title: Amino acids regulate expression of antizyme-1 to modulate ornithine decarboxylase activity.
abstract: In a glucose-salt solution (Earle's balanced salt solution), asparagine (Asn) stimulates ornithine decarboxylase (ODC) activity in a dose-dependent manner, and the addition of epidermal growth factor (EGF) potentiates the effect of Asn. However, EGF alone fails to activate ODC. Thus, the mechanism by which Asn activates ODC is important for understanding the regulation of ODC activity. Asn reduced antizyme-1 (AZ1) mRNA and protein. Among the amino acids tested, Asn and glutamine (Gln) effectively inhibited AZ1 expression, suggesting a differential role for amino acids in the regulation of ODC activity. Asn decreased the putrescine-induced AZ1 translation. The absence of amino acids increased the binding of eukaryotic initiation factor 4E-binding protein (4EBP1) to 5'-mRNA cap and thereby inhibited global protein synthesis. Asn failed to prevent the binding of 4EBP1 to mRNA, and the bound 4EBP1 was unphosphorylated, suggesting the involvement of the mammalian target of rapamycin (mTOR) in the regulation of AZ1 synthesis. Rapamycin treatment (4 h) failed to alter the expression of AZ1. However, extending the treatment (24 h) allowed expression in the presence of amino acids, indicating that AZ1 is expressed when TORC1 signaling is decreased. This suggests the involvement of cap-independent translation. However, transient inhibition of mTORC2 by PP242 completely abolished the phosphorylation of 4EBP1 and decreased basal as well as putrescine-induced AZ1 expression. Asn decreased the phosphorylation of mTOR-Ser(2448) and AKT-Ser(473), suggesting the inhibition of mTORC2. In the absence of amino acids, mTORC1 is inhibited, whereas mTORC2 is activated, leading to the inhibition of global protein synthesis and increased AZ1 synthesis via a cap-independent mechanism.
authors.affiliation: Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA. rray3@uthsc.edu
authors.forename: Ramesh M
authors.initials: RM
authors.lastname: Ray
authors.forename: Mary Jane
authors.initials: MJ
authors.lastname: Viar
authors.forename: Leonard R
authors.initials: LR
authors.lastname: Johnson
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D001216:Asparagine / Q000494:pharmacology*; D018797:Cell Cycle Proteins; D002460:Cell Line; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000502:physiology; D009955:Ornithine Decarboxylase / Q000096:biosynthesis / Q000235:genetics; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects* / Q000502:physiology; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012315:RNA Caps / Q000235:genetics / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C500984:CRTC1 protein, human; C493245:CRTC2 protein, human; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D010750:Phosphoproteins; D011506:Proteins; D012315:RNA Caps; D014157:Transcription Factors; C031017:ornithine decarboxylase antizyme; D001216:Asparagine; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D009955:Ornithine Decarboxylase