Selective Inhibition by Sodium Butyrate of Glucorticoid‐Induced Tyrosine Aminotransferase Synthesis in Hepatoma Tissue‐Cultured Cells

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Abstract
Sodium butyrate at a 5 mM concentration prevents the induction of tyrosine aminotransferase in hepatoma culture cells, without affecting the basal level of the enzyme. This effect is reversible immediately after the removal of butyrate, or after a lag, if butyrate was present for more than 2 h.Neither the amount of cellular RNA nor the rate of total RNA synthesis were affected by sodium butyrate. Furthermore butyrate does not inhibit protein synthesis: [35S] methionine incorporation into preteins, measured in a reticulocyte lysate system, shows to significant difference between the translation capacity of the RNAs from butyrate‐treated cells and from dexamethasone‐induced or uninduced cells. Nevertheless, when tyrosine aminotransferase was isolated from the amount of the enzyme synthesized in the presence of RNAs from dexamethasone/butyrate‐treated cells. These experiments indicate that the treatment of the cells with butyrate decreases the activity of the specific messenger RNA for tyrosine aminotransferase to a level close to the basal level.Butyrate does not prevent the penetration of the hormone and has a limited effect on the translocation of the glucocorticoid‐receptor complex to the nucleus.We therefore conclude that the effect of sodium butyrate might be inherent either to an impairment of an early step of the hormone‐chromatin interaction or to an alteration of the transcription process of some specific genes. The rapidity and the complete reversibility of the effects of butyrate suggest that it does not irreversibly alter the structure which are the targets of its action.