TRANSLATION OF TYROSINE-HYDROXYLASE FROM POLY(A)-MESSENGER RNA IN PHEOCHROMOCYTOMA CELLS IS ENHANCED BY DEXAMETHASONE

Polysomal poly(A)-mRNA was purified from a clonal cell line of rat pheochromocytoma (PC 12) and translated in a reticulocyte cell-free protein-synthesizing system. Tyrosine hydroxylase [tyrosine 3-monooxygenase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] was isolated from other proteins by immunoprecipitation and NaDodSO4/polyacrylamide gel electrophoresis. The MW and relative proportion of tyrosine hydroxylase to other proteins synthesized in vitro were identical to those of the enzyme synthesized in vivo in cultured cells. Incubation of PC 12 cells with 10 .mu.M dexamethasone increased the activity and amount of tyrosine hydroxylase 2.5-fold. The ratio of tyrosine hydroxylase to total protein translated from poly(A)-mRNA isolated from cells treated with dexamethasone was 2.5 times higher than the ratio of enzyme to total protein translated from an equal amount of poly(A)-mRNA from untreated cells. The dexamethasone-elicited induction of tyrosine hydroxylase in PC 12 cells therefore is a result of an increased relative amount or activity of tyrosine hydroxylase mRNA.