Reinitiation involving upstream ORFs regulates ATF4 mRNA translation in mammalian cells.

During cellular stresses, phosphorylation of eukaryotic initiation factor-2 (eIF2) elicits gene expression designed to ameliorate the underlying cellular disturbance. Central to this stress response is the transcriptional regulator activating transcription factor, ATF4. Here we describe the mechanism regulating ATF4 expression involving the differential contribution of two upstream ORFs (uORFs) in the 5' leader of the mouse ATF4 mRNA. The 5' proximal uORF1 is a positive-acting element that facilitates ribosome scanning and reinitiation at downstream coding regions in the ATF4 mRNA. When eIF2-GTP is abundant in nonstressed cells, ribosomes scanning downstream of uORF1 reinitiate at the next coding region, uORF2, an inhibitory element that blocks ATF4 expression. During stress conditions, phosphorylation of eIF2 and the accompanying reduction in the levels of eIF2-GTP increase the time required for the scanning ribosomes to become competent to reinitiate translation. This delayed reinitiation allows for ribosomes to scan through the inhibitory uORF2 and instead reinitiate at the ATF4-coding region. Increased expression of ATF4 would contribute to the expression of genes involved in remediation of cellular stress damage. These results suggest that the mechanism of translation reinitiation involving uORFs is conserved from yeast to mammals.

[1]  P. Sassone-Corsi,et al.  ATF4 Is a Substrate of RSK2 and an Essential Regulator of Osteoblast Biology Implication for Coffin-Lowry Syndrome , 2004, Cell.

[2]  Tsonwin Hai,et al.  Activating Transcription Factor 3 Is Integral to the Eukaryotic Initiation Factor 2 Kinase Stress Response , 2004, Molecular and Cellular Biology.

[3]  D. Scheuner,et al.  Phosphorylation of the α Subunit of Eukaryotic Initiation Factor 2 Is Required for Activation of NF-κB in Response to Diverse Cellular Stresses , 2003, Molecular and Cellular Biology.

[4]  R. Paules,et al.  An integrated stress response regulates amino acid metabolism and resistance to oxidative stress. , 2003, Molecular cell.

[5]  Xiaohua Shen,et al.  The unfolded protein response in nutrient sensing and differentiation , 2002, Nature Reviews Molecular Cell Biology.

[6]  T. E. Dever,et al.  Gene-Specific Regulation by General Translation Factors , 2002, Cell.

[7]  Krishnamurthy Natarajan,et al.  Gcn4p, a Master Regulator of Gene Expression, Is Controlled at Multiple Levels by Diverse Signals of Starvation and Stress , 2002, Eukaryotic Cell.

[8]  A. Hinnebusch,et al.  Physical evidence for distinct mechanisms of translational control by upstream open reading frames , 2001, The EMBO journal.

[9]  R. Wek,et al.  Mechanism of activation of the double-stranded-RNA-dependent protein kinase, PKR: role of dimerization and cellular localization in the stimulation of PKR phosphorylation of eukaryotic initiation factor-2 (eIF2). , 2001, European journal of biochemistry.

[10]  M. Marton,et al.  Transcriptional Profiling Shows that Gcn4p Is a Master Regulator of Gene Expression during Amino Acid Starvation in Yeast , 2001, Molecular and Cellular Biology.

[11]  E McEwen,et al.  Translational control is required for the unfolded protein response and in vivo glucose homeostasis. , 2001, Molecular cell.

[12]  M. Schapira,et al.  Regulated translation initiation controls stress-induced gene expression in mammalian cells. , 2000, Molecular cell.

[13]  D. Ron,et al.  Perk is essential for translational regulation and cell survival during the unfolded protein response. , 2000, Molecular cell.

[14]  B. Williams,et al.  PKR; a sentinel kinase for cellular stress , 1999, Oncogene.

[15]  A. Hinnebusch,et al.  Translational Regulation of Yeast GCN4 , 1997, The Journal of Biological Chemistry.

[16]  N. Sonenberg,et al.  Translational control of gene expression , 2000 .

[17]  R. Wek.  eIF-2 kinases: regulators of general and gene-specific translation initiation. , 1994, Trends in biochemical sciences.

[18]  A. Hinnebusch,et al.  Effect of sequence context at stop codons on efficiency of reinitiation in GCN4 translational control , 1994, Molecular and cellular biology.

[19]  A. Hinnebusch,et al.  Phosphorylation of initiation factor 2α by protein kinase GCN2 mediates gene-specific translational control of GCN4 in yeast , 1992, Cell.

[20]  M. Kozak.  Structural features in eukaryotic mRNAs that modulate the initiation of translation. , 1991, The Journal of biological chemistry.

[21]  B. M. Jackson,et al.  Suppression of ribosomal reinitiation at upstream open reading frames in amino acid-starved cells forms the basis for GCN4 translational control , 1991, Molecular and cellular biology.

[22]  M. Kozak,et al.  Circumstances and mechanisms of inhibition of translation by secondary structure in eucaryotic mRNAs , 1989, Molecular and cellular biology.

[23]  A. Hinnebusch,et al.  Sequences that surround the stop codons of upstream open reading frames in GCN4 mRNA determine their distinct functions in translational control. , 1989, Genes & development.

[24]  A. Hinnebusch,et al.  Multiple upstream AUG codons mediate translational control of GCN4 , 1986, Cell.

[25]  F. Urano,et al.  Transcriptional and translational control in the Mammalian unfolded protein response. , 2002, Annual review of cell and developmental biology.

[26]  N. Sonenberg,et al.  Translational control of gene expression , 2000 .