Genes for tRNA recycling are upregulated in response to infection with Theiler's mouse encephalitis virus

The concept of tRNA recycling has recently emerged from the studies of ribosome-associated quality control. Therein tRNase Z^S removes the 2', 3'>p from the ANKZF1-cleaved tRNA and the subsequent TRNT1 action re-generates the intact tRNA. To know the roles of the tRNA recycling in vivo, we investigated how viral infection affects the tRNA recycling system by analyzing the mRNA levels of tRNase Z^S and TRNT1. We found that both genes in HeLa cells are upregulated in response to infection of Theiler's mouse encephalitis virus but not to that of an influenza A virus. Upregulation was also observed in cells infected with encephalomyocarditis virus with reduced efficiency. The levels of the IFN-β mRNA appeared to positively correlate with those of the tRNase Z^S and TRNT1 mRNAs. The tRNase Z^S gene may be regulated post-transcriptionally in the cells infected with Theiler's mouse encephalitis virus.

Transcription from the proximal promoter of ELAC1, a gene for tRNA repair, is upregulated by interferons

tRNase Z^S (ELAC1) and TRNT1 function in tRNA recycling. Recently, we have shown that these genes are upregulated in the cells infected with Theiler's mouse encephalitis virus (TMEV), implying that tRNA recycling functions in response to viral infection. To address the molecular mechanism underlying the ELAC1 upregulation in the cells infected with TMEV, we performed luciferase assays using various plasmid constructs harboring the ELAC1 promoter region. The luciferase expression from a construct containing the full-length ELAC1 promoter was augmented by TMEV, poly IC, IFN-β, or IFN-γ. We identified four IFN-stimulated responsible elements (ISREs) in the proximal promoter region. The luciferase expression from the constructs that lack all the ISREs was strongly reduced compared with that from the constructs with the four ISREs in the presence of IFN-β or IFN-γ. The observation that the ISREs from the ELAC1 promoter are essential for the gene upregulation by IFN-β or IFN-γ suggests that the ELAC1 gene is upregulated by IFNs.