Biochemical and Biophysical Research Communications Insulin Induction of Tyrosine Amincyiransferase in Synchronized Hepatoma Cells

Abstract

Received February 20,1975 Summary: Addition of insulin to unsynchronized rat hepatoma cells, previously incubated with dexamethasone, promotes a rapid increase in tyrosine aminotransferase activity. Mitotic cells in the presence or absence of colcemid are not inducible by either insulin or dexamethasone. Inducibility by dexamethasone is restored only after the third hour of the Gl phase, presumably related to the appearance of the putative posttranscriptional repressor (Martin, D.W. et al. (1969). Proc. Nat. Acad. Sci., 63: 842-849). In contrast, inducibility by insulin is restored immediately upOn passage of the synchronized cells into Gl. These data suggest that insulin can induce tyrosine aminotransferase in the absence of the repressor. In an unsynchronized population of established rat hepatoma tissue culture (HTCl) cells, corticosteroid hormones induce a lo-fold increase in the rate of synthesis of tyrosine aminotransferase (E.C. 2.1.1.5) by a mechanism requiring RNA synthesis (1). HTC cells (2,3,4) as well as cells derived from normal rat liver (4), are sensitive to steroid induction of TAT' only in the mid and late Gl and S phases of the cell cycle; enzyme synthesis is constitutive and insensitive to steroid during G2, M and early Gl. Addition of insulin (5) or dialyzed bovine serum (6) to unsynchronized HTC cells, previously induced with dexamethasone in a chemically defined, serum-free medium, causes a further doubling in the amount of induced enzyme, by a mechanism which is independent of concomitant RNA synthesis. We have shown previously that corticosteroids, insulin and aerum all affect different aspects of the post-transcriptional control of expression of the same enzyme (7). In an attempt to elucidate further the differences in the modes of

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Cite this paper

@inproceedings{Rettig2003BiochemicalAB, title={Biochemical and Biophysical Research Communications Insulin Induction of Tyrosine Amincyiransferase in Synchronized Hepatoma Cells}, author={Janet Rettig and Thomas D. Gelehrter}, year={2003} }