Regulation of tyrosine aminotransferase messenger ribonucleic acid in rat liver. Effect of cycloheximide on messenger ribonucleic acid turnover

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Abstract
Tyrosine aminotransferase [TAT] mRNA activity in rat liver was rapidly increased 3- to 6-fold following in vivo administration of hydrocortisone acetate, dibutyryl cAMP or the protein synthesis inhibitor cycloheximide. Treatment with the steroid hormone or cyclic nucleotide in combination with cycloheximide resulted in levels of TAT mRNA 10- to 20-fold greater than control values. These changes in mRNA activity were not accompanied by changes in albumin mRNA or total liver template activity. The rapid decline in TAT mRNA activity following cordycepin inhibition of de novo RNA synthesis was prevented by cycloheximide treatment. This protection was not observed when pactamycin was substituted for cycloheximide, demonstrating that the inhibition of protein synthesis per se was not responsible for the stabilization of TAT mRNA. Based upon the effects of cycloheximide and pactamycin on rat liver polysome structure, it is concluded that the cycloheximide-mediated increase in TAT mRNA activity is the result of stabilization of the mRNA molecule which renders the message less susceptible to inactivation and degradation in the cytoplasm. The action of cycloheximide is very specific for TAT, phosphoenolpyruvate carboxykinase, and probably several other mRNA that code for minor liver proteins that turn over rapidly in response to hormonal or metabolic stimuli.