Uncharged tRNA Activates GCN2 by Displacing the Protein Kinase Moiety from a Bipartite tRNA-Binding Domain

Abstract

Protein kinase GCN2 regulates translation in amino acid-starved cells by phosphorylating elF2. GCN2 contains a regulatory domain related to histidyl-tRNA synthetase (HisRS) postulated to bind multiple deacylated tRNAs as a general sensor of starvation. In accordance with this model, GCN2 bound several deacylated tRNAs with similar affinities, and aminoacylation of tRNAphe weakened its interaction with GCN2. Unexpectedly, the C-terminal ribosome binding segment of GCN2 (C-term) was required in addition to the HisRS domain for strong tRNA binding. A combined HisRS+ C-term segment bound to the isolated protein kinase (PK) domain in vitro, and tRNA impeded this interaction. An activating mutation (GCN2c-E803V) that weakens PK-C-term association greatly enhanced tRNA binding by GCN2. These results provide strong evidence that tRNA stimulates the GCN2 kinase moiety by preventing an inhibitory interaction with the bipartite tRNA binding domain.

Upregulation of tryptophanyl-tRNA synthethase adapts human cancer cells to nutritional stress caused by tryptophan degradation

“…As Trp depletion mediates WARS induction and is known to activate GCN2 10 , we next asked whether GCN2 mediates the upregulation of WARS. For this purpose, GCN2 was knocked down in LN229 glioblastoma cells that were cultured with or without Trp (Figure 4A).…”

“…Trp shortage mediates WARS upregulation by signaling via the GCN2-peIF2a-ATF4 axis (Figure 4), as low levels of Trp result in the accumulation of uncharged tRNAs, which activate the stress kinase GCN2 10 . GCN2 then phosphorylates its substrate, eIF2a leading to reduced global protein synthesis, but increased translation of specific mRNAs such as ATF4 27,28 .…”

“…On the other hand, Trp depletion has been implicated in the proliferation arrest of CD8 + T cells 10 by the accumulation of uncharged transfer RNA (tRNA) and subsequent activation of the general control non-derepressible-2 (GCN2) kinase pathway 11,12 , while Gcn2 in T cells has recently been shown to be dispensable for the suppression of antitumor immune responses in experimental melanomas 13 .…”

Aminoacyl-tRNA synthetases: Versatile players in the changing theater of translation

“…There are other examples of alternative functions of aaRS and aaRS-like proteins in eukaryotic cells+ The E. coli ThrRS can regulate the translation level of itself by binding to an upstream region of its own mRNA, forming a structure analogous to that of the ThrRStRNA Thr complex (Torres-Larios, Asilomar)+ A similar regulatory role at the translational level has also been reported for yeast AspRS (Frugier, Asilomar)+ In the mitochondria of certain yeasts and fungi, TyrRS and LeuRS have well-established roles in promoting the splicing of cytochrome genes, most likely by recognizing tRNA-like motifs (Rho & Martinis, 2000;Myers et al+, 2002)+ During packaging of the HIV virus, human LysRS assists tRNA Lys3 to enter the virus particle to serve as a primer for viral replication (Javanbakht et al+, 2002)+ The DNA polymerase of mitochondria, Polg possesses a processivity subunit with a remarkable resemblance to the dimeric glycyl-tRNA synthetases (Carrodeguas et al+, 2001)+ In addition to these special mitochondrial activities, the importance of the aaRS in mitochondrial protein synthesis is receiving increased attention, owing in part to the study of syndromes arising from specific tRNA mutations (Rabilloud et al+, 2002)+ Lastly, recent work shows that the translation control protein GCN2, which appears to regulate translation in eucaryotic cells, possesses a HisRS-like domain that binds tRNA (Dong et al+, 2000)+ Aminoacyl-tRNA synthetases 1369…”

La kinase GCN2 régule le comportement alimentaire des omnivores afin de maintenir l’homéostasie des acides aminés

“…L'activité enzymatique de GCN2 est inductible par une carence en acides aminés indispensables. En effet, GCN2 possède un domaine homologue de l'histidyl-ARNt synthétase lui permettant de se lier aux ARN de transfert non chargés [8]. Il résulte de cette liaison un changement conformationnel permissif pour l'activité kinase.…”