Modulation of gene expression by human cytosolic tRNase Z^L through 5′-half-tRNA

A long form (tRNase Z^L) of tRNA 3′ processing endoribonuclease (tRNase Z, or 3′ tRNase) can cleave any target RNA at any desired site under the direction of artificial small guide RNA (sgRNA) that mimics a 5′-half portion of tRNA. Based on this enzymatic property, a gene silencing technology has been developed, in which a specific mRNA level can be downregulated by introducing into cells a synthetic 5′-half-tRNA that is designed to form a pre-tRNA-like complex with a part of the mRNA. Recently 5′-half-tRNA fragments have been reported to exist stably in various types of cells, although little is know about their physiological roles. We were curious to know if endogenous 5′-half-tRNA works as sgRNA for tRNase Z^L in the cells. Here we show that human cytosolic tRNase Z^L modulates gene expression through 5′-half-tRNA. We found that 5′-half-tRNA ^Glu, which co-immunoprecipitates with tRNase Z^L, exists predominantly in the cytoplasm, functions as sgRNA in vitro, and downregulates the level of a luciferase mRNA containing its target sequence in human kidney 293 cells. We also demonstrated that the PPM1F mRNA is one of the genuine targets of tRNase Z^L guided by 5′-half-tRNA ^Glu, Furthermore, the DNA microarray data suggested that tRNase Z^L is likely to be involved in the p53 signaling pathway and apoptosis.