Editors' ChoiceRNA Processing

USE During Stress

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Science Signaling  08 Feb 2011:
Vol. 4, Issue 159, pp. ec39
DOI: 10.1126/scisignal.4159ec39

The protease thrombin, which is encoded by the F2 gene, plays a role in blood coagulation, complement activation, and inflammatory responses. Active thrombin is produced upon enzymatic cleavage of prothrombin. F2 mRNA abundance is determined by the interplay between weak 3′ end formation signals that favor low abundance and an upstream sequence element (USE) that promotes higher abundance. Danckwardt et al. found that the abundance of F2 mRNA and other mRNAs containing USEs was increased in response to stress induced by anisomycin, and this effect required the mitogen-activated protein kinase (MAPK) p38. In addition, depletion of p38 by siRNA qualitatively changed the set of proteins that associated with a 21-mer containing the F2 USE in anisomycin-treated cells. Phosphorylation of the USE-binding proteins FBP1, FBP2, and FBP3 was increased by anisomycin treatment, and in vitro assays indicated that p38 could phosphorylate these proteins. Anisomycin treatment resulted in increased association of various USE-binding 3′ end processing factors (such as U2AF35, U2AF65, hnRNPI, and p54nrb). Nuclear extracts from stressed cells showed higher polyadenylation activity of a USE-containing RNA substrate compared with those from unstressed cells. The authors hypothesized that the degree of phosphorylation of FBP2 and FBP3 correlated with 3′ end processing efficiency. Addition of hypophosphorylated FBP2 and FBP3 decreased 3′ end processing efficiency in in vitro polyadenylation reactions; this effect was not seen with hyperphosphorylated FBP2 and FBP3 isolated from anisomycin-treated cells. RNAi-mediated depletion of FBP2 and FBP3 increased the abundance of USE-containing mRNAs, including F2, in unstressed cells. The livers of mice injected with lipopolysaccharide (LPS) to induce a systemic inflammatory response showed increased abundance of mRNAs encoding F2 and 3′ end processing factors, as well as increased F2 protein abundance. In livers of LPS-treated mice, the amount of F2 mRNA in FBP2 and FBP3 immunoprecipitates was decreased, whereas it was increased in immunoprecipitates of hnRNP1, which is required for USE-mediated 3′ end processing. In livers from individuals with metastatic colon carcinoma, F2 mRNA and protein abundance was higher at the tumor invasion front compared with the surrounding liver tissue. The authors propose that stress-induced activation of p38 results in increased phosphorylation of FBP2 and FBP3, which then dissociate from USE-containing mRNAs, thereby raising the efficiency of 3′ end processing and leading to increased abundance of these mRNAs.

S. Danckwardt, A.-S. Gantzert, S. Macher-Goeppinger, H. C. Probst, M. Gentzel, M. Wilm, H.-J. Gröne, P. Schirmacher, M. W. Hentze, A. E. Kulozik, p38 MAPK controls prothrombin expression by regulated RNA 3′ end processing. Mol. Cell 41, 298–310 (2011). [PubMed]

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