Insulin induction of tyrosine aminotransferase in synchronized hepatoma cells

Abstract

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 G1 phase, presumably related to the appearance of the putative posttranscriptional repressor ([3.]). In contrast, inducibility by insulin is restored immediately upon passage of the synchronized cells into G1. These data suggest that insulin can induce tyrosine aminotransferase in the absence of the repressor.