Induction of Tyrosine Aminotransferase with N6, O2‐Dibutyryl Adenosine 3′‐5′‐Monophosphate in Rat‐Hepatoma Cells Grown in Culture

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Abstract
The dibutyryl analogue of adenosine 3′:5′ monophosphate (Bu2‐Ado‐3′:5′‐P) stimulates tyrosine‐aminotransferase synthesis in rat‐hepatoma cells cultured in Dulbecco medium supplemented with excess L‐tyrosine. This effect of Bu2‐Ado‐3′ :5′‐P is not observed in cells incubated in regular Dulbecco medium. It has been shown previously that tyrosine‐aminotransferase activity increases in hepatoma cells incubated in a glucose‐free medium that is also supplemented with excess L‐tyrosine. The increase in enzyme activity observed after administration of Bu2‐Ado‐3′:5′‐P and after glucose removal can be prevented by cycloheximide or actinomycin‐D. Bu2‐Ado‐3′ :5′‐P in the absence of glucose does not cause an additive increase in tyrosine‐amino transferase activity. The latter observation suggests that increased enzyme synthesis in each circumstance occurs via the same mechanism. Combination experiments, using Bu2‐Ado‐3′ :5′‐P and cortisol, indicate that each of these inducers of tyrosine aminotransferase acts independently. In light of recent observations concerning β‐galactosidase induction in bacteria, a mechanism of tyrosine‐aminotransferase induction in these mammalian‐derived cells is discussed.