Angiogenin-Cleaved tRNA Halves Interact with Cytochrome c, Protecting Cells from Apoptosis during Osmotic Stress

Adaptation to changes in extracellular tonicity is essential for cell survival. However, severe or chronic hyperosmotic stress induces apoptosis, which involves cytochromec (Cytc ) release from mitochondria and subsequent apoptosome formation. Here, we show that angiogenin-induced accumulation of tRNA halves (or tiRNAs) is accompanied by increased survival in hyperosmotically stressed mouse embryonic fibroblasts. Treatment of cells with angiogenin inhibits stress-induced formation of the apoptosome and increases the interaction of small RNAs with released Cytc in a ribonucleoprotein (Cytc -RNP) complex. Next-generation sequencing of RNA isolated from the Cytc -RNP complex reveals that 20 tiRNAs are highly enriched in the Cytc -RNP complex. Preferred components of this complex are 5′ and 3′ tiRNAs of specific isodecoders within a family of isoacceptors. We also demonstrate that Cytc binds tiRNAsin vitro , and the pool of Cytc -interacting RNAs binds tighter than individual tiRNAs. Finally, we show that angiogenin treatment of primary cortical neurons exposed to hyperosmotic stress also decreases apoptosis. Our findings reveal a connection between angiogenin-generated tiRNAs and cell survival in response to hyperosmotic stress and suggest a novel cellular complex involving Cytc and tiRNAs that inhibits apoptosome formation and activity.