The cell and stress-specific canonical and non-canonical tRNA cleavage

Abstract

Following stress, tRNA is cleaved to generate tRNA halves (tiRNAs). These stress induced small RNAs have been shown to regulate processes such as translation initiation and stem cell function. To date, angiogenin (ANG) is considered the main enzyme that cleaves tRNA at its anti-codon site to generate 35 ~ 45 nucleotide long 5' and 3' tiRNA halves. Herein, using rat model of focal ischemia and 2 different rat neuronal cell lines exposed to different stresses, we show that tRNA cleavage is a selective process that is heterogenous amongst different tRNAs. We also report for the first time the existence of non-canonical tRNA cleavage that is angiogenin independent and that tRNA cleavage is cell specific and stress specific. Moreover, we show that angiogenin-mediated tRNA cleavage itself is tRNA selective and that angiogenin overexpression doesn't lead to the expected overt tRNA cleavage in the cells. Finally, the proposed enzymes responsible for this non-canonical tRNA cleavage do not appear to be regulated by RNH1, the angiogenin inhibitor.

The stress specific impact of ALKBH1 on tRNA cleavage and tiRNA generation

“…Moreover, In this work, we consistently observed the cleavage of several tRNAs into different fragments; the canonical 35 ~ 45 nucleotide fragments induced by angiogeninmediated cleavage, and several larger 'non-canonical' fragments. We have discussed this observation in other work [27], where we observed that the RNase/s responsible for this non-canonical cleavage was not regulated by RNH1, the angiogenin inhibitor [34,35]. Interestingly, we observed here that Alkbh1 mediates enrichment of various canonical and non-canonical fragments differently, indicating a probable role of tRNA methylation in regulating or guiding cleavage sites.…”

“…Certain tRNAs were shown to be bound to Alkbh1 using CLIP [17], thus, we probed some of these tRNA species as well as other non-Alkbh1 bound tRNAs according to Liu et al [17]. Interestingly, we observed cleavage of tRNA into multiple fragments, which we have observed previously (and dubbed the larger tiRNA fragments non-canonical fragments) [27]. Herein, not only we observed stress specific effects of Alkbh1 on tRNA cleavage, we also observed tiRNA fragment-specific effects as we will discuss.…”

Processing by RNase 1 forms tRNA halves and distinct Y RNA fragments in the extracellular environment

“…Notably, RNase 1-dependent cleavage of the CCA tail occurs between the two cytidine residues of the CCA tail, whereas angiogenin cleaves between the second cytidine and the adenosine, probably due to the substrate preference of this enzyme ( 71 ). Several recent studies claim that tRNA halves are produced in cells even in the absence of angiogenin ( 72 , 73 ), or that cleavage of tRNAs at both anticodon loop and CCA tail is performed in the absence of angiogenin ( 74 ). Further work is needed to establish whether RNase 1 is involved in formation of intracellular tRNA halves in response to stress.…”