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A mechanism by which adenovirus virus-associated RNAI controls translation in a transient expression assay.

The mechanism by which adenovirus virus-associated RNAI stimulates translational efficiency in a transient-expression assay in 293 cells was investigated. We showed that DNA transfection leads to activation of a protein kinase that phosphorylates the alpha subunit of eucaryotic initiation factor 2 and, as a consequence, inhibition of polypeptide chain initiation. Cotransfection of a plasmid encoding adenovirus type 2 virus-associated RNAI recovered the translational capacity by preventing activation of the kinase.

Adenoviruses, Human↗

Contribution of insulin to the translational control of protein synthesis in skeletal muscle by leucine.

Enhanced protein synthesis in skeletal muscle after ingestion of a balanced meal in postabsorptive rats is mimicked by oral leucine administration. To assess the contribution of insulin to the protein synthetic response to leucine, food-deprived (18 h) male rats (approximately 200 g) were intravenously administered a primed-constant infusion of somatostatin (60 microg + 3 microg.kg(-1).h(-1)) or vehicle beginning 1 h before administration of leucine (1.35 g L-leucine/kg) or saline (control). Rats were killed 15, 30, 45, 60, or 120 min after leucine administration. Compared with controls, serum insulin concentrations were elevated between 15 and 45 min after leucine administration but returned to basal values by 60 min. Somatostatin maintained insulin concentrations at basal levels throughout the time course. Protein synthesis was increased between 30 and 60 min, and this effect was blocked by somatostatin. Enhanced assembly of the mRNA cap-binding complex (composed of eukaryotic initiation factors eIF4E and eIF4G) and hyperphosphorylation of the eIF4E-binding protein 1 (4E-BP1), the 70-kDa ribosomal protein S6 kinase (S6K1), and the ribosomal protein S6 (rp S6) were observed as early as 15 min and persisted for at least 60 min. Somatostatin attenuated the leucine-induced changes in 4E-BP1 and S6K1 phosphorylation and completely blocked the change in rp S6 phosphorylation but had no effect on eIF4G small middle dot eIF4E assembly. Overall, the results suggest that the leucine-induced enhancement of protein synthesis and the phosphorylation states of 4E-BP1 and S6K1 are facilitated by the transient increase in serum insulin. In contrast, assembly of the mRNA cap-binding complex occurs independently of increases in insulin and, by itself, is insufficient to stimulate rates of protein synthesis in skeletal muscle after leucine administration.

Animals↗

Regulation of ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase in regenerating rat liver by various amines: Evidence for translational control.

The activity of ornithine decarboxylase in regenerating rat liver could be completely or partially inhibited in vivo by a single intraperitoneal injection of various amines. Un physiological, 1,3-diaminopropane depressed most effectively the activity of ornithine decarboxylase. It depressed also the activity of adenosylmethionine decarboxylase, which was not inhibited by other amines. The activity of tyrosine aminotransferase was invariably stimulated by injection of the amines. Cycloheximide caused a rapid decay of the activity of liver ornithine decarboxylase (half-life 15 min) and also a decay of the activity of adenosylmethionine decarboxylase (half-life 36 min). 1,3-Diaminopropane inhibited the activity of ornithine decarboxylase (half-life 13 min) and to lesser extent also the activity of adenosylmethionine decarboxylase (half-life 120 min). On the contrary, alpha-amanitin did not have any effect on the activity of the decarboxylases. These experiments are consistent with the view that diamines and spermidine might conceivably control the activity of ornithine decarboxylase in regenerating rat liver in vivo at steps beyond transcription. It is also possible that 1,3-diaminopropane similarly controls the activity of adenosylmethionine decarboxylase thus suggesting that the synthesis of ornithine and adenosylmethionine decarboxylases may be coordinatively regulated in liver.

Adenosylmethionine Decarboxylase↗