G-quadruplex structures contribute to the neuroprotective effects of angiogenin-induced tRNA fragments

• Published in: Proceedings of the National Academy of Sciences - PNAS 2014-12, Vol.111 (51), p.18201-18206
• Main Authors: Ivanov, Pavel, O'Day, Elizabeth, Emara, Mohamed M., Wagner, Gerhard, Lieberman, Judy, Anderson, Paul
• Format: Article
• Language: English
• Subjects: Amyotrophic lateral sclerosis; Anticodon; Binding sites; Biological Sciences; Cultured cells; Cytoprotection; DNA; G-Quadruplexes; Humans; Messenger RNA; Motor neurons; Neurochemistry; Neurodegeneration; Neurons; Neuropathology; Neuroprotective Agents - chemistry; Neuroprotective Agents - pharmacology; Ribonuclease, Pancreatic - pharmacology; Ribonucleases; RNA; RNA, Transfer - chemistry; RNA, Transfer - pharmacology; RNA-protein interactions; Transfer RNA; Western blotting
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1407361111

Angiogenin (ANG) is a stress-activated ribonuclease that promotes the survival of motor neurons. Ribonuclease inactivating point mutations are found in a subset of patients with ALS, a fatal neurodegenerative disease with no cure. We recently showed that ANG cleaves tRNA within anticodon loops to produce 5′- and 3′-fragments known as tRNA-derived, stress-induced RNAs (tiRNAs). Selected 5′-tiRNAs (e.g., tiRNA ᴬˡᵃ, tiRNA Cʸˢ) cooperate with the translational repressor Y-box binding protein 1 (YB-1) to displace the cap-binding complex eIF4F from capped mRNA, inhibit translation initiation, and induce the assembly of stress granules (SGs). Here, we show that translationally active tiRNAs assemble unique G-quadruplex (G4) structures that are required for translation inhibition. We show that tiRNA ᴬˡᵃ binds the cold shock domain of YB-1 to activate these translational reprogramming events. We discovered that 5′-tiDNA ᴬˡᵃ (the DNA equivalent of 5′-tiRNA ᴬˡᵃ) is a stable tiRNA analog that displaces eIF4F from capped mRNA, inhibits translation initiation, and induces the assembly of SGs. The 5′-tiDNA ᴬˡᵃ also assembles a G4 structure that allows it to enter motor neurons spontaneously and trigger a neuroprotective response in a YB-1–dependent manner. Remarkably, the ability of 5′-tiRNA ᴬˡᵃ to induce SG assembly is inhibited by G4 structures formed by pathological GGGGCC repeats found in C9ORF72, the most common genetic cause of ALS, suggesting that functional interactions between G4 RNAs may contribute to neurodegenerative disease. Significance Angiogenin is a stress-activated ribonuclease that cleaves tRNA to produce bioactive small noncoding RNAs [tRNA-derived, stress-induced RNAs (tiRNAs)] that function in a cytoprotective stress response program. Point mutations that reduce its ribonuclease activity are found in a subset of patients with ALS, a fatal neurodegenerative disease. We have found that selected tiRNAs assume G-quadruplex (G4) structures that are necessary for cytoprotective and prosurvival functions. Moreover, stable DNA analogs of these G4-containing tiRNAs spontaneously enter motor neurons and confer cytoprotection against stress. Our results identify tiRNAs as leading compounds for the development of a new class of neuroprotective drugs and give insights into the molecular mechanisms underlying the pathobiology of expanded G4-forming hexanucleotide repeats in the C9ORF72 gene.