Induction of tyrosine aminotransferase with N 6 ,O 2 -dibutyryl adenosine 3'-5'monophosphate in rat-hepatoma cells grown in culture

The influence of culture conditions on the induction of tyrosine aminotransferase by cyclic nucleotides in rat hepatoma cells

The increase in tyrosine aminotransferase activity which occurs in rat hepatoma tissue culture (HTC) cells in response to cyclic AMP analogs has been shown to be an enzyme induction, similar to the larger response observed in certain other hepatoma cells and in liver. A specific antibody to tyrosine aminotransferase has been used to show that the number of enzyme molecules and the rate of enzyme synthesis are increased by N6,O2'-dibutyryl cyclic AMP in HTC cells. The effect on tyrosine aminotransferase is also produced by various 8-substituted derivatives of cyclic AMP and occurs whether or not the enzyme has been preinduced with a glucocorticoid. The response of the enzyme is greater when HTC cells are maintained in monolayer than in suspension cultures. Neither cell growth nor serum is required for the response.

Regulation of hepatic tyrosine aminotransferase in the frog Rana temporaria

The regulation of hepatic tyrosine aminotransferase (L-tyrosine:2-oxoglutarate aminotransferase, EC 2.6.1.5) in the rat has been extensively studied but little is known about the enzyme from other sources. We have studied the regulation of this enzyme in the frog Rana temporaria and in this paper we report that: 1. Cortisone acetate, adrenocorticotropic hormone and alpha-methyl-p-tyrosine, an agent known to induce hepatic tyrosine aminotransferase in the rat via activation of the pituitary-adrenal axis, have no effect on the activity of the enzyme in the frog. 2. Dibutyryl-3',5'-cyclic AMP induces the enzyme to about 2-fold. 3. Injection of tyrosine methyl ester and a protein-rich diet result in an increase in the enzyme activity. This increase is of the same order of magnitude as that caused by dibutyryl cyclic AMP. 4. Glucose significantly reduces tyrosine aminotransferase activity in frog liver. These results suggest that cyclic AMP induces the enzyme via a mechanism independent of glucocorticoids. The frog offers a model for studies on the regulation of hepatic tyrosine aminotransferase in vivo without interference from secondary effects mediated by the adrenals.