GCN2- and eIF2α-phosphorylation-independent, but ATF4-dependent, induction of CARE-containing genes in methionine-deficient cells
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Amino-acid deprivation is sensed by the eIF2α kinase GCN2. Under conditions of essential amino-acid limitation, GCN2 phosphorylates eIF2α, inhibiting the formation of a new ternary complex and hence mRNA translation initiation. While decreasing global mRNA translation, eIF2α phosphorylation also increases the translation of the integrated stress response (ISR) transcription factor ATF4, which increases the expression of many stress response genes that contain a C/EBP-ATF response element (CARE), including Atf4, 4Ebp1, Asns, and Chop. Using wild-type as well as Gcn2 knockout and unphosphorylatable eIF2α mutant MEFs, we characterized a novel GCN2/eIF2α phosphorylation-independent, but ATF4-dependent, pathway that upregulates the expression of CARE-containing genes in MEFs lacking GCN2 or phosphorylatable eIF2α when these cells are exposed to methionine-deficient, and to a lesser extent arginine- or histidine-deficient, medium. Thus, we demonstrate a GCN2/eIF2α phosphorylation-independent pathway that converges with the GCN2/eIF2α kinase-dependent pathway at the level of ATF4 and similarly results in the upregulation of CARE-containing genes. We hypothesize that the essential role of methionine-charged initiator tRNA in forming ternary complex is responsible for the robust ability of methionine deficiency to induce ATF4 and the ISR even in the absence of GCN2 or eIF2α kinase activity.
KeywordsMethionine GCN2 eIF2α ATF4 CARE
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Conflict of interest
The authors declare that they have no conflict of interest.
This work was supported by Grants DK-083473 and DK-056649 from the National Institute of Diabetes and Digestive and Kidney Diseases.
This article does not contain any studies with human participants or animals performed by any of the authors.
- Unbehaun A, Borukhov SI, Hellen CUT, Pestova T V (2004) The 40S subunit in 48S complexes formed at the initiation codon of mRNA is bound to eukaryotic initiation factor (eIF) 3, eIF1, eIF1A, and an eIF2/GTP/Met-tRNA. Genes Dev 3078–3093Google Scholar
- Wanders D, Stone KP, Forney LA, Cortez CC, Dille KN, Simon J, Xu M, Hotard EC, Nikonorova IA, Pettit AP, Anthony TG, Gettys TW (2016) Role of GCN2-independent signaling through a noncanonical PERK/NRF2 pathway in the physiological responses to dietary methionine restriction. Diabetes 65:1499–1510CrossRefPubMedGoogle Scholar