An intact unfolded protein response in Trpt1 knockout mice reveals phylogenic divergence in pathways for RNA ligation
- Heather P. Harding1,2,
- Jeremy G. Lackey3,
- Hao-Chi Hsu1,2,
- Yuhong Zhang1,
- Jing Deng1,6,
- Rui-Ming Xu1,2,
- Masad J. Damha3, and
- David Ron1,4,5
- 1Kimmel Center for Biology and Medicine of the Skirball Institute, New York University School of Medicine, New York, New York 10016, USA
- 2Department of Pharmacology, New York University School of Medicine, New York, New York 10016, USA
- 3Department of Chemistry, McGill University, Montreal, QC, Canada H3A 2K6
- 4Department of Cell Biology, New York University School of Medicine, New York, New York 10016, USA
- 5Department of Medicine, New York University School of Medicine, New York, New York 10016, USA
Abstract
Unconventional mRNA splicing by an endoplasmic reticulum stress-inducible endoribonuclease, IRE1, is conserved in all known eukaryotes. It controls the expression of a transcription factor, Hac1p/XBP-1, that regulates gene expression in the unfolded protein response. In yeast, the RNA fragments generated by Ire1p are ligated by tRNA ligase (Trl1p) in a process that leaves a 2′-PO4 2− at the splice junction, which is subsequently removed by an essential 2′-phosphotransferase, Tpt1p. However, animals, unlike yeast, have two RNA ligation/repair pathways that could potentially rejoin the cleaved Xbp-1 mRNA fragments. We report that inactivation of the Trpt1 gene, encoding the only known mammalian homolog of Tpt1p, eliminates all detectable 2′-phosphotransferase activity from cultured mouse cells but has no measurable effect on spliced Xbp-1 translation. Furthermore, the relative translation rates of tyrosine-rich proteins is unaffected by the Trpt1 genotype, suggesting that the pool of (normally spliced) tRNATyr is fully functional in the Trpt1−/− mouse cells. These observations argue against the presence of a 2′-PO4 2− at the splice junction of ligated RNA molecules in Trpt1−/− cells, and suggest that Xbp-1 and tRNA ligation proceed by distinct pathways in yeast and mammals.
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Footnotes
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↵6 Present address: Dana-Farber Cancer Center, Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115, USA.
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Reprint requests to: Heather P. Harding, Kimmel Center for Biology and Medicine of the Skirball Institute, New York University School of Medicine, SI 3-10 540 First Avenue, New York, NY 10016, USA; e-mail: harding{at}saturn.med.nyu.edu; fax: (212) 263-8951.
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Article published online ahead of print. Article and publication date are at http://www.rnajournal.org/cgi/doi/10.1261/rna.859908.
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- Received October 2, 2007.
- Accepted November 8, 2007.
- Copyright © 2008 RNA Society