Reducing DNA Damage with Tyrosyl-tRNA Synthetase

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Sci. Signal.  04 Nov 2014:
Vol. 7, Issue 350, pp. ec311
DOI: 10.1126/scisignal.aaa2038

Protein synthesis occurs in the cytosol and requires tRNAs loaded with the appropriate amino acid, which is catalyzed by tRNA synthetases. However, tyrosyl-tRNA synthetase (TyrRS) has a nuclear localization signal that is blocked when TyrRS binds its cognate tRNA, suggesting a potential mechanism for regulating protein synthesis. Wei et al. exposed cultured cells to various stresses and found that conditions that produced oxidative stress, such as ultraviolet light, peroxide, and sodium arsenity, specifically stimulated the accumulation of TyrRS in the nucleus. Transcriptional profiling of cells overexpressing TyrRS compared with control cells indicated that genes involved in the DNA damage response and regulation of the cell cycle were specifically stimulated in the TyrRS-overexpressing cells. Targeted mRNA analysis of a subset of these genes showed that exposure to peroxide also stimulated the expression of these genes and that knockdown of TyrRS blocked this response. Cells in which TyrRS was knocked down and then reconstituted with either wild-type TyrRS or a mutant that could not translocate to the nucleus showed that basal expression and peroxide-stimulated induction of the DNA damage response genes was lower in the cells expressing the nuclear translocation-deficient TyrRS. Furthermore, the cells reconstituted with the nuclear translocation-deficient TyrRS had more DNA damage (γ-H2AX foci) than did cells reconstituted with wild-type TyrRS. Many of the TyrRS-dependent DNA damage response genes had a consensus binding site for the transcription factor E2F1. Binding of E2F1 to these genes, which included those involved in DNA repair, was reduced in cells reconstituted with nuclear translocation-deficient TyrRS. Interactome analysis by mass spectrometry indicated that TyrRS interacted with the transcriptional corepressor TRIM28 (also known as KAP1) and histone deacetylase 1 (HDAC1). TRIM28 recruits HDAC1 to E2F1 to repress the transcriptional activity of E2F1. Further analysis revealed that the interaction of TyrRS with HDAC1 was likely mediated by a direct interaction between TyrRS and TRIM28. Mapping the interaction site on TRIM28 for TyrRS revealed that this was the same site that interacted with E2F1, and overexpression of TyrRS reduced the interaction of E2F1 with TRIM28, consistent with competition for binding. Overexpression of a mutant TyrRS that could not interact with TRIM28 was less effective than overexpression of wild-type TyrRS at stimulating expression of the DNA damage response genes. The abundance of acetylated E2F1 increased in response to peroxide, and expression of the nuclear translocation-deficient TyrRS reduced this increase in acetylated E2F1, consistent with nuclear TyrRS binding TRIM28 and sequestering HDAC1 away from E2F1, thereby increasing the transcriptional activity of E2F1 and protecting cells from DNA damage by enhancing the expression of genes involved in DNA repair.

N. Wei, Y. Shi, L. N. Truong, K. M. Fisch, T. Xu, E. Gardiner, G. Fu, Y.-S. O. Hsu, S. Kishi, A. I. Su, X. Wu, X.-L. Yang, Oxidative stress diverts tRNA synthetase to nucleus for protection against DNA damage. Mol. Cell 56, 323–332 (2014). [PubMed]