Control of mRNA stability under stress conditions
Final Report Abstract
Control of mRNA degradation plays an important role in regulating gene expression. Caf1 is a ribonuclease that removes poly-A tails from mRNAs and thereby induces their degradation. The goal of this project was to identify mechanisms by which mRNA degradation and the activity of Caf1 are regulated under conditions of cellular stress. In the course of these studies, we found that Caf1a is posttranslationally modified by phosphorylation and acetylation. While this work is still ongoing, we have obtained very promising results indicating that these modifications control the activity of Caf1a. We also found two regulatory pathways that are specifically connected to the Caf1 enzyme: 1) mRNAs with AU-rich elements bind to the protein TTP, which in turn recruits Caf1 and thereby induces the rapid degradation of the bound mRNAs. 2) mRNAs with a stem-loop motif termed the constitutive decay element (CDE) bind to the protein Roquin, which also causes mRNA degradation by recruiting the Caf1 deadenylase. Future work on the CDE in the mRNA encoding TNFα, a major pro-inflammatory cytokine, will be directed towards the development of anti-inflammatory therapies. Once deadenylated, most mRNAs are decapped at the 5'end, which then leads to the final degradation of the mRNA body. We discovered that the scaffold protein Pat1b physically connects the Caf1 deadenylation complex with the Dcp2 decapping complex. We could also show that an N-terminal domain in Pat1b is important for the assembly of P-bodies, cytoplasmic foci containing enzymes (including Caf1 and Dcp2) required for mRNA degradation. Moreover, we examined the molecular interaction between the RNA helicase Rck and Pat1b, which indicated that Rck functions upstream of Pat1b in P-body assembly. Finally, we discovered that stress granules, cytoplasmic RNA granules that are related to P-bodies, are induced under conditions of cold shock. While P-bodies are thought to be sites of mRNA degradation, stress granules protect non-translating mRNAs form degradation under stress conditions. Importantly, we could show that suppression of global mRNA translation during cold shock is important for cellular survival under these conditions. In summary, work accomplished in this project made important contributions to the understanding of cytoplasmic RNA granules in the stress response, uncovered mRNA decay pathways that are dependent on the deadenylase Caf1, and identified modifications that regulate Caf1.
Publications
- Human Pat1b Connects Deadenylation with mRNA Decapping and Controls the Assembly of Processing-Bodies. Mol Cell Biol 2010;30:4308-23
Ozgur S, Chekulaeva M, Stoecklin G
(See online at https://dx.doi.org/10.1128/MCB.00429-10) - Not1 mediates recruitment of the deadenylase Caf1 to mRNAs targeted for degradation by tristetraprolin. Nucl Acids Res 2011;39:4373-86
Sandler H, Kreth J, Timmers HTM, Stoecklin G
(See online at https://dx.doi.org/10.1093/nar/gkr011) - Genome-wide assessment of AU-rich elements by the AREScore algorithm. PLoS Genet 2012;8:e1002433
Spasic M, Friedel CC, Schott J, Kreth J, Leppek K, Hofmann S, Ozgur S, Stoecklin G
(See online at https://doi.org/10.1371/journal.pgen.1002433) - Translation suppression promotes stress granule formation and cell survival in response to cold shock. Mol Biol Cell 2012;23:3786-800
Hofmann S, Cherkasova V, Bankhead P, Bukau B, Stoecklin G
(See online at https://doi.org/10.1091/mbc.E12-04-0296) - Role of Rck-Pat1b binding in assembly of processing-bodies. RNA Biol 2013;10:528-39
Ozgur S, Stoecklin G
(See online at https://doi.org/10.4161/rna.24086) - Roquin promotes constitutive mRNA decay via a conserved class of stem-loop recognition motifs. Cell 2013;153:869-81
Leppek K, Schott J, Reitter S, Poetz F, Hammond MC, Stoecklin G
(See online at https://doi.org/10.1016/j.cell.2013.04.016)
