Molecular basis for AU-rich element recognition and dimerization by the HuR C-terminal RRM.
Ripin NDepartment of Biology, Institute of Molecular Biology and Biophysics, ETH Zürich, 8093 Zürich, Switzerland; nina.ripin@mol.biol.ethz.ch nicole.meisner-kober@sbg.ac.at frederic.allain@mol.biol.ethz.ch.
Boudet JDepartment of Biology, Institute of Molecular Biology and Biophysics, ETH Zürich, 8093 Zürich, Switzerland.
Duszczyk MMDepartment of Biology, Institute of Molecular Biology and Biophysics, ETH Zürich, 8093 Zürich, Switzerland.
Hinniger ANovartis Institutes for BioMedical Research, 4002 Basel, Switzerland.
Faller MNovartis Institutes for BioMedical Research, 4002 Basel, Switzerland.
Krepl MInstitute of Biophysics, Czech Academy of Sciences, 612 65 Brno, Czech Republic.
Gadi ADepartment of Microbiology, New York University School of Medicine, New York, NY 10016.
Schneider RJDepartment of Microbiology, New York University School of Medicine, New York, NY 10016.
Šponer JInstitute of Biophysics, Czech Academy of Sciences, 612 65 Brno, Czech Republic.
Allain FHDepartment of Biology, Institute of Molecular Biology and Biophysics, ETH Zürich, 8093 Zürich, Switzerland; nina.ripin@mol.biol.ethz.ch nicole.meisner-kober@sbg.ac.at frederic.allain@mol.biol.ethz.ch.
English
Human antigen R (HuR) is a key regulator of cellular mRNAs containing adenylate/uridylate-rich elements (AU-rich elements; AREs). These are a major class of cis elements within 3' untranslated regions, targeting these mRNAs for rapid degradation. HuR contains three RNA recognition motifs (RRMs): a tandem RRM1 and 2, followed by a flexible linker and a C-terminal RRM3. While RRM1 and 2 are structurally characterized, little is known about RRM3. Here we present a 1.9-Å-resolution crystal structure of RRM3 bound to different ARE motifs. This structure together with biophysical methods and cell-culture assays revealed the mechanism of RRM3 ARE recognition and dimerization. While multiple RNA motifs can be bound, recognition of the canonical AUUUA pentameric motif is possible by binding to two registers. Additionally, RRM3 forms homodimers to increase its RNA binding affinity. Finally, although HuR stabilizes ARE-containing RNAs, we found that RRM3 counteracts this effect, as shown in a cell-based ARE reporter assay and by qPCR with native HuR mRNA targets containing multiple AUUUA motifs, possibly by competing with RRM12.