Control of phenylalanine hydroxylase synthesis in tissue culture by serum and insulin

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Abstract
Stationary-phase, minimal deviation hepatoma H4-II-E-C3 cell cultures that are serum-deprived respond with a biphasic time course of phenyl-alanine hydroxylase induction when dialyzed fetal calf serum or insulin is added. These two agents induce phenylalanine hydroxylase additively, during both the initial 3-hour and the delayed 24-hour phases. The initial phase of induction by insulin is inhibited by cycloheximide but not by actinomycin D. The delayed induction by both dialyzed fetal calf serum and insulin is inhibited by 10−6 M cycloheximide and 0.20 μg/ml actinomycin D. H4-II-E-C3 cells in culture do not synthesize the factor(s) in serum that induce phenylalanine hydroxylase.