TNF alpha and cortisone impair peptide chain initiation by altering the availability of initiation factor EIF-4E

Cheema, I. R.

doi:10.2741/1160

Cited by 1 publication

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References 21 publications

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“…Thus we were surprised to find that hyperoxia increased eIF4E protein expression in both nonpurified cell lysates and m 7 -GTP-purified lysates. Whereas downregulation of eIF4E protein has been reported in response to TNF-α, cortisone, and ischemia, only mammary gland development appears to enhance eIF4E expression under physiological conditions (5,8,21). Nonetheless, given that hyperoxia enhances activator protein (AP)-1 transcription, it is conceivable that binding of AP-1 to the AP-1 motifs in the eIF4E gene could upregulate eIF4E expression (20,22).…”

Section: Discussionmentioning

confidence: 99%

Hyperoxia alters the expression and phosphorylation of multiple factors regulating translation initiation

Shenberger¹,

Myers²,

Zimmer³

et al. 2005

American Journal of Physiology-Lung Cellular and Molecular Phys

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Hyperoxia is cytotoxic and depresses many cellular metabolic functions including protein synthesis. Translational control is exerted primarily during initiation by two mechanisms: 1) through inhibition of translation initiation complex formation via sequestration of the cap-binding protein, eukaryotic initiation factor (eIF) 4E, with inhibitory 4E-binding proteins (4E-BP); and 2) by prevention of formation and eIF2B activity by phosphorylated eIF2α. In this report, exposure of human lung fibroblasts to 95% O 2 decreased the incorporation of thymidine into DNA at 6 h and the incorporation of leucine into protein beginning at 12 h. The reductions in DNA and protein synthesis were accompanied by increased phosphorylation of eIF4E protein and reduced phosphorylation of 4E-BP1. At 24 h, hyperoxia shifted 4E-BP1 phosphorylation to lesserphosphorylated isoforms, increased eIF4E expression, and increased the association of eIF4E with 4E-BP1. Although hyperoxia did not change eIF2α expression, it increased its phosphorylation at Ser51, but not until 48 h. In addition, the activation of eIF2α was not accompanied by the formation of stress granules. These findings suggest that hyperoxia diminishes protein synthesis by increasing eIF4E phosphorylation and enhancing the affinity of 4E-BP1 for eIF4E. Keywordseukaryotic translation initiation factors; protein synthesis; lung; stress granules Exposure of the developing lung to high concentrations of inspired oxygen is known to inhibit lung growth, both acutely and chronically (7,26). Cell culture and whole animal studies indicate that hyperoxia inhibits not only DNA synthesis but also protein synthesis (2,7,15,23). In adult rats breathing 95% O 2 , the fractional rate of protein synthesis and the rate of protein synthesis per ribosome are depressed by 30% within 6 h (7). Similarly, whole lung slices from rats exposed to hyperoxia for 24 and 48 h show 25% reductions in protein synthetic capacity of both total protein and newly synthesized proteins (15). At the cellular level, Jornot and colleagues (12) revealed that exposure to 95% O 2 inhibited the incorporation of leucine into protein, delayed the ribosomal transit time, and marginally increased the polysome content of cultured endothelial cells. Yet despite the near universality of the inhibitory effect of hyperoxia In mammalian cells, translation is principally regulated by a family of eukaryotic initiation factors (eIF) that control the assembly of the ribosome on the mRNA. The efficiency of ribosome/mRNA binding is governed by the availability of the 5′ m 7 -GpppX (where X is any nucleotide) mRNA cap binding protein, eIF4E, which, together with eIF4G and eIF4A, comprises the heterotrimeric eIF4F initiation complex (reviewed in Refs. 29 and 34). The eIF4F complex, along with eIF3, facilitates the assembly of the 43S ribosomal subunit on the 5′ end of the mRNA. The low abundance of eIF4E relative to the other 4F components renders it rate limiting for eIF4F formation. The level of free eIF4E is regulated by a group o...

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