysis revealed increased expression levels of genes involved in iron uptake and/or iron homeostasis, suggesting an elevated level of intracellular iron in the trz2-overexpressing cells. Indeed, we showed that overexpressing trz2 increased the level of intracellular iron by ∼2-fold. We further showed that the iron chelator, bathophenanthroline disulfonic acid (BPS) nearly restored the viability of trz2-overexpression cells and reduced ROS levels in the cells. These results suggest that trz2 overexpression may cause mitochondrial dysfunction, which is likely to lead to perturbation of iron homeostasis, ROS accumulation and induction of apoptotic cell death in S. pombe.