GCN2- and eIF2α-phosphorylation-independent, but ATF4-dependent, induction of CARE-containing genes in methionine-deficient cells.
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.
Division of Nutritional Sciences, Cornell University, Savage Hall, Rm. 227, Ithaca, NY, 14853, USA.
Kevin M
KM
Mazor
Division of Nutritional Sciences, Cornell University, Savage Hall, Rm. 227, Ithaca, NY, 14853, USA. mhs6@cornell.edu.
Martha H
MH
Stipanuk
D051701:Activating Transcription Factor 4 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism; D015852:Eukaryotic Initiation Factor-2 / Q000235:genetics / Q000378:metabolism; D005347:Fibroblasts; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008715:Methionine / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D015398:Signal Transduction; D050801:Ternary Complex Factors / Q000737:chemistry / Q000235:genetics; D015533:Transcriptional Activation / Q000235:genetics
D000596:Amino Acids; C081452:Atf4 protein, mouse; D015852:Eukaryotic Initiation Factor-2; C495040:Gdnf protein, mouse; D051100:Glial Cell Line-Derived Neurotrophic Factor; D012333:RNA, Messenger; D050801:Ternary Complex Factors; D051701:Activating Transcription Factor 4; D008715:Methionine; C070634:Eif2ak4 protein, mouse; D017346:Protein Serine-Threonine Kinases
ATF4; CARE; GCN2; Methionine; eIF2α