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

Abstract

f Adaptation to changes in extracellular tonicity is essential for cell survival. However, severe or chronic hyperosmotic stress induces apoptosis, which involves cytochrome c (Cyt c) 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 Cyt c in a ribonucleoprotein (Cyt c-RNP) complex. Nextgeneration sequencing of RNA isolated from the Cyt c-RNP complex reveals that 20 tiRNAs are highly enriched in the Cyt c-RNP complex. Preferred components of this complex are 5= and 3= tiRNAs of specific isodecoders within a family of isoacceptors. We also demonstrate that Cyt c binds tiRNAs in vitro, and the pool of Cyt c-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 Cyt c and tiRNAs that inhibits apoptosome formation and activity.

The Many Virtues of tRNA-derived Stress-induced RNAs (tiRNAs): Discovering Novel Mechanisms of Stress Response and Effect on Human Health

“…ANG also protects neurons against hypoxic injury and endoplasmic reticulum stress-induced and trophic factor withdrawal-induced cell death, whereas ALS-associated ANG mutants exert no protective activity (62,63). Our own study showed that ANG protects primary neurons from hyperosmotic stress-induced cell death (27). A subset of ALS-associated ANG mutants have also been found in Parkinson disease (PD) patients (64).…”

“…In the intrinsic mechanism of apoptosis, mitochondria undergo biochemical and structural changes, leading to the release of various proteins from the intermembrane space, including cytochrome c (cyt c) (25,26). Our recent study showed that during hyperosmotic stress, ANG-induced tiRNAs bind cyt c and competitively inhibit the binding of cyt c to the apoptotic protease-activating factor 1 (APAF1) protein (27). The binding of cyt c and APAF1 is essential for the formation of the apoptosome and the downstream activation of cell death (28).…”

“…This collective evidence allows us to speculate that ANG-induced production of tiRNAs is essential for neuron survival during stress. Two potential mechanisms of protective actions exhibited by ANG might be due to the interaction of tiRNAs with cyt c, thus preventing apoptosis (27), or via translation regulation exhibited by tiRNAs during stress (23).…”

“…Loss of its RNase activity will reduce the production of ANG-induced tiRNAs. tiRNAs have been implicated in inhibition of protein synthesis (23), formation of stress granules (22), and inhibition of apoptosis via interaction with cyt c (27). The mechanisms for neurodegeneration in ALS are not completely understood; however, it has been reported that motor neuron degeneration in ALS structurally resembles apoptosis (94,95).…”

Angiogenin is upregulated during the alloreactive immune response and has no effect on the T-cell expansion phase, whereas it affects the contraction phase by inhibiting CD4+ T-cell apoptosis

“…Since numerous IRES-containing mRNAs encode pro-survival and anti-apoptotic genes, angiogenin protects cells from apoptosis during cell stress (6,7). In addition, the direct interaction of angiogenin with p53 (8), and interaction between tiRNAs and cytochrome c released from the mitochondria (9), have been detected to inhibit cell apoptosis.…”