Translation mediated by the internal ribosome entry site of the cat-1 mRNA is regulated by glucose availability in a PERK kinase-dependent manner.
The cationic amino acid transporter, Cat-1, is a high affinity transporter of the essential amino acids, arginine and lysine. Expression of the cat-1 gene is known to be regulated by amino acid availability. It is shown here that cat-1 gene expression is also induced by Glc limitation, which causes a 7-fold increase in cat-1 mRNA, a 30-fold induction of Cat-1 protein levels, and a 4-fold stimulation of arginine uptake. Glc limitation is known to induce the unfolded protein response (UPR) by altering protein glycosylation in the endoplasmic reticulum (ER). The studies here demonstrate that synthesis of Cat-1 occurs during the UPR when global protein synthesis is inhibited. The 5'-UTR of the cat-1 mRNA contains an internal ribosomal entry site (IRES) that is activated by amino acid starvation by a mechanism that involves phosphorylation of the translation initiation factor, eukaryotic initiation factor 2alpha, by the GCN2 kinase. It is shown here that translation from the cat-1/IRES is also induced by Glc deprivation in a manner dependent upon phosphorylation of eukaryotic initiation factor 2alpha by the transmembrane ER kinase, PERK. Because PERK is a key constituent of the UPR, it is concluded that induction of cat-1 gene expression is part of the adaptive response of cells to ER stress. These results also demonstrate that regulation of IRES activity in cellular mRNAs is part of the mechanism by which the UPR protects cells from unfolded proteins in the ER.
Fernandez
James
J
Department of Nutrition and Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4906, USA.
Bode
Barry
B
Koromilas
Antonis
A
Diehl
J Alan
JA
Krukovets
Irene
I
Snider
Martin D
MD
Hatzoglou
Maria
M
D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites; D015152:Blotting, Northern; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000378:metabolism; D020690:GTPase-Activating Proteins; D005799:Genes, Dominant; D005822:Genetic Vectors; D005947:Glucose / Q000378:metabolism*; D006031:Glycosylation; D007477:Ions; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008957:Models, Genetic; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D012270:Ribosomes / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D019892:eIF-2 Kinase / Q000378:metabolism*
D018797:Cell Cycle Proteins; D020690:GTPase-Activating Proteins; D005947:Glucose; D007477:Ions; D008156:Luciferases; D010750:Phosphoproteins; D012333:RNA, Messenger; D019892:eIF-2 Kinase; C120766:Git1 protein, mouse; C485648:Git1 protein, rat